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http://dx.doi.org/10.9718/JBER.2008.29.2.099

Time-Multiplexed RF Transmission to Improve $B_1$ Homogeneity in High Field MRI  

Han, Byung-Hee (Dept. of Biomedical Engineering, Kyung Hee University)
Seo, Jeung-Hun (Dept. of Biomedical Engineering, Kyung Hee University)
Heo, Hye-Young (Dept. of Biomedical Engineering, Kyung Hee University)
Lee, Soo-Yeol (Dept. of Biomedical Engineering, Kyung Hee University)
Publication Information
Journal of Biomedical Engineering Research / v.29, no.2, 2008 , pp. 99-106 More about this Journal
Abstract
To improve $B_1$ homogeneity in high field MRI, the RF power is applied to the transmit array coil elements sequentially in the time-multiplexed way. Since only a single coil element is activated in a time-multiplexing slot, the global standing wave formation in the human body is greatly suppressed. The time-multiplexing slot width is on the order of micro seconds, hence, high-order-harmonic slices can be placed far from the transmit coil and simultaneous multiple slice selection can be avoided. The $B_1$ homogeneities of a birdcage coil and an eight-channel transmit array coil have been compared through finite difference time domain simulations. The simulation results indicate that the proposed technique can reduce the peak-to-peak $B_1$ inhomogeneity down to one fourth of the transmission with a birdcage coil on the central plane of the human head model at 3 T. The mimicking experiments at 3 T, eight separate experiments with a single coil element activated and image reconstruction by combining the eight images, also show promising results. It is expected that the proposed technique has some advantages over other $B_1$ improving methods in real practice since simple RF switching circuitries are only necessary and electromagnetic coupling between the coil elements is out of concern in its realization.
Keywords
$B_1$ homogeneity; time-multiplexed transmission; transmit array coil; high field; dielectric effect;
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1 T. Vaughan, L. DelaBarre, C. Snyder, J. Tian, C. Akgun, D. Shrivastava, W. Liu, C. Olson, G. Adriany, J. Strupp, P. Andersen, A. Gopinath, P.-F. van de Moortele, M. Garwood, and K. Ugurbil, '9.4T human MRI: preliminary results,' Magn. Reson. Med., vol. 56, pp. 1274-1282, 2006   DOI   ScienceOn
2 D.C. Alsop, T.J. Connick, and G. Mizsei, 'A spiral volume coil for improved RF field homogeneity at highstatic magnetic field strength,' Magn. Reson. Med., 1998;40:4954
3 S. Saekho, F.E. Boada, D.C. Noll, and V.A. Stenger, 'Small tip angle three-dimensional tailored radiofrequency slab-select pulse for reduced $B_{1}$ inhomogeneity at 3T,' Magn. Reson. Med., vol. 53, pp. 479-484, 2005   DOI   ScienceOn
4 U. Katscher, P. Bernert, C. Leussler, and J.S. van den Brink, 'Transmit SENSE,' Magn. Reson. Med., vol. 49, pp. 144-150, 2003   DOI   ScienceOn
5 U. Katscher, P. Bornert, and J.S. van den Brink, 'Theoretical and numerical aspects of transmit SENSE,' IEEE Trans. Med. Imaging, vol. 23, pp. 520-525, 2004   DOI   ScienceOn
6 Z. Zhang, C.-Y. Yip, W. Grissom, D.C. Noll, F.E. Boada, and V.A. Stenger, 'Reduction of transmitter $B_{1}$ inhomogeneity with transmit SENSE slice-select pulses,' Magn. Reson. Med. vol. 57, pp. 842-847, 2007   DOI   ScienceOn
7 C.M. Collins, B.L. Beck, J.R. Fitzsimmons, S.J. Blackband, and M.B. Smith, 'Strengths and limitations of pulsing coils in an array sequentially to avoid RF interference in high field MRI,' in Proc. 13th Annual Meeting of ISMRM, Miami Beach, FL, USA, 2005, Abstract 816
8 J. Wang, S.H. Oh, M.B. Smith, and C.M. Collins, 'RF shimming considering both excitation homogeneity and SAR,' in Proc. 15th Annual Meeting of ISMRM, Berlin, Germany, 2007, Abstract 1022
9 X. Wu, C. Akgun, J.T. Vaughan, K. Ugurbil, P.F. Van de Moortele, 'SAR analysis for transmit SENSE at 7T with a human head model,' in Proc. 15th Annual Meeting of ISMRM, Berlin, Germany, 2007, Abstract 3350
