Image quality of lung perfusion with photon-counting-detector CT: comparison with dual-source, dual-energy CT.

PURPOSE: To evaluate the quality of lung perfusion imaging obtained with photon-counting-detector CT (PCD-CT) in comparison with dual-source, dual-energy CT (DECT). METHODS: Seventy-one consecutive patients scanned with PCD-CT were compared to a paired population scanned with dual-energy on a 3rd-generation DS-CT scanner using (a) for DS-CT (Group 1): collimation: 64 × 0.6 × 2 mm; pitch: 0.55; (b) for PCD-CT (Group 2): collimation: 144 × 0.4 mm; pitch: 1.5; single-source acquisition. The injection protocol was similar in both groups with the reconstruction of perfusion images by subtraction of high- and low-energy virtual monoenergetic images. RESULTS: Compared to Group 1, Group 2 examinations showed: (a) a shorter duration of data acquisition (0.93 ± 0.1 s vs 3.98 ± 0.35 s; p < 0.0001); (b) a significantly lower dose-length-product (172.6 ± 55.14 vs 339.4 ± 75.64 mGy·cm; p < 0.0001); and (c) a higher level of objective noise (p < 0.0001) on mediastinal images. On perfusion images: (a) the mean level of attenuation did not differ (p = 0.05) with less subjective image noise in Group 2 (p = 0.049); (b) the distribution of scores of fissure visualization differed between the 2 groups (p < 0.0001) with a higher proportion of fissures sharply delineated in Group 2 (n = 60; 84.5% vs n = 26; 26.6%); (c) the rating of cardiac motion artifacts differed between the 2 groups (p < 0.0001) with a predominance of examinations rated with mild artifacts in Group 2 (n = 69; 97.2%) while the most Group 1 examinations showed moderate artifacts (n = 52; 73.2%). CONCLUSION: PCD-CT acquisitions provided similar morphologic image quality and superior perfusion imaging at lower radiation doses. CLINICAL RELEVANCE STATEMENT: The improvement in the overall quality of perfusion images at lower radiation doses opens the door for wider applications of lung perfusion imaging in clinical practice. KEY POINTS: The speed of data acquisition with PCD-CT accounts for mild motion artifacts. Sharply delineated fissures are depicted on PCD-CT perfusion images. High-quality perfusion imaging was obtained with a 52% dose reduction.

Diagnosis of acute pulmonary embolism: when photon-counting-detector CT replaces energy-integrating-detector CT in daily routine.

PURPOSE: To compare the diagnostic approach of acute pulmonary embolism (PE) with photon-counting-detector CT (PCD-CT) and energy-integrating-detector CT (EID-CT). MATERIALS AND METHODS: Two cohorts underwent CT angiographic examinations with EID-CT (Group 1; n = 158) and PCD-CT (Group 2; n = 172), (b) with two options in Group 1, dual energy (Group 1a) or single energy (Group 1b) and a single option in Group 2 (spectral imaging with single source). RESULTS: In Group 2, all patients benefited from spectral imaging, only accessible to 105 patients (66.5%) in Group 1, with a mean acquisition time significantly shorter (0.9 ± 0.1 s vs 4.0 ± 0 .3 s; p < 0.001) and mean values of CTDIvol and DLP reduced by 46.3% and 47.7%, respectively. Comparing the quality of 70 keV (Group 2) and averaged (Group 1a) images: (a) the mean attenuation within pulmonary arteries did not differ (p = 0.13); (b) the image noise was significantly higher (p < 0.001) in Group 2 with no difference in subjective image noise (p = 0.29); and (c) 89% of examinations were devoid of artifacts in Group 2 vs 28.6% in Group 1a. The percentage of diagnostic examinations was 95.2% (100/105; Group 1a), 100% (53/53; Group 1b), and 95.3% (164/172; Group 2). There were 4.8% (5/105; Group 1a) and 4.7% (8/172; Group 2) of non-diagnostic examinations, mainly due to the suboptimal quality of vascular opacification with the restoration of a diagnostic image quality on low-energy images. CONCLUSION: Compared to EID-CT, morphology and perfusion imaging were available in all patients scanned with PCD-CT, with the radiation dose reduced by 48%. CLINICAL RELEVANCE STATEMENT: PCD-CT enables scanning patients with the advantages of both spectral imaging, including high-quality morphologic imaging and lung perfusion for all patients, and fast scanning-a combination that is not simultaneously accessible with EID-CT while reducing the radiation dose by almost 50%.

Myocardial Characterization with Extracellular Volume Mapping with a First-Generation Photon-counting Detector CT with MRI Reference.

