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.

CT Angiography of the Aorta Using Photon-counting Detector CT with Reduced Contrast Media Volume.

Purpose: To develop and evaluate a low-volume contrast media protocol for thoracoabdominal CT angiography (CTA) with photon-counting detector (PCD) CT. Materials and Methods: This prospective study included consecutive participants (April-September 2021) who underwent CTA with PCD CT of the thoracoabdominal aorta and previous CTA with energy-integrating detector (EID) CT at equal radiation doses. In PCD CT, virtual monoenergetic images (VMI) were reconstructed in 5-keV intervals from 40 to 60 keV. Attenuation of the aorta, image noise, and contrast-to-noise ratio (CNR) were measured, and subjective image quality was rated by two independent readers. In the first group of participants, the same contrast media protocol was used for both scans. CNR gain in PCD CT compared with EID CT served as the reference for contrast media volume reduction in the second group. Noninferiority analysis was used to test noninferior image quality of the low-volume contrast media protocol with PCD CT. Results: The study included 100 participants (mean age, 75 years ± 8 [SD]; 83 men). In the first group (n = 40), VMI at 50 keV provided the best trade-off between objective and subjective image quality, achieving 25% higher CNR compared with EID CT. Contrast media volume in the second group (n = 60) was reduced by 25% (52.5 mL). Mean differences in CNR and subjective image quality between EID CT and PCD CT at 50 keV were above the predefined boundaries of noninferiority (-0.54 [95% CI: -1.71, 0.62] and -0.36 [95% CI: -0.41, -0.31], respectively). Conclusion: CTA of the aorta with PCD CT was associated with higher CNR, which was translated into a low-volume contrast media protocol demonstrating noninferior image quality compared with EID CT at the same radiation dose.Keywords: CT Angiography, CT-Spectral, Vascular, Aorta, Contrast Agents-Intravenous, Technology Assessment© RSNA, 2023See also the commentary by Dundas and Leipsic in this issue.

Dual-Energy CT Pulmonary Angiography for the Assessment of Surgical Accessibility in Patients with Chronic Thromboembolic Pulmonary Hypertension.

We assessed the value of dual-energy CT pulmonary angiography (CTPA) for classification of the level of disease in chronic thromboembolic pulmonary hypertension (CTEPH) patients compared to the surgical Jamieson classification and prediction of hemodynamic changes after pulmonary endarterectomy. Forty-three CTEPH patients (mean age, 57 ± 16 years; 18 females) undergoing CTPA prior to surgery were retrospectively included. "Proximal" and "distal disease" were defined as L1 and 2a (main and lobar pulmonary artery [PA]) and L2b-4 (lower lobe basal trunk to subsegmental PA), respectively. Three radiologists had a moderate interobserver agreement for the radiological classification of disease (k = 0.55). Sensitivity was 92-100% and specificity was 24-53% to predict proximal disease according to the Jamieson classification. A median of 9 segments/patient had CTPA perfusion defects (range, 2-18 segments). L1 disease had a greater decrease in the mean pulmonary artery pressure (p = 0.029) and pulmonary vascular resistance (p = 0.011) after surgery compared to patients with L2a to L3 disease. The extent of perfusion defects was not associated with the level of disease or hemodynamic changes after surgery (p > 0.05 for all). CTPA is highly sensitive for predicting the level of disease in CTEPH patients with a moderate interobserver agreement. The radiological level of disease is associated with hemodynamic improvement after surgery.

Virtual monoenergetic images from dual-energy CT: systematic assessment of task-based image quality performance.

