LYSO-GAPD Photon Counting Detectors for DEXA Applications

Osteoporosis is the most common bone disease in humans, representing a major public health threat. Dual-energy X-ray absorptiometry (DEXA) is the most widely used densitometry method to assess bone mineral density (BMD), and it is the standard test used to diagnose osteoporosis, according to the classification of the World Health Organization (WHO). DEXA detector converts incident X-ray photons to electrical signals, and then each pulse can be compared with the four different energy thresholds. The events falling within the selected energy window are binned into each low- and high-energy band. In this manner of operation, DEXA detector works as a photon counting detector providing information on the number of counted photons separately for each energy bin. Semiconductor detectors such as cadmium-zinc-telluride (CZT) or cadmium telluride (CdTe), with excellent energy resolution, have been regarded as one of the most useful DEXA detectors. As an alternative, X-ray photon counting detectors, combining high-performance scintillation crystals with compact photosensors, have attracted interest for use in DEXA applications. The first commercial DEXA scanner based on this technology was recently introduced. This chapter begins with the basic principle and techniques for DEXA instrumentation. The main technical features in creating the dual-photon beams and employing the photon counting detectors are described and compared. Recent performance characterizations obtained from indirect photon counting detectors consisting of a Geiger mode avalanche photodiode (GAPD) coupled with widely utilized lutetium yttrium oxyorthosilicate (LYSO) for potential application in DEXA systems are introduced. Moreover, the rotatable detector designs providing the innovative benefits are discussed. Various phantom images acquired from fan-beam DEXA system based on LYSO-GAPD photon counting detector are presented.