@Article{ EhsesSMBJGG2012,
title = {IR TrueFISP with a golden-ratio-based radial readout: Fast quantification of T1, T2, and proton density},
journal = {Magnetic Resonance in Medicine},
year = {2013},
month = {1},
volume = {69},
number = {1},
pages = {71–81},
abstract = {A promising approach for the simultaneous quantification of relative proton density (M0), T1, and T2 is the inversion-recovery TrueFISP sequence, consisting of an inversion pulse followed by a series of balanced steady-state free precession acquisitions. Parameters can then be obtained from a mono-exponential fit to the series of images. However, a segmented acquisition is usually necessary, which increases the total acquisition time considerably. The goal of this study is to obtain M0, T1, and T2 maps using a single-shot acquisition, with T1 and T2 measurements in brain that are consistent with the published literature, with a 20-fold speed improvement over the segmented approach, and at a clinically relevant spatial resolution. To this end, a single-shot inversion-recovery TrueFISP sequence was combined with a radial view-sharing technique. The parameters M0, T1, and T2 were then obtained on a pixel-wise basis from a three fit parameter to the signal evolution. The accuracy of this method for quantifying these parameters is demonstrated in vivo. In addition, further corrections to the quantification necessary owing to other experimental factors, namely magnetization transfer and imperfect slice profiles, were developed. Including additional scans necessary for these corrections in the measurement protocol, the required scan time is increased from approximately 6 to 18-28 s per slice.},
web_url = {http://onlinelibrary.wiley.com/doi/10.1002/mrm.24225/pdf},
state = {published},
DOI = {10.1002/mrm.24225},
author = {Ehses P{ehses}{Department High-Field Magnetic Resonance}, Seiberlich N, Ma D, Breuer FA, Jakob PM, Griswold MA and Gulani V}
}

@Article{ SeiberlichLEDGG2011,
title = {Improved temporal resolution in cardiac imaging using through-time spiral GRAPPA},
journal = {Magnetic Resonance in Medicine},
year = {2011},
month = {12},
volume = {66},
number = {6},
pages = {1682–1688},
abstract = {Previous work has shown that the use of radial GRAPPA for the reconstruction of undersampled real-time free-breathing cardiac data allows for frame rates of up to 30 images/s. It is well known that the spiral trajectory offers a higher scan efficiency compared to radial trajectories. For this reason, we have developed a novel through-time spiral GRAPPA method and demonstrate its application to real-time cardiac imaging. By moving from the radial trajectory to the spiral trajectory, the temporal resolution can be further improved at lower acceleration factors compared to radial GRAPPA. In addition, the image quality is improved compared to those generated using the radial trajectory due to the lower acceleration factor. Here, we show that 2D frame rates of up to 56 images/s can be achieved using this parallel imaging method with the spiral trajectory.},
web_url = {http://onlinelibrary.wiley.com/doi/10.1002/mrm.22952/pdf},
state = {published},
DOI = {10.1002/mrm.22952},
author = {Seiberlich N, Lee G, Ehses P{ehses}, Duerk JL, Gilkeson R and Griswold MA}
}

@Article{ SeiberlichEDGG2011,
title = {Improved radial GRAPPA calibration for real-time free-breathing cardiac imaging},
journal = {Magnetic Resonance in Medicine},
year = {2011},
month = {2},
volume = {65},
number = {2},
pages = {492-505},
abstract = {To generate real-time, nongated, free-breathing cardiac images, the undersampled radial trajectory combined with parallel imaging in the form of radial GRAPPA has shown promise. However, this method starts to fail at high undersampling factors due to the assumptions that must be made for the purposes of calibrating the GRAPPA weight sets. In this manuscript, a novel through-time radial GRAPPA calibration scheme is proposed which greatly improves image quality for the high acceleration factors required for real-time cardiac imaging. This through-time calibration method offers better image quality than standard radial GRAPPA, but it requires many additional calibration frames to be acquired. By combining the through-time calibration method proposed here with the standard through-k-space radial GRAPPA calibration method, images with high acceleration factors can be reconstructed using few calibration frames. Both the through-time and the hybrid through-time/through-k-space methods are investigated to determine the most advantageous calibration parameters for an R = 6 in vivo short-axis cardiac image. Once the calibration parameters have been established, they are then used to reconstruct several in vivo real-time, free-breathing cardiac datasets with temporal resolutions better than 45 msec, including one with a temporal resolution of 35 msec and an in-plane resolution of 1.56 mm2.},
web_url = {http://onlinelibrary.wiley.com/doi/10.1002/mrm.22618/pdf},
state = {published},
DOI = {10.1002/mrm.22618},
author = {Seiberlich N, Ehses P{ehses}, Duerk J, Gilkeson R and Griswold M}
}

