Characterization of middle ear ossicular ligaments using photon counting detector CT.

To evaluate the patient-, vessel- and segment-based diagnostic performance of photon-counting detector CT (PCD-CT) compared to energy-integrating detector CT (EID-CT) for detecting ≥ 50% or ≥ 70% stenosis using invasive coronary angiography (ICA) as a reference standard. Patients with stable chest pain and ≥ 50% stenosis detected on dual source PCD-CT who subsequently underwent ICA were prospectively enroled. Diagnostic accuracy was calculated for PCD-CT vs ICA and additionally for a patient cohort scanned with EID-CT with similar risk profiles and disease prevalence. A Monte Carlo simulation based on diagnostic accuracy parameters was performed to estimate the potential reduction in ICA referrals. A total of 143 patients (66 ± 9 years, 27.3% female) with 572 vessels and 2431 segments were evaluated with PCD-CT and ICA. Regarding EID-CT, 109 patients (65 ± 9 years, 31.0% female), 436 vessels and 1853 segments were assessed, with every patient undergoing ICA. PCD-CT demonstrated significantly higher accuracy than EID-CT in detecting ≥ 50% stenosis: 88.1% vs 77.9% (patient level), 91.6% vs 77.8% (vessel level), and 97.7% vs 92.4% (segment level) (p < 0.01 for all). For detecting ≥ 70% stenosis, PCD-CT also showed higher accuracy than EID-CT: 90.9% vs 70.6% (patient level), 94.6% vs 80.9% (vessel level), and 98.6% vs 94.1% (segment level) (p < 0.01 for all). We demonstrated a potential mean reduction of 14.8% in ICA referrals when utilising PCD-CT compared to EID-CT. PCD-CT provides improved per-patient, per-vessel and per-segment diagnostic performance in detecting obstructive CAD in symptomatic patients when compared to patients scanned on EID-CT. PCD-CT may lead to a significant decrease in ICA utilisation. Question Accurate coronary CT angiography guides treatment, but its diagnostic accuracy is limited by various factors. Findings Photon counting detector (PCD)-CT improved diagnostic performance in detecting ≥ 50% or ≥ 70% stenosis, potentially reducing unnecessary ICA referrals by 14.8%. Clinical relevance PCD-CT improves diagnostic accuracy over EID-CT and may reduce unnecessary ICA.

Photon-counting detectors offer the potential for improved image quality for brain CT but have not yet been evaluated in vivo. The purpose of this study was to compare photon-counting detector CT with conventional energy-integrating detector CT for human brains. Radiation dose-matched energy-integrating detector and photon-counting detector head CT scans were acquired with standardized protocols (tube voltage/current, 120 kV(peak)/370 mAs) in both an anthropomorphic head phantom and 21 human asymptomatic volunteers (mean age, 58.9 ± 8.5 years). Photon-counting detector thresholds were 22 and 52 keV (low-energy bin, 22-52 keV; high-energy bin, 52-120 keV). Image noise, gray matter, and white matter signal-to-noise ratios and GM-WM contrast and contrast-to-noise ratios were measured. Image quality was scored by 2 neuroradiologists blinded to the CT detector type. Reproducibility was assessed with the intraclass correlation coefficient. Energy-integrating detector and photon-counting detector CT images were compared using a paired t test and the Wilcoxon signed rank test. Photon-counting detector CT images received higher reader scores for GM-WM differentiation with lower image noise (all P < .001). Intrareader and interreader reproducibility was excellent (intraclass correlation coefficient, ≥0.86 and 0.79, respectively). Quantitative analysis showed 12.8%-20.6% less image noise for photon-counting detector CT. The SNR of photon-counting detector CT was 19.0%-20.0% higher than of energy-integrating detector CT for GM and WM. The contrast-to-noise ratio of photon-counting detector CT was 15.7% higher for GM-WM contrast and 33.3% higher for GM-WM contrast-to-noise ratio. Photon-counting detector brain CT scans demonstrated greater gray-white matter contrast compared with conventional CT. This was due to both higher soft-tissue contrast and lower image noise for photon-counting CT.

