Department of Radiology, Weill Cornell Medicine, New York, New York, USA.
USC Mark and Mary Stevens Neuroimaging and Informatics Institute, Los Angeles, California, USA.
NMR Biomed. 2022 Dec;35(12):e4802. doi: 10.1002/nbm.4802. Epub 2022 Aug 10.
Lack of a body-sized, bore-mounted, radiofrequency (RF) body coil for ultrahigh field (UHF) magnetic resonance imaging (MRI) is one of the major drawbacks of UHF, hampering the clinical potential of the technology. Transmit field (B ) nonuniformity and low specific absorption rate (SAR) efficiencies in UHF MRI are two challenges to be overcome. To address these problems, and ultimately provide a pathway for the full clinical potential of the modality, we have designed and simulated two-dimensional cylindrical high-pass ladder (2D c-HPL) architectures for clinical bore-size dimensions, and demonstrated a simplified proof of concept with a head-sized prototype at 7 T. A new dispersion relation has been derived and electromagnetic simulations were used to verify coil modes. The coefficient of variation (CV) for brain, cerebellum, heart, and prostate tissues after B shimming in silico is reported and compared with previous works. Three prototypes were designed in simulation: a head-sized, body-sized, and long body-sized coil. The head-sized coil showed a CV of 12.3%, a B efficiency of 1.33 μT/√W, and a SAR efficiency of 2.14 μT/√(W/kg) for brain simulations. The body-sized 2D c-HPL coil was compared with same-sized transverse electromagnetic (TEM) and birdcage coils in silico with a four-port circularly polarized mode excitation. Improved B uniformity (26.9%) and SAR efficiency (16% and 50% better than birdcage and TEM coils, respectively) in spherical phantoms was observed. We achieved a CV of 12.3%, 4.9%, 16.7%, and 2.8% for the brain, cerebellum, heart, and prostate, respectively. Preliminary imaging results for the head-sized coil show good agreement between simulation and experiment. Extending the 1D birdcage coil concept to 2D c-HPLs provides improved B uniformity and SAR efficiency.
超高磁场 (UHF) 磁共振成像 (MRI) 缺乏一个适合人体大小、安装在磁体孔径内、用于发射射频 (RF) 信号的体线圈，这是 UHF 的主要缺点之一，限制了该技术的临床应用潜力。在 UHF MRI 中，发射场 (B )不均匀和低吸收率 (SAR) 效率是两个需要克服的挑战。为了解决这些问题，并最终为该模态的全部临床潜力提供途径，我们针对临床孔径尺寸设计并模拟了二维圆柱形高通 (2D c-HPL) 结构，并在 7 T 上用一个头模原型演示了简化的概念验证。已经推导出一个新的色散关系，并使用电磁模拟来验证线圈模式。报告了在计算机中对 B 进行匀场后的脑组织、小脑、心脏和前列腺组织的变异系数 (CV)，并与以前的工作进行了比较。在模拟中设计了三个原型：一个头模大小、一个体模大小和一个长体模大小的线圈。头模大小的线圈在脑模拟中显示出 12.3%的 CV、1.33 μT/√W 的 B 效率和 2.14 μT/√(W/kg)的 SAR 效率。体模大小的 2D c-HPL 线圈与相同大小的横电磁 (TEM) 和鸟笼线圈在计算机中进行了比较，采用四端口圆极化模式激励。在球形模体中观察到更好的 B 均匀性（比鸟笼和 TEM 线圈分别提高 26.9%和 16%和 50%）和 SAR 效率。对于脑、小脑、心脏和前列腺，我们分别实现了 12.3%、4.9%、16.7%和 2.8%的 CV。对头模大小的线圈进行的初步成像结果表明，模拟和实验之间具有良好的一致性。将 1D 鸟笼线圈的概念扩展到 2D c-HPL 可以提高 B 均匀性和 SAR 效率。
