<title>Computer simulation of the geometric unsharpness effect on radiologic images</title>

Abstract

The magnitude of the image geometric unsharpness depends on the location in the field where the object is hit by the x- ray beam. This phenomenon is known as field characteristics and is caused by the target plane angulation. This yields different effective focal spot sizes and shapes when it is 'seen' from different directions and locations in the x-ray field . Due to the effect of the field characteristics, a more detailed evaluation of focal spot behavior in radiology systems is needed. Hence the focal spot should be evaluated in all field locations, which is very complex with experimental procedures, although feasible by computer simulation. This work describes an algorithm with the aim of determining the size and shape of effective focal spots in any location of the radiation field, on the basis of the focal spot size measurement in the filed center. The results obtained by the program have agreed with those obtained by pinholes matrix exposures in several radiology faculties. The program has proved efficient in computing the size of the focal spot projections for mammography systems, with a standard deviation around 0.03-0.04 mm.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.