Evaluation of conventional imaging performance in a research whole-body CT system with a photon-counting detector array

Abstract

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.

Photon-Counting CT of the Brain: In Vivo Human Results and Image-Quality Assessment

“…8 However, recent advances in PCD technology with high-speed application-specific integrated circuits and small pixel sizes have led to the development of PCDs resistant to pulse pileup at clinically routine CT tube currents. 15 Another PCD artifact is charge sharing, which occurs when the energy of an x-ray photon is distributed across multiple adjacent detector pixels, reducing the accuracy of the detected photon energy. 8 Multiple anti-chargesharing techniques are currently being developed to limit this artifact.…”

“…To date, PCD CT scanning of a cadaver head 15 has suggested the feasibility of PCD for brain CT, but in vivo results have not been previously studied, to our knowledge. Thus, the purpose of the current study was to compare the image quality of PCD with that of conventional EID for human brain CT.…”

Image quality in coronary CT angiography: challenges and technical solutions

“…55 However, it is currently not clinically implemented as the limited count rate, energyintegrating detection, increased detector pixel crosstalk and electronic noise are major limitations of this technology. 56 Eventually, photon counting is expected to improve soft-tissue discrimination, to reduce the radiation dose and to provide higher spatial resolution. 57 Compared with dual energy, photoncounting coronary CTA will provide more detailed information about myocardial and coronary plaque components by analyzing differences in contrast agent concentration and/or spectral attenuation.…”

Dose-efficient ultrahigh-resolution scan mode using a photon counting detector computed tomography system

“…20,25,32,33 Previous studies using the system demonstrated that the PCD subsystem was capable of providing clinical image quality at clinically realistic levels of x-ray photon flux commensurate with commercial EID systems, and providing improved CNR relative to a state-of-the-art CT scanner using EIDs. 23,34 Recently, a UHR mode was implemented on the PCD subsystem of the research scanner to take advantage of the smaller native detector pixel size, and consequently, to improve spatial resolution to accommodate clinical applications in lung, vascular, musculoskeletal, and temporal bone CT imaging. In this mode, instead of grouping 4 × 4 detector pixels together to form a 0.9 mm × 0.9 mm macropixel, the pixel grouping was reduced to 2 × 2, reducing the macropixel size by half [ Fig.…”

“…The same x-ray tubes were used on the EID and PCD subsystems, each equipped with a UHR focal spot of nominal size 0.7 mm (Straton, Siemens Healthcare 35 ). Two scan protocols were available for the PCD UHR mode: (1) a head protocol using a carbon bowtie filter and (2) an abdominal protocol using both the carbon bowtie filter and an aluminum bowtie filter, 34 both with a 1 s rotation time. No comb filters were used for the PCD UHR mode, thus ensuring optimal dose efficiency.…”