PROBLEM TO BE SOLVED: To improve substance discrimination precision.SOLUTION: A computer tomography apparatus includes a radiation source and a processing section. The radiation source generates radiation. The processing section acquires detection data on photons of radiation passing through a subject for each of a plurality of energy bandwidths by using an output signal of a photon number detector which outputs a signal according to the incidence of the radiation, calculates non-linear detector response data from the detection data for each of the plurality of energy bandwidths, calculates linear detector response data by subtracting the calculated non-linear detector response data from the detection data, performs a substance discrimination by using the linear detector response data and calculates a projection length of each of a plurality of substances.SELECTED DRAWING: Figure 1【課題】物質弁別の精度を向上させること。【解決手段】実施形態のコンピュータ断層撮影装置は、放射線源と、処理部とを備える。放射線源は、放射線を発生させる。処理部は、前記放射線の入射に応じて信号を出力する光子計数検出器の出力信号を用いて、被検体を透過した放射線の光子の検出データを、複数のエネルギー帯域ごとに取得し、前記複数のエネルギー帯域ごとの検出データから非線形検出器応答のデータを算出し、算出した非線形検出器応答データを前記検出データから差し引いて、線形検出器応答のデータを算出し、前記線形検出器応答のデータを用いて物質弁別を行い、複数の物質それぞれの投影長を算出する。【選択図】図１
