Roi Cone-beam Ct on a Circular Orbit for Geometric Magnification Using Reprojection

We present an algorithm which allows us to investigate what is feasible when reconstructing a Region-Of-Interest (ROI) from transaxial truncated cone-beam projections obtained on a circular orbit in combination with information obtained at a different magnification level. We use the well-known fact that a rough estimate of the global properties of the Radon Transform is sufficient to obtain a reliable reconstruction of a local region. First, the complete object density function is reconstructed with the Feldkamp (FDK)-algorithm, starting from non-truncated cone-beam (CB) projections, to attain a low magnification image. Then we collect CB projections with a higher spatial resolution but that are truncated due to a limited field of view of the detector. To correct for the missing transaxial information, we then numerically reproject the reconstructed low-magnification image to assemble the missing ray integrals using a ray tracing method at high magnification. Finally, we reconstruct the completed projections with the FDK-algortihm to obtain an image with high spatial resolution within a certain ROI. This result can serve as a standard to what is possible when using additional information to truncated projections with the FDK-algorithm.