% % This file was created by the Typo3 extension % sevenpack version 0.7.14 % % --- Timezone: CET % Creation date: 2018-12-11 % Creation time: 01-26-09 % --- Number of references % 53 % @Article { AvdievichGBSSH2018, title = {Double‐row 18‐loop transceive–32‐loop receive tight‐fit array provides for whole‐brain coverage, high transmit performance, and SNR improvement near the brain center at 9.4T}, journal = {Magnetic Resonance in Medicine}, year = {2018}, month = {12}, volume = {Epub ahead}, abstract = {Purpose To improve the transmit (Tx) and receive (Rx) performance of a human head array and provide whole‐brain coverage at 9.4T, a novel 32‐element array design was developed, constructed, and tested. Methods The array consists of 18 transceiver (TxRx) surface loops and 14 Rx‐only vertical loops all placed in a single layer. The new design combines benefits of both TxRx and transmit‐only–receive‐only (ToRo) designs. The general idea of the design is that the total number of array elements (both TxRx and Rx) should not exceed the number of required Rx elements. First, the necessary number of TxRx loops is placed around the object tightly to optimize the Tx performance. The rest of the elements are loops, which are used only for reception. We also compared the performance of the new array with that of a state‐of‐the‐art ToRo array consisting of 16 Tx‐only loops and 31 Rx‐only loops. Results The new array provides whole‐brain coverage, \verb=~=1.5 times greater Tx efficiency and 1.3 times higher SNR near the brain center as compared to the ToRo array, while the latter delivers higher (up to 1.5 times) peripheral SNR. Conclusion In general, the new approach of constructing a single‐layer array consisting of both TxRx‐ and Rx‐only elements simplifies the array construction by minimizing the total number of elements and makes the entire design more robust and, therefore, safe. Overall, our work provides a recipe for a Tx‐ and Rx‐efficient head array coil suitable for parallel transmission and reception as well as whole‐brain imaging at UHF.}, department = {Department Scheffler}, department2 = {Research Group Henning}, web_url = {https://onlinelibrary.wiley.com/doi/epdf/10.1002/mrm.27602}, DOI = {10.1002/mrm.27602}, author = {Avdievich, NI and Giapitzakis, I-A and Bause, J and Shajan, G and Scheffler, K and Henning, A} } @Article { GiapitzakisBMAH2018_2, title = {Investigation of the influence of macromolecules and spline baseline in the fitting model of human brain spectra at 9.4T}, journal = {Magnetic Resonance in Medicine}, year = {2018}, month = {10}, volume = {Epub ahead}, abstract = {Purpose In this study, the influence of experimentally measured macromolecules and spline baseline on the quantification results of proton MRS data was investigated. Methods Proton MRS spectra from the left parietal lobe and the occipital lobe were acquired at 9.4T in the human brain using metabolite‐cycled semi‐LASER. Then, the left parietal lobe data, along with the occipital lobe, spectra were quantified and the influence of the inclusion of experimentally measured macromolecular basis sets in the fitting model was evaluated. Furthermore, the effect of the stiffness of the fitted spline baselines on the resulting metabolite concentrations was evaluated. Results In general, concentrations were higher for metabolites in occipital lobe than the left parietal lobe. The inclusion of an experimentally acquired measured macromolecular basis set from another brain region neither affected the quantification results nor the resulting spline baselines significantly. A highly flexible spline baseline led to overestimation or underestimation of metabolite concentrations. Differences of above 15\% in the quantification of metabolite levels for both lobes were observed for several metabolites using LCModel default settings for spline baselines and macromolecules in comparison to stiffer spline baselines. Conclusion Fitting with the default LCModel macromolecular basis set and spline baseline model had significant influence in the resulting spline baselines, leading to large deviations both in the concentrations and fitted macromolecular components. The number of knots in the spline may create overflexible baselines, which can potentially lead to quantification errors. Interestingly, the interchange of macromolecular basis set between occipital lobe and left parietal lobe spectra had less influence on the quantification results compared to the default LCModel settings.}, department = {Research Group Henning}, web_url = {https://onlinelibrary.wiley.com/doi/epdf/10.1002/mrm.27467}, DOI = {10.1002/mrm.27467}, author = {Giapitzakis, I-A and Borbath, T and Murali‐Manohar, S and Avdievich, N and Henning, A} } @Article { AvdievichGPSSH2018, title = {Decoupling of a double‐row 16‐element tight‐fit transceiver phased array for human whole‐brain imaging at 9.4 T}, journal = {NMR in Biomedicine}, year = {2018}, month = {9}, volume = {31}, number = {9}, pages = {1-13}, abstract = {One of the major challenges in constructing multi‐channel and multi‐row transmit (Tx) or transceiver (TxRx) arrays is the decoupling of the array's loop elements. Overlapping of the surface loops allows the decoupling of adjacent elements and also helps to improve the radiofrequency field profile by increasing the penetration depth and eliminating voids between the loops. This also simplifies the design by reducing the number of decoupling circuits. At the same time, overlapping may compromise decoupling by generating high resistive (electric) coupling near the overlap, which cannot be compensated for by common decoupling techniques. Previously, based on analytical modeling, we demonstrated that electric coupling has strong frequency and loading dependence, and, at 9.4 T, both the magnetic and electric coupling between two heavily loaded loops can be compensated at the same time simply by overlapping the loops. As a result, excellent decoupling was obtained between adjacent loops of an eight‐loop single‐row (1 \(\times\) 8) human head tight‐fit TxRx array. In this work, we designed and constructed a 9.4‐T (400‐MHz) 16‐loop double‐row (2 \(\times\) 8) overlapped TxRx head array based on the results of the analytical and numerical electromagnetic modeling. We demonstrated that, simply by the optimal overlap of array loops, a very good decoupling can be obtained without additional decoupling strategies. The constructed TxRx array provides whole‐brain coverage and approximately 1.5 times greater Tx efficiency relative to a transmit‐only/receive‐only (ToRo) array, which consists of a larger Tx‐only array and a nested tight‐fit 31‐loop receive (Rx)‐only array. At the same time, the ToRo array provides greater peripheral signal‐to‐noise ratio (SNR) and better Rx parallel performance in the head–feet direction. Overall, our work provides a recipe for a simple, robust and very Tx‐efficient design suitable for parallel transmission and whole‐brain imaging at ultra‐high fields.}, department = {Department Scheffler}, department2 = {Research Group Henning}, web_url = {https://onlinelibrary.wiley.com/doi/epdf/10.1002/nbm.3964}, DOI = {10.1002/nbm.3964}, EPUB = {e3964}, author = {Avdievich, NI and Giapitzakis, IA and Pfrommer, A and Shajan, G and Scheffler, K and Henning, A} } @Article { GiapitzakisAH2017, title = {Characterization of macromolecular baseline of human brain using metabolite cycled semi-LASER at 9.4T}, journal = {Magnetic Resonance in Medicine}, year = {2018}, month = {8}, volume = {80}, number = {2}, pages = {462-473}, abstract = {Purpose Macromolecular resonances (MM) arise mainly from cytosolic proteins and overlap with metabolites, influencing metabolite quantification. Macromolecules can serve as valuable biomarkers for diseases and pathologies. The objectives of this study were to characterize MM at 9.4T in the human brain (occipital and left parietal lobe) and to describe the RF coil setup used for MM acquisition in the two regions. Methods An adiabatic inversion pulse was optimised for metabolite nulling at 9.4T using double inversion recovery and was combined for the first time with metabolite cycled (MC) semi-LASER and appropriate coil configuration. MM spectra (seven volunteers) from two brain locations were averaged and smoothed creating MM templates, which were then parametrized using simulated Voigt-shaped lines within LCModel. Quantification was performed on individual data sets, including corrections for different tissue composition and the T1 and T2 relaxation of water. Results Our coil configuration method resulted in efficient math formula (>30 T/\(\sqrt{}\)kW) for both brain regions. The 15 MM components were detected and quantified in MM baselines of the two brain areas. No significant differences in concentration levels of MM between different regions were found. Two new MM peaks were reported (M7 \& M8). Conclusion Double inversion, which was combined with MC semi-LASER, enabled the acquisition of high spectral resolution MM spectra for both brain regions at 9.4T. The 15 MM components were detected and quantified. Two new MM peaks were reported for the first time (M7 \& M8) and preliminarily assigned to \(\beta\)-methylene protons of aspartyl-groups.}, department = {Research Group Henning}, web_url = {https://onlinelibrary.wiley.com/doi/epdf/10.1002/mrm.27070}, DOI = {10.1002/mrm.27070}, author = {Giapitzakis, IA and Avdievich, NI and Henning, A} } @Article { WyssBSGHFH2018, title = {In vivo estimation of transverse relaxation time constant (T2) of 17 human brain metabolites at 3T}, journal = {Magnetic Resonance in Medicine}, year = {2018}, month = {8}, volume = {80}, number = {2}, pages = {452-461}, abstract = {Purpose The transverse relaxation times T2 of 17 metabolites in vivo at 3T is reported and region specific differences are addressed. Methods An echo-time series protocol was applied to one, two, or three volumes of interest with different fraction of white and gray matter including a total number of 106 healthy volunteers and acquiring a total number of 128 spectra. The data were fitted with the 2D fitting tool ProFit2, which included individual line shape modeling for all metabolites and allowed the T2 calculation of 28 moieties of 17 metabolites. Results The T2 of 10 metabolites and their moieties have been reported for the first time. Region specific T2 differences in white and gray matter enriched tissue occur in 16 of 17 metabolites examined including single resonance lines and coupled spin systems. Conclusion The relaxation time T2 is regions specific and has to be considered when applying tissue composition correction for internal water referencing.}, department = {Research Group Henning}, web_url = {https://onlinelibrary.wiley.com/doi/epdf/10.1002/mrm.27067}, DOI = {10.1002/mrm.27067}, author = {Wyss, PO and Bianchini, C and Scheidegger, M and Giapitzakis, IA and Hock, A and Fuchs, A and Henning, A} } @Article { FichtnerGAMZHK2017_3, title = {In vivo characterization of the downfield part of 1H MR spectra of human brain at 9.4T: Magnetization exchange with water and relation to conventionally determined metabolite content}, journal = {Magnetic Resonance in Medicine}, year = {2018}, month = {6}, volume = {79}, number = {6}, pages = {2863-2873}, abstract = {Purpose To perform exchange-rate measurements on the in vivo human brain downfield spectrum (5–10 ppm) at 9.4 T and to compare the variation in concentrations of the downfield resonances and of known upfield metabolites to determine potential peak labels. Methods Non-water-suppressed metabolite cycling was used in combination with an inversion transfer technique in two brain locations in healthy volunteers to measure the exchange rates and T1 values of exchanging peaks. Spectra were fitted with a heuristic model of a series of 13 or 14 Voigt lines, and a Bloch–McConnell model was used to fit the exchange rate curves. Concentrations from non-water-inverted spectra upfield and downfield were compared. Results Mean T1 values ranged from 0.40 to 0.77 s, and exchange rates from 0.74 to 13.8 s−1. There were no significant correlations between downfield and upfield concentrations, except for N-acetylaspartate, with a correlation coefficient of 0.63 and P < 0.01. Conclusions Using ultrahigh field allowed improved separation of peaks in the 8.2 to 8.5 ppm amide proton region, and the exchange rates of multiple downfield resonances including the 5.8-ppm peak, previously tentatively assigned to urea, were measured in vivo in human brain. Downfield peaks consisted of overlapping components, and largely missing correlations between upfield and downfield resonances—although not conclusive—indicate limited contributions from metabolites present upfield to the downfield spectrum. Magn Reson Med, 2017. © 2017 International Society for Magnetic Resonance in Medicine.