The first-generation photon-counting detector CT was recently introduced into clinical practice and represents a promising innovation in high-resolution CT imaging. The purpose of this study was to assess the image quality of ultra-high-resolution photon-counting detector CT compared with energy-integrating detector CT and to explore different reconstruction kernel sharpness levels for the evaluation of intracranial aneurysms. Ten patients with intracranial saccular aneurysms who had previously undergone conventional energy-integrating detector CT were prospectively enrolled. CT angiograms were acquired on a clinical dual-source photon-counting detector CT in ultra-high-resolution mode and reconstructed with 4 vascular kernels (Bv36, Bv40, Bv44, Bv48). Quantitative and qualitative image-quality parameters of the intracranial arteries were evaluated. For the quantitative analysis (image noise, SNR, contrast-to-noise ratio), ROIs were manually placed at standard anatomic intracranial and extracranial locations by 1 author. In addition, vessel border sharpness was evaluated quantitatively. For the qualitative analysis, 3 blinded neuroradiologists rated photon-counting detector CT and energy-integrating detector CT image quality for the evaluation of the intracranial vessels (ie, the aneurysms and 9 standard vascular branching locations) on a 5-point Likert-type scale. Additionally, readers independently selected their preferred kernel among the 4 kernels evaluated on photon-counting detector CT. In terms of quantitative image quality, Bv48, the sharpest kernel, yielded increased image noise and decreased SNR and contrast-to-noise ratio parameters compared with Bv36, the smoothest kernel. Compared with energy-integrating detector CT, the Bv48 kernel offered better quantitative image quality for the evaluation of small intracranial vessels (P < .001). Image-quality ratings of the Bv48 were superior to those of the energy-integrating detector CT and not significantly different from ratings of the B44 reconstruction kernel. When comparing side by side all 4 photon-counting detector reconstruction kernels, readers selected the B48 kernel as the best to visualize the aneurysms in 80% of cases. Ultra-high-resolution photon-counting detector CT provides improved image quality for neurovascular imaging. Although the less sharp kernels provided superior SNR and contrast-to-noise ratio, the sharpest kernels delivered the best subjective image quality on photon-counting detector CT for the evaluation of intracranial aneurysms.

Hardening the x-ray beam, tin prefiltration is established for imaging of high-contrast subjects in energy-integrating detector computed tomography (EID-CT). With this work, we aimed to investigate the dose-saving potential of spectral shaping via tin prefiltration in photon-counting detector CT (PCD-CT) of the temporal bone. Deploying dose-matched scan protocols with and without tin prefiltration on a PCD-CT and EID-CT system (low-/intermediate-/full-dose: 4.8/7.6-7.7/27.0-27.1 mGy), 12 ultra-high-resolution examinations were performed on each of 5 cadaveric heads. While 120 kVp was applied for standard imaging, the protocols with spectral shaping used the highest potential available with tin prefiltration (EID-CT: Sn 150 kVp, PCD-CT: Sn 140 kVp). Contrast-to-noise ratios and dose-saving potential by spectral shaping were computed for each scanner. Three radiologists independently assessed the image quality of each examination with the intraclass correlation coefficient being computed to measure interrater agreement. Regardless of tin prefiltration, PCD-CT with low (171.2 ± 10.3 HU) and intermediate radiation dose (134.7 ± 4.5 HU) provided less image noise than full-dose EID-CT (177.0 ± 14.2 HU; P < 0.001). Targeting matched image noise to 120 kVp EID-CT, mean dose reduction of 79.3% ± 3.9% could be realized in 120 kVp PCD-CT. Subjective image quality of PCD-CT was better than of EID-CT on each dose level ( P < 0.050). While no distinction was found between dose-matched PCD-CT with and without tin prefiltration ( P ≥ 0.928), Sn 150 kVp EID-CT provided better image quality than 120 kVp EID-CT at high and intermediate dose levels ( P > 0.050). The majority of low-dose EID-CT examinations were considered not diagnostic, whereas PCD-CT scans of the same dose level received satisfactory or better ratings. Interrater reliability was excellent (intraclass correlation coefficient 0.903). PCD-CT provides superior image quality and significant dose savings compared with EID-CT for ultra-high-resolution examinations of the temporal bone. Aiming for matched image noise, high-voltage scan protocols with tin prefiltration facilitate additional dose saving in EID-CT, whereas superior inherent denoising decreases the dose reduction potential of spectral shaping in PCD-CT.

