應用於磁振造影的可靈活模組化射頻接收線圈陣列

Abstract

本論文旨在研究開發一具可靈活模組化的多通道磁振造影射頻接收線圈陣列，能靈活地由任意個獨立線圈模組來構成此一陣列，更能夠緊密地與各種受測物體貼合以得到最佳訊噪比。此設計立意係考量到在磁振造影的各種應用之中，常需要一具能適當符合受測物體大小以及外輪廓的接收線圈陣列，俾能更有效率地接收到受測體的磁振造影訊號。本論文中所提出的線圈陣列設計，係於每一獨立的線圈模組之內皆安置一立體堆疊環狀屏蔽結構：環繞於表面線圈周圍之屏蔽金屬箔片，而且只需要在各個線圈模組之間安排一微小間隙即可建構整個線圈陣列。因而能夠令整個線圈陣列緊貼於各種大小各式形狀的受測物體，同時亦能展現出強健的去除互耦效應的能力。 論文內容包括了全波段電磁模擬以及影像擷取實驗，並探討了兩種類型的環狀屏蔽結構。對於安置在各種不同曲率的假體表面上的模組化雙通道線圈陣列，電磁模擬與影像擷取實驗的結果皆顯示此一設計確實能夠良好地去除相鄰線圈模組之間的互耦效應：在電磁模擬的結果中，S21的數值皆落於-18.1 dB和-19.9 dB之間，而在影像擷取的實驗中，雜訊相關性矩陣的非對角線項目的平均值皆小於0.047。另外，我們在3T磁振造影系統上建構了一具七通道的原型，並用以擷取受測者的腦部、膝蓋和小腿的結構性影像。相較於標準商用三十二通道腦部接收線圈陣列和標準商用四通道可撓接收線圈陣列，此一原型於受測者表面深度50 mm內皆獲得較高的最大及平均訊噪比：分別能達到商用線圈陣列的2.63/1.35倍和3.89/1.50倍。綜合這些優點，可證明此一設計足以滿足各種臨床研究與應用。

We propose a flexible form-fitting MRI receiver coil array assembled by individual coil modules. This design targets MRI applications requiring a receiver array conforming to the anatomy of various shapes or sizes. Coil modules in our proposed array were arranged with gaps between them. Each coil module had a circumferential shielding structure stacked on top of the coil. Together they achieve robust decoupling when the array was bent differently. Two types of the circumferential shielding structure were investigated by using full-wave electromagnetic simulations and imaging experiments. Results showed that our flexible coil array had good decoupling between coils whether they were on a flat or curved surface with the S21 magnitude ranged between -18.1 dB and -19.9 dB in simulations, and with the average of off-diagonal entries of the noise correlation matrix less than 0.047 in experimental measurements. Anatomical images of human brain, calf, and knee were acquired by our seven-channel prototype on a 3T MRI system. The maximal and the average SNR within 50 mm from our array surpassed those from the commercial 32-channel head and 4-channel flexible coil arrays by 2.63/1.35-fold and 3.89/1.50-fold, respectively.