}, department = {Department Logothetis}, department2 = {Research Group Henning}, web_url = {http://onlinelibrary.wiley.com/doi/10.1002/mrm.26968/epdf}, DOI = {10.1002/mrm.26968}, author = {Fichtner, ND and Giapitzakis, I-A and Avdievich, N and Mekle, R and Zaldivar, D and Henning, A and Kreis, R} } @Article { GiapitzakisSAMKH2017, title = {Metabolite-cycled STEAM and semi-LASER localization for MR spectroscopy of the human brain at 9.4T}, journal = {Magnetic Resonance in Medicine}, year = {2018}, month = {4}, volume = {79}, number = {4}, pages = {1841-1850}, abstract = {Purpose Metabolite cycling (MC) is an MRS technique for the simultaneous acquisition of water and metabolite spectra that avoids chemical exchange saturation transfer effects and for which water may serve as a reference signal or contain additional information in functional or diffusion studies. Here, MC was developed for human investigations at ultrahigh field. Methods MC-STEAM and MC-semi-LASER are introduced at 9.4T with an optimized inversion pulse and elaborate coil setup. Experimental and simulation results are given for the implementation of adiabatic inversion pulses for MC. The two techniques are compared, and the effect of frequency and phase correction based on the MC water spectra is evaluated. Finally, absolute quantification of metabolites is performed. Results The proposed coil configuration results in a maximum math formula of 48 \(\mu\)Τ in a voxel within the occipital lobe. Frequency and phase correction of single acquisitions improve signal-to-noise ratio (SNR) and linewidth, leading to high-resolution spectra. The improvement of SNR of N-acetylaspartate (SNRNAA) for frequency aligned data, acquired with MC-STEAM and MC-semi-LASER, are 37\% and 30\%, respectively (P < 0.05). Moreover, a doubling of the SNRNAA for MC-semi-LASER in comparison with MC-STEAM is observed (P < 0.05). Concentration levels for 18 metabolites from the human occipital lobe are reported, as acquired with both MC-STEAM and MC-semi-LASER. Conclusion This work introduces a novel methodology for single-voxel MRS on a 9.4T whole-body scanner and highlights the advantages of semi-LASER compared to STEAM in terms of excitation profile. In comparison with MC-STEAM, MC-semi-LASER yields spectra with higher SNR.}, department = {Research Group Henning}, web_url = {http://onlinelibrary.wiley.com/doi/10.1002/mrm.26873/epdf}, DOI = {10.1002/mrm.26873}, author = {Giapitzakis, IA and Shao, T and Avdievich, NI and Mekle, R and Kreis, R and Henning, A} } @Article { AvdievichGPBH2017, title = {Combination of surface and ''vertical'' loop elements improves receive performance of a human head transceiver array at 9.4 T}, journal = {NMR in Biomedicine}, year = {2018}, month = {2}, volume = {31}, number = {2}, pages = {1-13}, abstract = {Ultra-high-field (UHF, ≥7 T) human magnetic resonance imaging (MRI) provides undisputed advantages over low-field MRI (\(\le\)3 T), but its development remains challenging because of numerous technical issues, including the low efficiency of transmit (Tx) radiofrequency (RF) coils caused by the increase in tissue power deposition with frequency. Tight-fit human head transceiver (TxRx) arrays improve Tx efficiency in comparison with Tx-only arrays, which are larger in order to fit multi-channel receive (Rx)-only arrays inside. A drawback of the TxRx design is that the number of elements in an array is limited by the number of available high-power RF Tx channels (commonly 8 or 16), which is not sufficient for optimal Rx performance. In this work, as a proof of concept, we developed a method for increasing the number of Rx elements in a human head TxRx surface loop array without the need to move the loops away from a sample, which compromises the array Tx performance. We designed and constructed a prototype 16-channel tight-fit array, which consists of eight TxRx surface loops placed on a cylindrical holder circumscribing a head, and eight Rx-only vertical loops positioned along the central axis (parallel to the magnetic field B0) of each TxRx loop, perpendicular to its surface. We demonstrated both experimentally and numerically that the addition of the vertical loops has no measurable effect on the Tx efficiency of the array. An increase in the maximum local specific absorption rate (SAR), evaluated using two human head voxel models (Duke and Ella), measured 3.4\% or less. At the same time, the 16-element array provided 30\% improvement of central signal-to-noise ratio (SNR) in vivo relative to a surface loop eight-element array. The novel array design also demonstrated an improvement in the parallel Rx performance in the transversal plane. Thus, using this method, both the Rx and Tx performance of the human head array can be optimized simultaneously.}, department = {Research Group Henning}, web_url = {http://onlinelibrary.wiley.com/doi/10.1002/nbm.3878/epdf}, DOI = {10.1002/nbm.3878}, EPUB = {e3878}, author = {Avdievich, NI and Giapitzakis, IA and Pfrommer, A and Borbath, T and Henning, A} } @Article { AvdievichGPH2017, title = {Decoupling of a tight-fit transceiver phased array for human brain imaging at 9.4T: Loop overlapping rediscovered}, journal = {Magnetic Resonance in Medicine}, year = {2018}, month = {2}, volume = {79}, number = {2}, pages = {1200–1211}, abstract = {Purpose To improve the decoupling of a transceiver human head phased array at ultra-high fields (UHF, ≥ 7T) and to optimize its transmit (Tx) and receive (Rx) performance, a single-row eight-element (1 \(\times\) 8) tight-fit transceiver overlapped loop array was developed and constructed. Overlapping the loops increases the RF field penetration depth but can compromise decoupling by generating substantial mutual resistance. Methods Based on analytical modeling, we optimized the loop geometry and relative positioning to simultaneously minimize the resistive and inductive coupling and constructed a 9.4T eight-loop transceiver head phased array decoupled entirely by overlapping loops. Results We demonstrated that both the magnetic and electric coupling between adjacent loops is compensated at the same time by overlapping and nearly perfect decoupling (below -30 dB) can be obtained without additional decoupling strategies. Tx-efficiency and SNR of the overlapped array outperformed that of a common UHF gapped array of similar dimensions. Parallel Rx-performance was also not compromised due to overlapping the loops. Conclusion As a proof of concept we developed and constructed a 9.4T (400 MHz) overlapped transceiver head array based on results of the analytical modeling. We demonstrated that at UHF overlapping loops not only provides excellent decoupling but also improves both Tx- and Rx-performance.}, department = {Research Group Henning}, web_url = {http://onlinelibrary.wiley.com/doi/10.1002/mrm.26754/epdf}, DOI = {10.1002/mrm.26754}, author = {Avdievich, NI and Giapitzakis, I-A and Pfrommer, A and Henning, A} } @Article { GiapitzakisBMAH2018, title = {Neurochemical Profile of Occipital and Left Parietal Lobes of Human Brain at 9.4 T: Investigation of the Influence of Macromolecular and Spline Baseline in the Fitting Model}, journal = {Magnetic Resonance in Medicine}, year = {2018}, month = {1}, department = {Research Group Henning}, state = {}, author = {Giapitzakis, I-A and Borbath, T and Murali-Manohar, S and Avdievich, N and Henning, A} } @Article { AvdievichPGH2017, title = {Analytical modeling provides new insight into complex mutual coupling between surface loops at ultrahigh fields}, journal = {NMR in Biomedicine}, year = {2017}, month = {10}, volume = {30}, number = {10}, pages = {1-13}, abstract = {Ultrahigh-field (UHF) (≥7 T) transmit (Tx) human head surface loop phased arrays improve both the Tx efficiency (B1+/\(\sqrt{}\)P) and homogeneity in comparison with single-channel quadrature Tx volume coils. For multi-channel arrays, decoupling becomes one of the major problems during the design process. Further insight into the coupling between array elements and its dependence on various factors can facilitate array development. The evaluation of the entire impedance matrix Z for an array loaded with a realistic voxel model or phantom is a time-consuming procedure when performed using electromagnetic (EM) solvers. This motivates the development of an analytical model, which could provide a quick assessment of the Z-matrix. In this work, an analytical model based on dyadic Green's functions was developed and validated using an EM solver and bench measurements. The model evaluates the complex coupling, including both the electric (mutual resistance) and magnetic (mutual inductance) coupling. Validation demonstrated that the model does well to describe the coupling at lower fields (\(\le\)3 T). At UHFs, the model also performs well for a practical case of low magnetic coupling. Based on the modeling, the geometry of a 400-MHz, two-loop transceiver array was optimized, such that, by simply overlapping the loops, both the mutual inductance and the mutual resistance were compensated at the same time. As a result, excellent decoupling (below −40 dB) was obtained without any additional decoupling circuits. An overlapped array prototype was compared (signal-to-noise ratio, Tx efficiency) favorably to a gapped array, a geometry which has been utilized previously in designs of UHF Tx arrays.}, department = {Research Group Henning}, web_url = {http://onlinelibrary.wiley.com/doi/10.1002/nbm.3759/epdf}, DOI = {10.1002/nbm.3759}, EPUB = {e3759}, author = {Avdievich, N and Pfrommer, A and Giapitzakis, IA and Henning, A} } @Article { AvdievichHSGSH2016, title = {Evaluation of transmit efficiency and SAR for a tight fit transceiver human head phased array at 9.4 T}, journal = {NMR in Biomedicine}, year = {2017}, month = {2}, volume = {30}, number = {2}, pages = {1-12}, abstract = {Ultra-high field (UHF, ≥7 T) tight fit transceiver phased arrays improve transmit (Tx) efficiency (B1+/\(\sqrt{}\)P) in comparison with Tx-only arrays, which are usually larger to fit receive (Rx)-only arrays inside. One of the major problems limiting applications of tight fit arrays at UHFs is the anticipated increase of local tissue heating, which is commonly evaluated by the local specific absorption rate (SAR). To investigate the tradeoff between Tx efficiency and SAR when a tight fit UHF human head transceiver phased array is used instead of a Tx-only/Rx-only RF system, a single-row eight-element prototype of a 400 MHz transceiver head phased array was constructed. The Tx efficiency and SAR of the array were evaluated and compared with that of a larger Tx-only array, which could also be used in combination with an 18-channel Rx-only array. Data were acquired on the Siemens Magnetom whole body 9.4 T human MRI system. Depending on the head size, positioning and the RF shim strategy, the smaller array provides from 11 to 23\% higher Tx efficiency. In general, the Tx performance, evaluated as B1+/\(\sqrt{}\)SAR, i.e. the safety excitation efficiency (SEE), is also not compromised. The two arrays provide very similar SEEs evaluated over 1000 random RF shim sets. We demonstrated that, in general, the tight fit transceiver array improves Tx performance without compromising SEE. However, in specific cases, the SEE value may vary, favoring one of the arrays, and therefore must be carefully evaluated.