The purpose of this study was to evaluate whether a misalignment correction algorithm reduces artifacts from breathing in patients undergoing computed tomography angiography (CTA) early after coronary artery bypass graft (CABG) surgery. In this retrospective study, consecutive patients undergoing CTA early after CABG surgery between November 2023 and March 2025 were screened. Patients exhibiting relevant breathing artifacts on standard reconstructions were included for the evaluation. CTA was acquired in the ECG-gated sequential mode on a dual-source CT. For each patient, standard reconstructions were compared with those using a misalignment correction algorithm designed to resolve discontinuities between adjacent image stacks (ZeeFree). Two blinded readers assessed artifacts across six anatomical regions (bypass grafts, coronary arteries, thoracic aorta, pulmonary trunk, lung/trachea, and sternum) using a 4-point visual analogue scale. Among 680 patients scanned at a median of 4 days (IQR 2–8 days) after CABG surgery, 75 patients (11

Metallic implants can cause relevant artifacts in computed tomography (CT) imaging, affecting the quality and diagnostic utility of scans. Previous advancements in metal artifact reduction techniques have shown promise but still exhibit limitations in artifact reduction, particularly close to metal implants. To evaluate a novel, advanced iterative metal artifact reduction (iMAR) algorithm for photon-counting detector CT in an experimental study focused on visualizing the vicinity of a fixation nail implant. Three bovine femur bones with titanium-based trochanteric fixation nail implants were scanned on a clinical photon-counting detector CT scanner. Images were reconstructed (1) without iMAR, (2) with the current iMAR algorithm, and (3) with a new prototype iMAR algorithm. The new iMAR prototype algorithm advances state-of-the-art iMAR for photon-counting detector CT by utilizing intrinsically available spectral information. Attenuation and artifact severity (SD of attenuation) were quantified by placing regions-of-interest on each reconstruction across 3 different axial slices: One in the bone marrow immediately adjacent to the metal implant and one in the water adjacent to the femur with the implant. Qualitative image quality, newly introduced artifacts, and diagnostic confidence were rated by 3 radiologists using 5-point Likert scales. Differences between reconstructions were tested using the Friedman test with Wilcoxon post hoc tests; interreader agreement was assessed using Krippendorff alpha. Artifact severity in the bone adjacent to the implant significantly decreased from 226 HU (no iMAR) to 174 HU (current iMAR) and to 159 HU with the new iMAR ( P < 0.001). Adjacent to the femur, artifact severity decreased from 63 HU to 48 HU and to 29 HU, respectively ( P < 0.05). Qualitative scores differed significantly between reconstructions ( P < 0.05), with highest ratings for new iMAR across all categories. Current iMAR introduced new artifacts near the implant, which did not occur with new iMAR ( P < 0.05). Experimental evidence from a bovine femur implant model suggests that a new, advanced iterative metal artifact reduction algorithm leveraging intrinsic spectral information from photon-counting detector CT effectively reduces metal artifacts and further improves the visualization of the metal-bone interface. Thus, this technique has the potential to enhance the assessment of implant-related complications such as aseptic loosening.

