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Performance optimization of local magnetic resonance surface coils and antennas.

机译：优化局部磁共振表面线圈和天线的性能。

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The signal-to-noise ratio (SNR) is a fundamental measure of the quality of the signals obtained in Magnetic Resonance (MR) Technology. The primary focus of this dissertation is the optimization of MR coils and antennas to maximize SNR, using analytical methods and field calculations by numerical electromagnetic method of moments (MoM) as well as experimental validation.;First, a biopsy needle MR imaging (MRI) antenna to collect biopsy samples from internal organs is developed. It can perform MRI at the needle position, for device tracking and high resolution imaging.;Second, a tunable planar strip array antenna that can be tuned with a size matched to specific MRI applications is developed. Then, a single element of the tunable planar strip array is analyzed by field calculations to optimize the SNR performance with respect to its geometric and electric parameters. The findings are summarized as design rules of thumb.;Third, the SNR performances of the following quadrature surface detectors are evaluated: (i) figure'8'/butterfly shaped loops combined with circular loop elements; (ii) a novel quadrature MRI detector that we developed comprised of a strip detector and a circular; and (iii) an overlapped array of two loops. The SNR is optimized for each pair and the SNR performance compared for detectors optimized to the same depth. The SNR-optimized figure-8 detector has a loop radius r8∼0.6d, so r8/r0∼1.3 in an optimized quadrature detector. The optimized butterfly coil has side length ∼ d and cross-over angle of ≥ 150° at the center.;Finally, detector noise figures (NFs) are used to characterize the SNR limits of circular loop coils. Loops made of copper wire and copper tapes are considered in the analysis. Losses from conductors, capacitors, solder joints, eddy currents in overlapped array coils and sample losses from 40-400 MHz are estimated using analytical and numerical electromagnetic calculations and measurements. From the analysis it is found that loops made of wire and tape, perform similarly, but tape coils in arrays have substantial eddy current losses.;The analysis involving numerical, analytical and experimental methods resulted in optimal MR resonator designs that can be incorporated in the modern day MR systems.
机译：信噪比（SNR）是磁共振（MR）技术中获得的信号质量的基本指标。本论文的主要重点是利用分析方法和通过矩量电磁方法（MoM）进行的场计算以及实验验证来优化MR线圈和天线以最大化SNR。首先，活检针MR成像（MRI）开发了从内部器官收集活检样本的天线。它可以在针头位置执行MRI，以进行设备跟踪和高分辨率成像。其次，开发了一种可调谐的平面条状阵列天线，其尺寸可以根据特定的MRI应用进行调整。然后，通过现场计算分析可调平面条状阵列的单个元素，以针对其几何和电参数优化SNR性能。第三，评估以下正交表面检测器的信噪比性能：（i）数字“ 8” /蝴蝶形环与圆环元件组合； （ii）我们开发的新型正交MRI检测器，包括条形检测器和圆形检测器； （iii）两个循环的重叠阵列。 SNR针对每对进行了优化，而SNR性能则针对针对相同深度进行了优化的检测器进行了比较。 SNR优化的数字8检测器的环路半径为r8〜0.6d，因此在优化的正交检测器中为r8 / r0〜1.3。优化的蝶形线圈的边长约为d，中心的交叉角≥150°;最后，使用探测器噪声系数（NFs）来表征圆环线圈的SNR极限。分析中考虑了由铜线和铜带制成的环。使用分析和数值电磁计算和测量来估算导体，电容器，焊点，重叠阵列线圈中的涡流和40-400 MHz范围内的样品损耗的损耗。从分析中发现，由金属丝和胶带制成的环路的性能相似，但是阵列中的胶带线圈具有很大的涡流损耗。;涉及数值，分析和实验方法的分析得出了最佳的MR谐振器设计，可以将其纳入设计中。现代MR系统。

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