Synthetic hematocrit from virtual non-contrast images for myocardial extracellular volume evaluation with photon-counting detector CT.

OBJECTIVES: To assess the accuracy of a synthetic hematocrit derived from virtual non-contrast (VNC) and virtual non-iodine images (VNI) for myocardial extracellular volume (ECV) computation with photon-counting detector computed tomography (PCD-CT). MATERIALS AND METHODS: Consecutive patients undergoing PCD-CT including a coronary CT angiography (CCTA) and a late enhancement (LE) scan and having a blood hematocrit were retrospectively included. In the first 75 patients (derivation cohort), CCTA and LE scans were reconstructed as VNI at 60, 70, and 80 keV and as VNC with quantum iterative reconstruction (QIR) strengths 2, 3, and 4. Blood pool attenuation (BPmean) was correlated to blood hematocrit. In the next 50 patients (validation cohort), synthetic hematocrit was calculated using BPmean. Myocardial ECV was computed using the synthetic hematocrit and compared with the ECV using the blood hematocrit as a reference. RESULTS: In the derivation cohort (49 men, mean age 79 ± 8 years), a correlation between BPmean and blood hematocrit ranged from poor for VNI of CCTA at 80 keV, QIR2 (R2 = 0.12) to moderate for VNI of LE at 60 keV, QIR4; 70 keV, QIR3 and 4; and VNC of LE, QIR3 and 4 (all, R2 = 0.58). In the validation cohort (29 men, age 75 ± 14 years), synthetic hematocrit was calculated from VNC of the LE scan, QIR3. Median ECV was 26.9% (interquartile range (IQR), 25.5%, 28.8%) using the blood hematocrit and 26.8% (IQR, 25.4%, 29.7%) using synthetic hematocrit (VNC, QIR3; mean difference, -0.2%; limits of agreement, -2.4%, 2.0%; p = 0.33). CONCLUSION: Synthetic hematocrit calculated from VNC images enables an accurate computation of myocardial ECV with PCD-CT. CLINICAL RELEVANCE STATEMENT: Virtual non-contrast images from cardiac late enhancement scans with photon-counting detector CT allow the calculation of a synthetic hematocrit, which enables accurate computation of myocardial extracellular volume. KEY POINTS: Blood hematocrit is mandatory for conventional myocardial extracellular volume computation. Synthetic hematocrit can be calculated from virtual non-iodine and non-contrast photon-counting detector CT images. Synthetic hematocrit from virtual non-contrast images enables computation of the myocardial extracellular volume.

Effect of Vessel Attenuation, VMI Level, and Reconstruction Kernel on Pericoronary Adipose Tissue Attenuation for EID CT and PCD CT: An Ex Vivo Porcine Heart Study.

Background: Pericoronary adipose tissue (PCAT) attenuation and fat attenuation index (FAI) may serve as markers of inflammation and risk of adverse cardiac events. However, standardization of relevant CT acquisition and reconstruction parameters is lacking. Objective: To investigate the influence of vessel attenuation, virtual monoenergetic image (VMI) level, and reconstruction kernel on PCAT attenuation and FAI using energy-integrating detector (EID) and photon-counting detector (PCD) CT systems in an ex-vivo porcine heart model. Methods: A porcine heart's right coronary artery (RCA) was injected with saline or varying contrast media dilutions to achieve vessel attenuations ranging from 0 to 1000 HU. After each injection, the heart was scanned with EID CT at 120 kVp and PCD CT at 140 kVp, at constant CTDIvol (10 mGy). For EID CT, polychromatic images were reconstructed with Qr40 kernel. For PCD CT, VMI (40-80 keV at 10-keV increments) were reconstructed with Qr40, Bv40, and Bv56 kernels. ROIs were placed to measure RCA and PCAT attenuation. FAI was determined using software; histogram analysis was performed of voxel attenuations in the volumes of interest for FAI calculation. Results: Correlations were observed between attenuation in the RCA and adjacent PCAT (r=0.3-1.0), and between vessel attenuation and FAI (r=-0.9-1.0). For PCAT attenuation and FAI, these associations became progressively weaker for progressively sharper kernels. For increasing vessel attenuation for EID CT and for increasing VMI level for PCD CT, FAI histograms showed right shifts of the peak attenuation; the percentage of histogram voxels meeting the threshold range for inclusion in FAI calculation for EID CT was 8-29% and for PCD CT at VMI levels of 70-80 keV was 5-42%. For PCD CT, sharper kernels were associated with left shifts in peak attenuations and greater percentages of voxels within the threshold range for inclusion in FAI calculations. Conclusion: PCAT attenuation and FAI are influenced by vessel lumen attenuation, VMI level, and reconstruction kernel. A minority of pericoronary voxels contribute to FAI measurements for polychromatic EID CT and for PCD CT at high VMI levels. Clinical Impact: These findings may help standardize acquisition and reconstruction parameters for PCAT attenuation and FAI measurements.

