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.
The scatter effect on detective quantum efficiency (DQE) of digital mammography is investigated using the
cascaded-systems model. The cascaded-systems model includes a scatter-reduction device as a binomial selection
stage. Quantum-noise-limited operation approximates the system DQE into the multiplication form of the
scatter-reduction device DQE and the conventional detector DQE. The developed DQE model is validated in
comparisons with the measured results using a CMOS flat-panel detector under scatter environments. For various
scatter-reduction devices, the slot-scan method shows the best scatter-cleanup performance in terms of DQE,
and the scatter-cleanup performance of the conventional one-dimensional grid is rather worse than the air gap.
The developed model can also be applied to general radiography and will be very useful for a better design of
We present a theoretical framework describing projections obtained from computed tomography systems considering physics of each component consisting of the systems. The projection model mainly consists of the attenuation of x-ray photons through objects including x-ray scatter and the detection of attenuated/scattered x-ray photons at pixel detector arrays. X-ray photons are attenuated by the Beers-Lambert law and scattered by using the Klein-Nishina formula. The cascaded signal-transfer model for the detector includes x-ray photon detection and light photon conversion/spreading in scintillators, light photon detection in photodiodes, and the addition of electronic noise quanta. On the other hand, image noise is considered by re-distributing the pixel signals in pixel-by-pixel ways at each image formation stage using the proper distribution functions. Instead of iterating the ray tracing over each energy bin in the x-ray spectrum, we first perform the ray tracing for an object only considering the thickness of each component. Then, we assign energy-dependent linear attenuation coefficients to each component in the projected images. This approach reduces the computation time by a factor of the number of energy bins in the x-ray spectrum divided by the number of components in the object compared with the conventional ray-tracing method. All the methods developed in this study are validated in comparisons with the measurements or the Monte Carlo simulations.