@Article{ LopezEBPGJ2010,
title = {A four-channel hole-slotted phased array at 7 Tesla},
journal = {Concepts in Magnetic Resonance B: Magnetic Resonance Engineering},
year = {2010},
month = {10},
volume = {37B},
number = {4},
pages = {226-236},
abstract = {In recent years, the phased array coil technology has found more and more its way in applications at high field small animal systems. However, these coil arrays are usually based on simple loops and are mostly used in rat imaging studies only. Mouse imaging studies are limited to the use of linear arrays or volume resonators. Recently, a novel surface coil design based on the hole-slot magnetron's geometry was introduced to MRI. The hole-slot magnetron is a vacuum tube which operates e.g. as a high frequency oscillator in radar applications. It has been shown that the magnetron surface coil allows for a deeper RF penetration than a conventional coil both at 1.5 and 4 Tesla.

The objective of this work was to find an optimal loop coil based on the hole-slot magnetron geometry in order to build a volume phased array for cardiac imaging with improved SNR on the centre of the sample. To achieve this goal, different magnetron loops were simulated and evaluated towards their performance. Based on these results the best performing hole-slot magnetron geometries were built and compared. In addition, the magnetron loop (referred as hole-slotted coil) with the best sensitivity was compared with conventional simple loop geometries. Furthermore, a four channel hole-slotted phased array based on the magnetron's design theory was built, evaluated and compared with a conventional four channel array. The four channel hole-slotted array shows improved RF penetration depth over the four channel array with simple loop geometry.},
web_url = {http://onlinelibrary.wiley.com/doi/10.1002/cmr.b.20173/pdf},
state = {published},
DOI = {10.1002/cmr.b.20173},
author = {Lopez MA, Ehses P{ehses}, Breuer FA, Ponce IP, Gareis D and Jakob PM}
}

@Article{ NordbeckWERWFHJLQB2009,
title = {Measuring RF-induced currents inside implants: Impact of device configuration on MRI safety of cardiac pacemaker leads},
journal = {Magnetic Resonance in Medicine},
year = {2009},
month = {3},
volume = {61},
number = {3},
pages = {570-578},
abstract = {Radiofrequency (RF)-related heating of cardiac pacemaker leads is a serious concern in magnetic resonance imaging (MRI). Recent investigations suggest such heating to be strongly dependent on an implant's position within the surrounding medium, but this issue is currently poorly understood. In this study, phantom measurements of the RF-induced electric currents inside a pacemaker lead were performed to investigate the impact of the device position and lead configuration on the amount of MRI-related heating at the lead tip. Seven hundred twenty device position/lead path configurations were investigated. The results show that certain configurations are associated with a highly increased risk to develop MRI-induced heating, whereas various configurations do not show any significant heating. It was possible to precisely infer implant heating on the basis of current intensity values measured inside a pacemaker lead. Device position and lead configuration relative to the surrounding medium are crucial to the amount of RF-induced heating in MRI. This indicates that a considerable number of implanted devices may incidentally not develop severe heating in MRI because of their specific configuration in the body. Small variations in configuration can, however, strongly increase the risk for such heating effects, meaning that hazardous situations might appear during MRI.},
web_url = {http://onlinelibrary.wiley.com/doi/10.1002/mrm.21881/pdf},
state = {published},
DOI = {10.1002/mrm.21881},
author = {Nordbeck P, Weiss I, Ehses P{ehses}, Ritter O, Warmuth M, Fidler F, Herold V, Jakob PM, Ladd ME, Quick HH and Bauer WR}
}

@Article{ SeiberlichBEMBJG2009,
title = {Using the GRAPPA operator and the generalized sampling theorem to reconstruct undersampled non-Cartesian data},
journal = {Magnetic Resonance in Medicine},
year = {2009},
month = {3},
volume = {61},
number = {3},
pages = {705-715},
abstract = {As expected from the generalized sampling theorem of Papoulis, the use of a bunched sampling acquisition scheme in conjunction with a conjugate gradient (CG) reconstruction algorithm can decrease scan time by reducing the number of phase-encoding lines needed to generate an unaliased image at a given resolution. However, the acquisition of such bunched data requires both modified pulse sequences and high gradient performance. A novel method of generating the “bunched” data using self-calibrating GRAPPA operator gridding (GROG), a parallel imaging method that shifts data points by small distances in k-space (with Δk usually less than 1.0, depending on the receiver coil) using the GRAPPA operator, is presented here. With the CG reconstruction method, these additional “bunched” points can then be used to reconstruct an image with reduced artifacts from undersampled data. This method is referred to as GROG-facilitated bunched phase encoding (BPE), or GROG-BPE. To better understand how the patterns of bunched points, maximal blip size, and number of bunched points affect the reconstruction quality, a number of simulations were performed using the GROG-BPE approach. Finally, to demonstrate that this method can be combined with a variety of trajectories, examples of images with reduced artifacts reconstructed from undersampled in vivo radial, spiral, and rosette data are shown.},
web_url = {http://onlinelibrary.wiley.com/doi/10.1002/mrm.21891/pdf},
state = {published},
DOI = {10.1002/mrm.21891},
author = {Seiberlich N, Breuer FA, Ehses P{ehses}, Moriguchi H, Blaimer M, Jakob PM and Griswold MA}
}

