超低磁場超導量子干涉元件核磁共振與造影之研究

Microtesla Nuclear Magnetic Resonance and Imaging with a Superconducting Quantum Interference Device

陳名傑(Ming-Jye Chen)

指導教授 ： 楊鴻昌

國立臺灣大學/理學院/物理學研究所/博士(2012年)

https://doi.org/10.6342/NTU.2012.01848

摘要

本文旨在研究超低磁場下的超導量子干涉元件核磁共振與造影；系統使用室溫的接收線圈並將其感測到的核磁共振訊號經由液態氮冷卻的變壓線圈藕和到高溫超導磁量計，待測樣品會先在600高斯的預先極化磁場磁化，再切換到100微米磁場量測；實驗的磁場產生裝置在實驗室自行建造，其中，測量磁場B0是由一組三對線圈組合的改良版Helmholtz線圈，梯度線圈則是由Maxwell對(Gz)，與雙平面線圈(Gx, Gy)等組成，從測量的核磁共振頻譜分析得到測量磁場能在5 x 5米見方的範圍內具有100 ppm的均勻度；此外，與在射頻磁場操作的傳統核磁共振系統相比，超低磁場超導量子干涉元件核磁共振系統在音頻範圍量測，具有電路簡化的優勢。
實驗研究去離子水含磁流體樣品的弛豫特性，透過改變預極化磁場磁化時間測量自旋-晶格弛豫速率(1/T1)，並使用多重自旋回波序列測量自旋-自旋弛豫速率(1/T2) ，結果顯示1/T1與1/T2兩者均與磁流體的磁化率成正比，推測是由於磁流體含量較高的樣品具有較高的磁化率，散佈在去離子水中會破壞局域的磁場均勻度，導致質子間的自旋相位分散，使得弛豫速率增加；實驗最後並以磁流體為對比劑實現T1對比影像，其造影的方法將在文中進一步的說明討論，此結果亦顯示超低磁場超導量子干涉元件核磁共振具有潛力進一步發展為癌症造影的檢驗工具。

關鍵字

超導 ； 超導量子干涉元件 ； 核磁共振 ； 磁振造影 ； 磁流體

並列摘要

This work studied nuclear magnetic resonance with a high-Tc superconducting quantum interference device(SQUID) in the microtesla magnetic fields. In the scheme of measurement, the NMR signal was detected by a cooper solenoid at room temperatures and coupled to a very sensitive high-Tc SQUID magnetometer via a cooper transformer at liquid-nitrogen temperature. The samples were pre-polarized at higher magnetic fields, 600 Gauss, and measured at 100 μT magnetic field. In such a low measurement field, apparatus can be easily obtained by homemade. We constructed a three-pair Helmholtz-like coil for Bo measurement field, a Maxwell pair for Gz gradient field, biplanar pairs for Gx and Gy gradient fields. The analysis from the linewidth of NMR spectrum revealed a very uniform measurement field ~ 100 ppm in range of 5 x 5 cm2. Since the measurement field was low as in audio frequency, it takes the advantage of the simplified electronics in contrast to the conventional NMR experiment working with radio-frequency electronics.
To demonstrate the potential application of the SQUID NMR/MRI, samples of ferrofluid diluted in water were examined to study the relaxation properties and magnetic resonance imaging. The intensity of spin-echo NMR signal as function of prepolarization time was used to drive the rate of spin-lattice relaxation (1/T1). The rate of spin-spin relaxation (1/T2) was derived by peak strength of multi-echo NMR signals which follow the free induction decay. It was found that both 1/T1 and 1/T2 increase linearly when the magnetic susceptibility χ of SPIO increases by increasing the concentration of SPIO dispersed in water. In an applied field, magnetic moments of SPIO generate microscopic field gradients that weaken the field homogeneity, in turn dephasing the proton’s nuclear spin and enhancing the relaxation rates. A T1-contrast image is demonstrated, using SPIO as the contrast agent and high-Tc superconducting quantum interference devices as the detector. T1-contrast imaging in microtesla fields might provide a potential modality for discriminating cancer.

並列關鍵字

Superconductivity ； SQUID ； NMR ； MRI ； Ferrofluid

參考文獻

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