Previous studies have shown improved image quality in pediatric cardiac imaging using photon-counting detector CT (PCDCT). However, these studies did not evaluate image quality and radiation dose when utilizing the full spectral capabilities of PCDCT scanners. The full spectral capability of PCDCT scanners allows the generation of the entire array of mono-energetic reconstructions, virtual non-contrast (VNC) images, and iodine maps, which have potential advantages in evaluating complex congenital heart disease. For example, following complex congenital cardiac repairs, when distinguishing intraluminal or soft tissue calcifications from contrast, or when evaluating intrastent thrombus. To compare image quality and radiation dose between high-pitch cardiac CT using full spectral PCDCT and dual-source energy-integrating detector CT (EIDCT). This retrospective, IRB-approved study analyzed high-pitch cardiac CTs from January 2021 to October 2023 in pediatric patients (< 18years). Patients were scanned using either PCDCT with full spectral technique ("QuantumPlus") or EIDCT. Radiation doses were measured by CT dose index (CTDI) and dose-length product (DLP). Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were also calculated, and image quality was assessed using a 5-point Likert scale. Statistical analysis included unpaired T-test, Shapiro-Wilk test, Mann-Whitney test, and kappa coefficients for interrater agreement. Two hundred patients were evaluated, with 100 scanned on PCDCT and 100 on EIDCT. In the PCDCT scanner, 47/100 (47%) were male and 53/100 were female (53%) (P = 0.01). In the EIDCT scanner, 65/100 were male (65%) and 35/100 (35%) were female (P = 0.01). In the PCDCT scanner, 68/100 (68%) (P = 0.05) were ≤ 12months, and 32/100 (32%) (P = 0.05) were > 12months. In the EIDCT, 80/100 (80%) (P = 0.05) were ≤ 12months, and 20/100 (20%) (P = 0.05) were > 12months.In patients ≤ 12months, the CNR were 31.61 in the PCDCT group and 32.14 in the EIDCT group (P = 0.39). For those > 12months, CNR were 30.07 for PCDCT and 25.27 for EIDCT (P = 0.17).In patients ≤ 12months, SNR was significantly lower (P < 0.0001) in PCDCT, compared to EIDCT for the teres minor muscles, while in patients > 12months, SNR was not significantly lower (P = 0.89); SNR was similar between scanners. Radiation doses were significantly higher for PCDCT across both age groups (P < 0.0001). High-pitch cardiac CT with PCDCT using spectral processing resulted in higher radiation doses and lower SNR in infants compared to EIDCT.

BACKGROUND. Photon-counting detector (PCD) CT could be useful to help address the typically high radiation doses of conventional energy-integrating detector (EID) CT of the lumbar spine. OBJECTIVE. The purpose of our study was to compare PCD CT and EID CT of the lumbar spine, both performed using tin filtration, in terms of radiation dose and image quality. METHODS. This study included a prospective sample of 39 patients (22 men, 17 women; mean age, 27.2 years) who underwent investigational PCD CT of the lumbar spine as part of a separate study and a retrospective sample of 39 patients (22 men, 17 women; mean age, 34.9 years) who underwent clinically indicated EID CT of the lumbar spine. In both groups, all examinations were performed using unenhanced technique with tin prefiltration between June 2022 and January 2023. Patients were matched between groups using age, sex, and BMI. A custom gaussian curve-fitting algorithm was used to automatically calculate image noise, SNR, and CNR for each examination, on the basis of all voxels within the image set. Three radiologists independently reviewed examinations to perform a subjective visual assessment of visualization of trabecular architecture, cortical bone, neuroforaminal content, paraspinal muscles, and intervertebral disk, as well as overall image quality, using a 4-point Likert scale (1 = poor, 4 = excellent). PCD CT and EID CT examinations were compared. RESULTS. Mean CTDIvol was 4.4 ± 1.0 (SD) mGy for PCD CT versus 11.1 ± 1.9 mGy for EID CT (p < .001). Mean size-specific dose estimate (SSDE) was 6.2 ± 1.0 (SD) mGy for PCD CT versus 14.2 ± 1.8 mGy for EID CT (p < .001). PCD CT and EID CT examinations were not significantly different in terms of image noise or SNR (both p > .05). PCD CT, in comparison with EID CT, showed significantly higher CNR (mean ± SD, 33.6 ± 3.3 vs 29.3 ± 4.1; p < .001). For all three readers, the median score for overall image quality was 4 (range, 3-4) for both PCD CT and EID CT. PCD CT and EID CT examinations showed no significant difference in terms of any qualitative measure for any reader (all p > .05). CONCLUSION. PCD CT, in comparison with EID CT, yielded significantly lower radiation dose with preserved image quality. CLINICAL IMPACT. The findings support expanded use of PCD CT for lumbar spine evaluation.

