The first generation CT scanner was of this form with one source and one detector and moved in steps to obtain the image and it is time consuming. Then came different generations and widely accepted form is that there is one X-ray source which produce a “fan-beam” of X-rays and then increased number of detectors as shown in Fig 4.16.
In the conventional CT systems, only one slice can be acquired at a time. If multiple slices are required to cover a large volume of the body, then the patient table is moved in discrete steps through the plane of the X-ray source and detector as shown in Fig 4.17. A single slice is acquired at each discrete table position, with an inevitable time delay between obtaining each image. This process is both time-inefficient and can result in spatial misregistrations between slices if the patient moves.