Magnetic Resonance Imaging of Rat’s Brain and Spine Using Curved Four-channel Phased Array Coil

磁振造影技術目前已廣泛應用於中樞神經系統的研究中，如解剖影像及擴散張量影像技術等。然而，由於大鼠的頸椎過深，目前商用的磁振造影線圈仍無法提供足夠的影像訊雜比，此減少了磁共振影像於腦脊髓區域研究之可行性。因此，本研究旨在設計與製作一以大鼠中樞神經系統為應用導向之可撓式陣列線圈平台，藉由提昇影像品質來促進磁振造影於腦脊髓之深入研究與探討。 首先，本研究針對大鼠腦脊髓形狀設計並製作了一四通道可撓式陣列線圈。其中，本研究利用幾何重疊與自製的低輸入阻抗前置放大器來降低線圈間之耦合影響。接著，仿體與大鼠之磁共振解剖影像用以評估及驗證此自製線圈之品質。最後，我們將此線圈應用於大鼠腦脊髓之擴散張量影像與神經纖維追蹤影像。 相較於傳統之平面式線圈，可撓式陣列線圈分別可以提供1.3倍與1.45倍的訊雜比增益於仿體與大鼠頸椎之解剖影像實驗中，也同時大幅提昇了脊髓灰白質間的對比雜訊比。此外，更結合寬頻磁振造影技術，以獲得加速11倍的大鼠三維解剖影像及高解析度擴散權重影像。在擴散張量影像的再現性實驗中，利用可撓式陣列線圈所取得的實驗再現性角度差減少為平面式線圈之77%，並且使用可撓式陣列線圈所得到之腦脊髓神經纖維追蹤影像也比用平面式線圈所得之更加完整。 本研究成功地製作了一四通道可撓式陣列線圈平台，除了利用仿體與活體實驗來評估其品質外，本研究更驗證了此線圈於大鼠中樞神經系統之擴散磁振造影的可行性。藉由訊雜比與對比雜訊比之提昇，此可撓式陣列線圈平台有助於更多磁振造影技術於中樞神經系統之研究與應用。Magnetic resonance imaging (MRI) techniques such as anatomical and diffusion tensor imaging (DTI) have been widely applied to investigate the central nervous system (CNS). However, commercial MRI coils could not provide sufficient signal-to-noise ratio (SNR) at the neck due to cervical lordosis (inward curvature), therefore hampering the applications from brain to the spine. The aim of this work was to design and implement a 4-channel curved array coil that provides uniform sensitivity along the CNS, improving studies of the head and spinal column. The 4-channel curved array coil was fabricated on a flexible printed circuit board that could be bent to fit the rat’s contour along the neck while a homemade low input impedance preamplifier eliminates the crosstalk between overlapping coils elements. We evaluated the performance of the coil through anatomical imaging of phantom and rat cervical spine, and finally perform rat cerebrospinal DTI and tractography to show the benefits of a curved array coil. Compared to conventional array coils, the curved array coil offered 1.3- and 1.45-fold SNR gain in phantom and anatomical images of the rat cervical spine respectively. In addition, the contrast-to-noise ratio (CNR) between gray and white matter in spine was alleviated. By combining Wideband MRI technique, the 3D anatomical and high-resolution diffusion weighted images were obtained with a 11-fold acceleration. In reproducibility of DTI, the experimental reproducibility deviation angle acquired by curved array coil was 77% of that by plane array coil. Moreover, the DTI tractography of rat nervous system using the curved array coil was more complete. The 4-channel curved array platform was successfully implemented for rat cerebrospinal MRI. We evaluated its performance by phantom as well as in vivo anatomical imaging and further demonstrated the feasibility of rat cerebrospinal DTI. With improved SNR and CNR, the curved array coil platform could improve or even create new possibilities for biomedical applications in cerebral nervous system