Impact of iterative reconstruction on CT coronary calcium quantification

BackgroundDeep learning image reconstructions (DLIR) have been recently introduced as an alternative to filtered back projection (FBP) and iterative reconstruction (IR) algorithms for computed tomography (CT) image reconstruction. The aim of this study was to evaluate the effect of DLIR on image quality and quantification of coronary artery calcium (CAC) in comparison to FBP.MethodsOne hundred patients were consecutively enrolled. Image quality–associated variables (noise, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR)) as well as CAC-derived parameters (Agatston score, mass, and volume) were calculated from images reconstructed by using FBP and three different strengths of DLIR (low (DLIR_L), medium (DLIR_M), and high (DLIR_H)). Patients were stratified into 4 risk categories according to the Coronary Artery Calcium - Data and Reporting System (CAC-DRS) classification: 0 Agatston score (very low risk), 1–99 Agatston score (mildly increased risk), Agatston 100–299 (moderately increased risk), and ≥ 300 Agatston score (moderately-to-severely increased risk).ResultsIn comparison to standard FBP, increasing strength of DLIR was associated with a significant and progressive decrease of image noise (p < 0.001) alongside a significant and progressive increase of both SNR and CNR (p < 0.001). The use of incremental levels of DLIR was associated with a significant decrease of Agatston CAC score and CAC volume (p < 0.001), while mass score remained unchanged when compared to FBP (p = 0.232). The underestimation of Agatston CAC led to a CAC-DRS misclassification rate of 8%.ConclusionDLIR systematically underestimates Agatston CAC score. Therefore, DLIR should be used cautiously for cardiovascular risk assessment.Key Points• In coronary artery calcium imaging, the implementation of deep learning image reconstructions improves image quality, by decreasing the level of image noise.• Deep learning image reconstructions systematically underestimate Agatston coronary artery calcium score.• Deep learning image reconstructions should be used cautiously in clinical routine to measure Agatston coronary artery calcium score for cardiovascular risk assessment.

Background and Aims Cardiovascular calcification is highly prevalent among patients with end-stage renal disease (ESRD). Low normal serum magnesium has been linked to a more severe degree of vascular calcification and a decrease in patient survival. An inhibitory effect of extracellular magnesium on osteogenic transformation of vascular smooth muscle cells and the upregulation of anti-calcification protein have been confirmed in vitro. Increased dialysate magnesium concentration has also been shown to lower calcification propensity of the serum of maintenance hemodialysis (HD) patients. Method This study is an investigator initiated, single-blinded, parallel-group, matched case-control clinical trial that investigated the effect of high dialysate magnesium concentration for 24 weeks on the progression of coronary artery calcification (CAC) in maintenance HD patients. The changes in laboratory data and bone mineral density (BMD) were also examined. Seventy-six ESRD patients underwent CAC screening by multi-slice computed tomography and BMD measurement by dual-x-ray absorptiometry. Only patients with Agatston score&amp;gt;300 were included. They were matched according to the initial CAC score that fell within 20% of one another. Twenty patients were assigned to high dialysate magnesium concentration of 1.75 mEq/L and the matched controls were kept on standard dialysate magnesium concentration of 0.7 mEq/L. CAC and BMD measurements were repeated after 24 weeks. Laboratory data were obtained prior to dialysis at study entry, 8-week intervals during the study and 2 weeks after the study ended. Results There were no significant differences in age, sex, BMI, underlying diseases, dialysis vintage, medications, baseline CAC scores and BMD. The median baseline CAC Agatston score (Volume score) were 1923 (720) and 1672 (785) in the standard and high dialysate groups, respectively. At the end of the study, a significant increase in the CAC score was observed in both groups. Because majority of the included patients had severe calcification burden at baseline, patients were categorized into 2 subgroups using the median baseline CAC Agatston (1600) and Volume scores (700) as cut-offs. Among patients with CAC Agatston score &amp;lt;=1600, CAC score increased significantly in the standard dialysate magnesium group (P&amp;lt;0.01) but was stable in the high dialysate magnesium group (P=0.33). Among patients with CAC Agatston score &amp;gt;1600, the severity of CAC worsened in both groups. The progression of CAC was analyzed by the difference between the follow-up and the baseline square root transformed Agatston and Volume scores. In subgroup of patients with less severe calcification, more patients in the standard dialysate magnesium group progressed compared to the high dialysate magnesium group (P=0.03). In subgroup of patients with more severe calcification, the number of progressors were comparable among the 2 groups. Serum and ionized magnesium levels increased substantially during the study and returned to baseline after the return to standard dialysate magnesium concentration. The highest predialysis serum magnesium was 3.8 mg/dL. Most patients who received high dialysate magnesium reported the disappearance of symptoms of muscle cramps (P=0.01) and requested the high dialysate magnesium be continued after the end of the study. There were no significant changes in serum calcium, phosphate or PTH levels. The decline in BMD was observed in both groups but the difference did not reach statistical significance. Conclusion High dialysate magnesium was well tolerated and could ameliorate the progression of CAC in maintenance HD patients with mild to moderate vascular calcification.

