Search

To investigate the accuracy of Agatston scoring and potential for radiation dose reduction of a coronary artery calcium scoring (CACS) CT protocol at 100 kV with tin filtration (Sn100kV) and kV-independent iterative reconstruction, compared to standard 120 kV acquisitions. With IRB approval and in HIPAA compliance, 114 patients (61.8 ± 9.6 years; 66 men) underwent CACS using a standard 120 kV protocol and an additional Sn100kV CACS scan. The two datasets were reconstructed using a medium sharp convolution algorithm and in addition the Sn100kV scans were reconstructed iteratively based on a kV-independent algorithm. Agatston scores and radiation dose values were compared between the Sn100kV and the standard 120 kV protocol. Median Agatston scores derived from the Sn100kV protocol with the kV-independent algorithm and the standard 120 kV were 21.4 (IQR, 0–173.8) and 24.7 (IQR, 0–171.1) respectively, with no significant differences (p= 0.18). Agatston scores derived from the two different protocols had an excellent correlation (r = 0.99). The dose-length-product was 11.5 ± 4.1 mGy × cm using Sn100kV and 50.4 ± 24.9 mGy × cm using the standard 120 kV protocol (p < 0.01), resulting in a significantly lower (77%) effective dose at Sn100kV (0.16 ± 0.06 mSv vs. 0.71 ± 0.35 mSv, p < 0.01). Additionally, 99% of the patients were classified into the same risk category (0, 1–10, 11–100, 101–400, or >400) using the Sn100kV protocol. CACS at Sn100kV using the kV-independent iterative algorithm is feasible and provides high accuracy when compared to standard 120 kV scanning. Furthermore, radiation dose can be significantly reduced for this screening application in a priori healthy individuals. [ABSTRACT FROM AUTHOR]

Abstract Computed tomographic (CT) coronary calcium scoring has been established by large prospective, population-based studies as the single best noninvasive predictor of atherosclerotic cardiovascular risk available today. The calcium score correlates highly with the total burden of coronary atherosclerosis demonstrated at autopsy. It adds significantly to traditional risk calculators such as the Framingham Risk Calculator or the Pooled Cohort Equations. The 2018 U.S. Cholesterol Guidelines endorse the use of CT coronary calcium scoring to refine risk estimates in the intermediate range of 7.5%–20% over 10 years. Most, but not all, adults with calcium scores of zero can reasonably elect to avoid or defer statin therapy, but repeating the calcium score should be considered in 5 to 10 years. Discussants at this roundtable urge that coronary calcium scoring be offered to many more adults than currently receiving this test, including those with borderline 10-year risk in the range of 5%–7.5%. CT coronary angiography is a procedure based on intravenous contrast injection, mostly used in low-risk patients with chest pain. In British guidelines, CT angiography is preferred over stress testing for initial assessment of suspected coronary symptoms. Carotid ultrasound evaluating both the carotid intima-media thickness and presence of plague is less predictive than coronary calcium scoring for overall atherosclerotic risk but more predictive for stroke risk. [ABSTRACT FROM AUTHOR]

Rationale and Objectives: Different computed tomography imaging protocols and patient characteristics can impact the accuracy and precision of the calcium score and may lead to inconsistent patient treatment recommendations. The aim of this work was to determine the impact of reconstruction algorithm and gender characteristics on coronary artery calcium scoring based on a phantom study using computed tomography.Materials and Methods: Four synthetic heart vessels with vessel diameters corresponding to female and male left main and left circumflex arteries containing calcification-mimicking materials (200-1000 HU) were inserted into a thorax phantom and were scanned with and without female breast plates (male and female phantoms, respectively). Ten scans were acquired and were reconstructed at 3-mm slices using filtered-back projection (FBP) and iterative reconstruction with medium and strong denoising (IR3 and IR5) algorithms. Agatston and calcium volume scores were estimated for each vessel. Calcium scores for each vessel and the total calcium score (summation of all four vessels) were compared between the two phantoms to quantify the impact of the breast plates and reconstruction parameters. Calcium scores were also compared among vessels of different diameters to investigate the impact of the vessel size.Results: The calcium scores were significantly larger for FBP reconstruction (FBP > IR3>IR5). Agatston scores (calcium volume score) for vessels in the male phantom scans were on average 4.8% (2.9%), 8.2% (7.1%), and 10.5% (9.4%) higher compared to those in the female phantom with FBP, IR3, and IR5, respectively, when exposure was conserved across phantoms. The total calcium scores from the male phantom were significantly larger than those from the female phantom (P <0.05). In general, calcium volume scores were underestimated (up to about 50%) for smaller vessels, especially when scanned in the female phantom.Conclusions: Calcium scores significantly decreased with iterative reconstruction and tended to be underestimated for female anatomy (smaller vessels and presence of breast plates). [ABSTRACT FROM AUTHOR]

