Infographics / Digital Radiography

Direct vs Indirect Conversion Detectors

Two panels compare digital detector conversion paths. Left: direct conversion in an amorphous selenium photoconductor, where an absorbed x-ray frees charge that is pulled straight down by an applied bias field with minimal lateral spread, landing on a single TFT pixel, giving sharper images. Right: indirect conversion, where an x-ray absorbed in a caesium iodide scintillator produces light that spreads sideways to several a-Si photodiode pixels, causing some blur. A footnote notes that x-ray absorption and DQE depend on detector material and thickness rather than the conversion type.

Direct vs indirect conversion in digital radiography detectors Two panels compare digital detector conversion paths. Left: direct conversion in an amorphous selenium photoconductor, where an absorbed x-ray frees charge that is pulled straight down by an applied bias field with minimal lateral spread, landing on a single TFT pixel, giving sharper images. Right: indirect conversion, where an x-ray absorbed in a caesium iodide scintillator produces light that spreads sideways to several a-Si photodiode pixels, causing some blur. A footnote notes that x-ray absorption and DQE depend on detector material and thickness rather than the conversion type. Direct conversion a-Se photoconductor x-ray amorphous selenium (a-Se) bias field charge (e⁻ / h⁺) pixels minimal spread Charge pulled straight down — sharper image (better MTF / resolution) Indirect conversion CsI scintillator → a-Si photodiode x-ray caesium iodide (CsI) light spreads pixels signal over several pixels Light scatters sideways in scintillator — some blur (lower high-frequency MTF) X-ray absorption and DQE depend on detector material and thickness, not the conversion type — only the resolution trade-off is shown here.
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