}, department = {Research Group Henning}, department2 = {Department Scheffler}, web_url = {http://onlinelibrary.wiley.com/doi/10.1002/nbm.3680/epdf}, DOI = {10.1002/nbm.3680}, EPUB = {e3680}, author = {Avdievich, NI and Hoffmann, J and Shajan, G and Pfrommer, A and Giapitzakis, IA and Scheffler, K and Henning, A} } @Article { AvdievichGH2015_6, title = {Novel splittable N-Tx/2N-Rx transceiver phased array to optimize both signal-to-noise ratio and transmit efficiency at 9.4T}, journal = {Magnetic Resonance in Medicine}, year = {2016}, month = {11}, volume = {76}, number = {5}, pages = {1621-1628}, abstract = {Purpose The goal of this study was to optimize signal-to-noise ratio (SNR) and parallel receive (Rx) performance of ultrahigh field (UHF) (≥7T) transceiver arrays without compromising their transmit (Tx) efficiency. UHF transceiver head phased arrays with a tight fit improve Tx efficiency in comparison with Tx-only arrays, which are usually larger so that Rx-only arrays can fit inside. However, having ≥16 elements inside a head transceiver array presents decoupling problems. Furthermore, the available number of Tx channels is limited. Methods A prototype of a splittable transceiver phased array was constructed. The array consisted of four flat surface Tx loops positioned in two rows. Each loop could be split into two smaller overlapped Rx loops during reception. Results Experimental data demonstrated that both SNR and parallel reception performance improved substantially by doubling the number of Rx elements from four to eight. Conclusion As a proof of concept, we developed and constructed a novel splittable transceiver phased array that allows doubling of the number of Rx elements while keeping both Tx and Rx elements at the same distance from the subject. Both Tx and Rx performance can be optimized at the same time using this method.}, department = {Research Group Henning}, web_url = {http://onlinelibrary.wiley.com/doi/10.1002/mrm.26051/epdf}, DOI = {10.1002/mrm.26051}, author = {Avdievich, NI and Giapitzakis, IA and Henning, A} } @Article { HoffmannHGSSP2015, title = {Safety testing and operational procedures for self-developed radiofrequency coils}, journal = {NMR in Biomedicine}, year = {2016}, month = {9}, volume = {29}, number = {9}, pages = {1131–1144}, abstract = {The development of novel radiofrequency (RF) coils for human ultrahigh-field (≥7 T), non-proton and body applications is an active field of research in many MR groups. Any RF coil must meet the strict requirements for safe application on humans with respect to mechanical and electrical safety, as well as the specific absorption rate (SAR) limits. For this purpose, regulations such as the International Electrotechnical Commission (IEC) standard for medical electrical equipment, vendor-suggested test specifications for third party coils and custom-developed test procedures exist. However, for higher frequencies and shorter wavelengths in ultrahigh-field MR, the RF fields may become extremely inhomogeneous in biological tissue and the risk of localized areas with elevated power deposition increases, which is usually not considered by existing safety testing and operational procedures. In addition, important aspects, such as risk analysis and comprehensive electrical performance and safety tests, are often neglected. In this article, we describe the guidelines used in our institution for electrical and mechanical safety tests, SAR simulation and verification, risk analysis and operational procedures, including coil documentation, user training and regular quality assurance testing, which help to recognize and eliminate safety issues during coil design and operation. Although the procedure is generally applicable to all field strengths, specific requirements with regard to SAR-related safety and electrical performance at ultrahigh-field are considered. The protocol describes an internal procedure and does not reflect consensus among a large number of research groups, but rather aims to stimulate further discussion related to minimum coil safety standards. Furthermore, it may help other research groups to establish their own procedures.}, department = {Department Scheffler}, department2 = {Research Group Henning}, web_url = {http://onlinelibrary.wiley.com/doi/10.1002/nbm.3290/epdf}, DOI = {10.1002/nbm.3290}, author = {Hoffmann, J and Henning, A and Giapitzakis, IA and Scheffler, K and Shajan, G and Pohmann, R and Avdievich, NI} } @Inbook { GiapitzakisH2018, title = {MRS Sequences and Protocols}, year = {2019}, month = {6}, pages = {-}, department = {Research Group Henning}, web_url = {http://www.springer.com/de/book/9783319528298}, editor = {McNulty, J. , P. Mullins}, publisher = {Springer International Publishing}, address = {Cham, Switzerland}, booktitle = {Clinical MR Spectroscopy}, state = {}, ISBN = {978-3-319-52829-8}, author = {Giapitzakis, IA and Henning, A} } @Poster { MuraliManoharBFGZKH2018, title = {Estimation of T2 Relaxation Times of Downfield Peaks in Human Brain at 9.4 T}, year = {2018}, month = {6}, day = {18}, number = {1330}, abstract = {T2 relaxations times for the downfield metabolites in human brain 1H MR spectra were estimated at 9.4 T. A possible new peak at 8.35 ppm with rapid T2 decay is reported. Due to the use of a non-water suppressed MRS method, the T2 of slowly exchanging peaks could be assessed. The shorter T2 relaxation times in the downfield compared to the upfield spectral areas leads us to suspect a macromolecular contribution, while also exchange effects may contribute to the short apparent T2s.}, department = {Research Group Henning}, web_url = {https://www.ismrm.org/18/program_files/TP01.htm}, web_url2 = {https://www.ismrm.org/18/Traditional_Posters.pdf}, event_place = {Paris, France}, event_name = {Joint Annual Meeting ISMRM-ESMRMB 2018}, author = {Murali Manohar, SV and Borbath, T and Fichtner, N and Giapitzakis, IA and Zaldivar, D and Kreis, R and Henning, A} } @Poster { GiapitzakisAH2017_2, title = {Characterization of macromolecular baseline of human brain using metabolite cycled semi-LASER at 9.4 T}, journal = {Magnetic Resonance Materials in Physics, Biology and Medicine}, year = {2017}, month = {10}, day = {21}, volume = {30}, number = {Supplement 1}, pages = {S475-S476}, abstract = {Purpose/Introduction: Macromolecular resonances (MM) arise mainly from cytosolic proteins overlapping with metabolites influencing metabolite quantification.This effect becomes even more severe in the case of short echo times (TE) due to their fast T2 relaxation time [1].Additionally, MM can be valuable biomarkers for several diseases and pathologies. The objective of this study was the characterization of human brain macromolecular baseline at 9.4T exploiting all the advantages arising from the utilization of UHF. Subjects and Methods: An adiabatic inversion pulse was developed for metabolite nulling at 9.4 T utilizing double inversion recovery [2] in combination with MC semiLASER [3] and appropriate coil configuration. MM spectra were acquired from 7 volunteers from two different brain locations, occipital lobe and left cerebral white matter. For each brain region, volunteer’s MM baselines were averaged creating a MM template which was parametrized using 15 simulated Lorentzian lines within LCModel. Quantification, corrected for different tissue composition and T1 relaxation, was performed for each MM component for each volunteer. Results: Double inversion recovery scheme for metabolite nulling at 9.4 T. A) Diagram of the sequence used for the acquisition of macromolecular spectra. Two adiabatic inversion pulses (AFP) preceded the actual localization scheme (MC semiLASER) utilizing optimizing inversion times (TI1 = 2360 ms and TI2 = 625 ms). B) Simulation of the effect of the double inversion recovery scheme in subplot A on the longitudinal magnetization for several T1 recovery times. T1 of macromolecules is assumed to be 400 ms and for other metabolites higher. Double inversion recovery scheme result in an efficient suppression of longer T1 metabolites. For inversion times TI1 and TI2,the fast T1 recovered MM resonances reach about 60\% of their maximum magnetization while the longitudinal magnetization of metabolites with longer T1 relaxation are relatively suppressed (Fig. 1). Parametrization of smoothed and averaged MM baselines for two brain locations: (left) occipital lobe and (right) left cerebral white matter. Totally 15 MM components are observed. The final number of MM peaks included in the model were recognized visually and also utilizing previous reported MM resonances in the literature. However, in this study 15 MM peaks were used to fit adequately the cubic spline-smoothed averaged MM baseline templates (Fig. 2). For both brain regions, the same number of MM compartments was used. Quantification results of 15 MM for two different brain areas, occipital lobe and left cerebral white matter, from 7 volunteers using LCModel. (Up) Concentrations levels in arbitrary units (a.u), normalized using water reference scans and corrected for GM, WM and CSF percentages and the different T1 relaxation of the water compartments. (Down) CRLB values in a.u calculated as: concentration level 9 CRLB (\%). Quantification results did not show any statistically significant difference in MM concentration levels between occipital lobe and white matter left cerebral (Fig. 3). The only exception was the M1 peak, where there was a trend for potential difference (no statistically significant level after multiple comparisons correction). Discussion/Conclusion: The averaged MM baselines for both brain locations do not show substantial differences from a visual inspection (Fig. 2).Moreover, MM spectra among different volunteers exhibit similar patterns except for macromolecules M2, M3, and M4 which is also confirmed from the quantifications results (Fig. 3).Noteworthy, the two MM peaks at 2.57 ppm (M7) and 2.74 ppm (M8) are easily observable. These peaks appear in MM spectra of other studies [1, 4–7] however, they have not been reported. M7 and M8 are most likely due to the beta-methylene protons of aspartyl-groups within cellular proteins [4,]. Quantification results (Fig. 3) show that for both brain regions there are not significant differences, except a small trend for M1.}, department = {Research Group Henning}, web_url = {https://link.springer.com/content/pdf/10.1007\%2Fs10334-017-0634-z.pdf}, event_place = {Barcelona, Spain}, event_name = {34th Annual Scientific Meeting of the European Society for Magnetic Resonance in Medicine and Biology (ESMRMB 2017)}, DOI = {10.1007/s10334-017-0634-z}, author = {Giapitzakis, I-A and Avdievich, N and Henning, A} } @Poster { AvdievichGH2017_5, title = {Double-Row 16-element Tight-Fit Transceiver Phased Array with High Transmit Performance for Whole Human Brain Imaging at 9.4T}, journal = {Magnetic Resonance Materials in Physics, Biology and Medicine}, year = {2017}, month = {10}, day = {20}, volume = {30}, number = {Supplement 1}, pages = {S256-S257}, abstract = {Purpose/Introduction: At ultra-high field (UHF, C7T), a simple increase of the length of a single-row human head transmit (Tx)-array cannot provide an adequate longitudinal coverage (1–4). Multi-row (C2) arrays and RF shimming have to be used instead (2, 3, 5). Tightfit surface loop transceiver (TxRx)-phased arrays (2, 4) improve Txefficiency in comparison to Tx-only arrays (5), which are larger to fit receive (Rx)-only arrays inside. Previously we demonstrated analytically (6) that at 9.4T both the magnetic and electric coupling between two loops can be compensated at the same time simply by overlapping, and excellent decoupling can be obtained for a single-row 8-element (1 9 8) human head Tx-array without additional decoupling strategies (7). In this work, we constructed a 9.4T human head 16-loop double-row (2 9 8) TxRx-array decoupled entirely by overlapping. The array provides efficient transmission and the whole brain coverage. Subjects and Methods: Loop size (10.5 cm x 10 cm) was first evaluated analytically and then adjusted on a bench. The array (Fig. 1) measures 20 cm 9 23 cm (left–right 9 anterior–posterior), and 17.5 cm in length. Overlapping provides very good decoupling (Fig. 1). To decrease radiation losses the array is shielded. We compared the performance of the TxRx-array with a larger 16-element Tx-only/30-element Rx-only(ToRo) surface loop phased array (28 cm–diameter, 19 cm-length) described previously (5). Electromagnetic(EM) simulations of the B1 + and the local SAR were performed using CST Studio Suite 2015 (CST, Darmstadt, Germany). Three voxel models were used, i.e. a head/shoulder (HS) phantom (5), and two multi-tissue models, ‘‘Duke’’ and ‘‘Ella’’. Experimental B1 + maps were obtained using the AFI sequence (8). Data were acquired on a Siemens Magnetom 9.4T human imaging system. Results: After EM modeling, we conducted in vivo experiments (Fig. 2). The tight-fit TxRx-array provides *45\% improvement in B1 +-efficiency (B1 +/HP) compared to the ToRo-array, which agrees well with EM simulations. Circular polarizition (CP) produces an inhomogeneous B1 + at UHF (Fig. 2A, B). Introduction of a 658-phase shift, {\ss}, between the rows (Fig. 2C) improves homogeneity (9). Invivo images (Fig. 3A) demonstrate whole-brain coverage. Figures 3B, C show SNR maps obtained in vivo using both arrays. While the ToRo-array has a better peripheral SNR, SNRs in the center are similar. We also evaluated the dependence of the maximum local SAR10g on b. At b * 658 maximal SAR10g decreased by 13\% as compared to the CP Mode. Discussion/Conclusion: We constructed a 9.4T (400 MHz) 2 9 8 head TxRx-array based on the results of the analytical modeling. We demonstrated that simply by overlapping good decoupling can be obtained without additional decoupling strategies. This provides a recipe for a simple, robust, very Tx-efficient design suitable for parallel transmission and whole brain imaging at UHF.