Digital radiology using active matrix readout of amorphous selenium: Theoretical analysis of detective quantum efficiency

<jats:p>A flat‐panel x‐ray imaging detector using a layer of amorphous selenium (<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp8097-math-0001.png" xlink:title="urn:x-wiley:00942405:media:mp8097:mp8097-math-0001"/>‐Se) for direct conversion of x rays (to charge) and an active matrix for self‐scanned readout is being investigated for digital radiology. A theoretical analysis of the spatial frequency dependent detective quantum efficiency <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp8097-math-0002.png" xlink:title="urn:x-wiley:00942405:media:mp8097:mp8097-math-0002"/> of the self‐scanned <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp8097-math-0003.png" xlink:title="urn:x-wiley:00942405:media:mp8097:mp8097-math-0003"/>‐Se detector is performed based on a model of signal and noise propagation in a cascaded imaging system. Because of the high intrinsic resolution of <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp8097-math-0004.png" xlink:title="urn:x-wiley:00942405:media:mp8097:mp8097-math-0004"/>‐Se and the pixelated active matrix readout method, such detectors are inherently undersampled and aliasing is present. The presampling modulation transfer function (MTF) and aliased noise power spectrum (NPS) of the detector were used in the analysis of <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp8097-math-0005.png" xlink:title="urn:x-wiley:00942405:media:mp8097:mp8097-math-0005"/> It is proven that the aliased NPS for the self‐scanned <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp8097-math-0006.png" xlink:title="urn:x-wiley:00942405:media:mp8097:mp8097-math-0006"/>‐Se detectors is white. Since the shape of <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp8097-math-0007.png" xlink:title="urn:x-wiley:00942405:media:mp8097:mp8097-math-0007"/> is determined by the ratio of MTF squared and the NPS, the shape of <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp8097-math-0008.png" xlink:title="urn:x-wiley:00942405:media:mp8097:mp8097-math-0008"/> follows the square of the presampling MTF of the detector as a result of the white NPS. The analysis also shows that DQE(0) is proportional to the pixel fill factor, i.e., the fraction of each pixel area used for image charge collection. The DQE analysis is applied to detector parameters for three x‐ray imaging applications: mammography, chest radiography, and fluoroscopy. The effects of pixel fill factor, imaging geometry (i.e., incident angle of x rays), and various sources of electronic noise on the detector <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mp8097-math-0009.png" xlink:title="urn:x-wiley:00942405:media:mp8097:mp8097-math-0009"/> are discussed. Strategies for maximizing detector DQE for each x‐ray imaging application are proposed.</jats:p>