BACKGROUND:Metallic implants can cause relevant artifacts in computed tomography (CT) imaging, affecting the quality and diagnostic utility of scans. Previous advancements in metal artifact reduction techniques have shown promise but still exhibit limitations in artifact reduction, particularly close to metal implants. PURPOSE:To evaluate a novel, advanced iterative metal artifact reduction (iMAR) algorithm for photon-counting detector CT in an experimental study focused on visualizing the vicinity of a fixation nail implant. METHODS:Three bovine femur bones with titanium-based trochanteric fixation nail implants were scanned on a clinical photon-counting detector CT scanner. Images were reconstructed (1) without iMAR, (2) with the current iMAR algorithm, and (3) with a new prototype iMAR algorithm. The new iMAR prototype algorithm advances state-of-the-art iMAR for photon-counting detector CT by utilizing intrinsically available spectral information. Attenuation and artifact severity (SD of attenuation) were quantified by placing regions-of-interest on each reconstruction across 3 different axial slices: One in the bone marrow immediately adjacent to the metal implant and one in the water adjacent to the femur with the implant. Qualitative image quality, newly introduced artifacts, and diagnostic confidence were rated by 3 radiologists using 5-point Likert scales. Differences between reconstructions were tested using the Friedman test with Wilcoxon post hoc tests; interreader agreement was assessed using Krippendorff alpha. RESULTS:Artifact severity in the bone adjacent to the implant significantly decreased from 226 HU (no iMAR) to 174 HU (current iMAR) and to 159 HU with the new iMAR (P < 0.001). Adjacent to the femur, artifact severity decreased from 63 HU to 48 HU and to 29 HU, respectively (P < 0.05). Qualitative scores differed significantly between reconstructions (P < 0.05), with highest ratings for new iMAR across all categories. Current iMAR introduced new artifacts near the implant, which did not occur with new iMAR (P < 0.05). CONCLUSION:Experimental evidence from a bovine femur implant model suggests that a new, advanced iterative metal artifact reduction algorithm leveraging intrinsic spectral information from photon-counting detector CT effectively reduces metal artifacts and further improves the visualization of the metal-bone interface. Thus, this technique has the potential to enhance the assessment of implant-related complications such as aseptic loosening.

OBJECTIVES:Spontaneous coronary artery dissection (SCAD) is a rare cause of acute coronary syndrome and myocardial infarction. Accurate diagnosis is crucial for appropriate management. This study aimed to compare late enhancement (LE) imaging using photon-counting detector (PCD)-CT with cardiac MRI in patients with SCAD in the acute phase and during follow-up and to introduce a novel approach for visualizing myocardial extracellular volume (ECV) distribution in the myocardium. MATERIALS AND METHODS:This single-center prospective study enrolled patients with SCAD diagnosed with invasive coronary angiography. LE iodine imaging with spectral dual-source PCD-CT and cardiac MRI was performed early after symptom onset and at short-term follow-up. CT included coronary angiography and LE imaging (5 minutes after contrast). LE CT was assessed using the combination of conventional LE images, overlay images, polar maps, and with newly developed atlas maps. Atlas maps represent 2-dimensional maps with prefiltering applied to enable a simpler and more intuitive reading of ECV distribution across the myocardium. Cardiac MRI served as the reference standard for identifying pathologic myocardial segments based on late gadolinium enhancement (LGE) and edema on T2-weighted and T2-mapping images. Agreement between modalities was evaluated using Cohen's κ. RESULTS:Seventeen patients (median age, 44 years [interquartile range, 36-52]; 11 women) underwent 24 LE CT and cardiac MRI scans. Sixteen patients (median age, 44 years; 10 women) underwent acute phase imaging (median 6 days after symptom onset), and 8 patients (median age, 45 years; 6 women) underwent follow-up imaging (median 120 days after symptom onset). Atlas maps were helpful in detecting segments with pathological ECV and to adjudicate corresponding myocardial segments. Agreement between LE CT with LGE cardiac MRI was strong in the acute phase (κ = 0.832), improving to almost perfect when comparing LE-CT with both LGE and edema in cardiac MRI (κ = 0.944). At follow-up imaging, agreement further improved as edema resolved (κ = 0.956). CONCLUSIONS:LE imaging with PCD-CT demonstrated strong agreement with cardiac MRI for detecting myocardial injury in SCAD, which further improved at follow-up when edema resolved. Newly introduced atlas maps proved useful for a simple and intuitive visualization of myocardial injury.