}, department = {Research Group Henning}, web_url = {https://link.springer.com/content/pdf/10.1007\%2Fs10334-017-0633-0.pdf}, event_place = {Barcelona, Spain}, event_name = {34th Annual Scientific Meeting of the European Society for Magnetic Resonance in Medicine and Biology (ESMRMB 2017)}, DOI = {10.1007/s10334-017-0633-0}, author = {Avdievich, N and Giapitzakis, I and Henning, A} } @Poster { GiapitzakisH2017, title = {Basis set optimization for quantification of semi-LASER at 9.4T under consideration of CP effect and relaxation}, year = {2017}, month = {4}, day = {27}, number = {2992}, abstract = {In this abstract, we evaluated the Carr-Purcell behavior of semi-LASER sequence at 9.4T and we studied the influence of different relaxation times between the different moieties of NAA and NAAG using in-vivo acquired from occipital lobe and simulated spectra. The results indicate that differences in the relaxation time between different moieties can affect the fitting results and the metabolites levels. Moreover, an estimated value for the relaxation time of NAA-aspartate moiety is given. This work indicates that more measurements and investigation should be done, studying more metabolites and brain regions.}, department = {Research Group Henning}, web_url = {http://www.ismrm.org/17/program_files/TP14.htm}, event_place = {Honolulu, HI, USA}, event_name = {25th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2017)}, author = {Giapitzakis, I-A and Henning, A} } @Poster { BorbathGMH2017, title = {Fitting comparison for 9.4T 1D semi-LASER and 2D-J-resolved semi-LASER data}, year = {2017}, month = {4}, day = {27}, number = {2995}, abstract = {In this abstract, we present an adapted version of the ProFit-V2 fitting software to fit J-resolved semi-LASER data at 9.4T. Simulated basis sets with ideal pulses show the need to reduce the echo time to account for the spin locking effect of the adiabatic pulses. Further, a comparison of the fitting error estimations using correlation matrices and Cramer-Rao Lower Bounds with a metabolite cycled semi-LASER fitted with LCModel is done.}, department = {Research Group Henning}, web_url = {http://www.ismrm.org/17/program_files/TP14.htm}, event_place = {Honolulu, HI, USA}, event_name = {25th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2017)}, author = {Borb{\'a}th, T and Giapitzakis, IA and Murali Manohar, SV and Henning, A} } @Poster { FichtnerGAMZHK2017_2, title = {Magnetization exchange between water and downfield metabolites in human brain at 9.4T}, year = {2017}, month = {4}, day = {27}, number = {5466}, abstract = {Ultra-high field strengths provide higher signal to noise ratio and improved separation of metabolites in spectroscopy, allowing for more precise characterization of peaks. In particular, this improved peak resolution may be of benefit for characterization of the downfield (5-10ppm) spectrum, which is not yet well characterized; this experiment aims to improve knowledge of downfield peaks by investigating their exchange rates and T1 values at 9.4T, using inversion transfer experiments and metabolite cycling to allow for non-water suppressed acquisition.}, department = {Research Group Henning}, department2 = {Department Logothetis}, web_url = {http://www.ismrm.org/17/program_files/EP20.htm}, event_place = {Honolulu, HI, USA}, event_name = {25th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2017)}, author = {Fichtner, N and Giapitzakis, I-A and Avdievich, N and Mekle, R and Zaldivar, D and Henning, A and Kreis, R} } @Poster { MuraliManoharGBGH2017, title = {Qualitative Comparison between In Vivo J-Resolved Semi-LASER at 3 T and 9.4 T}, year = {2017}, month = {4}, day = {27}, number = {3015}, abstract = {J-resolved semi-LASER with maximum-echo sampling is optimized at 9.4T and compared with the same implementation at 3T in terms of SNR and spectral resolution. SODA scheme is appreciated for the sequence rather than the MC scheme. SNR at 9.4T (t1 steps: 85) was approximately 5.8 times greater than at 3T (t1 steps: 100) and strongly coupled peaks are well-resolved. However, the trade-off between SNR and spectral resolution is explained as lactate (1.32 ppm), a weakly-coupled metabolite, is better resolved at 3T. Higher band-width AFP pulses helped in almost vanishing the J-refocused peaks which made the J-resolved peaks clearly distinguishable. A few interesting downfield peaks and the doublet of NAA (7.82ppm) are observed.}, department = {Research Group Henning}, web_url = {http://www.ismrm.org/17/program_files/TP14.htm}, event_place = {Honolulu, HI, USA}, event_name = {25th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2017)}, author = {Murali Manohar, SV and Giapitzakis, IA and Borb{\'a}th, T and Gaertner, M and Henning, A} } @Poster { FillmerGMAHIS2017, title = {Very Short Echo Time MRS for Single Voxel Spectroscopy in Small Voxels}, year = {2017}, month = {4}, day = {27}, number = {3017}, abstract = {This work presents the combination of metabolite cycling with a non-water-suppressed SPECIAL localization scheme in order to enable improved averaging coherence for very short echo time MRS in small voxels or voxels that suffer otherwise from low SNR or frequency instabilities.}, department = {Research Group Henning}, web_url = {http://www.ismrm.org/17/program_files/TP14.htm}, event_place = {Honolulu, HI, USA}, event_name = {25th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2017)}, author = {Fillmer, A and Giapitzakis, I and Mekle, R and Aydin, S and Henning, A and Ittermann, B and Schubert, R} } @Poster { AvdievichGH2017, title = {Double-Row 16-element Tight-Fit Transceiver Phased Array with High Transmit Performance for Whole Human Brain Imaging at 9.4T}, year = {2017}, month = {4}, day = {26}, volume = {0759}, pages = {469}, abstract = {At ultra-high fields (UHF, >7T) a simple increase of the length of a single-row human head transmit (Tx) phased array cannot provide an adequate longitudinal coverage for the whole brain imaging. Multi-row (>2) arrays together with RF shimming have to be used instead. In this work, we constructed a 9.4T (400 MHz) 16-loop double-row transceiver array based on the analytical modeling. We demonstrated that simply by overlapping a very good decoupling can be obtained without additional decoupling strategies. This provides a recipe of a simple, robust, and very Tx-efficient design for parallel transmission and whole brain imaging at UHFs.}, department = {Research Group Henning}, web_url = {http://www.ismrm.org/17/program_files/PP22.htm}, event_place = {Honolulu, HI, USA}, event_name = {25th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2017)}, author = {Avdievich, N and Giapitzakis, I and Henning, A} } @Poster { AvdievichGH2017_2, title = {Effect of Mismatching on the Transmit and Receive Performance of a Human Head 9.4T Tight-Fit Transceiver Phased Array}, year = {2017}, month = {4}, day = {25}, number = {4301}, abstract = {Tight-fit multi-channel ultra-high field (UHF, >7T) transceiver (TxRx) phased arrays improve transmit (Tx) efficiency in comparison to larger Tx-only arrays. However, tight-fit TxRx-arrays may require matching for each subject. To evaluate a potential use of tight-fit TxRx-arrays without matching, we investigated both numerically and experimentally an effect of a strong mismatch on performance of a 9.4T 8-channel human head TxRx-array. We demonstrated that mismatching caused only \verb=~=5\% decrease of the B1+ field, while may have stronger effect on the maximum local SAR. Additionally it also effects the SNR distribution. While overmatching favors SNR, undermatching may enhance Tx-efficiency evaluated as B1+/\(\sqrt{}\)SAR10g.}, department = {Research Group Henning}, web_url = {http://www.ismrm.org/17/program_files/EP09.htm}, event_place = {Honolulu, HI, USA}, event_name = {25th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2017)}, author = {Avdievich, N and Giapitzakis, I and Henning, A} } @Poster { AvdievichGH2017_3, title = {Optimization of the Receive Performance of a Tight-Fit Transceiver Phased Array for Human Brain Imaging at 9.4T}, year = {2017}, month = {4}, day = {25}, number = {4309}, abstract = {Tight-fit ultra-high field (UHF) (>7T) surface loop transceiver (TxRx)-phased arrays improve transmit (Tx) efficiency in comparison to Tx-only arrays built larger to accommodate for receive (Rx)-only array inserts. However, the number of elements in TxRx-arrays is restricted by the number of available RF Tx-channels (commonly 8 or 16), which limits the Rx-performance. A prototype of a 16-element array, which consists of 8 TxRx-surface loops circumscribing a head and 8 additional “vertical” Rx-only loops positioned in the center of each TxRx-loop perpendicularly, was constructed. This addition improves the Rx-performance substantially and has a minimal effect on both the Tx-efficiency and maximal local SAR.}, department = {Research Group Henning}, web_url = {http://www.ismrm.org/17/program_files/EP09.htm}, event_place = {Honolulu, HI, USA}, event_name = {25th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2017)}, author = {Avdievich, N and Giapitzakis, I and Henning, A} } @Poster { FichtnerGAHK2016, title = {Downfield spectra of human brain obtained with and without water suppression at 9.4T}, year = {2016}, month = {5}, day = {11}, number = {4010}, abstract = {Ultra high field strengths offer the benefit of higher signal to noise ratio as well as improved separation of metabolites in spectroscopy, which is beneficial for evaluating downfield peaks. In the current work, the metabolite cycling technique is implemented at 9.4T in order to evaluate the downfield part of the human brain spectrum. The 9.4T spectra confirm the 3T findings on exchanging peaks, and indicate that the higher field strength improves metabolite separation, allowing for better quantification of exchanging peaks, which is also of great interest for chemical exchange dependent saturation transfer experiments.}, department = {Research Group Henning}, web_url = {http://www.ismrm.org/16/program_files/EP16.htm}, event_place = {Singapore}, event_name = {24th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2016)}, author = {Fichtner, ND and Giapitzakis, IA and Avdievich, N and Henning, A and Kreis, R} } @Poster { AvdievichPGH2016, title = {Analytical Modeling of the Coupling within a Human Head Surface Loop Transmit Phased Array at Ultra-High Fields}, year = {2016}, month = {5}, day = {10}, number = {3525}, abstract = {Decoupling of multi-channel ultra-high field (>7T) transmit and transceiver arrays is a major issue. Analytical modeling of the coupling can facilitate the array optimization. We developed an analytical model describing the impedance matrix for two rectangular loops placed on a cylindrical surface and mimicking the human head array geometry. The developed model was comprehensively validated and allows for the optimization of the geometry and positioning of the loops. The latter enabled simultaneous cancellation of resistive and inductive coupling without additional decoupling circuits. The resulting overlapped array element arrangement improves both transmit and receive performance in comparison to conventional gapped arrays.