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An Inter-Projection Interpolation (IPI) Approach for the Synchronized Moving Grid (SMOG) to Reduce Dose in Cone Beam CT

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H Zhang

H Zhang1*, V Kong1 , L Ren2 , J Jin1 , (1) Georgia Regents University, Augusta, GA, (2) Duke University Medical Center, Durham, NC


SU-D-12A-1 Sunday 2:05PM - 3:00PM Room: 12A

Purpose:Synchronized moving grid is a promising technique to reduce scatter and ghost artifacts in cone beam computed tomography (CBCT). However, it requires 2 projections in the same gantry angle to obtain full information due to signal blockage by the grid. We proposed an inter-projection interpolation (IPI) method to estimate blocked signals, which may reduce the scan time and the dose. This study aims to provide a framework to achieve a balance between speed, dose and image quality.

Methods:The IPI method is based on the hypothesis that an abrupt signal in a projection can be well predicted by the information in the two immediate neighboring projections if the gantry angle step is small. The study was performed on a Catphan and a head phantom. The SMOG was simulated by erasing the information (filling with “0”) of the areas in each projection corresponding to the grid. An IPI algorithm was applied on each projection to recover the erased information. FDK algorithm was used to reconstruct CBCT images for the IPI-processed projections, and compared with the original image in term of signal to noise ratio (SNR) measured in the whole reconstruction image range. The effect of gantry angle step was investigated by comparing the CBCT images from projection sets of various gantry intervals, with IPI-predicted projections to fill the missing projection in the interval.

Results:The IPI procession time was 1.79s±0.53s for each projection. SNR after IPI was 29.0db and 28.1db for the Catphan and head phantom, respectively, comparing to 15.3db and 22.7db for an inpainting based interpolation technique. SNR was 28.3, 28.3, 21.8, 19.3 and 17.3 db for gantry angle intervals of 1, 1.5, 2, 2.5 and 3 degrees, respectively.

Conclusion:IPI is feasible to estimate the missing information, and achieve an reasonable CBCT image quality with reduced dose and scan time.

Funding Support, Disclosures, and Conflict of Interest: This study is supported by NIH/NCI grant 1R01CA166948-01

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