Coronary CT Calcium Score in Patients With Prior Nongated CT,Is it Necessary?

PurposeTo evaluate the percentage of patients undergoing gated coronary artery calcium score CTs that had a prior nongated chest CT. To assess the accuracy of prior nongated chest CTs in the detection of coronary calcium.BackgroundCardiovascular disease is the most common cause of death worldwide. Quantifying coronary artery calcification on gated calcium score CT has proven to be strongly predictive of adverse coronary artery disease events. However, visual estimation and ordinal scoring on nongated chest CTs is predictive of coronary calcium burden.MethodsConsecutive gated calcium score CTs at a single institution from 10/2014 to 10/2016 were retrospectively evaluated with IRB approval/waiver of informed consent. The presence or absence of coronary calcium and ordinal score on nongated chest CT was compared to Agatston score on gated calcium score CT.ResultsForty-two of 441 patients (9.5%) with a gated calcium score had a prior nongated chest CT, with a mean time difference of 810 days. Of the 42 prior chest CTs, 69% had coronary artery calcium (CAC) and 31% did not, with 100% predictive accuracy for the presence or absence of CAC on subsequent gated calcium score CTs. There was 86% correlation of Agatston score on gated calcium score CT with ordinal score on the prior chest CT. Ordinal score divided into independent groups of severity was related to increased severity of Agatston score on the gated calcium score CT (P< 0.001). A majority of prior chest CT studies with coronary calcium failed to include this information in the final report.ConclusionsA large percentage of gated calcium score CTs were performed despite a prior chest CT. The ordinal score on chest CTs correlated with Agatston score on gated calcium score CTs. The presence of CAC on chest CTs was underreported in a majority of cases.     

A method for calcium quantification by means of CT coronary angiography using 64-multidetector CT: very high correlation with agatston and volume scores

To find out whether calcium scoring of the coronary arteries (CAC scoring) could be carried out with a CT angiography of the coronary arteries (CTCA) in a single CT data acquisition. The Agatston and V130 scores for 113 patients were assessed. A calcium volume score (V600 score) was compiled from the CTCA data sets. Intra- and interobserver correlations were excellent (ρ > 0.97). The intra- and interobserver repeatability coefficients were extremely low, increasing in magnitude from the V600 score to the V130 and Agatston scores. The V600 score underestimates the coronary calcium burden. However, it has a linear relation to the Agatston and V130 scores. Thus, they are predictable from the values of the V600 score. The V600 score shows a linear relation to the classic CAC scores. Due to its extremely high reliability, the score may be a feasible alternative for classic CAC scoring methods in order to reduce radiation dosages.     

High-pitch dual-source CT for coronary artery calcium scoring: A head-to-head comparison of non-triggered chest versus triggered cardiac acquisition

BackgroundTo determine the effect of low-dose, high-pitch non-electrocardiographic (ECG)-triggered chest CT on coronary artery calcium (CAC) detection, quantification and risk stratification, compared to ECG-triggered cardiac CT.MethodsWe selected 1,000 participants from the ImaLife study, 50% with coronary calcification on cardiac CT. All participants underwent non-contrast cardiac CT followed by chest CT using third-generation dual-source technology. Reconstruction settings were equal for both acquisitions. CAC scores were determined by Agatston's method, and divided dichotomously (0, >0), and into risk categories (0, 1–99, 100–399, ≥400). We investigated the influence of heart rate and body mass index (BMI) on risk reclassification.ResultsPositive CAC scores on cardiac CT ranged from 1 to 6926 (median 39). Compared to cardiac CT, chest CT had sensitivity of 0.96 (95%CI 0.94–0.98) and specificity of 0.99 (95%CI 0.97–0.99) for CAC detection (κ = 0.95). In participants with coronary calcification on cardiac CT, CAC score on chest CT was lower than on cardiac CT (median 30 versus 40, p?0.001). Agreement in CAC-based risk strata was excellent (weighted κ = 0.95). Sixty-five cases (6.5%) were reclassified by one risk category in chest CT, with fifty-five (84.6%) shifting downward. Higher BMI resulted in higher reclassification rate (13% for BMI ≥30 versus 5.2% for BMI <30, p = 0.001), but there was no effect of heart rate.ConclusionLow-dose, high-pitch chest CT, using third-generation dual-source technology shows almost perfect agreement with cardiac CT in CAC detection and risk stratification. However, low-dose chest CT mainly underestimates the CAC score as compared to cardiac CT, and results in inaccurate risk categorization in BMI ≥30.     

