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• Pancreatic, renal, and appendicular inflammatory processes have different optimal windows. Window setting of 150HU:440HU represents an ideal compromise for detecting pancreatitis and pyelonephritis. • Windowing for solid parenchyma organs is higher than mucosal enhancement and background structures whose optimal detection occurs at manufacturer recommended settings of (50HU:380HU). • Simplex optimization may offer a robust method to tailor window settings to enable better lesion conspicuity compared to default manufacturer window settings, potentially improving diagnostic accuracy. To determine optimal window settings for conspicuity of abdominal inflammatory processes on 50 keV low-monoenergetic images derived from dual-energy spectral CT (DECT). A retrospective study of 30 patients with clinically proven pancreatitis (15/30) or pyelonephritis (15/30) with inflammatory lesions visible on DECT scans were selected to serve as reference populations. 50 keV low-monoenergetic images in the portal venous phase were iteratively evaluated by 6 abdominal radiologists in twenty-one different windows (7-350HU center; 120-580HU width), selected using a simplex optimization algorithm. Each reader graded the conspicuity of the parenchymal hypodense lesions and image background quality. Three-dimensional contour maps expressing the relationship between overall reader grade and window center and width were constructed and used to find the ideal window for inflammatory pancreatic and renal processes and the image background quality. Finally, 15 appendicitis cases were reviewed on optimal pancreas and kidney windows and the manufacturer recommended conventional abdominal window settings for conventional imaging. Convergence to optimal windowing was achieved based upon a total of 3,780 reads (21 window settings × 6 readers × 15 cases for pancreas and kidney). Highest conspicuity grade (>4.5 ± 0.0) for pancreas inflammatory lesions was seen at 116HU/430HU, whereas hypodense pyelonephritis had highest conspicuity at 290HU/570HU. This rendered an ideal "compromise" window (>4 ± 0.2) of 150HU/450HU which differed substantially from conventional manufacturer recommended settings of 50HU/380HU (2.1 ± 1.0, p = 0.00001). Appendix mucosal enhancement was best visualized at manufacturer settings. Optimal visualization of inflammatory processes in abdominal organs on 50 keV low-monoenergetic images may require tailored refinement of window settings. [ABSTRACT FROM AUTHOR]

• Metal artifact are common and decrease diagnostic value of CT images. • Effectiveness of DECT and MAR algorithms depends on metal implant type. • Recommendations for DECT and MAR algorithms are provided for implant categories. • Photon counting CT provides better image quality than DECT. • Results of deep learning based metal artifacts reduction algorithms are promising. Metal artifacts degrade CT image quality, hampering clinical assessment. Numerous metal artifact reduction methods are available to improve the image quality of CT images with metal implants. In this review, an overview of traditional methods is provided including the modification of acquisition and reconstruction parameters, projection-based metal artifact reduction techniques (MAR), dual energy CT (DECT) and the combination of these techniques. Furthermore, the additional value and challenges of novel metal artifact reduction techniques that have been introduced over the past years are discussed such as photon counting CT (PCCT) and deep learning based metal artifact reduction techniques. [ABSTRACT FROM AUTHOR]

• Ultrasound is the gold standard imaging modality for the evaluation of thyroid lesions. Thyroid Imaging Reporting and Data System divides thyroid lesions into high risk (TI-RADS 4–5) and low-risk (TI-RADS 2–3) nodules. • Conventional CT images are not reliable for the characterization thyroid nodules. • Spectral Detector Computed Tomography (SDCT) results may assist in differentiating high risk from low risk nodules. • High risk thyroid nodules demonstrate higher estimated enhancement compared to low risk nodules. To characterize thyroid nodules seen on Spectral Detector computed tomography (SDCT) in respect to their Thyroid Imaging Reporting and Data System (TI-RADS) category on Ultrasound (US). We included patients that underwent US examination for the evaluation of thyroid nodules and contrast-enhanced SDCT examination of the neck/thorax, between the years 2018–2020. The SDCT and US were performed within 6 months of each other. Only patients with a visible thyroid nodule on SDCT were included. Attenuation measurements of the nodules in Hounsfield units (HU) were performed on the conventional CT images, virtual non-contrast (VNC) images and virtual monoenergetic images of 40 keV and 100 keV. The Iodine concentration, spectral slope and enhancement estimation results of the nodules were measured. We compared the spectral results between two groups of nodules, according to the US report: TI-RADS 2–3 and TI-RADS 4–5 groups. Thirty-eight nodules were included in the study, 22 nodules in the TI-RADS 2–3 group and 16 in the TI-RADS 4–5 group. The nodules of the TI-RADS 4–5 group had significantly higher Iodine concentration measurement, 4.6 ± 1.8 mg/ml, compared to 2.3 ± 1.2 mg/ml in the TI-RADS 2–3 group; significantly higher estimated enhancement, 3.9 ± 1.5, compared to 2.2 ± 0.7; and significantly higher calculated spectral slope, 5.6 ± 2.2 compared to 2.9 ± 1.5 (p < 0.001). Spectral results of SDCT may assist in differentiating intermediate-high risk (TI-RADS 4–5) from low risk (TI-RADS 2–3) thyroid nodules. Advances in knowledge: SDCT offers additional information for the characterization of thyroid nodules. [ABSTRACT FROM AUTHOR]