Photon counting detector (PCD) CT benefits from reduced noise compared with conventional energy-integrating detector (EID) CT, which should translate to improved image quality and reduced radiation exposure for pediatric patients undergoing chest CT with IV contrast. To determine the differences in radiation exposure and image quality of PCD CT and EID CT in pediatric chest CT with intravenous (IV) contrast. In this institutional review board-approved retrospective observational study, 20 scan pairs (20 PCD CT; 20 EID CT) for children who underwent chest CT with IV contrast on both a PCD CT (Siemens NAEOTOM Alpha) and an EID CT (Siemens SOMATOM Definition Edge or Force) within 12months were reviewed independently by three pediatric radiologists for three subjective quality features on 5-point Likert scales: overall quality, small structure delineation, and motion artifact. Objective measures of image quality (image noise, signal-to-noise ratio, and contrast-to-noise ratio) were assessed by a single radiologist in several locations in the chest through region of interest measurement of Hounsfield units (HU) and standard deviation. Patient-related and radiation exposure parameters were collected for each scan and summarized with median and interquartile range (IQR). The Wilcoxon rank-sum test was utilized to compare groups. A P < 0.05 indicated statistical significance. Inter-observer agreement of subjective image quality metrics was analyzed using weighted kappa. Age (14.2years vs 13.8years, P= 0.15), height (P= 0.13), weight (P= 0.21), and BMI (P = 0.24) did not significantly differ between groups. There were 10 male and 3 female patients. Compared to EID CT, PCD CT showed lower radiation exposure parameters including volumetric CT dose index, 1.7mGy (IQR 1.1-2.4mGy) vs 3.8mGy (IQR 2.0-4.7mGy) (P< 0.01), and size-specific dose estimate, 2.6mGy (IQR 1.8-3.1mGy) vs 5.0mGy (IQR 3.3-6.2mGy) (P< 0.01). Objective image quality of lung parenchyma was improved on the PCD CT scanner, including image noise 119.5 HU (IQR 95.4-135.7 HU) vs 143.1 HU (IQR 125.4-169.8 HU) (P < 0.01), signal-to-noise ratio (SNR) -6.1 (IQR -8.4 to -4.8) vs -4.9 (IQR -5.6 to -3.8) (P= 0.01), and contrast-to-noise ratio -63.9 (-84.1 to -57.5) vs -60.5 (-76.3 to -52.5) (P = 0.01). Motion artifact was improved on the PCD CT scanner (P< 0.01). No significant differences in overall image quality or small structure delineation were identified (P= 0.06 and P= 0.31). PCD CT pediatric chest CT had significantly reduced radiation exposure, improved image quality, and reduced motion artifact compared with EID CT.

BACKGROUND. Photon-counting detector (PCD) CT may allow lower radiation doses than used for conventional energy-integrating detector (EID) CT, with preserved image quality. OBJECTIVE. The purpose of this study was to compare PCD CT and EID CT, reconstructed with and without a denoising tool, in terms of image quality of the osseous pelvis in a phantom, with attention to low radiation doses. METHODS. A pelvic phantom comprising human bones in acrylic material mimicking soft tissue underwent PCD CT and EID CT at various tube potentials and radiation doses ranging from 0.05 to 5.00 mGy. Additional denoised reconstructions were generated using a commercial tool. Noise was measured in the acrylic material. Two readers performed independent qualitative assessments that entailed determining the denoised EID CT reconstruction with the lowest acceptable dose and then comparing this reference reconstruction with PCD CT reconstructions without and with denoising, using subjective Likert scales. RESULTS. Noise was lower for PCD CT than for EID CT. For instance, at 0.05 mGy and 100 kV with tin filter, noise was 38.4 HU for PCD CT versus 48.8 HU for EID CT. Denoising further reduced noise; for example, for PCD CT at 100 kV with tin filter at 0.25 mGy, noise was 19.9 HU without denoising versus 9.7 HU with denoising. For both readers, lowest acceptable dose for EID CT was 0.10 mGy (total score, 11 of 15 for both readers). Both readers somewhat agreed that PCD CT without denoising at 0.10 mGy (reflecting reference reconstruction dose) was relatively better than the reference reconstruction in terms of osseous structures, artifacts, and image quality. Both readers also somewhat agreed that denoised PCD CT reconstructions at 0.10 mGy and 0.05 mGy (reflecting matched and lower doses, respectively, with respect to reference reconstruction dose) were relatively better than the reference reconstruction for the image quality measures. CONCLUSION. PCD CT showed better-quality images than EID CT when performed at the lowest acceptable radiation dose for EID CT. PCD CT with denoising yielded better-quality images at a dose lower than lowest acceptable dose for EID CT. CLINICAL IMPACT. PCD CT with denoising could facilitate lower radiation doses for pelvic imaging.