Background and Aims In the CaLIPSO study, SNF472 significantly attenuated progression of coronary artery calcium (CAC) volume score compared with placebo. This pre-specified analysis examined the effect of SNF472 on CAC progression in key subgroups of patients in CaLIPSO. Method Patients with a CAC Agatston score of 100 to 3500 at baseline were randomized to SNF472 300 mg (n=92), SNF472 600 mg (n=91), or placebo (n=91), infused during hemodialysis (HD) thrice weekly for 52 weeks. Patients received standard of care therapy, including phosphate binders and calcimimetics as determined by investigator. The primary endpoint (change in log CAC volume score from baseline to week 52 in the combined dose groups vs placebo) was analyzed for patients who received SNF472 or placebo and had an evaluable CT scan post-randomization (modified ITT population). Sensitivity analysis was also performed for the per protocol population of patients that met entry criteria, received 80% of scheduled treatment, completed the study procedures, and had both a baseline and week 52 evaluable CT scan. The analysis plan pre-specified key subgroups: age, sex, diabetes, dialysis vintage, and arteriosclerotic cardiovascular disease (ASCVD), as well as baseline use of non-calcium phosphate binders, calcium-based phosphate binders, calcimimetics, activated vitamin D, warfarin, or statins. Results Demographics and disease characteristics were similar across the treatment groups. Age (mean±SD) at baseline was 63.6±8.9 years and 39% of the patients were female; 62% had diabetes and 41% had prior ASCVD. Median dialysis vintage was 42.4 months; 33% had received hemodialysis for ≥5 years. Concomitant medications at baseline were: non-calcium phosphate binders, 62%; calcium-based phosphate binders, 28%; calcimimetics, 31%; activated vitamin D, 51%; warfarin, 8%; and statins, 64%. CAC volume progression was 11% for the combined dose groups and 20% for placebo (p=0.016). Treatment differences for CAC volume score progression from baseline to week 52 were similar across the subgroups (FIGURE). All interaction p-values were non-significant, and comparisons favored SNF472 vs placebo in each subgroup for both the modified ITT and per protocol population. Conclusion SNF472 treatment for 52 weeks attenuated CAC progression compared with placebo in all subgroups of the CaLIPSO study. These results support the potential benefit of SNF472 across a broad population of patients with cardiovascular calcification. Future studies are needed to determine the effects of SNF472 on cardiovascular events in patients receiving HD.

The purpose of this study was to examine the individual and joint associations of obesity and cardiorespiratory fitness (CRF) with indices of coronary artery calcification (CAC) in 2090 middle-aged men. Obesity was defined as a body mass index (BMI) ≥25 kg/m2 and a waist circumference (WC) ≥90 cm. Cardiorespiratory fitness was operationally defined as peak oxygen uptake (V˙o2peak) directly measured using gas analysis. Participants were then divided into unfit and fit categories based on age-specific V˙o2peak percentiles. Agatston scores >100 and volume and density scores >75th percentile were defined as indices of CAC, signifying advanced subclinical atherosclerosis. Obese men had increased CAC Agatston, volume, and density scores, while higher CRF was associated with lower Agatston and volume scores after adjusting for potential confounders. In the joint analysis, unfit-obese men had higher CAC Agatston and CAC volume. The fit-obesity category was not associated with CAC Agatston (OR = 0.91: 95% CI, 0.66-1.25, for BMI and OR = 1.21: 95% CI, 0.86-1.70, for WC) and CAC volume (OR = 1.14: 95% CI, 0.85-1.53, for BMI and OR = 1.23: 95% CI, 0.90-1.69, for WC), which were similar to estimates for the fit-normal weight category. These findings demonstrate that while obesity is positively associated with the prevalence of moderate to severe CAC scores, CRF is inversely associated with the prevalence of moderate to severe CAC scores. Additionally, the combination of being fit and obese was not associated with CAC scores, which could potentially reinforce the fat-but-fit paradigm.

