THE QUALITY OF 3D RECONSTRUCTIONS FROM 1.0 AND 1.5 PITCH HELICAL AND CONVENTIONAL CT

Purpose: CT data are commonly used to create 3D images. For this purpo se, thin and overlapped slices are desirable. Helical (spiral) CT offe rs the ability to adjust the slice reconstruction interval from 0 to 1 00%. However, its use in 1.0 and 1.5 pitch helical CT and 3D imaging, especially with respect to surface detail, is relatively untested. Met hod: Ten objects selected for their varying size, shape, and density w ere 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 wi th 0-75% overlapping of the reconstructed slices. Each of the 24 diffe rent sequences per scanned object was reconstructed into identical set s (projections) of 3D images displayed on color film. The 24 3D image sets for each object were submitted to six blinded radiologists who se parately ranked them from best to worst. Results: 3D reconstructions o btained from CT scans with a thinner slice thickness, half-field (15 c m FOV), and helical technique were rated as statistically superior. Th e 1.0 and 1.5 helical sequences obtained with a 4 or 8 mm slice thickn ess scored statistically better than 3D reconstructions from equivalen t conventional scans. Overlapping of the reconstructed helical slices by 25-75% generally improved the quality of the 3D reconstruction. Con clusion: Helical CT with either a 1.0 or a 1.5 pitch offers the abilit y to obtain higher quality 3D reconstructions than from comparable con ventional CT scans.