Patent ID: 8121246

Claim:
A radiographic apparatus for acquiring 3D sectional images comprising an emission source for emitting radiation to an object under examination; a detecting device for detecting said radiation emitted to and transmitted through said object under examination; a revolving device, when an axis extending between said emission source and detecting device is regarded as a central axis, one of axes perpendicular to the central axis as a body axis, a plane perpendicular to the body axis and including said central axis as a central sectional plane, and an angle formed on the central sectional plane between a predetermined coordinate axis and the central axis as a projection angle, for revolving at least one of the emission source/detecting device and the object under examination about said body axis; and an arithmetic processing device, when carrying out a back projection arithmetic process on projection data detected by the detecting device to carry out reconstruction of a sectional image, for carrying out said reconstruction using data derived from an addition average according to a value determined by a reconstruction position and said projection angle, and wherein the value determined by said reconstruction position and said projection angle is a range on said detecting device to which radiation transmitted through a thickness in a direction of the body axis of the object under examination to be collected is projected, and said arithmetic processing device carries out said reconstruction using data derived from an addition average according to said range, and wherein, when a width in the direction along the body axis of said range is L, said thickness is w, the plane perpendicular to said body axis is an xy plane, coordinates of the reconstruction position projected to the xy plane are X and Y, respectively, said projection angle is θ, a focus of said emission source is F, an arriving point on said detecting device of a center of a beam of said radiation is D, a revolution center of revolution about said body axis is O, a distance from said focus F to said arriving point D is FD, and a distance from said focus F to said revolution center O is FO, said width L is determined from an equation L=FD×w /( FO−X cos θ− Y sin θ).