The present invention discloses a method for performing
CT imaging on a
region of interest of an object under examination, comprising: acquiring the CT projection data of the
region of interest; acquiring the CT projection data of region B; selecting a group of PI line segments covering the
region of interest, and calculating the reconstruction image value for each PI
line segment in the group; and combining the reconstruction image values in all the PI line segments to obtain the image of the region of interest. The present invention further discloses a
CT imaging device using this method and a data processor therein. Since the 2D / 3D slice image of the region of interest can be exactly reconstructed and obtained as long as the X-
ray beam covers the region of interest and the region B, it is possible to use a small-sized
detector to perform
CT imaging on the region of interest at any position of a large-sized object, which reduces to a great extent the
radiation dose of the X-
ray during the CT scanning.