利用高介电常数材料降低7T MR成像用高阻抗射频阵列中的电场与SAR
Electric Field and SAR Reduction in High Impedance RF Arrays by Using High Permittivity Materials for 7T MR Imaging
AI总结：
针对7T高阻抗射频线圈因低电容元件导致高电场和SAR的安全问题，提出用高介电常数材料降低电场与SAR，同时保持B1效率和解耦性能。
摘要：
在超高场条件下，更高的频率和更短的波长带来了显著的设计问题，使多通道阵列装置成为超高场MR成像的关键组成部分。对多通道阵列的需求，以及不断增加阵列通道数量的努力，始终受到阵元间耦合这一主要问题的限制。这种耦合会影响电流和场分布、通道间噪声相关性以及阵列元件的频率，从而降低成像质量和性能。为充分发挥UHF MRI的潜力，必须确保将阵列元件之间的耦合降至最低。高阻抗线圈能够提供最佳隔离，同时只需极少的设计修改，从而使阵列系统充分发挥其潜力。但这些微小的设计改动需要在传统回路上使用低电容以产生升高的阻抗，由此带来不可忽视的重大安全隐患。低电容集总元件两端会形成高电场，可能导致受检者体内SAR值升高、沉积更多功率，并最终给人体样本带来更大的与组织发热相关的损伤风险。针对这一重要安全问题，我们提出一种创新方法：利用高介电常数材料有效降低成像样本中的电场和SAR值，同时保持B1效率和阵列元件之间的阵元解耦，并且对由高阻抗线圈组成的现有阵列设计仅作最小改动。
英文摘要：
Higher frequencies and shorter wavelengths present significant design issues at ultra-high fields, making multi-channel array setup a critical component for ultra-high field MR imaging. The requirement for multi-channel arrays, as well as ongoing efforts to increase the number of channels in an array, are always limited by the major issue known as inter-element coupling. This coupling affects the current and field distribution, noise correlation between channels, and frequency of array elements, lowering imaging quality and performance. To realize the full potential of UHF MRI, we must ensure that the coupling between array elements is kept to a minimum. High-impedance coils allow array systems to completely realize their potential by providing optimal isolation while requiring minimal design modifications. These minor design changes, which demand the use of low capacitance on the conventional loop to induce elevated impedance, result in a significant safety hazard that cannot be overlooked. High electric fields are formed across these low capacitance lumped elements, which may result in higher SAR values in the imaging subject, depositing more power and, ultimately, providing a greater risk of tissue heating-related injury to the human sample. We propose an innovative method of utilizing high-dielectric material to effectively reduce electric fields and SAR values in the imaging sample while preserving the B1 efficiency and inter-element decoupling between the array elements to address this important safety concern with minimal changes to the existing array design comprising high-impedance coils.
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