Pulmonary nodule visualization and evaluation of AI-based detection at various ultra-low-dose levels using photon-counting detector CT.

BACKGROUND: Radiation dose should be as low as reasonably achievable. With the invention of photon-counting detector computed tomography (PCD-CT), the radiation dose may be considerably reduced. PURPOSE: To evaluate the potential of PCD-CT for dose reduction in pulmonary nodule visualization for human readers as well as for computer-aided detection (CAD) studies. MATERIAL AND METHODS: A chest phantom containing pulmonary nodules of different sizes/densities (range 3-12 mm and -800-100 HU) was scanned on a PCD-CT with standard low-dose protocol as well as with half, quarter, and 1/40 dose (CTDIvol 0.4-0.03 mGy). Dose-matched scans were performed on a third-generation energy-integrating detector CT (EID-CT). Evaluation of nodule visualization and detectability was performed by two blinded radiologists. Subjective image quality was rated on a 5-point Likert scale. Artificial intelligence (AI)-based nodule detection was performed using commercially available software. RESULTS: Highest image noise was found at the lowest dose setting of 1/40 radiation dose (eff. dose = 0.01mSv) with 166.1 ± 18.5 HU for PCD-CT and 351.8 ± 53.0 HU for EID-CT. Overall sensitivity was 100% versus 93% at standard low-dose protocol (eff. dose = 0.2 mSv) for PCD-CT and EID-CT, respectively. At the half radiation dose, sensitivity remained 100% for human reader and CAD studies in PCD-CT. At the quarter radiation dose, PCD-CT achieved the same results as EID-CT at the standard radiation dose setting (93%, P = 1.00) in human reading studies. The AI-CAD system delivered a sensitivity of 93% at the lowest radiation dose level in PCD-CT. CONCLUSION: At half dose, PCD CT showed pulmonary nodules similar to full-dose PCD, and at quarter dose, PCD CT performed comparably to standard low-dose EID CT. The CAD algorithm is effective even at ultra-low doses.

Atherosclerosis of the iliac arteries for the prediction of erectile dysfunction and epistaxis in men undergoing abdominal CT scan.

BACKGROUND: To investigate the association between erectile dysfunction (ED) as well as epistaxis (ES) in relation to the extent of iliac atherosclerosis. METHODS: In this retrospective cross-sectional study, all consecutive male patients treated at our institution from 01/2016 to 12/2020 undergoing abdominal CT scan were evaluated. Patients (n = 1272) were invited by mail to participate in the study in returning two questionnaires for the evaluation of ED (IIEF-5) and ES. Patients who returned filled-in questionnaires within a 3-month deadline were included in the study. The extent of atherosclerosis in the common iliac artery (CIA) and the internal iliac artery (IIA) was assessed by calcium scoring on unenhanced CT. Stratification of results was performed according to reported IIEF-5 scores and consequential ED groups. RESULTS: In total, 437 patients (34.4% of contacted) met the inclusion criteria. Forty-two patients did not fulfill predefined age requirements (< 75 years) and 120 patients had to be excluded as calcium scoring on nonenhanced CT was not feasible. Finally, 275 patients were included in the analysis and stratified into groups of "no-mild" (n = 146) and "moderate-severe" (n = 129) ED. The calcium score (r=-0.28, p < 0.001) and the number of atherosclerotic lesions (r=-0.32, p < 0.001) in the CIA + IIA showed a significant negative correlation to the IIEF-5 score, respectively. Patients differed significantly in CIA + IIA calcium score (difference: 167.4, p < 0.001) and number of atherosclerotic lesions (difference: 5.00, p < 0.001) when belonging to the "no-mild" vs. "moderate-severe" ED group, respectively. A multivariable regression model, after adjusting for relevant baseline characteristics, showed that the number of atherosclerotic CIA + IIA lesions was an independent predictor of ED (OR = 1.05, p = 0.036), whereas CIA + IIA calcium score was not (OR = 1.00031, p = 0.20). No relevant correlation was found between ES episodes and IIEF-5 scores (r=-0.069, p = 0.25), CIA + IIA calcium score (r=-0.10, p = 0.87) or number of atherosclerotic CIA + IIA lesions (r=-0.032, p = 0.60), respectively. CONCLUSIONS: The number of atherosclerotic lesions in the iliac arteries on nonenhanced abdominal CT scans is associated with the severity of ED. This may be used to identify subclinical cardiovascular disease and to quantify the risk for cardiovascular hazards in the future. TRIAL REGISTRATION: BASEC-Nr. 2020 - 01637.

