Minimum entrance exposure estimates for information recording in diagnostic radiology

Based upon previously derived expressions, a procedure is given for estimating the minimum entrance exposure necessary to record a desired information set for use in any diagnostic radiological situation. By separating the different variables contributing to the final image and making suitable approximations, a simple relationship of four separable components is obtained. Some typical examples are given to illustrate the relative importance of each component, and to obtain numerical estimates of exposure values. These examples show that the theoretical entrance exposure range for most diagnostic situations, where a realistic information set is desired, lies between 2.5 X 10(-3) and 1.2 X 10(-2) mC/kg (10-50 mR). It is also concluded that a 75-kVp x-ray source, filtered to remove the low-energy photons and with a mean photon energy of 40 keV, should be sufficiently close to optimum in most diagnostic situations to record the desired information in the above entrance exposure range.