Olivier F. Clerc

Coronary computed tomography angiography with model-based iterative reconstruction using a radiation exposure similar to chest X-ray examination

Aims To evaluate the feasibility and image quality of coronary computed tomography angiography (CCTA) acquisition with a submillisievert fraction of effective radiation dose using model-based iterative reconstruction (MBIR) for noise reduction. Methods and results In 42 patients undergoing standard low-dose (100–120 kV; 450–700 mA) and additional ultra-low-dose CCTA (80–100 kV; 150–210 mA) reconstructed with MBIR, segmental image quality was graded on a four-point scale [(i): non-evaluative, (ii): good, (iii): adequate, and (iv): excellent]. Signal-to-noise ratio (SNR) was calculated dividing left main artery (LMA) and right coronary artery (RCA) attenuation by the aortic root noise. Over a wide range of body mass index (18–40 kg/m2), the estimated median radiation dose exposure was 1.19 mSv [interquartile range (IQR): 1.07–1.30 mSv] for standard and 0.21 mSv (IQR: 0.18–0.23 mSv) for ultra-low-dose CCTA (P < 0.001). The median image quality score per segment was 3.5 (IQR: 3.0–4.0) in standard CCTA vs. 3.5 (IQR: 2.5–4.0) in ultra-low dose with MBIR (P = 0.29). Diagnostic image quality (scores 2–4) was found in 98.7 vs. 97.8% coronary segments (P = 0.36). Introduction of MBIR for ultra-low-dose CCTA resulted in a significant increase in SNR (P < 0.001) for LMA (from 15 ± 5 to 29 ± 7) and RCA (from 14 ± 4 to 27 ± 6) despite 82% dose reduction. Conclusion Coronary computed tomography angiography acquisition with diagnostic image quality is feasible at an ultra-low radiation dose of 0.21 mSv, e.g. in the range reported for a postero-anterior and lateral chest X-ray.

First experience with single-source, dual-energy CCTA for monochromatic stent imaging

AIMS Single-source, dual-energy coronary computed tomography angiography (CCTA) with monochromatic image reconstruction allows significant noise reduction. The aim of the study was to evaluate the impact of monochromatic CCTA image reconstruction on coronary stent imaging, as the latter is known to be affected by artefacts from highly attenuating strut material resulting in artificial luminal narrowing. METHODS AND RESULTS Twenty-one patients with 62 stents underwent invasive coronary angiography and single-source, dual-energy CCTA after stent implantation. Standard polychromatic images as well as eight monochromatic series (50, 60, 70, 80, 90, 100, 120, and 140 keV) were reconstructed for each CCTA. Signal and noise were measured within the stent lumen and in the aortic root. Mean in-stent luminal diameter was assessed in all CCTA reconstructions and compared with quantitative invasive coronary angiography (QCA). Luminal attenuation was higher in the stent than in the aortic root throughout all monochromatic reconstructions (P < 0.001). An increase in monochromatic energy was associated with a decrease in luminal attenuation values (P < 0.001). The mean in-stent luminal diameter underestimation by monochromatic CCTA compared with QCA was 90% at low monochromatic energy (50 keV) and improved to 37% at high monochromatic (140 keV) reconstruction while stent diameter was underestimated by 39% with standard CCTA. CONCLUSION Monochromatic CCTA can be used reliably in patients with coronary stents. However, reconstructions with energies below 80 keV are not recommended as the blooming artefacts are most pronounced at such low energies, resulting in up to 90% stent diameter underestimation.

Minimized Radiation and Contrast Agent Exposure for Coronary Computed Tomography Angiography: First Clinical Experience on a Latest Generation 256-slice Scanner

