Contact

Dr. Nikolai Avdievitch

Address: Spemannstr. 41
72076 Tübingen
Room number: 4.B.07
Phone: +49 7071 601 713
Fax: +49 7071 601 702
E-Mail: Nikolai.Avdievitch

 

Picture of Avdievitch, Nikolai, Dr.

Nikolai Avdievitch

Position: Senior Research Scientist  Unit: Henning Scheffler

Optimization of Transmit and Receive Performance of a Head Transceiver Phased Array at 9.4 T

Motivation

Despite the intrinsic advantages of ultra-high (>7 T) field (UHF) spectroscopic imaging (SI), increased signal-to noise-ratio (SNR) and spectral resolution, few studies have been reported to date. This limitation is largely due to technical hurdles associated with radio frequency (RF) magnetic field, B1, inhomogeneity and decrease in transmit (Tx) efficiency (B1/√kW) (1). Transmit phased arrays combined with RF shimming have been shown to improve both Tx performance and homogeneity for head imaging at UHF (2,3). A common approach of optimizing receive (Rx) performance is to use a nested combination of two coils/ arrays, i.e. a smaller multi-channel  Rx-only phased array placed inside of a larger Tx-only coil/ array (3). Current state-of-the-art Rx-only phased arrays contain >30 elements to satisfy requirements for both parallel reception and high SNR. Increasing the size of a Tx coil decreases its performance, which does not impose such a problem at lower (< 3T) field strength due to higher transmit efficiency and a higher available RF power at the coil plug. However, at UHF the enlarged Tx-arrays cannot satisfy anymore requirements in high B1 and bandwidth for SI. One of the solution of the problem is using transceiver (Tx/Rx) head phased arrays with a tight fit, in which the same elements are used for both transmission and reception (2). On the other side, increasing the number of elements in head transceiver arrays above 16 is rather complicated and unpractical due to difficulties in decoupling and the limited number of available independent Tx-channels (commonly 8 or 16). My work focuses on development of UHF transceiver phased arrays, which provide for efficient transmission and the same time do not compromise SNR and parallel receive performance.

 

Transmit efficiency and SAR

An important issue in designing the UHF arrays is evaluation of a local specific absorption rate (SAR), i.e. a local heat produced by an RF coil in the human tissue. Obviously a tight fit RF coil may increase the local SAR, which should be carefully evaluated. As a prove of concept we designed and constructed a tight fit 9.4 T (400 MHz) 8-channel surface loop transceiver head array shown in Fig.1.

Figure 1

We evaluated the array Tx performance and SAR. As an example Fig.2 presents experimentally measured and simulated maps of transmit B1 field obtained for a tissue-mimicking phantom for two central projections and an example of SAR simulations. The tight fit array improves the overall axial B1+ distribution with elevated maximal and peripheral efficiency. However, the small number of array elements (8) may limit the SNR and parallel Rx performance as compared with Rx-arrays with 30 and above elements (3).

 

Figure 2

Receive Performance

We plan to apply several approaches to improve receive performance of the transceiver array. To demonstrate one of them we developed and constructed a 4-channel Tx / 8-channel Rx prototype of a novel splittable transceiver phased array. The splittable array allows doubling the number of Rx-elements without necessity of moving the Tx-elements further away from the subject. Both Tx and Rx performance can be optimized at the same time using this technology. The array (Fig.3) consists of 4 flat surface Tx-loops. Each loop can be split into two smaller

Figure 3

overlapped Rx-loops during the reception (Fig. 3B). Splitting is provided by 4 PIN diode switches, S1, S2. Figure 4 shows improvements in SNR and parallel performance (g-factor map) obtained using the splittable phased array in either 4 or 8-channel Rx mode for the same coronal slice located near the surface of the array.

Figure 4

 

References: 1) Vaughan JT et al, Magn Reson Med, 46:24-30, 2001. 2) Avdievich NI et al, Appl Magn Reson, 41(2):483-506, 2011. 3) Shajan G et al, Magn Reson Med, 71:870-879, 2014.

