Visualization of X-ray fields, overlaps, and over-beaming on surface of the head in spiral computed tomography using computer-aided design-based X-ray beam modeling.

To visualize the X-ray fields, overlaps, and over-beaming on the skin surface during spiral head CT scanning. The measured pitch factors were determined by measuring 3 rotation times, 11 table-feed speeds, and an X-ray beam width. The X-ray fields, overlaps, and over-beaming on the skin surface were calculated via computer-aided design-based X-ray beam modeling, and the values obtained using the nominal pitch and measured pitch factors were compared. The X-ray fields with measured pitch factors exceeded those with nominal pitch factors. The overlaps increased with a decrease in the nominal pitch and measured pitch factors and were observed even at a nominal pitch factor of 1.0. The most stretched over-beaming field was observed with the measured pitch factor of 0.670. The technique can show the overlaps of the X-ray fields and may determine the adequate start angle to prevent overlaps to the eye lens.