Coronary calcium measurements by double helical computed tomography. Using the average instead of peak density algorithm improves reproducibility

Coronary calcium density in relation to coronary heart disease and cardiovascular disease in adults with diabetes or metabolic syndrome: the Multi-ethnic Study of Atherosclerosis (MESA)

BACKGROUND

Coronary artery calcium (CAC) density is inversely associated with coronary heart disease (CHD) and cardiovascular disease (CVD) risk. We examined this relation in those with diabetes mellitus (DM) or metabolic syndrome (MetS).

METHODS

We studied 3,818 participants with non-zero CAC scores from the Multiethnic Study of Atherosclerosis and classified them as DM, MetS (without DM) or neither DM/MetS. Risk factor-adjusted CAC density was calculated and examined in relation to incident CHD and CVD events over a median follow-up of 15 years among these three disease groups.

RESULTS

Adjusted CAC density was 2.54, 2.61 and 2.69 among those with DM, MetS or neither DM/MetS. Hazard ratios (HRs) for CHD per 1 SD increase of CAC density was 0.91 (95% CI: 0.72-1.16), 0.70 (95% CI: 0.56-0.87) and 0.79 (95% CI: 0.66-0.95) for those with DM, MetS or neither DM/MetS groups and were 0.77 (95% CI: 0.64-0.94), 0.83 (95% CI: 0.70-0.99) and 0.82 (95% CI: 0.71-0.95) for CVD, respectively. Adjustment for CAC density increased the HRs of CAC volume for CHD/CVD events. Compared to prediction models with or without single CAC measures, c-statistics of models with CAC volume and density were the highest ranging 0.67-0.72.

CONCLUSION

CAC density is lower among patients with DM or MetS than those with neither DM/MetS and is inversely associated with future CHD/CVD risk among them. Including CAC density in risk assessment among those with MetS may improve prediction of CHD and CVD.

Assessing Agreement When Agreement Is Hard to Assess-The Agatston Score for Coronary Calcification

Method comparison studies comprised simple scatterplots of paired measurements, a 45-degree line as benchmark, and correlation coefficients up to the advent of Bland-Altman analysis in the 1980s. The Agatston score for coronary calcification is based on computed tomography of the heart, and it originated in 1990. A peculiarity of the Agatston score is the often-observed skewed distribution in screening populations. As the Agatston score has manifested itself in preventive cardiology, it is of interest to investigate how reproducibility of the Agatston score has been established. This review is based on literature findings indexed in MEDLINE/PubMed before 20 November 2021. Out of 503 identified articles, 49 papers were included in this review. Sample sizes were highly variable (10-9761), the main focus comprised intra- and interrater as well as intra- and interscanner variability assessments. Simple analysis tools such as scatterplots and correlation coefficients were successively supplemented by first difference, later Bland-Altman plots; however, only very few publications were capable of deriving Limits of Agreement that fit the observed data visually in a convincing way. Moreover, several attempts have been made in the recent past to improve the analysis and reporting of method comparison studies. These warrant increased attention in the future.

Evolving Role of Calcium Density in Coronary Artery Calcium Scoring and Atherosclerotic Cardiovascular Disease Risk

Coronary artery calcium (CAC) is a specific marker of coronary atherosclerosis that can be used to measure calcified subclinical atherosclerotic burden. The Agatston method is the most widely used scoring algorithm for quantifying CAC and is expressed as the product of total calcium area and a quantized peak calcium density weighting factor defined by the calcification attenuation in HU on noncontrast computed tomography. Calcium density has emerged as an important area of inquiry because the Agatston score is upweighted based on the assumption that peak calcium density and atherosclerotic cardiovascular disease (ASCVD) risk are positively correlated. However, recent evidence demonstrates that calcium density is inversely associated with lesion vulnerability and ASCVD risk in population-based cohorts when accounting for age and plaque area. Here, we review calcium density by focusing on 3 main areas: 1) CAC scan acquisition parameters; 2) pathophysiology of calcified plaques; and 3) epidemiologic evidence relating calcium density to ASCVD outcomes. Through this process, we hope to provide further insight into the evolution of CAC scoring on noncontrast computed tomography.

Association of Coronary Artery Calcium in Adults Aged 32 to 46 Years With Incident Coronary Heart Disease and Death

Importance

Coronary artery calcium (CAC) is associated with coronary heart disease (CHD) and cardiovascular disease (CVD); however, prognostic data on CAC are limited in younger adults.

Objective

To determine if CAC in adults aged 32 to 46 years is associated with incident clinical CHD, CVD, and all-cause mortality during 12.5 years of follow-up.

