Advanced investigations on rapid steady-state MR imaging and its clinical applications (1/3)

本計畫第一年特定目標，係探討三維 穩定態自由旋進成像法中，偏折角之選取 對於腦脊髓液與腦實質對比的影響，同時 檢查切面方向外來假影的嚴重程度。理論 推導顯示偏折角減小有利於減輕切面方向 外來假影，但相對犧牲腦脊髓液與周邊腦 實質的對比。六位健康受試者與四位病患 的實驗結果指出，在常用的700 偏折角 下，外來假影可影響將近多達三分之一的 切面而減至400 之後，外來假影減少60%、 僅犧牲20%的影像對比。實驗結果與理論 預測高度相符。因此在臨床可接受的假影 範圍內，我們建議三維穩定態自由旋進技 術做腦室腦池影像擷取時，應採用400 的偏 折角。The specific aim for the first fiscal year of this project is to investigate the effects of flip angle setting in 3D balanced steady-state free precession (SSFP) imaging on the image contrast between cerebrospinal fluid (CSF) and its surrounding cerebral parenchyma, at the same time to examine the presence and extent of aliasing artifacts along the slice selection direction. Theoretical derivations of the signal behavior in the steady state regime indicated that the extent of slice aliasing artifacts decreased as the flip angle was lowered, at the expense of a sacrifice in CSF-parenchyma contrast. Experimental data from six healthy subjects and four patients showed that prominent slice aliasing artifacts were found to affect nearly 30% of the imaging slices when using the commonly employed 700 flip angle. The extent of slice aliasing artifacts and CSF-parenchyma contrast agreed well with theoretical predictions. In particular, a designated flip angle of 400 showed nearly 60% reduction in the extent of slice aliasing with only 20% decrease in CSF-parenchyma contrast, as compared with the use of 700 flip angle. A flip angle of about 400 is thus recommended for 3D balanced SSFP MR ventriculocisternography with sufficient CSFparenchyma contrast at a clinically acceptable level of slice aliasing artifacts