Tissue-air ratios and scatter-air ratios for diagnostic radiology (1-4 mm Al HVL).

Tissue-air and scatter-air ratios for use in diagnostic radiology (1-4 mm Al HVL) have been calculated from previously reported measurements of percentage depth doses (PDD) and backscatter factors (BSF) for the same quality range. Tabulations of TAR are presented. The calculated TARs are compared with direct measurements of TAR which have been carried out by other workers. TARs and SARs are shown to be functions of peak tube potential for a given first HVL as a consequence of a similar dependence of PDD. This emphasises once again the inadequacy of the first HVL alone as a specifier of beam quality.