Quantum Iterative Reconstruction for Abdominal Photon-counting Detector CT Improves Image Quality.

Background An iterative reconstruction (IR) algorithm was introduced for clinical photon-counting detector (PCD) CT. Purpose To investigate the image quality and the optimal strength level of a quantum IR algorithm (QIR; Siemens Healthcare) for virtual monoenergetic images and polychromatic images (T3D) in a phantom and in patients undergoing portal venous abdominal PCD CT. Materials and Methods In this retrospective study, noise power spectrum (NPS) was measured in a water-filled phantom. Consecutive oncologic patients who underwent portal venous abdominal PCD CT between March and April 2021 were included. Virtual monoenergetic images at 60 keV and T3D were reconstructed without QIR (QIR-off; reference standard) and with QIR at four levels (QIR 1-4; index tests). Global noise index, contrast-to-noise ratio (CNR), and voxel-wise CT attenuation differences were measured. Noise and texture, artifacts, diagnostic confidence, and overall quality were assessed qualitatively. Conspicuity of hypodense liver lesions was rated by four readers. Parametric (analyses of variance, paired t tests) and nonparametric tests (Friedman, post hoc Wilcoxon signed-rank tests) were used to compare quantitative and qualitative image quality among reconstructions. Results In the phantom, NPS showed unchanged noise texture across reconstructions with maximum spatial frequency differences of 0.01 per millimeter. Fifty patients (mean age, 59 years ± 16 [standard deviation]; 31 women) were included. Global noise index was reduced from QIR-off to QIR-4 by 45% for 60 keV and by 44% for T3D (both, P < .001). CNR of the liver improved from QIR-off to QIR-4 by 74% for 60 keV and by 69% for T3D (both, P < .001). No evidence of difference was found in mean attenuation of fat and liver (P = .79-.84) and on a voxel-wise basis among reconstructions. Qualitatively, QIR-4 outperformed all reconstructions in every category for 60 keV and T3D (P value range, <.001 to .01). All four readers rated QIR-4 superior to other strengths for lesion conspicuity (P value range, <.001 to .04). Conclusion In portal venous abdominal photon-counting detector CT, an iterative reconstruction algorithm (QIR; Siemens Healthcare) at high strength levels improved image quality by reducing noise and improving contrast-to-noise ratio and lesion conspicuity without compromising image texture or CT attenuation values. © RSNA, 2022 Online supplemental material is available for this article. See also the editorial by Sinitsyn in this issue.

Virtual Noncontrast Abdominal Imaging with Photon-counting Detector CT.

Background Accurate CT attenuation and diagnostic quality of virtual noncontrast (VNC) images acquired with photon-counting detector (PCD) CT are needed to replace true noncontrast (TNC) scans. Purpose To assess the attenuation errors and image quality of VNC images from abdominal PCD CT compared with TNC images. Materials and Methods In this retrospective study, consecutive adult patients who underwent a triphasic examination with PCD CT from July 2021 to October 2021 were included. VNC images were reconstructed from arterial and portal venous phase CT. The absolute attenuation error of VNC compared with TNC images was measured in multiple structures by two readers. Then, two readers blinded to image reconstruction assessed the overall image quality, image noise, noise texture, and delineation of small structures using five-point discrete visual scales (5 = excellent, 1 = nondiagnostic). Overall image quality greater than or equal to 3 was deemed diagnostic. In a phantom, noise texture, spatial resolution, and detectability index were assessed. A detectability index greater than or equal to 5 indicated high diagnostic accuracy. Interreader agreement was evaluated using the Krippendorff α coefficient. The paired t test and Friedman test were applied to compare objective and subjective results. Results Overall, 100 patients (mean age, 72 years ± 10 [SD]; 81 men) were included. In patients, VNC image attenuation values were consistent between readers (α = .60), with errors less than 5 HU in 76% and less than 10 HU in 95% of measurements. There was no evidence of a difference in error of VNC images from arterial or portal venous phase CT (3.3 HU vs 3.5 HU, P = .16). Subjective image quality was rated lower in VNC images for all categories (all, P < .001). Diagnostic quality of VNC images was reached in 99% and 100% of patients for readers 1 and 2, respectively. In the phantom, VNC images exhibited 33% higher noise, blotchier noise texture, similar spatial resolution, and inferior but overall good image quality (detectability index >20) compared with TNC images. Conclusion Abdominal virtual noncontrast images from the arterial and portal venous phase of photon-counting detector CT yielded accurate CT attenuation and good image quality compared with true noncontrast images. © RSNA, 2022 Online supplemental material is available for this article See also the editorial by Sosna in this issue.