Influence of scoring parameter settings on Agatston and volume scores for coronary calcification

Current multi-detector CT and electron beam tomography (EBT) technology enables the evaluation of coronary calcification. Multiple software packages are available to quantify calcification using several scoring algorithms implementing user-definable scoring parameters. We investigated the effect of scoring parameters on the calcium score outcome. Three parameters (four-connected or eight-connected, lesion size threshold and interpolation) are evaluated. Their theoretical influence on the scoring outcome is shown using simplified examples. To evaluate the effect in real data, we performed calcium scoring on randomly chosen EBT scans from 50 participants in an epidemiological study. Both the Agatston and volume scores were calculated. Changing from eight-connected to four-connected connectivity decreased both Agatston and volume scores (mean variability Agatston 3.15% and volume score –3.52%). Decreasing the threshold from 4 to 2 pixels increased the calcium scores because smaller lesions were also selected as calcified plaques (mean variability Agatston 16.23% and volume score 18.66%). Finally, the use of interpolation had a large negative effect on the volume score (mean variability –29.67%) and almost no effect on the Agatston score. Parameter settings in software for quantification for coronary calcification affect the calcium score outcome. Therefore, parameter settings for calcium scoring should be standardized.     

Practical tips and tricks in cardiovascular computed tomography: Non-contrast “heartscans”—beyond the calcium score

The Agatston total coronary artery calcium (CAC) score, derived from a non-contrast CT scan of the heart (also known as the “heartscan”) in asymptomatic and symptomatic patients, has been shown to provide incremental and independent assessment to conventional risk factors based upon literally hundreds of studies published from around the world. However, recent data have emerged to indicate that there is additional information which can be derived from a “heartscan” beyond the calcium score. These include recent data on the applicability across ethnic sub-groups, prognostication in the elderly, defining “heart age” versus chronological age for individual risk stratification, evaluating CAC distribution in addition to total CAC score, and looking beyond the coronary arteries regarding left ventricular size, arotic root/thoracic aorta diameter, and epicardial fat.     

Reliability of Coronary Artery Calcium Severity Assessment on Non-Electrocardiogram-Gated CT: A Meta-Analysis

ObjectiveThe purpose of this meta-analysis was to investigate the pooled agreements of the coronary artery calcium (CAC) severities assessed by electrocardiogram (ECG)-gated and non-ECG-gated CT and evaluate the impact of the scan parameters.Materials and MethodsPubMed, EMBASE, and the Cochrane library were systematically searched. A modified Quality Assessment of Diagnostic Accuracy Studies-2 tool was used to evaluate the quality of the studies. Meta-analytic methods were utilized to determine the pooled weighted bias, limits of agreement (LOA), and the correlation coefficient of the CAC scores or the weighted kappa for the categorization of the CAC severities detected by the two modalities. The heterogeneity among the studies was also assessed. Subgroup analyses were performed based on factors that could affect the measurement of the CAC score and severity: slice thickness, reconstruction kernel, and radiation dose for non-ECG-gated CT.ResultsA total of 4000 patients from 16 studies were included. The pooled bias was 62.60, 95% LOA were −36.19 to 161.40, and the pooled correlation coefficient was 0.94 (95% confidence interval [CI] = 0.89–0.97) for the CAC score. The pooled weighted kappa of the CAC severity was 0.85 (95% CI = 0.79–0.91). Heterogeneity was observed in the studies (I² > 50%, p < 0.1). In the subgroup analysis, the agreement between the CAC categorizations was better when the two CT examinations had reconstructions based on the same slice thickness and kernel.ConclusionThe pooled agreement of the CAC severities assessed by the ECG-gated and non-ECG-gated CT was excellent; however, it was significantly affected by scan parameters, such as slice thickness and the reconstruction kernel.     

