以螺旋槳式造影加速Q球擴散影像的擷取

Abstract

背景與目的：擴散造影技術已經廣泛地應用在活體的纖維結構偵測上，由於纖維交叉的問題，愈來愈多研究傾向於使用高角度解析擴散影像技術(HARDI)來解決這個問題，然而因為高角度擴散影像技術需要更多角度的擴散影像，因此掃描時間則會非常的長，有鑑於此，如何解決掃描時間則會是一個重要的課題。螺旋槳造影技術已被證明可以解決回訊平面影像的扭曲問題，但時間反而會增加，螺旋槳技術的資料互享觀念被提出之後，則可能可以同時解決掃描時間以及影像扭曲兩個問題，因此這個研究的目的便是應用螺旋槳技術的資料互享技術來加速Q球影像的造影。材料與方法：為了將螺旋槳造影技術應用在Q球造影上，252個方向的擴散影像，根據鄰近的擴散方向，分成14組，每組含有18個擴散方向，傳統Q球造影以及螺旋槳Q球造影都是在3T磁振造影儀完成，掃描時間可以縮短30%以上。結果：螺旋槳Q球造影的GFA跟ODF的影像扭曲都有降低，而且GFA的影像對比以及ODF中的纖維方向跟傳統Q球造影的結果幾乎一樣，不過影像解析度有相對較低的現象。討論與結論：螺旋槳Q球造影同時解決了掃描時間跟影像扭曲的問題，此外由於螺旋槳Q球造影有內在高訊雜比的優勢，因此結果會更可信。然而螺旋槳的每張影像在局部地方存有剩餘的擴散扭曲，若使用額外的影像對位方式，相信螺旋槳Q球造影的影像品質會更可信。

Background and purpose: Diffusion imaging techniques have been widely used to study fiber structure in vivo. Recently, more and more studies tend to using high angular resolution diffusion imaging (HARDI) techniques to solve fiber crossing problems. However, the scan time of HARDI technique is proportional to the number of diffusion directions being used in acquisition. Search for a technique suitable of accelerating data acquisition becomes an important issue. Propeller EPI has been demonstrated to be capable of reducing susceptibility distortion in EPI, especially in conjunction with parallel imaging, but this technique requires longer scan time to obtain single image. After data-sharing concept of propeller reconstruction was introduced, the image acceleration in EPI acquisition becomes possible. Therefore, the purpose of this study is to investigate the feasibility of accelerating q-ball imaging by propeller acquisition. Material and methods: In this study, q-ball imaging was selected for acceleration because it is a model-free technique and takes shorter scan time to achieve high angular resolution in q-space. To implement propeller imaging on q-ball imaging, the 252 icosahedral diffusion directions were separated into 14 groups, each consists of 18 diffusion directions, according to their diffusion directions with close distance. The data acquisition of conventional QBI and propeller QBI were conducted in a 3T MR scanner (Philips Achieva, Best, Netherlands). Scan time of propeller QBI was reduced more than 30% by using propeller and parallel imaging. Results: The resultant GFA and ODF of conventional QBI and propeller QBI were compared slice-by-slice. In propeller QBI, the susceptibility distortion was reduced both in GFA and ODF maps. Besides, propeller QBI shows almost same GFA contrast and fiber orientations, but appears relative low image resolution which may due to keyhole reconstruction in propeller. Discussion and conclusions: Propeller imaging technique helps reduce susceptibility distortion and scan time in q-ball imaging. Besides, propeller QBI has inherent higher SNR in each blade DWI, and therefore it has more reliable results. However, there remains residual local distortion among all of blade DWIs, thus, further distortion correction was suggested to achieve better image quality of propeller QBI. This study utilized propeller imaging to reduce the scan time of q-ball imaging. The results suggested that propeller QBI could be a suitable technique in clinical applications.