Conventional Cone Beam CT (CBCT) is composed of a single source and a large detector to aquire a full sinogram of the object. Multi-source inverse geometry CT system (IGCT) consists, for its part in using several sources and a small detector to acquire several partial sinograms of the object. For technological, financial and medical reasons the reduction of the number of sources and the reduction of the detector size are interesting but induce to solve an ill-posed and ill-conditionned problem. We propose a regularized iterative algorithm which is able to reconstruct the object volume from partial sinograms acquired with a an optimized multi-source IGCT system : we will demonstrate the performance of the proposed algorithm when we reduce the size of the detector and the number of sources. Realistically simulated CT data is reconstructed with the proposed algorithm and the results are compared to those obtained by filtered backprojection (FBP) and those obtained by a maximum likelihood estimation to show the impact of the regularization.
Recent advances in the domain of energy-resolved semiconductor detectors stimulate research in X-ray computed
tomography (CT). However, the imperfections of these detectors induce errors that should be considered for further
applications. Charge sharing and pile-up effects due to high photon fluxes can degrade image quality or yield wrong
material identification. Basis component decomposition provides separate images of principal components, based on the
energy related information acquired in each energy bin. The object is typically either decomposed in photoelectric and
Compton physical effects or in basis materials functions.
This work presents a simulation study taking into account the properties of an energy-resolved CdTe detector with
flexible energy thresholds in the context of materials decomposition CT. We consider the effects of a first order pile-up
model with triangular pulses of a non-paralyzable detector and a realistic response matrix. We address the problem of
quantifying mineral content in bone based on a polynomial approach for material decomposition in the case of two and
three energy bins. The basis component line integrals are parameterized directly in the projection domain and a
conventional filtered back-projection reconstruction is performed to obtain the material component images. We use
figures of merit such as noise and bias to select the optimal thresholds and quantify the mineral content in bone. The
results obtained with an energy resolved detector for two and three energy bins are compared with the ones obtained for
the dual-kVp technique using an integrating-mode detector with filters and voltages optimized for bone densitometry.
Dynamic X-ray imagers require large surface, fast and highly sensitive X-ray absorbers and dedicated readout
electronics. Monocrystalline photoconductors offer the sensitivity, speed, and MTF performances. Polycristalline
photoconductors offer the large surface at a moderate cost. The challenge for them is to maintain the first performances
at a compatible level with the medical applications requirements. This work has been focused on polycristalline CdTe
grown by Close Space Sublimation (CSS) technique. This technique offers the possibility to grow large layers with a
high material evaporation yield. This paper presents the results obtained with an image demonstrator using 350μm thick
CdTe_css layers coupled to a CMOS readout circuit with Indium bumping. The present demonstrator has 200 x 200
pixels, with a pixel pitch of 75μm ×75μm. A total image surface of 15mm × 15mm has then been obtained. The ASIC works in an integration mode, i.e. each pixel accumulates the charges coming from the CdTe layer on a capacitor, converting them to a voltage. Single images as well as video sequences have been obtained. X-ray performance at 16 frames per second rate is measured. In particular a readout noise of 0.5 X ray, an MTF of 50% at 4 lp/mm and a DQE of 20% at 4lp/mm and 600 nGy are obtained. Although present demonstrator surface is moderate, it demonstrates that high performance can be expected from this assembly concept and its interest for medical applications.
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