Prospective gating with 320-MDCT angiography: effect of volume scan length on radiation dose.

Objective: The purpose of this study was to evaluate the relation between radiation dose reduction and volume scan length for prospectively ECG-gated 320-MDCT angiography in the diagnosis of coronary artery disease.
Materials and Methods: MDCT with prospective ECG gating was performed at one of the three volume scan lengths depending on heart length. Of 175 patients, 95 (55%; body mass index, 29 ± 5.9; mean heart rate, 59 ± 7 beats/min) underwent scanning at 160 mm; 46 (26%; body mass index, 30 ± 4.1; mean heart rate, 56 ± 5.74 beats/min) at 140 mm; and 34 (19%; body mass index, 30 ± 3.71; mean heart rate, 58 ± 3.96 beats/min) at 120 mm.
Results: The median radiation doses were 6.5 mSv (95% CI, 6.03-7.2 mSv) for the 95 patients who underwent scanning at a volume scan length of 160 mm, 4.33 mSv (95% CI, 4.06-6.62 mSv) for the 46 patients who underwent scanning at 140 mm, and 3.47 mSv (95% CI, 3.15-3.62 mSv) for the 34 patients who underwent scanning at 120 mm. The reduction in scan length from 160 to 140 mm represented a reduction in scan length of 12.5% and the reduction to 120 mm a reduction of 25%. The median radiation dose was reduced 33% when volume scan length was changed to 140 mm and 47% when the length was changed to 120 mm.
Conclusion: Dose optimization remains an important concern in cardiac CT, and for 320-MDCT angiography, substantial dose reduction can be achieved by reducing volume scan length so that it is in concert with the patient's heart length.