Electron beam CT versus 16-MDCT on the variability of repeated coronary artery calcium measurements in a variable heart rate phantom

OBJECTIVE: High reproducibility of coronary artery calcium (CAC) scoring is a key requirement for monitoring the progression of coronary atherosclerosis. The purposes of this study were to compare electron beam CT and 16-MDCT scanners in the variability of repeated CAC measurements and to assess the factors influencing this variability. MATERIALS AND METHODS: CAC models of different sizes attached to a cardiac phantom with a programmable variable heart rate were scanned three times, and interscan variability of the CAC measurement was calculated each time. For helical CT, different slice-thickness images of either retrospective ECG-gated or prospective ECG-triggering reconstruction were obtained. The detection of small amounts of calcium, variability of the Agatston score, and CAC measurement algorithms (Agatston, volume, and mass scores) were compared between CT scanners and protocols. RESULTS: All 1-mm-sized calcium models were detected on 0.625- and 1.25-mm helical CT, whereas some were missed on electron beam CT and 2.5-mm helical CT. Retrospective ECG-gated thin-slice helical CT showed the lowest variability. Reduction of variability by volume and mass scoring algorithms was less effective on 0.625- and 1.25-mm-thickness CT. CONCLUSION: Retrospective ECG-gated thin-slice helical CT has the potential to be a useful tool for monitoring coronary atherosclerosis.     

High-pitch versus sequential mode for coronary calcium in individuals with a high heart rate: Potential for dose reduction

BackgroundTo determine the impact of high-pitch spiral acquisition on radiation dose and cardiovascular disease (CVD) risk stratification by coronary artery calcium (CAC) assessment with computed tomography in individuals with a high heart rate.MethodsOf the ROBINSCA trial, 1990 participants with regular rhythm and heart rates >65 beats per minute (bpm) were included. As reference, 390 participants with regular heart rates ≤65 bpm were used. All participants underwent prospectively electrocardiographically(ECG)-triggered imaging of the coronary arteries using dual source CT at 120 kVp, 80 ref mAs using both high-pitch spiral mode and sequential mode. Radiation dose, Agatston score, number of positive scores, as well as median absolute difference of the Agatston score were determined and participants were stratified into CVD risk categories.ResultsA similar percentage of participants with low heart rates and high heart rates had a positive CAC score in data sets acquired in high-pitch spiral (low heart rate: 57.7%, high heart rate: 55.8%) and sequential mode (58.0%, 54.7%, p = n.s.). The median absolute difference in Agatston scores between acquisition modes was 14.2% and 9.2%, for the high and low heart rate groups, respectively. Excellent agreement for risk categorization between the two data acquisition modes was found for the high (κ = 0.927) and low (κ = 0.946) heart rate groups. Radiation dose was 48% lower for high-pitch spiral versus sequential acquisitions.ConclusionRadiation dose for the quantification of coronary calcium can be reduced by 48% when using the high-pitch spiral acquisition mode compared to the sequential mode in participants with a regular high heart rate. CVD risk stratification agreement between the two modes of data acquisition is excellent.     

A novel density-volume calcium score by non-contrast CT predicts coronary plaque burden on coronary CT angiography: Results from the MACS (Multicenter AIDS cohort study)

