MTF measurement and a phantom study for scatter correction in CBCT using primary modulation

Recently, we proposed a scatter correction methods for X-ray imaging using primary modulation. A primary modulator with spatially variant attenuating materials is inserted between the X-ray source and the object to make the scatter and part of the primary distributions strongly separated in the Fourier domain. Linear filtering and demodulation techniques suffice to extract and correct the scatter for this modified system. The method has been verified by computer simulations and preliminary experimental results. In this work, we look into a hybrid method using both primary modulation and an anti-scatter grid. The reconstructed image resolution using the proposed approach is evaluated by MTF measurements, and the scatter correction performance is also investigated by experiments on a human chest phantom. The results using the proposed hybrid method are compared with those using an antiscatter grid only. Experiments with scatter inherently suppressed using a narrowly opened collimator and an anti-scatter grid (a slot-scan geometry) were also carried out. The comparison shows that the filtering in the proposed algorithm does not impair the image resolution, and the primary modulation method can effectively suppress the scatter artifacts. In the central region of interest, the reconstruction error relative to the image obtained using a slot-scan geometry is reduced from 18.10% to 0.48% for the human chest phantom, if the primary modulation method is used.