The evolution of scintillating medical detectors

The principle of scintillation detectors has been among the first realizati ons of radiation detectors. Despite ongoing attempts to switch to direct co nverting detectors, scintillators have shown great persistence in the field of medical imaging. In radiography, computer tomography and nuclear medici ne, a variety of scintillating devices are the 'workhorses' of the clinicia n today. For radiography, flat X-ray detectors (FDs) with evaporated scinti llation layers are at the level of product introduction. However, X-ray ima ge intensifier tubes (XIIs) are competitive and still have features that wi ll be hard to beat in the near future. Although XIIs have disadvantages, th ey have experienced a significant evolution in robust image quality and cos t reduction over the decades. The so-called 'offline' detectors from film t o storage phosphors seemed to have reached a plateau since the late 1970s. However, the distinction between on- and offline may soften in the future, because of new readout concepts. Detectors in computer tomography (CT) have evolved from scintillators to gaseous direct converters back to scintillat ors. Extreme timing requirements and detector modularity have ruled out des igns that would rank as 'high performance' in other fields. Modern ultra-fa st ceramic scintillation detectors are a prerequisite of subsecond CT and l eave breathing room for future scan times even below 0.5 s. The field of nu clear medicine is a good example of how difficult it is, to replace a cheap and reliable technology. Since many years, direct converters like CdTe and the likes are discussed to overthrow the regime of NaI:TI in combination w ith photomultipliers (PMTs). Both components are well known since the 1950s and have shown remarkable staying power. Still the scintillator with the h ighest light output, NaI:TI in combination with the basically noiseless PMT is almost unbeatable in low cost. In combination with modern digital elect ronics, drawbacks of analog circuitry like temperature drift and energy dep endence can be made practically invisible to the user. New ultra-compact PM T designs could drive the design of the gamma camera towards more compactne ss, even without direct converting detectors. (C) 2000 Elsevier Science B.V . All rights reserved.