[Required dose of imaging systems--nuclear medicine]

The required dose of imaging systems in nuclear medicine is based upon the statistical properties of radioactive decay. In contrast to the absorbed dose, the radioactivity can be directly and easily measured. The International Commission on Radiological Protection (ICRP) has developed the concept of effective dose. Based on this concept, radiation exposure by nuclear medicine and radiodiagnostic procedures can be compared to the natural radiation burden. In addition, the hypothetical risk associated with exposure to ionizing radiation can be estimated and compared to that in daily life. Radiation exposure in nuclear medicine procedures including PET remain within the limits of annual natural radiation exposure (1-6 mSv). The overall risk of any diagnostic procedure employing ionizing radiation in radiology appears to be negligible. The activity used for procedures in nuclear medicine is a compromise between radiation safety and image quality. A recent representative evaluation revealed that the average activity used for nuclear medicine procedures in Germany is lower than in other European states. While for most adult procedures a standard dose is given, the accepted method for children is the weight method. Any procedure employing ionizing radiation is usually performed only if alternative diagnostic imaging modalities such as ultrasound and MRI cannot answer a specific test question appropriately. In addition to the latter, there are several ways to minimize radiation exposure. The most important way of assuring quality in any procedure is a strong quality-control program. Furthermore, comprehensive knowledge encompassing the indications for a study, the technical aspects of its acquisition and processing, and the final interpretation of its results are of great importance. Finally, it is known that prolonged data acquisition will result in improved image quality; however, this is clearly limited by the acceptance of the patient.