低場磁振造影之主動磁屏蔽研究

經歷了超過半個世紀的發展，磁振造影(magnetic resonance imaging，MRI)已成為極重要的非侵入性醫學影像。雖然傳統的磁振造影技術已經相當地成熟，但高磁場使其建造與維護的成本高昂，而且導致系統操作有潛在的危險性。近十餘年來，微小磁場量測技術的進步使低場磁振造影逐漸成為可能，這也引起了世界各地學者的研究興趣。如何克服環境低頻磁雜訊是低場磁振造影技術亟須解決的主要問題之一。本論文針對低場磁振造影所需克服的低頻磁雜訊，探討主動磁屏蔽系統的特性。此系統以磁通閘磁力計(fluxgate magnetometer)監測環境磁場，利用磁力計的輸出電壓作比例積分控制，透過Helmholz線圈產生反向磁場，使低頻(10 Hz以下)的環境磁雜訊降低至1/20以下。本研究成果顯示，主動磁屏蔽確實可以改進靜磁場的穩定性。如何將其整合於低場磁振造影系統，值得未來繼續研究。

關鍵字

低場磁振造影；磁通閘磁力計；主動式磁屏蔽

並列摘要

The magnetic resonance imaging (MRI) has become one of the most important non-invasive medical imaging techniques since the discovery of nuclear magnetic resonance (NMR) more than a half century ago. Nowadays the magnetic resonance imaging is a mature technology for clinic diagnostics. However, the necessary high magnetic field makes the conventional MRI system costly in both construction and maintenance. Moreover, the strong magnetic field is prone to hazards in case of mis-operation. In recent decades, the progresses in low-noise magnetometers allow the further development of the low-field MRI technique, and this interests more and more researchers worldwide. One of the major obstacles to practical low-field MRI is the low-frequency magnetic disturbances in conventional environments. In this study, an active magnetic shielding system is designed, built, and characterized in order to get over the low-frequency environmental magnetic noise. The system monitors the nearly static environmental magnetic field by using a fluxgate magnetometer, and generates a field counter to the environment with a Helmholtz coil, which is driven by a proportional-integral controller with the input connected to the fluxgate magnetometer. With the active shielding, the low-frequency magnetic noise in the environment was reduced to less than 1/20. The result suggests that the static magnetic field in a low-field MRI system can be stabilized effectively with this technique, and it will be worthwhile to further investigate the integration of active shielding and low-field magnetic resonance imaging in the future.

並列關鍵字

Low-field MRI ； fluxgate magnetometer ； Active Shielding

參考文獻

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低場磁振造影之主動磁屏蔽研究

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