Epicardial Adipose Tissue Attenuation and Fat Attenuation Index: Phantom Study and In Vivo Measurements With Photon-Counting Detector CT.

BACKGROUND. Epicardial adipose tissue (EAT) attenuation is a vascular inflammation marker predictive of adverse cardiac events. The fat attenuation index (FAI) assesses fat attenuation for predefined coronary segments. Photon-counting detector (PCD) CT uses routine virtual monoenergetic image (VMI) reconstructions. VMI energy level may affect EAT attenuation and FAI measurements. OBJECTIVE. The purpose of this article was to assess EAT attenuation and FAI measurements at different monoenergetic energy levels in patients undergoing coronary CTA using a first-generation whole-body dual-source PCD CT scanner. METHODS. An anthropomorphic phantom at two sizes with a fat insert was imaged on a first-generation dual-source PCD CT scanner and, as a reference, on a conventional energy-integrating detector (EID) CT scanner at 120 kV. Thirty patients (11 women, 19 men; mean age, 48 ± 10 years; Agatston score < 60) who underwent an ECG-gated unenhanced calcium-scoring scan and contrast-enhanced coronary CTA by PCD CT were retrospectively evaluated. VMIs from 55 to 80 keV at 5-keV increments were reconstructed. EAT attenuation was manually measured on unenhanced and contrast-enhanced images. FAI was calculated using semiautomated software. RESULTS. The attenuation of the phantom fat insert was -69 HU for the reference EID CT; the closest attenuation for PCD CT was observed at 70 keV for the small (-69 HU) and large (-70 HU) phantoms. In patients, EAT attenuation increased for unenhanced acquisition from -111 ± 11 HU at 55 keV to -82 ± 9 HU at 80 keV and for contrast-enhanced acquisition from -104 ± 11 HU at 55 keV to -81 ± 9 HU at 80 keV. The mean attenuation difference between unenhanced and contrast-enhanced scans decreased with increasing energy level (from 7 ± 12 HU to 1 ± 10 HU). The FAI increased from -89 ± 8 HU at 55 keV to -77 ± 12 HU at 80 keV for the right coronary artery, -95 ± 11 HU at 55 keV to -85 ± 11 HU at 80 keV for the left anterior descending artery, and -87 ± 10 HU at 55 keV to -80 ± 12 HU at 80 keV for the circumflex artery. CONCLUSION. EAT attenuation and FAI measurements using PCD CT are impacted by VMI energy level and contrast enhancement. Use of VMI reconstruction at 70 keV provides fat attenuation approximating conventional polychromatic measurements. CLINICAL IMPACT. The findings may help standardize evaluation of pericoronary inflammation by PCD CT as a measure of patients' cardiac risk.

Diagnostic performance of quantitative and qualitative parameters for the diagnosis of aortic graft infection using [18F]-FDG PET/CT.

PURPOSE: The aim of this study was the evaluation of quantitative and qualitative parameters for the diagnosis of aortic graft infection (AGI) using [18F]-FDG PET/CT. METHODS: PET/CT was performed in 50 patients with clinically suspected AGI. 12 oncological patients with aortic repair but without suspicion of AGI were included in the analysis to serve as control cohort. The [18F]-FDG uptake pattern around the graft was assessed using (a) a five-point visual grading scale (VGS), (b) SUVmax and (c) different graft-to-background ratios (GBRs). The diagnostic performance of VGS, SUVmax and GBRs was assessed and compared by ROC analysis. RESULTS: 28 infected and 34 uninfected grafts were identified by standard of reference. SUVmax and VGS were the most powerful predictors for the diagnosis of AGI according to the area under the curve (AUC 0.988 and 0.983, respectively) without a significant difference compared to GBRs. SUVmax and VGS showed congruent and accurate findings in 54 patients (i.e. either both positive or negative), yielding sensitivity and specificity (100%) in this subgroup of patients. CONCLUSION: Quantitative analysis by SUVmax and qualitative analysis by VGS are highly effective in the diagnosis of AGI and should be tested as an outcome measure in prospective trials.

18F-FDG PET/MRI compared with clinical and serological markers for monitoring disease activity in patients with aortitis and chronic periaortitis.

