Helical volume CT and its clinical significance

Helical Volume CT (HVCT) is an X-ray CT scanning technique in which the patient is scanned continuously while the couch-top is moved in the axial direction. It is performed using the Toshiba TCT-900S CT scanner jointly developed by the authors and Toshiba Corporation. This scanner features a large central opening, the inner surface of which is lined with a circular array of 2,304 detectors. The X-ray tube rotates outside the detector array at the rate of one revolution per second. Electrical power is supplied to the X-ray tube through a slip ring mechanism, permitting the X-ray to be continuously generated without any interscan delay. The X-ray tube and detectors move in a "nutate/rotate" pattern. The maximum scanning time is 30 seconds (equivalent to a single breath-hold). To improve image quality, the slice thickness can be selected to equal the distance over which the couch-top moves in one second. The clinical advantages of HVCT are as follows: (1) the examination time is significantly reduced (to minimize the patient's discomfort), (2) continuous data of anatomical structures can be obtained without artifacts due to respiratory motion, and (3) it is possible to obtain superior images for multiplanar reconstruction (MPR), cine-display, and three-dimensional reconstruction.