Objectives: To compare objective and subjective image quality between low keV virtual monoenergetic images (VMI) of the excretory phase and conventional venous phase images derived from spectral dual-energy CT (DECT) in the assessment of urothelial carcinoma.Methods: 26 consecutive patients with histologically confirmed urothelial carcinoma who received clinically indicated venous- and excretory phase abdominal CT scans were included retrospectively. Attenuation, image noise as well as signal- and contrast-to-noise-ratio (SNR, CNR) in venous and excretory phase CT and excretory phase VMI from 40 to 70 keV were obtained from ROI-based measurements in the following regions: urothelial carcinoma, liver, pancreas, renal cortex, subcutaneous fat, renal vein/artery, portal vein, urinary bladder wall, lymph nodes, prostate/uterus. Subjective vessel contrast and delineation of primary tumor manifestations and distant metastases were rated on 5-point Likert scales.Results: In comparison to venous phase CT, attenuation and SNR in excretory phase VMI40keV were higher (p < 0.001), except for liver parenchyma, where they were comparable (p = 0.07 and p = 0.17, respectively). Regarding image noise, no significant difference was found between venous phase CT and excretory phase VMI40keV (p-range: 0.08-1.00), except for liver, portal vein and renal artery, where it was lower in VMI40keV (p < 0.05). CNR of urothelial carcinoma to circumjacent bladder wall was significantly higher in excretory phase VMI40keV compared to venous phase CT. Subjective vessel contrast and delineation of primary tumor and distant metastases received equivalent or higher Likert scores in excretory phase VMI40keV than in venous phase CT.Conclusion: This feasibility study indicates that in the assessment of urothelial carcinoma, virtual monoenergetic excretory phase images at 40 keV acquired with spectral DECT could be feasible to maintain subjective and objective image quality as provided by conventional venous phase images. Still, equivalence with regards to metastatic lesion detection requires further investigation before employing this technique in a potential signal-scan, single-bolus approach. [ABSTRACT FROM AUTHOR]

Background: The aim of this study was to assess the potential of rest-stress DECT iodine quantification to discriminate between normal, ischemic, and infarcted myocardium.Methods: Patients who underwent rest-stress DECT on a 2nd generation dual-source system and cardiac magnetic resonance (CMR) were retrospectively included from a prospective study cohort. CMR was performed to identify ischemic and infarcted myocardium and categorize patients into ischemic, infarcted, and control groups. Controls were analyzed on a per-slice and per-segment basis. Regions of interest (ROIs) were placed in ischemic and infarcted areas based on CMR. Additionally, ROIs were placed in the septal area to assess normal and remote myocardium.Results: We included 42 patients: 10 ischemic, 17 infarcted, and 15 controls. Iodine concentrations showed no significant between segments in controls. Iodine concentrations for normal myocardium increased significantly from rest to stress (median 3.7 mg/mL (interquartile range 3.5-3.9) vs. 4.5 mg/mL (4.3-4.9)) (p < 0.001). Iodine concentrations in diseased myocardium were significantly lower than in normal myocardium; 1.3 mg/mL (0.9-1.8) and 0.6 mg/mL (0.4-0.8) at rest and stress in ischemic myocardium, and 0.3 mg/mL (0.3-0.5) and 0.5 mg/mL (0.5-0.7) at rest and stress in infarcted myocardium (p < 0.005 and p < 0.001). At rest only, iodine concentrations were significantly lower in infarcted vs. ischemic myocardium (p < 0.001). The optimal threshold for differentiating diseased from normal myocardium was 2.5 mg/mL and 2.1 mg/mL for rest and stress (AUC 1.00). To discriminate ischemic from infarcted myocardium, the optimal threshold was 1.0 mg/ml (AUC 0.944) at rest.Conclusion: DECT iodine concentration from rest-stress imaging can potentially differentiate between normal, ischemic, and infarcted myocardium. [ABSTRACT FROM AUTHOR]

Objective: To assess virtual non-enhanced dual energy computed tomography (DECT) reconstruction as a potential alternative to true non-enhanced thoracic and abdominal CT scans in patients with suspected active hemorrhage.Methods and Materials: Ninety-seven consecutive patients with suspected active bleeding, who underwent routine triphasic CT with intravenous contrast, were included. All patients underwent single energy non-enhanced (TNE) and arterial phase CT as well as venous DECT. Using commercially available software, venous dual energy images were used to generate virtual non-enhanced images (VNE). TNE and VNE were evaluated regarding subjective image quality and diagnostic confidence on a 5-point-scale. The consistency of interpretation with respect to presence and type of hemorrhage between conventional triphasic CT including TNE and biphasic CT with simulated VNE was assessed by two blinded independent readers.Results: Among the included subjects (mean age: 66.3 ± 14.5 years, 63.9% male), 37.1% were diagnosed with acute hemorrhage. VNE yielded significantly lower image quality but superior reduction of artefacts as compared to TNE (p ≤ 0.001). Diagnostic confidence was rated high for both TNE and VNE with a significant superiority of TNE (p = 0.003). Triphasic and biphasic CT datasets yielded perfect intrareader agreement regarding presence and type of hemorrhage. The interrater agreement was almost perfect (K = 0.955). Radiation dose was significantly reduced using biphasic dual energy CT with VNE (p ≤ 0.001).Conclusion: Virtual non-enhanced images yield comparable diagnostic confidence and perfect agreement with true non-enhanced images for assessment of acute hemorrhage. This suggests that true non-enhanced images could be replaced by virtual non-enhanced images resulting in a significant reduction of radiation dose. [ABSTRACT FROM AUTHOR]