BACKGROUND: To compare task-based image quality (TB-IQ) among virtual monoenergetic images (VMI) and linear-blended images (LBI) from dual-energy CT as a function of contrast task, radiation dose, size, and lesion diameter. METHODS: A TB-IQ phantom (Mercury Phantom 4.0, Sun Nuclear Corporation) was imaged on a third-generation dual-source dual-energy CT with 100/Sn150 kVp at three volume CT dose levels (5, 10, 15 mGy). Three size sections (diameters 16, 26, 36 cm) with subsections for image noise and spatial resolution analysis were used. High-contrast tasks (e.g., calcium-containing stone and vascular lesion) were emulated using bone and iodine inserts. A low-contrast task (e.g., low-contrast lesion or hematoma) was emulated using a polystyrene insert. VMI at 40-190 keV and LBI were reconstructed. Noise power spectrum (NPS) determined the noise magnitude and texture. Spatial resolution was assessed using the task-transfer function (TTF) of the three inserts. The detectability index (d') served as TB-IQ metric. RESULTS: Noise magnitude increased with increasing phantom size, decreasing dose, and decreasing VMI-energy. Overall, noise magnitude was higher for VMI at 40-60 keV compared to LBI (range of noise increase, 3-124%). Blotchier noise texture was found for low and high VMIs (40-60 keV, 130-190 keV) compared to LBI. No difference in spatial resolution was observed for high contrast tasks. d' increased with increasing dose level or lesion diameter and decreasing size. For high-contrast tasks, d' was higher at 40-80 keV and lower at high VMIs. For the low-contrast task, d' was higher for VMI at 70-90 keV and lower at 40-60 keV. CONCLUSIONS: Task-based image quality differed among VMI-energy and LBI dependent on the contrast task, dose level, phantom size, and lesion diameter. Image quality could be optimized by tailoring VMI-energy to the contrast task. Considering the clinical relevance of iodine, VMIs at 50-60 keV could be proposed as an alternative to LBI.

Contrast-Enhanced Abdominal CT with Clinical Photon-Counting Detector CT: Assessment of Image Quality and Comparison with Energy-Integrating Detector CT.

RATIONALE AND OBJECTIVES: To determine quantitative and qualitative image quality of contrast-enhanced abdominal photon-counting detector CT (PCD-CT) compared to energy-integrating detector CT (EID-CT) in the same patients. MATERIAL AND METHODS: Thirty-nine patients (mean age 63 ± 10 years, 10 females, mean BMI 26.0 ± 5.7 kg/m2) were retrospectively included who underwent clinically indicated, contrast-enhanced abdominal CT in portal-venous phase with first-generation dual-source PCD-CT and who underwent previous abdominal CT with EID-CT. For both scan, same contrast media protocol was used. PCD-CT was performed in QuantumPlus mode (obtaining full spectral information) at 120kVp. EID-CT was performed using automated tube voltage selection (reference tube voltage 100kVp). In PCD-CT, virtual monoenergetic images (VMI) were reconstructed in 10keV intervals (40-90 keV). Tube current-time product in PCD-CT was modified in each patient to obtain same volume CT-dose-index (CTDIvol) as with EID-CT. Attenuation of organs and vascular structures were measured, noise quantified, and contrast-to-noise ratio (CNR) calculated. Two independent, blinded radiologists assessed subjective image quality using a 5-point Likert scale (overall image quality, image noise, contrast, and liver lesion conspicuity). RESULTS: Median time interval between the scan was 12 months. BMI (p = 0.905) and CTDIvol (p = 0.984) were similar between scans. CNRparenchymal and CNRvascular of VMI from PCD-CT at 40 and 50keV were significantly higher than EID-CT (all, p < 0.05). Overall, inter-reader agreement for all subjective image quality readings was substantial (Krippendorff's alpha = 0.773). Overall image quality of VMI was rated similar at 50 and 60 keV compared to EID-CT (all, p > 0.05). Subjective image noise was significantly higher at 40-50 keV, contrast significantly higher at 40-60 keV (all, p < 0.05). Lesion conspicuity was rated similar on all images. CONCLUSION: Our intra-individual analysis of abdominal PCD-CT indicates that VMI at 50 keV shows significantly higher CNR at similar subjective image quality as compared to EID-CT at identical radiation dose.

Assessment of Bone Mineral Density From a Computed Tomography Topogram of Photon-Counting Detector Computed Tomography-Effect of Phantom Size and Tube Voltage.

