Center for Advanced Imaging Innovation and Research and Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, New York, USA.
The Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, New York, USA.
Magn Reson Med. 2018 Mar;79(3):1789-1803. doi: 10.1002/mrm.26803. Epub 2017 Jul 4.
Previous work with body-size objects suggested that loops are optimal MR detectors at low fields, whereas electric dipoles are required to maximize signal-to-noise ratio (SNR) at ultrahigh fields ( ≥ 7 T). Here we investigated how many loops and/or dipoles are needed to approach the ultimate intrinsic SNR (UISNR) at various field strengths.
We calculated the UISNR inside dielectric cylinders mimicking different anatomical regions. We assessed the performance of various arrays with respect to the UISNR. We validated our results by comparing simulated and experimental coil performance maps.
Arrays with an increasing number of loops can rapidly approach the UISNR at fields up to 3 T, but are suboptimal at ultrahigh fields for body-size objects. The opposite is true for dipole arrays. At 7 T and above, 16 dipoles provide considerably larger central SNR than any possible loop array, and minimal g factor penalty for parallel imaging.
Electric dipoles can be advantageous at ultrahigh fields because they can produce both curl-free and divergence-free currents, whereas loops are limited to divergence-free contributions only. Combining loops and dipoles may be optimal for body imaging at 3 T, whereas arrays of loops or dipoles alone may perform better at lower or higher field strengths, respectively. Magn Reson Med 79:1789-1803, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
以往对体型物体的研究表明，在低场下，环路是最优的磁共振探测器，而在超高场（≥7T）下，需要电偶极子来最大化信噪比（SNR）。在此，我们研究了在不同场强下需要多少个环路和/或电偶极子才能接近极限固有 SNR（UISNR）。
我们计算了模拟不同解剖区域的介电圆柱内的 UISNR。我们评估了各种阵列相对于 UISNR 的性能。我们通过比较模拟和实验线圈性能图来验证我们的结果。
随着环路数量的增加，阵列可以在高达 3T 的场强下快速接近 UISNR，但在超高场强下对体型物体的性能并不理想。对于偶极子阵列则相反。在 7T 及以上，16 个偶极子提供的中心 SNR 明显大于任何可能的环路阵列，并且对并行成像的最小 g 因子惩罚也较小。
在超高场强下，电偶极子可能具有优势，因为它们可以产生无旋和无散电流，而环路仅局限于无散电流贡献。在 3T 时，环路和偶极子的组合可能是体成像的最佳选择，而单独的环路或偶极子阵列在较低或较高场强下的性能可能更好。磁共振医学 79:1789-1803, 2018。©2017 国际磁共振学会。
