Empirical and theoretical investigation of the noise performance of indirect detection, active matrix flat-panel imagers (AMFPIs) for diagnostic radiology

• Published in: Medical physics (Lancaster) Vol. 24; no. 1; pp. 71 - 89
• Main Authors: Siewerdsen, J. H., Antonuk, L. E., El-Mohri, Y., Yorkston, J., Huang, W., Boudry, J. M., Cunningham, I. A.
• Format: Journal Article
• Language: English
• Published: United States American Association of Physicists in Medicine 01-01-1997
• Subjects: 87.56.01.g; 87.56.02; 87.56.06; biomedical equipment; diagnostic radiography; Electronics; Equipment Design; Female; Fluoroscopy; Humans; Mammography; Medical image noise; Medical imaging; Medical X‐ray imaging; Models, Theoretical; noise; Non‐ionizing radiation equipment and techniques; Phosphors; Quantum Theory; Radiography; Radiography - instrumentation; Radiography - methods; Reproducibility of Results; X‐ray detectors; X‐ray imaging; X‐ray optics; 87.56.01.g; 87.56.02; 87.56.06
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1118/1.597919

Noise properties of active matrix, flat-panel imagers under conditions relevant to diagnostic radiology are investigated. These studies focus on imagers based upon arrays with pixels incorporating a discrete photodiode coupled to a thin-film transistor, both fabricated from hydrogenated amorphous silicon. These optically sensitive arrays are operated with an overlying x-ray converter to allow indirect detection of incident x rays. External electronics, including gate driver circuits and preamplification circuits, are also required to operate the arrays. A theoretical model describing the signal and noise transfer properties of the imagers under conditions relevant to diagnostic radiography, fluoroscopy, and mammography is developed. This frequency-dependent model is based upon a cascaded systems analysis wherein the imager is conceptually divided into a series of stages having intrinsic gain and spreading properties. Predictions from the model are compared with x-ray sensitivity and noise measurements obtained from individual pixels from an imager with a pixel format of 1536×1920 pixels at a pixel pitch of 127 μm. The model is shown to be in excellent agreement with measurements obtained with diagnostic x rays using various phosphor screens. The model is used to explore the potential performance of existing and hypothetical imagers for application in radiography, fluoroscopy, and mammography as a function of exposure, additive noise, and fill factor. These theoretical predictions suggest that imagers of this general design incorporating a CsI:Tl intensifying screen can be optimized to provide detective quantum efficiency (DQE) superior to existing screen-film and storage phosphor systems for general radiography and mammography. For fluoroscopy, the model predicts that with further optimization of a-Si:H imagers, DQE performance approaching that of the best x-ray image intensifier systems may be possible. The results of this analysis suggest strategies for future improvements of this imaging technology.