Feasibility of transmission microCT with two fan-beam sources

We study in simulation the properties of a transmission CT system using two fan-beam sources both illuminating a single detector. Using traditional X-ray sources, such a system would be expensive, slow, and unwieldy. With the development of new X-ray sources based on nanofabrication methods, however, such a dual-source system becomes feasible. The principal advantage of the new geometry is that a shorter fan-beam (or cone-beam) focal length can be used while achieving the same field-of-view. The shorter focal length should achieve approximately the same spatial resolution since the magnification is offset by the increased effect of nonzero focal spot size. However, the shorter focal length should give better efficiency through inverse square law effects. A disadvantage is that analytical reconstruction methods based on filtered backprojection may not be effective since each source does not view the entire subject. We demonstrate that iterative reconstruction techniques can solve this problem. We also demonstrate the potential improvement in resolution for an ideal source using a microCT simulation by comparing a conventional single source fan-beam CT with 50 cm focal length to a dual-source system with 30.5 cm focal length, both giving approximately the same transverse field of view. We found that the ideal dual-source system improved transverse spatial resolution (FWHM) by 4-14%, although wider tails (FWTM) were noted in point spread estimates. We conclude that use of multiple fan-beam sources is feasible to create transmission CT devices with shorter focal lengths.