BackgroundThe purpose of this study is to determine if a new score calculated with coronary artery calcium (CAC) density and volume is associated with total coronary artery plaque burden and composition on coronary CT angiography (CCTA) compared to the Agatston score (AS).MethodsWe identified 347 men enrolled in the Multicenter AIDS cohort study who underwent contrast and non-contrast CCTs, and had CAC>0. CAC densities (mean Hounsfield Units [HU]) per plaque) and volumes on non-contrast CCT were measured. A Density-Volume Calcium score was calculated by multiplying the plaque volume by a factor based on the mean HU of the plaque (4, 3, 2 and 1 for 130–199, 200–299, 300–399, and ≥400HU). Total Density-Volume Calcium score was determined by the sum of these individual scores. The semi-quantitative partially calcified and total plaque scores (PCPS and TPS) on CCTA were calculated. The associations between Density-Volume Calcium score, PCPS and TPS were examined.ResultsOverall, 2879 CAC plaques were assessed. Multivariable linear regression models demonstrated a stronger association between the log Density-Volume Calcium score and both the PCPS (β 0.99, 95%CI 0.80–1.19) and TPS (β 2.15, 95%CI 1.88–2.42) compared to the log of AS (PCPS: β 0.77, 95%CI 0.61–0.94; TPS: β 1.70, 95%CI 1.48–1.94). Similar results were observed for numbers of PC or TP segments.ConclusionThe new CAC score weighted towards lower density demonstrated improved correlation with semi-quantitative PC and TP burden on CCTA compared to the traditional AS, which suggests it has utility as an alternative measure of atherosclerotic burden.     

Prevalence of silent myocardial ischemia in asymptomatic individuals with subclinical atherosclerosis detected by electron beam tomography

BACKGROUND: Electron beam tomography coronary calcium imaging is an evolving technique for the early detection of coronary atherosclerosis, and recent studies have established its prognostic value in asymptomatic individuals. The relationship of coronary artery calcium scores (CAC) to obstructive coronary artery disease (CAD) has been poorly studied but is clinically relevant because it determines which individuals are likely to benefit from revascularization procedures. Hence, we prospectively evaluated the prevalence of myocardial ischemia in asymptomatic patients with cardiovascular risk factors and subclinical atherosclerosis. METHODS AND RESULTS: We studied 864 asymptomatic patients with no previous CAD but with cardiovascular risk factors, referred for electron beam tomography coronary calcium imaging to our institution over an 18-month period. From this group, 220 consecutive patients (85% men; mean age, 61 +/- 9 years; age range, 31-84 years) with moderate to severe atherosclerotic disease (coronary calcium score > or =100 Agatston units) were prospectively evaluated by technetium 99m sestamibi single photon emission computed tomography (SPECT). Patients were followed up (mean follow-up, 14 months) and data regarding their subsequent clinical management recorded. Of the 220 patients, 119 had moderate atherosclerosis (CAC score of 100-400 Agatston units) and 101 had severe atherosclerosis (CAC score > or =400 Agatston units). Abnormal SPECT findings were seen in 18% of patients with moderate atherosclerosis (n = 21) and 45% of patients with severe atherosclerosis (n = 45). Increasing severity of atherosclerosis was related to increasing ischemic burden (summed difference score = 1 +/- 0.2 for CAC score of 100-400 Agatston units and 3.2 +/- 0.5 for CAC score > or =400 Agatston units). In a multivariate linear regression model incorporating risk factors, CAC was the only predictor of silent ischemia. CONCLUSION: In comparison to previously published data, we detected a higher prevalence of silent ischemia even in patients with moderate coronary atherosclerosis (18%). This may reflect the differing risk factor profile of our patient population. When coronary calcium screening is used to preselect asymptomatic patients with cardiovascular risk factors for myocardial perfusion imaging, the optimum coronary calcium score threshold will depend on the population prevalence of risk factors and asymptomatic obstructive CAD.     

急性胸痛患者总冠状动脉钙化和局部钙化的差异与急性冠脉综合征及主要病变之间的关系

目的 探讨急性冠状动脉综合征(ACS)总冠状动脉钙化(CAC)负荷和局部CAC与主要病变之间的关系.方法 对37例ACS患者及223例对照患者进行计算机CAC检查和CT血管造影评估显著狭窄和高风险斑块的表现,测量总评分和节段Agatston评分.对ACS患者的主要病变进行评价.结果 37例ACS患者的CAC总评分较非A...     

