Coronary artery calcium assessed with calibrated mass scoring in asymptomatic individuals: results from the Copenhagen General Population Study.

BACKGROUND: Coronary artery calcification (CAC) is commonly assessed with Agatston score (AS). A higher sensitivity and precision for the detection of CAC has been demonstrated with calibrated mass score (cMS). We hypothesized that cMS would detect low-level CAC not detectable with AS in a large asymptomatic background population. METHODS: Participants (N = 2985) from the Copenhagen General Population Study were evaluated for CAC using both conventional AS and cMS. The population was grouped according to number of traditional risk factors and heart score was used to assess the risk of event for those with no CAC, those with only cMS > 0 and those with both AS and cMS > 0. RESULTS: In participants with an AS = 0, 11% had cMS > 0. The risk profile of this cMS-only group was between that of the CAC-negative participants and those with AS > 0 and cMS > 0. Overall, 6% of the population belonged to the cMS-only group independent of the number of risk factors. CONCLUSION: In individuals with AS = 0, a fraction was found to have cMS > 0. Based on traditional risk factors, this group has a higher 10-year risk than individuals with both AS = 0 and cMS = 0; cMS might offer very early cardiovascular risk assessment in asymptomatic individuals. KEY POINTS: • In individuals with AS=0, a fraction has CAC with highly sensitive cMS. • This fraction has a higher 10-year risk of cardiovascular disease. • Regardless of risk factors, 6% has CAC detectable only with cMS. • cMS might offer very early cardiovascular risk assessment in asymptomatic individuals.

Assessment of coronary calcification using calibrated mass score with two different multidetector computed tomography scanners in the Copenhagen General Population Study.

OBJECTIVE: Population studies have shown coronary calcium score to improve risk stratification in subjects suspected for cardiovascular disease. The aim of this work was to assess the validity of multidetector computed tomography (MDCT) for measurement of calibrated mass scores (MS) in a phantom study, and to investigate inter-scanner variability for MS and Agaston score (AS) recorded in a population study on two different high-end MDCT scanners. MATERIALS AND METHODS: A calcium phantom was scanned by a first (A) and second (B) generation 320-MDCT. MS was measured for each calcium deposit from repeated measurements in each scanner and compared to known physical phantom mass. Random samples of human subjects from the Copenhagen General Population Study were scanned with scanner A (N=254) and scanner B (N=253) where MS and AS distributions of these two groups were compared. RESULTS: The mean total MS of the phantom was 32.9±0.8mg and 33.1±0.9mg (p=0.43) assessed by scanner A and B respectively - the physical calcium mass was 34.0mg. Correlation between measured MS and physical calcium mass was R2=0.99 in both scanners. In the population study the median total MS was 16.8mg (interquartile range (IQR): 3.5-81.1) and 15.8mg (IQR: 3.8-63.4) in scanner A and B (p=0.88). The corresponding median total AS were 92 (IQR: 23-471) and 89 (IQR: 40-384) (p=0.64). CONCLUSION: Calibrated calcium mass score may be assessed with very high accuracy in a calcium phantom by different generations of 320-MDCT scanners. In population studies, it appears acceptable to pool calcium scores acquired on different 320-MDCT scanners.

Very small calcifications are detected and scored in the coronary arteries from small voxel MDCT images using a new automated/calibrated scoring method with statistical and patient specific plaque definitions.

A negative (zero) Agatston coronary calcium score (CCS) by current methods confers a very low risk for hard coronary events during the next years. However, controversy remains on how to use a negative score since some hard events still occur. We report on a new method with improved detection sensitivity for very small calcifications with the potential to more confidently rule out early atherosclerotic disease. Seventy-eight (78) patients with negative Agatston scores by conventional methods with 2.5 mm slices were selected from routine GE 64 MDCT scans. Each scan was reconstructed a second time from the same data to create 0.625 mm isotropic voxels. The 2.5 mm images were manually scored by the usual Agatston method using the GE SmartScore™ software. Both the 2.5 and 0.625 mm image sets were scored with a new automated and calibrated method (N-vivo™, Image Analysis). The software automatically computes dual scoring thresholds that are statistically defined and specific for each patient, scanner, and scan. The images were hybrid calibrated by simultaneous scanned phantoms in combination with in vivo blood/muscle references. The output reported the calibrated mass scores along with the number of plaques using 18 pt, 3-D connectivity criteria. A CCS Test phantom with known CaHA microspheres was used to validate the method. Twenty-three percent (18 of 78) of the patients with negative Agatston scores by the conventional method scored positive for coronary calcifications by the N-vivo method. The number of small plaques scored per patient varied from 1 to 4. One patient with a single small calcification suffered a hard coronary event during the CT scan. All of the detected plaques were located in the proximal heart. The conventional CCS method misclassified 23% of these patients as having negative coronary calcium scores. The N-vivo automated scoring method with small voxel CT images increased the detection sensitivity of small calcifications with no increase in radiation dose. Detection of small coronary calcified plaques occult to conventional scoring methods may increase the negative predictive power of calcium scoring and may improve plaque composition analysis.

Coronary calcium test phantom containing true CaHA microspheres for evaluation of advanced CT calcium scoring methods.

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 mm(3)) 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 mm(3) and 0.27 mm(3), 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.

Peak SNR in automated coronary calcium scoring: selecting CT scan parameters and statistically defined scoring thresholds.

PURPOSE: Development and verification of peak signal-to-noise ratio (SNR(P)) equations for determining optimum CT scanning and scoring parameters for a new automated coronary calcium scoring program (N-vivo). Experimental evaluation of the new program for scoring small calcium hydroxyapatite (CaHA) microspheres with small voxel CT images. METHODS: Theoretical SNR(P) equations were developed using measures of noise, resolution, contrast, scatter, and x-ray photon energy. A coronary calcium scoring test phantom containing very small CaHA microspheres was scanned simultaneously with a calibration phantom at three kVps, three voxel sizes, and three phantom sizes. Agatston and calibrated mass scores, noise standard deviations, peak noise, and peak signal voxel intensities were measured by the N-vivo method for individual microspheres and in patient CT scans. RESULTS: The SNR(P) equation was predictive of the optimum voxel size, kVp, and phantom size, and allowed automated computation of mass scoring thresholds specific to each patient and CT scan. The smallest microcalcification scored in the full sized phantom with the N-vivo method by calibrated mass score (volume 0.075 mm3, mass 0.17 mg) was approximately four times smaller than that scored with the Agatston method (0.27 mm3, mass 0.63 mg). CONCLUSIONS: The SNR(P) equation can be used to model and optimize calcium scoring and CT scan parameters. The common assumptions that noise is too high in thin slice CT or requires high radiation dose for CAC scoring are shown to be misleading. The N-vivo method showed higher detection sensitivity for small microspheres and more consistent mass scores at different beam energies than the conventional Agatston method. Advanced calcium scoring methods with higher sensitivity may allow improved monitoring of plaque changes and provide earlier detection of atherosclerosis.