PROBLEM TO BE SOLVED: To provide a technique which enables reconstruction of a highly precise image effective for utilization for diagnosis, and which can reduce a dosage.SOLUTION: This X-ray CT apparatus is equipped with a reconstruction means for reconstructing a pre-scanned image of a subject to be examined from X-ray transmission data based on pre-scanning, and for reconstructing a main-scanned image of the subject from X-ray transmission data based on main scanning a judging means for judging the start of the main scanning on the basis of a change in the CT value of the pre-scanned image and a scanning controlling means for performing the main scanning, while changing a helical pitch toward the terminal end of a direct image reconstruction area from a stopped position of a bed by the pre-scanning, on the basis of the result of judging by the judging means. The scanning controlling means starts the main scanning at the starting end of the image reconstruction range with a first helical pitch enabling the application of X-rays equivalent to a predetermined number of views, and continues the main scanning by changing the first helical pitch to a second predetermined helical pitch, after the application of the X-rays equivalent to the predetermined number of views.COPYRIGHT: (C)2008,JPO&INPIT【課題】診断利用に効果的な精度の高い画像を再構成でき、しかも被爆量を低減することのできる技術を提供する。【解決手段】プリスキャンに基づくX線透過データから被検体のプリスキャン画像を再構成するとともに、本スキャンに基づくX線透過データから被検体の本スキャン画像を再構成する再構成手段と、プリスキャン画像のCT値変化に基づき、本スキャンの開始を判断する判断手段と、判断手段の判断結果に基づいて、プリスキャンによる寝台の停止位置から直接画像再構成範囲の終端に向けてヘリカルピッチを変更させながら本スキャンさせるスキャン制御手段を備え、スキャン制御手段は、画像再構成範囲の始端に所定ビュー数分のX線を曝射可能な第1のヘリカルピッチで本スキャンを開始させ、所定ビュー数分のX線を曝射後、予め定められた第2のヘリカルピッチに変更して続けて本スキャンをさせる。【選択図】図3
