A CT angiography apparatus compensates for respiratory motion. During a helical scan, a radiation source and a detector generate data sets corresponding to a plurality of sub-volumes of a blood vessel over a plurality of cardiac cycles. Sub-volume data sets corresponding to a selected cardiac phase are reconstructed into a plurality of sub-volume images. Characteristic points in the sub-volume images are identified. A computer routine or processor calculates a respiratory motion vector based on the identified characteristic points in a plurality of the sub-volume images. An image reconstruction routine or processor reconstructs the original sub-volume data in the selected cardiac phase into a volume image representation using the calculated respiratory motion vector.