@Article{ EhsesFNPWJB2008,
title = {MRI thermometry: Fast mapping of RF-induced heating along conductive wires},
journal = {Magnetic Resonance in Medicine},
year = {2008},
month = {8},
volume = {60},
number = {2},
pages = {457-461},
abstract = {Conductive implants are in most cases a strict contraindication for MRI examinations, as RF pulses applied during the MRI measurement can lead to severe heating of the surrounding tissue. Understanding and mapping of these heating effects is therefore crucial for determining the circumstances under which patient examinations are safe. The use of fluoroptic probes is the standard procedure for monitoring these heating effects. However, the observed temperature increase is highly dependent on the positioning of such a probe, as it can only determine the temperature locally. Temperature mapping with MRI after RF heating can be used, but cooling effects during imaging lead to a significant underestimation of the heating effect. In this work, an MRI thermometry method was combined with an MRI heating sequence, allowing for temperature mapping during RF heating. This technique may provide new opportunities for implant safety investigations.},
web_url = {http://onlinelibrary.wiley.com/doi/10.1002/mrm.21417/pdf},
state = {published},
DOI = {10.1002/mrm.21417},
author = {Ehses P{ehses}, Fidler F, Nordbeck P, Pracht ED, Warmuth M, Jakob PM and Bauer WR}
}

@Article{ CeymannHESPSF2008,
title = {Solution structure of the Legionella pneumophila Mip-rapamycin complex},
journal = {BMC Structural Biology},
year = {2008},
month = {8},
volume = {8},
number = {17},
pages = {1-12},
abstract = {Background
Legionella pneumphila is the causative agent of Legionnaires' disease. A major virulence factor of the pathogen is the homodimeric surface protein Mip. It shows peptidyl-prolyl cis/trans isomerase activty and is a receptor of FK506 and rapamycin, which both inhibit its enzymatic function. Insight into the binding process may be used for the design of novel Mip inhibitors as potential drugs against Legionnaires' disease.
Results
We have solved the solution structure of free Mip77–213 and the Mip77–213-rapamycin complex by NMR spectroscopy. Mip77–213 showed the typical FKBP-fold and only minor rearrangements upon binding of rapamycin. Apart from the configuration of a flexible hairpin loop, which is partly stabilized upon binding, the solution structure confirms the crystal structure. Comparisons to the structures of free FKBP12 and the FKBP12-rapamycin complex suggested an identical binding mode for both proteins.
Conclusion
The structural similarity of the Mip-rapamycin and FKBP12-rapamycin complexes suggests that FKBP12 ligands may be promising starting points for the design of novel Mip inhibitors. The search for a novel drug against Legionnaires' disease may therefore benefit from the large variety of known FKBP12 inhibitors.},
web_url = {http://www.biomedcentral.com/content/pdf/1472-6807-8-17.pdf},
state = {published},
DOI = {10.1186/1472-6807-8-17},
author = {Ceymann A, Horstmann M, Ehses P{ehses}, Schweimer K, Paschke A-K, Steinert M and Faber C}
}

