Performance Analysis of Imaging Systems

The ultimate performance test of an imaging system is its medical utility. This requires clinical use and evaluation of how well the system improves the delivery of health care. The radioactive source and the medium through which it travels, the collimator, detector electronics, and display system, comprise the major components that must be calculated in judging any imaging system. The subjective role of the observer and clinical physician interpreting and utilizing the information also must be considered in the overall scheme. A variety of qualitative and quantitative methods exist for analyzing the performance of imaging systems. Detectors deal with three interrelated properties which are resolution, sensitivity and observation time. Sensitivity measurements deal with counts per unit time obtained from a point or planar source placed a specific distance from the face of the detector system. Resolution measurements deal with the ability to discriminate between adjacent point or line sources. Full width at half maximum and modulation transfer function measurements of resolution are discussed in detail. Various types of geometric absorption, and anatomical phantoms are available to assist in making these determinations. In this review, attention is mostly drawn to the instrumental aspects of the system, since these are reasonably understood and somewhat controllable. However, the elements at opposite ends of the system, the biological mechanisms in the patients body, and the human observer using the information are really the most important, if least understood and controllable elements.