The quality of 3D reconstructions from 1.0 and 1.5 pitch helical and conventional CT

CT data are commonly used to create 3D images. For this purpose, thin and overlapped slices are desirable. Helical (spiral) CT offers the ability to adjust the slice reconstruction interval from 0 to 100%. However, its use in 1.0 and 1.5 pitch helical CT and 3D imaging, especially with respect to surface detail, is relatively untested.

Ten objects selected for their varying size, shape, and density were scanned (fourth generation Picker PQ2000) by contiguous 2,4 and 8 mm conventional and helical sequences. The latter were obtained with a pitch of both 1.0 and 1.5 and were reconstructed into a 3D image with 0-75% overlapping of the reconstructed slices. Each of the 24 different sequences per scanned object was reconstructed into identical sets (projections) of 3D images displayed on color film. The 24 3D image sets for each object were submitted to six blinded radiologists who separately ranked them from best to worst.

3D reconstructions obtained from CT scans with a thinner slice thickness, half-field (15 cm FOV), and helical technique were rated as statistically superior. The 1.0 and 1.5 helical sequences obtained with a 4 or 8 mm slice thickness scored statistically better than 3D reconstructions from equivalent conventional scans. Overlapping of the reconstructed helical slices by 25-75% generally improved the quality of the 3D reconstruction.

Helical CT with either a 1.0 or a 1.5 pitch offers the ability to obtain higher quality 3D reconstructions than from comparable conventional CT scans.