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An experimental comparison of detector performance for direct and indirect digital radiography systems
Author(s) -
Samei Ehsan,
Flynn Michael J.
Publication year - 2003
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.1561285
Subject(s) - detective quantum efficiency , optical transfer function , optics , detector , x ray detector , flat panel detector , computed radiography , digital radiography , physics , image sensor , noise (video) , materials science , radiography , image quality , nuclear physics , computer science , artificial intelligence , image (mathematics)
Current flat‐panel detectors either directly convert x‐ray energy to electronic charge or use indirect conversion with an intermediate optical process. The purpose of this work was to compare direct and indirect detectors in terms of their modulation transfer function (MTF), noise power spectrum (NPS), and detective quantum efficiency (DQE). Measurements were made on three flat‐panel detectors, Hologic Direct‐Ray DR‐1000 (DRC), GE Revolution XQ/i (XQ/i), and Philips Digital Diagnost (DiDi) using the IEC‐defined RQA5 (∼74 kVp, 21 mm Al) and RQA9 (∼120 kVp, 40 mm Al) radiographic techniques. The presampled MTFs of the systems were measured using an edge method [Samei et al., Med. Phys. 25 , 102 (1998)]. The NPS of the systems were determined for a range of exposure levels by two‐dimensional (2D) Fourier analysis of uniformly exposed radiographs [Flynn and Samei, Med. Phys. 26 , 1612 (1999)]. The DQEs were assessed from the measured MTF, NPS, exposure, and estimated ideal signal‐to‐noise ratios. For the direct system, the MTF was found to be significantly higher than that for the indirect systems and very close to an ideal function associated with the detector pixel size. The NPS for the direct system was found to be constant in relation to frequency. For the XQ/i and DRC systems, the DQE results reflected expected differences based on the absorption efficiency of the different detector materials. Using RQA5, the measured DQE values in the diagonal (and axial) direction(s) at spatial frequencies of 0 . 15 mm − 1and 2 . 5 mm − 1were 64% (64%) and 20% (15%) for the XQ/i system, and 38% (38%) and 20% (20%) for the DRC, respectively. The DQE results of the DiDi system were difficult to interpret due to additional preprocessing steps in that system.