Objectives: To investigate the utilization of virtual mono-energetic images (MonoE) at low kiloelectron volt (keV) levels derived from a dual-layer spectral detector CT (SDCT) for the assessment of abdominal arteries in venous contrast phase scans using arterial phase imaging as an internal reference standard.Materials and Methods: A total of 50 patients who received arterial and venous phase imaging of the abdomen on a SDCT system were included in this study. Absolute attenuation, noise, signal- and contrast to noise ratios (SNR; CNR) as well as arterial diameters in defined landmarks were assessed. In arterial phase, conventional reconstructions (CRART) as well as MonoEART at 40keV and in venous phase, conventional reconstructions (CRVEN) as well as MonoEVEN at 70 and 40keV were investigated and intra-individual comparisons were performed. If an artery stenosis (10 patients) was present, the degree of stenosis was assessed according to the system of the North American Symptomatic Carotid Endarterectomy Trial (NASCET).Results: MonoE 40keV yielded significantly higher attenuation values (in arterial as well as in venous phase) compared to CRART (p<0.001) while noise levels were substantially low. This resulted in markedly superior SNR and CNR in large vessel compared to CRART. Luminal diameters were significantly smaller in MonoE 40keV in both contrast phases compared to CRART (p<0.001), whereas no significant differences were found between both MonoE reconstructions (p≥0.92). The degree of vessel stenosis was significantly higher in MonoE 40keV of both contrast phases compared to CRART (p≥0.02).Conclusion: MonoE at low keV of venous contrast phase scans derived from a novel SDCT are suitable for the assessment of arteries in the abdomen and subsequent stenosis assessment. However, MonoE at 40keV constantly showed significant smaller luminal diameters than the corresponding conventional reconstructions (including the reference standard). This is possibly due to an improved differentiation of the vessel lumen from the wall and raises the question, which imaging technique should be used as an appropriate reference standard for vascular SDCT imaging studies. [ABSTRACT FROM AUTHOR]

Objective: To evaluate the influence of monoenergetic reconstructions using a spectral detector CT (SDCT) on the computer aided detection (CAD) of pulmonary artery embolism (PAE) on CT pulmonary angiography (CTPA) and CT in venous contrast phase (CTV).Material and Methods: A retrospective data base search identified 15 patients with CTPA and 18 patients with CTV and diagnosis of PAE. For these patients, monoenergetic (monoE) images at different energy levels or with a fixed attenuation in the pulmonary artery were generated and independently analyzed using a commercially available computer aided detection (CAD) tool. Attenuation in the pulmonary artery and in the embolus was measured.Results: For CTPA and CTV, in monoenergetic images the difference in attenuation between vessel and embolus was significantly higher than in conventional images. In CTPA the detection rate was highest in the >500 HU monoE images with 67,9% detected emboli and 93,3% of patients correctly identified as having PAE. At the same time the false positive rate could be significantly reduced by using monoE images compared to conventional images. Detection rates for CTV were lower than in CTPA but were raised significantly by monoE reconstructions.Conclusions: The combination of SDCT and CAD improves the diagnostic accuracy of CAD and enables CAD interpretation of CTV. [ABSTRACT FROM AUTHOR]

Objective: Metastatic disease in melanoma has an unpredictable nature with deposits in rare locations such as musculature. Dual energy CT (DECT) provides high contrast-visualization of enhancement by using spectral properties of iodine. Purpose of this study was to evaluate whether iodine maps from DECT improve lesion detection in staging examinations of melanoma patients.Methods: This retrospective study was approved by IRB and written informed consent was obtained from all patients. 75 contrast-enhanced DECT scans (thorax and abdomen) from 75 melanoma patients (n=69 stage IV; n=6 stage III) were analysed. For each patient, conventional CT and iodine maps were reviewed independently by two radiologists. The number of lesions detected by reviewing the iodine maps following conventional CT was recorded. Unweighted Cohens Kappa coefficient (κ) was used for concordance analysis, Wilcoxon test for comparing lesion detection rates.Results: In 26 patients, at least one reader found additional lesions on iodine maps (inter-reader agreement 89%, κ=0.74 (0.742-0.747)). Compared to grey-scale images, mean detection rate for metastases improved from 86% (range 82-90) to 94% (90-99%) (p≤0.01), for muscle metastases from 8% (8-8%) to 99% (98-100%) (p≤0.06). Findings included 2 pulmonary emboli.Conclusion: Iodine maps from DECT improve detection of metastases, especially muscle metastases, and relevant findings in staging examinations of melanoma patients. [ABSTRACT FROM AUTHOR]

Objective: To determine the optimal monochromatic energy level for lung parenchyma analysis in spectral CT.Methods: All 50 examinations (58% men, 64.8±16yo) from an IRB-approved prospective study on single-source dual energy chest CT were retrospectively included and analyzed. Monochromatic images in lung window reconstructed every 5keV from 40 to 140keV were independently assessed by two chest radiologists. Based on the overall image quality and the depiction/conspicuity of parenchymal lesions, each reader had to designate for every patient the keV level providing the best diagnostic and image quality.Results: 72% of the examinations exhibited parenchymal lesions. Reader 1 picked the 55keV monochromatic reconstruction in 52% of cases, 50 in 30% and 60 in 18%. Reader 2 chose 50keV in 52% cases, 55 in 40%, 60 in 6% and 40 in 2%. The 50 and 55keV levels were chosen by at least one reader in 64% and 76% of all patients, respectively. Merging 50 and 55keV into one category results in an optimal setting selected by reader 1 in 82% of patients and by reader 2 in 92%, with a 74% concomitant agreement.Conclusion: The best image quality for lung parenchyma in spectral CT is obtained with the 50-55keV monochromatic reconstructions. [ABSTRACT FROM AUTHOR]