@Article{ NordbeckFWWFEGRJLQB2008,
title = {Spatial distribution of RF-induced E-fields and implant heating in MRI},
journal = {Magnetic Resonance in Medicine},
year = {2008},
month = {8},
volume = {60},
number = {2},
pages = {312-319},
abstract = {The purpose of this study was to assess the distribution of RF-induced E-fields inside a gel-filled phantom of the human head and torso and compare the results with the RF-induced temperature rise at the tip of a straight conductive implant, specifically examining the dependence of the temperature rise on the position of the implant inside the gel. MRI experiments were performed in two different 1.5T MR systems of the same manufacturer. E-field distribution inside the liquid was assessed using a custom measurement system. The temperature rise at the implant tip was measured in various implant positions and orientations using fluoroptic thermometry. The results show that local E-field strength in the direction of the implant is a critical factor in RF-related tissue heating. The actual E-field distribution, which is dependent on phantom/body properties and the MR-system employed, must be considered when assessing the effects of RF power deposition in implant safety investigations.},
web_url = {http://onlinelibrary.wiley.com/doi/10.1002/mrm.21475/pdf},
state = {published},
DOI = {10.1002/mrm.21475},
author = {Nordbeck P, Fidler F, Weiss I, Warmuth M, Friedrich MT, Ehses P{ehses}, Geistert W, Ritter O, Jakob PM, Ladd ME, Quick HH and Bauer WR}
}

@Article{ HorstmannESSKFHRF2006,
title = {Domain Motions of the Mip Protein from Legionella pneumophila},
journal = {Biochemistry},
year = {2006},
month = {10},
volume = {45},
number = {40},
pages = {12303-12311},
abstract = {The homodimeric 45.6 kDa (total mass) Mip protein, a virulence factor from Legionella pneumophila, was investigated with solution NMR spectroscopy and molecular dynamics (MD) simulations. Two Mip monomers are dimerized via an N-terminal helix bundle that is connected via a long α-helix to a C-terminal FKBP domain in each subunit. More than 85% of the amino acids were identified in triple-resonance NMR spectra. 15N relaxation analysis showed a bimodal distribution of R1/R2 values, with the lower ratio in the N-terminal domain. Relaxation dispersion measurements confirmed that these reduced ratios did not originate from conformational exchange. Thus, two different correlation times (τc) can be deduced, reflecting partly uncoupled motions of both domains. Relaxation data of a Mip77-213 monomer mutant were similar to those observed in the dimer, corroborating that the FKBP domain, including part of the connecting helix, behaves as one dynamic entity. MD simulations (18 ns) of the Mip dimer also yielded two different correlation times for the two domains and thus confirm the independence of the domain motions. Principal component analysis of the dihedral space covariance matrix calculated from the MD trajectory suggests a flexible region in the long connecting helix that acts as a hinge between the two domains. Such motion provides a possible explanation of how Mip can bind to complex molecular components of the extracellular matrix and mediate alveolar damage and bacterial spread in the lung.},
web_url = {http://pubs.acs.org/doi/abs/10.1021/bi060818i},
state = {published},
DOI = {10.1021/bi060818i},
author = {Horstmann M, Ehses P{ehses}, Schweimer K, Steinert M, Kamphausen T, Fischer G, Hacker J, R\"osch P and Faber C}
}

@Poster{ EhsesBSS2012,
title = {Distortion-free high-resolution fMRI at 9.4 T},
year = {2012},
month = {5},
volume = {20},
number = {0329},
abstract = {SNR benefits allow for significantly higher resolution in BOLD fMRI at ultra-high fields. On the flip side, faster T2* relaxation leads to blurring and increased B0 field inhomogeneities aggravate distortion artifacts in EPI BOLD imaging at higher fields. In this work, a single-echo gradient-echo sequence is presented, that is optimized for high BOLD SNR by combining the concept of echo-shifting with an interleaved slice order. The method is demonstrated in finger tapping experiments on a human 9.4T system. The result is a BOLD activation map with 1mm isotropic resolution virtually free from distortions.},
web_url = {http://www.ismrm.org/12/},
event_name = {20th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2012)},
event_place = {Melbourne, Australia},
state = {published},
author = {Ehses P{ehses}{Department High-Field Magnetic Resonance}, Budde J{juliane}{Department High-Field Magnetic Resonance}, Shajan G{shajang}{Department High-Field Magnetic Resonance} and Scheffler K{scheffler}{Department High-Field Magnetic Resonance}}
}

@Poster{ BreuerESBJG2012,
title = {High quality Real-Time Cardiac MRI using Self-Calibrating Radial GRAPPA with Sparsification},
year = {2012},
month = {5},
volume = {20},
number = {4246},
abstract = {In this work an improved self-calibrating radial GRAPPA algorithm for real-time cardiac MRI is presented. It is shown that by subtracting the temporal average prior to the parallel MRI reconstruction significantly improved image quality can be achieved over pure radial GRAPPA. Real-time cardiac imaging data at a frame rate of 20fps in 2mm in-plane resolution are shown using only 16 radial projections per frame.},
web_url = {http://www.ismrm.org/12/},
event_name = {20th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2012)},
event_place = {Melbourne, Australia},
state = {published},
author = {Breuer F, Ehses P{ehses}{Department High-Field Magnetic Resonance}, Seiberlich N, Blaimer M, Jakob P and Griswold M}
}

