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 kV_p) 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 kV_p showed less metal artifacts than 120 kV_p or 100 kV_p. 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.