  Flat-panel cone-beam CT (CBCT) has been applied clinically in a number of
high-resolution applications. Increasing geometric magnification can
potentially improve resolution, but also increases blur due to an extended
x-ray focal-spot. We present a shift-variant focal-spot blur model and
incorporate it into a model-based iterative-reconstruction algorithm. We apply
this algorithm to simulation and CBCT test-bench data. In a trabecular bone
simulation study, we find traditional reconstruction approaches without a blur
model exhibit shift-variant resolution properties that depend greatly on the
acquisition protocol (e.g. short vs. full scans) and the anode angles of the
rays used to reconstruct a particular region. For physical CBCT experiments
focal spot blur was characterized and a spatial resolution phantom was scanned
and reconstructed. In both experiments image quality using the shift-variant
model was significantly improved over approaches that modeled no blur or only a
shift-invariant blur, suggesting a potential means to overcome traditional CBCT
spatial resolution and system design limitations.