Abstract Objective To determine optimal reconstruction parameters for dental implant imaging using photon-counting detector CT (PCD-CT), including ultra-high-resolution (UHR) images, virtual monoenergetic images (VMI), and iterative metal artifact reduction (iMAR). Materials and methods In this ex vivo study, six pig mandibles were prepared with two titanium-based implants and imaged on a PCD-CT. Scans were reconstructed as UHR images and VMI from 70–190 keV at 10 keV increments with and without iMAR. Two independent readers qualitatively evaluated image quality and artifact severity using five-point visual rating scales (5 = excellent, no or minimal artifacts; and 1 = very poor, non-diagnostic, severe artifacts). Two readers quantified artifact severity, defined as the standard deviations in attenuation in regions of interest adjacent to the implants. Results UHR images without iMAR yielded high image quality (median 5 for both readers) with minor artifact severity (median 4 for both), whereas iMAR reduced image quality (median 3 for both). VMI without iMAR showed decreasing artifacts at higher energy levels. VMI at 120–130 keV achieved optimal image quality (median 5 for both readers at 120 keV, and medians 4 and 5 at 130 keV) with minimal artifacts (median 5 for both), whereas iMAR reduced quality. Quantitative artifact burden decreased with higher energy levels (from 200 HU at 70 keV to 113 HU at 190 keV), and no improvement was observed using iMAR. Conclusions PCD-CT effectively reduces metal-induced artifacts in dental implant imaging, with UHR images and VMI at 120–130 keV providing optimal image quality, while reconstructions with iMAR offered no further benefit. Relevance statement PCD-CT provides excellent dental implant visualization while minimizing the impact of metal artifacts. Key Points In this ex vivo study, ultra-high-resolution images and virtual monoenergetic images at 120–130 keV from PCD-CT effectively reduce metal artifacts from dental implants. Effective artifact reduction offers excellent visualization of the bone-implant interface. Iterative metal artifact reduction (iMAR) did not provide additional benefit for visualization of the bone-implant interface. Graphical Abstract

Introduction This ex vivo study aimed to determine the optimal energy level for virtual monoenergetic imaging (VMI) using photon-counting detector computed tomography (PCD-CT) and to evaluate the effectiveness of iterative metal artifact reduction (iMAR) in assessing simulated endodontic challenges and complications. Methods Sixteen extracted third molars were simulated with one of eight distinct endodontic diagnostic challenges and imaged using PCD-CT at radiation doses equivalent to standard-dose cone-beam CT. VMIs were reconstructed from 70-190 keV at 10 keV increments, both with and without iMAR. Diagnostic accuracy, depiction quality of endodontic challenges, artifact severity, and visualization of key endodontic anatomical structures were independently assessed by 2 observers using a 5-point visual analogue scale (1 = least favourable, 5 = most favourable). Descriptive statistics were calculated, and inter-reader agreement was analysed using Krippendorff’s alpha coefficient. Results VMIs achieved excellent diagnostic accuracy (97%) and high-quality visualization of endodontic challenges (median: 5, IQRs: 4-5 or 4.25-5; α = 0.63-1.00) across the entire reconstructed energy spectrum (70-190 keV), with minimal artifacts, particularly at ≥ 110 keV (α = 1.0). Task-specific analysis demonstrated optimal visualization of caries at 70-80 keV and fractured files at 70-100 keV. For other pathologies, VMI at ≥100 keV effectively reduced artifacts without compromising anatomical detail. IMAR did not improve image quality and consistently reduced diagnostic performance. Conclusions VMI from PCD-CT provides high-quality imaging with minimal artifacts, well-suited for indication-specific endodontic diagnostics. Clinical Relevance PCD-CT supports novel, indication-specific workflows in endodontic imaging, potentially enhancing diagnostic precision and long-term treatment follow-up.