Concordance of coronary artery calcium estimates between MDCT and electron beam tomography

OBJECTIVE: The objective of our study was to compare MDCT with electron beam tomography (EBT) for the quantification of coronary artery calcification (CAC). MATERIALS AND METHODS: Sixty-eight patients underwent both MDCT and EBT within 2 months for the quantification of CAC. The images were scored in a blinded fashion and independently by two observers with a minimum of 7 days between the interpretations of images obtained from one scanner type to the other. RESULTS: Presence versus absence of CAC was discordant by EBT versus MDCT in 6% (n = 4) of the cases by observer 1, with one of these cases also discordant by observer 2. All cases except one (aortic calcium misidentified as CAC) were among those with a mean Agatston score of less than 5 present on EBT but absent on MDCT. EBT and MDCT scores correlated well (r = 0.98-0.99). The relative median variability between EBT and MDCT for the Agatston score was 24% for observer 1 and 27% for observer 2 and was 18% and 14%, respectively, for volume score (average for both observers: 27% for Agatston score and 16% for volume score). Scores were higher for EBT than MDCT in approximately half of the cases, with little systematic difference between the two (median EBT-MDCT difference: Agatston score, -0.55; volume score, 3.4 mm3). The absolute median difference averaged for the two observers was 28.75 for the Agatston score and 15.4 mm3 for the volume score. CONCLUSION: Differences in CAC measurements using EBT and MDCT are similar to interscan differences in CAC measurements previously reported for EBT or for other MDCT scanners individually.     

Impact of iterative reconstruction on CT coronary calcium quantification

Objectives

We evaluated the influence of sinogram-affirmed iterative reconstruction (SAFIRE) on the coronary artery calcium (CAC) score by computed tomography (CT).

Materials and methods

Seventy patients underwent CAC imaging by 128-slice dual-source CT. CAC volume, mass and Agatston score were calculated from images reconstructed by filtered back projection (FBP) without and with incremental degrees of the SAFIRE algorithm (10-50 %). We used the repeated measuring test and the Steel-Dwass test for multiple comparisons of values and the difference ratio among different SAFIRE groups using the FBP as reference.

Results

The median Agatston score (range) decreased with incremental SAFIRE degrees: 163 (0.1???3,393.3), 158.4 (0.3???3,079.3), 137.7 (0.1???2,978.0), 120.6 (0???2,783.6), 102.6 (0???2,468.4) and 84.1 (0???2,186.9) for 0 % (FBP), 10 %, 20 %, 30 %, 40 % and 50 % SAFIRE, respectively (P?<?0.05). In comparison with FBP, CAC volume (from 8.1 % to 47.7 %), CAC mass (from 5.3 % to 44.7 %) and CAC Agatston score (from 7.3 % to 48.4 %) all decreased with increasing SAFIRE from 10 % to 50 %, respectively (P?<?0.05). High-grade SAFIRE resulted in the disappearance of detectable calcium in three cases with low calcium burden.

Conclusion

SAFIRE noise reduction techniques significantly affected the CAC, which potentially alters perceived cardiovascular risk.

Key points

? Iterative reconstruction reduces the amount of coronary calcium detected. ? Iterative reconstruction potentially changes the calcium-based cardiovascular risk estimation. ? Incidentally, calcium is no longer detectable using iterative reconstruction.     

Coronary artery calcium: a multi-institutional, multimanufacturer international standard for quantification at cardiac CT

PURPOSE: To develop a consensus standard for quantification of coronary artery calcium (CAC). MATERIALS AND METHODS: A standard for CAC quantification was developed by a multi-institutional, multimanufacturer international consortium of cardiac radiologists, medical physicists, and industry representatives. This report specifically describes the standardization of scan acquisition and reconstruction parameters, the use of patient size-specific tube current values to achieve a prescribed image noise, and the use of the calcium mass score to eliminate scanner- and patient size-based variations. An anthropomorphic phantom containing calibration inserts and additional phantom rings were used to simulate small, medium-size, and large patients. The three phantoms were scanned by using the recommended protocols for various computed tomography (CT) systems to determine the calibration factors that relate measured CT numbers to calcium hydroxyapatite density and to determine the tube current values that yield comparable noise values. Calculation of the calcium mass score was standardized, and the variance in Agatston, volume, and mass scores was compared among CT systems. RESULTS: Use of the recommended scanning parameters resulted in similar noise for small, medium-size, and large phantoms with all multi-detector row CT scanners. Volume scores had greater interscanner variance than did Agatston and calcium mass scores. Use of a fixed calcium hydroxyapatite density threshold (100 mg/cm(3)), as compared with use of a fixed CT number threshold (130 HU), reduced interscanner variability in Agatston and calcium mass scores. With use of a density segmentation threshold, the calcium mass score had the smallest variance as a function of patient size. CONCLUSION: Standardized quantification of CAC yielded comparable image noise, spatial resolution, and mass scores among different patient sizes and different CT systems and facilitated reduced radiation dose for small and medium-size patients.     

