A semi-automated quantitative comparison of metal artifact reduction in photon-counting computed tomography by energy-selective thresholding

An evaluation of energy thresholding and acquisition mode for metal artifact reduction in Photon-counting detector CT (PCD-CT) compared to conventional energy-integrating detector CT (EID-CT) was performed. Images of a hip prosthesis phantom placed in a water bath were acquired on a scanner with PCD-CT and EID-CT (tube potentials: 100, 120 and 140 kVp) and energy thresholds (above 55–75 keV) in Macro and Chess mode. Only high-energy threshold images (HTI) were used. Metal artifacts were quantified by a semi-automated segmentation algorithm, calculating artifact volumes, means and standard deviations of CT numbers. Images of a human cadaver with hip prosthesis were acquired on the PCD-CT in Macro mode as proof-of-concept. Images at 140 kVp showed less metal artifacts than 120 kVp or 100 kVp. HTI (70, 75 keV) had fewer artifacts than low energy thresholds (55, 60, 65 keV). Fewer artifacts were observed in the Macro-HTI (8.9–13.3%) for cortical bone compared to Chess-HTI (9.4–19.1%) and EID-CT (10.7–19.0%) whereas in bone marrow Chess-HTI (19.9–45.1%) showed less artifacts compared to Macro-HTI (21.9–38.3%) and EID-CT (36.4–54.9%). Noise for PCD-CT (56–81 HU) was higher than EID-CT (33–36 HU) irrespective of tube potential. High-energy thresholding could be used for metal artifact reduction in PCD-CT, but further investigation of acquisition modes depending on target structure is required.

Thresholds of ultraperipheral processes

Threshold behavior of the cross-sections of ultraperipheral nuclear interactions is studied. Production of [Formula: see text] and [Formula: see text] pairs as well as [Formula: see text] and parapositronium is treated. The values of corresponding energy thresholds are presented and the total cross-sections of these processes at the newly constructed NICA and FAIR facilities are estimated.

Ultraperipheral vs. Ordinary Nuclear Interactions

It is argued that the cross sections of ultraperipheral interactions of heavy nuclei can become comparable in value to those of their ordinary hadronic interactions at high energies. Simple estimates of corresponding “preasymptotic energy thresholds” are provided. The method of equivalent photons is compared with the perturbative approach. The situation at NICA/FAIR energies is discussed.

Threshold Driven Energy-Efficient and Scalable Dual Cluster Head Protocol

In WSN cluster-based routing approach is a major step in the direction of energy efficiency. However, research shows that energy dissipation in a cluster-based approach predominantly occurs in two cases; first during data transmission to the base station and second during data fusion/aggregation. Eventually, this leads to sizable energy dissipation, the early death of CHs and results in lower network lifetime. Moreover, in most of the recent proposed works, it is never assured that an individual node selected as a Cluster-Head would perform all the assigned tasks without dying in the process. Thus to address these problems, a new approach is proposed in this paper, where two cluster-heads (CHs) in every cluster are selected; first cluster-head being used for data aggregation (Primary-CH) and second for data transmission (Secondary-CH), which assists in reducing the burden of a single Cluster Head. Along with the dual Cluster-Heads, another key feature adopted in this paper is the Energy Threshold values for PCH and SCH. These Energy Thresholds for different CHs calculates the minimum energy required by a node to perform all the tasks assigned to it when elected as CH. So, while electing Primary Cluster-Head (PCH) and Secondary Cluster-Head (SCH) along with other criterions energy threshold values for PCH (EPO) and energy threshold values for SCH (ESO) are also used. Any node with remaining energy less than that of energy thresholds would never be considered for Cluster-Heads. Therefore, by employing the above-mentioned criterions, this article proposes a new protocol that uses dual heads and assists in enhancing the network life of a network as compared to LEACH protocol.

Photon-counting cine-cardiac CT in the mouse

The maturation of photon-counting detector (PCD) technology promises to enhance routine CT imaging applications with high-fidelity spectral information. In this paper, we demonstrate the power of this synergy and our complementary reconstruction techniques, performing 4D, cardiac PCD-CT data acquisition and reconstruction in a mouse model of atherosclerosis, including calcified plaque. Specifically,in vivocardiac micro-CT scans were performed in four ApoE knockout mice, following their development of calcified plaques. The scans were performed with a prototype PCD (DECTRIS, Ltd.) with 4 energy thresholds. Projection sampling was performed with 10 ms temporal resolution, allowing the reconstruction of 10 cardiac phases at each of 4 energies (40, 3D volumes per mouse scan). Reconstruction was performed iteratively using the split Bregman method with constraints on spectral rank and spatio-temporal gradient sparsity. The reconstructed images represent the firstin vivo, 4D PCD-CT data in a mouse model of atherosclerosis. Robust regularization during iterative reconstruction yields high-fidelity results: an 8-fold reduction in noise standard deviation for the highest energy threshold (relative to algebraic reconstruction), while absolute spectral bias measurements remain below 13 Hounsfield units across all energy thresholds and scans. Qualitatively, image domain material decomposition results show clear separation of iodinated contrast and soft tissue from calcified plaque in thein vivodata. Quantitatively, spatial, spectral, and temporal fidelity are verified through a water phantom scan and a realistic MOBY phantom simulation experiment: spatial resolution is robustly preserved by iterative reconstruction (10% MTF: 2.8-3.0 lp/mm), left-ventricle, cardiac functional metrics can be measured from iodine map segmentations with ∼1% error, and small calcifications (615 μm) can be detected during slow moving phases of the cardiac cycle. Given these preliminary results, we believe that PCD technology will enhance dynamic CT imaging applications with high-fidelity spectral and material information.