MR用簡易ファントムを用いた磁化率強調画像（Susceptibility－Weighted Imaging：SWI）の基礎的検討

摘要

MRTにおける磁化率強調画像（susceptibility-weighted imaging：SWI）は，Haackeらによって提唱された撮像 法で，位相情報を用い，各組織間の磁化率を強調 してコントラストを得る方法である．SWIの臨床応 用については，微小出血の検出や静脈奇形の診断にお ける有用件が報告されている．しかし，ファント ムを用いた基礎的な検討はほとんど行われていない． 生体の微小な領域における磁化率効果を，特製のファ ントムによって模擬することは容易ではないと予想 される．%We evaluated the visibility of hypointensity regions on susceptibility-weighted(SW)magnetic resonance imaging (MRI). A commercial simple phantom filled uniformly with a gel material was demonstrated to include small regions affected by different magnetic susceptibilities compared to their surroundings. For detection of these regions in the phantom, the three-dimensional SW imaging(SWI)technique is superior to a conventional two-dimensional gradient-recalled-echo(GRE)MRI technique. The mean contrast between the hypointensity regions and their surroundings on GRE images (T2~* weighted images) of 4 mm slice thickness is approximately 88% less than that on SWI of 4 mm effective slice thickness. When the effective slice thickness of SWI is increased more than 4 mm, the contrast on SW images is decreased. While the mean contrast on SWI of 7 mm effective slice thickness is approximately 75-65% compared to that of 4 mm effective slice thickness, its contrast of 7 mm is determined to be higher than that on GRE images of 4 mm slice thickness; this suggests that the SWI technique could be applied to whole brain examination by reducing the acquisition time. The quantitative results in this article are considered to be useful for evaluating the visibility of hypointensity regions on SWI, when comparing them with GRE images and varying the effective slice thickness of SWI.