Background Photon-counting detector (PCD) CT provides comprehensive spectral data with every acquisition, but studies evaluating myocardial extracellular volume (ECV) quantification with use of PCD CT compared with an MRI reference remain lacking. Purpose To compare ECV quantification for myocardial tissue characterization between a first-generation PCD CT system and cardiac MRI. Materials and Methods In this single-center prospective study, adults without contraindication to iodine-based contrast media underwent same-day cardiac PCD CT and MRI with native and postcontrast T1 mapping and late gadolinium enhancement for various clinical indications for cardiac MRI (the reference standard) between July 2021 and January 2022. Global and midventricular ECV were assessed with use of three methods: single-energy PCD CT, dual-energy PCD CT, and MRI T1 mapping. Quantitative comparisons among all techniques were performed. Correlation and reliability between different methods of ECV quantification were assessed with use of the Pearson correlation coefficient (r) and the intraclass correlation coefficient. Results The final sample included 29 study participants (mean age ± SD, 54 years ± 17; 15 men). There was a strong correlation of ECV between dual- and single-energy PCD CT (r = 0.91, P < .001). Radiation dose was 40% lower with dual-energy versus single-energy PCD CT (volume CT dose index, 10.1 mGy vs 16.8 mGy, respectively; P < .001). In comparison with MRI, dual-energy PCD CT showed strong correlation (r = 0.82 and 0.91, both P < .001) and good to excellent reliability (intraclass correlation coefficients, 0.81 and 0.90) for midventricular and global ECV quantification, but it overestimated ECV by approximately 2%. Single-energy PCD CT showed similar relationship with MRI but underestimated ECV by 3%. Conclusion Myocardial tissue characterization with photon-counting detector CT-based quantitative extracellular volume analysis showed a strong correlation to MRI. © RSNA, 2023 Supplemental material is available for this article.

The technical development of photon-counting detector CT.

Since 1971 and Hounsfield's first CT system, clinical CT systems have used scintillating energy-integrating detectors (EIDs) that use a two-step detection process. First, the X-ray energy is converted into visible light, and second, the visible light is converted to electronic signals. An alternative, one-step, direct X-ray conversion process using energy-resolving, photon-counting detectors (PCDs) has been studied in detail and early clinical benefits reported using investigational PCD-CT systems. Subsequently, the first clinical PCD-CT system was commercially introduced in 2021. Relative to EIDs, PCDs offer better spatial resolution, higher contrast-to-noise ratio, elimination of electronic noise, improved dose efficiency, and routine multi-energy imaging. In this review article, we provide a technical introduction to the use of PCDs for CT imaging and describe their benefits, limitations, and potential technical improvements. We discuss different implementations of PCD-CT ranging from small-animal systems to whole-body clinical scanners and summarize the imaging benefits of PCDs reported using preclinical and clinical systems. KEY POINTS: • Energy-resolving, photon-counting-detector CT is an important advance in CT technology. • Relative to current energy-integrating scintillating detectors, energy-resolving, photon-counting-detector CT offers improved spatial resolution, improved contrast-to-noise ratio, elimination of electronic noise, increased radiation and iodine dose efficiency, and simultaneous multi-energy imaging. • High-spatial-resolution, multi-energy imaging using energy-resolving, photon-counting-detector CT has been used in investigations into new imaging approaches, including multi-contrast imaging.

Ultra-high resolution CT imaging of interstitial lung disease: impact of photon-counting CT in 112 patients.

OBJECTIVES: To compare lung parenchyma analysis on ultra-high resolution (UHR) images of a photon-counting CT (PCCT) scanner with that of high-resolution (HR) images of an energy-integrating detector CT (EID-CT). METHODS: A total of 112 patients with stable interstitial lung disease (ILD) were investigated (a) at T0 with HRCT on a 3rd-generation dual-source CT scanner; (b) at T1 with UHR on a PCCT scanner; (c) with a comparison of 1-mm-thick lung images. RESULTS: Despite a higher level of objective noise at T1 (74.1 ± 14.1 UH vs 38.1 ± 8.7 UH; p < 0.0001), higher qualitative scores were observed at T1 with (a) visualization of more distal bronchial divisions (median order; Q1-Q3) (T1: 10th division [9-10]; T0: 9th division [8-9]; p < 0.0001); (b) greater scores of sharpness of bronchial walls (p < 0.0001) and right major fissure (p < 0.0001). The scores of visualization of CT features of ILD were significantly superior at T1 (micronodules: p = 0.03; linear opacities, intralobular reticulation, bronchiectasis, bronchiolectasis, and honeycombing: p < 0.0001), leading to the reclassification of 4 patients with non-fibrotic ILD at T0, recognized with fibrotic ILD at T1. At T1, the mean (± SD) radiation dose (CTDI vol: 2.7 ± 0.5 mGy; DLP: 88.5 ± 21 mGy.cm) was significantly lower than that delivered at T0 (CTDI vol: 3.6 ± 0.9 mGy; DLP: 129.8 ± 31.7 mGy.cm) (p < 0.0001), corresponding to a mean reduction of 27% and 32% for the CTDIvol and DLP, respectively. CONCLUSIONS: The UHR scanning mode of PCCT allowed a more precise depiction of CT features of ILDs and reclassification of ILD patterns with significant radiation dose reduction. CLINICAL RELEVANCE STATEMENT: Evaluation of lung parenchymal structures with ultra-high-resolution makes subtle changes at the level of the secondary pulmonary lobules and lung microcirculation becoming visually accessible, opening new options for synergistic collaborations between highly-detailed morphology and artificial intelligence. KEY POINTS: • Photon-counting CT (PCCT) provides a more precise analysis of lung parenchymal structures and CT features of interstitial lung diseases (ILDs). • The UHR mode ensures a more precise delineation of fine fibrotic abnormalities with the potential of modifying the categorization of ILD patterns. • Better image quality at a lower radiation dose with PCCT opens new horizons for further dose reduction in noncontrast UHR examinations.

