The invention relates to an examination apparatus and a method for perfusion studies in a patient (1). According to the method, a rotational X-ray device (10) is moved on a closed, preferably non-planar trajectory (T) while continuously generating projections of the patient (1) after the injection of a contrast agent with an injection device (20). The projections are used by a data processing system (30) in a sliding window technique to reconstruct three-dimensional images of the body volume. The resulting sequence of 3D images may be displayed on a monitor (31) to reveal the desired information about the perfusion process.