Correction Factors for CT Coronary Artery Calcium Scoring Using Advanced Modeled Iterative Reconstruction Instead of Filtered Back Projection

Aim: To investigate if estimation of the amount of calcium in the coronary system utilizing a visual coronary artery calcium scoring (CACS) system (Kirsch et al. Detection of coronary calcium during standard chest computed tomography correlates with multi-detector computed tomography coronary artery calcium score) in non - electrocardiogram (ECG) gated chest computed tomography (CT) scans maintains its strong correlation with the Agatston CACS on dedicated ECG gated cardiac CT exams across two or more points in time per patient. Methods: A visual scoring system (Weston score, WCS) was previously developed assigning a score (0-3, total score 0-12) for each coronary vessel including the left main trunk. Predetermined score cutoffs in both Agatston and Weston scoring methods were designated for risk stratification. Following institutional review board approval, we retrospectively analyzed 127 total body CT scans on 53 low-risk patients referred by executive health who had received repeat CT scans between 2007 and 2018 and compared the traditional Agatston CACS with the Weston score. Analysis: The data were gathered from a total of 53 executive health patients ages 33 to 71, with an average age of 51. 83.6% were male and 16.4% were female. 118 scans were examined, taken between 307 and 2,792 days apart, with an average of 937 days between scans. The Weston and Agatston scores predicted the same risk classification for 79.7% of the first set of scans, with 10.2% uprisked and 10.2% downrisked by their Weston scores. For the second set of scans, 78.0% had the same classification, with 10.2% uprisked and 11.9% downrisked by their Weston scores. Weston scores predicted 100% of scans within one risk classification of the corresponding Agatston score across all pairs of scans.The average CACS utilizing the Agatston scoring method was 54.3, with a standard deviation of 148.6 due to a large positive skew in the data. The corresponding Weston scores had an average of 1.1, with a standard deviation of 2.14. Conclusion: A visual CACS system (WCS) performed on non-gated CT scans allows risk stratification for cardiac events in a similar manner as the Agatston CACS on ECG-gated CT scans even at separate points in time.

Association of aortic root calcification severity with the extent of coronary artery calcification assessed by calcium-scoring dual-source computed tomography

Improved dose calculation accuracy for low energy brachytherapy by optimizing dual energy CT imaging protocols for noise reduction using sinogram affirmed iterative reconstruction

Introduction: Coronary artery calcium (CAC) scoring is a powerful tool for cardiovascular disease (CVD) risk prediction. The Agatston score weighs lesion area upward for density, and is consistent across computed tomography (CT) scanner type. Considering volume and density separately improves risk prediction, but has not been evaluated by CT scanner type. Hypothesis: Our hypothesis was that the predictive value of volume and density scoring would be superior to the Agatston score across CT scanner types. Methods: We used data from MESA (Multi-Ethnic Study of Atherosclerosis), a prospective cohort study of participants free of baseline clinical cardiovascular disease. CAC was measured using either EBCT (electron beam CT) or MDCT (multi-detector CT). We compared risk prediction for coronary heart disease (CHD) and CVD events using the Agatston method and the volume and density scores by scanner type using Cox proportional hazards models with multivariable adjustment among those with baseline CAC &gt; 0. HRs are presented as per standard deviation. Results: The 3,362 MESA participants with CAC &gt;0 were studied. Using the Agatston method, the HR [95% CI] for CHD was 1.28 [1.16-1.42] for EBCT and 1.22 [1.12-1.34] for MDCT. Using the volume score adjusted for density, the HR for CHD was 2.11 [1.70-2.63] for EBCT and 1.71 [1.41-2.07] for MDCT. Density was strongly and inversely associated with CHD. Similar results were seen for CVD risk and in analyses stratified by sex, BMI, age, and baseline statin use. The volume score demonstrated higher areas under the curve (AUC) than the Agatston score with EBCT (0.702, 95% CI 0.665-0.738 vs 0.677, 95% CI 0.638-0.715, p=0.013) and MDCT (0.669, 95% CI 0.632-0.705 vs 0.653, 95% CI 0.616-0.690, p=0.107). Conclusions: Compared with the Agatston score, the CAC volume score, adjusted for density, provides better risk prediction for CHD and CVD events, regardless of CT scanner type. CAC density was strongly and inversely associated with CVD risk.