}, department = {Research Group Henning}, web_url = {http://www.ismrm.org/16/program_files/EP10.htm}, event_place = {Singapore}, event_name = {24th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2016)}, author = {Avdievich, NI and Pfrommer, A and Giapitzakis, IA and Henning, A} } @Poster { FichtnerHGZABK2016, title = {Downfield MR Spectroscopy at Ultrahigh Magnetic Fields}, year = {2016}, month = {3}, day = {31}, pages = {36}, abstract = {Introduction: Magnetic resonance spectroscopy benefits from using ultrahigh field scanners, as both the signal to noise ratio (SNR) and the separation of peaks improve. Inclusion of the downfield part of the spectrum (left of water peak) in addition to the generally used upfield part of the 1H MR spectrum is expected to allow for better monitoring of pathologies and metabolism in humans. The downfield part at 5-10ppm is less well characterized than the upfield spectrum, although some data is available for animal brain at high fields, as well as human brain at 3T. Experiments have been performed to elucidate the downfield spectrum in human brain and to quantify metabolite relaxation times T1 and T2 in grey matter at 7T using series of spectra with variable inversion recovery (IR) and echo time (TE) delays. Initial downfield experiments have also been performed in humans at 9.4T. Materials and Methods: Acquisition methods at 7T used a Philips 7T whole body scanner (UZH/ETH Z{\"u}rich), with a voxel of interest placed in the visual cortex. A series of TEs and IRs was acquired in a total of 22 healthy volunteers. At 9.4T, spectra were acquired in three healthy volunteers on a Siemens whole-body MRI scanner (MPI Tuebingen). Results and Discussion: The spectra acquired at 7T and 9.4T demonstrate significant improvements in SNR and peak separation compared to those at lower field strengths. The averaged data sets from the 7T series were combined to develop a spectral model of partially overlapping signals this heuristic model describes the experimental data well and the results for many of the peaks are very consistent across subjects. T1 values found at 7T are mostly higher than those found at 3T, in particular for the NAA peak. Several peaks show a particularly short T1 in comparison to the others, indicating that they predominantly originate from macromolecules. The T2 values are in general much shorter than those found for upfield peaks.}, department = {Department B{\"u}lthoff}, web_url = {http://www.neuroscience.unibe.ch/unibe/portal/microsites/micro_clinicneuro/content/e253873/e382049/e418296/11th_Annual_Meeting_Tagungsmappe.pdf}, event_place = {Bern, Switzerland}, event_name = {11th Annual Meeting Brain Connectivity}, author = {Fichtner, N and Henning, A and Giapitzakis, I and Zoelch, N and Avdievich, N and Boesch, C and Kreis, R} } @Poster { NassirpourKGH2015, title = {Accelerated Multi-slice 1H FID-MRSI in the human brain at 9.4 T}, year = {2015}, month = {6}, day = {4}, volume = {23}, number = {4711}, abstract = {Magnetic resonance spectroscopic imaging (MRSI) at ultra-high field strengths is a promising technique for mapping of the metabolites over the entire brain volume with a high signal to noise ratio. However, long acquisition time is a major limitation in MRSI. Along with short repetition times (TR) [4] parallel imaging strategies can help accelerate the scan by acquiring only a fraction of the data points in k-space, but an appropriate unfolding reconstruction algorithm is required. To that end, a target driven SENSE [3] reconstruction algorithm has been introduced [1], which minimizes the effects of voxel bleeding. This study represents the first demonstration of short TR twofold SENSE accelerated multi-slice FID MRSI of the human brain at 9.4T.}, department = {Research Group Henning}, web_url = {http://www.ismrm.org/15/program_files/ThuEPS03.htm}, event_place = {Toronto, Canada}, event_name = {23rd Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2015)}, author = {Nassirpour, S and Kirchner, T and Giapitzakis, IA and Henning, A} } @Poster { GiapitzakisNAKH2015_2, title = {Metabolite cycled single voxel 1H spectroscopy at 9.4T}, year = {2015}, month = {6}, day = {4}, volume = {23}, number = {4696}, abstract = {Metabolite cycled proton magnetic resonance spectroscopy (MC 1H-MRS) has been proved to enhance the frequency resolution and the signal to noise ratio (SNR) of the spectrum at static magnetic fields ranging from 1.5 to 7 Tesla. The purposes of this study were to: 1) develop a short duration WS scheme for implementation with a STEAM sequence [5] 2) examine the performance of MC H-MRS compared to a WS STEAM sequence and 3) create spectrum with high frequency resolution at 9.4T enabling the detection of several metabolites.}, department = {Research Group Henning}, web_url = {http://www.ismrm.org/15/program_files/ThuEPS03.htm}, event_place = {Toronto, Canada}, event_name = {23rd Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2015)}, author = {Giapitzakis, IA and Nassirpour, S and Avdievich, N and Kreis, R and Henning, A} } @Poster { GiapitzakisH2015, title = {Comparison of different methods for combination of multichannel spectroscopy data}, year = {2015}, month = {6}, day = {3}, volume = {23}, number = {1978}, abstract = {Single voxel spectroscopy benefits from the use of multi-channel coils. Several methods have been proposed in order to increase the signal to noise ratio of the combined spectrum. In particular, three methods (Brown’s method, singular value decomposition method and generalized least square) were studied to access their performance and robustness. For this purpose, simulated data were created mimicking spectrum under different decoupling conditions, in vivo data were also used. The results demonstrated that the methods produces combined spectra with similar values of SNR. However, their robustness varies in a high degree.}, department = {Research Group Henning}, web_url = {http://www.ismrm.org/15/program_files/WedTP02.htm}, event_place = {Toronto, Canada}, event_name = {23rd Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2015)}, author = {Giapitzakis, IA and Henning, A} } @Poster { AvdievichGH2015, title = {Novel Splittable N-Tx/2N-Rx Transceiver Phased Array to Optimize both SNR and Transmit Efficiency at 9.4 T}, year = {2015}, month = {6}, day = {2}, volume = {23}, number = {1814}, abstract = {Surface loop transceiver head phased arrays improve transmit efficiency in comparison to larger Tx-only arrays due to tighter fit. However, the number of elements is limited by the number of available Tx-channels and decoupling issues, which compromises SNR and parallel receive performance. As a proof of concept we developed and constructed a novel splittable 9.4T transceiver array. Splitting of each Tx-loop doubles the number of Rx-elements without necessity of moving the array away from the subject, which allows optimization of both Tx and Rx performance at the same time. Splitting in a larger number of Rx-elements, (e.g.4, 8), is possible.}, department = {Research Group Henning}, web_url = {http://www.ismrm.org/15/program_files/TueTP06.htm}, event_place = {Toronto, Canada}, event_name = {23rd Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2015)}, author = {Avdievich, NI and Giapitzakis, IA and Henning, A} } @Poster { AvdievichGH2015_2, title = {Asymmetric Transceiver Phased Array for Functional Imaging and Spectroscopy of the Visual Cortex at 9.4 T}, year = {2015}, month = {6}, day = {1}, volume = {23}, number = {3177}, abstract = {Ultra-high field (>7T) RF coil design is challenging due to decreased transmit efficiency and strongly distorted B1 field profile. For functional SI of the visual cortex open RF coils are highly suitable since they provide an easy access and increased transmit efficiency by focusing RF field. In this work we demonstrated that a 9.4T 5-channel array with asymmetric arrangement of 4 transmit and 4 receive elements improves the transmit profile without compromising the reception. We also evaluated changes in the transmit efficiency, penetration depth and SAR due to variation in the array size and the phase shift between the elements.}, department = {Research Group Henning}, web_url = {http://www.ismrm.org/15/program_files/MonEPS03.htm}, event_place = {Toronto, Canada}, event_name = {23rd Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2015)}, author = {Avdievich, NI and Giapitzakis, IA and Henning, A} } @Poster { GiapitzakisNKAH2015, title = {Metabolite cycled proton magnetic resonance spectroscopy at 9.4T}, year = {2015}, month = {3}, day = {19}, volume = {10}, number = {382}, abstract = {Introduction Non-water suppressed metabolite cycled proton magnetic resonance spectroscopy (MC 1H-MRS) has been proven to enhance the frequency resolution and the signal to noise ratio (SNR) of the spectrum at 3 Tesla [1-2]. Previously the adiabatic inversion pulse for MC 1H-MRS was optimized to exploit these advantages for application in the human brain at 9.4T [3]. In this work, we examine the performance of STEAM [4] based MC 1H-MRS [3,5] compared to water suppressed 1H-MRS using a numerically optimized short water suppression (WS) sequence with respect to spectral resolution and signal-to-noise ratio (SNR) in the human brain at 9.4T. Methods All experiments were carried out using a 4 channel transceiver array coil [6] connected to a whole body 9.4Tesla Magnetom SIEMENS scanner. For 1H MRS localization a STEAM sequence (TE/TM/TR: 10/50/3000ms) was used. An optimized water suppression scheme consisting of 7 excitation pulses and orthogonal spoiler gradients was developed. The post processing of the data included in the given order: frequency alignment using the water reference [7], averaging, ECC [8], channel combination [9] and zero filling using factor of 2. Both sequences were applied on healthy volunteers (fig. 1-2) (NEX: 128-320, voxel size: 15x15x15mm3) placing a grey matter voxel in the occipital lobe. The optimized MC inversion pulse (IP) for the resulting B1+ of 22\(\mu\)T had a duration of 23ms and a frequency offset of 350Hz. Results The in vivo data (fig. 1) demonstrated that the simultaneously acquired water reference of MC data allowed for frequency and phase alignment of the different averages (fig. 4) leading to a line width of 25.9Hz and SNR of 38.2. In addition, the MC technique provided a WS factor of 99.8\%. On the other hand, the WS spectrum resulted in a line width of 28.9Hz (+3Hz difference), SNR of 33.3 (-5dB difference) and a WS factor of 99.7\%. The difference in SNR and linewidth is mainly produced by physiological motion (e.g. breathing, blood flow) as well as motion of the volunteer demonstrating the importance of the simultaneously acquired water reference spectrum both for the ECC and correct averaging of the acquisitions (fig. 2). Finally the MC data enabled the reconstruction of high frequency resolution spectra similar with other studies conducted on 9.4T [10]. Conclusions 1) MC 1H-MRS enables phase and frequency alignment of individual acquisitions as well as ECC of the spectrum at 9.4T 2) MC 1H-MRS performs better in terms of SNR and line width and thus effective spectral resolution compared to WS 1H-MRS and 3) MC 1H-MRS results in a free of gradient modulation sidebands and eddy current artefacts spectrum and excellent WS performance.}, department = {Research Group Henning}, web_url = {http://www.e-smi.eu/index.php?id=emim-2015-tubingen}, event_place = {T{\"u}bingen, Germany}, event_name = {10th Annual Meeting of the European Society for Molecular Imaging (EMIM 2015)}, state = {accepted}, author = {Giapitzakis, IA and Nassirpour, S and Kreis, R and Avdievich, NI and Henning, A} } @Poster { GiapitzakisSAKH2014, title = {Optimisation of Asymmetric Adiabatic Pulses for Single Voxel Metabolite Cycled 1H-MRS in the Human Brain at 9.4 Tesla}, year = {2014}, month = {5}, day = {15}, number = {2895}, abstract = {Asymmetric adiabatic pulses have been used for metabolite cycled 1H-MRS at 3 Tesla and 7 Tesla enabling better spectral resolution and post-processing of the measured data without scan time prolongation. In this abstract, the frequency excitation profile of the adiabatic pulses was extensively studied with regards to time duration, the B1+ field and the frequency sweep range. Optimum values for the characteristics of the inversion pulses were found for implementation in a STEAM sequence at 9.4T. Both phantom and in vivo measurements on a healthy volunteer verified the simulations and showed that metabolite cycled 1H-MRS is feasible at 9.4T.