BACKGROUND:Blooming artifacts from calcified plaques can obscure the vessel lumen, leading to overestimation of stenosis severity. Spectral coronary angiography with photon-counting detector CT (PCD-CT) provides virtual monoenergetic images (VMIs) for coronary artery disease assessment. While VMIs at high VMI energy levels reduce calcium blooming, iodine contrast is diminished, limiting diagnostic value. This study evaluated whether contrast media with an atomic number higher than iodine (high-Z) preserve vascular contrast using high VMI energy levels, thereby improving the accuracy of stenosis quantification. METHODS:A phantom with 4 and 6 mm diameter rods to mimic small diameter vessels containing eccentric calcified plaques causing 25%, 50%, and 75% diameter stenoses was scanned with a dual-source PCD-CT system. Five different contrast media, including iodine, tungsten, holmium, hafnium, and bismuth, were tested. VMIs were reconstructed from 40 to 190 keV in 1-keV steps. Vessel attenuation, contrast-to-noise ratio (CNR), and stenoses were measured. Qualitative assessment of image quality was performed. RESULTS:Iodine attenuation was high at lower VMI energy levels and dropped below 250 HU at >100 keV. Tungsten, holmium, hafnium, and bismuth maintained >250 HU attenuation throughout the entire energy range. Vessel CNR of iodine was high at lower and decreased at higher VMI energy levels, similar to the CNR of holmium and bismuth, though to a lesser extent. In distinction, CNRs of tungsten and hafnium were lower at lower VMI energy levels and increased to a relatively constant level at higher keV. Tungsten CNR increased with energy, approaching ~40 at high keV. Across all contrast media and stenosis degrees, stenoses were overestimated on low VMI energy levels (24% to 32.5% at 40 keV), while the degree of overestimation decreased at higher VMI energy levels (0% to 13.5% at 190 keV). At 190 keV, tungsten, hafnium, and bismuth showed ≤2.5% stenosis overestimation, compared with iodine (10% to 13.5%). Image quality varied between contrast media and energy levels: new very high-Z contrast media achieved higher scores, while iodine peaked at lower keV (55 to 70 keV) and, due to loss of contrast at higher energies, received the lowest overall scores. CONCLUSIONS:As compared with iodine, very high-Z contrast media enable superior lumen definition and more accurate stenosis assessment, also at high VMI energy levels, which minimize calcium blooming.

OBJECTIVES:The aim of this study was to evaluate the feasibility and reproducibility of a novel deep learning (DL)-based coronary plaque quantification tool with automatic case preparation in patients undergoing ultra-high resolution (UHR) photon-counting detector CT coronary angiography (CCTA), and to assess the influence of temporal resolution on plaque quantification. MATERIALS AND METHODS:In this retrospective single-center study, 45 patients undergoing clinically indicated UHR CCTA were included. In each scan, 2 image data sets were reconstructed: one in the dual-source mode with 66 ms temporal resolution and one simulating a single-source mode with 125 ms temporal resolution. A novel, DL-based algorithm for fully automated coronary segmentation and intensity-based plaque quantification was applied to both data sets in each patient. Plaque volume quantification was performed at the vessel-level for the entire left anterior descending artery (LAD), left circumflex artery (CX), and right coronary artery (RCA), as well as at the lesion-level for the largest coronary plaque in each vessel. Diameter stenosis grade was quantified for the coronary lesion with the greatest longitudinal extent in each vessel. To assess reproducibility, the algorithm was rerun 3 times in 10 randomly selected patients, and all outputs were visually reviewed and confirmed by an expert reader. Paired Wilcoxon signed-rank tests with Benjamini-Hochberg correction were used for statistical comparisons. RESULTS:One hundred nineteen out of 135 (88.1%) coronary arteries showed atherosclerotic plaques and were included in the analysis. In the reproducibility analysis, repeated runs of the algorithm yielded identical results across all plaque and lumen measurements ( P > 0.999). All outputs were confirmed to be anatomically correct, visually consistent, and did not require manual correction. At the vessel level, total plaque volumes were higher in the 125 ms reconstructions compared with the 66 ms reconstructions in 28 of 45 patients (62%), with both calcified and noncalcified plaque volumes being higher in 32 (71%) and 28 (62%) patients, respectively. Total plaque volumes in the LAD, CX, and RCA were significantly higher in the 125 ms reconstructions (681.3 vs. 647.8  mm 3 , P  < 0.05). At the lesion level, total plaque volumes were higher in the 125 ms reconstructions in 44 of 45 patients (98%; 447.3 vs. 414.9  mm 3 , P  < 0.001), with both calcified and noncalcified plaque volumes being higher in 42 of 45 patients (93%). The median diameter stenosis grades for all vessels were significantly higher in the 125 ms reconstructions (35.4% vs. 28.1%, P  < 0.01). CONCLUSIONS:This study evaluated a novel DL-based tool with automatic case preparation for quantitative coronary plaque in UHR CCTA data sets. The algorithm was technically robust and reproducible, delivering anatomically consistent outputs not requiring manual correction. Reconstructions with lower temporal resolution (125 ms) systematically overestimated plaque burden compared with higher temporal resolution (66 ms), underscoring that protocol standardization is essential for reliable DL-based plaque quantification.

