Dosimetry in Medical X-ray Imaging

摘要

X-ray computed tomography is by far the largest contributor to the radiation burden of patients. Therefore, good clinical practice in medical X-ray imaging requires the quantification of radiation exposure to optimize the image quality in relation to the absorbed dose ratio. This article covers the dosimetry part but not the quantification of image quality. Dose measurements in X-ray imaging are fundamental for two purposes: First, to set and check standards of good practice and second, to assist in assessing detriment or harm. Different application specific dose quantities are defined for general radiography and fluoroscopy, mammography and computed tomography. These provide the basis for quality assurance in X-ray imaging - for example, for acceptance testing, or for application-specific diagnostic reference levels. Non-invasive X-ray multimeters are used for quality control measurements in the beams of diagnostic X-ray devices. The patient dose is usually evaluated as the absorbed dose in organs and tissues from which the risk-related quantity "effective dose" is estimated. The latter quantity allows an estimate of the patient's risk to suffer from stochastic radiation effects. The effective dose is estimated from the measured applicationspecific dose quantities by use of dose conversion coefficients. These cannot be measured directly. Instead, they are calculated by means of Monte- Carlo simulations using computational reference models of the human body. Alternatively, they can be determined by dose measurements in adequate physical (anthropomorphic) phantoms. Simulations and dose measurements are important requirements for the development of personalized dosimetry in computed tomography.