WORK EXPERIENCE:

Jan. 2013-Current

Senior Research Scientist, Department for Ultra-High Field MRI, Max Planck Institute for Biological Cybernetics, Tübingen, Germany.

 

July 2012- Dec 2012

Senior RF Engineer, Resonance Research Instruments, Inc., Billerica, MA, USA.

 

Jan. 2007-June 2012

Associate Research Scientist, Magnetic Resonance Research Center, Department of Neurosergery, Yale University, New Haven, CT, USA.

 

Oct. 2000-Dec. 2006

Associate in Radiology, Magnetic Resonance Research Center, Department of Radiology, Albert Einstein Medical College, Bronx, NY, USA.

 

Feb. 1998-Oct. 2000

Electron Spin Resonance (ESR) Lab Manager, ESR Research Resource Center, Department of Physiology & Biophysics, Albert Einstein Medical College, Bronx, NY, USA.

 

1994-Feb. 1998

Postdoctoral Associate, Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA.

 

1993-1994

Researcher, Laboratory of Spin and Magnetic Phenomena, International Tomography Center, Russian Academy of Science (Siberian Branch), Novosibirsk, Russia.

 

1992-1993

Researcher, Laboratory of Magnetic Phenomena, Institute of Chemical Kinetics and Combustion, Russian Academy of Science (Siberian Branch), Novosibirsk, Russia.

 

1987-1992

Junior Researcher, Laboratory of Magnetic Phenomena, Institute of Chemical Kinetics and  Combustion, Russian Academy of Science (Siberian Branch), Novosibirsk, Russia.

 

1985-1987

Engineer, Laboratory of Physical Methods of Chemical Kinetics, Institute of Chemical Kinetics and Combustion, Russian Academy of Science (Siberian Branch), Novosibirsk, Russia.

 

1983-1985

Research Technician, Laboratory of Physical Methods of Chemical Kinetics, Institute of Chemical Kinetics and Combustion, Russian Academy of Science (Siberian Branch), Novosibirsk, Russia.

 

EDUCATION:

1993

Ph.D. in Physical Chemistry, Institute of Chemical Kinetic and Combustion, Russian Academy of Science (Siberian Branch), Novosibirsk, Russia.

1985

M.S., Chemical Physics, Department of Physics, Novosibirsk State University, Novosibirsk, Russia.

1983

B.S., Radiophysics, Department of Physics, Novosibirsk State University, Novosibirsk, Russia.

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Articles (51):