• We compared different dual energy technologies, including dual source and beam filtration techniques (TwinBeam). • We used a dual energy phantom with reference values of Iodine concentration, atomic number and electron density. • The quantification of low Iodine content in lung nodules has high uncertainty that limits its clinical applicability. • We took into account the variability due acquisition and reconstruction parameters. To evaluated the accuracy of spectral parameters quantification of four different CT scanners in dual energy examinations of the lung using a dedicated phantom. Measurements were made with different technologies of the same vendor: one dual source CT scanner (DSCT), one TwinBeam (i.e. split filter) and two sequential acquisition single source scanners (SSCT). Angular separation of Calcium and Iodine signals were calculated from scatter plots of low-kVp versus high-kVp HUs. Electron density (ρe), effective atomic number (Zeff) and Iodine concentration (Iconc) were measured using Syngo.via software. Accuracy (A) of ρe, Zeff and Iconc was evaluated as the absolute percentage difference (D%) between reference values and measured ones, while precision (P) was evaluated as the variability σ obtained by repeating the measurement with different acquisition/reconstruction settings. Angular separation was significantly larger for DSCT (α = 9.7°) and for sequential SSCT (α = 9.9°) systems. TwinBeam was less performing in material separation (α = 5.0°). The lowest average A was observed for TwinBeam (A ρe = [4.7 ± 1.0], A Z = [9.1 ± 3.1], A Iconc = [19.4 ± 4.4]), while the best average A was obtained for Flash (A ρe = [1.8 ± 0.4], A Z = [3.5 ± 0.7], A Iconc = [7.3 ± 1.8]). TwinBeam presented inferior average P (P ρe = [0.6 ± 0.1], P Z = [1.1 ± 0.2], P Iconc = [10.9 ± 4.9]), while other technologies demonstrate a comparable average. Different technologies performed material separation and spectral parameter quantification with different degrees of accuracy and precision. DSCT performed better while TwinBeam demonstrated not excellent performance. Iodine concentration measurements exhibited high variability due to low Iodine absolute content in lung nodules, thus limiting its clinical usefulness in pulmonary applications. [ABSTRACT FROM AUTHOR]

Computed tomography pulmonary angiography (CTPA) has become the primary imaging modality for evaluating the pulmonary arteries. Although pulmonary embolism is the primary indication for CTPA, various pulmonary vascular abnormalities can be detected in adults. Knowledge of these disease entities and understanding technical pitfalls that can occur when performing CTPA are essential to enable accurate diagnosis and allow timely management. This review will cover a spectrum of acquired abnormalities including pulmonary embolism due to thrombus and foreign bodies, primary and metastatic tumor involving the pulmonary arteries, pulmonary hypertension, as well as pulmonary artery aneurysms and stenoses. Additionally, methods to overcome technical pitfalls and interventional treatment options will be addressed. [ABSTRACT FROM AUTHOR]

Purpose: In patients with small bowel obstruction (SBO), it is challenging to detect early ischemia. The purpose of this study is to evaluate the quantitative and qualitative benefits of virtual monoenergetic image (VMI) reconstruction in the assessment of small bowel mural enhancement on dual source dual energy computed tomography (CT) scans of the abdomen. Materials and Methods: Institutional review board approval was obtained, for this retrospective analysis. 72 consecutive patients with acute SBO were scanned using a second generation 128-slice dual source, CT system. Images were reconstructed at VMI energy levels from 40 to 110keV in 10keV increments and were analysed quantitatively and qualitatively. Contrast to noise ratios (CNR) and signal to noise ratios (SNR) for mural enhancement were recorded for all VMI datasets and compared to conventional polychromatic images (PCI) at 120kVp. Subjective analysis of mural enhancement on VMI and PCI was performed by 3 blinded readers. Results: Optimal CNR values for small intestinal mural enhancement were observed at 70keV. Qualitative assessment revealed that there was no statistical difference in diagnostic accuracy between VMI and PCI. All readers reported improved confidence when assessing the contrast enhancement on the 70keV VMI dataset and in our series, 2 additional cases of ischemia were identified on this reconstruction. Conclusion: Contrast-enhanced dual source dual energy CT with VMI reconstruction at 70keV maximizes the CNR of small bowel mural enhancement and increases the overall diagnostic confidence in assessing mural enhancement in patients with SBO. [ABSTRACT FROM AUTHOR]

Objectives: To evaluate optimal window settings for display of virtual monoenergetic reconstructions in third-generation dual-source, dual-energy computed tomography (DECT) of the liver. Methods: Twenty-nine subjects were prospectively evaluated with DECT in arterial (AP) and portal venous (PVP) phases. Three reconstructed datasets were calculated: standard linearly-blended (LB120), 70-keV standard virtual monoenergetic (M70), and 50-keV advanced image-based virtual monoenergetic (M50+). Two readers assessed optimal window settings (width and level, W/L), establishing a mean for each reconstruction which was used for a blinded assessment of liver lesions. Results: The optimal W/L for M50+ were significantly higher for both AP (W=429.3 ± 44.6 HU, L=129.4 ± 9.7 HU) and PVP (W=376.1 ± 14.2HU, L=146.6 ± 7.0 HU) than for LB120 (AP, W=215.9 ± 16.9 HU, L=82.3 ± 9.4 HU) (PVP, W=173.4 ± 8.9 HU, L=69.3 ± 6.0 HU) and M70 (AP, W=247.1 ± 22.2 HU, L=72.9 ± 6.8 HU) (PVP, W=232.0 ± 27.9 HU, L=91.6 ± 14.4 HU). Use of the optimal window setting for M50+ vs. LB120 resulted in higher sensitivity (AP, 100% vs. 86%; PVP, 96% vs. 63%). Conclusions: Application of dedicated window settings results in improved liver lesion detection rates in advanced image-based virtual monoenergetic DECT when customized for arterial and portal venous phases. [ABSTRACT FROM AUTHOR]

