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Fig. 1A —Placement of region of interest (ROI, circles) in 64-year-old man complaining of chest pain (heart rate, 68 beats per minute; body weight, 62 kg). Transaxial helical CT images of heart obtained using 100-mA (A), first 60-mA (B), and second 60-mA (C) protocols. Mean and SD CT attenuation values (Hounsfield units) in ROIs set in aorta at level of left coronary artery were 49 ± 14, 47 ± 19, and 45 ± 19 H, respectively. Value means + 2 x SD were 76, 85, and 83 H, respectively. Calcium in left main coronary and anterior descending arteries is well shown on all helical CT scans.