Metal artifact correction in photon‐counting detector computed tomography: metal trace replacement using high‐energy data
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Bibliographic record
Abstract
Abstract Background Metal artifacts have been an outstanding issue in computed tomography (CT) since its first uses in the clinic and continue to interfere. Metal artifact reduction (MAR) methods continue to be proposed and photon‐counting detectors (PCDs) have recently been the subject of research toward this purpose. PCDs offer the ability to distinguish the energy of incident x‐rays and sort them in a set number of energy bins. High‐energy data captured using PCDs have been shown to reduce metal artifacts in reconstructions due to reduced beam hardening. Purpose High‐energy reconstructions using PCD‐CT have their drawbacks, such as reduced image contrast and increased noise. Here, we demonstrate a MAR algorithm, trace replacement MAR (TRMAR), in which the data corrupted by metal artifacts in full energy spectrum projections are corrected using the high‐energy data captured during the same scan. The resulting reconstructions offer similar MAR to that seen in high‐energy reconstructions, but with improved image quality. Methods Experimental data were collected using a bench‐top PCD‐CT system with a cadmium zinc telluride PCD. Simulations were performed to determine the optimal high‐energy threshold and to test TRMAR in simulations using the XCAT phantom and a biological sample. For experiments a 100‐mm diameter cylindrical phantom containing vials of water, two screws, various densities of Ca(ClO 4 ) 2 , and a spatial resolution phantom was imaged with and without the screws. The screws were segmented in the initial reconstruction and forward projected to identify them in the sinogram space in order to perform TRMAR. The resulting reconstructions were compared to the control and to reconstructions corrected using normalized metal artifact reduction (NMAR). Additionally, a beef short rib was imaged with and without metal to provide a more realistic phantom. Results XCAT simulations showed a reduction in the streak artifact from −978 HU in uncorrected images to −10 HU with TRMAR. The magnitude of the metal artifact in uncorrected images of the 100‐mm phantom was −442 HU, compared to the desired −81 HU with no metal. TRMAR reduced the magnitude of the artifact to −142 HU, with NMAR reducing the magnitude to −96 HU. Relative image noise was reduced from 176% in the high‐energy image to 56% using TRMAR. Density quantification was better with NMAR, with the Ca(ClO 4 ) 2 vial affected most by metal artifacts showing 0.8% error compared to 2.1% with TRMAR. Small features were preserved to a greater extent with TRMAR, with the limiting spatial frequency at 20% of the MTF fully maintained at 1.31 lp/mm, while with NMAR it was reduced to 1.22 lp/mm. Images of the beef short rib showed better delineation of the shape of the metal using TRMAR. Conclusions NMAR offers slightly better performance compared to TRMAR in streak reduction and image quality metrics. However, TRMAR is less susceptible to metal segmentation errors and can closely approximate the reduction in the streak metal artifact seen in NMAR at 1/3 the computation time. With the recent introduction of PCD‐CT into the clinic, TRMAR offers notable potential for fast, effective MAR.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from it