Background and Purpose: Calculated monoenergetic ultra-low keV datasets did not lead to improved contrast-to-noise ratio (CNR) due to the dramatic increase in image noise. The aim of the present study was to evaluate the objective image quality of ultra-low keV monoenergetic images (MEIs) calculated from carotid DECT angiography data with a new monoenergetic imaging algorithm using a frequency-split technique. Materials and Methods: 20 patients (12 male; mean age 53±17 years) were retrospectively analyzed. MEIs from 40 to 120 keV were reconstructed using the monoenergetic split frequency approach (MFSA). Additionally MEIs were reconstructed for 40 and 50 keV using a conventional monoenergetic (CM) software application. Signal intensity, noise, signal-to-noise ratio (SNR) and CNR were assessed in the basilar, common, internal carotid arteries. Results: Ultra-low keV MEIs at 40 keV and 50 keV demonstrated highest vessel attenuation, significantly greater than those of the polyenergetic images (PEI) (all p-values <0.05). The highest SNR level and CNR level was found at 40 keV and 50 keV (all p-values <0.05). MEIs with MFSA showed significantly lower noise levels than those processed with CM (all p-values <0.05) and no significant differences in vessel attenuation (p>0.05). Thus MEIs with MFSA showed significantly higher SNR and CNR compared to MEIs with CM. Conclusion: Combining the lower spatial frequency stack for contrast at low keV levels with the high spatial frequency stack for noise at high keV levels (frequency-split technique) leads to improved image quality of ultra-low keV monoenergetic DECT datasets when compared to previous monoenergetic reconstruction techniques without the frequency-split technique. [ABSTRACT FROM AUTHOR]

Coronary CT angiography (CCTA) is an established imaging technique used for the non-invasive morphological assessment of coronary artery disease. As in invasive coronary angiography, CCTA anatomical assessment of coronary stenosis does not adequately predict hemodynamic relevance. However, recent technical improvements provide the possibility of CT myocardial perfusion imaging (CTMPI). Two distinct CT techniques are currently available for myocardial perfusion assessment: static CT myocardial perfusion imaging (sCTMPI), with single- or dual-energy modality, and dynamic CT myocardial perfusion imaging (dCTMPI). The combination of CCTA morphological assessment and CTMPI functional evaluation holds promise for achieving a comprehensive assessment of coronary artery anatomy and myocardial perfusion using a single image modality. [ABSTRACT FROM AUTHOR]

Objective: Dual-energy (DE) brings numerous significant improvements in pulmonary CT angiography (CTPA), but is associated with a 15-50% increase in radiation dose that prevents its widespread use. We hypothesize that thanks to iterative reconstruction (IR), single source DE-CTPA acquired at the same radiation dose that a single-energy examination will maintain an equivalent quantitative and qualitative image quality, allowing a more extensive use of the DE technique in the clinical routine.Material and Methods: Fifty patients (58% men, mean age 64.8yo ± 16.2, mean BMI 25.6 ± 4.5) were prospectively included and underwent single source DE-CTPA with acquisition parameters (275 mA fixed tube current, 50% IR) tweaked to target a radiation dose similar to a 100 kV single-energy CTPA (SE-CTPA), i.e., a DLP of 260 mGy cm. Thirty patients (47% men, 64.4yo ± 18.6, BMI 26.2 ± 4.6) from a previous prospective study on DE-CTPA (375 mA fixed tube current, reconstruction with filtered-back projection) were used as the reference group. Thirty-five consecutive patients (57% men, 65.8yo ± 15.5, BMI 25.7 ± 4.4) who underwent SE-CTPA on the same scanner (automated tube current modulation, 50% IR) served as a comparison. Subjective image quality was scored by two radiologists using a 5-level scale and compared with a Kruskal-Wallis nonparametric test. Density measurements on the 65 keV monochromatic reconstructions were used to calculate signal-to-noise (SNR) and contrast-to-noise (CNR) ratios that were compared using a Student's t test. Correlations between image quality, SNR, CNR and BMI were sought using a Pearson's test. p<0.05 was considered significant.Results: All examinations were of diagnostic quality (score ≥ 3). In comparison with the reference DE-CTPA and the SE-CTPA protocols, the DE-IR group exhibited a non-inferior image quality (p=0.95 and p=0.21, respectively) and a significantly lower mean image noise (p<0.01 and p=0.01) thus slightly improving the SNR (p=0.09 and p=0.47) and the CNR (p=0.12 and p=0.51). There was a strong negative relationship between BMI and SNR/CNR (ρ=-0.59 and -0.55 respectively), but only a moderate negative relationship between BMI and image quality (ρ=-0.27).Conclusion: With iterative reconstruction, objective and subjective image quality of single source DE-CTPA are preserved even though the radiation dose is lowered to that of a single-energy examination, overcoming a major limitation of the DE technique and allowing a widespread use in the clinical routine. [ABSTRACT FROM AUTHOR]

Objectives Factors affecting the improvement in the lung perfused blood volume (LPBV) were evaluated based on the presence of intrapulmonary clots (IPCs) after anti-coagulation therapy using 64-slice dual-energy CT. Materials and methods 96 patients exhibiting venous thromboembolism underwent initial and repeated LPBV examinations between December 2008 and July 2014. Fifteen patients were excluded due to pulmonary comorbidities, and a total of 81 patients were included in this study. Acute pulmonary embolism (PE) was diagnosed in 46 of the patients (56.7%). LPBV images were three-dimensionally reconstructed with two threshold ranges: 1–120 HU (V 120 ) and 1–5 HU (V 5 ), and the relative value of V 5 per V 120 expressed as %V 5 . These values were subsequently compared with indicators of the severity of PE, such as the D-dimer level, heart rate and CT measurements. This study was approved by the local ethics committee. Results In patients with IPCs, the D-dimer, V 5 and %V 5 values were significantly larger ( p ≤ 0.01) in the initial LPBV, although these differences disappeared in subsequent LPBV after treatment. The right ventricular (RV) diameter, RV/left ventricular (RV/LV) diameter ratio and %V 5 values were also significantly reduced, whereas the V 5 value did not significantly decrease ( p = 0.07), but V 120 value significantly increased ( p < 0.001) after treatment. However, in patients with IPCs the change rate in %V 5 [(subsequent-initial)/initial %V 5 ] showed a better correlation with that in V 5 ( r = 0.94, p < 0.001) rate than that in V 120 ( r = 0.19, p = 0.19) after treatment. Conclusions Increased whole lung perfusion (V 120 ) and a decreased low perfusion volume (V 5 ) affect the improvement in the %V 5 values after treatment. [ABSTRACT FROM AUTHOR]