OBJECTIVES: We compared the diagnostic value of fully integrated 18F-FDG PET/MRI to that of clinical and serological markers for monitoring disease activity in patients with aortitis/chronic periaortitis (A/CPA) during immunosuppressive therapy. METHODS: Patients positive for A/CPA at the initial and at least 2 consecutive PET/MRI studies were included for retrospective analysis. Imaging (qualitative and quantitative analysis), clinical, and serologic (C-reactive protein, erythrocyte sedimentation rate) assessments were determined at each visit, and their findings compared. Differences in various PET/MRI parameters, clinical symptoms, and serologic markers during therapy between first and second visits were tested for statistical significance. Spearman's rank correlation coefficient was calculated to relate imaging to serologic marker changes between the first 2 visits. RESULTS: Serial assessments were performed in 12 patients with A/CPA, over 34 visits. PET/MRI suggested active disease in 22/34 (64.7%) studies, whereas clinical assessment and serological analysis were positive in only 18/34 (52.9%) and 17/34 (50%) cases, respectively. Disease activity assessment differed between PET/MRI, and clinical and serological markers, in 8/34 (23.5%) and 9/34 (26.5%) cases, respectively. Imaging and serologic parameters (p < 0.009) and clinical symptoms (p = 0.063) predominantly improved at the second visit. Changes from the first to the second visit were not correlated between PET/MRI and serologic markers. CONCLUSIONS: Fully integrated 18F-FDG PET/MRI provides a comprehensive imaging approach with data on vascular/perivascular inflammation that is complementary to clinical and laboratory assessments. This highlights the potential value of imaging-based disease activity monitoring, which might have a crucial impact on clinical management in patients with A/CPA.

Saving Contrast Media in Coronary CT Angiography with Photon-Counting Detector CT.

RATIONALE AND OBJECTIVES: To determine the optimal virtual monoenergetic image (VMI) energy level and the potential of contrast-media (CM) reduction for coronary computed tomography angiography (CCTA) with photon-counting detector CT (PCD-CT). MATERIALS AND METHODS: In this institutional review board-approved study, patients who underwent CCTA with dual-source PCD-CT with an identical scan protocol and radiation dose were included. In group 1, CCTA was performed with our standard CM protocol (volume: 72-85.2 mL, 370 mg iodine/mL). VMIs were reconstructed from 40 to 60 keV at 5 keV increments. Objective image quality (IQ) (vascular attenuation, image noise, and contrast-to-noise ratio [CNR]) was measured. Two blinded, independent readers rated subjective IQ (overall IQ, subjective image contrast, and subjective noise using a five-point discrete visual scale). Results of group 1 served to determine the best VMI level for CCTA. In group 2, CM volume was reduced by 20%, and in group 3 by another 20%. RESULTS: A total of 100 patients were enrolled (45 females, mean age 54 ± 13 years). Inter-reader agreement was good-to-excellent for all comparisons (κ > 0.6). In group 1, the best VMI level regarding objective and subjective IQ was 45 keV, which was selected as the reference for groups 2 and 3. For group 2, mean vascular attenuation was 890 Hounsfield units (HU) and mean CNR was 26, with no differences compared to group 1, 45 keV for both objective and subjective IQ. For group 3, mean vascular attenuation was 676 HU and mean CNR was 21, and all patients were rated as diagnostic except one (severe motion artifacts). CONCLUSION: Increased IQ of PCD-CT can be used for considerable CM volume reduction while still maintaining a diagnostic IQ of CCTA.

Advanced myocardial characterization and function with cardiac CT.

Non-invasive imaging with characterization and quantification of the myocardium with computed tomography (CT) became feasible owing to recent technical developments in CT technology. Cardiac CT can serve as an alternative modality when cardiac magnetic resonance imaging and/or echocardiography are contraindicated, not feasible, inconclusive, or non-diagnostic. This review summarizes the current and potential future role of cardiac CT for myocardial characterization including a summary of late enhancement techniques, extracellular volume quantification, and strain analysis. In addition, this review highlights potential fields for research about myocardial characterization with CT to possibly include it in clinical routine in the future.

Photon-Counting Detector CT for Liver Lesion Detection-Optimal Virtual Monoenergetic Energy for Different Simulated Patient Sizes and Radiation Doses.