RATIONALE AND OBJECTIVES The aim of the study was to evaluate the impact of the latest coronary computed tomography angiography (CCTA) techniques allowing a radiation- and contrast-sparing protocol on image quality in unselected patients referred for exclusion of suspected coronary artery disease (CAD). MATERIALS AND METHODS This prospective study was approved by the local ethics committee, and all patients provided written informed consent. Between March and June 2015, 89 consecutive patients (61% male; mean age 55 ± 11 years) referred for exclusion of CAD by 256-slice CCTA using prospective electrocardiogram triggering were included. Tube voltage (80-120 kVp), tube current (180-310 mA) as well contrast agent volume (25-45 mL) and flow rate (3.5-5 mL/s) were adapted to body mass index. Signal intensity was measured by placing a region of interest in the aortic root, the left main artery, and the proximal right coronary artery. Image noise was measured in the aortic root. Two independent blinded readers semi-quantitatively assessed the image quality regarding motion, noise, and contrast on a 4-point scale. RESULTS Median contrast agent volume and median effective radiation dose were 35 mL (interquartile range, 30-40 mL) and 0.5 mSv (interquartile range, 0.4-0.6 mSv), respectively. Mean attenuation in the aortic root was 412 ± 89 Hounsfield units. Diagnostic image quality was obtained in 1050 of 1067 (98.4%) coronary segments and, on an intention-to-diagnosis basis, in 85 of 89 (95.5%) patients. Below a cut-off heart rate of 67 beats/min, only 1 of 974 (0.1%) coronary segments was nondiagnostic. CONCLUSION A radiation- and contrast-sparing protocol for CCTA on a latest generation 256-slice computed tomography scanner yields diagnostic image quality in patients referred for CAD exclusion in daily clinical routine.

Adaptive Statistical Iterative Reconstruction-V: Impact on Image Quality in Ultralow-Dose Coronary Computed Tomography Angiography.

Objective The clinical utility of a latest generation iterative reconstruction algorithm (adaptive statistical iterative reconstruction [ASiR-V]) has yet to be elucidated for coronary computed tomography angiography (CCTA). This study evaluates the impact of ASiR-V on signal, noise and image quality in CCTA. Methods Sixty-five patients underwent clinically indicated CCTA on a 256-slice CT scanner using an ultralow-dose protocol. Data sets from each patient were reconstructed at 6 different levels of ASiR-V. Signal intensity was measured by placing a region of interest in the aortic root, LMA, and RCA. Similarly, noise was measured in the aortic root. Image quality was visually assessed by 2 readers. Results Median radiation dose was 0.49 mSv. Image noise decreased with increasing levels of ASiR-V resulting in a significant increase in signal-to-noise ratio in the RCA and LMA (P < 0.001). Correspondingly, image quality significantly increased with higher levels of ASiR-V (P < 0.001). Conclusions ASiR-V yields substantial noise reduction and improved image quality enabling introduction of ultralow-dose CCTA.

Prevalence and characteristics of coronary artery anomalies detected by coronary computed tomography angiography in 5 634 consecutive patients in a single centre in Switzerland.

STUDY PRINCIPLES Coronary computed tomography angiography (CCTA) allows three-dimensional visualisation of the origin, course and ending of the coronary vessels with high spatial resolution, yielding an accurate depiction of coronary artery anomalies (CAAs). This study sought to determine the prevalence, incidence and characteristics of CAAs detected with CCTA in a single centre in Switzerland. METHODS CAAs were retrospectively identified in 5 634 consecutive patients referred for CCTA between March 2007 and July 2015. Single coronary arteries, Bland-White-Garland syndrome, anomalous coronary arteries originating from the opposite site of the sinus of Valsalva (ACAOS) with an interarterial course and coronary artery fistulas were classified as potentially malignant CAAs. RESULTS We identified 145 patients with CAAs, resulting in an overall prevalence of 2.6% and cumulative incidence of 2.1% in all patients referred for CCTA in the observation period. Forty-nine (33.8%) patients showed malignant CAAs including 1 (0.7%) patient with Bland-White-Garland syndrome, 7 (4.8%) with single coronary arteries, 36 (24.8%) with ACAOS and an interarterial course, and 5 (3.5%) with coronary artery fistulas. The remaining 96 (66.2%) patients were classified as having benign variants. CONCLUSIONS The prevalence of CAA detected by CCTA is not negligible. Because of its noninvasive nature, relatively low cost and low radiation exposure, a further increase in the utilisation of CCTA may be expected, which may consequently be paralleled by an increasing absolute number of incidentally detected CAAs. Hence, awareness of the main issues and possible management strategies regarding CAAs is of importance for every treating physician.