PURPOSE: The aim of this study was to assess the accuracy and impact of different sizes and tube voltages on bone mineral density (BMD) assessment using a computed tomography (CT) topogram acquired with photon-counting detector CT in an osteopenic ex vivo animal spine. MATERIALS AND METHODS: The lumbar back of a piglet was used to simulate osteopenia of the lumbar spine. Five fat layers (each with a thickness of 3 cm) were consecutively placed on top of the excised spine to emulate a total of 5 different sizes. Each size was repeatedly imaged on (A) a conventional dual-energy x-ray absorptiometry scanner as the reference standard, (B) a prototype photon-counting detector CT system at 120 kVp with energy thresholds at 20 and 70 keV, and (C) the same prototype system at 140 kVp with thresholds at 20 and 75 keV. Material-specific data were reconstructed from spectral topograms for B and C. Bone mineral density was measured for 3 lumbar vertebrae (L2-L4). A linear mixed-effects model was used to estimate the impact of vertebra, imaging setup, size, and their interaction term on BMD. RESULTS: The BMD of the lumbar spine corresponded to a T score in humans between -4.2 and -4.8, which is seen in osteoporosis. Averaged across the 3 vertebrae and 5 sizes, mean BMD was 0.56 ± 0.03, 0.55 ± 0.02, and 0.55 ± 0.02 g/cm2 for setup A, B, and C, respectively. There was no significant influence of imaging setup (P = 0.7), simulated size (P = 0.67), and their interaction term (both P > 0.2) on BMD. Bone mineral density decreased significantly from L2 to L4 for all 3 setups (all P < 0.0001). Bone mineral density was 0.59 ± 0.01, 0.57 ± 0.01, and 0.52 ± 0.02 g/cm2 for L2, L3, and L4, respectively, for setup A; 0.57 ± 0.02, 0.55 ± 0.01, and 0.53 ± 0.01 g/cm2 for setup B; and 0.57 ± 0.01, 0.55 ± 0.01, and 0.53 ± 0.01 g/cm2 for setup C. CONCLUSION: A single CT topogram acquired on photon-counting detector CT with 2 energy thresholds enabled BMD quantification with similar accuracy compared with dual-energy x-ray absorptiometry over a range of simulated sizes and tube voltages in an osteopenic ex vivo animal spine.

Photon-Counting Multienergy Computed Tomography With Spectrally Optimized Contrast Media for Plaque Removal and Stenosis Assessment.

PURPOSE: The aim of this study was to systematically evaluate the potential to combine investigational contrast media with spectrally optimized energy-thresholding of photon-counting detector computed tomography (PCCT) for subtraction of calcified plaques in a coronary artery stenosis phantom. METHODS: A small vessel phantom containing 3 fillable tubes (diameter, 3 mm each) with calcified plaques was placed into an anthropomorphic chest phantom. The plaques had incremental thicknesses ranging from 0.3 to 2.7 mm, simulating vessel stenoses ranging from 10% to 90% of the lumen diameter. The phantom was filled with 5 different investigational contrast media (iodine, bismuth, hafnium, holmium, and tungsten) at equal mass concentrations (15 mg/mL) and was imaged on a prototype PCCT at 140 kVp using optimized, contrast media-dependent energy thresholds. Contrast maps (CMs) were reconstructed for each contrast medium by applying a linear 2-material decomposition algorithm. Image noise magnitude and noise texture of CM were compared among the contrast media using the noise power spectrum. Two blinded readers independently rated the vessel lumen visualization on short-axis and the overall subjective image quality on long-axis CM relative to iodine as the reference standard. Four readers determined the highest degree of stenosis that could be assessed with high diagnostic confidence on long-axis CM. RESULTS: Average image noise on CM was lower for tungsten (49 HU) and hafnium (62 HU) and higher for bismuth (81 HU) and holmium (165 HU) compared with iodine (78 HU). Noise texture of CM was similar among the contrast media. Interreader agreement for vessel lumen visualization on short-axis CM ranged from moderate to excellent (k = 0.567-0.814). Compared with iodine, lumen visualization of each reader was improved using tungsten (P < 0.001 for both readers), similar to improved using hafnium (P = 0.008, P = 0.29), similar using bismuth (P = 0.38, P = 0.69), and decreased using holmium (both, P < 0.001). Overall subjective image quality was similar for holmium and superior for tungsten, hafnium, and bismuth as compared with iodine. Higher-degree stenoses were evaluable with high confidence using tungsten (mean, 70%; interquartile range, 70%-70%), bismuth (70%; 60%-70%), and hafnium (75%; 70%-80%) compared with iodine (50%; 50%-60%) and holmium (50%; 50%-60%). CONCLUSIONS: Spectral optimization in PCCT combined with investigational contrast media can improve calcium subtraction and stenosis assessment in small vessels. Contrast maps of tungsten and, to a lesser extent, hafnium as contrast media yielded superior image noise properties and improved vessel lumen visualization, along with a higher subjective image quality compared with the reference standard iodine.