Very low-dose coronary artery calcium scanning with high-pitch spiral acquisition mode: Comparison between 120-kV and 100-kV tube voltage protocols

BackgroundEffective radiation dose from a single coronary artery calcification CT scan can range from 0.8 to 10.5 mSv, depending on the protocol. Reducing the effective radiation dose to reasonable levels without affecting diagnostic image quality can result in substantial dose reduction in CT.ObjectivesWe prospectively compared tube voltages of 120 and 100 kV in a low-dose CT acquisition protocol for measuring coronary artery calcified plaque with prospectively electrocardiogram (ECG)–triggered high-pitch spiral acquisition.MethodsIn 150 consecutive patients, measurement of coronary artery calcified plaque was performed with prospectively ECG-triggered high-pitch spiral acquisition. Imaging was first done with tube voltage of 120 kV voltage and subsequently repeated with 100 kV and otherwise unchanged parameters. CT was performed with a dual-source CT system with 280 milliseconds of rotation time, 2 × 128 slices, pitch of 3.4, triggered at 60% of the R–R interval. Tube current for both protocols was set at 80 mAs. With the use of a medium sharp reconstruction kernel (Siemens B35f), cross-sectional images were reconstructed with 3.0-mm slice thickness and 1.5-mm increment. Agatston scores were determined per patient for both scan settings by 2 independent readers with the use of a standard threshold of 130 HU for calcium detection. In addition, the Agatston score was calculated with a previously proposed threshold of 147 HU for 100-kV acquisitions.ResultsMean image noise was 20 ± 5 and 27 ± 7 for 120 and 100 kV, respectively (P < 0.0001). Mean dose length product was 24 ± 6 cm · cGy for the 120-kV protocol and 14 ± 4 cm · cGy for the 100-kV protocol, corresponding to average estimated effective doses of 0.3 and 0.2 mSv (P < 0.0001). Five patients were excluded from the analysis. In the remaining 145 patients, using the standard tube voltage of 120 kV, any coronary calcium was detected in 76 identical patients by both observers. In 75 of these patients, calcium was also identified by both observers in 100-kV data sets, whereas 1 patient was scored negative by 1 reader and was assigned an Agatston score of 0.7 (threshold, 130 HU) and 0.2 (threshold, 147 HU) by the other. Interobserver disagreement for assigning a patient a zero Agatston score was the same for both scan settings (each 4 patients). The mean Agatston scores for 120-kV and 100-kV (threshold, 147 HU) scans were 105 ± 245 (range, 0–1865) and 116 ± 261 (range, 0–1917), respectively (P < 0.0001). Bland-Altman analysis indicated a systematic overestimation of the Agatston score with tube voltage of 100 kV and threshold of 147 HU (mean difference, 11; 95% limits of agreement, 62 to -40). Similar results were observed for coronary calcium volume scores.ConclusionHigh-pitch spiral acquisition allows coronary calcium scoring with effective doses below 0.5 mSv. The use of 100-kV tube voltage further reduces effective radiation dose compared with the standard of 120 kV; however, it leads to significant overestimation of the Agatston score when the standard threshold of 130 HU is used. Adjusting the threshold to 147 HU leads to a better agreement compared with standard 120 kV protocols yet with a remaining systematic bias toward overestimation of the Agatston score. For high-pitch spiral acquisition mode, effective radiation dose reduction when using a 100-kV setting is minimal compared with the standard 120-kV setting and may be considered nonsignificant in a clinical setting.     