Stent imaging on a clinical dual-source photon-counting detector CT system-impact of luminal attenuation and sharp kernels on lumen visibility.

OBJECTIVES: To assess the impact of scan modes and reconstruction kernels using a novel dual-source photon-counting detector CT (PCD-CT) on lumen visibility and sharpness of different stent sizes. METHODS: A phantom containing six balloon-expandable stents (2.5 to 9 mm diameter) in silicone tubing was scanned on a PCD-CT with standard (0.6 mm and 0.4 mm thicknesses) and ultra-high-resolution (0.2 mm thickness) modes. With the use of increasing contrast medium concentrations, densities of 0, 200, 400, and 600 HU were achieved. Standard-resolution scans were reconstructed using increasing sharpness kernels, using both polyenergetic quantitative soft tissue "conventional" ((Qr40c(0.6 mm), Qr40c(0.4 mm), Qr72c(0.2 mm)) and vascular (Bv) virtual monoenergetic reconstructions (Bv44m(0.4 mm), Bv60m(0.4 mm)) at 70 keV. In-stent lumen visibility, sharpness (max. ΔHU of the stent measured in profile plots), and in-stent noise (standard deviation of HU) were measured. RESULTS: In-stent lumen visibility was highest for Qr72c(0.2 mm) (86.5 ± 2.8% to 88.3 ± 2.6%) and in Bv60m(0.4 mm) reconstructions (77.3 ± 2.9 to 82.7 ± 2.5%). Lumen visibility was lowest in the smallest stent (2.5 mm) ranging from 54.1% in Qr40c(0.6 mm) to 74.1% in Qr72c(0.2 mm) and highest in the largest stent (9 mm) ranging from 93.8% in Qr40c(0.6 mm) to 99.1% in the Qr72c(0.2 mm) series. Lumen visibility decreased by 2.1% for every 200-HU increase in lumen attenuation. Max. ΔHU between stents and stent lumen was highest in Qr72c(0.2 mm) (ΔHU 892 ± 504 to 1526 ± 517) and Bv60m(0.4 mm) series (ΔHU 480 ± 357 to 1030 ± 344). Improvement of lumen visibility and sharpness in UHR and Bv60m(0.4 mm) series was strongest in smaller stent sizes. CONCLUSION: UHR acquisition mode and sharp reconstruction kernels on a novel PCD-CT system significantly improve in-stent lumen visibility and sharpness-especially for smaller stent sizes. KEY POINTS: • In-stent lumen visibility and sharpness of stents significantly improve using sharp reconstruction kernels (Bv60) and ultra-high-resolution mode in photon-counting detector computed tomography. • The observed improvement of stent-lumen visibility was highest in smaller stent sizes.

Clinical applications of photon counting detector CT.

The X-ray detector is a fundamental component of a CT system that determines the image quality and dose efficiency. Until the approval of the first clinical photon-counting-detector (PCD) system in 2021, all clinical CT scanners used scintillating detectors, which do not capture information about individual photons in the two-step detection process. In contrast, PCDs use a one-step process whereby X-ray energy is converted directly into an electrical signal. This preserves information about individual photons such that the numbers of X-ray in different energy ranges can be counted. Primary advantages of PCDs include the absence of electronic noise, improved radiation dose efficiency, increased iodine signal and the ability to use lower doses of iodinated contrast material, and better spatial resolution. PCDs with more than one energy threshold can sort the detected photons into two or more energy bins, making energy-resolved information available for all acquisitions. This allows for material classification or quantitation tasks to be performed in conjunction with high spatial resolution, and in the case of dual-source CT, high pitch, or high temporal resolution acquisitions. Some of the most promising applications of PCD-CT involve imaging of anatomy where exquisite spatial resolution adds clinical value. These include imaging of the inner ear, bones, small blood vessels, heart, and lung. This review describes the clinical benefits observed to date and future directions for this technical advance in CT imaging. KEY POINTS: • Beneficial characteristics of photon-counting detectors include the absence of electronic noise, increased iodine signal-to-noise ratio, improved spatial resolution, and full-time multi-energy imaging. • Promising applications of PCD-CT involve imaging of anatomy where exquisite spatial resolution adds clinical value and applications requiring multi-energy data simultaneous with high spatial and/or temporal resolution. • Future applications of PCD-CT technology may include extremely high spatial resolution tasks, such as the detection of breast micro-calcifications, and quantitative imaging of native tissue types and novel contrast agents.

Dual-Energy CT Perfusion of Invasive Tumor Front in Non-Small Cell Lung Cancers.

