Energy imparted and effective doses in computed tomography.

The radiation risk to patients undergoing computed tomography (CT) examinations may be characterized by using the dose descriptors of effective dose equivalent (HE) and effective dose (E). Values of HE and E, however, are much more difficult to obtain than the total energy imparted (epsilon) to the patient. In this study, representative values of the ratios HE/epsilon and E/epsilon were obtained using published Monte Carlo organ dose computations for typical CT x-ray spectra. Values of patient dose per unit energy imparted can be combined with independent estimates of energy imparted to quantify the dose to a patient undergoing any type of CT examination.