Background Inadequate intake of polyunsaturated fatty acids (PUFAs) is recognized as a modifiable risk factor for atherosclerotic cardiovascular disease (CVD) (1,2). The n-6 PUFA linoleic acid (LA) constitutes the predominant portion of total dietary PUFAs (3). However, whereas cardiometabolic effects of PUFAs belonging to the n-3 series have been studied for decades, less attention has been payed to potential health effects from n-6 PUFAs (4). Further, there has been concern regarding possible proinflammatory properties of several n-6 PUFA related metabolites. Purpose We explored correlations of serum total PUFAs, LA and the n-3 PUFA docosahexaenoic acid (DHA) with the inflammation marker GlycA. Further, we evaluated associations of total PUFAs, LA and DHA with the extension of atherosclerosis, as determined by the Agatston coronary artery calcium (CAC) score (5). Methods The study includes 250 patients who were hospitalized due to acute chest pain and referred to coronary CT angiography (CCTA) during in hospital stay. Exclusion criteria included diagnosis of acute myocardial infarction and/or revascularization within 24 hours after admittance. Serum levels of total PUFAs, LA, DHA and GlycA were analyzed by NMR technology in samples that had been frozen and stored at −80°C. After logarithmic transformation, relations of total PUFA, LA, and DHA with GlycA were evaluated by Pearson correlation analyses. The associations with CAC score were visualized in generalized additive regression plots and further evaluated in linear regression models including age, gender, body mass index, diabetes, hypertension and smoking status as independent covariables. Results Mean (SD) age was 57.6 (12.0) years, and 91 (36.4%) of the patients were women. Median (25th-75th percentiles) serum levels (in mmol/L) were for total PUFA 6.36 (5.76–7.06), LA 5.00 (4.51–5.55), DHA 0.36 (0.31–0.43) and GlycA 1.04 (0.94–1.13). Interestingly, GlycA was strongly, positively correlated with total PUFA (r=0.54). LA (r=0.53) and DHA (r=0.27), all P&amp;lt;0.001. In contrast, total PUFA and LA were inversely associated with CAC score both providing standardized betas of −0.17, P=0.03 after multivariable adjustments. No significant associations were found between CAC score and DHA or GlycA (P≥0.22). Further, the addition of GlycA to the multivariable model did not materially affect the relationship between CAC score and total PUFA or LA, which remained statistically significant (P=0.04). Conclusion In patients undergoing CCTA due to acute chest pain, serum levels of total PUFA and LA were strongly positively correlated with the pro-inflammatory marker GlycA. Still, total PUFA and LA were both inversely associated with the CAC score and the associations remained statistically significant after adjustments for CVD risk factors and GlycA levels. Future studies should further address the diverse effects of n-6 PUFAs on inflammatory pathways, atherogenesis and coronary calcification. Funding Acknowledgement Type of funding sources: Public hospital(s). Main funding source(s): Western Norway Regional Health Authority

To assess the accuracy of an iterative reconstruction (IR) technique for coronary artery calcium scoring with reduced radiation dose. 163 consecutive patients underwent twofold scanning by 320-row detector CT at 120 kVp. A low-dose scan at 25% tube current but with standard scan length (14 cm) was followed by a standard dose scan with routine tube current but reduced scan length (10 cm). Reduced dose images were constructed using filtered back-projection (FBP) and IR (adaptive iterative dose reduction in three dimensions). The standard dose scan reconstructed with FBP served as the gold standard for comparisons. Image noise and Agatston coronary calcium scores were determined and compared between the groups. Compared with FBP at standard dose, noise at reduced dose increased markedly with FBP but remained low with IR. Mean Agatston score with FBP at reduced dose showed a significant increase as compared with FBP at standard dose. No significant difference was observed when applying IR at reduced dose. At reduced dose, 38 (23.3%) patients were reassigned to a different cardiovascular risk category with FBP but only 8 (4.9%) with IR. Out of 47 patients with a zero Agatston score, 15 patients (31.9%) were false-positive with FBP at reduced dose, but no false positives were found with IR. IR allows accurate coronary artery calcium scoring with a radiation dose reduced by 75%. Advances in knowledge: The application of adaptive iterative dose reduction in three dimensions allows the maintenance of accurate Agatston scores and risk stratification at significantly reduced tube current, thus reducing the patient's exposure to ionizing radiation.

