Coronary calcium: the case for helical computed tomography

Multislice computed tomography for determination of coronary artery disease in a symptomatic patient population

BACKGROUND

Multislice computed tomography (MSCT) has started to replace Electron beam CT for quantitation of coronary artery calcium. However no study has evaluated the diagnostic accuracy of MSCT for prediction of coronary artery disease (CAD) in a symptomatic patient population using the volume score.

METHODS AND RESULTS

1347 symptomatic subjects (male = 803, mean age = 62 years) with suspected CAD underwent MSCT studies 1 +/- 2 days before the coronary angiogram. The Agatston (ACS) and Volumetric calcium score (VCS) were calculated using a proprietary workstation. Statistical analyses included the Pearson's correlation coefficient and the nonparametric Mann-Whitney U-test to compare the calcium score in different age groups and between men and women. Sensitivity, specificity and predictive accuracy were calculated for different calcium thresholds for prediction of CAD. ROC curve analyses were used to establish relations between the coronary calcium score and presence or absence of CAD. In 720 (53%) subjects (male = 419) angiography revealed a minimal lumen diameter stenosis greater than 50%. Patients with significant CAD had significantly higher total calcium score values than patients without CAD (P = 0.001). ACS and VCS demonstrate a close correlation for the whole study group, r = 0.99. The overall sensitivity of any calcium to predict stenosis was 99%, specificity = 32%. Exclusion of calcium was highly accurate for exclusion of CAD in subjects older than 50 years (predictive accuracy = 98%). An absolute cutoff >100 and an age and sex specific threshold (score over 75th percentile) were identified as the cutoff levels with the highest sensitivities (86-89%) and lowest false positive rates (20-22%). ROC analyses revealed MSCT calcium scanning as a good clinical test which can be performed with similar accuracy in all age groups with an area under the curve of 0.84.

CONCLUSION

Determination of coronary calcium with MSCT is an accurate imaging modality for prediction of significant CAD in a patient population with intermediate likelihood of CAD. Exclusion of any calcium provided strong evidence that patients older than 50 years did not have obstructive CAD. ACS and VCS show an equivalent diagnostic accuracy.

Vascular Diseases of the Thorax: Evaluation with Multidetector CT

The list of vascular diseases in the thorax has been narrowed to three, which are considered essential information for radiologists interpreting CT scans of the thorax: (1) aortic dissection and its variants, intramural hematoma and penetrating atherosclerotic ulcer; (2) acute pulmonary embolism; and (3) coronary artery disease. The spatial resolution of multidetector CT is such that CT has become the imaging modality of choice for aortic dissection and pulmonary embolism. This move away from angiography has transpired over the last decade; perhaps the next decade will see the same occur for evaluation of coronary artery disease.

Calcified coronary artery plaque measurement with cardiac CT in population-based studies: standardized protocol of Multi-Ethnic Study of Atherosclerosis (MESA) and Coronary Artery Risk Development in Young Adults (CARDIA) study

Calcified coronary artery plaque, measured at cardiac computed tomography (CT), is a predictor of cardiovascular disease and may play an increasing role in cardiovascular disease risk assessment. The Multi-Ethnic Study of Atherosclerosis (MESA) and the Coronary Artery Risk Development in Young Adults (CARDIA) study of the National Heart, Lung, and Blood Institute are population-based studies in which calcified coronary artery plaque was measured with electron-beam and multi-detector row CT and a standardized protocol in 6814 (MESA) and 3044 (CARDIA study) participants. The studies were approved by the appropriate institutional review board from the study site or agency, and written informed consent was obtained from each participant. Participation in the CT examination was high, image quality was good, and agreement for the presence of calcified plaque was high (kappa = 0.92, MESA; kappa = 0.77, CARDIA study). Extremely high agreement was observed between and within CT image analysts for the presence (kappa > 0.90, all) and amount (intraclass correlation coefficients, >0.99) of calcified plaque. Measurement of calcified coronary artery plaque with cardiac CT is well accepted by participants and can be implemented with consistently high-quality results with a standardized protocol and trained personnel. If predictive value of calcified coronary artery plaque for cardiovascular events proves sufficient to justify screening a segment of the population, then a standardized cardiac CT protocol is feasible and will provide reproducible results for health care providers and the public.

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.

Improving mass measurement of coronary artery calcification using threshold correction and thin collimation in multi-detector row computed tomography

RATIONALE AND OBJECTIVES

This in vitro study was designed to improve the accuracy of coronary calcium mass measurement from computed tomography (CT) images by developing threshold-based calcium CT number correction and thin-slice spiral techniques.

MATERIALS AND METHODS

A cardiac CT phantom containing simulated calcified cylinders of known calcium density was scanned with sequential 4 x 2.5-, spiral 16 x 1.5-, and spiral 16 x 0.75-mm collimation on 4- and 16-detector row CT scanners. The images obtained from the spiral scans were reconstructed in various slice widths. The calcified cylinders were imaged and their mean CT number and size were measured at thresholds ranging from 50 to 390 Hounsfield unit. The calcium mass measured was compared with the actual value to determine errors, and threshold-based correction factors were derived to minimize the errors.

RESULTS

The minimum amount of measurable calcium in 1-mm cylinder was 0.3 mg at the 16 X 1.5-mm protocol and 0.2 mg at the 16 x 0.75-mm protocol. Compared with 2.5-mm sequential protocol, thin-slice spiral protocols yielded a higher radiation exposure and lower or similar image noise levels. The error in calcium mass after correction was significantly smaller than that in measured mass (P < .0001) and was consistent between the imaging protocols (P = .49). The accuracy of mass measurements was clearly improved by using thin-slice imaging protocols especially in 200-mg/cm3 calcium density (P < .0001).

CONCLUSION

The accuracy of calcium mass CT measurement can be improved by threshold-based calcium CT number correction and thin collimation spiral techniques.

Morphologic assessment of patent ductus arteriosus in adults using retrospectively ECG-gated multidetector CT

OBJECTIVE

Noninvasive imaging of a persistently patent ductus arteriosus in adults remains a challenge. Bearing in mind the excellent spatial resolution provided by multidetector CT (MDCT), we postulated that MDCT might be used to evaluate this anatomic defect. We sought to show that MDCT can depict in detail patent ductus arteriosus in adults and allow determination of the size of the duct, degree of calcification, and morphologic classification.

CONCLUSION

MDCT represents a novel method of noninvasively assessing patent ductus arteriosus in adults that provides detailed anatomic information. Comparison with invasive angiographic findings is needed to validate the technique of sizing of ducts using MDCT.

Multislice computed tomography cardiac imaging: current status

Non-invasive CT coronary artery imaging has previously had little relevance to most UK radiologists due to the limited availability of electron beam CT scanners. Major advances in CT technology have promoted new applications for helical CT, which include cardiac imaging. Widespread installation of 'multislice' helical CT scanners will make CT coronary artery imaging available for the first time in many UK hospitals. The technical advances and early clinical trial data are reviewed and multislice helical CT cardiac imaging in general is discussed.