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研究生： 楊曜豪
Yao-Hao Yang
論文名稱： 面迴訊影像扭曲之快速修正:通用圖型運算單元之平行計算
Accelerating phase modulation for correcting EPI geometric distortion by modern GPGPU parallel computation
指導教授： 黃騰毅
Teng-Yi Huang
口試委員: 林益如
Yi-Ru Lin
蔡尚岳
Shang-Yueh Tsai
學位類別： 碩士
Master
系所名稱： 電資學院 - 電機工程系
Department of Electrical Engineering
論文出版年： 2010
畢業學年度： 98
語文別： 英文
論文頁數： 54
中文關鍵詞： 相位調變 、面迴訊影像 、幾何扭曲 、螺旋槳式磁振平面迴訊影像 、通用圖形平行運算
外文關鍵詞： phase modulation, EPI, geometric distortion, PROPELLER EPI, GPGPU
相關次數： 點閱：167  下載：3 
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    • 在磁振造影之面迴訊取像技術中，幾何扭曲的假影問題，前人提出以磁場映象搭配相位調變法來加以改善。然而，因為每做一次相位編碼會累積分散的相位，而相位調變的運算複雜度等同於作離散的傅立列轉換並且由於在K空間中，不均勻的相位累積導致無法減少運算量。因此，在修正所有大量的動態研究(例如:功能性的磁振造影(fMRI)或是微灌流(perfusion)影像)，一般都需要花上幾分鐘甚至使用較先進的電腦設備也亦是如此。近年來，通用圖形平行運算技術(GPGPU)逐漸展現出能夠加速科學運算，並應用在當演算法是能被平行處理。在我們的研究，提出以通用圖形平行運算單元運用在相位調變的運算上，減少整個運算過程的時間。當應用在螺旋槳式磁振平面迴訊影像(PROPELLER EPI)上，平行運算的演算法也從原本所需約1750秒改善到約100秒的計算時間。總結，我們提出的通用圖形平行運算有希望去加速面迴訊影像幾何扭曲的修正。

    Phase modulation combined with field map has been shown a practical method to correct the EPI geometric distortion. However, since the phase dispersion accumulates on each phase encoding step, the calculation complexity of phase modulation is Ny-fold higher than conventional image reconstruction and cannot be reduced due to asymmetric phase accumulation in the k-space. Thus, correcting all volumes of dynamic studies (e.g. fMRI or perfusion) generally takes minutes even using the state-of-the-art computer hardware. Recently, the parallel computing using general-purpose computation on graphics processing units (GPGPU) shows able to accelerate the scientific computing if the algorithm can be parallelized. In our study, we proposed to incorporate the GPGPU technique into phase-modulation calculation to reduce the whole computation time. Applying on the PROPELLER EPI data set, the parallel algorithm reduced the computation time from ~1750 seconds to ~100 seconds. We conclude that the GPU computing is a promising method to accelerate EPI geometric correction.

    Abstract 摘要 1.INTRODUCTION Introduction 1.1 Echo planar imaging (EPI) 1.2 Graphic accelerators – graphic processing unit (GPU) 1.3 Motivation 2.THEORY 2.1 Geometric distortion in EPI 2.2 Mapping of the off-resonance field 2.3 The phase modulation method 2.4 Parallelized data processing 3.MATERIAL AND METHOD 3.1 Implementation: MEX-function, field mapping, phase modulation 3.2 Experiment 4.RESULTS 5.DISCUSSION AND CONCLUSION 5.1 Discussion 5.2 Conclusion 6.REFERENCE

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