Evaluation of ECG gating and hybrid subtraction for intraarterial digital subtraction thoracic aortography.

A comparative study was made of ECG-gated and nongated intraarterial digital subtraction angiography of the thoracic aorta by using conventional temporal subtraction and combined temporal/energy (hybrid) subtraction. ECG-gated studies were acquired at three frames per cardiac cycle. In 85% of patients, gated conventional subtraction resulted in studies of superior image quality in comparison with those obtained with hybrid techniques, both gated and nongated. In the 15% in whom hybrid subtraction studies were judged superior, the hybrid images were almost exclusively integrated by video frame averaging and thus were nongated. In a separate subset of patients who had conventional nongated studies, there was no difference in the percentage of diagnostic studies (93%) and nondiagnostic studies (7%) when compared with conventional gated temporal subtraction. Cardiac gating appears to be superior to hybrid subtraction for studies of the thoracic aorta that use intraarterial digital subtraction angiography, but neither technique offered any significant advantage over conventional nongated acquisition.