X 線用のピンホールカメラに用いるコリメータ径の最適化と画像周辺部での検出効率低下の補正手法の提案

抄録

  A visual image of the scattered X-ray distributions gives us useful information for beginners to study radiation physics. A pin-hole camera for X-rays can be made by use of simple materials as well as a two-dimensional X-ray detector (imaging plate: IP). In contrast with a pin-hole camera for the visible radiations, a pin-hole camera for X-rays uses a collimator, having a sufficient thickness to reduce X-rays. This design causes the following problem: in the case in which the X-rays are incident to the collimator from the diagonal direction, the some X-rays are absorbed by the wall of the collimator. Namely, the images in the surrounding part of the IP are underrepresented. The aim of this study is to suggest a correction method of the underrepresentation. We used a pin-hole camera (320 mm(long)×270 mm(wide)×300 mm(depth)) by means of the clinically applied IP (10×12 inch). In order to determine proper conditions for a size of collimators (pin-hole), experiments using medical X-ray equipments were carried out. The efficiencies and resolutions were experimentally determined for the collimator sizes of 2 to 8 mm^φ. Then, images of scattered X-ray distributions were measured by the irradiation of a head phantom, and considerations were taken for a practical use of the pin-hole camera. Moreover, an exponential absorption of X-rays in the phantom was visualized by our camera in order to indicate a potential of quantitative analysis based on the image of scattered X-ray distributions.