}, department = {Research Group Henning}, web_url = {http://www.ismrm.org/14/program_files/TP14.htm}, event_place = {Milano, Italy}, event_name = {Joint Annual Meeting ISMRM-ESMRMB 2014}, author = {Giapitzakis, IA and Shao, T and Avdievich, N and Kreis, R and Henning, A} } @Poster { GiapitzakisQW2013, title = {Co-analysis of resting state functional magnetic resonance imaging and diffusion tensor imaging for correlation of default mode network and ultra-structural deficit in posterior cortical atrophy}, journal = {Magnetic Resonance Materials in Physics, Biology and Medicine}, year = {2013}, month = {10}, day = {3}, volume = {19}, number = {Supplement 1}, pages = {84-85}, abstract = {Purpose/Introduction: Posterior cortical atrophy (PCA) is a progressive dementia syndrome characterised by early visuospatial and executive dysfunction, and differential parietal and occipital lobe atrophy; it is typically a variant of Alzheimer’s disease. This study used DTI and rsfMRI to examine the relationship between structural and functional connectivity to examine the nature of regional deficits in PCA and as proof of principle for other specific neurodegenerative disorders whose regional predilection reflects specific functional deficit. Purpose/Introduction: Posterior cortical atrophy (PCA) is a progressive dementia syndrome characterised by early visuospatial and executive dysfunction, and differential parietal and occipital lobe atrophy; it is typically a variant of Alzheimer’s disease. This study used DTI and rsfMRI to examine the relationship between structural and functional connectivity to examine the nature of regional deficits in PCA and as proof of principle for other specific neurodegenerative disorders whose regional predilection reflects specific functional deficit. Subjects and Methods: 8 PCA subjects and 12 age-matched healthy controls were compared. Data from 15 younger subjects were used to develop regional functional connectivity templates. Analyses were performed using FMRIB Software Library (FSL). Indices of functional connectivity were calculated using MELODIC (1). These were compared with structural connectivity measures within defined functional networks derived from DTI data using tract-based spatial statistics (TBSS;2). Results: There were significant differences (p<0.05) in the co-activation of the default Mode Network (DMN) and in white matter in PCA subjects compared to healthy people. Functional connectivity differed between healthy controls and PCA patients in the PCC to left and right ILPLs connections and rILPL-lILPL connection. Structural connectivity differed between healthy controls and PCA patients in the left and right ILPLs to PCC connections, rILPL-lILPL connection, MPFC-rILPL connection and MPFC-PCC connection.}, web_url = {http://link.springer.com/content/pdf/10.1007\%2Fs10334-013-0382-7.pdf}, event_place = {Toulouse, France}, event_name = {30th Annual Scientific Meeting ESMRMB 2013}, DOI = {10.1007/s10334-013-0382-7}, author = {Giapitzakis, I and Quest, RA and Waldman, AD} } @Conference { AvdievichGH2018, title = {32-Channel Combined Surface Loop / “Vertical” Loop Tight-Fit Array Provides for Full-Brain Coverage, High Transmit Performance, and SNR Improvement at 9.4T: an Alternative to Surface Loop / Dipole Antenna Combination}, year = {2018}, month = {6}, day = {18}, number = {0140}, abstract = {Tight-fit human head ultra-high field (UHF,>7T) transceiver (TxRx) surface loop phased arrays improve transmit (Tx)-efficiency in comparison to Tx-only arrays, which are larger to fit receive (Rx)-only arrays inside. A drawback of the TxRx-design is that the number of array elements is restricted by the number of available RF Tx-channels (commonly <16), which limits the Rx-performance. A new 32-element tight-fit human head array, which consists of 18 TxRx-loops and 14 Rx-only vertical loops, was constructed. The array provides for full-brain coverage, \verb=~=50\% greater B , and \verb=~=30\% greater SNR near the brain center as compared to common Tx-only/ Rx-only (ToRo) array.}, department = {Research Group Henning}, talk_type = {Abstract Talk}, web_url = {https://www.ismrm.org/18/program_files/O83.htm}, web_url2 = {https://www.ismrm.org/18/ToC.pdf}, event_place = {Paris, France}, event_name = {Joint Annual Meeting ISMRM-ESMRMB 2018}, author = {Avdievich, N and Giapitzakis, IA and Henning, A} } @Conference { AvdievichGH2017_6, title = {Combined Surface Loop/''Vertical'' Loop Elements Improve Receive Performance of a Human Head Transceiver Phased Array at 9.4T: an Alternative to Surface Loop/Dipole Antenna Combination}, journal = {Magnetic Resonance Materials in Physics, Biology and Medicine}, year = {2017}, month = {10}, day = {20}, volume = {30}, number = {Supplement 1}, pages = {S297-S298}, abstract = {Purpose/Introduction: Tight-fit human head ultra-high field (UHF, C7T) transceiver (TxRx) surface loop phased arrays (1, 2) improve transmit (Tx)-efficiency in comparison to Tx-only arrays, which are larger to fit receive (Rx)-only arrays inside (3). However, the number of TxRx-array elements is restricted by the number of Tx-channels (commonly B16), which limits Rx-performance. In this work we developed a method of increasing the number of Rx-elements without necessity of increasing the array size. We constructed a prototype of a human head array, which consists of 8 TxRx-surface ‘‘horizontal’’ loops, and 8 Rx-only ‘‘vertical’’ loops positioned perpendicularly in the center of each TxRx-loop. Subjects and Methods: The entire array measures 20 cm 9 23 cm, while horizontal and vertical loops measure 10.5 cm 9 10 cm and 3.3 cm 9 10 cm, respectively (Fig. 1). Overlapping of adjacent horizontal loops provides decoupling below -30 dB (Fig. 1) (4). Vertical loops are decoupled by preamplifier decoupling and actively detuned during transmission. The array is shielded. Electromagnetic simulations of B1 + and SAR were performed using CST Studio Suite 2015 (CST, Darmstadt, Germany) with all 16 loops included into simulations. Three voxel models were used, i.e. a head/shoulder(HS) phantom (3), which was constructed to match tissue properties at 400 MHz (3), and two voxel models, ‘‘Duke’’ and ‘‘Ella’’. Experimental B1 + maps were obtained using the AFI sequence (5). All data were acquired on a Siemens Magnetom 9.4T human imaging system. Results: EM simulations showed that introduction of vertical loops have negligible effect on the local SAR and B1 +. Experimentally measured (Fig. 2) B1 + was also similar (\textbackslashB1 +[*12.5uT/HkW) for both 16- and 8-channel arrays. Introduction of the vertical loops improved SNR up to 40\%, and at the center by *28\% (Fig. 2). Parallel Rx-performance was also improved (Fig. 3). Discussion/Conclusion: Combining horizontal and vertical loops is similar to combining surface loops with dipole antennas (6,7). This combination is required to optimize SNR at UHF (6,7). In our case instead of dipoles we used vertical loops, which are much smaller, and easier to construct. As a proof of concept we developed a method of increasing the number of Rx-elements in a human head tight-fit TxRx-array. We constructed a prototype of a 16-channel 9.4T array, which consists of 8 horizontal TxRx-surface loops and 8 Rx-only vertical loops. We demonstrated both experimentally and numerically that addition of the vertical loops substantially improves the Rx-performance without compromising the Tx-performance and the local SAR. To further improve SNR and longitudinal coverage, increasing the overall number of array elements, (double-row 16-TxRx-element/32-Rxelement array) is required.}, department = {Research Group Henning}, talk_type = {Abstract Talk}, web_url = {https://link.springer.com/content/pdf/10.1007\%2Fs10334-017-0633-0.pdf}, event_place = {Barcelona, Spain}, event_name = {34th Annual Scientific Meeting of the European Society for Magnetic Resonance in Medicine and Biology (ESMRMB 2017)}, DOI = {10.1007/s10334-017-0633-0}, author = {Avdievich, N and Giapitzakis, I and Henning, A} } @Conference { GiapitzakisFZAMKH2017, title = {Simultaneous detection of water and metabolites alternations under visual stimulation in human visual cortex utilizing metabolite cycled semi-LASER at 9.4T: preliminary results}, journal = {Magnetic Resonance Materials in Physics, Biology and Medicine}, year = {2017}, month = {10}, day = {20}, volume = {30}, number = {Supplement 1}, pages = {S246-S247}, abstract = {Purpose/Introduction: Several studies utilize the advantages of 7T to investigate the dynamic changes of brain metabolites (fMRS) under different types of functional stimulation.1–5 The purpose of this work is to exploit the even higher sensitivity of a metabolite cycled (MC) semi-LASER sequence6,7 applied at 9.4 T for fMRS under visual stimulation to verify previous results with regard to these additional metabolic adaptations. The MC technique also allows for simultaneous acquisition of water and metabolite spectra enabling the synchronous investigation of dynamic alternations of BOLD effect and metabolite levels. Subjects and Methods: All measurements were performed on a 9.4 T whole-body MRI scanner (Siemens Healthcare, Germany) using a home-built coil.8 11 volunteers participated in this study. A visual stimulus consisted of a radial red–black checkerboard that flickered with 10 Hz (ON), alternating with a black screen (OFF; Fig. 2) was applied. During the stimulation, fMRS data (NEX: 224) were acquired from a voxel (2 9 2 9 2 cm3) in the occipital lobe using MC semi-LASER sequence7 (TE/TR: 24/6000 ms). Neither water suppression nor outer volume suppression was implemented. fMRS data were processed9 and analyzed. FIDs from all volunteer were averaged and smoothed using a moving average over 16 acquisition (94 timepoints). All the acquisitions of OFF and ON periods across volunteers were summed together forming two blocks of 610 averages each. Next, the OFF block was multiplied with correction factors for linewidth using a lorentzian function, frequency shift and zero order phase. Results: The pattern of SNRwater acquired using the MC technique follows the stimulation paradigm and reflects the BOLD effect equivalent to fMRI studies (Fig. 1). High correlation coefficients between the changes of SNRwater and FWHMwater (R = -0.99), between FHWMNAA and SNRwater (R = -0.87), as well as, between FHWMtCr and FWHMwater (R = -0.92) are found (Fig. 1). Changes in Glu and GABA are reported (Fig. 2). Quantification of macromolecular baseline included the basis-set varies during different timepoints. However, these alterations are not correlated with Glu timecourse pattern indicating real changes in Glu (Fig. 3). SNR of water signal acquired during visual stimulation MC follows the paradigm pattern (red line), while SNR of water signal acquired without stimulation does not show any correlation with the paradigm blocks (blue line). In addition, changes in FHWM of water, NAA and tCr are highly correlated with the changes of water SNR indicating the BOLD effect Discussion/Conclusion: This is the first fMRS study at 9.4 T and it indicates Glu and GABA alterations in the visual cortex. For the first time, water and metabolite alterations are detected simultaneously. Correlation of FWHMwater and FWHMNAA with SNRwater shows that linewidth changes are the result of the BOLD effect10. The influence of the variations of LCModel macromolecular baseline in metabolites time-courses is evaluated. More datasets will be acquired to fully verify and confirm these results.}, department = {Research Group Henning}, department2 = {Department Logothetis}, talk_type = {Abstract Talk}, web_url = {https://link.springer.com/content/pdf/10.1007\%2Fs10334-017-0633-0.pdf}, event_place = {Barcelona, Spain}, event_name = {34th Annual Scientific Meeting of the European Society for Magnetic Resonance in Medicine and Biology (ESMRMB 2017)}, DOI = {10.1007/s10334-017-0633-0}, author = {Giapitzakis, I-A and Fichtner, N and Zaldivar, D and Avdievich, N and Manohar, S and Kreis, R and Henning, A} } @Conference { BorbathGMH2017_2, title = {Do macromolecular and spline baselines affect the metabolite quantification at 9.4T?