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A 72 year old man attended for follow up computed tomography (CT) of a chronic type A aortic dissection, three years on from his original presentation. The contrast enhanced multislice CT was acquired using retrospective ECG gating. Subsequent reconstruction of the CT images was from a diastolic “reconstruction window” centred at 75% of the RR interval. This mode of acquisition provided images of the thoracic aorta free of motion artefact. The chronic dissection flap could clearly be seen arising in the proximal, aneurysmal ascending aorta (panel A, axial CT section), extending to the head and neck vessels (panel B, sagittal CT section), and progressing distally to the descending aorta (panel C, three dimensional reconstruction in sagittal section). Advanced post-processing using volume rendering techniques demonstrated the dissection (panel C) and the aneurysm (panel D) in three dimension.
Aortic motion artefact is the most common cause of false positive detection of dissection of the ascending aorta. Motion artefact can be reduced by lowering the patient’s heart rate but also by the use of ECG gating in the scan acquisition. Selection of the diastolic “reconstruction window” with the best image quality can be predicted according to the patient’s heart rate. In this case the heart rate was 65 beats per minute and the “reconstruction window” selected was centred at 75% of the RR interval.
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