Sensitivity of two electron beam tomography protocols for the detection and quantification of coronary artery calcium

OBJECTIVE. The purpose of this study was to compare the sensitivity of two electron beam tomography protocols for detection and quantification of coro nary artery calcium. SUBJECTS AND METHODS. We selected 101 patients (57% men, mean age 53 +/- 10 years) to undergo two consecutive electron beam tomography and acquired im aging with both a 6-mm and a 3-mm slicing protocol. Three pixels (area, 1.0 3 mm(2)) and a minimal density of 130 H were used for definition of calcifi ed plaque. RESULTS. We found coronary artery calcifications in 46 patients when we use d a 6-mm protocol and in 61 patients when we used a 3-mm protocol (p < 0.00 1). The average total calcium score was 77 (+/-140) with a 6-mm protocol an d 251 (+/-395) with a 3-mm protocol (p < 0.005). The average number of calc ified lesions per patient was 1.7 for a 6-mm protocol and 3.7 for a 3-mm pr otocol (p < 0.01). Of 179 individual lesions seen using a 3-mm protocol, 10 3 (58%) were missed using a 6-mm protocol, and only 27% of the lesions with a calcium score less than or equal to 40 seen with a 3-mm protocol were de tected with 6-mm slicing (p < 0.001). The mean lesion attenuation with a 6- mm protocol was 160 (+/-42) H, compared with 218 (+/-44) H with a 3-mm prot ocol (p < 0.001), indicating a significantly greater partial volume averagi ng with the former protocol. CONCLUSION. A 6-mm slicing protocol is significantly less sensitive than a 3-mm protocol for the detection and quantification of coronary artery calci um. Since one third of coronary events occur in patients with low calcium s cores, a 6-mm protocol might he unreliable For risk assessment because of s ubstantial loss of information in this calcium score range.