Machine learning-based CT fractional flow reserve assessment in acute chest pain: first experience.

BACKGROUND: Computed tomography (CT)-derived fractional flow reserve (FFRCT) enables the non-invasive functional assessment of coronary artery stenosis. We evaluated the feasibility and potential clinical role of FFRCT in patients presenting to the emergency department with acute chest pain who underwent chest-pain CT (CPCT). METHODS: For this retrospective IRB-approved study, we included 56 patients (median age: 62 years, 14 females) with acute chest pain who underwent CPCT and who had at least a mild (≥25% diameter) coronary artery stenosis. CPCT was evaluated for the presence of acute plaque rupture and vulnerable plaque features. FFRCT measurements were performed using a machine learning-based software. We assessed the agreement between the results from FFRCT and patient outcome (including results from invasive catheter angiography and from any non-invasive cardiac imaging test, final clinical diagnosis and revascularization) for a follow-up of 3 months. RESULTS: FFRCT was technically feasible in 38/56 patients (68%). Eleven of the 38 patients (29%) showed acute plaque rupture in CPCT; all of them underwent immediate coronary revascularization. Of the remaining 27 patients (71%), 16 patients showed vulnerable plaque features (59%), of whom 11 (69%) were diagnosed with acute coronary syndrome (ACS) and 10 (63%) underwent coronary revascularization. In patients with vulnerable plaque features in CPCT, FFRCT had an agreement with outcome in 12/16 patients (75%). In patients without vulnerable plaque features (n=11), one patient showed myocardial ischemia (9%). In these patients, FFRCT and patient outcome showed an agreement in 10/11 patients (91%). CONCLUSIONS: Our preliminary data show that FFRCT is feasible in patients with acute chest pain who undergo CPCT provided that image quality is sufficient. FFRCT has the potential to improve patient triage by reducing further downstream testing but appears of limited value in patients with CT signs of acute plaque rupture.

Volumetric assessment of solid pulmonary nodules on ultralow-dose CT: a phantom study.

BACKGROUND: To reduce the radiation exposure from chest computed tomography (CT), ultralow-dose CT (ULDCT) protocols performed at sub-millisievert levels were previously tested for the evaluation of pulmonary nodules (PNs). The purpose of our study was to investigate the effect of ULDCT and iterative image reconstruction on volumetric measurements of solid PNs. METHODS: CT datasets of an anthropomorphic chest phantom containing solid microspheres were obtained with a third-generation dual-source CT at standard dose, 1/8th, 1/20th and 1/70th of standard dose [CT volume dose index (CTDIvol): 0.03-2.03 mGy]. Semi-automated volumetric measurements were performed on CT datasets reconstructed with filtered back projection (FBP) and advanced modelled iterative reconstruction (ADMIRE), at strength level 3 and 5. Absolute percentage error (APE) evaluated measurement accuracy related to the effective volume. Scan repetition differences were evaluated using Bland-Altman analysis. Two-way analysis of variance (ANOVA) assessed influence of different scan parameters on APE. Proportional differences (PDs) tested the effect of dose settings and reconstruction algorithms on volumetric measurements, as compared to the standard protocol (standard dose-FBP). RESULTS: Bland-Altman analysis revealed small mean interscan differences of APE with narrow limits of agreement (-0.1%±4.3% to -0.3%±3.8%). Dose settings (P<0.001), reconstruction algorithms (P<0.001), nodule diameters (P<0.001) and nodule density (P=0.011) had statistically significant influence on APE. Post-hoc Bonferroni tests showed slightly higher APE when scanning with 1/70th of standard dose [mean difference: 3.4%, 95% confidence interval (CI): 2.5-4.3%; P<0.001], and for image reconstruction with ADMIRE5 (mean difference: 1.8%, 95% CI: 1.0-2.5%; P<0.001). No significant differences for scanning with 1/20th of standard dose (P=0.42), and image reconstruction with ADMIRE3 (P=0.19) were found. Scanning with 1/70th of standard dose and image reconstruction with FBP showed the widest range of PDs (-16.8% to 23.4%) compared to standard dose-FBP. CONCLUSIONS: Our phantom study showed no significant difference between nodule volume measurements on standard dose CT (CTDIvol: 2 mGy) and ULDCT with 1/20th of standard dose (CTDIvol: 0.10 mGy).