To investigate the image quality and the performance of photon-counting detector (PCD) CT compared to conventional energy-integrating detector (EID) CT in identifying subsolid nodule (SSN) characteristics. Participants with SSNs who underwent same-day EID CT and PCD CT between October 2023 and April 2024 were prospectively included. The 1.0 mm EID CT images and, subsequently, 1.0 mm, 0.4 mm, and 0.2 mm PCD CT images were reviewed to assess image noise and subjective image quality on a 5-point Likert scale. SSN characteristics, including lobulation, spiculation, pleural retraction, air cavities, intra-nodular vessel signs, internal vascular changes, and heterogeneous solid components, were evaluated. Additionally, a step-by-step observation and comparison method was used to determine the presence of any additional characteristics. Forty-eight participants (mean age: 56 ± 11 years; 16 males) with 89 SSNs were included. PCD CT significantly reduced radiation dose when using matched scans (1.79 ± 0.39 vs 2.17 ± 0.57 mSv, p < 0.001). Compared to 1.0 mm EID CT, 1.0 mm PCD CT images exhibited significantly lower objective image noise and higher subjective image quality (all p < 0.001). Compared to EID CT, PCD CT demonstrated enhanced visualization of subtle characteristics, except for lobulation, with a 0.4 mm section thickness offering a favorable balance between ultra-high resolution and perceived image quality for radiologists. PCD CT facilitated radiation dose reduction and outperformed conventional EID CT in terms of image quality and visualization of SSN characteristics. Question PCD CT, featuring ultra-high-resolution mode acquisition and a thinner reconstruction, has not been fully explored for characterizing SSNs. Findings Compared to EID CT, PCD CT was associated with lower objective image noise, higher subjective image quality, and superior SSN characterization. Clinical relevance PCD CT effectively reduced the radiation dose delivered to the patients and enabled more precise SSN characterization.

This work examined the iodine quantification accuracy on a prototype deep silicon (dSi) photon-counting detector (PCD) computed tomography (CT) system compared to a rapid kV switching energy-integrating detector (EID) dual-energy (DE) CT system. Iodine-containing rods (0-20mg I/mL) in a phantom (Gammex MECT) were scanned with the prototype dSi PCD and DECT systems. Iodine (water) material density images were made with prototype and commercially available material decomposition algorithms, respectively. Circular regions of interest were placed over the center of the iodine rods to measure iodine accuracy in each slice, and slices were averaged. A correction based on the known issue of background material difference from true water was determined from the 0mg I/mL (solid water) rod and the relative rod densities and was applied to the iodine quantification. Iodine percent error was defined as the difference between corrected iodine quantification and known iodine quantification, divided by the known iodine, multiplied by 100. The corrected iodine quantification was within 0.15mg I/mL for 0-20mg I/mL iodine rods on the prototype PCD CT and 0.2mg I/mL for the EID DECT. This translates to iodine percent errors of 0.4-4.3% on the PCD CT and 1.1-76% on the EID DECT for 0.2-20mg I/mL rods. Iodine quantification on the prototype dSi PCD CT was within 4.3% for all tested iodine-containing rods, which is similar or better than the performance of the EID DECT system and previous work on the prototype dSi system.

