a-Se detector
Amorphous selenium flat-panel detector. Direct-conversion X-ray detector — selenium converts incident X-ray photons directly to electrical charge, without an intermediate scintillator step. Used in modern mammography (Hologic, Siemens) and in selected DR. Sharper at the relevant low-energy mammography spectrum than a-Si / CsI scintillator detectors but shorter useful lifespan under clinical duty cycle.
Why it matters to buyers: Detector age is the #1 refurb value driver on Selenia Dimensions and 3Dimensions. Useful life: 5–9 years on 2009+ panels; ~3 years on earlier panels. A 2015 Dimensions with a 2020 detector replacement is worth substantially more than a 2017 Dimensions with its original panel. See Clarity HD detector for the modern Hologic example.
Why it matters to engineers: Ghosting, dead-pixel clusters, lag artifacts = end-of-life. Replacement is the largest service event on a mammography unit short of full chassis swap. Daily / weekly QC catches drift before it becomes clinically visible; failing physicist phantom imaging is the documentation-of-record. Selenium is toxic — disposal via certified medical-electronics recycler, not general waste.