Minimum dose calculation for different imaging tasks in digital projection radiography

Abstract

In diagnostic radiology it is a common interest of patient and medical staff to keep the exposure as low as reasonably achievable (ALARA). In spite of this task being well known there is no consensus about how low the exposure for a specific diagnostic examination can be. The methods presented in this paper allow for the mathematical determination of the lowest exposure necessary to perform basic, well defined imaging tasks in digital radiography. The model quantifies how different demands on the result influence the necessary exposure. Dependences on parameters describing the beam quality used and the detector are implemented into the model. A strong rise of the necessary exposure to detect a certain contrast of lower amplitude or with higher certainty was determined. The effects of a change of the energy of the irradiation are as a first step investigated via the connected change of the transmission of a main absorber. By specification of the specimen to be observed the result is connected to beam energies which can be correlated with the energy dependent response of a realistic detector system. The calculations give basic information about the best exposure in a simplified view of patient dimensions and diagnostic needs. Especially in pediatric radiology optimized adaptations to the patient and the clinical question are expected to take great effects due to the great variations of patient sizes.