Design, Setting, and Participants

The Coronary Artery Risk Development in Young Adults (CARDIA) Study is a prospective community-based study that recruited 5115 black and white participants aged 18 to 30 years from March 25, 1985, to June 7, 1986. The cohort has been under surveillance for 30 years, with CAC measured 15 (n = 3043), 20 (n = 3141), and 25 (n = 3189) years after recruitment. The mean follow-up period for incident events was 12.5 years, from the year 15 computed tomographic scan through August 31, 2014.

Main Outcomes and Measures

Incident CHD included fatal or nonfatal myocardial infarction, acute coronary syndrome without myocardial infarction, coronary revascularization, or CHD death. Incident CVD included CHD, stroke, heart failure, and peripheral arterial disease. Death included all causes. The probability of developing CAC by age 32 to 56 years was estimated using clinical risk factors measured 7 years apart between ages 18 and 38 years.

Results

At year 15 of the study among 3043 participants (mean [SD] age, 40.3 [3.6] years; 1383 men and 1660 women), 309 individuals (10.2%) had CAC, with a geometric mean Agatston score of 21.6 (interquartile range, 17.3-26.8). Participants were followed up for 12.5 years, with 57 incident CHD events and 108 incident CVD events observed. After adjusting for demographics, risk factors, and treatments, those with any CAC experienced a 5-fold increase in CHD events (hazard ratio [HR], 5.0; 95% CI, 2.8-8.7) and 3-fold increase in CVD events (HR, 3.0; 95% CI, 1.9-4.7). Within CAC score strata of 1-19, 20-99, and 100 or more, the HRs for CHD were 2.6 (95% CI, 1.0-5.7), 5.8 (95% CI, 2.6-12.1), and 9.8 (95% CI, 4.5-20.5), respectively. A CAC score of 100 or more had an incidence of 22.4 deaths per 100 participants (HR, 3.7; 95% CI, 1.5-10.0); of the 13 deaths in participants with a CAC score of 100 or more, 10 were adjudicated as CHD events. Risk factors for CVD in early adult life identified those above the median risk for developing CAC and, if applied, in a selective CAC screening strategy could reduce the number of people screened for CAC by 50% and the number imaged needed to find 1 person with CAC from 3.5 to 2.2.

Conclusions and Relevance

The presence of CAC among individuals aged between 32 and 46 years was associated with increased risk of fatal and nonfatal CHD during 12.5 years of follow-up. A CAC score of 100 or more was associated with early death. Adults younger than 50 years with any CAC, even with very low scores, identified on a computed tomographic scan are at elevated risk of clinical CHD, CVD, and death. Selective use of screening for CAC might be considered in individuals with risk factors in early adulthood to inform discussions about primary prevention.

Associations of coronary artery calcified plaque density with mortality in type 2 diabetes: the Diabetes Heart Study

Background

Coronary artery calcified plaque (CAC) is strongly predictive of cardiovascular disease (CVD) events and mortality, both in general populations and individuals with type 2 diabetes at high risk for CVD. CAC is typically reported as an Agatston score, which is weighted for increased plaque density. However, the role of CAC density in CVD risk prediction, independently and with CAC volume, remains unclear.

Methods

We examined the role of CAC density in individuals with type 2 diabetes from the family-based Diabetes Heart Study and the African American-Diabetes Heart Study. CAC density was calculated as mass divided by volume, and associations with incident all-cause and CVD mortality [median follow-up 10.2 years European Americans (n = 902, n = 286 deceased), 5.2 years African Americans (n = 552, n = 93 deceased)] were examined using Cox proportional hazards models, independently and in models adjusted for CAC volume.

Results

In European Americans, CAC density, like Agatston score and volume, was consistently associated with increased risk of all-cause and CVD mortality (p ≤ 0.002) in models adjusted for age, sex, statin use, total cholesterol, HDL, systolic blood pressure, high blood pressure medication use, and current smoking. However, these associations were no longer significant when models were additionally adjusted for CAC volume. CAC density was not significantly associated with mortality, either alone or adjusted for CAC volume, in African Americans.

Conclusions

CAC density is not associated with mortality independent from CAC volume in European Americans and African Americans with type 2 diabetes.

Electronic supplementary material

The online version of this article (10.1186/s12933-018-0714-z) contains supplementary material, which is available to authorized users.

Tracking Progression of Heart Disease with Cardiac Computed Tomography

The ability to follow changes in atherosclerotic plaque burden over time should provide an accurate measure of efficacy for different cardiovascular therapies. Coronary calcifications are associated with atherosclerotic coronary artery plaque, and the amount of coronary calcifications has been shown to correlate with the overall coronary plaque burden. The presence and extent of coronary calcifications can be assessed noninvasively by monitoring the progression of coronary calcification with electron beam tomography. With annual progression rates of 22% to 52% and a median interscan variability of only 5% to 8%, this technology provides an opportunity to monitor patients to assess the clinical efficacy of medical therapies in studies as short as 1 year. Several studies have demonstrated that the successful pharmacologic reduction of low-density lipoprotein cholesterol significantly mitigated the progression of the calcium score. Studies using serial computed tomographic scans indicate that the annual progression of coronary calcium varies between 30% and 50% in symptomatic or high-risk individuals and from 0% to 20% in patients treated effectively with lipid-lowering medication. An increased rate of progression of coronary calcium seems to indicate a substantially increased risk for adverse cardiac events, suggesting that this modality can be used to monitor the efficacy of therapy.

