摘要
本研究結合了超導量子干涉元件(Superconducting quantum interference device, SQUID )磁性量測技術，並使用預先極化技術提升磁矩的磁化率，在鋁屏蔽屋裡建造低場磁振造影系統(Low-field MRI)。為了降低地球磁場對系統的影響，設計了一對地球磁場補償線圈，用來抵銷地球磁場的垂直分量，並旋轉系統主磁場方向與地球磁場的水平分量平行，藉此方便調整主磁場的強度，最後使用三個方向的梯度線圈，使磁場均勻度提升，以及造影所需頻率、相位編碼之應用。
在磁振造影部分，藉由改變系統的共振頻率，以及梯度磁場的造影序列，我們大幅提升了訊雜比(signal-to-noise ratio, SNR)，原本的SNR由213.15提升至533.14，影像品質進而提升許多。
為了驗證低場磁振造影系統應用的可行性，我們造影出清晰的蔬果結構性影像，並藉由水果二維與三維的磁振造影，可以判斷水果損傷的確切位置。在生醫方面的應用，我們進行手臂的磁振造影，也能夠得到結構性影像；豬肉的磁振造影也能觀察到輪廓，初步驗證本研究之低場磁振造影系統，做為生物醫學應用的可行性，此外系統造價成本及維護費用低廉，極具產業化的價值與潛力。
關鍵字：低場磁振造影、超導量子干涉元件、預先極化技術

Abstract
In this study, the low-field magnetic resonance imaging (MRI) system exploits the pre-polarization technique to enhance the magnetic moment and superconducting quantum interference device (SQUID) for data capture. The magnetic field coils and SQUID were set up inside a shielded room and a shielded cylinder which were made out of aluminum to reduce the surrounding noise. We also designed a pair of coils to cancel the Earth's magnetic field for reducing the ambient noise. The three pairs of gradient coils were employed to improve the magnetic field uniformity. By modulating the resonance frequency and image sequence, the quality of magnetic resonance image and signal-to-noise ratio has been optimized. The feasibility of biomedical applications, such as arm imaging and fruit damage was demonstrated. Furthermore, the cost of this system is pretty low. The low-field MRI has high potential of industrialization.

Key words: Low-field MRI, SQUID, Pre-polarization technique

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