CdTe and CdZnTe detectors in nuclear medicine

Nuclear medicine diagnostic applications are growing in search for more disease specific or more physiologically relevant imaging. The data are obtained non-invasively from large field γ cameras or from miniaturised probes. As far as single photon emitters are concerned, often labelled with 99mTc (140 keV, γ), nuclear instrumentation deals with poor counting statistics due to the method of spatial localisation and low contrast to noise due to scatter in the body. Since the 1960s attempts have been made to replace the NaI scintillator by semiconductor detectors with better spectrometric characteristics to improve contrast and quantitative measurements. They allow direct conversion of energy and thus more compact sensors. Room-temperature semiconductor detectors such as cadmium tellure and cadmium zinc tellure have favourable physical characteristics for medical applications which have been investigated in the 1980s. During one decade, they have been used in miniaturised probes such as for inter-operative surgery guidance which is today in a fast growing phase. This material suffers from charge transport problems which has slowed down imaging applications. Owing to a considerable research work on material, contacts and dedicated electronics small field of view compact pixellated γ cameras have been prototyped and one already marketed. Although extended clinical evaluation has to be conducted and long-term reliability assesed, the available data already confirm the expected gain in image contrast. Medical interest for dedicated imaging systems is greater than it was in the 1980s when the first mobile γ cameras were marketed. The future of CdTe or CdZnTe-based imager for routine use now relies at first on industrial costs.