Direct-conversion flat-panel X-ray image detectors

Flat-panel X-ray image detectors have been shown to be suitable to replace the conventional X-ray filmjscreen cassettes for medical radiography (static or snapshot imaging). They are capable of capturing the X-ray image digitally immediately after the X-ray exposure which permits a convenient clinical transition to digital radiography. There are two general approaches to the flat-panel X-ray detector technology: direct and indirect conversions. The authors review the operating principles for direct conversion, and formulate and review the required X-ray photoconductor properties for enabling a successful direct conversion detector. Two important photoconductor requirements are discussed in detail, the X-ray sensitivity and dark current, both of which are topical current research areas in seeking the best photoconductor amongst a number of candidate semiconductors such a-Se, PbI2, HgI2 and others. The requirements of medical fluoroscopy (real-time imaging at very low exposure levels) is challenging this technology and demanding even higher X-ray sensitivity.