10 D.I. Hoult, 'The principle of reciprocity in signal strength calculations-A mathematical guide,' Concepts Magn. Reson., vol. 12, pp. 173-187, 2000   DOI   ScienceOn
11 W. Mao, Z. Wang, M.B. Smith, and C.M. Collins, 'Calculation of SAR for transmit coil arrays,' Concepts Magn. Reson. Part B, vol. 31B, pp.127-131, 2007   DOI   ScienceOn
12 C.M. Collins, Z. Wang, W. Mao, J. Fang, W. Liu, G. Adriany, J.T. Vaughan, K. Ugurbil, and M.B. Smith, 'Multi-coil composite pulses for whole-brain homogeneity improved over RF shimming alone,' in Proc. 14th Annual Meeting of ISMRM, Seattle, USA, 2006, Abstract 702
13 P. Bottomley, and E. Andrews, 'RF magnetic field penetration, phase shift and power dissipation in biological tissue: implications for NMR imaging,' Phys. Med. Biol., vol. 23, pp. 630-643, 1978   DOI   ScienceOn
14 T.S. Ibrahim, R. Lee, B.A. Baertlein, A.M. Abduljalil, H. Zhu, and P.L. Robitaille, 'Effect of RF coil excitation on field inhomogeneity at ultra high fields: a field optimized TEM resonator,' Magn. Reson. Imag., vol. 19, pp. 1339-1347, 2001   DOI   ScienceOn
15 C.A.T. Van den Berg, B. Van den Bergen, J.B. Van de Kamer, B.W. Raaymakers, H. Kroeze, L. Bartels, J.J. Lagendijk, 'Simultaneous $B_{1}+$ homogenization and specific absorption rate hotspot suppression using a magnetic resonance phase array transmit coil,' Magn. Reson. Med., vol. 57, pp. 577-586, 2007   DOI   ScienceOn
16 R. Deichmann, C.D. Good, and R. Turner, 'RF inhomogeneity compensation in structural brain imaging,' Magn. Reson. Med., vol. 47, pp. 398-402, 2002   DOI   ScienceOn
17 Y.D. Zhu, 'Parallel excitation with an array of transmit coils,' Magn. Reson. Med., vol. 51, pp. 775-784, 2004.   DOI   ScienceOn
18 S. Conolly, D. Nishimura, and A. Macovski, 'A selective adiabatic spin-echo pulse,' J. Magn. Reson., vol. 83, pp. 324-334, 1989
19 S. Saekho, C. Yip, D.C. Noll, F.E. Boada, and VA Stenger, 'Fast-kz three-dimensional tailored radiofrequency pulse for reduced $B_{1}$ inhomogeneity,' Magn. Reson. Med., vol. 55, pp. 719-724, 2006   DOI   ScienceOn
20 C.M. Collins, W. Liu, B.J. Swift, and MB. Smith, 'Combination of optimized transmit arrays and some receive array reconstruction methods can yield homogeneous imagesat very high frequencies,' Magn. Reson. Med., vol. 54, pp. 1327-1332, 2005   DOI   ScienceOn
21 P. Ulhnann, S. Junge, M. Wick, F. Seifert, W. Ruhm, and J. Hennig, 'Experimental analysis of parallel excitation using dedicated coil setups and simultaneous RF transmission on multiple channels,' Magn. Reson. Med., vol. 54, pp. 994-1001, 2005   DOI   ScienceOn
22 K. Setsompop, L.L. Wald, V. Alagappan, B. Gagoski, F. Hebrank, U. Fontius, F. Schmitt, and E. Adalsteinsson, 'Parallel RF transmission with eight channels at 3 Tesla,' Magn. Reson. Med., vol. 56, pp. 1163-1171. 2006   DOI   ScienceOn
23 J.T. Vaughan, H.P. Hetherington, J.O. Out, J.W. Pan, and G.M. Pohost, 'High frequency volume coils for clinical NMR imaging and spectroscopy,' Magn. Reson. Med., vol. 32, pp. 206-218, 1994   DOI
24 C.M. Collins, Z. Wang, W. Mao, J. Fang, W. Liu, and M.B. Smith, 'Array-optimized composite pulse for excellent whole-brain homogeneity in high-field MRI,' Magn. Reson. Med., vol. 57, pp. 470-474, 2007   DOI   ScienceOn
25 A.C. Zelinski, Y.K. Goyal, L. Angelone, G. Bonmassar, L.L. Wald, and E. Adalsteinsson, 'Designing RF pulses with optimal specific absorption rate (SAR) characteristics and exploring excitation fidelity, SAR and duration tradeoffs,' in Proc. 15th Annual Meeting of ISMRM, Berlin, Germany, 2007, Abstract 1699
26 J.T. Vaughan, G. Adriany, C.J. Snyder, J. Tian, T. Thiel, L. BOlinger, H. Liu, L. DelaBarre, and K. Ugurbil, 'Efficient high-frequency body coil for high-field MRI,' Magn. Reson. Med., vol. 52, pp. 851-859, 2004   DOI   ScienceOn
27 W. Mao, M.B. Smith, and C.M. Collins, 'Exploring the limits of RF shimming for high-field MRI of the human head,' Magn. Reson. Med., vol. 56, pp. 918-922, 2006   DOI   ScienceOn