Noise characteristics of 3D reconstruction on tilted plane: cone beam vs. semicone-beam

In multidetector-row helical CT employing a 2D back-projector, the reconstruction of an image through fan beam filtered back-projection on a tilted reconstruction plane (RP) can significantly suppress helical and cone beam artifacts. In helical volumetric CT employing a 3D back-projector, particularly at very high helical pitches, a tilted RP is still useful, because it can substantially suppress the helical artifacts due to data inconsistence in helical data acquisition process and increase the achievable field of view that can be appropriately reconstructed. Consequently, the highest available helical pitch for a helical volumetric CT scanner, which is vital in speed-critical clinical procedures, can be increased dramatically. An investigation into the image quality of helical volumetric CT using 3D back-projection on tilted RPs has been conducted in this paper, in which both the full-cone-beam and semicone-beam modes are involved. The output shows that, similar to 3D reconstruction on orthogonal reconstruction planes, the noise, noise uniformity and the noise characteristics over pitch of an image reconstructed on a tilted RP can be significantly improved through 3D reconstruction under the semicone-beam geometry.