Dosimetry and Quality Control in Medical Imaging Applications

Abstract

Radiation exposure to medical diagnostic procedures is becoming a topic of increasing relevance and social interest. A primary aim of modern diagnostic procedures is to provide sufficient information for a particular diagnostic task with exposures kept as low as practicable. The ALARP principle (As Low As Reasonably Practicable) is the driving force behind a number of innovations and ongoing research activities over the past 30–40 years.

To evaluate the performance of diagnostic imaging systems it is necessary to correlate image quality and dose and, therefore, be able to evaluate both. This can, on the one hand, involve advanced measurement tools and methods that attempt to measure imaging system parameters such as MTF, NPS, and NEQ as well as dose (quanta) dependent image/information quality parameters such DQE. However, whilst such measurements provide information concerning the physical performance capabilities of systems employed in diagnostic procedures under well defined exposure conditions, they do not permit us to verify optimal performance in daily clinical use. For this latter purpose it would be necessary to routinely perform measurements of image quality and associated dosimetric evaluations, ideally for every patient. Under such circumstances the ALARP principle could then be said to apply to each and every patient or group of patients.

In this paper the development of meaningful patient dosimetry methods and techniques for various patient specific radiological applications, as well as image quality control procedures will be reviewed. The importance of ongoing technological developments will be discussed in relation to the present situation and future progress that might be possible in the field of patient radiation protection. For example in the UK during the past 5 years there has been a complete transfer from film based to digital radiographic techniques. Equally, ongoing developments in CT technology continue to create increased imaging information albeit at much higher doses. The effects of these changes on scientific support to patient dosimetry and quality control in diagnostic radiology as well as future possibilities for improved application of the ALARP principle will be highlighted.