OBJECTIVES: The aim of this study was to evaluate the optimal energy level of virtual monoenergetic images (VMIs) from photon-counting detector computed tomography (CT) for the detection of liver lesions as a function of phantom size and radiation dose. MATERIALS AND METHODS: An anthropomorphic abdominal phantom with liver parenchyma and lesions was imaged on a dual-source photon-counting detector CT at 120 kVp. Five hypoattenuating lesions with a lesion-to-background contrast difference of -30 HU and -45 HU and 3 hyperattenuating lesions with +30 HU and +90 HU were used. The lesion diameter was 5-10 mm. Rings of fat-equivalent material were added to emulate medium- or large-sized patients. The medium size was imaged at a volume CT dose index of 5, 2.5, and 1.25 mGy and the large size at 5 and 2.5 mGy, respectively. Each setup was imaged 10 times. For each setup, VMIs from 40 to 80 keV at 5 keV increments were reconstructed with quantum iterative reconstruction at a strength level of 4 (QIR-4). Lesion detectability was measured as area under the receiver operating curve (AUC) using a channelized Hotelling model observer with 10 dense differences of Gaussian channels. RESULTS: Overall, highest detectability was found at 65 and 70 keV for both hypoattenuating and hyperattenuating lesions in the medium and large phantom independent of radiation dose (AUC range, 0.91-1.0 for the medium and 0.94-0.99 for the large phantom, respectively). The lowest detectability was found at 40 keV irrespective of the radiation dose and phantom size (AUC range, 0.78-0.99). A more pronounced reduction in detectability was apparent at 40-50 keV as compared with 65-75 keV when radiation dose was decreased. At equal radiation dose, detection as a function of VMI energy differed stronger for the large size as compared with the medium-sized phantom (12% vs 6%). CONCLUSIONS: Detectability of hypoattenuating and hyperattenuating liver lesions differed between VMI energies for different phantom sizes and radiation doses. Virtual monoenergetic images at 65 and 70 keV yielded highest detectability independent of phantom size and radiation dose.

A Novel Reconstruction Technique to Reduce Stair-Step Artifacts in Sequential Mode Coronary CT Angiography.

PURPOSE: Prospective electrocardiography-triggering is one of the most commonly used cardiac computed tomography (CT) scan modes but can be susceptible to stair-step artifacts in the transition areas of an acquisition over multiple cardiac cycles. We evaluated a novel reconstruction algorithm to reduce the occurrence and severity of such artifacts in sequential coronary CT angiography. MATERIALS AND METHODS: In this institutional review board-approved, retrospective study, 50 consecutive patients (16 females; mean age, 58.9 ± 15.2) were included who underwent coronary CT angiography on a dual-source photon-counting detector CT in the sequential ultra-high-resolution mode with a detector collimation of 120 × 0.2 mm. Each scan was reconstructed without (hereafter called standard reconstruction) and with the novel ZeeFree reconstruction algorithm, which aims to minimize stair-step artifacts. The presence and extent of stair-step artifacts were rated by 2 independent, blinded readers on a 4-point discrete visual scale. The relationship between the occurrences of artifacts was correlated with the average and variability of heart rate and with patient characteristics. RESULTS: A total of 504 coronary segments were included into the analyses. In standard reconstructions, reader 1 reported stair-step artifacts in 40/504 (7.9%) segments, from which 12/504 led to nondiagnostic image quality (2.4% of all segments). Reader 2 reported 56/504 (11.1%) stair-step artifacts, from which 11/504 lead to nondiagnostic image quality (2.2% of all segments). With the ZeeFree algorithm, 9/12 (75%) and 8/11 (73%) of the nondiagnostic segments improved to a diagnostic quality for readers 1 and 2, respectively. The ZeeFree reconstruction algorithm significantly reduced the frequency and extent of stair-step artifacts compared with standard reconstructions for both readers ( P < 0.001, each). Heart rate variability and body mass index were significantly related to the occurrence of stair-step artifacts ( P < 0.05). CONCLUSIONS: Our study demonstrates the feasibility and effectiveness of a novel reconstruction algorithm leading to a significant reduction of stair-step artifacts and, hence, a reduction of coronary segments with a nondiagnostic image quality in sequential ultra-high-resolution coronary photon-counting detector CT angiography.

Effect of temporal resolution on calcium scoring: insights from photon-counting detector CT.

To intra-individually investigate the variation of coronary artery calcium (CAC), aortic valve calcium (AVC), and mitral annular calcium (MAC) scores and the presence of blur artifacts as a function of temporal resolution in patients undergoing non-contrast cardiac CT on a dual-source photon counting detector (PCD) CT. This retrospective, IRB-approved study included 70 patients (30 women, 40 men, mean age 78 ± 9 years) who underwent ECG-gated cardiac non-contrast CT with PCD-CT (gantry rotation time 0.25 s) prior to transcatheter aortic valve replacement. Each scan was reconstructed at a temporal resolution of 66 ms using the dual-source information and at 125 ms using the single-source information. Average heart rate and heart rate variability were calculated from the recorded ECG. CAC, AVC, and MAC were quantified according to the Agatston method on images with both temporal resolutions. Two readers assessed blur artifacts using a 4-point visual grading scale. The influence of average heart rate and heart rate variability on calcium quantification and blur artifacts of the respective structures were analyzed by linear regression analysis. Mean heart rate and heart rate variability during data acquisition were 76 ± 17 beats per minute (bpm) and 4 ± 6 bpm, respectively. CAC scores were smaller on 66 ms (median, 511; interquartile range, 220-978) than on 125 ms reconstructions (538; 203-1050, p < 0.001). Median AVC scores [2809 (2009-3952) versus 3177 (2158-4273)] and median MAC scores [226 (0-1284) versus 251 (0-1574)] were also significantly smaller on 66ms than on 125ms reconstructions (p < 0.001). Reclassification of CAC and AVC risk categories occurred in 4% and 11% of cases, respectively, whereby the risk category was always overestimated on 125ms reconstructions. Image blur artifacts were significantly less on 66ms as opposed to 125 ms reconstructions (p < 0.001). Intra-individual analyses indicate that temporal resolution significantly impacts on calcium scoring with cardiac CT, with CAC, MAC, and AVC being overestimated at lower temporal resolution because of increased motion artifacts eventually leading to an overestimation of patient risk.