Abstract: Objectives: To evaluate the feasibility and incremental diagnostic value of xenon-enhanced dual-energy CT in mechanically ventilated intensive care patients with worsening respiratory function. Methods: The study was performed in 13 mechanically ventilated patients with severe pulmonary conditions (acute respiratory distress syndrome (ARDS), n =5; status post lung transplantation, n =5; other, n =3) and declining respiratory function. CT scans were performed using a dual-source CT scanner at an expiratory xenon concentration of 30%. Both ventilation images (Xe-DECT) and standard CT images were reconstructed from a single CT scan. Findings were recorded for Xe-DECT and standard CT images separately. Ventilation defects on xenon images were matched to morphological findings on standard CT images and incremental diagnostic information of xenon ventilation images was recorded if present. Results: Mean xenon consumption was 2.95l per patient. No adverse events occurred under xenon inhalation. In the visual CT analysis, the Xe-DECT ventilation defects matched with pathologic changes in lung parenchyma seen in the standard CT images in all patients. Xe-DECT provided additional diagnostic findings in 4/13 patients. These included preserved ventilation despite early pneumonia (n =1), more confident discrimination between a large bulla and pneumothorax (n =1), detection of an airway-to-pneumothorax fistula (n =1) and exclusion of a suspected airway-to-mediastinum fistula (n =1). In all 4 patients, the additional findings had a substantial impact on patients’ management. Conclusions: Xenon-enhanced DECT is safely feasible and can add relevant diagnostic information in mechanically ventilated intensive care patients with worsening respiratory function. [Copyright &y& Elsevier]

Abstract: Purpose: Recent innovations in CT enable the evolution from mere morphologic imaging to dynamic and functional testing. We describe our initial experience performing myocardial stress perfusion CT in a clinical population with acute chest pain. Methods and materials: Myocardial stress perfusion CT was performed on twenty consecutive patients (15 men, 5 women; mean age 65±8 years) who presented with acute chest pain and were clinically referred for stress/rest SPECT and cardiac MRI. Prior to CT each patient was randomly assigned either to Group A or to Group B in a consecutive order (10 patients per group). Group A underwent adenosine-stress dynamic real-time myocardial perfusion CT using a novel “shuttle” mode on a 2nd generation dual-source CT. Group B underwent adenosine-stress first-pass dual-energy myocardial perfusion CT using the same CT scanner in dual-energy mode. Two experienced observers visually analyzed all CT perfusion studies. CT findings were compared with MRI and SPECT. Results: In Group A 149/170 myocardial segments (88%) could be evaluated. Real-time perfusion CT (versus SPECT) had 86% (84%) sensitivity, 98% (92%) specificity, 94% (88%) positive predictive value, and 96% (92%) negative predictive value in comparison with perfusion MRI for the detection of myocardial perfusion defects. In Group B all myocardial segments were available for analysis. Compared with MRI, dual-energy myocardial perfusion CT (versus SPECT) had 93% (94%) sensitivity, 99% (98%) specificity, 92% (88%) positive predictive value, and 96% (94%) negative predictive value for detecting hypoperfused myocardial segments. Conclusion: Our results suggest the clinical feasibility of myocardial perfusion CT imaging in patients with acute chest pain. Compared to MRI and SPECT both, dynamic real-time perfusion CT and first-pass dual-energy perfusion CT showed good agreement for the detection of myocardial perfusion defects. [Copyright &y& Elsevier]

Abstract: Purpose: To prospectively evaluate the feasibility of dual-energy (DE) split-bolus CT-urography (CTU) and the quality of virtual non-enhanced images (VNEI) and DE combined nephrographic-excretory phase images (CNEPI), and to estimate radiation dose reduction if true non-enhanced images (TNEI) could be omitted. Patients and methods: Between August and September 2011, 30 consecutive patients with confirmed or suspected urothelial cancer or with hematuria underwent DE CT. Single-energy TNEI and DE CNEPI were obtained. VNEI was reconstructed from CNEPI. Image quality of CNEPI and VNEI was evaluated using a 5-point scale. The attenuation of urine in the bladder on TNEI and VNEI was measured. The CT dose index volume (CTDI (vol)) of the two scans was recorded. Results: The mean image quality score of CNEPI and VNEI was 4.7 and 3.3, respectively. The mean differences in urine attenuation between VNEI and TNEI were 14±15 [SD] and −16±29 in the anterior and posterior parts of the bladder, respectively. The mean CTDI (vol) for TNEI and CNEPI was 11.8 and 10.9mGy, respectively. Omission of TNEI could reduce the total radiation dose by 52%. Conclusion: DE split-bolus CTU is technically feasible and can reduce radiation exposure; however, an additional TNEI scan is necessary when the VNEI quality is poor or quantitative evaluation of urine attenuation is required. [Copyright &y& Elsevier]