Background Impaired myocardial flow reserve (MFR) is a marker of coronary vascular dysfunction with prognostic significance. Objectives We aimed to investigate the relationship between epicardial fat volume (EFV) measured from noncontrast CT and impaired MFR derived from rest-stress Rb-82 positron emission tomography (PET). Methods We retrospectively studied 85 consecutive patients without known coronary artery disease who underwent rest-stress Rb-82 myocardial PET/CT and were subsequently referred for invasive coronary angiography. EFV was computed from noncontrast CT by validated software and indexed to body surface area (EFVi, cm 3 /m 2 ). Global stress and rest MFR were automatically derived from PET. Patient age, sex, cardiovascular risk factors, coronary calcium score (CCS), and EFVi were combined by boosted ensemble machine learning algorithm into a novel composite risk score, using 10-fold cross-validation, to predict impaired global MFR (MFR ≤2.0) by PET. Results Patients with impaired MFR (44 of 85; 52%) were older (71 vs 65 years; P = .03) and had higher frequency of CCS (≥400; P = .02) with significantly higher EFVi (63.1 ± 20.4 vs 51.3 ± 14.1 cm 3 /m 2 ; P = .003). On multivariate logistic regression (with age, sex, number of risk factors, CCS, and EFVi), EFVi was the only independent predictor of impaired MFR (odds ratio, 7.39; P = .02). The machine learning composite risk score significantly improved risk reclassification of impaired MFR compared to CCS or EFVi alone (integrated discrimination improvement = 0.19; P = .007 and IDI = 0.22; P = .002, respectively). Conclusions Increased EFVi and composite risk score combining EFVi and CCS significantly improve identification of impaired global MFR by PET. [ABSTRACT FROM AUTHOR]

Background: Reducing tube voltage from 120 kV to 100 kV during noncontrast CT for the detection of coronary artery calcium reduces patient radiation exposure. Objective: We investigated whether coronary calcium scoring by multidetector row CT can be performed at reduced tube current, resulting in lower radiation dose to the patient. Methods: Sixty-six outpatients were scanned on the same visit by dual-source CT (DSCT) with a standard protocol (120 kVp, 150 mAs), followed by a scan with reduced tube current: 85 mAs for patients with body mass index (BMI) ≤ 30 kg/m2 and weight ≤ 85 kg, and 120 mAs for patients with BMI > 30 kg/m2 or weight > 85 kg. Low-dose scans were scored by an experienced reader blinded to the standard scan. Results: Agatston scores (ASs) and calcium volume for standard versus low-dose scans were 236 ± 581 versus 234 ± 586 (P = 0.65, NS), and 189 ± 460 mm3 versus 184 ± 455 mm3 with excellent correlation (r = 1.0, P < 0.0001), and no significant difference (P = 0.14, NS). Effective radiation dose for the low-dose protocol (1.0 ± 0.2 mSv) was significantly lower than for the standard protocol (1.7 ± 0.2 mSv; P < 0.0001). Image noise was higher for the low-dose scan (18.8 ± 5.5 HU vs 15.2 ± 4.8 HU; P < 0.0001), but both were within target limits. Conclusion: Noncontrast CT for measurement of coronary artery calcium with lower tube current optimized for patient body size is equivalent to standard methods at 40% lower radiation dose, indicating that radiation dose can be lowered for coronary calcium scanning. [ABSTRACT FROM AUTHOR]

Background: Test phantoms with simulated micro-calcifications of true calcium hydroxyapatite (CaHA) density were not available to validate advanced calcium scoring methods or plaque density measurements. Objectives: We evaluated a coronary calcium scoring (CCS) test phantom containing very small CaHA microspheres and validated a new scoring method for measurements of plaque densities. Methods: The semianthropomorphic CCS phantom was constructed with CaHA microspheres (volumes, 0.05–3.1 mm3) with the approximate density of biologic calcifications. QRM and CCS phantoms were scored with a new calibrated and automated calcium scoring method (N-vivo; Image Analysis). The densities of the microspheres and 609 individual patient plaques were measured. Results: The range of measured densities of the CaHA microspheres was approximately equivalent to that measured in the patient coronary calcifications. The smallest microspheres scored with the calibrated/automated and the Agatston methods had volumes of 0.075 mm3 and 0.27 mm3, respectively. The standard deviations of the mass scores of the microspheres ranged from 0.02 to 0.17 mg with regression slope of 0.962 and R 2 = 0.997. The relationship of measured density to measured mass of the patient plaques was similar to that of the microspheres, suggesting that vascular calcifications are CaHA density. Conclusions: The CaHA microspheres of the CCS test phantom were found to be representative in density and size of coronary calcifications. The measurements show that CT calcium scoring underestimates plaque density and greatly overestimates volume. The heterogeneity of calcium concentration densities measured in the patient plaques was due largely to CT scanner measurement errors. [ABSTRACT FROM AUTHOR]

Background: Technical advances to minimize radiation exposure because of imaging are in accord with the “as low as reasonably achievable” principle. Objective: We aimed to determine whether coronary calcium scoring (CCS) by multidetector CT at a tube voltage of 100 kVp yields comparable results to the standard 120-kVp protocol while reducing radiation dose. Methods: Sixty consecutive outpatients were scanned with a dual-source CT scanner with both the120- and 100-kVp protocols. The calcium threshold was 130 Hounsfield units (HUs) for 120 kVp and 147 HU for 100 kVp, as determined from phantom data. All 100-kVp scans were scored by an experienced reader blinded to 120-kVp data. Results: Image quality was comparable for 100- and 120- kVp scans. Mean Agatston scores for 100 and 120 kVp were 189 ± 484 and 189 ± 498 (P = 0.92), with perfect correlation (r = 1.0; P < 0.0001; 95% limits of agreement, -36 to 37; bias, 0.6). Mean coronary calcium volume scores for 100 and 120 kVp were 143 ± 370 mm3 and 149 ± 392 mm3 (P = 0.26), with perfect correlation (r = 1.0; P < 0.0001; 95% limits of agreement, -35 to 32 mm3; bias, -1.4 mm3). The mean absolute difference for Agatston scores between the protocols was 16.9, with excellent agreement (κ = 0.95; P < 0.0001). Mean effective radiation dose for the 100-kVp protocol was significantly lower (1.17 mSv versus 1.70 mSv; P < 0.0001). Conclusion: A reduced tube current protocol using 100 kVp gives equivalent CCS results at reduced radiation exposure compared with a standard protocol at 120 kVp. [Copyright &y& Elsevier]