富含的超高極化氙-129於3T磁振造影研究

The Design and Application of Enriched Hyperpolarized 129 Xe in 3T-MRI

劉原甫(Yuan-Fu Liu)

指導教授 ： 陳志宏

國立臺灣大學/電機資訊學院/電機工程學研究所/碩士(2009年)

https://doi.org/10.6342/NTU.2009.01651

摘要

磁振造影(magnetic resonance image; MRI)是一種非侵入式並且對人體無害的造影技術，在醫學領域中扮演著一項相當重要的角色。傳統上以氫原子為主的磁振造影，對於含氫原子過少的部位造影十分困難，例如體內的空腔部位。因此近來發展出了利用極化氣體做為磁振造影訊號來源的方法。
現今大多數在肺部取非氫核之核磁共振影像，大多是利用氦氣體，由於其經過超高極化後具有較高極化程度與影像訊雜比。氦-3（3He）及氙-129（129Xe）為惰性氣體，在一般正常吸入量下對人體無副作用，經過激光抽運的過程後可以獲得在正常熱平衡狀態下訊號數千至萬倍以上的增加，因此我們希望利用氙-129此一特性作為磁振造影的訊號來源。氦氣在自然界中的含量稀少，氙-129則具有較多的存量，我們可以較輕易獲得與使用。但是氙-129可以達到的極化程度較低，因此在磁振造影時影像訊雜比會較差。為了改善此一缺點，我們使用了富含的氙-129的氣體，其中氙-129的濃度為85%以上，大量增加訊號來源的量以獲得較好的影像。
我們設計了一套適合批次式生產高純度極化氙-129的激光抽運的系統。首要的就是光學抽運室的設計，光學抽運室是氣體進行超高極化的容器。並且整合了雷射裝置、加熱裝置、外圍磁場與運送裝置，穩定的生產出超高極化的氙-129。另外也設計了符合氙氣共振頻率的雙頻線圈，此雙頻線圈的目的是可以利用快速切換線圈的共振頻率來利用氫原子定位並且用氙造影。我們利用生產出來的高純度超高極化氙-129，在3T-MRI下做了一些訊號特性的分析，在經過超高極化後我們得到氙-129的峰值訊號強度相對於穩定狀態下的訊號約提昇了1300倍。在仿體的影像中，我們可以發現影像的訊雜比相對於先前連續式所產生的訊雜比提升了2到4倍。另外也建構了一套可以使用的氣體輸送裝置，經由測試可以在活體內偵測到氙-129的訊號。未來期望可以更完善連結磁振造影系統及超高極化系統，利用氙-129高極化程度及氣體可進入人體肺部的優點來達到人體空腔的造影。

關鍵字

核磁共振造影 ； 超高極化 ； 激光抽運 ； 富含的

並列摘要

Magnetic resonance imaging (MRI) is a non-invasive imaging system, and it’s an important technique in modern medicine. Traditional MRI is not able to acquire images in a cavity of body. Therefore, some experiments use the hyperpolarized gas as the signal source. Most researches in magnetic resonance image of different nucleon use 3 He, because hyperpolarized 3 He provided better signal to noise ratio with high degree of polarization. 3 He and 129 Xe are inert gases that do not cause biological effects to human body. The signal of hyperpolarized gas can be increased by more than thousand or ten thousand times. Although129 Xe is abundant in the nature, its lower degree of hyperpolarization limits its applications in MR; the signal to noise ratio (SNR) of image is relatively low. In this article, the gas containing approximately 85% of enriched 129 Xe was used to overcome this problem for better MR images. A batch pumping process of producing enriched HP-129 Xe had been set up. The design of optical pumping cell, which is the container for hyperpolarized process, is
very crucial. We combine the laser device, heating device, magnetic system and delivery device to produce steady hyperpolarized gas. In addition, we designed and implemented the dual frequency coil suited for 129 Xe and proton to avoid misregistration.
The enriched HP-129 Xe was characterized in 3T-MRI. The peak signal intensity of hyperpolarized gas we produced can increase 1300 times approximately by using this technology. In the batch pumping process system, the phantom images showed that the SNR is 2~4 relative to the continuous system. The gas delivery system was also set up that we can detect the signal of 129 Xe in vivo. In the Future, with better integrate hyperpolarized MR system; we are expecting to acquire the lung imaging in human body.

並列關鍵字

magnetic resonance image ； hyperpolarized ； optical pumping

參考文獻

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