Jennings R J
Office of Science and Technology, Center for Devices and Radiological Health, Rockville, Maryland 20857.
Med Phys. 1988 Jul-Aug;15(4):588-99. doi: 10.1118/1.596210.
The necessity for using adequate beam filtration in diagnostic radiology is well known. Although aluminum is the most widely used filter material for diagnostic x-ray applications, the possibility that other materials might have superior properties has prompted a number of studies that have attempted to determine both the type and the amount of filtration most appropriate for a given situation. This paper describes a method based on precise matching of spectral shape that permits the absolute ranking of beam-hardening materials. Matching of spectral shape ensures equality of such parameters as image contrast and patient dose. Spectrally equivalent filters can then be ranked on the basis of the transmission of one relative to another. Following the development of the theory behind the method and an algorithm for implementing it, the method is applied to the evaluation of a variety of materials for use as filters in diagnostic radiology. Experimental verification of a few of the calculated results is also described. Both calculated and experimental results show that normal aluminum filters are about 10% less efficient than filters of materials such as copper, brass, or iron. Since the approach followed here was the basis for several early investigations of filtration for orthovoltage therapy, a brief comparison of results from these early reports with results calculated using the method developed here is also presented.