BackgroundWe compared photon-counting detector computed tomography (PCD-CT) polyenergetic images, PCD-CT virtual monoenergetic images (VMI), and energy-integrating detector computed tomography (EID-CT) polyenergetic images regarding bone visualization and metal artifacts in patients with titanium wrist prostheses.MethodsAfter ethical approval, 15 patients were examined with PCD-CT and EID-CT. Polyenergetic images were reconstructed, as well as 130-keV VMI for PCD-CT. Five radiologists evaluated bone visualization, interpretability at metal-bone interface and metal artifacts using a 7-point ordinal scale. Streak artifacts and artifacts at the bone-metal interface were quantitatively assessed. Differences between image setups were analyzed using Friedman test and one-way ANOVA with post hoc tests.ResultsBone visualization was superior in PCD-CT polyenergetic images (median rating 6, range 3–7) compared with VMI (5, 3–7; p < 0.001) and EID-CT (5, 3–7; p = 0.018). Streak artifacts were more pronounced with PCD-CT polyenergetic images (4, 3–6) compared with EID-CT (5, 4–6; p = 0.003) and PCD-CT VMI (5, 3–7; p = 0.002), with quantitative results showing least streak artifacts in PCD-CT VMI, followed by EID-CT and PCD-CT polyenergetic images (50 ± 7%, 70 ± 6%, and 79 ± 5%, respectively; p < 0.001). Interpretability at bone-metal interface was better with PCD-CT polyenergetic images (5, 2–7; p = 0.045) and EID-CT (5, 3–6; p = 0.018) compared with PCD-CT VMI (4, 2–6), without quantitative differences.ConclusionStreak artifacts from titanium wrist prostheses were reduced using 130-keV PCD-CT VMI, while bone visualization was highest using PCD-CT polyenergetic images.Relevance statementIn patients with wrist implants, photon-counting detector CT allows for effective metal artifact reduction using virtual monoenergetic images and improved bone visualization using polyenergetic images. As polyenergetic images and VMI have different advantages, access to both image setups may benefit diagnostic evaluation.Key PointsVirtual monoenergetic images (VMI) presented a substantial reduction of metal streak artifacts.Polyenergetic images exhibited better image quality for bone imaging compared with VMI.A combination of image reconstructions should be preferred depending on the diagnostic task.Graphical

Intra-individual comparison of image quality of the coronary arteries between photon-counting detector and energy-integrating detector CT systems

Background Photon-counting detector (PCD) CT and deep learning noise reduction may improve spatial resolution at lower radiation doses compared with energy-integrating detector (EID) CT. Purpose To demonstrate the diagnostic impact of improved spatial resolution in whole-body low-dose CT scans for viewing multiple myeloma by using PCD CT with deep learning denoising compared with conventional EID CT. Materials and Methods Between April and July 2021, adult participants who underwent a whole-body EID CT scan were prospectively enrolled and scanned with a PCD CT system in ultra-high-resolution mode at matched radiation dose (8 mSv for an average adult) at an academic medical center. EID CT and PCD CT images were reconstructed with Br44 and Br64 kernels at 2-mm section thickness. PCD CT images were also reconstructed with Br44 and Br76 kernels at 0.6-mm section thickness. The thinner PCD CT images were denoised by using a convolutional neural network. Image quality was objectively quantified in two phantoms and a randomly selected subset of participants (10 participants; median age, 63.5 years; five men). Two radiologists scored PCD CT images relative to EID CT by using a five-point Likert scale to detect findings reflecting multiple myeloma. The scoring for the matched reconstruction series was blinded to scanner type. Reader-averaged scores were tested with the null hypothesis of equivalent visualization between EID and PCD. Results Twenty-seven participants (median age, 68 years; IQR, 61-72 years; 16 men) were included. The blinded assessment of 2-mm images demonstrated improvement in viewing lytic lesions, intramedullary lesions, fatty metamorphosis, and pathologic fractures for PCD CT versus EID CT (P < .05 for all comparisons). The 0.6-mm PCD CT images with convolutional neural network denoising also demonstrated improvement in viewing all four pathologic abnormalities and detected one or more lytic lesions in 21 of 27 participants compared with the 2-mm EID CT images (P < .001). Conclusion Ultra-high-resolution photon-counting detector CT improved the visibility of multiple myeloma lesions relative to energy-integrating detector CT. © RSNA, 2022 Online supplemental material is available for this article.