Scoring of coronary artery calcium scans: history, assumptions, current limitations, and future directions

Coronary artery calcium (CAC) scanning is a reliable, noninvasive technique for estimating overall coronary plaque burden and for identifying risk for future cardiac events. Arthur Agatston and Warren Janowitz published the first technique for scoring CAC scans in 1990. Given the lack of available data correlating CAC with burden of coronary atherosclerosis at that time, their scoring algorithm was remarkable, but somewhat arbitrary. Since then, a few other scoring techniques have been proposed for the measurement of CAC including the Volume score and Mass score. Yet despite new data, little in this field has changed in the last 15 years. The main focus of our paper is to review the implications of the current approach to scoring CAC scans in terms of correlation with the central disease - coronary atherosclerosis. We first discuss the methodology of each available scoring system, describing how each of these scores make important indirect assumptions in the way they account (or do not account) for calcium density, location of calcium, spatial distribution of calcium, and microcalcification/emerging calcium that might limit their predictive power. These assumptions require further study in well-designed, large event-driven studies. In general, all of these scores are adequate and are highly correlated with each other. Despite its age, the Agatston score remains the most extensively studied and widely accepted technique in both the clinical and research settings. After discussing CAC scoring in the era of contrast enhanced coronary CT angiography, we discuss suggested potential modifications to current CAC scanning protocols with respect to tube voltage, tube current, and slice thickness which may further improve the value of CAC scoring. We close with a focused discussion of the most important future directions in the field of CAC scoring.

Coronary calcification: effect of small variation of scan starting position on Agatston, volume, and mass scores

PURPOSE

To retrospectively evaluate the effect of a small variation of scan starting position on coronary artery calcium scores based on nonoverlapping 3-mm multidetector computed tomographic (CT) data sets.

MATERIALS AND METHODS

Informed consent and institutional review board approval were obtained. A retrospective study was performed by using prospective unenhanced electrocardiographically triggered cardiac multidetector CT scans in 228 women (mean age, 67 years +/- 5 [standard deviation]). From the original 1.5-mm data set, two sets of adjacent images with a section thickness of 3 mm and a variation in starting point of 1.5 mm were obtained. Calcium scoring was performed to acquire Agatston, volume, and mass scores. Subjects were assigned to one of five risk categories (I-V) according to the Agatston score of each 3-mm data set and the average score. Kappa value was calculated to assess agreement in risk category assignment. Differences and relative differences between scores obtained for both 3-mm data sets were calculated overall and according to risk category. The effect of scoring algorithm on the relative differences between scores was analyzed with the Wilcoxon signed rank test.

RESULTS

Categories I-V contained 102, 35, 48, 31, and 12 subjects, respectively. For all scoring algorithms, median relative differences decreased from more than 130% in category II to less than 10% in category V. In the three highest categories, relative differences were significantly smaller for volume and mass scores than for Agatston scores (P < .05). Twenty-one subjects were assigned to different risk categories between the two data sets (kappa = 0.87). Eleven patients were assigned a nonzero score in one and a zero score in the other data set.

CONCLUSION

A small variation in scan starting position can substantially influence calcium measurements and poses an inherent limit to calcium scoring with contiguous 3-mm sections. Mass and volume scores are slightly less affected than are Agatston scores.

Coronary Artery Calcium Scoring With Multislice Computed Tomography

OBJECTIVES

We sought to compare an 80-kVp coronary calcium scoring protocol with the standard protocol of 120 kVp in terms of accuracy and reproducibility and to assess its dose reduction potential.

MATERIALS AND METHOD

An anthropomorphic heart phantom with calcium cylinders was scanned with different tube currents at 80 kVp and 120 kVp using a 16-slice multislice CT (MSCT) scanner. An adapted threshold for 80 kVp was calculated. Accuracy and reproducibility for calcium mass, volume, and Agatston score were analyzed using F-tests. The radiation doses needed to produce artifact-free images were determined.

RESULTS

Accuracy (measurement errors: mass 120 kVp +4.6%, mass 80 kVp -6.9%, volume 120 kVp +78.8%, volume 80 kVp +58.2%) and reproducibility (F-tests: mass: P = 0.4998, volume: P = 0.9168, Agatston: P = 0.5422) were comparable at both tube voltages. Avoiding the appearance of artificial lesions, a CTDI(w,eff) of 10.7 mGy was needed at 120 kVp versus 4.6 mGy at 80 kVp (dose reduction of 57%).