Background Active endothelial cell proliferation occurs at the tumor edge, known as the invading-tumor front. This study focused on perfusion analysis of non-small cell lung cancers. Purpose To analyze dual-phase, dual-energy CT perfusion according to the degree of tumor hypoxia. Materials and Methods This prospective study was performed 2016-2017. A two-phase dual-energy CT protocol was obtained for consecutive participants with operable non-small cell lung cancer. The first pass and delayed iodine concentration within the tumor and normalized iodine uptake, corresponding to the iodine concentration within the tumor normalized to iodine concentration within the aorta, were calculated for the entire tumor and within three peripheral layers automatically segmented (ie, 2-mm-thick concentric subvolumes). The expression of the membranous carbonic anhydrase (mCA) IX, a marker of tumor hypoxia, was assessed in tumor specimens. Comparative analyses according to the histologic subtypes, type of resected tumors, and mCA IX expression were performed. Results There were 33 mCA IX-positive tumors and 16 mCA IX-negative tumors. In the entire tumor, the mean normalized iodine uptake was higher on delayed than on first-pass acquisitions (0.35 ± 0.17 vs 0.13 ± 0.15, respectively; P < .001). A single layer, located at the edge of the tumor, showed higher values of the iodine concentration (median, 0.53 mg/mL vs 0.21 mg/mL, respectively; P = .03) and normalized iodine uptake (0.04 vs 0.02, respectively; P = .03) at first pass in mCA IX-positive versus mCA IX-negative tumors. Within this layer, a functional profile of neovascularization was found in 23 of 33 (70%) of mCA IX-positive tumors, and the median mCA IX score of these tumors was higher than in tumors with a nonfunctional profile of neovascularization (median mCA IX score, 20 vs 2, respectively; P = .03). Conclusion A two-phase dual-energy CT examination depicted higher perfusion between the tumor edge and lung parenchyma in hypoxic tumors. © RSNA, 2021 Online supplemental material is available for this article. See also the editorial by Murphy and Ryan in this issue.

First Clinical Photon-counting Detector CT System: Technical Evaluation.

Background The first clinical CT system to use photon-counting detector (PCD) technology has become available for patient care. Purpose To assess the technical performance of the PCD CT system with use of phantoms and representative participant examinations. Materials and Methods Institutional review board approval and written informed consent from four participants were obtained. Technical performance of a dual-source PCD CT system was measured for standard and high-spatial-resolution (HR) collimations. Noise power spectrum, modulation transfer function, section sensitivity profile, iodine CT number accuracy in virtual monoenergetic images (VMIs), and iodine concentration accuracy were measured. Four participants were enrolled (between May 2021 and August 2021) in this prospective study and scanned using similar or lower radiation doses as their respective clinical examinations performed on the same day using energy-integrating detector (EID) CT. Image quality and findings from the participants' PCD CT and EID CT examinations were compared. Results All standard technical performance measures met accreditation and regulatory requirements. Relative to filtered back-projection reconstructions, images from iterative reconstruction had lower noise magnitude but preserved noise power spectrum shape and peak frequency. Maximum in-plane spatial resolutions of 125 and 208 µm were measured for HR and standard PCD CT scans, respectively. Minimum values for section sensitivity profile full width at half maximum measurements were 0.34 mm (0.2-mm nominal section thickness) and 0.64 mm (0.4-mm nominal section thickness) for HR and standard PCD CT scans, respectively. In a 120-kV standard PCD CT scan of a 40-cm phantom, VMI iodine CT numbers had a mean percentage error of 5.7%, and iodine concentration had root mean squared error of 0.5 mg/cm3, similar to previously reported values for EID CT. VMIs, iodine maps, and virtual noncontrast images were created for a coronary CT angiogram acquired with 66-msec temporal resolution. Participant PCD CT images showed up to 47% lower noise and/or improved spatial resolution compared with EID CT. Conclusion Technical performance of clinical photon-counting detector (PCD) CT is improved relative to that of a current state-of-the-art CT system. The dual-source PCD geometry facilitated 66-msec temporal resolution multienergy cardiac imaging. Study participant images illustrated the effect of the improved technical performance. © RSNA, 2022 Online supplemental material is available for this article. See also the editorial by Willemink and Grist in this issue.

Dual-Energy CT Vital Iodine Tumor Burden for Response Assessment in Patients With Metastatic GIST Undergoing TKI Therapy: Comparison With Standard CT and FDG PET/CT Criteria.

BACKGROUND. CT-based criteria for assessing the gastrointestinal stromal tumor (GIST) response to tyrosine kinase inhibitor (TKI) therapy are limited in part because tumor attenuation is influenced by treatment-related changes including hemorrhage and calcification. The iodine concentration may be less impacted by such changes. OBJECTIVE. The purpose of this study was to determine whether the dual-energy CT (DECT) vital iodine tumor burden (TB) allows improved differentiation between treatment responders and nonresponders among patients with metastatic GIST who are undergoing TKI therapy compared with established CT and PET/CT criteria. METHODS. An anthropomorphic phantom with spherical inserts mimicking GIST lesions of varying iodine concentrations and having nonenhancing central necrotic cores underwent DECT to determine a threshold iodine concentration. Forty patients (25 women and 15 men; median age, 57 years) who were treated with TKI for metastatic GIST were retrospectively evaluated. Patients underwent baseline and follow-up DECT and FDG PET/CT. Response assessment was performed using RECIST 1.1, modified Choi (mChoi) criteria, vascular tumor burden (VTB) criteria, DECT vital iodine TB criteria, and European Organization for Research and Treatment of Cancer (EORTC) PET criteria. DECT vital iodine TB criteria used the same percentage changes as RECIST 1.1 response categories. Progression-free survival was compared between responders and nonresponders for each response criterion by use of Cox proportional hazard ratios and Harrell C-indexes (i.e., concordance indexes). RESULTS. The phantom experiment identified a threshold of 0.5 mg/mL to differentiate vital from nonvital tissue. With use of the DECT vital iodine TB, median progression-free survival was significantly different between responders and nonresponders (623 vs 104 days; p < .001).. For nonresponders versus responders, the hazard ratio for disease progression for DECT vital iodine TB was 6.9 versus 7.6 for EORTC PET criteria, 3.3 for VTB criteria, 2.3 for RECIST 1.1, and 2.1 for mChoi criteria. The C-index was 0.74 for EORTC PET criteria, 0.73 for DECT vital iodine TB criteria, 0.67 for VTB criteria, 0.61 for RECIST 1.1, and 0.58 for mChoi criteria. The C-index was significantly greater for DECT vital iodine TB criteria than for RECIST 1.1 (p = .02) and mChoi criteria (p = .002), but it was not different from that for VTB and EORTC PET criteria (p > .05). CONCLUSION. DECT vital iodine TB criteria showed performance comparable to that of EORTC PET criteria and outperformed RECIST 1.1 and mChoi criteria for response assessment of metastatic GIST treated with TKI therapy. CLINICAL IMPACT. DECT vital iodine TB could help guide early management decisions in patients receiving TKI therapy.

