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

Abstract

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.

Photon-Counting Detector CT Virtual Monoengergetic Images for Cochlear Implant Visualization—A Head to Head Comparison to Energy-Integrating Detector CT

“…Do et al, (2020) compared different energy thresholds and acquisition modes for PCD-CT and EID-CT after scanning a hip prosthesis phantom. Fewer metal artifacts were found in high-energy threshold images compared to low-energy thresholds and the choice of acquisition mode had an influence on the number of artifacts seen in relevant structures such as cortical bone and bone marrow [ 26 ]. These findings warrant further investigation in future studies in order to corroborate the findings of this study and to identify the ideal settings for postoperative CI imaging with the novel PCD-CT technology.…”

Full field-of-view, high-resolution, photon-counting detector CT: technical assessment and initial patient experience

“…Fundamentally, the direct-conversion PCD technology enables uniform photon weighting across x-ray energies, small detector-pixel design, and energy thresholding and photon binning for multi-energy imaging. This has led to superior imaging capabilities compared to conventional CT which uses energy integrating detectors (EIDs), such as elimination of electronic noise ( Yu et al, 2016b ), facilitation of ultra-high resolution (UHR) imaging using smaller detector pixels ( Leng et al, 2016 , Pourmorteza et al, 2018 ), reduction of metal artifacts ( Do et al, 2020 , Zhou et al, 2019 ), and improvement of iodine contrast-to-noise ratio ( Gutjahr et al, 2016 , Schmidt, 2009 ). In addition, the energy-binning feature of PCDs allows measurements above and below the K-edge of high-Z materials.…”

“…Investigations involving a whole-body research PCD-CT system built using a modified 2 nd generation dual-source CT platform, with the B-subsystem equipped with a CdTe PCD array ( Kappler et al, 2014 , Leng et al, 2018 , Pourmorteza et al, 2016 , Symons et al, 2016 , Yu et al, 2016a ), have shown superior imaging performance relative to EID-CT in phantoms, animals, and patients. In humans, this system has demonstrated dose-efficient ultra-high resolution (UHR) imaging without comb/grid filters ( Bartlett et al, 2019 , Leng et al, 2016 , Pourmorteza et al, 2018 ), radiation dose reduction ( Klein et al, 2020 , Rajendran et al, 2020 , Symons et al, 2016 ), metal artifact reduction using high-energy thresholding and a tin filter ( Do et al, 2020 , Zhou et al, 2019 ), and multi-energy capabilities ( Leng et al, 2018 , Pourmorteza et al, 2016 , Symons et al, 2018 ) focusing on neurological, musculoskeletal, thoracic, vascular and abdominal imaging applications. Additionally, phantom and animal studies using this system have shown the potential for multi-contrast imaging ( Ren et al, 2020 , Symons et al, 2017 ) and improved stent delineation ( Mannil et al, 2018 , von Spiczak et al, 2018 ).…”

Spectral Photon-Counting CT Technology in Chest Imaging

“…Another metal artifact-reduction technique is the reconstruction of an image using only photons measured over 70 keV. The resulting high-threshold image presents an increased CNR compared to conventional images in presence of metal artifacts [26]. The optimal weight for differentiating calcium from water is derived from the attenuation coefficients subtraction (dashed lines).…”

“…Another metal artifact-reduction technique is the reconstruction of an image using only photons measured over 70 keV. The resulting high-threshold image presents an increased CNR compared to conventional images in presence of metal artifacts [26].…”