CONCLUSIONS

Using an 80-kVp protocol in coronary calcium scoring, a relevant dose reduction is possible without compromising reproducibility and accuracy.

Frequency of coronary artery calcification on low-dose computed tomography screening for lung cancer

PURPOSE

The purpose of this study was to determine the frequency of coronary artery calcification (CAC) in high-risk people undergoing computed tomography (CT) screening for lung cancer.

METHODS

Between 1999 and 2004, we performed CT screening for lung cancer on 4250 participants, all without documented prior cardiovascular disease, using multidetector-row (MD) CT. Of the patients, 1102 underwent imaging with a four-detector-row CT at 120 kVp and 40 mA, with pitch 1.5 and collimation of 2.5 mm in a single breath hold of 15-20 seconds, and 3148 did with an eight-detector-row CT at the same kVp, mA, and pitch settings but with collimation of 1.25 mm. Visualized CACs in each coronary artery (main, left anterior descending, circumflex, and right) were scored separately as 0 (absent), 1 (mild), 2 (moderate), or 3 (severe), yielding a possible score of 0-12 for each person. Frequency distributions by gender, age, and pack-years of smoking were determined. Odds ratios (ORs) were calculated using logistic regression analysis of the prevalence of CAC as a joint function of gender, age, pack-years of smoking, and presence of diabetes.

RESULTS

Among the subjects younger than 50 years, positive CAC scores were three times more frequent for men than for women (22% vs. 7%); among those older than 50 years, the frequency increased for both men and women but the increase for women was greater than that for men. The frequency of positive CAC scores increased with increasing pack-years of smoking; it was always higher for men than for women. The ORs were 2.6 for male gender (P<.0001), 3.7 and 9.6 for ages 60-69 years and 70 years or older, respectively, for increasing age (P<.0001 for both), 1.6 and 2.3 for 30-59 pack-years and 60 pack-years or longer, respectively, for increasing pack-years of smoking (P<.0001 for both), and 1.6 for having diabetes (P=.016).

CONCLUSION

The CAC score can be derived from ungated low-dose MDCT images. This information can contribute to risk stratification and management of coronary artery disease.

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.

Update on using coronary calcium screening by computed tomography to measure risk for coronary heart disease

Coronary artery disease (CAD) is the number one killer of adults in the United States, claiming one-half million deaths annually. Early detection and prevention strategies clearly remain a top priority for health care providers in order to reduce the high mortality rate of heart disease. As an unequivocal reflection of arteriosclerosis, coronary arterial calcium (CAC) may provide a means to qualitatively assess the overall disease severity and likewise serve as a means to assess risk for CHD. It is known that patients with heavy calcium burdens have more advanced CAD, a concomitantly a higher likelihood of coronary stenoses, and a concomitant higher risk for acute cardiac events. Computed tomography has been shown to be an accurate, non-invasive method to quantify coronary calcification burden in patients. Evidence shows that calcium measurements by CT correlate well with histological plaque analyses, and that CAC measurements accurately reflect disease severity and can be useful to assess individual risk for CHD. The purpose of this article is to summarize the currently available evidence that has attempted to validate CAC screening as a screening exam and risk predictor for coronary heart disease.

Accelerated Progression of Coronary Calcification: Four-year Follow-up in Patients with Stable Coronary Artery Disease

PURPOSE

To prospectively assess the 4-year progression rate of coronary artery calcium (CAC) in patients with clinically stable coronary artery disease (CAD) with multi-detector row computed tomography (CT).

MATERIALS AND METHODS

The study group consisted of 382 consecutive patients. All underwent baseline dual-sector spiral CT, and CT was repeated at 2 and 4 years later. Progression of CAC was assessed with measurement of the increase in total calcium score (TCS) and with repeated-measures analysis and multivariate linear regression models. Logistic regression model was used to predict incidence of new lesions.

RESULTS

Eighty-seven percent (333 of 382) of the study group were men, with mean age of 65 years +/- 11, and 13% (49 of 382) were women, with mean age of 68 years +/- 11. The average TCS increased after 4 years by sixfold from baseline in the 1st quartile, and by four-, two- and 1.5-fold in the 2nd, 3rd, and 4th quartiles of baseline TCS (P <.01), respectively. Multiple linear regression analysis included age; sex; natural logarithm of baseline TCS; history of hypertension, diabetes mellitus, current smoking, hypercholesterolemia, and lipid-lowering therapy with cholesterol synthesis enzyme inhibitor (statin); and family history of premature CAD. Results demonstrated that natural logarithm of baseline TCS and history of current smoking were independent predictors of the 4th-year natural logarithm of TCS levels (R(2) = 0.85, P <.001). New lesions were diagnosed in 56 (15%) patients. History of statin therapy (odds ratio = 0.35; 95% confidence interval [CI]: 0.16, 0.77; P <.01), age with an increment of 5 years (odds ratio = 0.76; 95% CI: 0.64, 0.90; P =.01), and natural logarithm of baseline TCS (odds ratio = 0.73; 95% CI: 0.62, 0.86; P <.01) were independent predictors for new calcific lesions during 4 years.

