3D cone-beam rebinning and reconstruction for animal PET transmission tomography

In PET scanners, one or multiple collimated point sources are used to acquire transmission measurements to generate attenuation maps for emission tomography. The transmission acquisition is, intrinsically, 3D cone beam geometry. The acquired list-mode data are transformed into sinograms in the histogram process. Thereafter, transmission images are reconstructed from the sinograms, which are then re-projected to generate an attenuation map. Conventionally, a 2D rebinning method is used to transform the list-mode data into 2D parallel beam sinograms, and, accordingly, 2D reconstruction algorithms are employed to generate transmission images. Due to the inaccuracy of the 2D rebinning method, only limited oblique Lines of Response (LOR) can be used, causing limited axial coverage. If more oblique LORs were to be accepted in the rebinning process, artifacts would be introduced in the transmission images that may result in inaccurate attenuation correction factors. To address this issue, a 3D cone-beam rebinning process is proposed to faithfully transform the list-mode data, and the associated reconstruction algorithms for cone-beam geometry have been adopted to generate the transmission images. The experimental results showed the new method produced better images, especially in the axial direction.