  Pencil x-ray beam imaging provides superior spatial resolution than other
imaging geometries like sheet beam and cone beam geometries due to the
illumination of a line instead of an area or volume. However, the pencil beam
geometry suffers from long scan times and concerns over dose discourage
laboratory use of pencil beam x-ray sources. Molecular imaging techniques like
XLCT imaging benefit most from pencil beam imaging to accurately localize the
distribution of contrast agents embedded in a small animal object. To
investigate the dose deposited by pencil beam x-ray imaging in XLCT, dose
estimations from one angular projection scan by three different x-ray source
energies were performed on a small animal object composed of water, bone, and
blood with a Monte Carlo simulation platform, GATE (Geant4 Application for
Tomographic Emission). Our results indicate that, with an adequate x-ray
benchtop source with high brilliance and quasi-monochromatic properties like
the Sigray source, the dose concerns can be reduced. With the Sigray source,
the bone marrow was estimated to have a radiation dose of 30 mGy for a typical
XLCT imaging, in which we have 6 angular projections, 100 micrometer scan step
size, and 10^6 x-ray photons per linear scan.
