PROBLEM TO BE SOLVED: To accurately obtain noise intensity by a projection data division method using data after fan-para conversion.SOLUTION: In an image reconstruction device: a plurality of pieces of projection data acquired by irradiating radiation onto a subject are received, and the data is subjected to predetermined data conversion； the data after the conversion is divided into two or more sets, a reconstruction image is generated for each piece of data of each set, the generated reconstruction image of each set is differentiated, and a difference image is generated； an index is calculated, which indicates variations in pixel values for one or more predetermined regions of the difference image； and the value of the index is corrected by a correction value obtained beforehand, and the index value after the correction is made the noise intensity of the region.SELECTED DRAWING: Figure 7【課題】ファン－パラ変換後のデータを用いて投影データ分割法により精度よくノイズ強度を求める。【解決手段】被検体に放射線を照射して得た複数の投影データを受け取って、所定のデータ変換を行い、前記変換後のデータを、２以上の集合に分割し、各集合のデータごとに再構成画像を生成し、生成した前記各集合の前記再構成画像を差分し、差分画像を生成する。前記差分画像の所定の１以上の領域について画素値のばらつきを示す指標を算出し、前記指標の値を、予め求めておいた補正値によって補正し、補正後の前記指標値を前記領域のノイズ強度とする。【選択図】 図７
