OBJECTIVE. This study was performed to evaluate new scoring methods for quantitat- ing coronary artery calcifications with helical CT and to compare the results with those of quantitative coronary angiography in patients with suspected coronary artery disease. SUBJECTS AND METHODS. Unenhanced dual-slice helical CT and coronary angiography were performed within 24 hr of each other in 101 patients with symptoms of coronary artery disease. Coronary artery calcifications with a density above 90 H were identified on each slice and, with the same regions of interest, quantitative scoring was per- formed at thresholds of 90 H (new) and 130 H (old). Two mathematical algorithms (one new and one old) were evaluated for both thresholds (yielding four scoring systems). By CT imaging, we defined disease as a score of greater than zero. By angiography, we defined disease as a 50% or greater reduction in the luminal diameter of any major vessel. Interobserver variations in calcification scoring were evaluated. Seventeen of our patients also underwent a second, consecutive CT scan to determine reproducibility. RESULTS. With the new threshold and the new algorithm, the sensitivity, specificity, and accuracy of helical CT in predicting disease were 88%, 52%, and 76%, respectively. We found a moderate positive association between the total CT calcification score and the number of stenotic coronary arteries at angiography (Pearson’s correlation coefficient, .43; p = .05 [analysis of variance]). The accuracy and the area under the receiver operating characteristic curve were higher with the new threshold and the new algorithm. Interob- server agreement in calcification scoring was high (intraclass correlation coefficient, .99 [Pt = 851), as was reproducibility (intraclass correlation coefficient, .94 [n = 17]). Reproduc- ibility was higher when scoring was based on the new threshold and the new algorithm. CONCLUSION. The quantity ofcoronary artery calcifications as measured by helical CT correlated positively with obstructive coronary artery disease as measured by angiogra- phy. Interobserver agreement and reproducibility were excellent. A new scoring method AJR:167, August 1996 439 Measurement of Coronary Artery Calcium with Dual-Slice Helical CT Compared with Coronary Angiography: Evaluation of CT Scoring Methods, Interobserver Variations, and Reproducibility Lynn S. Broderick1 Joseph Shemesh2’3 Robert L. Wilensky4 George J. Eckert5 Xiao-hua Zhou5 William E. Torres6 Michael A. Balk7 WendyJ. Rogers1 Dewey J. Conces, Jr.1 Kenyon K. Kopecky1 Received September 25, 1995; accepted after revision February 22, 1996. 1Department of Radiology, Indiana University School of Medicine, Indiana University Hospital 0279, 550 N. Uni- versity Blvd., Indianapolis, IN 46202-5253. Address corre- spondence to L S. Broderick. 2The Cardiac Rehabilitation Institute, Sheba Medical Center, Tel Aviv, Israel. 3Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel. 4 Division of Cardiology, Department of Medicine, Indiana University School of Medicine, Indianapolis, IN 46202. tDivision of Biostatistics, Department of Medicine, Indi- ana University School of Medicine, Indianapolis, IN 46202. tDepartment of Radiology, Emory University School of Medicine, Atlanta, GA 30322. 7Division of Cardiology, Department of Medicine, Emory University School of Medicine, Atlanta, GA 30322. AJR 1996;167:439-444 0361-803X/96/1672-439 © American Roentgen Ray Society showed promise. E lectron beam CT has been used to evaluate the heart because it can acquire axial images in 0.1 sec with electrocardiographic gating and because the heart can be imaged with non- overlapping 3-mm slices in 30-40 sec (a breath-hold). The quantity of coronary artery calcium as measured by unenhanced electron beam CT correlates positively with obstructive coronary artery disease as measured by angiography. Because of this correlation, CT has been used as a diagnos- tic test to evaluate symptomatic patients with suspected or known coronary artery disease and also as a screening tool for asymptomatic subjects [1-1 11. Single-slice helical CT acquires a volume of spatial information over several seconds without electrocardiographic gating. These data can be reconstructed into thin overlap- ping axial images, with an acquisition time for each image of approximately 0.6-1 .0 sec. Dual-slice helical CT is the same as single- slice helical CT, except that it acquires data twice as fast because it has two parallel arcs of detectors that are simultaneously irradiated by a single anode. With helical CT (single or dual slice), the heart can be imaged with 3- mm slices within 30 sec (a breath-hold). If the quantitation of coronary artery calcifications can be performed with helical CT at an accu- racy similar to that of electron beam CT, as