PROBLEM TO BE SOLVED: To certainly put the projection data by the X-ray beam near to the reconstruction surface in the projection data collected by helical scanning to practical use when reconstructing a CT image.SOLUTION: The weighting coefficient to be subjected to the multiplication of the projection data s(&alphadi, &betadi, &gammadi) and s(&alphaci, &betaci, &gammaci), wherein corresponding X-ray beams pass through the pixels P on the reconstruction surface RP in the reconstruction algorithm of pixel data and the view angle directions thereof are opposed to each other, is calculated according to a numerical formula using a term of the distance &DeltaZ between an X-ray data collecting system 41 when collecting the projection data and the reconstruction surface RP + an offset distance &DeltaZoffset. For example, the projection data s(&alphadi, &betadi, &gammadi) is multiplied by the weighting coefficient. Herein, the weighting coefficient is weighting coefficient &omegadi=(&DeltaZci+&DeltaZoffset)/[(&DeltaZdi+&DeltaZoffset)+(&DeltaZci+&DeltaZoffset)] (wherein both of &DeltaZdi and &DeltaZci take a minute value and, even if the ratio of &DeltaZdi and &DeltaZci is largely biased, a state becoming extremely small in one weighting coefficient is prevented by the presence of &DeltaZoffset).COPYRIGHT: (C)2010,JPO&INPIT【課題】CT画像を再構成する際に、ヘリカルスキャンにより収集された投影データのうち再構成面に近いX線ビームによる投影データを確実に活用する。【解決手段】画素データの再構成アルゴリズム(algorithm)において、対応するX線ビームが再構成面RP上の画素Pを通りそのビュー角度方向が互いに対向する投影データs(αdi,βdi,γdi),s(αci,βci,γci)に乗算すべき加重係数を、その投影データ収集時のX線データ収集系41と再構成面RPとの距離ΔZ+オフセット距離ΔZoffsetの項を用いた数式にて算出する。例えば、投影データs(αdi,βdi,γdi)に乗算する加重係数ωdi=(ΔZci+ΔZoffset)/[(ΔZdi+ΔZoffset)+(ΔZci+ΔZoffset)]。ΔZdi,ΔZciのいずれもが微小な値を取りΔZdi,ΔZciの比が大きく偏っても、ΔZoffsetの存在により一方の加重係数が極端に小さくなる状態を防ぐ。【選択図】 図6