@Conference{ EhsesBSS2013,
title = {T2-weighted BOLD fMRI at 9.4 T using a S2-SSFP-EPI sequence},
year = {2013},
month = {4},
volume = {21},
number = {0414},
abstract = {It has been hypothesized that T2-weighted BOLD fMRI at ultra-high field shows higher spatial specificity than T2*-weighted BOLD, since the main signal contribution is expected to come from the extravascular spins of the microvasculature. Unfortunately, the number of slices that can be acquired in multi-slice SE-EPI is limited at ultra-high field due to SAR constraints. T2-weighted steady-state sequences, such as S2-SSFP, have been previously used as an alternative to spin-echo based BOLD fMRI. In this work, we present a 3D S2-SSFP sequence that is accelerated using an EPI readout and show first results from finger tapping experiments at 9.4 T.},
file_url = {fileadmin/user_upload/files/publications/2013/ISMRM-2013-0414.pdf},
web_url = {http://www.ismrm.org/13/session41.htm},
event_name = {21st Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2013)},
event_place = {Salt Lake City, UT, USA},
state = {published},
author = {Ehses P{ehses}{Department High-Field Magnetic Resonance}, Budde J{juliane}{Department High-Field Magnetic Resonance}, Shajan G{shajang}{Department High-Field Magnetic Resonance} and Scheffler K{scheffler}{Department High-Field Magnetic Resonance}}
}

@Conference{ OttEBBJB2012,
title = {Towards a full 3D MR parameter quantification by means of (demodulated) off-resonance insensitive balanced SSFP},
journal = {Magnetic Resonance Materials in Physics, Biology and Medicine},
year = {2012},
month = {10},
volume = {25},
number = {Supplement 1},
pages = {63},
abstract = {Purpose/Introduction: Quantitative MR parameter mapping has been demonstrated to allow for improved diagnosis and staging of diseases[1]. In this work, a novel procedure for the simultaneous quantification of the relaxation times T1, T2, the relative spin-density PD and the off-resonance frequency Δω is proposed. To this end a series of different phase-cycled 3D-bSSFP measurements are employed. The contrast behavior of the bSSFP sequence depends on both T1 and T2 and varies strongly with the applied phase-cycle and the local off-resonance frequency. We show, that the data can be numerically fitted to the bSSFP signal equation allowing for the simultaneous extraction of T1, T2, PD and Δω. An advantage of this approach is that it provides an intrinsic compensation for bSSFP off-resonance effects. The methodology is validated in a phantom study and the applicability is demonstrated in-vivo.
Subjects and Methods: A series of 3D-bSSFP-experiments with different phase-cycles are acquired. The corresponding signal equation is well known[2] and has been shown to resemble an ellipse-equation[3]. By fitting the data
numerically onto the ellipse signal-equation T1, T2, PD and the local offresonance frequency Δω for each voxel in the 3D image can be obtained.
Phantom experiments were performed on containers doped with different Gd-concentrations to provide a wide range of T1- and T2-values. In addition, in-vivo brain data has been acquired from a volunteers with an isotropic resolution of 1.3x1.3x1.3mm³ within 21min.
Results: The obtained phantom parameter maps show good agreement with reference values. A comparison is depicted in the Fig.1. The parameter maps do not suffer from banding-artifacts due to “off-resonant”-spins despite the
relatively long TR. In contrast to other methods T2-values small as 10 to 20ms can be measured in high accuracy.
The in-vivo data in Fig.2 shows accurate T1, T2 as well as PD and Δω (not shown) maps. Off-resonance effects, usually present in the frontal cortex, are compensated.
Discussion/Conclusion: A novel method for parameter quantification has been presented. The method is based on a single bSSFP-sequence with fixed TR and a single flip-angle. Only the phase-cycle is changed during the measurement.
We have shown that full 3D-MR-parameter mapping in high isotropic resolution is feasible. We hypothesize that significant scan-time reductions can be achieved by employing acceleration techniques such as parallel imaging
or Compressed Sensing, making the method an promising candidate for clinical applications.},
web_url = {http://www.springerlink.com/content/l06327757h0k661u/},
event_name = {29th Annual Scientific Meeting ESMRMB 2012},
event_place = {Lisboa, Portugal},
state = {published},
DOI = {10.1007/s10334-012-0321-z},
author = {Ott M, Ehses P{ehses}{Department High-Field Magnetic Resonance}, Blaimer M, Benkert T, Jakob P and Breuer F}
}