Corrected coronary opacification decrease from coronary computed tomography angiography: Validation with quantitative 13N-ammonia positron emission tomography

AbstractBackgroundTo assess the functional relevance of a coronary artery stenosis, corrected coronary opacification (CCO) decrease derived from coronary computed tomography angiography (CCTA) has been proposed. The present study aims at validating CCO decrease with quantitative 13N-ammonia positron emission tomography (PET) myocardial perfusion imaging (MPI).Methods and ResultsThis retrospective study consists of 39 patients who underwent hybrid CCTA/PET-MPI. From CCTA, attenuation in the coronary lumen was measured before and after a stenosis and corrected to the aorta to calculate CCO and its decrease. Relative flow reserve (RFR) was calculated by dividing the stress myocardial blood flow (MBF) of a vessel territory subtended by a stenotic coronary by the stress MBF of the reference territories without stenoses. RFR was abnormal in 11 vessel territories (27%). CCO decrease yielded a sensitivity, specificity, negative predictive value, positive predictive value, and accuracy for prediction of an abnormal RFR of 73%, 70%, 88%, 47%, and 70%, respectively. ConclusionsCCTA-derived CCO decrease has moderate diagnostic accuracy to predict an abnormal RFR in PET-MPI. However, its high negative predictive value to rule out functional relevance of a given lesion may confer clinical implications in the diagnostic work-up of patients with a coronary stenosis.

Long-term outcome prediction by functional parameters derived from coronary computed tomography angiography

BACKGROUND Estimation of hemodynamic relevance of a coronary stenosis from coronary computed angiography (CCTA) has raised substantial interest. Recently, the corrected coronary opacification (CCO) decrease and the transluminal attenuation gradient (TAG) have been suggested as faster alternatives to the FFRCT. The aim of the study was to evaluate whether the diagnostic accuracy of CCO decrease and TAG translates into an added prognostic value in patients evaluated for coronary artery disease (CAD). METHODS This retrospective study consists of 162 consecutive patients referred for evaluation of known or suspected CAD by CCTA. CCO decrease was defined as difference of mean luminal coronary attenuation normalized to aorta attenuation proximal-distal of a stenosis. To calculate TAG, mean attenuation was measured at 5-mm intervals from the ostium to a distal segment with a minimal cross-sectional area of 2.0mm2. Death, myocardial infarction, unstable angina requiring hospitalization, and coronary revascularization were defined as major adverse cardiac events (MACE). Multivariate analysis included covariates age, sex, ≥3 cardiovascular risk factors and stenosis severity. RESULTS Follow-up was completed in 154 patients, CAD was found in 72. During median follow-up of 6.1years (interquartile range, 5.8-6.9years), 55 patients experienced a MACE. Among CAD patients, the presence of an abnormal CCO decrease (p<0.05) but not TAG (p=0.894) was associated with a worse MACE-free survival. In multivariate analysis, CCO decrease was an independent predictor of MACE (HR, 2.27; 95% CI, 1.14-4.52; p=0.02) while TAG was not predictive (p=0.895). CONCLUSION In CAD patients, CCO decrease adds long-term prognostic value over clinical characteristics and stenosis severity while TAG does not.

Real-time respiratory triggered SPECT myocardial perfusion imaging using CZT technology: impact of respiratory phase matching between SPECT and low-dose CT for attenuation correction

Aims To assess the impact of respiratory phase matching between single-photon-emission computed tomography myocardial perfusion imaging (SPECT-MPI) and low-dose computed tomography (CT) for attenuation correction (AC). Methods and results Forty patients underwent 1-day 99mTc-tetrofosmin pharmacological stress/rest SPECT-MPI using a cadmium–zinc–telluride gamma camera. Low-dose CT for AC was performed at deep-inspiration breath-hold. SPECT-MPI was acquired once with free-breathing (FB) and repeated at deep-inspiration breath-hold (BH) to match the respiratory phase of AC. From these acquisitions we reconstructed four data sets: free-breathing SPECT-MPI without AC (non-corrected; FB-NC), breath-hold SPECT-MPI without AC (non-corrected; BH-NC), free-breathing SPECT-MPI with AC (FB-AC), and breath-hold SPECT-MPI with AC (BH-AC), the latter representing respiratory-phase-matched AC SPECT-MPI. We compared semi-quantitative segmental tracer uptake, visual diagnosis, inter-observer agreement, and image quality. Compared with FB-NC, deep-inspiration BH-NC increases inferior and lateral uptake, but decreases septal uptake. Addition of AC to FB increases inferior and septal uptake, but decreases anterolateral uptake. Combining breath-hold MPI with breath-hold CT AC (BH-AC) increases inferior, inferolateral, and septal uptake, but reduces apical uptake, without affecting anterolateral uptake, with significant differences to all other protocols. Frequency of normal scans increases across protocols: 10% with FB-NC, 21% with BH-NC, 38% with FB-AC, and 51% with BH-AC. Image quality and inter-observer agreement were highest for BH-AC among all protocols. Conclusion Compared with non-corrected breath-hold SPECT-MPI and with free-breathing AC SPECT-MPI, respiratory-phase-matched AC SPECT-MPI significantly affects segmental semi-quantitative uptake, increases the frequency of normal scans, yields the best inter-observer agreement, and significantly improves image quality. These findings suggest a potential role of respiratory triggered SPECT-MPI in clinical routine.