}, journal = {Magnetic Resonance Materials in Physics, Biology and Medicine}, year = {2017}, month = {10}, day = {19}, volume = {30}, number = {Supplement 1}, pages = {S115-S116}, abstract = {Purpose/Introduction: One of the major goals in order to make MRSpectroscopy relevant for clinical practice is to ensure a robust quantitation of the spectra. Several previous studies investigated the influence of the macromolecular baseline(MMB) on the spectral quantification accuracy and precision1–12. This work extends previous work by investigating the influence of (1) the brain region specificity of the macromolecular baseline model and (2) the parameters of the additional spline-baseline on the quantification accuracy of spectra measured in the human brain at 9.4T. Subjects and Methods: Metabolite-cycled semiLASER (MCsLASER) 13 spectra (TR = 6000 ms/TE = 24 ms) were acquired from 8 volunteers(aged 28 ± 3) at a 9.4T Siemens Magnetom scanner from the occipital lobe(Occ.) with a mixed grey(40\%) and white matter(56\%) content, and from the left parietal lobe (lPar.) with a high white matter content(80\%). MMB models were created from data acquired using a double inversion MCsLASER sequence(-TI1 = 2360 ms/TI2 = 625 ms)14 from both regions (Fig. 1). using either of the two different MMB models to fit spectra from both brain regions; (2) varying parameters of the spline-baseline stiffness. The paired Wilcoxon test was used to find statistically significant differences in metabolite concentrations. Results: Up to 16 metabolites were readily quantified for both regions with Cramer Rao Lower Bounds of less than 20\%. The changes in concentrations for quantifying the spectra using the MMB from the corresponding region, versus using the MMB from the other region showed no significant difference (Fig. 2). The parameter settings for the spline-baseline did not influence this result. A-B show the fitted metabolite concentrations and their standard deviations for the different subjects, comparing the use of the different MMB for the fitting of the left parietal and the occipital lobe respectively (dkntmn = 1). The lowest measured p-value for a metabolite concentration change upon changing the MMB was 0.093 (not corrected for multiple comparisons). C-D show sample fit results for using the different MMBs for a left parietal spectrum. However, changes in the stiffness of the fitted spline-baseline lead to statistically significant concentration differences for multiple metabolites between stiff and more flexible spline-baselines (Fig. 3). Already moderately flexible spline-baselines (dkntmn\textbackslash0.5) influence the accuracy and precision of concentration estimates for several metabolites. A–B show the fitted metabolite concentrations and their standard deviations for the different subjects, comparing the use of the different stiffness parameters of the spline baseline for the fitting (the region specific MMB was used). The red stars indicate metabolite concentration pairs for which a significant change in concentrations was observed (p-value\textbackslash0.05, not corrected for multiple comparisons). C-D show sample fit results for using the different spline baseline stiffness values for an occipital spectrum. Discussion/Conclusion: This work shows for the first time, that using MMBs from different locations (lPar. and Occ.), with different underlying tissue composition does not lead to significant changes in the fitting results of the metabolites at 9.4T human studies. However, it was found, that the stiffness of the additional spline-baseline fit can significantly influence the metabolite concentrations, hence the flexibility of the spline-baseline should be restricted when quantifying spectra.}, department = {Research Group Henning}, talk_type = {Abstract Talk}, web_url = {https://link.springer.com/content/pdf/10.1007\%2Fs10334-017-0632-1.pdf}, event_place = {Barcelona, Spain}, event_name = {34th Annual Scientific Meeting of the European Society for Magnetic Resonance in Medicine and Biology (ESMRMB 2017)}, DOI = {10.1007/s10334-017-0632-1}, author = {Borb{\'a}th, T and Giapitzakis, I and Murali Manohar, SV and Henning, A} } @Conference { GiapitzakisSAFMKH2017, title = {Metabolite cycled semi-LASER and STEAM at 9.4T: Comparison and in vivo results}, year = {2017}, month = {4}, day = {27}, number = {1061}, pages = {619-620}, abstract = {The purpose of this study was the development of two new localization schemes for ultra high field (UHF) spectroscopic applications while utilizing the advantages of the Metabolite Cycling (MC) technique. In particular, a semi-adiabatic asymmetric pulse optimized for MC at 9.4T was incorporated into STEAM and semi-LASER localization schemes. In this study, these two new sequences along with the appropriate hardware setup were used to acquire in vivo 1H MRS data from the occipital lobe of the human brain and compare the corresponding results. In addition, the effect of frequency and phase correction based on the MC water spectra on data quality was investigated.}, department = {Research Group Henning}, talk_type = {Abstract Talk}, web_url = {http://www.ismrm.org/17/program_files/O46.htm}, event_place = {Honolulu, HI, USA}, event_name = {25th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2017)}, author = {Giapitzakis, I-A and Shao, T and Avdievitsch, N and Fichtner, N and Merkle, R and Kreis, R and Henning, A} } @Conference { MartinezMaestroLGM2017, title = {Dynamic changes of glutamate detected by functional MR spectroscopy in human visual cortex in regions with positive and negative BOLD response}, year = {2017}, month = {4}, day = {25}, number = {0404}, pages = {278}, abstract = {Dynamic changes of metabolite concentrations have been presented in human visual cortex in response to stimulus that induce a positive BOLD response (PBR). The present study compares the metabolic profile of the positive and the negative bold response (NBR). The application of different fMRS block designs showed a significant increase in Glutamate (+7.3\%) during the PBR stimulation paradigm in agreement with previous studies and a decrease (-6.6\%) during the NBR, which provides new information about its underlaying mechanisms.}, department = {Research Group Henning}, talk_type = {Abstract Talk}, web_url = {http://www.ismrm.org/17/program_files/O43.htm}, event_place = {Honolulu, HI, USA}, event_name = {25th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2017)}, author = {Mart{\'i}nez-Maestro, M and Labadie, C and Giapitzakis, I and M{\"o}ller, H} } @Conference { GiapitzakisAMFKH2017, title = {Functional Magnetic Resonance Spectroscopy (fMRS) using metabolite cycled semi-LASER at 9.4T: a pilot study}, year = {2017}, month = {4}, day = {25}, number = {0402}, pages = {277}, abstract = {The purpose of this work is to explore the potentials of fMRS under a visual stimulation at 9.4T using a metabolite cycled (MC) semi-LASER sequence. The MC technique allows for simultaneous acquisition of water and metabolite spectra enabling the synchronous investigation of dynamic alternations of BOLD signal and metabolite levels. Correlation of FWHMCr and FWHMNAA with SNRwater is demonstrated. The influence of misaligned subtraction is evaluated and the requirement of linewidth, frequency and phase-correction is highlighted. Finally, all previously reported alterations of upfield metabolites are confirmed and for first time also potential difference of downfield metabolites are observed.}, department = {Research Group Henning}, talk_type = {Abstract Talk}, web_url = {http://www.ismrm.org/17/program_files/O43.htm}, event_place = {Honolulu, HI, USA}, event_name = {25th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2017)}, author = {Giapitzakis, IA and Avdievitch, N and Manohar, SM and Fichtner, N and Kreis, R and Henning, A} } @Conference { FichtnerGAMZHK2017, title = {Measuring Exchange Between Brain Metabolites and Water Using Ultra-High Field Magnetic Resonance Spectroscopy}, year = {2017}, month = {2}, day = {2}, abstract = {Introduction: In the human brain, magnetic resonance spectroscopy is able to measure various metabolites of interest, visualized as peaks along a spectrum, which can be related to metabolism and functional processes. It is also able to measure chemical exchange at equilibrium, without disrupting the system. In this study, proton exchange between water and urea has been measured for the first time in human brain in vivo, at 9.4 tesla, the highest magnetic field strength human scanner available worldwide. Materials and Methods: Magnetic resonance spectroscopy data were acquired on a 9.4T magnet in a white matter region of the brain in eleven healthy volunteers and in a grey matter region of the brain in a further ten volunteers. Exchange with water was measured using an inversion transfer experiment, which involves specifically perturbing (inverting) the water proton magnetization, and waiting for certain delay times before data acquisition in order to measure varying amounts of exchange between the water protons and the other metabolites such as urea. The data were averaged and a model was developed to fit the fourteen visible peaks in the averaged spectra, including urea, at the various delay times. Results and discussion: The inversion transfer average series visualizes peaks that are strongly modulated in intensity by exchanging magnetization with the inverted water signal. In particular, the fast-exchanging peaks include urea at 5.8ppm and amide protons (related to proteins) in the 8.2-8.5ppm range. The preliminary fitting model captures most of the peaks very well, and the improved peak separation at ultra-high field has allowed for more peaks to be included in the model compared to the ones used at lower magnetic field strengths such as 3T (clinical strength) or 7T. Exchange rates for the different peaks will be obtained by Bloch McConnell simulations, which take both magnetization and exchange into account.}, department = {Research Group Henning}, department2 = {Department Logothetis}, talk_type = {Abstract Talk}, web_url = {https://www.conftool.net/gcb-symp/index.php?page=browseSessions\&form_session=27\#paperID241}, event_place = {Bern, Switzerland}, event_name = {GCB Symposium 2017: Graduate School for Cellular and Biomedical Sciences}, author = {Fichtner, ND and Giapitzakis, I-A and Avdievich, N and Merkle, R and Zaldivar, D and Henning, A and Kreis, R} } @Conference { Giapitzakis2016, title = {Metabolite Cycled Semi-LASER in Human Brain at 9.4T: In-Vivo Results}, year = {2016}, month = {8}, day = {16}, department = {Research Group Henning}, talk_type = {Abstract Talk}, web_url = {http://www.ismrm.org/workshops/Spectroscopy16/program.htm}, event_place = {Allensbach-Hegne, Germany}, event_name = {ISMRM Workshop on MR Spectroscopy: From Current Best Practice to Latest Frontiers}, author = {Giapitzakis, I-A} } @Conference { GiapitzakisKH2016, title = {Characterization of the macromolecular baseline with a metabolite-cycled double-inversion recovery sequence in the human brain at 9.4T}, year = {2016}, month = {5}, day = {9}, number = {0016}, abstract = {Macromolecular resonances (MM) overlap with metabolites resulting in inaccurate quantification of the metabolites due to baseline distortion. This effect becomes even more severe in case of short echo times (TE). The purpose of this study was the development of an adiabatic pulse for double inversion recovery and investigation of impact to include MM into quantification of 9.4T MRS data of human brain. This is the first study where MC-STEAM is combined with a double inversion technique. The results showed the advantages of UHF and MC as well as the necessity of the inclusion of MM baseline in the basis set.}, department = {Research Group Henning}, talk_type = {Abstract Talk}, web_url = {http://www.ismrm.org/16/program_files/O57.htm}, event_place = {Singapore}, event_name = {24th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2016)}, author = {Giapitzakis, IA and Kreis, R and Henning, A} } @Conference { AvdievichGPH2016, title = {Optimization of the Transceiver Phased Array for Human Brain Imaging at 9.4T: Loop Overlapping Rediscovered}, year = {2016}, month = {5}, day = {9}, number = {0169}, abstract = {Ultra-high field (UHF) (>7T) transmit (Tx) and transceiver surface loop phased arrays improve Tx-efficiency and homogeneity for human brain imaging. Overlapping the loops enhances Tx-efficiency and SNR by increasing the penetration depth. However, overlapping can compromise decoupling and SNR by generating a substantial mutual resistance. Therefore, UHF Tx-arrays are commonly constructed using gapped loops. Based on analytical optimization we constructed a 9.4T 8-loop head transceiver array. Both the magnetic and electric coupling were compensated at the same time by overlapping and excellent decoupling was obtained. Tx- and Rx-performance of the array was compared favorably to that of a gaped array.