雙通道高溫超導射頻陣列線圈在7T磁振造影系統之開發與應用

Abstract

求高時間及空間解析度為目前磁振造影發展的趨勢，越高的訊雜比能換得的時空解析度也越高，因此高訊雜比為提升時空解析度的關鍵因子。相較於傳統磁振造影線圈，使用低電阻的高溫超導材料已是公認可以大幅提升訊雜比的方法。然而，使用高溫超導線圈來加大可視範圍(Field-of-View)的高溫超導相位陣列線圈之研究仍在初步階段。因此本論文的目標為在7T小動物磁振造影系統建立雙通道高溫超導陣列線圈平台，目的為加大可視範圍與展示其高訊雜比的優勢。 首先，建立高溫超導陣列線圈的電磁模型計算其訊雜比的增益與B1場的均勻性。第二，將雙通道高溫超導陣列線圈之間的耦合效應最小化。同時針對此雙通道高溫超導陣列線圈量身製作一低溫裝置，使超導線圈能維持在77K的低溫下。第三，以仿體與活體大鼠為掃描樣品，驗證高溫超導陣列線圈平台的可行性。最後，將此平台應用於大鼠脊髓的擴散張量造影上。 相較於相同大小、形狀之自製銅陣列射頻線圈，本論文於先由電磁模擬平台由理論獲取2.2倍的訊雜比增益，且於實際雙通道高溫超導射頻陣列線圈平台獲得約1.9倍之大鼠脊髓解剖影像的訊雜比增益。此外，在大鼠的擴散張量造影上的角度差分析結果，高溫超導陣列線圈將差異之角度標準差由26.7度縮短至18.9度。 藉由高溫超導陣列線圈高訊雜比與大可視範圍的雙重優勢下，此一成果未來勢必能對神經科學的基礎研究有所幫助。

The signal-to-noise ratio (SNR) is the key factor while magnetic resonance imaging (MRI) towards high spatial and temporal resolution. Compared with copper, the high temperature superconducting (HTS) coil has been proposed as a promising technique for SNR improvement in MRI. However, the HTS coil is not fully demonstrated its capability such as using HTS coil array to enlarge field-of-view. Hence, this study aimed to implement a 2-channel HTS coil array platform for small animal imaging at 7T MRI. First, the electromagnetic model of HTS coil array was built to simulate the SNR gain and B1 field homogeneity. Second, the 2-channel HTS coil array was implemented with minimized coupling effect. In the meanwhile, the Dewar for this coil configuration was fabricated to maintain the HTS coil array at low temperature of 77K. Third, the capability and feasibility of the homemade HTS coil array was verified by phantom and in-vivo rat body MR experiments. Finally, this HTS coil array platform was applied to the diffusion tensor imaging (DTI) of rat spine. In the theoretical and simulation results, the SNR gain of using 2-channel HTS coil array was approximate 2.2-time to the conventional copper coil array in the same configuration. Our experimental results show the HTS coil array at 7T MRI can provide a 1.9-time SNR gain in both of phantom and in-vivo rat spine scans while compared to copper coil array. In DTI experiment, the standard deviation of the deviation angle was dramatically reduced from 26.7-degree (by 2-channel copper coil array) to 18.9-degree (by 2-channel HTS coil array). In the future, the study will be potentially useful to facilitate the basic research of neuroscience and clinic diagnosis by the advantages of high SNR and larger field-of-view (FOV) of HTS phased array.