Recommendations for standardization of EBT and MSCT scanning

CT of Coronary Artery Disease

The clinical relevance of coronary artery disease has considerably driven the recent development of radiologic tools for noninvasive cardiac imaging. Modern multidetector row computed tomographic (MDCT) systems combine high temporal and spatial resolution, electrocardiographic synchronization, and ease of use. In cardiac imaging, MDCT has not only replaced electron-beam CT, but also challenges competing methods such as magnetic resonance imaging, echocardiography, or even coronary catheterization. Noncontrast material-enhanced assessment of atherosclerotic plaques (CT calcium scoring) seems useful for the cardiac risk stratification in asymptomatic patients and monitoring of medical (statin) therapy. Contrast material-enhanced CT coronary angiography has become established as a valuable method for several clinical indications such as evaluation of coronary artery anomalies, bypass patency, or preoperative planning. Particularly, the high negative predictive value of a normal CT coronary angiogram allows reliable exclusion of coronary artery stenosis. Plaque characterization is another promising area of research in MDCT cardiac imaging. However, with current technology a reliable distinction between atheroma and fibroatheroma is impaired by restrictions in spatial resolution. Recent studies indicate that CT angiography may also be suited for other clinical applications such as triage of patients with acute coronary syndrome and inconclusive clinical presentation, patients with symptomatic chest pain, and intermediate risk profile or cardiac risk stratification in asymptomatic patients.

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.

CT of coronary artery disease

The socioeconomic importance of heart disease provides considerable motivation for development of radiologic tools for noninvasive imaging of the coronary arteries. Current computed tomographic (CT) techniques combine high speed and spatial resolution with sophisticated electrocardiographic synchronization and robustness of use. Application of these modalities for evaluation of coronary artery disease is a topic of active current research. Coronary artery calcium measurements with different CT techniques have been used for determining the risk of coronary events, but the exact role of this marker for cardiac risk stratification remains unclear pending results of population-based studies. Contrast material-enhanced CT coronary angiography has become an established clinical indication for some scenarios (eg, coronary artery anomalies, bypass patency, surgical planning). With current technology, the accuracy of CT coronary angiography for detection of coronary artery stenoses appears promising enough to warrant pursuit of this application, but sensitivity is still not high enough for routine diagnostic needs. The high negative predictive value of a normal CT coronary angiogram, however, may be useful for reliable exclusion of coronary artery stenosis. The cross-sectional nature of CT may allow noninvasive assessment of the coronary artery wall. Use of contrast-enhanced CT coronary angiography for detection, characterization, and quantification of atherosclerotic changes and total disease burden in coronary arteries as a potential tool for cardiac risk stratification is currently being investigated.

Evaluation of reconstruction windows for multislice computed tomography in quantification of coronary calcium

RATIONALE AND OBJECTIVES

To search for an optimum reconstruction window in retrospectively gated multislice computed tomography (MSCT) for quantification of coronary calcium.

MATERIALS AND METHODS

Coronary calcium quantified was examined as Agatston and volume scores by two experienced observers at 10 time points across the R-R interval of the electrocardiogram in 42 patients. A combination of statistical approaches was used to evaluate the distributions of minimum and maximum scores and of interobserver variability for both scoring methods across the cardiac cycle.

RESULTS

Based on the combination of evaluation approaches, 60% to 70% of the R-R interval appeared to be the optimum time point for obtaining maximum calcium scores with minimum interobserver variability. The optimum time point was more clearly defined for the Agatston score than for the volume score.

CONCLUSION

A reconstruction window beginning at 60% to 70% of the R-R interval seems to be most advantageous for retrospective gating of MSCT studies performed to quantify coronary calcium.