Objectives:Spontaneous coronary artery dissection (SCAD) is a rare cause of acute coronary syndrome and myocardial infarction. Accurate diagnosis is crucial for appropriate management. This study aimed to compare late enhancement (LE) imaging using photon-counting detector (PCD)-CT with cardiac MRI in patients with SCAD in the acute phase and during follow-up and to introduce a novel approach for visualizing myocardial extracellular volume (ECV) distribution in the myocardium.Materials and Methods:This single-center prospective study enrolled patients with SCAD diagnosed with invasive coronary angiography. LE iodine imaging with spectral dual-source PCD-CT and cardiac MRI was performed early after symptom onset and at short-term follow-up. CT included coronary angiography and LE imaging (5 minutes after contrast). LE CT was assessed using the combination of conventional LE images, overlay images, polar maps, and with newly developed atlas maps. Atlas maps represent 2-dimensional maps with prefiltering applied to enable a simpler and more intuitive reading of ECV distribution across the myocardium. Cardiac MRI served as the reference standard for identifying pathologic myocardial segments based on late gadolinium enhancement (LGE) and edema on T2-weighted and T2-mapping images. Agreement between modalities was evaluated using Cohen's kappa.Results:Seventeen patients (median age, 44 years [interquartile range, 36-52]; 11 women) underwent 24 LE CT and cardiac MRI scans. Sixteen patients (median age, 44 years; 10 women) underwent acute phase imaging (median 6 days after symptom onset), and 8 patients (median age, 45 years; 6 women) underwent follow-up imaging (median 120 days after symptom onset). Atlas maps were helpful in detecting segments with pathological ECV and to adjudicate corresponding myocardial segments. Agreement between LE CT with LGE cardiac MRI was strong in the acute phase (kappa = 0.832), improving to almost perfect when comparing LE-CT with both LGE and edema in cardiac MRI (kappa = 0.944). At follow-up imaging, agreement further improved as edema resolved (kappa = 0.956).Conclusions:LE imaging with PCD-CT demonstrated strong agreement with cardiac MRI for detecting myocardial injury in SCAD, which further improved at follow-up when edema resolved. Newly introduced atlas maps proved useful for a simple and intuitive visualization of myocardial injury.

Background: Metal artifacts in computed tomography (CT) can be reduced with high energy virtual monoenergetic images (VMI) and iterative metal artifact reduction (IMAR) algorithms. At high VMI energies, however, iodinated contrast media show decreased attenuation. High atomic number (high-Z) contrast media potentially preserve vessel contrast near metal implants even at high VMI energies. Hence, the purpose of this study was to assess the effect of high-Z contrast media on vessel visualization near metal implants in photon-counting detector (PCD)-CT across VMI energies, with and without IMAR and for different metal types. Methods: A pelvis phantom containing titanium or steel inserts and contrast media inserts including iodine, bismuth, holmium, or tungsten was scanned using photon-counting detector computed tomography (PCD-CT). VMI (40-190 keV, 1 keV steps) were reconstructed with and without IMAR. Three predefined regions of interest (ROI) were placed in the background (background noise, standard deviation of HU), in the contrast media inserts (vessel attenuation, mean HU), and between the metal and contrast inserts (metal artifacts, defined as standard deviation of HU). An artifact-adjusted contrast-to-noise ratio (CNR) was calculated using background noise, vessel attenuation and metal artifacts, and averaged across three VMI energy ranges: 40-90, 90-140, and 140-190 keV. Peak CNR was the maximum value across all VMI energies. Wilcoxon rank sum tests with Benjamini-Hochberg correction were applied. Results: Metal artifacts decreased with increasing VMI energy (P<0.001). Titanium caused fewer artifacts than steel, and IMAR further reduced artifacts from both metal types: at 40-90 keV without IMAR, metal artifacts averaged over all contrast media were 71 Hounsfield units (HU) (titanium) vs. 116 HU (steel), decreasing to 27 and 32 HU with IMAR (P<0.001). At 40-90 keV in titanium with IMAR, holmium showed the highest vessel attenuation and CNR (451 HU/24), followed by iodine (296 HU/15), bismuth (267 HU/14) and tungsten (259 HU/13). At 140-190 keV, tungsten showed the highest vessel attenuation and CNR (269 HU/19), followed by bismuth (250 HU/17), holmium (144 HU/10) and iodine (31 HU/2). Peak CNR [34] was achieved with holmium, titanium, IMAR, and VMI at 40 keV. Conclusions: High-Z contrast media provide superior vessel contrast compared to iodine near metal implants in PCD-CT, both at low VMI energy with holmium and at high VMI energy with tungsten and bismuth, where metal artifacts are additionally reduced. Under metal artifact conditions, vessel contrast can be further improved by applying IMAR.

