Advanced single-slice rebinning in cone-beam spiral CT

To achieve higher volume coverage at improved z-resolution in computed tomo graphy (CT), systems with a large number of detector rows are demanded. How ever, handling an increased number of detector rows, as compared to today's four-slice scanners, requires to accounting for the cone geometry of the b eams. Many so-called cone-beam reconstruction algorithms have been proposed during the last decade. None met all the requirements of the medical spira l cone-beam CT in regard to the need for high image quality, low patient do se and low reconstruction times. We therefore propose an approximate cone-b eam algorithm which uses virtual reconstruction planes tilted to optimally fit 180 degrees spiral segments, i.e., the advanced single-slice rebinning (ASSR) algorithm. Our algorithm is a modification of the single-slice rebin ning algorithm proposed by Noo et nl. [Phys. Med. Biol. 44, 561-570 (1999)] since we use tilted reconstruction slices instead of transaxial slices to approximate the spiral path. Theoretical considerations as well as the reco nstruction of simulated phantom data in comparison to the gold standard 180 degrees LI (single-slice spiral CT) were carried out. Image artifacts, z-r esolution as well as noise levels were evaluated for all simulated scanners . Even for a high number of detector rows the artifact level in the reconst ructed images remains comparable to that of 180 degrees LI. Multiplanar ref ormations of the Defrise phantom show none of the typical cone-beam artifac ts usually appearing when going to larger cone angles. Image noise as well as the shape of the respective slice sensitivity profiles are equivalent to the single-slice spiral reconstruction, z-resolution is slightly decreased . The ASSR has the potential to became a practical tool for medical spiral cone-beam CT. Its computational complexity lies in the order of standard si ngle-slice CT and it allows to use available 2D backprojection hardware. (C ) 2000 American Association of Physicists in Medicine.