Zoelch N, Hock A, Heinzer-Schweizer S, Avdievitch N and Henning A (August-2017) Accurate determination of brain metabolite concentrations using ERETIC as external reference NMR in Biomedicine 30(8) 1-16.
Giapitzakis IA, Avdievich NI and Henning A (July-2017) Characterization of macromolecular baseline at 9.4 T Magnetic Resonance in Medicine . submitted
Fichtner N, Giapitzakis IA, Avdievich N, Mekle R, Zaldivar D, Henning A and Kreis R (July-2017) 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 NeuroImage . submitted
Avdievich NI, Giapitzakis IA and Henning A (July-2017) Combined Surface Loop/"Vertical" Loop Element Improve Receive Performance of a Human Head Transceiver Array at 9.4T: an Alternative to Surface Loop/Dipole Antenna Combination NMR in Biomedicine . in revision
Giapitzakis IA, Shao T, Avdievich NI, Mekle R, Kreis R and Henning A (July-2017) Metabolite-cycled STEAM and semi-LASER localization for MR spectroscopy of the human brain at 9.4T Magnetic Resonance in Medicine . in revision
Avdievich N, Pfrommer A, Giapitzakis IA and Henninmg A (June-2017) Analytical modeling provides new insight into complex mutual coupling between surface loops at ultrahigh fields NMR in Biomedicine Epub ahead.
Avdievich NI, Giapitzakis I-A, Pfrommer A and Henning A (June-2017) Decoupling of a tight-fit transceiver phased array for human brain imaging at 9.4T: Loop overlapping rediscovered Magnetic Resonance in Medicine Epub ahead.
Avdievich NI, Hoffmann J, Shajan G, Pfrommer A, Giapitzakis IA, Scheffler K and Henning A (February-2017) Evaluation of transmit efficiency and SAR for a tight fit transceiver human head phased array at 9.4 T NMR in Biomedicine 30(2) 1-12.
Avdievich NI, Giapitzakis IA and Henning A (November-2016) Novel splittable N-Tx/2N-Rx transceiver phased array to optimize both signal-to-noise ratio and transmit efficiency at 9.4T Magnetic Resonance in Medicine 76(5) 1621-1628.
Hoffmann J, Henning A, Giapitzakis IA, Scheffler K, Shajan G, Pohmann R and Avdievich NI (September-2016) Safety testing and operational procedures for self-developed radiofrequency coils NMR in Biomedicine 29(9) 1131–1144.
Avdievich NI, Pan JW and Hetherington HP (November-2013) Resonant inductive decoupling (RID) for transceiver arrays to compensate for both reactive and resistive components of the mutual impedance NMR in Biomedicine 26(11) 1547–1554.
Pan JW, Dockrow RB, Spencer DD, Avidievich NI and Hetherington HP (February-2013) Selective homonuclear polarization transfer for spectroscopic imaging of GABA at 7T Magnetic Resonance in Medicine 69(2) 310–316.
Avdievich NI (December-2011) Transceiver-Phased Arrays for Human Brain Studies at 7 T Applied Magnetic Resonance 41(2-4) 483-506.
Pan JW, Avdievich N and Hetherington HP (November-2010) J-refocused coherence transfer spectroscopic imaging at 7 T in human brain Magnetic Resonance in Medicine 64(5) 1237–1246.
Avdievich NI, Oh S, Hetherington HP and Collins CM (August-2010) Improved homogeneity of the transmit field by simultaneous transmission with phased array and volume coil Journal of Magnetic Resonance Imaging 32(2) 476–481.
Hetherington HP, Avdievich NI, Kuznetsov AM and Pan JW (January-2010) F shimming for spectroscopic localization in the human brain at 7 T Magnetic Resonance in Medicine 63(1) 9–19.
Avdievich NI and Hetherington HP (November-2009) High-field head radiofrequency volume coils using transverse electromagnetic (TEM) and phased array technologies NMR in Biomedicine 22(9) 960–974.
Avdievich NI, Pan JW, Baehring JM, Spencer DD and Hetherington HP (July-2009) Short echo spectroscopic imaging of the human brain at 7T using transceiver arrays Magnetic Resonance in Medicine 62(1) 17–25.
Avdievich NI, Hetherington HP, Kuznetsov AM and Pan JW (February-2009) 7T head volume coils: Improvements for rostral brain imaging Journal of Magnetic Resonance Imaging 29(2) 461–465.
