Estimating the magnitude of scatter in small animal cone-beam CT

Small animal anatomical imaging with x-ray computed tomography (CT) in cone-beam geometry suffers from inaccuracies in the measured attenuation coefficient due to the acceptance of scattered radiation. This work seeks to estimate the magnitude and effect of scatter in a commercial cone-beam microCT scanner in both projections and reconstructed images. The scatter-to-primary ratio (SPR) is estimated from projections using the beam stop method and from simulation. We also make initial attempts to quantitate the amount of inaccuracy in the measured image values under different scatter environments by reducing our 3D cone-beam geometry into a 2D fan-beam system. The extrapolated and simulated SPR (~0.3 for a mouse-sized object) for this microCT scanner indicates that the magnitude of scatter is not as high as in a prototype clinical cone-beam system. From the imaging studies, the resulting attenuation coefficients for the high scatter environment are about 10% lower than those for a low scatter environment. Further investigation is needed to determine the magnitude of errors caused by scatter and beam hardening separately because physical measurements suffer from compounding beam hardening effects. Simulations of the tomographic process are planned to individually evaluate the contribution of each of these effects