To assess the diagnostic performance of photon-counting detector computed tomography (PCD-CT) and cone-beam computed tomography (CBCT) at dose-matched radiation levels (high, standard, and low) for detecting and evaluating simulated endodontic conditions, treatments, and associated complications. Sixteen extracted third molars with eight endodontic tasks were imaged using PCD-CT and CBCT. Qualitative (image quality, artifact susceptibility, diagnostic interpretability) and quantitative (endodontic working length) parameters were assessed by two observers using a five-point Likert scale. Descriptive statistics and weighted kappa (κ) were used for data analysis. High- and standard-dose PCD-CT demonstrated superior image quality and anatomical visualization compared to CBCT (median 5, IQR 5–5; κ = 1.0; all p < 0.001). Low-dose PCD-CT remained diagnostically robust, outperforming CBCT, except in root canal visualization, where both performed similarly. Diagnostic accuracy of pathologies and complications was slightly higher with PCD-CT (80–88

OBJECTIVES:To determine the feasibility and accuracy of photon-counting detector (PCD)-CT for iron and fat quantification in the myocardium. METHODS:Cylindrical tubes were filled with porcine myocardium and iron citrate with iron concentrations of 0-20 mg Fe g-1. Dilution series were prepared with myocardium and iron (no-fat probes) and with 5% fat (fat probes). The tubes were positioned in a chest phantom and were scanned with a calcium-scoring protocol on a PCD-CT. A re-parameterized 3-material decomposition was used to separate iron and fat from myocardium. RESULTS:On virtual monoenergetic images, attenuation increased linearly with iron concentrations in both fat and no-fat probes. In no-fat probes, linear regression yielded a slope of 1.2 HU (mg Fe g-1)-1 with an intercept of 35.8 HU (R2 = 0.964). In the fat probes, the slope was similar at 1.1 HU (mg Fe g-1)-1, while the regression line shifted downwards by 6.1 HU with an intercept of 29.6 HU (R2 = 0.985). Iron maps separated fat from iron with calculated median fat fractions of 4.85 in the fat and 0.90 in the no-fat probes. In iron images, attenuation increased linearly with increasing iron concentrations, with similar slopes between fat and no-fat probes and negligible differences in the intercept. CONCLUSIONS:Experimental evidence indicates the feasibility and accuracy of PCD-CT for iron and fat quantification in the myocardium. Iron-specific 3-material decomposition eliminates the confounding effect of fat on myocardial iron quantification. ADVANCES IN KNOWLEDGE:This study highlights the value of dual-energy CT with 3-material decomposition for quantifying iron and fat in the myocardium. Thus, CT could serve as alternative for the current reference standard MRI.

Severe coronary artery calcification leads to blooming artifacts in conventional coronary CT angiography (CCTA), which may reduce diagnostic accuracy. Ultra-high resolution (UHR) photon-counting detector CT (PCD-CT) reduces calcium blooming. This study aimed to evaluate the diagnostic performance of UHR CCTA with PCD-CT for detecting coronary stenoses in patients with a high coronary calcium burden compared to invasive coronary angiography (ICA). In this IRB-approved single-center study, patients with Agatston scores > 600 were included, who underwent ICA and coronary UHR PCD-CT angiography within 2 months. 94

The advent of photon-counting detector CT brought up various new interesting possibilities for coronary imaging including different scan modes and various post-processing options. The two main scan modes include spectral data acquisition with inherent energy-resolved imaging and ultra-high-resolution scanning with unprecedented high spatial resolution, both at the highest available temporal resolution. Post-processing options include the generation of virtual monoenergetic images at different levels and the generation of virtual non-calcium images. Many early studies indicated the potential of each of these options for coronary CT angiography but also show that much more work is needed to clarify the optimal scan mode for each individual patient and clinical setting.