Evaluating a calcium-aware kernel for CT CAC scoring with varying surrounding materials and heart rates: a dynamic phantom study.

OBJECTIVES: The purpose of this study was twofold. First, the influence of a novel calcium-aware (Ca-aware) computed tomography (CT) reconstruction technique on coronary artery calcium (CAC) scores surrounded by a variety of tissues was assessed. Second, the performance of the Ca-aware reconstruction technique on moving CAC was evaluated with a dynamic phantom. METHODS: An artificial coronary artery, containing two CAC of equal size and different densities (196 ± 3, 380 ± 2 mg hydroxyapatite cm-3), was moved in the center compartment of an anthropomorphic thorax phantom at different heart rates. The center compartment was filled with mixtures, which resembled fat, water, and soft tissue equivalent CT numbers. Raw data was acquired with a routine clinical CAC protocol, at 120 peak kilovolt (kVp). Subsequently, reduced tube voltage (100 kVp) and tin-filtration (150Sn kVp) acquisitions were performed. Raw data was reconstructed with a standard and a novel Ca-aware reconstruction technique. Agatston scores of all reconstructions were compared with the reference (120 kVp) and standard reconstruction technique, with relevant deviations defined as > 10%. RESULTS: For all heart rates, Agatston scores for CAC submerged in fat were comparable to the reference, for the reduced-kVp acquisition with Ca-aware reconstruction kernel. For water and soft tissue, medium-density Agatston scores were again comparable to the reference for all heart rates. Low-density Agatston scores showed relevant deviations, up to 15% and 23% for water and soft tissue, respectively. CONCLUSION: CT CAC scoring with varying surrounding materials and heart rates is feasible at patient-specific tube voltages with the novel Ca-aware reconstruction technique. KEY POINTS: • A dedicated calcium-aware reconstruction kernel results in similar Agatston scores for CAC surrounded by fatty materials regardless of CAC density and heart rate. • Application of a dedicated calcium-aware reconstruction kernel allows for radiation dose reduction. • Mass scores determined with CT underestimated physical mass.

Machine learning automatically detects COVID-19 using chest CTs in a large multicenter cohort.

OBJECTIVES: To investigate machine learning classifiers and interpretable models using chest CT for detection of COVID-19 and differentiation from other pneumonias, interstitial lung disease (ILD) and normal CTs. METHODS: Our retrospective multi-institutional study obtained 2446 chest CTs from 16 institutions (including 1161 COVID-19 patients). Training/validation/testing cohorts included 1011/50/100 COVID-19, 388/16/33 ILD, 189/16/33 other pneumonias, and 559/17/34 normal (no pathologies) CTs. A metric-based approach for the classification of COVID-19 used interpretable features, relying on logistic regression and random forests. A deep learning-based classifier differentiated COVID-19 via 3D features extracted directly from CT attenuation and probability distribution of airspace opacities. RESULTS: Most discriminative features of COVID-19 are the percentage of airspace opacity and peripheral and basal predominant opacities, concordant with the typical characterization of COVID-19 in the literature. Unsupervised hierarchical clustering compares feature distribution across COVID-19 and control cohorts. The metrics-based classifier achieved AUC = 0.83, sensitivity = 0.74, and specificity = 0.79 versus respectively 0.93, 0.90, and 0.83 for the DL-based classifier. Most of ambiguity comes from non-COVID-19 pneumonia with manifestations that overlap with COVID-19, as well as mild COVID-19 cases. Non-COVID-19 classification performance is 91% for ILD, 64% for other pneumonias, and 94% for no pathologies, which demonstrates the robustness of our method against different compositions of control groups. CONCLUSIONS: Our new method accurately discriminates COVID-19 from other types of pneumonia, ILD, and CTs with no pathologies, using quantitative imaging features derived from chest CT, while balancing interpretability of results and classification performance and, therefore, may be useful to facilitate diagnosis of COVID-19. KEY POINTS: • Unsupervised clustering reveals the key tomographic features including percent airspace opacity and peripheral and basal opacities most typical of COVID-19 relative to control groups. • COVID-19-positive CTs were compared with COVID-19-negative chest CTs (including a balanced distribution of non-COVID-19 pneumonia, ILD, and no pathologies). Classification accuracies for COVID-19, pneumonia, ILD, and CT scans with no pathologies are respectively 90%, 64%, 91%, and 94%. • Our deep learning (DL)-based classification method demonstrates an AUC of 0.93 (sensitivity 90%, specificity 83%). Machine learning methods applied to quantitative chest CT metrics can therefore improve diagnostic accuracy in suspected COVID-19, particularly in resource-constrained environments.

