Fan-beam computerized tomography systems with rotating and with stationary detector arrays ('third' and 'fourth' generation).

Part I of the present work describes the fundamental problems important for understanding the function of fan-beam computerized tomography systems. First, the relationship between the number of detectors, the number of attenuation profiles, the number of volume elements in which the object slice is decomposed and the number of picture elements in the final image is explained. Then the influence of both the detector width and the sampling distance on the accuracy at which the attenuation profiles can be measured, is defined. Three spatial frequencies play an important part: the aperture cutoff frequency, the sampling frequency, and, coupled with the latter, the Nyquist frequency. Finally, the modulation transfer function, one of the most important quantitative characteristics of any computerized tomography system, is described. Part II of the present work describes the essential design characteristics of fan-beam computerized tomography systems with rotating as well as with stationary detector arrays. It is shown that both types of CT systems have been produced with different implementations. It is further explained that both CT types apply different sampling processes and, moreover, differ in image reconstruction techniques. However, it should be noted that this work presents only fundamental facts and does not attempt to be detailed.