This study evaluated the conventional imaging performance of a research whole-body photon-counting CT system and investigated its feasibility for imaging using clinically realistic levels of x-ray photon flux. This research system was built on the platform of a 2nd generation dual-source CT system: one source coupled to an energy integrating detector (EID) and the other coupled to a photon-counting detector (PCD). Phantom studies were conducted to measure CT number accuracy and uniformity for water, CT number energy dependency for high-Z materials, spatial resolution, noise, and contrast-to-noise ratio. The results from the EID and PCD subsystems were compared. The impact of high photon flux, such as pulse pile-up, was assessed by studying the noise-to-tube-current relationship using a neonate water phantom and high x-ray photon flux. Finally, clinical feasibility of the PCD subsystem was investigated using anthropomorphic phantoms, a cadaveric head, and a whole-body cadaver, which were scanned at dose levels equivalent to or higher than those used clinically. Phantom measurements demonstrated that the PCD subsystem provided comparable image quality to the EID subsystem, except that the PCD subsystem provided slightly better longitudinal spatial resolution and about 25% improvement in contrast-to-noise ratio for iodine. The impact of high photon flux was found to be negligible for the PCD subsystem: only subtle high-flux effects were noticed for tube currents higher than 300 mA in images of the neonate water phantom. Results of the anthropomorphic phantom and cadaver scans demonstrated comparable image quality between the EID and PCD subsystems. There were no noticeable ring, streaking, or cupping/capping artifacts in the PCD images. In addition, the PCD subsystem provided spectral information. Our experiments demonstrated that the research whole-body photon-counting CT system is capable of providing clinical image quality at clinically realistic levels of x-ray photon flux.

This work describes and validates a computationally efficient technique for noise map estimation directly from CT images, and an adaptive NLM filtering based on this noise map, on phantom and patient data. Both the noise map calculation and the adaptive NLM filtering can be performed in times that allow integration with clinical workflow. The adaptive NLM algorithm provides effective denoising of CT data throughout a volume, and may allow significant lowering of radiation dose.

Objectives The purpose of this work was to measure and compare the iodine contrast-to-noise ratio (CNR) between a commercial energy-integrating-detector (EID) CT system and a photon-counting-detector (PCD) CT scanner capable of human imaging at clinical dose rates, as well as to determine clinical feasibility using human cadavers. Materials & Methods A research dual-source PCD-CT scanner was used, where the “A” tube/detector subsystem used an EID and the “B” tube/detector subsystem used a PCD. Iodine CNR was measured in 4 anthropomorphic phantoms, simulating 4 patient sizes, at 4 tube potential settings. Following biospecimen committee approval, PCD scans were performed on a fresh-frozen human head and a whole-body cadaver using clinical dose rates, repeated using the EID and identical parameters, and qualitative side-by-side comparisons performed. Results For the same photon fluence, phantom measurements demonstrated a mean increase in CNR of 11, 23, 31, 38% for the PCD system, relative to the EID system, at 80, 100, 120, and 140 kV, respectively. PCD-CT additionally provided energy-selective imaging, where low-and high-energy images reflected the energy dependence of the iodine signal. PCD images of cadaveric anatomy demonstrated decreased beam hardening and calcium blooming in the high-energy bin images and increased contrast in the low-energy bins images relative to the EID images. Threshold-based PCD images were qualitatively deemed equivalent in other aspects. Conclusions The evaluated research PCD-CT system was capable of clinical levels of image quality at clinical dose rates. It further provided improved CNR relative to state-of-the-art EID-CT. The energy selective bin images provide further opportunity for dual-and multi-energy analyses.

, "Dose-efficient ultrahighresolution scan mode using a photon counting detector computed tomography system," J. Med. Imag. 3(4), 043504 (2016), doi: 10.1117/1.JMI.3.4.043504. Abstract. An ultrahigh-resolution (UHR) data collection mode was enabled on a whole-body, research photon counting detector (PCD) computed tomography system. In this mode, 64 rows of 0.45 mm × 0.45 mm detector pixels were used, which corresponded to a pixel size of 0.25 mm × 0.25 mm at the isocenter. Spatial resolution and image noise were quantitatively assessed for the UHR PCD scan mode, as well as for a commercially available UHR scan mode that uses an energy-integrating detector (EID) and a set of comb filters to decrease the effective detector size. Images of an anthropomorphic lung phantom, cadaveric swine lung, swine heart specimen, and cadaveric human temporal bone were qualitatively assessed. Nearly equivalent spatial resolution was demonstrated by the modulation transfer function measurements: 15.3 and 20.3 lp∕cm spatial frequencies were achieved at 10% and 2% modulation, respectively, for the PCD system and 14.2 and 18.6 lp∕cm for the EID system. Noise was 29% lower in the PCD UHR images compared to the EID UHR images, representing a potential dose savings of 50% for equivalent image noise. PCD UHR images from the anthropomorphic phantom and cadaveric specimens showed clear delineation of small structures.

Purpose To determine the dose reduction that could be achieved without degrading low-contrast spatial resolution (LCR) performance for two commercial iterative reconstruction (IR) techniques, each evaluated at two strengths with many repeated scans. Materials and Methods Two scanner models were used to image the American College of Radiology (ACR) CT Accreditation Phantom LCR section at volume CT dose indexes of 8, 12, and 16 mGy. Images were reconstructed by using filtered-back projection (FBP) and two manufacturers’ IR techniques, each at two strengths (moderate and strong). Data acquisition and reconstruction were repeated 100 times for each, yielding 1800 images. Three diagnostic medical physicists reviewed the LCR images in a blinded fashion and graded the visibility of four 6-mm rods with a six-point scale. Noninferiority and inferiority-superiority analyses were used to interpret the differences in LCR relative to FBP images acquired at 16 mGy. Results LCR decreased with decreasing dose for all reconstructions. Relative to FBP and full dose, 25%–50% dose reductions resulted in inferior LCR for vendors 1 and 2 for FBP and 25% dose reductions resulted in inferior and equivalent performance for vendor 1 and equivalent and superior performance for vendor 2 at moderate and strong IR settings, respectively. When dose was reduced by 50%, both IR techniques resulted in inferior LCR at both strength settings. Conclusion For radiation dose reductions of 25% or more, the ability to resolve the four 6-mm rods in the ACR CT Accreditation Phantom can be lost.