螺旋槳式面迴訊影像重建結合 N/2 ghost 假影修正方法

在這篇論文中，提出了兩個改良型的二維相位修正方法，能夠提升它們抑制面迴訊影像N/2鬼影假影的效能；並克服當物體存在大範圍無信號時無效的修正問題。N/2 鬼影假影是面迴訊影像值得注意的問題。因此，在每個螺旋槳式面迴訊影像的葉片資料影像，抑制N/2鬼影假影是一個必須的處理步驟。螺旋槳式面迴訊影像透過採集一系列的k空間葉片資料，且每一葉片資料均實行不同的旋轉角度的相位編碼方向，最後由所以葉片資料組合成完整的k空間資料。幾乎所有轉動葉片都是傾斜的採集方式，並使用面迴訊影像技術讀取訊號。這個傾斜的採集方式會造成傾斜 N/2 鬼影假影，它同時包含迴波位移與交錯的取樣方式。相較於一維相位修正方法，無論是基於參考掃描的改良型二維相位修正方法，或者是無參考掃描的改良型二維相位修正方法，均能夠幫助減低殘餘的傾斜N/2鬼影；因此，能夠在進行螺旋槳式面迴訊影像重建前，提高每個葉片資料影像的影像品質。此提出的改良型二維相位修正方法，同時展現了具有良好的運動免疫能力。三個初步的螺旋槳式面迴訊擴散影像臨床應用測試結果，包括測量腮腺的擴散系數、腦部擴散權重影像結合運動校正、以及自然呼吸肝臟擴散權重影像。螺旋槳式面迴訊擴散影像臨床測試結果展現了兩個改良型二維相位修正法的應用。此外，無參考掃描二維相位修正方法，能夠排除每個葉片影像額外的參考描掃時間，可能擴展螺旋槳式面迴訊擴散影像的應用。

關鍵字

螺旋槳式磁振造影；面迴訊影像； N/2鬼影假影；二維相位修正；擴散影像；擴散係數測量；腮腺擴散權重影像；腦部擴散權重影像；肝臟擴散權重影像；運動校正

並列摘要

Two improved 2D phase correction methods were proposed in this thesis to increase the effectiveness of ghost reductions of low-resolution blade images, and to solve the issue of ghost reduction within large signal-free regions. N/2 ghost artifact is a significant issue of EPI readout techniques. Thus, ghost reduction of each blade data is an essential processing step prior to PROPELLER-EPI reconstruction. PROPELLER-EPI acquires a set of rotating blades with different rotating angles to fill out the entire k-space. Most of rotating blades are oblique acquisition with EPI readout, which result in oblique ghost with echo shift and interlaced sampling. Either the improved reference-based 2D phase correction or the improved reference-free 2D phase correction can help to reduce the residual oblique ghost when using 1D phase correction, thus increase the image quality of each blade data before applying PROPELLER-EPI reconstruction. The proposed improved 2D phase correction methods were demonstrated, both of which exhibit good immunity to motion. Three preliminary clinical results, ADC measurement in parotid glands, brain DWI with motion correction, and free-breathing liver DWI, showed the possible application of PROPELLER-DW-EPI with the two improved 2D phase correction methods. In addition, the reference-free 2D phase correction method can eliminate the need of reference scan time of each blade, and thus may broaden the clinical use of PROPELLER-DW-EPI.

並列關鍵字

PROPELLER ； EPI ； N/2 ghost ； 2D phase correction ； diffusion imaging ； ADC measurement ； parotid gland DWI ； brain DWI ； liver DWI ； motion correction

參考文獻

1. Wang FN, Huang TY, Lin FH, et al. PROPELLER EPI: an MRI technique suitable for diffusion tensor imaging at high field strength with reduced geometric distortions. Magn Reson Med 2005; 54:1232-1240.

2. Skare S, Newbould RD, Clayton DB, Bammer R. Propeller EPI in the other direction. Magn Reson Med 2006; 55:1298-1307.

3. Pipe JG. Motion correction with PROPELLER MRI: application to head motion and free-breathing cardiac imaging. Magn Reson Med 1999; 42:963-969.

4. Chuang TC, Huang TY, Lin FH, et al. PROPELLER-EPI with parallel imaging using a circularly symmetric phased-array RF coil at 3.0 T: application to high-resolution diffusion tensor imaging. Magn Reson Med 2006; 56:1352-1358.

5. Chen NK, Wyrwicz AM. Correction for EPI distortions using multi-echo gradient-echo imaging. Magn Reson Med 1999; 41:1206-1213.

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螺旋槳式面迴訊影像重建結合 N/2 ghost 假影修正方法

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