The objective of this study was to evaluate the radiation dose reduction potential of a novel image-based denoising technique in pediatric abdominopelvic and chest CT examinations and compare it with a commercial iterative reconstruction method. Data were retrospectively collected from 50 (25 abdominopelvic and 25 chest) clinically indicated pediatric CT examinations. For each examination, a validated noise-insertion tool was used to simulate half-dose data, which were reconstructed using filtered back-projection (FBP) and sinogram-affirmed iterative reconstruction (SAFIRE) methods. A newly developed denoising technique, adaptive nonlocal means (aNLM), was also applied. For each of the 50 patients, three pediatric radiologists evaluated four datasets: full dose plus FBP, half dose plus FBP, half dose plus SAFIRE, and half dose plus aNLM. For each examination, the order of preference for the four datasets was ranked. The organ-specific diagnosis and diagnostic confidence for five primary organs were recorded. The mean (± SD) volume CT dose index for the full-dose scan was 5.3 ± 2.1 mGy for abdominopelvic examinations and 2.4 ± 1.1 mGy for chest examinations. For abdominopelvic examinations, there was no statistically significant difference between the half dose plus aNLM dataset and the full dose plus FBP dataset (3.6 ± 1.0 vs 3.6 ± 0.9, respectively; p = 0.52), and aNLM performed better than SAFIRE. For chest examinations, there was no statistically significant difference between the half dose plus SAFIRE and the full dose plus FBP (4.1 ± 0.6 vs 4.2 ± 0.6, respectively; p = 0.67), and SAFIRE performed better than aNLM. For all organs, there was more than 85% agreement in organ-specific diagnosis among the three half-dose configurations and the full dose plus FBP configuration. Although a novel image-based denoising technique performed better than a commercial iterative reconstruction method in pediatric abdominopelvic CT examinations, it performed worse in pediatric chest CT examinations. A 50% dose reduction can be achieved while maintaining diagnostic quality.

Background: To compare the quality of computerized tomography (CT) imaging of coronary artery stents between low tube voltage (100 kVp) scan combined with sinogram affirmed iterative reconstruction (SAFIRE) and routine tube voltage (120 kVp) scan combined with traditional filtered back projection (FBP). Objectives: The purpose of this study was to compare the quality of CT imaging of coronary artery stents between low tube voltage scan (100 kVp) combined with sinogram affirmed iterative reconstruction (SAFIRE) and routine tube voltage scan (120 kVp) with FBP. Patients and Methods: Second generation dual source CT was performed on 156 patients with implanted coronary stents (group A, 86 cases with 100 kVp and SAFIRE; group B, 70 cases with 120 kVp and FBP). The mean attenuation, image noise, signal-to-noise ratio (SNR), stent-lumen attenuation increase ratio (SAIR), image quality scores, lesion assessment of the stents, and radiation dosage were compared between the two groups. Results: The mean attenuation and SAIR of the aortic root, in-stent, and the coronary artery above the stent had no significant difference between the two groups (P 0.05). The diagnostic information of stents by 100 kVp combined with SAFIRE had no significant difference with those by 120 kVp FBP (P > 0.05). The effective dose of group A were about 51.5% lower than group B. Conclusion: SAFIRE combined with lower tube voltage on coronary artery stent CT imaging could maintain image quality while significantly reduce the radiation dosage.

Coronary artery calcium (CAC) scoring with computed tomography (CT) is an established tool for quantifying calcified atherosclerotic plaque burden. Despite the widespread use of novel image reconstruction techniques in CT, the effect of iterative model reconstruction on CAC score remains unclear. We sought to assess the impact of iterative model based reconstruction (IMR) on coronary artery calcium quantification as compared to the standard filtered back projection (FBP) algorithm and hybrid iterative reconstruction (HIR). In addition, we aimed to simulate the impact of iterative reconstruction techniques on calcium scoring based risk stratification of a larger asymptomatic population. We studied 63 individuals who underwent CAC scoring. Images were reconstructed with FBP, HIR and IMR and CAC scores were measured. We estimated the cardiovascular risk reclassification rate of IMR versus HIR and FBP in a larger asymptomatic population (n = 504). The median CAC scores were 147.7 (IQR 9.6-582.9), 107.0 (IQR 5.9-526.6) and 115.1 (IQR 9.3-508.3) for FBP, HIR and IMR, respectively. The HIR and IMR resulted in lower CAC scores as compared to FBP (both p < 0.001), however there was no difference between HIR and IMR (p = 0.855). The CAC score decreased by 7.2 % in HIR and 7.3 % in IMR as compared to FBP, resulting in a risk reclassification rate of 2.4 % for both HIR and IMR. The utilization of IMR for CAC scoring reduces the measured calcium quantity. However, the CAC score based risk stratification demonstrated modest reclassification in IMR and HIR versus FBP.

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