Multi-Energy Low-Kiloelectron Volt versus Single-Energy Low-Kilovolt Images for Endoleak Detection at CT Angiography of the Aorta.

Purpose To compare image quality, diagnostic performance, and conspicuity between single-energy and multi-energy images for endoleak detection at CT angiography (CTA) after endovascular aortic repair (EVAR). Materials and Methods In this single-center prospective randomized controlled trial, individuals undergoing CTA after EVAR between August 2020 and May 2022 were allocated to imaging using either low-kilovolt single-energy images (SEI; 80 kV, group A) or low-kiloelectron volt virtual monoenergetic images (VMI) at 40 and 50 keV from multi-energy CT (80/Sn150 kV, group B). Scan protocols were dose matched (volume CT dose index: mean, 4.5 mGy ± 1.8 [SD] vs 4.7 mGy ± 1.3, P = .41). Contrast-to-noise ratio (CNR) was measured. Two expert radiologists established the reference standard for the presence of endoleaks. Detection and conspicuity of endoleaks and subjective image quality were assessed by two different blinded radiologists. Interreader agreement was calculated. Nonparametric statistical tests were used. Results A total of 125 participants (mean age, 76 years ± 8; 103 men) were allocated to groups A (n = 64) and B (n = 61). CNR was significantly lower for 40-keV VMI (mean, 19.1; P = .048) and 50-keV VMI (mean, 16.8; P < .001) as compared with SEI (mean, 22.2). In total, 45 endoleaks were present (A: 23 vs B: 22). Sensitivity for endoleak detection was higher for SEI (82.6%, 19 of 23; P = .88) and 50-keV VMI (81.8%, 18 of 22; P = .90) as compared with 40-keV VMI (77.3%, 17 of 22). Specificity was comparable among groups (SEI: 92.7%, 38 of 41; both VMI energies: 92.3%, 35 of 38; P = .99), with an interreader agreement of 1. Conspicuity of endoleaks was comparable between SEI (median, 2.99) and VMI (both energies: median, 2.87; P = .04). Overall subjective image quality was rated significantly higher for SEI (median, 4 [IQR, 4-4) as compared with 40 and 50 keV (both energies: median, 4 [IQR, 3-4]; P < .001). Conclusion SEI demonstrated higher image quality and comparable diagnostic accuracy as compared with 50-keV VMI for endoleak detection at CTA after EVAR. Keywords: Aneurysms, CT, CT Angiography, Vascular, Aorta, Technology Assessment, Multidetector CT, Abdominal Aortic Aneurysms, Endoleaks, Perigraft Leak Supplemental material is available for this article. © RSNA, 2024.

Increasing the rate of datasets amenable to CTFFR and quantitative plaque analysis: Value of software for reducing stair-step artifacts demonstrated in photon-counting detector CT.