CONCLUSION

Accelerated progression of CAC during 4 years was found in clinically stable patients with CAD.

Electron beam CT versus helical CT scans for assessing coronary calcification: current utility and future directions

BACKGROUND

Traditional risk factors for coronary artery disease predict the development of atherosclerosis; however, their ability to identify individual patients at risk of events is limited.

METHODS

Coronary artery calcium (CAC) is a specific marker of atherosclerosis. It can be visualized and measured noninvasively by various imaging techniques, which may add incremental prognostic value to conventional coronary factors.

RESULTS

The field of atherosclerosis imaging has expanded rapidly in the last decade, and technologies such as electron-beam computed tomography (EBCT) have contributed to our understanding of the prevalence of occult coronary artery disease and its consequences. Other modalities have been previously limited by the decreased temporal and spatial resolution and slower acquisition. Recent advances in helical CT (HCT) imaging with the development of multiple row detectors CT (MDCT) and improvements in the temporal resolution have renewed clinicians' interests in using this modality to evaluate CAC, although the scores obtained with MDCT may differ somewhat from those obtained with the EBCT technology. This study critically analyzes the literature comparing the utility of EBCT and HCT in detecting coronary calcium to identify individuals at increased risk for future coronary events.

CONCLUSIONS

MDCT is a promising tool for coronary calcium scoring; however, more studies are needed comparing EBCT and MDCT, especially at lower CAC levels.

Imaging of coronary calcification by computed tomography

As an unequivocal biomarker for arteriosclerosis, the presence of coronary calcium serves as a qualitative reflection of the severity of coronary artery disease (CAD). Greater calcium burdens correlate with more advanced disease, a higher likelihood of coronary stenoses, and a higher risk for coronary heart disease (CHD). Empirically, the quantification of coronary calcium not only provides an accurate reflection of disease severity, but also has great potential as a screening tool for CHD. Computed tomography (CT) has been shown to be capable of providing accurate, noninvasive measurements of coronary calcification. Evidence shows that calcium measurements by CT correlate well with histological plaque analyses, and that calcium burdens accurately reflect disease severity and can be used to assess individual risk for CHD. The purpose of this review article is to examine the accumulated evidence that has attempted to validate CT as a diagnostic tool for CAD and as a screening exam for CHD.

Coronary Artery Calcium Scoring

PURPOSE

To compare the diagnostic power of different software implementations for the quantification of coronary artery calcium.

MATERIALS AND METHODS

Electron beam computed tomography was performed in 109 heart transplant recipients at the same time as catheter coronary angiography and intracoronary ultrasound. Electron beam computed tomography images were analyzed by 3 software packages marketed for the quantification of coronary calcifications using the same software settings, and the resultant calcium scores correlated with the invasive reference methods by Bland-Altman plots and analysis of the receiver operating characteristics.

RESULTS

Although all scoring systems displayed close correlations upon regression analysis (r2=0.94-0.99), their ability to detect disease as per the invasive reference method varied significantly in some instances. The area under the ROC curve varied between Az=0.78 and 0.85 for the detection of coronary artery stenosis upon coronary angiography (P=0.05-0.13), and between Az=0.75 and 0.83 for the detection of accelerated intimal proliferation (P=0.03-0.18).

CONCLUSIONS

Different software implementations for the quantification of coronary artery calcium load may display diagnostically relevant differences in spite of close direct correlation.

Coronary calcium quantification using various calibration phantoms and scoring thresholds

RATIONALE AND OBJECTIVES

To compare scoring threshold and calibration method-dependent accuracy and variability of coronary calcium measurements by multidetector computed tomography (MDCT).

METHODS

Ninety-five subjects were scanned with MDCT. We calculated Agatston score and volume score. Mineral mass (MM) was calculated using patient-based and scanner-based calibration methods. Accuracy of calibration was validated using artificial calcium cylinders.

RESULTS

Patient-based and scanner-based calibration permitted accurate quantification of artificial calcium cylinders (bias: 0 mg and -2 mg). In the subjects, the mean relative difference of MM measurements performed at 90 and 130 Hounsfield units threshold (59%) was lower than for Agatston score (94%) and volume score (109%; P < 0.05). Patient-based and scanner-based calibration yielded systematically different MM measurements (bias: 22%).

CONCLUSIONS

MM lowers threshold-dependent variability of coronary calcium measurements. Patient-based and scanner-based calibration allows accurate calcium quantification ex vivo but reveal systematic differences in subjects. Patient-based calibration may better account for subject size and composition.

