診断用X線撮影装置を用いたCdTe検出器の応答関数の実測とモンテカルロシミュレーションコードの評価

摘要

An X-ray spectrum measured with CdTe detector has to be corrected with response function, because the spectrum is composed of full energy peaks (FEP) and escape peaks (EP). Recently, various simulation codes were developed, and using them the response functions can be calculated easily. The aim of this study is to propose a new method for measuring the response function and to compare it with the calculated value by the Monte Carlo simulation code. In this study, characteristic X-rays were used for measuring the response function. These X-rays were produced by the irradiation of diagnostic X-rays with metallic atoms. In the measured spectrum, there was a background contamination, which was caused by the Compton scattering of the irradiated X-ray in the sample material. Therefore, we thought of a new experimental methodology to reduce this background. The experimentally derived spectrum was analyzed and then the ratios of EP divided by FEP (EP/FEP) were calculated to compare the simulated values. In this article, we showed the property of the measured response functions and the analysis accuracy of the EP/FEP, and we indicated that the values calculated by Monte Carlo simulation code could be evaluated by using our method.%X線スペクトルは，X線撮影装置のquality assurance (QA)やquality control(QC)だけでなく，医用画像を解析するときに必要な基礎情報である.近年では，フォトンカウンティング技術やデュマルエネルギー技術などの個々の光子エネルギーに着目した技術が実用化されつつあり，X線強度および平均エネルギーを測定する既往のシステムとは異なる原理の診断機器が診療の現場で使用されている.これらの診断機器を用いて取得された医用画像を解析するためにはX線スぺクトルを実測する必要がある.また，X線検出器内で起こる相互作用とスペクトルを関係づける応答関数について熟知することが医用画像の理解につながると考える.