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Radiation exposure is represented by the gray shade. (a) Helical CT coronary angiography (CTCA) without ECG tube modulation. (b) Retrospectively gated helical CTCA with ECG tube modulation (E ≈ 10-20 mSv in 64-slice CT). (c) Prospectively gated axial CTCA or step-and-shoot algorithm (E ≈ 2-3 mSv in 64-slice CT).
