磁化率加權影像處理應用快速穩定態旋進梯度迴訊磁振造影序列

Abstract

磁化率加權影像如今廣泛地運用於加強腦部靜脈血管構造顯示;傳統上,是利用激發射頻破壞梯度迴訊序列列,擷取磁振相位影像去設計出一相位遮罩,進而 加強在磁振矩量影像上微小血管的對比程度。 因而快速穩定態造影序列可提供多樣化影像對比與其優越的訊號雜噪比,本論文研究的目標在於研究快速穩定態造影序列,搭配磁化率加權影像處理方法的潛在效益。 為了得到合適的磁振掃描參數,我們帶入數值模擬去評估快速穩定態造影序列的訊號表現。我們也呈現了了兩種不同的磁振造影序列列在磁化率加權影像上影像品質與對比程度的比較。 快速穩定態旋進造影序列應用於磁化率加權影像能夠在每次實驗中獲得有效的雜訊下降。因此顯示出擁有較佳的影像品質如訊雜比、對比程度對照於傳統的破壞梯度迴訊序列的影像結果。 結論是,我們此快速穩定態旋進造影序列得以進一步地成為進階磁化率加權影像應用領域的新興影像研究方法;同時,期待此研究可貢獻於穩定態自由旋進梯度迴訊序列的現今研究發展上。

Susceptibility-weighted imaging (SWI) is now extensively used in clinical neural applications to enhance the depiction of vascular architecture. The traditional procedure of SWI uses the phase information from RF-spoiled gradient-echo (SPGR) sequence to calculate a phase mask for improving contrast of small venous vessels, which is subsequently applied to enhance contrast of the magnitude image. The aim of this study is to investigate potential benefits of using the fast imaging with steady-state free precession (FISP) sequence on SWI application, for its variety of image contrast and high SNR efficiency. To obtain a proper set of MR scan parameters, the numerical simulation were employed to evaluate the signal performance of this proposed FISP sequence. We also presented the comparison in image quality and contrast between the FISP images and a standard SPGR sequence for SWI. The images of FISP-SWI led to a reduction of noise level for all subjects and all regions. Thus, it showed higher image quality such as SNR and CNR in some iron-rich brain tissues in contrast to SPGR-SWI. In conclusion, we expect that this proposed FISP sequence would be a promising imaging probe for other advanced SWI applications, and, meanwhile, this work may contribute to the current developments of the steady-state free-precession (SSFP).