CT撮像系におけるスライス面の位置と方向に対する解像力特性の評価

摘要

CT撮像系における等方位性データは被写体の歪が ほとんどなく，三次元的観察における一貫性におい て，臨床的意義は非常に高い．近年，撮像はマル チスライスCTによって三次元可視化画像の構築を 前提とすることが多くなっており，その画質を重視し て，コーン角の問題を考慮した再構成法を搭載した装 置も開発された．%Analysis of the detailed physical property in CT system is important in an understanding of a clinical image. In this study, we evaluated resolution power property about the positions and direction for in-plane in CT system. The indexes of the resolving power property of CT images were measured by MTFs using the thin metal wire (diameter of 0.2mm). We measured the positions of the iso-center and the off-center (32mm, 64mm, 96mm, 128mm) in in-plane. One-dimensional MTFs for the X-direction and Y-direction were calculated by the numerical slit scanning method. Then, MTF was calculated from the corresponding direction. As a result, when a filter kernel of high resolutions (B70) is used in the position of 128mm, the resolution of X-direction was inferior to the Y-direction about 30% (at the MTF-value of 0.5cycles/mm). Moreover, the resolution of X-direction at the position of 128mm was inferior to the center about 33% (at the MTF-value of 0.5cycles/mm). The resolving power property of in-plane in CT system was decreased in the calculation from the numerical slit that becomes perpendicular to the direction of centrifugal and, decreased proportionately with the distance from the center. Also, the resolutions along the centrifugal direction fell off remarkably at the peripheral area. And also, it turned out that the declining trend becomes larger, when the filter function for high-resolving power that is adapted for lungs is used.