Quantitative lobar pulmonary perfusion assessment on dual-energy CT pulmonary angiography: applications in pulmonary embolism.

PURPOSE: To assess quantitative lobar pulmonary perfusion on DECT-PA in patients with and without pulmonary embolism (PE). MATERIALS AND METHODS: Our retrospective study included 88 adult patients (mean age 56 ± 19 years; 38 men, 50 women) who underwent DECT-PA (40 PE present; 48 PE absent) on a 384-slice, third-generation, dual-source CT. All DECT-PA examinations were reviewed to record the presence and location of occlusive and non-occlusive PE. Transverse thin (1 mm) DECT images (80/150 kV) were de-identified and exported offline for processing on a stand-alone deep learning-based prototype for automatic lung lobe segmentation and to obtain the mean attenuation numbers (in HU), contrast amount (in mg), and normalized iodine concentration per lung and lobe. The zonal volumes and mean enhancement were obtained from the Lung Analysis™ application. Data were analyzed with receiver operating characteristics (ROC) and analysis of variance (ANOVA). RESULTS: The automatic lung lobe segmentation was accurate in all DECT-PA (88; 100%). Both lobar and zonal perfusions were significantly lower in patients with PE compared with those without PE (p < 0.0001). The mean attenuation numbers, contrast amounts, and normalized iodine concentrations in different lobes were significantly lower in the patients with PE compared with those in the patients without PE (AUC 0.70-0.78; p < 0.0001). Patients with occlusive PE had significantly lower quantitative perfusion compared with those without occlusive PE (p < 0.0001). CONCLUSION: The deep learning-based prototype enables accurate lung lobe segmentation and assessment of quantitative lobar perfusion from DECT-PA. KEY POINTS: • Deep learning-based prototype enables accurate lung lobe segmentation and assessment of quantitative lobar perfusion from DECT-PA. • Quantitative lobar perfusion parameters (AUC up to 0.78) have a higher predicting presence of PE on DECT-PA examinations compared with the zonal perfusion parameters (AUC up to 0.72). • The lobar-normalized iodine concentration has the highest AUC for both presence of PE and for differentiating occlusive and non-occlusive PE.

Detection of insulinoma: one-stop pancreatic perfusion CT with calculated mean temporal images can replace the combination of bi-phasic plus perfusion scan.

OBJECTIVE: To evaluate the feasibility of one-stop pancreatic perfusion CT with mean temporal (MT) imaging replacing the combination of a bi-phasic scan plus a perfusion scan to detect insulinoma. MATERIAL AND METHODS: Forty-five patients with suspected insulinoma, who underwent both biphasic and perfusion CT, were enrolled in this retrospective study. MT datasets including images for different delineation purposes were generated by averaging 3 dynamic datasets from perfusion CT, which are MTA for arterial, MTPV for portal vein and MTO for lesions. Two readers assessed the image quality and diagnostic performance separately for biphasic and MT datasets. Radiation doses were also assessed. Paired t tests, Wilcoxon signed-rank tests and McNemar's tests were applied for comparison. RESULTS: Compared with bi-phasic CT images, image noise, SNR and CNR of the MTA and MTPV datasets were all non-inferior (noise and CNR of the portal vein, p = 0.565 and p = 0.227, respectively) or superior (p ≤ 0.001). The subjective image quality was better in the MTA and MTPV images (p < 0.001 to p = 0.004). The sensitivity and NPV of MT images were also better (95% vs 75% and 75% vs 37.5% for reader 1; 97.5% vs 72.5% and 85.7% vs 35.3% for reader 2). Omitting the bi-phasic scan resulted in a dose reduction of 25% ± 4%. CONCLUSION: MT imaging can allow pancreatic perfusion CT to be used alone without the need for an additional bi-phasic CT in the detection of insulinoma. KEY POINTS: • Mean temporal images reconstructed from perfusion CT with an averaging technique reproduce usual bi-phasic images (arterial and portal phases). • The image quality of mean temporal images is non-inferior or superior to native bi-phasic CT. The sensitivity and NPV for the diagnosis of insulinoma are better for mean temporal images than for traditional bi-phasic CT. • Mean temporal imaging can allow pancreatic perfusion CT to be used alone without the need for an additional bi-phasic CT in the detection of insulinoma. Radiation dose saving is important.

Pediatric chest computed tomography at 100 kVp with tin filtration: comparison of image quality with 70-kVp imaging at comparable radiation dose.