Blooming artifacts from calcified plaques can obscure the vessel lumen, leading to overestimation of stenosis severity. Spectral coronary angiography with photon-counting detector CT (PCD-CT) provides virtual monoenergetic images (VMIs) for coronary artery disease assessment. While VMIs at high VMI energy levels reduce calcium blooming, iodine contrast is diminished, limiting diagnostic value. This study evaluated whether contrast media with an atomic number higher than iodine (high-Z) preserve vascular contrast using high VMI energy levels, thereby improving the accuracy of stenosis quantification. A phantom with 4 and 6 mm diameter rods to mimic small diameter vessels containing eccentric calcified plaques causing 25%, 50%, and 75% diameter stenoses was scanned with a dual-source PCD-CT system. Five different contrast media, including iodine, tungsten, holmium, hafnium, and bismuth, were tested. VMIs were reconstructed from 40 to 190 keV in 1-keV steps. Vessel attenuation, contrast-to-noise ratio (CNR), and stenoses were measured. Qualitative assessment of image quality was performed. Iodine attenuation was high at lower VMI energy levels and dropped below 250 HU at >100 keV. Tungsten, holmium, hafnium, and bismuth maintained >250 HU attenuation throughout the entire energy range. Vessel CNR of iodine was high at lower and decreased at higher VMI energy levels, similar to the CNR of holmium and bismuth, though to a lesser extent. In distinction, CNRs of tungsten and hafnium were lower at lower VMI energy levels and increased to a relatively constant level at higher keV. Tungsten CNR increased with energy, approaching ~40 at high keV. Across all contrast media and stenosis degrees, stenoses were overestimated on low VMI energy levels (24% to 32.5% at 40 keV), while the degree of overestimation decreased at higher VMI energy levels (0% to 13.5% at 190 keV). At 190 keV, tungsten, hafnium, and bismuth showed ≤2.5% stenosis overestimation, compared with iodine (10% to 13.5%). Image quality varied between contrast media and energy levels: new very high-Z contrast media achieved higher scores, while iodine peaked at lower keV (55 to 70 keV) and, due to loss of contrast at higher energies, received the lowest overall scores. As compared with iodine, very high-Z contrast media enable superior lumen definition and more accurate stenosis assessment, also at high VMI energy levels, which minimize calcium blooming.

To evaluate whether task-based automatic keV selection of photon-counting detector (PCD)-CT with optimizing radiation and contrast media (CM) dose yields consistent image quality in CT angiography (CTA). PCD-CTA of the aorta was performed in six healthy minipigs across two scan sessions, with virtual monoenergetic images (VMI) reconstructed. In the first session, three protocols were conducted: the reference protocol A1 simulated standard CTA (210 mg iodine/kg CM, image quality (IQ)-level 117, non-contrast task, VMI: 70 keV); protocol A2 reduced radiation while keeping CM dose constant (210 mgI/kg, IQ-level 117, vascular task, VMI: 55 keV); and protocol A3 reduced CM dose while maintaining radiation (164 mgI/kg, IQ-level 117, non-contrast task, VMI: 55 keV). In the second session, protocols A2 and A3 were repeated as B1 and B2 to assess reproducibility, and protocol B3 further reduced the radiation dose with increased CM dose (252 mgI/kg, IQ-level 81, vascular task, VMI: 55 keV). Aortic CNR was measured; subjective assessments included contrast, noise, IQ, and visibility of intrahepatic arteries using a 4-point discrete visual scale. The median CTDIvol was 3.8 mGy (A1, A3), 2.4 mGy (A2, B1), 3.9 mGy (B2), and 1.6 mGy (B3), respectively; median CM doses were 23 mL (A1, A2, B1), 18 mL (A3, B2), and 28 mL (B3), respectively. CNR was comparable across protocols (p = 0.906–0.947). Subjective metrics indicated diagnostic image quality (scores ≥ 2) for all protocols, with A1 and A3 having higher noise (p = 0.007–0.008) and lower vascular contrast (p = 0.003–0.008). Subjective image quality (p = 0.226–0.342) and visibility of intrahepatic arteries (p = 0.604–0.873) were similar. Task-based automatic keV selection enables optimization of radiation and CM dose in PCD-CTA while maintaining image quality. Protocols can be balanced to either save radiation or CM dose, depending on individual patient needs. Question Balancing radiation and contrast media doses in CT angiography is essential, yet the full potential of photon-counting detector (PCD)CT for dose optimization remains underexplored. Findings Task-based automatic keV selection of PCD-CT enabled a 22