Purpose: To determine the value of an algorithm for reducing stair-step artifacts for advanced coronary analyses in sequential mode coronary CT angiography (CCTA). Methods: Forty patients undergoing sequential mode photon-counting detector CCTA with at least one stair-step artifact were included. Twenty patients (14 males; mean age 57±17years) with 45 segments showing stair-step artifacts and without atherosclerosis were included for CTFFR analysis. Twenty patients (20 males; mean age 74±13years) with 22 segments showing stair-step artifacts crossing an atherosclerotic plaque were included for quantitative plaque analysis. Artifacts were graded, and CTFFR and quantitative coronary plaque analyses were performed in standard reconstructions and in those reconstructed with a software (entitled ZeeFree) for artifact reduction. Results: Stair-step artifacts were significantly reduced in ZeeFree compared to standard reconstructions (p<0.05). In standard reconstructions, CTFFR was not feasible in 3/45 (7 %) segments but was feasible in all ZeeFree reconstructions. In 9/45 (20 %) segments without atherosclerosis, the ZeeFree algorithm led to a change of CTFFR values from pathologic in standard to physiologic values in ZeeFree reconstructions. In one segment (1/22, 5 %), quantitative plaque analysis was not feasible in standard but only in ZeeFree reconstruction. The mean overall plaque volume (111±60 mm3), the calcific (77±47 mm3), fibrotic (31±28 mm3), and lipidic (4±3 mm3) plaque components were higher in standard than in ZeeFree reconstructions (overall 75±50 mm3, p<0.001; calcific 51±42 mm3, p<0.001; fibrotic 22±19 mm3, p<0.05; lipidic 3±3 mm3, p=0.055). Conclusion: Despite the lack of reference standard modalities for CTFFR and coronary plaque analysis, initial evidence indicates that an algorithm for reducing stair-step artifacts in sequential mode CCTA increases the rate and quality of datasets amenable to advanced coronary artery analysis, hereby potentially improving patient management.

Assessment of interstitial lung disease in a systemic sclerosis patient cohort using photon-counting detector CT with ultra-high resolution and a 1024-pixel image matrix.

PURPOSE: This study assessed the potential of ultra-high-resolution (UHR) and a 1024-matrix in photon-counting-detector CT (PCD-CT) for evaluating interstitial lung disease (ILD) in systemic sclerosis (SSc) patients. MATERIALS AND METHODS: Sixty-six SSc patients who underwent ILD-CT screening on a first-generation PCD-CT were retrospectively included. Scans were performed in UHR mode at 100 kVp with two different matrix sizes (512x512 and 1024x1024) and reconstructed at slice thicknesses of 1.5 mm and 0.2 mm. Image noise, subjective image quality, and ILD changes (1) were evaluated on a 5-point Likert-scale by two independent readers. RESULTS: Interreader agreement for subjective image quality ranged from fair to almost perfect (Krippendorff-Alpha: 0.258-0.862). Overall image quality was highest for 1.5 mm/1024matrix images ((reader 1: 4 (4.4), reader 2: 5 (4.5)). Image sharpness was rated significantly better in 0.2 mm images (p < 0.001). Regarding ILD changes, 0.2 mm slice thickness outperformed 1.5 mm slice thickness significantly (p < 0.001), while there was no significant difference between the two matrix sizes. 1024 matrix size demonstrated superiority in evaluating coarse reticulations compared to 512matrix size. CONCLUSION: UHR mode with a 0.2 mm slice thickness showed enhanced image sharpness and improved visibility of ILD changes compared to standard reconstructions. This has the potential to enable the early detection of subtle disease manifestations. ADVANCES IN KNOWLEDGE: With the invention of PCD-CT different reconstruction algorithms need to be evaluated for specific pathologies. In our study ILD UHR mode with 0.2 mm slice thickness showed to be beneficial in the detection of parenchymal changes in patients with scleroderma.

Virtual calcium removal in calcified coronary arteries with photon-counting detector CT-first in-vivo experience.

Purpose: To evaluate the feasibility and accuracy of quantification of calcified coronary stenoses using virtual non-calcium (VNCa) images in coronary CT angiography (CCTA) with photon-counting detector (PCD) CT compared with quantitative coronary angiography (QCA). Materials and methods: This retrospective, institutional-review board approved study included consecutive patients with calcified coronary artery plaques undergoing CCTA with PCD-CT and invasive coronary angiography between July and December 2022. Virtual monoenergetic images (VMI) and VNCa images were reconstructed. Diameter stenoses were quantified on VMI and VNCa images by two readers. 3D-QCA served as the standard of reference. Measurements were compared using Bland-Altman analyses, Wilcoxon tests, and intraclass correlation coefficients (ICC). Results: Thirty patients [mean age, 64 years ± 8 (standard deviation); 26 men] with 81 coronary stenoses from calcified plaques were included. Ten of the 81 stenoses (12%) had to be excluded because of erroneous plaque subtraction on VNCa images. Median diameter stenosis determined on 3D-QCA was 22% (interquartile range, 11%-35%; total range, 4%-88%). As compared with 3D-QCA, VMI overestimated diameter stenoses (mean differences -10%, p < .001, ICC: .87 and -7%, p < .001, ICC: .84 for reader 1 and 2, respectively), whereas VNCa images showed similar diameter stenoses (mean differences 0%, p = .68, ICC: .94 and 1%, p = .07, ICC: .93 for reader 1 and 2, respectively). Conclusion: First experience in mainly minimal to moderate stenoses suggests that virtual calcium removal in CCTA with PCD-CT, when feasible, has the potential to improve the quantification of calcified stenoses.