Assessment of calcium scoring performance in cardiac computed tomography

Electron beam tomography (EBT) has been used for cardiac diagnosis and the quantitative assessment of coronary calcium since the late 1980s. The introduction of mechanical multi-slice spiral CT (MSCT) scanners with shorter rotation times opened new possibilities of cardiac imaging with conventional CT scanners. The purpose of this work was to qualitatively and quantitatively evaluate the performance for EBT and MSCT for the task of coronary artery calcium imaging as a function of acquisition protocol, heart rate, spiral reconstruction algorithm (where applicable) and calcium scoring method. A cardiac CT semi-anthropomorphic phantom was designed and manufactured for the investigation of all relevant image quality parameters in cardiac CT. This phantom includes various test objects, some of which can be moved within the anthropomorphic phantom in a manner that mimics realistic heart motion. These tools were used to qualitatively and quantitatively demonstrate the accuracy of coronary calcium imaging using typical protocols for an electron beam (Evolution C-150XP, Imatron, South San Francisco, Calif.) and a 0.5-s four-slice spiral CT scanner (Sensation 4, Siemens, Erlangen, Germany). A special focus was put on the method of quantifying coronary calcium, and three scoring systems were evaluated (Agatston, volume, and mass scoring). Good reproducibility in coronary calcium scoring is always the result of a combination of high temporal and spatial resolution; consequently, thin-slice protocols in combination with retrospective gating on MSCT scanners yielded the best results. The Agatston score was found to be the least reproducible scoring method. The hydroxyapatite mass, being better reproducible and comparable on different scanners and being a physical quantitative measure, appears to be the method of choice for future clinical studies. The hydroxyapatite mass is highly correlated to the Agatston score. The introduced phantoms can be used to quantitatively assess the performance characteristics of, for example, different scanners, reconstruction algorithms, and quantification methods in cardiac CT. This is especially important for quantitative tasks, such as the determination of the amount of calcium in the coronary arteries, to achieve high and constant quality in this field.

EKG-triggered CT data acquisition to reduce variability in coronary arterial calcium score

PURPOSE

To test the hypothesis that computed tomographic (CT) scanning during optimal electrocardiographic (EKG) triggering can minimize image motion artifact and reduce interexamination variation of coronary arterial calcification (CAC) score at electron-beam CT.

MATERIALS AND METHODS

Two hundred patients underwent electron-beam CT once and again 5 minutes later to evaluate interexamination variability of CAC score. Group 1 (104 patients) underwent scanning with use of an optimal EKG-triggering protocol (EKG triggering performed individually at the time of least coronary arterial motion during the cardiac cycle); group 2 (96 patients) underwent scanning with use of conventional 80% R-R interval triggering (the most common protocol with the electron-beam CT scanner). Interexamination, intraobserver, and interobserver variations of CAC measurements were compared between groups by using unpaired t tests for both Agatston and volumetric scores (in square millimeters).

RESULTS

Coronary arterial motion artifacts were found in 26% (27 of 104) versus 80% (77 of 96) of patients in groups 1 and 2, respectively (P <.0001). Intraobserver, interobserver, and interexamination variabilities in volumetric score were derived, with values of 1.2%, 9.2%, and 15.9% in group 1 and 2.1%, 11.3%, and 25.9% in group 2, respectively. Interexamination variabilities in both Agatston and volumetric score were significantly reduced with individualized EKG triggering, as compared with conventional triggering (P <.05), but intra- and interobserver variabilities were not (P >.05).

CONCLUSION

Optimal EKG triggering improves the reproducibility of CAC measurement by reducing coronary arterial motion artifacts.

Causes of interscan variability of coronary artery calcium measurements at electron-beam CT

RATIONALE AND OBJECTIVES

The authors performed this study to investigate the causes of interscan variability of coronary artery calcium measurements at electron-beam computed tomography (CT).

MATERIALS AND METHODS

Two sets of electron-beam CT scans were obtained in 298 consecutive patients who underwent electron-beam CT to screen for coronary artery calcium. Interscan variations of coronary artery calcium characteristics and the effects of heart rate, electrocardiographic (ECG) triggering method, image noise, and coronary motion on interscan variability were analyzed.

RESULTS

The interscan mean variabilities were 21.6% (median, 11.7%) and 17.8% (median, 10.8%) with the Agatston and volumetric score, respectively (P < .01). Variability decreased with increasing calcification score (34.6% for a score of 11-50 and 9.4% for a score of 400-1,000, P < .0001). The absolute difference in Agatston score between scans was 44.1 +/- 95.6. The correlation coefficient between the first and second sets of scans was 0.99 (P < .0001). Lower interscan variability was found in younger patients (<60 years), patients with stable heart rates (heart rate changing less than 10 beats per minute during scanning), patients with no visible coronary motion, and those with an optimal ECG triggering method (P < .05 for all). Results of multivariate logistic analysis showed that changes in calcium volume, mean attenuation, and peak attenuation were significant predictors of interscan variability and caused the interscan variations of the coronary artery calcium measurements (r2 = 0.83, P < .0001).