Outcome in middle-aged individuals with anomalous origin of the coronary artery from the opposite sinus: a matched cohort study

Aims Anomalous origin of a coronary artery from the opposite sinus (ACAOS) has been associated with adverse cardiac events in the young. It remains unknown whether this holds true for middle-aged patients with uncorrected ACAOS as well. We assessed the outcome in middle-aged patients with newly diagnosed ACAOS by coronary computed tomography angiography (CCTA) compared with a matched cohort. Methods and results We retrospectively identified 68 consecutive patients with ACAOS documented by CCTA. ACAOS with a course of the anomalous vessel between the aorta and pulmonary artery were classified as interarterial course (IAC). Each patient with ACAOS was matched to two controls without ACAOS. Major adverse cardiac events (i.e. myocardial infarction, revascularization and cardiac death) were recorded for all patients and controls. Two (3%) patients were lost to follow-up. Thus, 66 patients with ACAOS were included in the final analysis and matched with 132 controls. Mean age of patients was 56 ± 11 years, 73% were male and the mean follow-up was 49 months. Forty (65%) patients were classified as having ACAOS with IAC. The annual event rate of ACAOS vs. controls was 4.9 and 4.8%, the hazard ratio (HR) 0.94 (0.39-2.28, P = 0.89). The annual event rate of ACAOS with IAC compared with their matched controls was 5.2 and 4.3%, and the HR 1.01 (95% CI 0.39-2.58, P = 0.99). Conclusions In middle-aged individuals with newly diagnosed ACAOS mid-term outcome is not statistically different to a matched control cohort without coronary artery anomalies, regardless of whether ACAOS with or without IAC variants are present.

Head-to-head comparison of adaptive statistical and model-based iterative reconstruction algorithms for submillisievert coronary CT angiography

Aims Iterative reconstruction (IR) algorithms allow for a significant reduction in radiation dose of coronary computed tomography angiography (CCTA). We performed a head-to-head comparison of adaptive statistical IR (ASiR) and model-based IR (MBIR) algorithms to assess their impact on quantitative image parameters and diagnostic accuracy for submillisievert CCTA. Methods and results CCTA datasets of 91 patients were reconstructed using filtered back projection (FBP), increasing contributions of ASiR (20, 40, 60, 80, and 100%), and MBIR. Signal and noise were measured in the aortic root to calculate signal-to-noise ratio (SNR). In a subgroup of 36 patients, diagnostic accuracy of ASiR 40%, ASiR 100%, and MBIR for diagnosis of coronary artery disease (CAD) was compared with invasive coronary angiography. Median radiation dose was 0.21 mSv for CCTA. While increasing levels of ASiR gradually reduced image noise compared with FBP (up to - 48%, P < 0.001), MBIR provided largest noise reduction (-79% compared with FBP) outperforming ASiR (-59% compared with ASiR 100%; P < 0.001). Increased noise and lower SNR with ASiR 40% and ASiR 100% resulted in substantially lower diagnostic accuracy to detect CAD as diagnosed by invasive coronary angiography compared with MBIR: sensitivity and specificity were 100 and 37%, 100 and 57%, and 100 and 74% for ASiR 40%, ASiR 100%, and MBIR, respectively. Conclusion MBIR offers substantial noise reduction with increased SNR, paving the way for implementation of submillisievert CCTA protocols in clinical routine. In contrast, inferior noise reduction by ASiR negatively affects diagnostic accuracy of submillisievert CCTA for CAD detection.