Abstract: Objective: Aims were (1) to determine the diagnostic accuracy of Dual Energy CT (DECT) in the detection of perfusion defects and (2) to evaluate the potential of DECT to improve the sensitivity for PE. Methods: 15 patients underwent Dual Energy pulmonary CT angiography (DE CTPA) and a combination of lung perfusion SPECT/CT and ventilation scintigraphy. CTPA and DE iodine distribution maps as well as perfusion SPECT/CT and inhalation scintigrams were reviewed for pulmonary embolism (PE) diagnosis. DECT and SPECT perfusion images were assessed regarding localization and extent of perfusion defects. Diagnostic accuracy of DE iodine (perfusion) maps was determined with reference to SPECT/CT. Diagnostic accuracies for PE detection of DECT and of SPECT/CT with ventilation scintigraphy were calculated with reference to the consensus reading of all modalities. Results: DE CTPA had a sensitivity/specificity of 100%/100% for acute PE, while the combination of SPECT/CT and ventilation scintigraphy had a sensitivity/specificity of 85.7%/87.5%. For perfusion defects, DECT iodine maps had a sensitivity/specificity of 76.7% and 98.2%. Conclusion: DECT is able to identify pulmonary perfusion defects with good accuracy. This technique may potentially enhance the diagnostic accuracy in the assessment of PE. [Copyright &y& Elsevier]

Abstract: Objective: To compare different CT acquisition techniques regarding for attenuation-based characterization of coronary atherosclerotic plaques using histopathology as the standard of reference. Materials and methods: In a post mortem study 17 human hearts were studied with dual-source CT (DSCT) and dual energy CT (DECT) mode on a DSCT as well as with 16-slice single-source CT (SSCT). At autopsy, atherosclerotic lesions were cut at 5μm sections. Histopathologic classification of the plaques according to the American Heart Association (AHA) criteria was performed by two pathologists. Attenuation values of all plaques were measured in DSCT, DECT and SSCT studies, respectively and classified based on attenuation according to modified AHA criteria. Results: 58 coronary plaques were identified at autopsy. Regardless of the CT technique only 52/58 plaques were found at CT (sensitivity=89.6%). There was no significant difference between the mean attenuation values of different plaque types between DSCT, DECT, and SSCT: type IV: 11HU/8HU/19HU; type Va: 44HU/45HU/52HU; type Vb: 1088HU/966HU/1079HU). The sensitivity for correct classification varied depending on the plaque type (type II=0%, type III=0%, type IV=43%, type Va=58%, Vb=97%). Conclusion: Independent of the used acquisition technique, SSCT, DSCT and DECT show similar results for attenuation-based characterization of atherosclerotic coronary plaques. [Copyright &y& Elsevier]

Abstract: Background: Although the quality of imaging techniques available for neurovascular angiography in the hospital environment has significantly improved over the last decades, the equipment used for clinical work is not always suited for neurovascular research in animal models. We have previously investigated the suitability of synchrotron-based K-edge digital subtraction angiography (KEDSA) after intravenous injection of iodinated contrast agent for neurovascular angiography in radiography mode in both rabbit and pig models. We now have used the KEDSA technique for the acquisition of three-dimensional images and dual energy CT. Materials and methods: All experiments were conducted at the biomedical beamline ID 17 of the European Synchrotron Radiation Facility (ESRF). A solid state germanium (Ge) detector was used for the acquisition of image pairs at 33.0 and 33.3keV. Three-dimensional images were reconstructed from an image series containing 60 single images taken throughout a full rotation of 360°. CT images were reconstructed from two half-acquisitions with 720 projections each. Results: The small detector field of view was a limiting factor in our experiments. Nevertheless, we were able to show that dual energy CT using the KEDSA technique available at ID 17 is suitable for neurovascular research in animal models. [Copyright &y& Elsevier]

Abstract: Purpose: To assess the feasibility of dual energy CT (DECT) after aerosol inhalation of iodinated contrast medium for the evaluation of ventilation function in rabbits with airway obstruction. Materials and methods: The study was approved by our institutional animal experimental committee and performed according to animal care guidelines. Airway obstruction was created by injecting gelatin sponge into the right bronchus of 6 New Zealand rabbits. One additional rabbit served as control without airway obstruction. All 7 rabbits then underwent inhalation of aerosol iodinated contrast medium for 5min, followed by DECT of the lungs from which ventilation CT images were created. CT number and overlay value (calculated iodine enhancement on the ventilation images in hounsfield unit) of the obstructed and non-obstructed lung lobes were measured at 80-kVp, 140-kVp, and weighted average 120-kVp. Immediately after DECT scan, the rabbits were sacrificed, the lungs were removed and detailed pathological examination of the locations and parenchymal changes of the obstructed lung lobes were performed and correlated with DECT ventilation imaging findings. Results: Data from one rabbit with airway obstruction were excluded because of post-procedure pneumatothorax. Seventeen normal lung lobes without airway obstruction proven by histopathology had nearly homogeneous ventilation, while 13 abnormal lung lobes had ventilation defects on DECT ventilation images. CT numbers and overlay values of the normal (CT number, −737.77±71.46HU, −768.84±73.86HU, −731.86±65.92HU for 140-kVp, 80-kVp, and weighted average 120-kVp; overlay value, 46.58±19.49HU) and abnormal lung lobes (CT number, −183.58±173.37HU, −124.93±242.23HU, −166.07±191.57HU for 140-kVp, 80-kVp, and weighted average 120-kVp; overlay value, 0.00±0.00HU) were significantly different at 80-kVp, 140-kVp, and weighted average 120-kVp (P <0.001 for all). Diffuse hemorrhage, inflammatory cell infiltration, and exudation were observed at histopathology in the obstructed lung lobes. Conclusions: It is feasible to study regional lung ventilation function using DECT after aerosol inhalation of iodinated contrast medium in rabbit. The safety of inhalation of iodine contrast medium is unknown, and has to be investigated further before use of this new method in humans. [Copyright &y& Elsevier]