CONCLUSION

Coronary calcification at electron-beam CT varies from scan to scan. Volumetric scoring and optimal ECG triggering should be used to reduce interscan variability. Baseline calcium score and interscan variability must be considered in the evaluation of calcium progression.

Coronary artery calcium: absolute quantification in nonenhanced and contrast-enhanced multi-detector row CT studies

PURPOSE

(a) To determine the accuracy of multi-detector row computed tomography (CT) in the measurement of the calcium concentration in a cardiac CT calibration phantom and (b) to assess the correlation of a traditional 3-mm section width CT coronary screening protocol and a 1.25-mm section width CT angiography imaging protocol in the quantification of the absolute mass of coronary calcium in patients who underwent both coronary screening and CT angiography with a multi-detector row CT scanner.

MATERIALS AND METHODS

A heart phantom containing calcified cylinders was scanned to determine calibration factors and absolute calcium mass. In 50 patients, the variability (value 1 - value 2/mean value 1 - value 2), limit of agreement (+/-2SD value 1 - value 2), and systematic error (mean value 1 - value 2) of the total amount of coronary calcium calculated at traditional 3-mm section width CT and at 1.25-mm section width CT angiography were determined.

RESULTS

The correlation coefficient between the 3-mm section width, nonenhanced protocol and the 1.25-mm section width CT angiography protocol was very high (r = 0.977) and the mean variability was low (19.7%) for the absolute mass. There was a systematic error of -6.7 mg and a limit of agreement between 45.0 mg and -58.5 mg.

CONCLUSION

Use of the mass quantification algorithm in combination with a calibration phantom allows accurate quantification of coronary calcium. Measurements of calcium mass obtained at 1.25-mm section width CT angiography have the best agreement with those obtained at the traditional 3-mm section width imaging protocol.

Coronary artery calcium measurement: agreement of multirow detector and electron beam CT

OBJECTIVE

The purpose of our study was to establish the most suitable algorithm to compare coronary artery calcium measurements performed with electron beam CT and multirow detector CT for the assessment of coronary artery disease.

SUBJECTS AND METHODS

Coronary artery screening was performed in 100 patients with both electron beam and multirow detector CT. The images were transferred to a dedicated workstation for determination of the calcium score, volume, mass, density, and number of lesions. In addition to the traditional threshold of 130 H, the score of multirow detector CT studies was reevaluated at a threshold of 90 H. Fifty-nine of the patients underwent conventional coronary catheterization. Receiver operating characteristic curve analysis of the different scoring algorithms for detection of significant coronary artery stenosis was performed.

RESULTS

The correlation between electron beam CT and multirow detector CT was high for every quantification algorithm. Determination of the score and the number of lesions with multirow detector CT revealed a systematic error of the measurement compared with electron beam CT. The areas under the curve in the receiver operating characteristic curve analyses for electron beam and multirow detector CT were similar for the score, volume, and mass, whereas they were lower for the density. No significant difference was found for the areas under the curve between scores using a 130-H and those using a 90-H threshold.

CONCLUSION

Volume and mass indexes are superior to the traditional score, density, and number of lesions for comparing the results of electron beam and multirow detector CT and for determining significant coronary artery disease.

Imaging of coronary calcium: a case for electron beam computed tomography

Coronary arterial calcification has unequivocally been shown to be a marker of atherosclerosis. To date, much research interest has been generated regarding the quantification of coronary calcification by electron beam computed tomography, and how best to use such measurements to identify and predict those at greatest risk for an adverse cardiac event. This article represents an attempt to provide an objective review of the literature regarding the potential role electron beam computed tomography (EBCT) has as an accurate and cost effective screening modality for coronary arterial disease, as well as a predictor for coronary heart disease.

Tracking coronary calcification by using dual-section spiral CT: a 3-year follow-up

PURPOSE

To investigate the accuracy of dual-section spiral computed tomography (CT) in tracking the progression of coronary calcification, as measured during a 3-year follow-up.

MATERIALS AND METHODS

Two hundred forty-six patients with hypertension (mean age, 66 years +/- 6 [SD]) were preselected in accordance with the International Nifedipine Study Intervention as a Goal for Hypertension Therapy protocol. Subjects had no clinical coronary arterial disease prior to the study and no cardiovascular events during follow-up. All participants underwent baseline CT (3.2-mm section thickness; reconstruction increment, 1.5 mm) and follow-up CT after 3 years. Calcification progression was defined as any increase in total calcification score (TCS) and analyzed in accordance with five baseline TCS categories: 1-9, 10-35, 36-100, 101-250, and greater than 250.

