鉍鍶鈣銅氧高溫超導磁共振表面線圈之研究與應用

磁共振影像（Magnetic Resonance Imaging, MRI）技術的發展主要有兩大目標，一是加快掃描速度，一是增強影像解析度。一個影響掃描速度和解析度極限的重要條件是影像的訊雜比。MRI 中雜訊的來源主要有受測物體和線圈，其中降低線圈雜訊的方法之一就是使用電阻極低的高溫超導線圈。目前已有的高溫超導線圈大致上可分為兩類：帶狀超導線材及薄膜線圈。其中帶狀超導線較適合直徑大於六公分之表面線圈及體線圈，薄膜線圈則較適合製作小尺度的表面線圈。本論文從適用於 3T MRI 之帶狀超導表面線圈開始進行製作和測試，並設計出薄膜線圈幾何結構和配合之恆溫器系統。本論文中以 Bi2Sr2Ca2Cu3Ox 超導帶製作直徑七公分的表面線圈，以不同導電度的假體得到其對相同結構銅線圈的訊雜比增益大致符合理論計算結果。此超導線圈在水果及鼠腦影像中獲得的訊雜比分別是傳統表面線圈的二點四倍與二點七倍，估算約可將取像時間縮短為原來的五分之一，這在需要較長掃描時間的實驗例如擴散影像中將可節省數十分鐘甚至數小時的可觀時間。在較小尺度的線圈我們選擇在 LaAlO3 基版上鍍 YBa2Cu3O7 薄膜為材料。我們以軟體成功模擬在 3T MRI 中心頻率 125.3MHz 共振之螺旋線圈型式及磁場分佈，並針對 Bruker S116 mini 梯度線圈系統設計一套以 G10 玻璃纖維材質之低溫恆溫器，此恆溫器約可將線圈維持在 84 K 之工作溫度 52 分鐘。採用超導線圈所能得到的訊雜比增益隨受測物的尺度下降而上升，因此可預期若能將超導線圈應用在本實驗室進行中的分子影像上，大幅改善的訊雜比十分有利於提供分子影像所需的小範圍的高解析度影像。我們也預備製作高溫超導多通道陣列線圈，再配合平行影像方法和其他提高訊號之技術如氙對比影像，以期達成快速掃描、影像高解析度及高訊雜比的目標。

關鍵字

鉍鍶鈣銅氧

並列摘要

Abstract There are two main purposes of the development of Magnetic Resonance Imaging (MRI) techniques. One is to increase scanning speed; another is to increase image resolution. An important factor that affects the limitation of acquisition time and resolution is the signal-to-noise ratio (SNR). There are two main sources of MRI noises: sample and receiving coil. Thus one way to reduce the coil noise is using non-resistive high-temperature superconducting (HTS) coils. Previous works on HTS coils can be put into two categories: tape coils and thin-film coils. Tape coils are suitable for surface coils with diameters larger than 6 cm or volume coils; thin-film coils are more suitable for a smaller planar surface coil. In this work we began from making tape coils to be used on Bruker 3T MRI system, to the design of thin-film surface coil pattern and the cryostat. Commercialized Bi2Sr2Ca2Cu3Ox tape was used to fabricate a HTS tape coil with a diameter of 7 cm. Tested by phantoms of different conductivity, we got a plot of HTS SNR gain over an equivalent copper coil that was in agreement with theoretical prediction. A SNR gain of about 2.4 can be obtained from the HTS tape coil over a conventional copper surface coil in kiwi fruit images and the acquisition time was expected to reduce to one-fifth the original time when keeping the same SNR. This is very beneficial when doing experiments that usually takes a long time (as conventional diffusion imaging); the saved time length can be up to several hours. YBa2Cu3O7 (YBCO) coated on LaAlO3 substrate was chosen to make the small scale surface coil. Successful simulations of double-sided YBCO coils on a 2cm*2cm LaAlO3 substrate were done by Sonnet 6.0a. A spiral pattern of the HTS film that resonates at 125.3 MHz was decided, and its B1 field was also found out. We also designed a G10 glass fiber cryostat to be fit in the Bruker S116 mini gradient system. This cryostat can keep the HTS coil at 84 K for about 52 minutes. The SNR gain of HTS coils increases as the sample size goes down, so we can expect it to improve the SNR significantly when implemented in molecular imaging that needs very small FOV and high resolution. We also aim on developing multi-channel HTS phased arrays, together with other techniques that can raise signal voltage (for example, xenon imaging), to achieve the goal of ultra fast, high resolution and high SNR imaging.

並列關鍵字

Bi-2223

參考文獻

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鉍鍶鈣銅氧高溫超導磁共振表面線圈之研究與應用

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