Abstract: Purpose: We sought to evaluate the feasibility and efficiency of dual energy (DE) bone and plaque removal in head and neck CT angiography. Materials and methods: 20 patients with suspected carotid stenoses received head and neck DE-CTA as part of their pre-interventional workup. Visual grading using multiplanar reformations (MPR), thick slab maximum intensity projections (MIP) and quantitative vessel analysis (QVA) of stenoses was performed prior and after DE bone removal. Results were evaluated for the detection of relevant stenoses (vessel area reduction >70%). Vessel segmentation errors were analyzed. Results: Segmentation errors occurred in 19% of all vessel segments. Nevertheless, most post-bone removal artifacts could be recognized using the MPR technique for reading. Compared to MPR reading prior to bone removal, sensitivity, specificity, positive and negative predictive values after bone removal were 100%, 98%, 88% and 100% for MPR reading and 100%, 91%, 63% and 100% for exclusive MIP reading, respectively. There was a good agreement between the QVA results prior and post-DE plaque removal (r 2 =0.8858). Conclusion: DE bone and plaque removal for head and neck angiography is feasible and offers a rapid and highly sensitive overview over vascular head and neck studies. Due to a slightly limited specificity of the MIP technique due to segmentation errors, possible stenoses should be verified and graded using MPR techniques. [ABSTRACT FROM AUTHOR]

Abstract: During the past years, multi-detector row CT (MDCT) has evolved into clinical practice with a rapid increase of the number of detector slices. Today''s 64 slice CT systems allow whole-body examinations with sub-millimeter resolution in short scan times. As an alternative to adding even more detector slices, we describe the system concept and design of a CT scanner with two X-ray tubes and two detectors (mounted on a CT gantry with a mechanical offset of 90°) that has the potential to overcome limitations of conventional MDCT systems, such as temporal resolution for cardiac imaging. A dual source CT (DSCT) scanner provides temporal resolution equivalent to a quarter of the gantry rotation time, independent of the patient''s heart rate (83ms at 0.33s rotation time). In addition to the benefits for cardiac scanning, it allows to go beyond conventional CT imaging by obtaining dual energy information if the two tubes are operated at different voltages. Furthermore, we discuss how both acquisition systems can be used to add the power reserve of two X-ray tubes for long scan ranges and obese patients. Finally, future advances of DSCT are highlighted. [Copyright &y& Elsevier]

Purpose: To investigate the value of dual-energy CT imaging to discriminate low- from high- risk type II endoleaks (T2EL) after endovascular aneurysm repair (EVAR)., Method: Study participants were consecutive patients referred for CT at 1-month post-EVAR. CT imaging acquisition included a dual-energy CT angiography (DECTA) and a delayed single-energy CT (SECT) imaging. Patients diagnosed with T2EL were re-examined at 6-months post-EVAR to assess the aneurysm sac growth (ASG). Upon ASG recorded, patients were categorized as having low- (group A) or high- risk (group B) T2EL. DECTA image data were employed to calculate the normalized effective atomic number (NZ eff ), the normalized iodine concentration, the slope of HU endoleak /HU aorta against monochromatic energy, the dual-energy index and an improvised endoleak index (EI) for each T2EL. Statistical analysis was employed to compare all above parameters regarding their ability to differentiate low- from high- risk T2EL., Results: Among 40 patients examined at 1-month post-EVAR, 14 patients were diagnosed with T2EL. NZ eff and EI were found to be significantly lower in group A. NZ eff was found to have the highest power to discriminate high-risk T2EL with an area-under-curve of 86.7%, showing100% specificity and 60% sensitivity. The optimal contrast-to-noise ratio for T2EL demonstrated a median peak conspicuity level at 54-keV. The mean effective dose from DECTA and SECT scans was 27.8% lower compared to the sum of three SECT acquisitions., Conclusions: NZ eff and EI were found to have a significant power in predicting the aggressiveness of T2EL lesions. Virtual monochromatic images at 54-keV may enhance T2EL detection efficiency., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Objectives: To determine whether contrast enhanced DECT low monoenergetic can improve diagnostic conspicuity of inflamed kidney foci in acute pyelonephritis compared to conventional images.Materials and Methods: A retrospective study of 45 patients with clinical signs of acute pyelonephritis undergoing contrast-enhanced exams on a single source-DECT was conducted. Representative conventional and monoenergetic images were randomized and presented to four abdominal radiologists to determine their preference for inflamed kidney foci detection, and to determine the number of foci identified. Clinical impact of monoenergetic images was assessed using multivariant analysis. Contrast and signal to noise ratios were compared between the images using paired t-tests.Results: A greater number of foci were detected on the low energetic images for each patient (6.4 ± 5.3 vs. 4.2 ± 3.8, p < 0.02). Additionally, a consistent linear increase in the number of detected foci on the monoenergetic compared to the conventional images was seen (y = 0.10X + 0.36 R2 = 0.76). Most notably, in 16% of kidneys a clearly definable focus was detected only on monoenergetic images. SNR and CNR were increased by 2 and 1.5 fold for monoenergetic compared to conventional images (p < 0.001). Monoenergetic images were preferred by all readers for detecting inflamed foci (162/180 reads, P < 0.05), with 79% interreader reliability.Conclusion: Low monoenergetic images enable increased detection of inflamed kidney parenchyma, and permit identification of pathologic foci some of which were not seen on the conventional images. Along with the strong preference of radiologists, these images should be considered beneficial for evaluating acute pyelonephritis. [ABSTRACT FROM AUTHOR]