}, department = {Research Group Henning}, talk_type = {Abstract Talk}, web_url = {http://www.ismrm.org/16/program_files/O40.htm}, event_place = {Singapore}, event_name = {24th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2016)}, author = {Avdievich, NI and Giapitzakis, IA and Pfrommer, A and Henning, A} } @Conference { GiapitzakisNAKH2015, title = {1H single voxel spectroscopy at occipital lobe of human brain at 9.4 T}, journal = {Magnetic Resonance Materials in Physics, Biology and Medicine}, year = {2015}, month = {10}, volume = {28}, number = {1 Supplement}, pages = {S208-S209}, abstract = {Purpose/Introduction: Non-water suppressed metabolite cycled proton magnetic resonance spectroscopy (MC 1H-MRS) enables shotby-shot frequency and phase alignment due to the simultaneous acquisition of water and metabolite spectra [1] enhancing both frequency resolution and signal to noise ratio (SNR). In a previous study the adiabatic inversion pulse for MC 1H-MRS was optimized to exploit these advantages for application in the human brain at 9.4T [2]. In this work, we examine the performance of STEAM [3] based MC 1H-MRS compared to water suppressed 1H-MRS using a numerically optimized short water suppression (WS) sequence in human brain at 9.4T. Subjects and Methods: All experiments were conducted using a 4 channel transceiver array coil connected to a whole body 9.4 Tesla Magnetom SIEMENS scanner. For 1H MRS localization a STEAM sequence (TE/TM/TR: 10/50/3000 ms) was used. An optimized water suppression scheme was developed resulting in a WS scheme with duration of 190 ms. The WS scheme was tested on a spherical phantom filled with an aqueous solution of acetate and lactate (Fig. 1). Finally, both sequences were applied on 4 healthy volunteers (Figs. 2, 3) placing a grey matter voxel in the occipital lobe. Results: She simultaneously acquired water reference of MC data allowed frequency and phase alignment for the different averages (Fig. 2) leading to a linewidth of 25.9 Hz and SNR of 38.2. Additionally, the MC technique provided a WS factor of 99.8 \%. On the other hand, the WS spectrum resulted in a linewidth of 28.9 Hz (+3 Hz), SNR of 33.3 (-5 dB) and a WS factor of 99.7 \%. The difference in SNR and linewidth mainly arises from physiological and volunteer motion demonstrating the importance of the simultaneous acquisition of water reference spectrum both for the ECC and averaging of the acquisitions (Fig. 2). The MC data enabled the reconstruction of high frequency resolution spectra similar to other studies conducted on 9.4T [4]. Discussion/Conclusion: The conclusions of this study are: (1) MC 1H-MRS enables phase and frequency alignment of individual acquisitions and ECC of the spectrum at 9.4T, (2) MC 1H-MRS performs better in terms of SNR and line width and thus effective spectral resolution compared to WS 1H-MRS and (3) MC 1H-MRS results in a spectrum free of gradient modulation sidebands and eddy current artefacts and excellent WS performance.}, department = {Research Group Henning}, talk_type = {Abstract Talk}, web_url = {http://link.springer.com/content/pdf/10.1007\%2Fs10334-015-0488-1.pdf}, event_place = {Edinburgh, UK}, event_name = {32nd Annual Scientific Meeting ESMRMB 2015}, DOI = {10.1007/s10334-015-0488-1}, author = {Giapitzakis, IA and Nassirpour, S and Avdievich, NI and Kreis, R and Henning, A} } @Conference { AvdievichGH2015_5, title = {Novel Splittable N-Tx/2N-Rx Transceiver Phased Array to Optimize both SNR and Transmit Efficiency at 9.4T}, journal = {Magnetic Resonance Materials in Physics, Biology and Medicine}, year = {2015}, month = {10}, volume = {28}, number = {1 Supplement}, pages = {S57}, abstract = {Purpose/Introduction: Ultra-high field (UHF) (C7 T) tight fit transceiver head phased arrays improve Tx-efficiency (1, 2) in comparison to larger Tx-only arrays (3). However, increasing the number of elements above 16 is difficult due to decoupling problems and the limited number of Tx-channels. The number of Rx-elements needs to be higher to improve SNR and parallel Rx-perfomance (3). In this work, we developed and constructed a novel splittable transceiver array at 9.4 T (400 MHz). The array doubles the number of Rxelements while keeping both Tx- and Rx-elements at the same distance to a subject. Both Tx and Rx-performance are optimized using this technology. Subjects and Methods: The array (Fig. 1) consists of 4 Tx-loops (8 9 9 cm). Each loop can be split into two smaller Rx-loops (Fig. 1b). Splitting is provided by 4 PIN diode switches, S1, S2. During transmission four larger loops are produced by shortening S1 and opening S2 switches. Open S1 and shortened S2 switches produce two Rx-loops during reception. All switches are connected in series and driven by 100 mA current. The array can also be used in 4-channel mode without splitting. In both modes a 4-way splitter with 1008 phase shift between the loops was used during transmission. B1 + maps were obtained using the AFI sequence (4) and a rectangular phantom (26 9 20 9 12 cm) matching tissue properties (3). SNR and g-factor maps were obtained using non-accelerated and GRAPPA accelarated GREs (3). Data were acquired on the Siemens Magnetom Discussion/Conclusion: Both SNR and parallel reception were substantially improved by doubling the number of Rx-elements. Arrangement of elements can be adapted to future head or body applications. The direction of splitting can be chosen depending on the most beneficial direction of acceleration. Tx-elements splittable into a larger number of Rx-elements (4, 8) would allow acceleration in both directions. As a proof of concept we developed a novel splittable transceiver phased array. Both Tx- and Rx-performance are optimized using this method.}, department = {Research Group Henning}, talk_type = {Abstract Talk}, web_url = {http://link.springer.com/content/pdf/10.1007\%2Fs10334-015-0487-2.pdf}, event_place = {Edinburgh, UK}, event_name = {32nd Annual Scientific Meeting ESMRMB 2015}, DOI = {10.1007/s10334-015-0487-2}, author = {Avdievich, NI and Giapitzakis, IA and Henning, A} } @Conference { GiapitzakisNH2015, title = {Short duration water suppresion using optimised flip angles (SODA) at ultra high fields}, journal = {Magnetic Resonance Materials in Physics, Biology and Medicine}, year = {2015}, month = {10}, volume = {28}, number = {1 Supplement}, pages = {S401-S402}, abstract = {Purpose/Introduction: Proton magnetic resonance spectroscopy (MRS) enables the detection of several metabolites within the human body. The concentration of water is av thousand times higher than those of the metabolites. As a consequence, it introduces baseline distortions, eddy current and gradient modulation artifacts in the final spectrum [1–2]. Several techniques have been developed trying to suppress the water peak using special water suppression (WS) methods [3–4] etc. At low magnetic fields (i.e.\textbackslash3 T) the performance of the aforementioned WS techniques can be quite good. However, at higher magnetic fields this is a difficult task due to B1 + inhomogeneity. A solution to this problem is the development of VAPOR [5]. This method enables very good WS against B1 + ingomogeneity at the expense of time (*700 ms). This duration can prolong significantly the examination time, especially in case of time consuming sequences (e.g. multi slice MRSI). For this reason, the aim of this study was the development of a short duration water suppression using optimised flip angles (SODA) at 9.4 T. Subjects and Methods: An algorithm was developed trying to minimize the residual longitudinal magnetization for different number of CHESS [4] pulses, T1 relaxation times, B1 + inhomogeneity and time delays (Fig. 1). After the determination of the desired flip angles and time delays, an algorithm was written in order to find the best combination of gradient amplitudes for the suppression of the unwanted coherence pathways (Fig. 2; after n pulses, 3n coherence pathways are produced). Afterwards, the final WS sequence was incorporated with a STEAM technique and tested on a phantom and a healthy volunteer. All the experiments were carried out using a 4 channel transceiver array coil connected to a whole body 9.4 Tesla SIEMENS scanner. Results: The phantom results demonstrated a suppression of 99.7 \% of the initial water peak (suppression factor = 449; Fig. 3). In addition, in vivo results showed that SODA scheme allows sufficient WS giving a suppression factor[1300. Discussion/Conclusion: In this study we demonstrated a short duration WS scheme using optimized flip angles (SODA) and gradients showing preliminary results of this study. This method has a lot of room for improvements such as the introduction of phase cycling during SODA and the replacement of the Gaussian pulses with pulses with better profiles.}, department = {Research Group Henning}, talk_type = {Abstract Talk}, web_url = {http://link.springer.com/content/pdf/10.1007\%2Fs10334-015-0489-0.pdf}, event_place = {Edinburgh, UK}, event_name = {32nd Annual Scientific Meeting ESMRMB 2015}, DOI = {10.1007/s10334-015-0489-0}, author = {Giapitzakis, IA and Nassirpour, S and Henning, A} } @Conference { ScheideggerFAKGJBSH2015_2, title = {Observation of synaptic plasticity in the healthy human brain upon Ketamine infusion by 11C-ABP688-PET and 2D J-resolved 1H MRS}, year = {2015}, month = {3}, day = {20}, volume = {10}, number = {300}, abstract = {Introduction Information processing in the brain relies on the release and diffusion of neurotransmitter molecules across the synaptic cleft and on functional coupling to postsynaptic receptors, which in turn depends on the receptor plasticity. Here, we investigate the functional interplay between the major excitatory neurotransmitter glutamate (Glu) as measured by 1H-MRS and the density of the metabotropic glutamate receptor subtype 5 (mGluR5) assessed by PET. As a tool compound, we used the NMDA-receptor antagonist ketamine that was robustly shown to increase synaptic glutamate release (1). Methods 20 sex- and age-matched healthy subjects completed two imaging sessions (7 days apart) including 11C-ABP688-PET (2) performed on a PET/CT scanner (GE Medical Systems) followed by a 2D J-resolved PRESS 1H-MRS sequence scan (3) on a 3T whole-body MRI scanner (Philips Healthcare). Single voxel spectra were quantified using ProFit V2.0 (3). Metabolite levels were normalized to internal water and a segmentation based volume tissue composition correction was applied (4). PET data were analyzed using PMOD according to well established routines (5); averaged mGluR5 densities from the spectroscopy VOI were extracted. Before PET scanning, either placebo or S-ketamine (i.v. bolus of 0.12 mg/kg, infusion of 0.25 mg/kg/h over 40 min) was administered in a cross-over, double-blind, and randomized study design. Results We found highly significant correlations between post-infusion glutamate levels and mGluR5 densities (r = -.614, p = .005) as well as between post-infusion glutamate and choline levels (r=0.620, p=0.005) in the PACC following ketamine challenge, whereas none of these correlations were apparent under placebo conditions (Fig 2). Additional pairwise comparisons revealed increased total choline (tCho) metabolite levels (p = .044) after ketamine administration (0.440 ± 0.051) compared to placebo (0.418 ± 0.042). Conclusions Pharmacological modulation of the glutamatergic neurotransmitter – receptor system is assessed in the human brain for the first time. The increase in total choline levels along with the glutamate – choline correlation following ketamine infusion are likely to reflect an increase in synaptic glutamate release and related remodeling of cell membranes.}, department = {Research Group Henning}, talk_type = {Abstract Talk}, web_url = {http://www.e-smi.eu/index.php?id=emim-2015-tubingen}, event_place = {T{\"u}bingen, Germany}, event_name = {10th Annual Meeting of the European Society for Molecular Imaging (EMIM 2015)}, author = {Scheidegger, M and Fuchs, A and Ametamey, S and Kuhn, F and Giapitzakis, IA and Johayem, A and Buck, A and Seifritz, E and Henning, A} } @Conference { Giapitzakis2013, title = {Functional magnetic resonance spectroscopy at ultra-high field strength}, year = {2013}, month = {9}, day = {13}, department = {Research Group Henning}, department2 = {Department Scheffler}, talk_type = {Invited Lecture}, web_url = {http://www.neuroschool-tuebingen-cogni.de/index.php?id=374}, event_place = {T{\"u}bingen, Germany}, event_name = {Networks! 2013: 4th German Neurophysiology PhD Meeting}, author = {Giapitzakis, I} }