Purpose: We propose a half beam blocker-based scatter correction method combined with local filtration algorithm to remove the scatter-induced artifacts in single-scan cone-beam CT(CBCT) imaging.
Methods: A head phantom and an electron density phantom were scanned in our in-house developed CBCT platform. A half beam blocker composed of lead strips was inserted between the x-ray source and the phantom, and used to block about half of the beam area. The shaded regions behind lead strips were considered as scatter signal. The scatter signal was smoothened with a threshold-based local filtration algorithm. Finally, the scatter free projections were produced by subtracting the estimated scatter from the unblocked half projections, and were used for volumetric reconstruction with FDK algorithm. The scatter corrected CBCT images were compared with fan beam CT and those without scatter correction.
Results: Compared with the CBCT without correction, the error of CT number was reduced from more than 200 HU to less than 7 HU for the electron density phantom, and from more than 148 HU to less than 14 HU for the head phantom. The spatial uniformity was improved by a factor of 3.
Conclusion: The proposed scatter correction method obtained accurate CT numbers and improved image spatial uniformity, without additional effort of another scan. This method has promising application in CBCT guided radiotherapy for better adaptive radiation dose calculation.