Volumetric computerized tomography (spiral CT). Technical principles and possible applications in the thorax

: Spiral volumetric CT is a new volume scanning technique allowing the one-acquisition imaging of an anatomical volume, by advancing the patient through a continuously rotating X-ray tube. As a result, the X-ray tube moves in spirals around the patient and this is the reason why this new technique is called Spiral CT. At the end of the acquisition, planar images are reconstructed by means of a dedicated image reconstruction algorithm with a linear interpolation between two contiguous spiral segments. Spiral CT offers many advantages, all resulting from the possibility of evaluating anatomical volumes in a short time: the organs which are subject to respiratory motion can be studied in a single breath-hold scan, the quality of secondary reconstructions (2/3 dimensional) is improved, the use of contrast media is optimal and finally motion artifacts are reduced. The authors report their early experience with spiral CT in the chest. Spiral CT is more reliable than conventional CT in the evaluation of pulmonary nodules, which can be easily identified with no risk of missing small lesions, and of the pulmonary apex and of the diaphragm. Moreover, contrast media can be used at a lower dosage than usually recommended with conventional CT.