Coronary calcium scanning independently detects coronary artery disease in asymptomatic firefighters: A prospective study

BackgroundSudden cardiac death is the leading cause of death among firefighters in the United States. Fire departments commonly maintain physical examination protocols, often with exercise stress testing, to detect risk of coronary heart disease.ObjectiveWe sought to determine whether coronary calcium detected by electron beam computed tomography (EBCT) adds incremental risk stratification beyond the traditional risk factors in asymptomatic community-based firefighters.MethodsThree hundred ninety nine asymptomatic firefighters underwent a coronary calcium scan on a GE/Imatron C-150 Ultrafast EBCT scanner, using standardized imaging protocols. Framingham risk factor data were obtained on each patient by using a questionnaire. Agatston scores were derived and compared with national database of Agatston scores for asymptomatic populations on the basis of age and sex, allowing determination of a calcium percentile for each score.ResultsCoronary calcium was found only in men >34 years of age. Of the 53% who had positive scans (Agatston score > 0), 87% had higher than average Agatston scores compared with a national database (P < 0.01). Agatston score above the 75th percentile was found in 57% of firefighters. No correlation was observed between traditional risk factors and those with and without coronary calcium.ConclusionsFirefighters have a high burden of calcified coronary atherosclerosis, greater than anticipated on the basis of age and coronary risk factors.     

Coronary artery calcium measurement with multi-detector row CT and low radiation dose: comparison between 55 and 165 mAs

PURPOSE: To prospectively compare the results of coronary artery calcium (CAC) measurements obtained with 55- and 165-mAs electrocardiographically gated multi-detector row computed tomography (CT). MATERIALS AND METHODS: Institutional clinical study review board approval and written informed consent were obtained. Fifty-one consecutive subjects (mean age, 59 years +/- 10) were scanned consecutively by using 165 and 55 mAs. For each examination, the number of lesions, total calcium score (TCS) calculated with Agatston algorithm (130-HU threshold), and calcium mass (in milligrams) were measured. Noise was measured by averaging 1 standard deviation of the CT attenuation values in five consecutive transverse sections of the ascending aorta. Paired t test and Pearson correlation were used to compare measurements between the examinations. RESULTS: By using 55 mAs, CAC was detected (TCS > 0) in all 33 subjects in whom CAC was initially detected with 165 mAs. The mean values of CAC measures with 165 and 55 mAs, respectively, were as follows: number of lesions, 6.2 +/- 9.6 and 6.1 +/- 9.4; TCS, 123 +/- 223 and 126 +/- 225; and calcium mass, 23.25 mg +/- 43 and 24.25 mg +/- 44 (P value was not significant for all parameters). Significant high correlation was found between the two methods for all measures (r > 0.90, P < .01). Similar results were obtained with analysis by coronary vessel. Image noise was 9.3 HU +/- 2.1 with 165 mAs and 14.7 HU +/- 3.9 with 55 mAs (P < .001), with a parallel decrease in the volume CT dose index from 12 to 4 mGy. CONCLUSION: Radiation dose can be reduced (eg, 55 mAs) for CAC detection and measurement at multi-detector row CT and provides results comparable to those obtained with 165 mAs.     

Risk stratification of non-contrast CT beyond the coronary calcium scan

Coronary artery calcification (CAC) is a well-known marker for coronary artery disease and has important prognostic implications. CAC is able to provide clinicians with a reliable source of information related to cardiovascular atherosclerosis, which carries incremental information beyond Framingham risk. However, non-contrast scans of the heart provide additional information beyond the Agatston score. These studies are also able to measure various sources of fat, including intrathoracic (eg, pericardial or epicardial) and hepatic, both of which are thought to be metabolically active and linked to increased incidence of subclinical atherosclerosis as well as increased prevalence of type 2  diabetes. Testing for CAC is also useful in identifying extracoronary sources of calcification. Specifically, aortic valve calcification, mitral annular calcification, and thoracic aortic calcium (TAC) provide additional risk stratification information for cardiovascular events. Finally, scanning for CAC is able to evaluate myocardial scaring due to myocardial infarcts, which may also add incremental prognostic information. To ensure the benefits outweigh the risks of a scanning for CAC for an appropriately selected asymptomatic patient, the full utility of the scan should be realized. This review describes the current state of the art interpretation of non-contrast cardiac CT, which clinically should go well beyond coronary artery Agatston scoring alone.     