Bigal ME, Hetherington H, Pan J, Tsang A, Grosberg B, Avdievich N, Friedman B and Lipton RB (May-2008) Occipital levels of GABA are related to severe headaches in migraine Neurology 70(22) 2078–2080.
Avdievich NI, Bradshaw K, Lee J-H, Kuznetsov AM and Hetherington HP (August-2007) 4 T split TEM volume head and knee coils for improved sensitivity and patient accessibility Journal of Magnetic Resonance 187(2) 234–241.
Avdievich NI and Hetherington HP (June-2007) 4 T Actively detuneable double-tuned 1H/31P head volume coil and four-channel 31P phased array for human brain spectroscopy Journal of Magnetic Resonance 186(2) 341–346.
Avdievich NI, Bradshaw K, Kuznetsov AM and Hetherington HP (June-2007) High-field actively detuneable transverse electromagnetic (TEM) coil with low-bias voltage for high-power RF transmission Magnetic Resonance in Medicine 57(6) 1190–1195.
Avdievich NI, Peshkovsky AS, Kennan RP and Hetherington HP (October-2006) SENSE imaging with a quadrature half-volume transverse electromagnetic (TEM) coil at 4T Journal of Magnetic Resonance Imaging 24(4) 934–938.
Peshkovsky AS, Cerioni L, Osan TM, Avidievich NI and Pusiol DJ (September-2006) Three-dimensional high-inductance birdcage coil for NQR applications Solid State Nuclear Magnetic Resonance 30(2) 75–80.
Forbes MDE, Dukes KE, Avdievich NI, Harbron EJ and DeSimone JM (February-2006) Flexible Biradicals in Liquid and Supercritical Carbon Dioxide:  The Exchange Interaction, the Chain Dynamics, and a Comparison with Conventional Solvents Journal of Physical Chemistry A 110(5) 1767–1774.
Peshkovsky A, Kennan RP, Nagel RL and Avdievich NI (January-2006) Sensitivity enhancement and compensation of RF penetration artifact with planar actively detunable quadrature surface coil Magnetic Resonance Imaging 24(1) 81–87.
Peshkovsky AS, Kennan RP, Fabri ME and Avdievich NI (April-2005) Open half-volume quadrature transverse electromagnetic coil for high-field magnetic resonance imaging Magnetic Resonance in Medicine 53(4) 937–943.
Avdievich NI and Hetherington HP (December-2004) 4 T actively detunable transmit/receive transverse electromagnetic coil and 4-channel receive-only phased array for 1H human brain studies Magnetic Resonance in Medicine 52(6) 1459–1464.
Avdievich NI, Krymov VN and Hetherington HP (July-2003) Modified perturbation method for transverse electromagnetic (TEM) coil tuning and evaluation Magnetic Resonance in Medicine 50(1) 13–18.
Burns CS, Aronoff-Spencer E, Dunham CM, Lario P, Avdievich NI, Antholine WE, Olmstead MM, Vrielink A, Gerfen GJ, Peisach J, Scott WG and Millhauser GL (March-2002) Molecular Features of the Copper Binding Sites in the Octarepeat Domain of the Prion Protein Biochemistry 41(12) 3991-4001.
Avdievich NI and Gerfen GJ (December-2001) Multifrequency Probe for Pulsed EPR and ENDOR Spectroscopy Journal of Magnetic Resonance 153(2) 178–185.
Aronoff-Spencer E, Burns CS, Avdievich NI, Gerfen GJ, Pelsach J, Antholine WE, Ball HL, Cohen FE, Prusiner SE and Millhauser GL (November-2000) Identification of the Cu2+ Binding Sites in the N-Terminal Domain of the Prion Protein by EPR and CD Spectroscopy Biochemistry 39(45) 13760–13771.
Tsentalovich YP, Morozova OB, Avdievich NI, Ananchenko GS, Yurkovskaya AV, Ball JD and Forbes MDE (November-1997) Influence of Molecular Structure on the Rate of Intersystem Crossing in Flexible Biradicals Journal of Physical Chemistry A 101(47) 8809–8816.
Avdievich NI, Dukes KE, Forbes MDE and DeSimone JM (January-1997) Time-Resolved EPR Study of a 1,9-Flexible Biradical Dissolved in Liquid Carbon Dioxide. Observation of a New Spin-Relaxation Phenomenon:  Alternating Intensities in Spin-Correlated Radical Pair Spectra Journal of Physical Chemistry A 101(4) 617–621.
