Novel Applications of High Temperature Superconducting Coils for MR Imaging

由於生醫科技蓬勃發展，磁振造影是基礎研究及臨床診斷中相當重要的一個方法，不論是基礎研究或臨床診斷都期盼更高的空間和時間解析度來觀察更細微的組織結構。然而，影像解析度的提升將會降低訊雜比。相較於傳統的磁振造影線圈，使用低電阻的高溫超導材料已是公認可以大幅提升線圈品質的方式。然而，此方法應用於臨床上的可行性仍需要作進一步之驗證。 因此，本論文的主要目的為實現高溫超導線圈於核磁共振造影上應用的可行性，並且可分為下列三部份。第一為建立高溫超導表面線圈及其應用。第二為發展高溫超導體線圈及其應用。最後，運用高溫超導表面線圈來作病理上的觀測。 第一部份中，首先專注研究高溫超導表面線圈於3T MRI的模擬和量測，我們驗證了在現有的系統中，運用直徑 40毫米的高溫超導表面線圈的訊雜比為300 K下自製銅表面線圈的3.8倍。接著，運用高溫超導線圈於擴散張量磁振造影上，更可將差異角度之標準差由44.38度縮小為18.66度，也同時增進了神經追蹤之準確度，並將此技術應用在自發性腫瘤鼠腦上。最後，探討直徑20厘米的高溫超導射頻共振器系統應用於人手的研究證實為可行，並得到1.95倍訊雜比增益。第二部份中，著重討論高溫超導體線圈用以獲取小鼠的全身影像，77 K下的高溫超導體線圈的訊雜比為300K下的自製銅體線圈的兩倍。 第三部份中，首先是散曈劑誘發海馬迴損傷所產生的匹羅卡品大鼠模型，數據顯示，增強影像的對比度可能有助於早期針對性的預測，因而減少腦損傷及其相關疾病發病率。接著，連續觀察三週血管內皮生長因子（VEGF）189的變化，結果顯示，在誘導腫瘤血管生成上，有助於觀測其不同作用的VEGF異構體。 總結而言，我們驗證了高溫超導表面線圈於磁振造影上應用的可行性，也建立此技術於臨床上進一步應用之潛力。此外，我們建立起高溫超導體線圈，利用高溫超導體線圈不僅改善了訊雜比，也使小鼠的全身掃描更便利。最後，在臨床研究上，我們率先將其應用於自發性鼠腦腫瘤、癲癇及肺線癌研究上，並且驗證了此方法有助於臨床研究上。本論文成功地建立了高溫超導線圈於核磁共振造影上，透過提升訊雜比，相信對未來神經科學的基礎研究或是臨床診斷都有極大的助益。Throughout the development in biomedicine, magnetic resonance imaging (MRI) has become an important approach for neuroscience research and clinical applications. Neuroscience research and clinical applications both higher spatial and higher temporal resolutions are expected to help acquire finer details of the imaging object. However, as the imaging resolution goes higher, signal-to-noise ratio (SNR) limits the accuracy of quantitative MR microscopy. Compared with conventional diffusion MRI techniques, high-temperature superconducting (HTS) radio-frequency (RF) coils have been proposed as a promising tool for tissue microscopy with high resolution because of its low-resistance characteristic for MR probe design. However, the potential of HTS RF coils on clinical applications has not been well demonstrated yet. Therefore, the overall objective of this dissertation is threefold and targeted to facilitate the techniques of HTS RF coils for the use of MRI. First, we built the HTS RF surface coils and its applications. Second, we developed a HTS RF volume coil and its applications. Finally, we verified the HTS RF surface coils on the investigations of the clinical research. In Part I, we aim at the study of simulations and measurements of the HTS RF surface coils in a 3T MRI. Our results showed that HTS RF surface coil of a 40 mm in diameter provided an average SNR gain of approximately 3.8 folds on our 3T MRI system. Next, we concentrate on the use of the HTS surface coils in enhancing the diffusion tensor imaging. Results showed that the cooled HTS surface coil with a standard deviation of deviation angles significantly reduced from 44.38° to 18.66°. Furthermore, the fiber tractography of a rat’s corpus callosum (CC) demonstrated the advantage of using a cooled HTS surface coil to investigate the neural connectivity as well and a spontaneous tumor of rat brain is presented with a HTS surface coil. Finally, it was also demonstrated that the SNR using the HTS surface coil of 200 mm in diameter was higher than that of a copper surface coil for the MRI study of a human hand by 1.95 folds. In Part II, we focus on a new Bi-2223 superconducting saddle coil and designed for the magnetic resonance image of a mice’s whole body in a Bruker 3T MRI system. The SNR of a HTS saddle coil at 77 K doubled compared with that of a home-made copper saddle coil for a mice whole body MR study. In Part III, we focused on the studies of edilepticus-induced hippocampal injury in the pilocarpine rat model. These data suggested an enhanced image contrast that may contribute to the early targeted intervention which could minimize brain injury and its associated morbidities. Then, we focused on the three-week observation of vascular endothelial growth factor (VEGF) isoform 189 by using a HTS coil. The results helped elucidate the role of different VEGF isoforms in inducing tumor angiogenesis, the interaction between the structure of tumor angiogenesis, and the mechanisms underlying the association between the expression of a specific VEGF isoform in a tumor and the patient’s clinical outcome in human cancers. In summary, we successfully demonstrated the potential of HTS RF coils on clinical applications. Additionally, we built a HTS volume coil. The use of a HTS volume coil not only improved SNR but also enabled a simple one scan of a mouse’s whole body. Finally, we apply the HTS RF coils with the study of a spontaneous tumor of rat brain, edilepticus-induced hippocampal injury and VEGF 189. And we demonstrated the HTS RF coils be helpful in clinical research. Conclusively, our proposed methods successfully built the HTS RF coil on MRI by increasing SNR, which will be potentially useful to facilitate the neuroscience research and clinical applications