Abstract
Rationale and objectivesThe purpose of this study was to evaluate the feasibility of unconstrained three-material decomposition in a human tissue specimen containing iodinated contrast agent, using an experimental multi-bin photon-counting silicon detector. It was further to evaluate potential added clinical value compared to a 1st-generation state-of-the-art dual-energy computed tomography system.Materials and methodsA prototype photon-counting silicon detector in a bench-top setup for x-ray tomographic imaging was calibrated using a multi-material calibration phantom. A heart with calcified plaque was obtained from a deceased patient, and the coronary arteries were injected with an iodinated contrast agent mixed with gelatin. The heart was imaged in the experimental setup and on a 1st-generation state-of-the-art dual-energy computed tomography system. Projection-based three-material decomposition without any constraints was performed with the photon-counting detector data, and the resulting images were compared with those obtained from the dual-energy system.ResultsThe photon-counting detector images show better separation of iodine and calcium compared to the dual-energy images. Additional experiments confirmed that unbiased estimates of soft tissue, calcium, and iodine could be achieved without any constraints.ConclusionThe proposed experimental system could provide added clinical value compared to current dual-energy systems for imaging tasks where mix-up of iodine and calcium is an issue, and the anatomy is sufficiently small to allow iodine to be differentiated from calcium. Considering its previously shown count rate capability, these results show promise for future integration of this detector in a clinical CT scanner.Key Points• Spectral photon-counting detectors can solve some of the fundamental problems with conventional single-energy CT.• Dual-energy methods can be used to differentiate iodine and calcium, but to do so must rely on constraints, since solving for three unknowns with only two measurements is not possible. Photon-counting detectors can improve upon these methods by allowing unconstrained three-material decomposition.• A prototype photon-counting silicon detector with high count rate capability allows performing unconstrained three-material decomposition and qualitatively shows better differentiation of iodine and calcium than dual-energy CT.
Highlights
Photon-counting detectors can improve upon these methods by allowing unconstrained three-material decomposition
It is well known that the development efforts of photoncounting detectors (PCDs) for computed tomography (CT) are motivated by a desire to resolve some of the fundamental problems with single-energy CT using energy-integrating detectors
Each pixel of the PCD consists of nine strata, each connected to a channel of a photon-counting application-specific integrated circuit (ASIC), which sorts photon counts into eight energy bins with configurable thresholds [35]
Summary
It is well known that the development efforts of photoncounting detectors (PCDs) for computed tomography (CT) are motivated by a desire to resolve some of the fundamental problems with single-energy CT using energy-integrating detectors These include limited spatial resolution, limited lowdose performance [1], and non-quantitative imaging [2]. Since dual-energy systems only provide measurements at two effective energies, some kind of constraint (typically mass preservation) needs to be imposed in order to estimate a third component This enables visualization of k-edge materials with dual-energy systems, any deviation in the imaged object from the assumptions of the constraint results in bias in the decomposition [4], which in practice can result in poor differentiation of iodine and calcium
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