寬頻磁振造影技術在高時空解析度擴散張量影像之研究

Study of High Temporal and Spatial Resolution Diffusion Tensor Imaging based on Wideband MRI Technology

莊永豪(Yung-Hao Chuang)

指導教授 ： 陳志宏

共同指導教授 ： 闕志達

國立臺灣大學/電機資訊學院/生醫電子與資訊學研究所/碩士(2014年)

https://doi.org/10.6342/NTU.2014.10894

摘要

擴散磁振造影現今在非侵入式醫學影像應用上，有非常重要的研究和貢獻。而其中的擴散張量造影，使用磁振造影儀器取得一組影像所花費的時間往往相當地長，因為至少要取得七張影像或者以上的影像。擴散權重影像 (Diffusion Weighted Image, DWI) 的品質容易受到雜訊的影響。要求的訊雜比不能夠太低，不開擴散梯度影像的訊雜比至少要40左右[1]。目前，已經有非常多不同的技術致力於克服取得DWI花費時間太長的問題，像是選取特定編碼方向來取得更好的DWI影像或者減少取樣點縮短掃描時間[2, 3]、使用主磁場較高的磁共振造影機器[4, 5]、使用表面線圈 (surface coil)和高溫導表面線圈降低熱雜訊來提高訊雜比[6]、以及平行影像技術 (Parallel Imaging)來縮短掃描時間。本研究是在探討寬頻磁振造影 (Wideband Magnetic Resonance Imaging, Wideband MRI) 技術應用於DTI上，達到縮短取得DTI所耗費的時間,或者耗費相同的掃描時間來提高DWI影像的解析度。本實驗室所研發的寬頻磁振造影技術，已成功應用在解剖影像、血管磁振造影影像和功能性磁振造影影像等。
在本論文中，我們探討Wideband DTI以及傳統DTI在單一方向神經束的差異性。藉由DTI所常用的資訊包括平均擴散系數指標 (Mean Diffusion Index, MD) 和非等向性強度指標 (Fractional Anisotropic Index, FA)，這兩個指標分別代表水分子在空間中平均擴散的速率，以及擴散的非等向性。我們運用去離子水 (DT-Water) 和丙酮 (Acetone) 兩種液體以及健康大鼠來驗證Wideband DTI在水分子擴散係數的一致性和神經構造的對比度。應用在大鼠海馬迴以及胼胝體神經纖維結構上，最後也使用四倍加速的方式取得小鼠脊椎神經和五倍加速的方式取得大鼠脊椎神經DWI影像，並經由MIP影像處理，重建出由大鼠脊椎節和脊椎節中間沿伸出來的坐骨神經，也經由解剖影像的結果對照技術的可行性。藉此來說明Wideband MRI在未來醫學臨床應用以及神經相關研究上的潛力。
關鍵字：寬頻磁振造影、核磁共振影像、擴散張量影像

關鍵字

寬頻磁振造影 ； 核磁共振影像 ； 擴散張量影像 ； 坐骨神經

並列摘要

Diffusion magnetic resonance imaging, which is benefit for the non-invasive properties and provides the neural fiber information, has become an essential modality. Diffusion tensor imaging (DTI) costs a long scan time, since at least 7 diffusion weighted images are required. It needs at less 40 of SNR value in null DWI images. There are a lot of methods to reduce the scan time, such as partial k-space method, higher magnetic field or using surface coil to generate higher SNR, or parallel imaging method. In this research, we are aiming to implement Wideband MRI on DTI, in order to reduce scan time or trade the scan time for higher spatial resolution. Wideband MRI introduced by our lab was used to accelerate the scan time was successful apply in the anatomy scan, MR angiography, and functional MRI.
In this study, we research the difference in single direction neural fiber between conventional and SCWB DTI. In addition, we compare the mean diffusion index (MD), fractional anisotropic index (FA) and the angle variation acquired by Wideband DTI and conventional DTI with DT-Water, Acetone and healthy rat brain. And we utilize SCWB DTI technique to get higher image resolution in rat hippocampus and corpus callosum. Finally, we successfully complete to accelerate scan time by W=4 SCWB 3D DTI technique with mouse spine from 12 hours to three hours. And we complete to accelerate scan time by W=5 SCWB 3D DTI technique with rat spine from 22.5 hours to 4.5 hours. After MIP processing, we reconstruct the rat sciatica nerves and compare with anatomy images. It shows the capability and potentiality to the clinical application and the brain neural research.

Keyword： Wideband MRI, Diffusion Tensor Imaging, Magnetic Resonance Imaging

並列關鍵字

Wideband MRI ； Magnetic Resonance Imaging ； Diffusion Tensor Imaging ； Sciatic Nerve

參考文獻

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[3] P. B. Kingsley, "Introduction to diffusion tensor imaging mathematics: Part II. Anisotropy, diffusion‐weighting factors, and gradient encoding schemes," Concepts in Magnetic Resonance Part A, vol. 28, pp. 123-154, 2006.

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[5] S. Choi, D. T. Cunningham, F. Aguila, J. D. Corrigan, J. Bogner, W. J. Mysiw, et al., "DTI at 7 and 3 T: systematic comparison of SNR and its influence on quantitative metrics," Magnetic resonance imaging, vol. 29, pp. 739-751, 2011.