BACKGROUND: Radiation dose reduction is a primary objective in pediatric populations owing to the well-known risks of radiation-induced cancers. Low-energy photons participate in the radiation dose without significantly contributing to image formation. Their suppression by means of tin filtration should decrease the image noise, anticipating a subsequent application to dose saving. OBJECTIVE: To investigate the level of noise reduction achievable with tin (Sn) filtration at 100 kVp for chest computed tomography (CT) in comparison with a standard scanning mode at 70 kVp with comparable radiation dose. MATERIALS AND METHODS: Fifty consecutive children (Group 1) underwent non-contrast chest CT examinations on a third-generation dual-source CT system at tin-filtered 100 kVp and pitch 2. The tube-current time product (mAs) was adjusted to maintain the predicted dose length product (DLP) value at 70 kVp for the respective patient. Each child was then paired by weight and age to a child scanned at 70 kVp on the same CT unit (Group 2); Group 2 patients were consecutive patients, retrospectively selected from our database of children prospectively scanned at 70 kVp. Objective and subjective image quality were compared between the two groups of patients to investigate the overall image quality and level of noise reduction that could be subsequently achievable with tin filtration in clinical practice. RESULTS: The mean image noise was significantly lower in Group 1 compared to Group 2 when measured in the air (P<0.0001) and inside the aorta (P<0.001). The mean noise reduction was 21.6% (standard deviation [SD] 16.1) around the thorax and 12.0% (SD 32.7) inside the thorax. There was no significant difference in subjective image quality of lung and mediastinal images with excellent overall subjective scores in both groups. CONCLUSION: At comparable radiation dose, the image noise was found to be reduced by 21.6% compared to the 70-kVp protocol, providing basis for dose reduction without altering image quality in further investigations.

CT Angiography of the Aorta: Contrast Timing by Using a Fixed versus a Patient-specific Trigger Delay.

Background Optimal timing of the CT scan relative to the contrast media bolus remains a challenging task given the shorter scan durations of modern CT scanners, as well as interpatient variability. Purpose To compare contrast opacification in CT angiography of the aorta between a cohort with fixed trigger delay and a cohort with patient-specific individualized trigger delay for contrast media timing with bolus tracking. Materials and Methods In this prospective study (January-August 2018), CT angiography of the thoracoabdominal aorta with bolus tracking was performed in two different study cohorts: one with a fixed trigger delay of 4 seconds (fixed cohort) and one with a patient-specific trigger delay (individualized cohort). All CT and contrast media protocol parameters were kept identical among cohorts. Objective image quality was evaluated by one reader; two readers assessed subjective image quality. Student t test was used to test for differences in mean attenuation; the Wilcoxon-Mann-Whitney test was used to test for differences in noise, contrast-to-noise ratio, and subjective image quality. Results The fixed cohort had 108 study participants (16 women; mean age ± standard deviation, 72 years ± 10); the individualized cohort had 108 participants (16 women; mean age, 72 years ± 12). The trigger delay in the individualized cohort ranged from 6.4-11.3 seconds (mean, 9.2 seconds). There was higher overall attenuation in the individualized cohort than in the fixed cohort (486 HU ± 92 for individualized vs 438 HU ± 99 for fixed; P < .001), with increasing differences from the aortic arch (8 HU) to the iliac arteries (95 HU). The regression model indicated uniform attenuation in the individualized cohort and decreasing attenuation in the fixed cohort (decrease of 87 HU by the iliac arteries; P < .001). There was no difference between cohorts for image noise (20 vs 19; P = .41), but contrast-to-noise ratio (21 vs 19; P = .04) and subjective image quality were higher in the individualized cohort than in the fixed cohort (excellent or good image quality, 100% vs 67%; P < .001). Conclusion Compared with a fixed delay time after bolus tracking, a patient-specific individualized trigger delay improves image quality and provides uniform contrast attenuation for CT angiography of the aorta. ©RSNA, 2019.

Accuracy of iodine quantification using dual energy CT in latest generation dual source and dual layer CT.

OBJECTIVE: To determine the accuracy of iodine quantification with dual energy computed tomography (DECT) in two high-end CT systems with different spectral imaging techniques. METHODS: Five tubes with different iodine concentrations (0, 5, 10, 15, 20 mg/ml) were analysed in an anthropomorphic thoracic phantom. Adding two phantom rings simulated increased patient size. For third-generation dual source CT (DSCT), tube voltage combinations of 150Sn and 70, 80, 90, 100 kVp were analysed. For dual layer CT (DLCT), 120 and 140 kVp were used. Scans were repeated three times. Median normalized values and interquartile ranges (IQRs) were calculated for all kVp settings and phantom sizes. RESULTS: Correlation between measured and known iodine concentrations was excellent for both systems (R = 0.999-1.000, p < 0.0001). For DSCT, median measurement errors ranged from -0.5% (IQR -2.0, 2.0%) at 150Sn/70 kVp and -2.3% (IQR -4.0, -0.1%) at 150Sn/80 kVp to -4.0% (IQR -6.0, -2.8%) at 150Sn/90 kVp. For DLCT, median measurement errors ranged from -3.3% (IQR -4.9, -1.5%) at 140 kVp to -4.6% (IQR -6.0, -3.6%) at 120 kVp. Larger phantom sizes increased variability of iodine measurements (p < 0.05). CONCLUSION: Iodine concentration can be accurately quantified with state-of-the-art DECT systems from two vendors. The lowest absolute errors were found for DSCT using the 150Sn/70 kVp or 150Sn/80 kVp combinations, which was slightly more accurate than 140 kVp in DLCT. KEY POINTS: • High-end CT scanners allow accurate iodine quantification using different DECT techniques. • Lowest measurement error was found in scans with largest photon energy separation. • Dual-source CT quantified iodine slightly more accurately than dual layer CT.