Forbes MDE, Schulz GE and Avdievich NI (October-1996) Unusual Dynamics of Micellized Radical Pairs Generated from Photochemically Active Amphiphiles Journal of the American Chemical Society 118(43) 10652–10653.
Forbes MDE, Avdievich NI, Ball JD and Schulz GR (August-1996) Chain Dynamics Cause the Disappearance of Spin-Correlated Radical Pair Polarization in Flexible Biradicals Journal of Physical Chemistry 100(33) 13887–13891.
Forbes MDE, Ball JD and Avdievich NI (May-1996) In Search of Through-Solvent Electronic Coupling in Flexible Biradicals Journal of the American Chemical Society 118(19) 4707–4708.
Avdievich NI, Jeevarajan AS and Forbes MDE (March-1996) Photoionization of N,N,N‘,N‘-Tetramethylphenylenediamine Studied by Q-Band Time-Resolved EPR Spectroscopy. Separation of Singlet and Triplet Ionization Channels Journal of Physical Chemistry 100(13) 5334–5342.
Avdievich NI and Forbes MDE (February-1996) Strong Modulation of the Exchange Interaction in a Spin-Polarized, Aryl Ether-Linked 1,14-Biradical Journal of Physical Chemistry 100(6) 1993–1995.
Jeevarajan AS, Kispert LD, Avdievich NI and Forbes MDE (January-1996) Role of Excited Singlet State in the Photooxidation of Carotenoids:  A Time-Resolved Q-Band EPR Study Journal of Physical Chemistry 100(2) 669–671.
Avdievich NI and Forbes MDE (June-1995) Dynamic Effects in Spin-Correlated Radical Pair Theory: J Modulation and a New Look at the Phenomenon of Alternating Line Widths in the EPR Spectra of Flexible Biradicals Journal of Physical Chemistry 99(24) 9660–9667.
Tarasov VF, Bagranskaya EG, Shkrob IA, Avdievich NI, Ghatlia ND, Lukzen NN, Turro NJ and Sagdeev RZ (January-1995) Examination of the Exchange Interaction through Micellar Size. 3. Stimulated Nuclear Polarization and Time Resolved Electron Spin Resonance Spectra from the Photolysis of Methyldeoxybenzoin in Alkyl Sulfate Micelles of Different Sizes Journal of the American Chemical Society 117(1) 110–118.
Tarasov VF, Ghatila ND, Avdievich NI, Shkrob IA, Buchachenko AL and Turro NJ (March-1994) Examination of the Exchange Interaction through Micelle Size. 2. Isotope Separation Efficiency as an Experimental Probe Journal of the American Chemical Society 116(6) 2281–2291.
Polyakov NE, Taraban MB, Kruppa AI, Avdievich NI, Mokrushin VV, Schastnev PV, Leshina TV, Lüsis V, Muceniece D and Duburs G (August-1993) The mechanisms of oxidation of NADH analogues 3. Stimulated nuclear polarization (SNP) and chemically induced dynamic nuclear polarization (CIDNP) in low magnetic fields in photo-oxidation reactions of 1,4-dihydropyridines with quinones Journal of Photochemistry and Photobiology A: Chemistry 74(1) 75-79.
Tarasov VF, Ghatlia ND, Avdievich NI and Turro NJ (January-1993) Exchange Interaction in Micellized Radical Pairs Zeitschrift für Physikalische Chemie 182(1-2) 227–244.
Avdievich NI, Bagryanskaya EG, Tarasov VF and Sagdeev RZ (January-1993) Investigation of Micellized Radical Pairs in the Photolysis of Ketones by Time-Resolved Stimulated Nuclear Polarization Zeitschrift für Physikalische Chemie 182(1-2) 107–117.
Bagryanskaya EG, Tarasov VF, Avdievich NI and Shkrob IA (May-1992) Electron spin exchange in micellized radical pairs. III. 13C low-field ratio frequency stimulated nuclear polarization spectroscopy (LF SNP) Chemical Physics 162(1) 213–223.
Bagryanskaya EG, Avdievich NI, Grishin YA and Sagdeev RZ (July-1989) The study of microwave-induced nuclear polarization in the sensitized trans-cis isomerization of fumaronitrile Chemical Physics 135(1) 123–129.
Avdievich NI, Bagryanskaya EG, Grishin YA and Sagdeev RZ (February-1989) Time-resolved stimulated nuclear polarization Chemical Physics Letters 155(2) 141–145.
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Last updated: Monday, 22.05.2017