X-ray scatter correction for cone-beam CT using moving blocker array

Scatter correction is an active research topic in cone beam computed tomography (CBCT) because CBCT (especially flat-panel detector (FPD) based) systems have large scatter-to-primary ratios. Scatter produces artifact and contrast reduction, and is difficult to model accurately. Direct measurement using a beam blocker array provides accurate scatter estimates. However, since the blocker array also blocks primary radiation, imaging requires a second (or subsequent) scan without the blocker array in place. This approach is inefficient in terms of scanning time and patient dose. To combine accurate scatter estimation and reconstruction into one single scan, a new approach based on an array of moving blockers has been developed. The blocker array moves from projection to projection, such that every detector pixel is not consecutively blocked during the data acquisition, and the missing primary data in the blocker shadows are estimated by interpolation. Using different blocker array trajectories, the algorithm has been evaluated through software phantom studies using Monte Carlo simulations and image processing techniques. Results show that this approach is able to greatly reduce the effect of scatter in the reconstruction. By properly choosing blocker distance and primary data interpolation method, the mean square error of the reconstructed image decreases from 32.3% to 1.13%, and the induced visual artifacts are significantly reduced when a raster-scanning blocker array trajectory is used. Further analysis also shows that artifact arises mostly due to inaccurate scatter estimates, rather than due to interpolation of the primary data.