RESULTS

At baseline CT, 152 patients had a TCS greater than 0, and 106 (70%) showed progression after 3 years, while 94 had a baseline TCS of 0; of these, 26 (28%) showed progression (P: <.01 between groups). The mean TCS was significantly higher in each baseline TCS category after 3 years. The percentage increase was negatively correlated with baseline TCS (P: <.01) and ranged from 466% in the lowest category to 38% in the highest.

CONCLUSION

Dual-section spiral CT depicts significant change in TCS over time and is useful in tracking calcified coronary atherosclerosis.

Evaluation of subsecond gated helical CT for quantification of coronary artery calcium and comparison with electron beam CT

OBJECTIVE

Since its introduction early in the 1990s, helical CT has become the predominant technology for obtaining CT images for medical applications. Recent improvements in the temporal resolution of helical CT (subsecond) and the addition of retrospective cardiac gating are combined in this report evaluating cardiac-gated helical CT for quantifying coronary artery calcium. We compare total calcium scores determined on subsecond gated helical CT with the current reference for coronary calcium evaluation, electron beam CT.

MATERIALS AND METHODS

We compared total calcium scores obtained using a general purpose, unmodified helical CT scanner with scores obtained using electron beam CT in 36 individuals who were 68+/-11 years old (age range, 41-85 years).

RESULTS

Correlation coefficients ranged from 0.97 to 0.98 (Pearson's product moment) and from 0.95 to 0.96 (Spearman's rank order), depending on the coronary calcium scoring method used. Agreement in the classification of participants as "healthy" or "diseased" at threshold total calcium scores of 10, 100, 160, 200, 400, and 680 was, respectively, 94%, 97%, 89%, 92%, 94%, and 100% using the conventional electron beam CT scoring method and an equivalent method with helical CT.

CONCLUSION

A general purpose, current generation helical CT scanner equipped for retrospective cardiac gating can accurately quantify coronary calcium, and the results are highly correlated to scores obtained with electron beam CT. As an alternative method for measuring coronary calcium, gated subsecond cardiac helical CT offers greater availability and lower cost, thereby making population-based screening for coronary artery calcium more feasible.

Comparison of two different software systems for electron-beam CT-derived quantification of coronary calcification

OBJECTIVE

The growing interest in coronary calcium quantification by electron-beam CT (EBCT) has led to the development of various software systems for the analysis of EBCT raw data, but it is unknown whether these software systems yield comparable results.

METHODS

Two sets of EBCT scans were obtained in 73 asymptomatic patients less than 15 minutes apart. Both scans of each patient were analyzed using two different software systems, the Mayo Clinic software and the AccuImage Scoring System. The authors compared the calcium quantities yielded by the two different software systems, analyzed the interscan variability, and calculated the interobserver variability. Finally, they investigated the influence of the CT density factor inherent in the widely used Agatston score for the quantification of coronary calcium on reproducibility.

RESULTS

The mean score determined by the Mayo Clinic software was 14% greater than that determined by the AccuImage system. The mean difference between the two systems was 14% +/- 25%, and the median difference was 3%. The relative mean and the median difference between the two scans of one patient were 15.3% and 6% determined by the AccuImage system and 17% and 6.5% determined by the Mayo Clinic software. The interobserver reliability calculated by the Mayo Clinic software was better than that of the AccuImage system. There was a trend for better reproducibility using calcium area rather than the Agatson score.

CONCLUSIONS

Two different scoring systems do not necessarily yield the same result. Calcium quantities were systematically determined to be greater by one system than the other, and there were significant differences with regard to interobserver reliability. Hence, software should be tested with regard to reproducibility data, and the interpretation of calcium quantities should acknowledge which type of software was used.

Double-helical CT as a new tool for tracking of allograft atherosclerosis in heart transplant recipients

RATIONALE AND OBJECTIVES

Tracking the progression of allograft atherosclerosis in heart transplant recipients is currently accomplished using invasive techniques. If its monitoring feasibility is demonstrated, spiral CT could be a non-invasive alternative for this objective.

METHODS

Twenty-four consecutive heart transplant patients (21 men, 3 women, mean age 55 +/- 11 years) were scanned using double-helical CT. The first scan was performed 1.9 +/- 1.3 years after transplantation. After 2 years of follow-up, 4 patients died and the remaining 20 underwent a second scan. All scans were performed according to a previously reported double-helical CT protocol.

RESULTS

The incidence of coronary calcification at the first scan was 4.2% (1/24); it increased to 40% (8/20) at the second scan (P < 0.001). Spiral CT identified new but very mild calcific deposits in seven patients with a mean total calcium score of 6.7 +/- 4.0.

CONCLUSIONS

Double-helical CT is a viable tool to diagnose and track newly developed allograft atherosclerosis.