Feasibility of spectral shaping for detection and quantification of coronary calcifications in ultra-low dose CT.

OBJECTIVES: To evaluate detectability and quantification of coronary calcifications for CT with a tin filter for spectral shaping. METHODS: Phantom inserts with 100 small and 9 large calcifications, and a moving artificial artery with 3 calcifications (speed 0-30 mm/s) were placed in a thorax phantom simulating different patient sizes. The phantom was scanned in high-pitch spiral mode at 100 kVp with tin filter (Sn100 kVp), and at a reference of 120 kVp, with electrocardiographic (ECG) gating. Detectability and quantification of calcifications were analyzed for standard (130 HU) and adapted thresholds. RESULTS: Sn100 kVp yielded lower detectability of calcifications (9 % versus 12 %, p = 0.027) and lower Agatston scores (p < 0.008), irrespective of calcification, patient size and speed. Volume scores of the moving calcifications for Sn100 kVp at speed 10-30 mm/s were lower (p < 0.001), while mass scores were similar (p = 0.131). For Sn100 kVp with adapted threshold of 117 HU, detectability (p = 1.000) and Agatston score (p > 0.206) were similar to 120 kVp. Spectral shaping resulted in median dose reduction of 62.3 % (range 59.0-73.4 %). CONCLUSIONS: Coronary calcium scanning with spectral shaping yields lower detectability of calcifications and lower Agatston scores compared to 120 kVp scanning, for which a HU threshold correction should be developed. KEY POINTS: • Sn100kVp yields lower detectability and lower Agatston scores compared to 120kVp • Adapted HU threshold for Sn100kVp provides Agatston scores comparable to 120kVp • Sn100 kVp considerably reduces dose in calcium scoring versus 120 kVp.

Dual-Phase Dual-Energy CT in Patients Treated with Erlotinib for Advanced Non-Small Cell Lung Cancer: Possible Benefits of Iodine Quantification in Response Assessment.

OBJECTIVES: To investigate the relationship of dual-phase dual-energy CT (DE-CT) and tumour size in the evaluation of the response to anti-EGFR therapy in patients with advanced non-small cell lung cancer (NSCLC). METHODS: Dual-phase DE-CT was performed in 31 patients with NSCLC before the onset of anti-EGFR (erlotinib) therapy and as follow-up (mean 8 weeks). Iodine uptake (IU; mg/mL) was quantified using prototype software in arterial and venous phases; arterial enhancement fraction (AEF) was calculated. The change of IU before and after therapy onset was compared with anatomical evaluation in maximal transverse diameter and volume (responders vs. non-responders). RESULTS: A significant decrease of IU in venous phase was proved in responders according to all anatomical parameters (p=0.002-0.016). In groups of non-responders, a significant change of IU was not proved with variable trends of development. The most significant change was observed using the anatomical parameter of volume (cut-off 73 %). A significant difference of percentage change in AEF was proved between responding and non-responders (p=0.019-0.043). CONCLUSION: Dual-phase DE-CT with iodine uptake quantification is a feasible method with potential benefit in advanced assessment of anti-EGFR therapy response. We demonstrated a decrease in vascularization in the responding primary tumours and non-significant variable development of vascularization in non-responding tumours. KEY POINTS: • Dual-phase DE-CT is feasible for vascularization assessment of NSCLC with anti-EGFR therapy. • There was a significant decrease of iodine uptake in responding tumours. • There was a non-significant and variable development in non-responding tumours. • There was significant difference of AEF percentage change between responders and non-responders.

Is bronchial wall imaging affected by temporal resolution? comparative evaluation at 140 and 75 ms in 90 patients.

PURPOSE: To evaluate the influence of temporal resolution (TR) on cardiogenic artefacts at the level of bronchial walls. MATERIAL AND METHODS: Ninety patients underwent a dual-source, single-energy chest CT examination enabling reconstruction of images with a TR of 75 ms (i.e., optimized TR) (Group 1) and 140 ms (i.e., standard TR) (Group 2). Cardiogenic artefacts were analyzed at the level of eight target bronchi, i.e., right (R) and left (L) B1, B5, B7, and B10 (total number of bronchi examined: n = 720). RESULTS: Cardiogenic artefacts were significantly less frequent and less severe in Group 1 than in Group 2 (p < 0.0001) with the highest scores of discordant ratings for bronchi in close contact with cardiac cavities: RB5 (61/90; 68%); LB5 (66/90; 73%); LB7 (63/90; 70%). In Group 1, 78% (560/720) of bronchi showed no cardiac motion artefacts, whereas 22% of bronchi (160/720) showed artefacts rated as mild (152/160; 95%), moderate (7/160; 4%), and severe (1/160; 1%). In Group 2, 70% of bronchi (503/720) showed artefacts rated as mild (410/503; 82%), moderate (82/503; 16%), and severe (11/503; 2%). CONCLUSION: At 75 ms, most bronchi can be depicted without cardiogenic artefacts. KEY POINTS: • Quantitative CT helps analyze morphologic changes in COPD patients • Cardiogenic artefacts may hamper precise analysis of bronchial dimensions • Temporal resolution of CT acquisitions is an important parameter for bronchial imaging.