[Characteristics and limitations of three-dimensional spiral CT--experimental evaluation]

We evaluated the image quality of three-dimensional (3D) spiral CT using a Somatom Plus CT scanner (Siemens, Germany). A T-shaped acrylate plastic model was made and scanning was performed with a table speed of 5 mm/sec for 24 seconds. The thickness of the X-ray beam was 5mm with one second per rotation. The various images of the model were created based on the shaded surface display (SSD) method and the effect of threshold and rotation (spin and tilt) on the quality of the 3D images was studied. The increase of threshold caused a rapid decrease in the diameter of the stick observed on the film, and this phenomenon was particularly remarkable on the transverse stick and the junctional portion of the longitudinal stick. The change of spin or tilt did not affect the diameter of the stick on the film. It was found that the depth perception of the stick could be achieved with the gray scale technique. We concluded that the interpretation of the 3D spiral CT image obtained with SSD needs caution and the diagnosis should not be made only on this image.