Controversies about effects of low-kilovoltage MDCT acquisition on Agatston calcium scoring

Recent articles have advocated the possibility of obtaining Agatston coronary calcium scoring at 100 kVp by using a single adapted elevated calcium threshold. To evaluate the influence of kilovoltage potential protocols on the Agatston score, we acquired successive scans of a calcium scoring phantom at 4 levels of kilovoltage potential (80, 100, 120, and 140 kVp, 55 mAs) and measured semiautomatically the individual and the total Agatston score of 6 inserts (of 5-mm and 3-mm diameter) containing hydroxyapatite at different concentrations (800, 400, 200 mg/cm³). Our results showed that Agatston scores obtained at various low-kilovoltage potential protocols can be highly overestimated in some particular cases. At 80 kVp, for example, mean measured Agatston score was multiplied by a factor from 1.06 (5-mm highest density insert) to 2.67 (3-mm lowest density insert) compared with the Agatston scores performed at 120 kVp. Indeed in the one hand, reducing kilovoltage potential in multidetector CT acquisitions increase the CT density of coronary calcifications that can be measured on the reconstructed images. On the other hand, Agatston score is a multi-threshold measurement (with a step weighting function). Consequently low kilovoltage potential can lead to overweight some calcifications scores. For these reasons, Agatston score with low kilovoltage potential acquisition cannot be reliably adapted by a unique recalibration of the standard calcium attenuation threshold of 130 HU and requires a standardized CT acquisition protocol at 120 kVp. Alternatives to performing low-dose coronary artery calcium scans are either using coronary calcium scans with reduced tube current (low mAs) at 120 kVp with the iterative reconstructions or using mass/volume scoring (not influenced by kilovoltage potential variations). Finally, we emphasized that incorrect Agatston score evaluation may have important clinical, financial, and health care implications.     

Influence of coronary dominance on coronary artery calcification burden

ObjectiveTo evaluate the influence of coronary artery dominance on observed coronary artery calcification burden in outpatients presenting for coronary computed tomography angiography (CCTA).MethodsA 12-month retrospective review was performed of all CCTAs at a single institution. Coronary arterial dominance, Agatston score and presence or absence of cardiovascular risk factors including hypertension (HTN), hyperlipidemia (HLD), diabetes and smoking were recorded. Dominance groups were compared in terms of calcium score adjusted for covariates using analysis of covariance based on ranks. Only covariates observed to be significant independent predictors of the relevant outcome were included in each analysis. All statistical tests were conducted at the two-sided 5% significance level.Results1223 individuals, 618 women and 605 men were included, mean age 60 years (24–93 years). Right coronary dominance was observed in 91.7% (n = 1109), left dominance in 8% (n = 98), and codominance in 1.3% (n = 16). The distribution of patients among Agatston score severity categories significantly differed between codominant and left (p = 0.008), and codominant and right (p = 0.022) groups, with higher prevalence of either zero or severe CAC in the codominant patients. There was no significant difference in Agatston score between dominance groups. In the subset of individuals with coronary artery calcification, Agatston score was significantly higher in codominant versus left dominant patients (mean Agatston score 595 ± 520 vs. mean 289 ± 607, respectively; p = 0.049), with a trend towards higher scores in comparison to the right-dominant group (p = 0.093). Significance was not maintained upon adjustment for covariates.ConclusionsWhile the distribution of Agatston score severity categories differed in codominant versus right- or left-dominant patients, there was no significant difference in Agatston score based on coronary dominance pattern in our cohort. Reporting and inclusion of codominant subsets in larger investigations may elucidate whether codominant anatomy is associated with differing risk.