ABSTRACT Objectives The aim of this ex vivo study was to assess the performance of photon‐counting detector computed tomography (PCD‐CT) compared with cone‐beam computed tomography (CBCT) at equivalent radiation doses for detecting and evaluating mandibular and dental anatomical structures in porcine cadavers. Material and Methods This intermodal comparative study evaluated imaging protocols at three radiation dose levels (high: 360 μSv, standard: 145 μSv, low: 20 μSv) in six porcine cadaver heads, analyzing 12 CBCT and 18 PCD‐CT volumes. Two blinded observers assessed image quality, artifact susceptibility, and diagnostic interpretability using a 5‐point Likert scale (5 = highest, 1 = lowest). Statistical analysis included descriptive statistics and interobserver reliability, assessed by weighted kappa (κ) analysis. Results PCD‐CT either matched or outperformed CBCT at standard‐ and low‐dose protocols, demonstrating superior anatomy coverage, density, contrast, and less artifact susceptibility. High‐ and standard‐dose protocols achieved perfect scores 5 (SD = 0). At low‐dose levels, PCD‐CT showed slightly lower scores but still outperformed CBCT. PCD‐CT showed minimal artifacts, with no significant artifacts in high and standard doses. Inter‐ and intra‐reader reliability was higher for PCD‐CT (κ: 0.694–1; p < 0.001) compared to CBCT (0.55–0.916; p < 0.001), with the difference being largest at low doses. Conclusion PCD‐CT outperforms CBCT in diagnostic interpretability and artifact reduction across various radiation dose levels, offering a promising alternative for dentomaxillofacial imaging that aligns with the ALADAIP principle.

Purpose:This ex vivo study was performed to determine the optimal energy level for virtual monoenergetic images (VMIs) generated with photon-counting detector computed tomography (PCD-CT) to minimize metal artifacts from dental implants. Materials and Methods:Twelve implants from various manufacturers were placed in 6 pig mandibles and scanned with PCD-CT. VMIs were reconstructed at energy levels from 70 keV to 150 keV in 20-keV increments. Three readers with varying experience qualitatively assessed the image quality, artifact burden, and diagnostic interpretability of peri-implant soft and hard tissues using a 5-point discrete visual scale. Objective analyses included quantitative line profile analysis of implant-induced artifacts. Descriptive statistics were calculated, and inter-reader agreement was assessed using percentage agreement and the Krippendorff alpha coefficient. Results:Qualitative analysis demonstrated excellent image quality for VMIs at ≥110 keV (median=5), with minimal artifacts observed at 130-150 keV. In contrast, lower-energy VMIs (70-90 keV) showed inferior performance due to artifact-related limitations in diagnostic interpretability. Inter-reader agreement ranged from moderate to perfect, with perfect reliability (α=1) for VMIs ≥110 keV. Quantitative line-profile analysis confirmed reduced artifact burden at higher energy levels, particularly for VMIs ≥110 keV. Conclusion:VMI at energy levels ≥110 keV on PCD-CT reduced dental implant-related metal artifacts and offered excellent image quality, including assessment of both peri-implant soft and hard tissues. These findings suggest that optimized PCD-CT VMI may enhance postoperative follow-up imaging. Future in vivo studies are warranted to validate these findings in clinical practice.