Flow diverters are a crucial element in the treatment of intracranial aneurysms. However, the optimal non-invasive follow-up imaging modality, particularly for the detection of in-stent stenosis, remains uncertain. This study aims to compare the performance of photon-counting detector CT (PCD-CT) in ultra-high-resolution (UHR) mode with flat-panel CT (FP-CT) for the evaluation of intracranial flow diverters. A phantom model for intracranial vessels was used to evaluate 15 flow diverters of various sizes and designs. Imaging was performed using both PCD-CT and FP-CT. Qualitative assessment of the stent lumen was conducted by three experienced neuroradiologists using a 5-point Likert scale. Quantitative analysis included measurements of lumen area, contrast to noise ratio and signal to noise ratio. FP-CT provided a significantly larger assessable stent lumen than PCD-CT at all dose levels (p < 0.05), with no significant differences between PCD-CT dose levels (p = 0.999). Increasing PCD-CT dose did not improve lumen visualization. SNR and CNR increased with PCD-CT dose (p < 0.001), peaking at CTDI 20, but showed diminishing returns beyond CTDI 10. Flow diverter diameter correlated positively with SNR and CNR (p < 0.05). Subjective image quality improved with PCD-CT dose (p < 0.001) but showed no significant difference beyond 10 mGy (p > 0.05). FRED devices had the lowest ratings, independent of imaging modality (p = 0.80). Our study demonstrated that while FP-CT provided superior visualization of the flow diverter lumen in a head phantom vessel model, subjective assessability ratings were comparable between FP-CT and PCD-CT when evaluated by experienced readers. PCD-CT at a CTDIvol of 10 mGy offered the best balance between image quality and radiation dose, making it a viable alternative for post-interventional assessment of flow diverters.

Photon-counting detector (PCD) CT allows for reduced intravenous iodinated contrast dosing with preserved or improved image quality across anatomical regions as compared to conventional energy-integrating detector (EID) CT in adults. However, there is limited evidence to support this in pediatric CT, particularly for pediatric chest CT. To compare image quality of photon-counting detector (PCD) chest CT with energy-integrating detector (EID) CT at varying iodinated contrast doses in pediatric patients. This retrospective observational study included 60 contrast-enhanced chest CT studies in pediatric patients. The cohort included three groups: 20 PCD CT scans with a 1.5mL/kg weight-based iodinated contrast dose, 20 EID CT scans with a 1.5mL/kg dose, and 20 EID CT scans with a 2.0mL/kg dose. Image noise, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) were assessed through region-of-interest measurement of Hounsfield units (HU) and standard deviation (SD). Assessed locations were the lung parenchyma, thoracic aorta, main pulmonary artery, left ventricle cavity, subcutaneous tissue, and pectoralis muscle. Blinded review by three pediatric radiologists assessed overall contrast enhancement, soft tissue delineation, and streak artifact from dense contrast using 5-point Likert scales (1 - excellent to 5 - non-diagnostic). Group comparisons were analyzed using Wilcoxon signed-rank, Chi-square, and Kruskal-Wallis tests. Twenty patients were included for each group (60 patients total). Compared to equivalent-contrast dose EID CT at 1.5mL/kg, PCD CT showed higher left ventricle cavity SNR (21.6 [IQR 16.3-25.1] vs 16.2 [IQR 12.3-19.3], P = 0.05) and CNR (16.0 [IQR 11.3-19.5] vs 10.3 [8.8-13.7] P = 0.05), and lower image noise in pectoralis muscle (P = 0.04) and subcutaneous fat (P < 0.01). Furthermore, objective image quality on PCD CT demonstrated improvements in lung parenchyma noise, SNR, and CNR, as well as subcutaneous fat SNR and CNR (all P < 0.01) compared with both equivalent (1.5mL/kg) and standard (2.0mL/kg) contrast dosing in EID CT. No significant differences between PCD CT and EID CT were observed with other objective measures of image quality. Subjective assessments favored PCD CT for overall contrast enhancement to EID CT at equivalent (1.5mL/kg) contrast dosing (median 1, IQR 1-1 vs median 2, IQR 1-5, P = 0.02) and soft tissue delineation compared with EID CT with higher (2.0mL/kg) contrast dosing (median 1, IQR 1-2 vs median 2, IQR 1-2, P = 0.05). Pediatric chest CT using photon-counting detector technology enables iodinated contrast dose reduction while preserving image quality compared with conventional EID CT at standard contrast doses.