The authors have developed a sandwich-like multilayer detector capable of imaging a large field of view. Two detector layers use the same photodiode arrays based on complementary metal-oxide-semiconductor active pixel technology while the scintillators of the front and rear detectors are composed of Gd<sub>2</sub>O<sub>2</sub>S : Tb and CsI : Tl, respectively. The front detector is implemented on a flexible printed-circuit board (FPCB) that is electrically connected to a corresponding control/readout PCB located under the rear detector’s control/readout PCB. The energy separation between two detector layers can be improved by using additional interlayer filters. Imaging performance of each detector layer is investigated for various filter designs. The imaging performance is evaluated in terms of large-area signal and noise, modulation-transfer function, noise-power spectrum, and detective quantum efficiency.
Sandwich-like multilayer detectors can measure dual-energy images at a single x-ray shot and the resulting images are free from the motion artifacts. In case of phosphor-coupled photodiode detector-based multilayer detectors, the direct x-ray interaction within the front photodiode layer can be a significant noise source. In this study, we propose to use a fiber-optic faceplate (FOP) between the front phosphor and photodiode layers, instead of the intermediate metal filter between the front and rear detector layers. This detector design is based on the fact that the FOP can reduce the probability of direct interaction of x-ray photons with the front photodiode as well as prevent x-ray photons with lower energies from reaching the rear detector layer. We develop a cascaded-systems model to describe the signal and noise characteristics in multilayer detector designs with the FOP. With the developed model, we investigate the imaging performance of the proposed detector designs for various FOP thicknesses in comparisons with the experimental measurements. The cascaded-systems analysis and demonstration dual-energy images of a postmortem mouse show that the proposed design is feasible for dual-energy imaging.
This paper describes the development of an active-pixel sensor (APS) panel, which has a field-of-view of 23.1×17.1 cm
and features 70-μm-sized pixels arranged in a 3300×2442 array format, for digital mammographic applications. The
APS panel was realized on 12-inch wafers based on the standard complementary metal-oxide-semiconductor (CMOS)
technology without physical tiling processes of several small-area sensor arrays. Electrical performance of the developed
panel is described in terms of dark current, full-well capacity and leakage current map. For mammographic imaging, the
optimized CsI:Tl scintillator is experimentally determined by being combined with the developed panel and analyzing im
aging characteristics, such as modulation-transfer function, noise-power spectrum, detective quantum efficiency, image l
ag, and contrast-detail analysis by using the CDMAM 3.4 phantom. With these results, we suggest that the developed
CMOS-based detector can be used for conventional and advanced digital mammographic applications.
Complementary metal-oxide-semiconductor (CMOS) active pixel sensors (APSs) with high electrical and optical
performances are now being attractive for digital radiography (DR) and dental cone-beam computed tomography
(CBCT). In this study, we report our prototype CMOS-based detectors capable of real-time imaging. The field-of-view
of the detector is 12 × 14.4 cm. The detector employs a CsI:Tl scintillator as an x-ray-to-light converter. The electrical
performance of the CMOS APS, such as readout noise and full-well capacity, was evaluated. The x-ray imaging
characteristics of the detector were evaluated in terms of characteristic curve, pre-sampling modulation transfer function,
noise power spectrum, detective quantum efficiency, and image lag. The overall performance of the detector is
demonstrated with phantom images obtained for DR and CBCT applications. The detailed development description and
measurement results are addressed. With the results, we suggest that the prototype CMOS-based detector has the
potential for CBCT and real-time x-ray imaging applications.
For a detector consisting of a phosphor screen and a photodiode array made by complementary metal-oxidesemiconductor
(CMOS) process, we have experimentally re-investigated the long-term stability of the signal and noise
characteristics as a function of the accumulated dose at the entrance surface of the detector in addition to the previous
study [IEEE Trans. Nucl. Sci. 56(3) 1121 (2009)]. The irradiation and analysis were more systematically performed. We
report the aging effect in image quality in terms of dark pixel signal, dynamic range, modulation-transfer function (MTF),
and noise-power spectrum (NPS). Unlike the previous study, the electronic noise was dominantly increased with the total
dose and the other statistical and structural noise sources were nearly independent on the cumulative dose. Similarly, the
increase of dark pixel signal and the related noise gradually reduces the dynamic range as the total dose increases. While
MTF was almost insensitive to the total dose, degradation in NPS was observed. Therefore, preprocessing without
properly updated offset and gain images would underestimate the detective quantum efficiency when performing quality
control of a detector in the field. Restoration of degraded dark signals due to aging is demonstrated by annealing the aged
detector with thermal activation energy. This study provides a motivation that the periodic monitoring of the imagequality
degradation is of great importance for the long-term and healthy use of digital x-ray imaging detectors.