Room: Track 1
To quantitatively evaluate metal artifact reduction by energy-selective thresholds in photon-counting computed tomography (PCCT), comparing different acquisition settings and thresholds to conventional CT.
A custom-made phantom (titan hip endoprothesis in foam cortical bone model), submerged in water, was acquired in a whole-body PCCT prototype (SOMATOM CounT, Siemens Healthineers, Germany) with energy-selective thresholds in macro- (one high-energy threshold) and chess-mode (two high-energy thresholds simultaneously) at following tube potential/threshold combinations: 140kVp/90keV, 120kVp/85keV, 100kVp/80keV, 140kVp/75keV, 120kVp/70keV, 100kVp/65keV (macro-mode), 140kVp/75keV/65keV, 120kVp/70keV/60keV, 100kVp/65keV/55keV (chess-mode). Conventional images (CI) at 140kVp, 120kVp, and 100kVp were obtained from data completion scans with energy-integrating detector. CTDIvol was matched between all acquisitions (20mGy). High-energy threshold images (HTI) were reconstructed with filtered back-projection (B70f) by considering only photons above the high-energy threshold. For chess-mode, two HTI were reconstructed and evaluated separately (one for each threshold). Relative volumes of metal artifacts in cortical bone, bone marrow and water were calculated with a segmentation-based thresholding algorithm for HTI and CI. Noise was assessed by measuring standard deviation of CT numbers in water without phantom.
Metal artifacts decreased with increasing tube potential, increasing energy-selective threshold of HTI, and increasing distance from metal. In bone marrow, HTI showed reduced metal artifacts (11.4%-45.1%) compared to CI (36.4%-54.9%). In bone, macro-mode HTI showed reduced metal artifacts (6.7%-13.3%) compared to CI (10.7%-19.0%), but chess-mode HTI did so only for highest thresholds (9.4%-13.5%), not for lower thresholds (11.3%-19.1%). In water, metal artifacts were lower in CI (1.7%-3.7%) than in HTI (2.0%-6.1%). At same thresholds, chess-mode HTI (19.9%-35.6%) performed better than macro-mode HTI (21.9%-38.3%) in bone marrow, but not in bone and water. Noise was increased in both macro-mode HTI (55.2HU-101.1HU) and chess-mode HTI (59.2HU-77.4HU) compared to CI (32.8HU-33.6HU).
PCCT images reconstructed with high-energy thresholds can reduce metal artifacts, depending on acquisition mode and energy threshold.
Not Applicable / None Entered.