臺灣博碩士論文加值系統

本論文旨在研究發展高品質多通道核磁共振接受器，研究分為二部分。第一部分發展3T 32通道頭部相列線圈，此線圈為環狀對稱排列，針對一維或二維的加速影像重建設計。利用信噪比及重建影像雜訊放大率(g-factor)作為衡量標準，與商用32通道足球型頭部相列線圈相比，結果顯示本線圈設計在加速情況下擁有較高的信噪比與較低的g-factor。我們所研發的頭部相列線圈之信噪比在造影外圍區域為足球型頭部相列線圈的2.36倍，而中心區域大約是0.8倍。第二部分為磁場偵測器系統設計與應用，此系統可偵測動態磁場變化，校正渦電流(eddy current)及梯度線圈不完美造成的k空間軌跡偏移。在應用方面，我們展示此系統運用在重建螺旋軌跡(spiral trajectory)之影像重建上。本研究也提出，利用特製激發線圈可以同時確保磁場偵測器不受成像物體訊號干擾，並同時可獲得高品質核磁共振信號。總結來說，此環狀對稱頭部線圈用於加速影像重建上，可提供高品質的人腦影像，而場偵測器系統則可應用於偵測k-space軌跡與影像校正的一項利器。

This research aims at developing multi-channel radio-frequency (RF) receiver systems. In the first part of the thesis, I developed a 32-channel 3T head coil array with circular symmetric (CS) geometry tailored for 1D and 2D accelerated acquisitions and image reconstructions. Compared to a commercial 32-channel head coil array with soccer-ball geometry (SB array), the CS array has higher signal-to-noise ratio (SNR) and lower reconstruction image noise amplification (g-factor) in accelerated acquisitions. The SNR in the CS array was about 236% and 80% of the SB array at the periphery and the center of the FOV, respectively. The second part of the thesis summarizes the efforts of developing field probe systems. Field probe systems can monitor magnetic field fluctuation caused by imperfect gradients, and eddy current. The information can be used to correct k-space trajectory. Images acquired from a spiral k-space trajectory were used to demonstrate the effectiveness of our field probe system by comparing the image reconstructed with/without the measured k-space trajectory. We also present a novel transceiver field probe system to allow high quality monitoring local magnetic field disturbances dynamically at the same frequency of the imaging object with minimized interferences. In conclusion, the CS array can be a helpful tool to provide high quality images of the human brain in accelerated MRI acquisitions. Field probe systems are useful tools in calibrating the k-space trajectory.

摘要...ii
Abstract...iii
List of Figures...viii
List of Tables...xiii
Introduction...1
Part I...4
1. Introduction...5
2. Method...8
2.1. Circularly symmetric 32-channel array design...8
2.2. Bench measurements...12
2.3. Single channel control experiment...13
2.4. Imaging experiments...14
3.2.1. Noise covariance matrix, SNR, g-factor maps, and anatomical images...14
3.2.2. Parallel MRI using a Cartesian k-space trajectory...17
3.2.3. Parallel MRI using a radial k-space trajectory...17
3. Results...18
3.1. Bench measurements...18
3.2. Single channel control experiment...19
3.3. Imaging experiments...20
3.3.1. Noise covariance matrix, SNR profiles, and anatomical images...20
3.3.2. Parallel MRI using a Cartesian k-space trajectory...22
3.3.3. Parallel MRI using a radial k-space trajectory...33
4. Discussion...34
Part II...38
1. Introduction...39
2. Method...42
2.1. Field probe construction and optimizing the susceptibility matching...42
2.2. Coupling reduction between probes and RF coils...44
2.3. Isolation between probes and image object...48
2.4. A Field probe transceiver system with controllable RF coupling and decoupling...49
2.5. Field probe application...52
2.5.1. Magnetic Field Measurement...52
2.5.2. An application of spiral trajectory with 2D correction using 8-channel Field probes monitoring system with susceptibility matching type C and RF shield...53
3. Result...55
3.1. Field probe construction with optimizing susceptibility matching...55
3.2. Coupling reduction between probes and RF coils...59
3.3. Isolation between probes and image object...60
3.4. A field probe transceiver system with controllable RF coupling and decoupling...62
3.5. An application of spiral trajectory with 2D correction using 8-channelField probes monitoring system...63
4. Discussion...67
Conclusion...71
Reference...72

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