國立臺灣大學電機工程學系暨研究所鍾孝文2006-07-252018-07-062006-07-252018-07-062003-07-31http://ntur.lib.ntu.edu.tw//handle/246246/7926一般咸信由 TrueFISP 技術所取得之 磁振影像為 T2/T1 對比。本計畫中顯示， 若以常見的「半偏折角」準備方式，影像 擷取當中進入穩定態的時間將接近於全部 信號讀取時間，表示暫態響應將會主導影 像對比。本計畫取得志願受試者腦部之二 維影像，並且改變相位編碼的數目，以觀 察不同暫態響應的作用。隨著相位編碼數 的提高，腦部灰質與白質的對比由質子密 度逐漸進入T2/T1 對比，並且與理論計算 吻合。結果顯示在一般TrueFISP 影像中， 對比形式應為質子密度與T2/T1 對比的綜 合體，其加權比重則由暫態響應時間長短 所決定。臨床判讀TrueFISP 影像特性因此 需加以謹慎考量。Images acquired using the TrueFISP technique (true Fast Imaging with Steady-state Precession) are generally believed to exhibit T2/T1-weighting. In this project, it is demonstrated that with the widely used half-flip-angle preparation scheme, approaching the steady state requires a time length comparable to the scan time such that the transient-state response may dominate the TrueFISP image contrast. Two-dimensional images of the human brain were obtained using various phase encoding matrices to investigate the transient-state signal behavior. Contrast between gray and white matter was found to change significantly from proton-density- to T2/T1-weighted as the phase encoding matrix size increased, which was in good agreement with theoretical predictions. It is concluded that TrueFISP images in general exhibit T2/T1-contrast, but should be more appropriately regarded as exhibiting a transient-state combination of proton-density and T2/T1 contrast under particular imaging conditions. Interpretation of tissue characteristics from TrueFISP images in clinical practice thus needs to be exercised with caution.application/pdf185957 bytesapplication/pdfzh-TW國立臺灣大學電機工程學系暨研究所磁振造影穩定態快速成像穩 定態自由旋進暫態響應灰白質對比TrueFISPsteady-state free precessiontransient stategray/white matter contrastreporthttp://ntur.lib.ntu.edu.tw/bitstream/246246/7926/1/912213E002078.pdf