Scatter Correction for X-ray Imaging Using Primary Modulation: A Phantom Study for CBCT

Abstract

Recently, we have developed a scatter correction algorithm for x-ray imaging that provides accurate scatter correction without additional patient exposure. A calibration sheet (primary modulator) with a checkerboard pattern of attenuating materials is inserted between the x-ray source and the object, so that the scatter and part of the primary distributions are strongly separate in the Fourier domain. Linear filtering and demodulation techniques suffice to extract the low-frequency components of the primary and hence obtain the scatter estimation and correction. The algorithm has been verified by Monte Carlo simulations. In this work, a physical primary modulator was built using aluminum, and experiments were carried out on our bench-top CBCT system with the insertion of the modulator. A standard evaluation phantom and a human chest phantom were used in the study. Scatter corrected images using the primary modulator are compared with those without scatter correction and with scatter inherently suppressed with the collimator narrowly opened. The results show that the primary modulation approach reduces the relative error of the reconstructed image around the central region of interest from 31.80% to 2.30% for the evaluation phantom without the anti-scatter grid, and from 17.54% to 0.47% for the human chest phantom with the anti-scatter grid in place. The reconstructions of the resolution test objects also reveal that this algorithm has no noticeable impact on the resolution of the reconstructed image, although a filtering-based technique is used.