TH‐C‐103‐05: A Novel Method to Improve Single Phase Reconstruction Quality From Conventional CBCT Dataset

Purpose: to present a method to generate retrospectively a pre‐selected motion phase cone‐beam CT image from the full motion cone‐beam CT acquired at standard rotation speed. Materials and Methods: the method consists of subtracting from the full CBCT all of the undesired motion phases and obtain a motion de‐blurred single‐phase CBCT image CTnm. This is accomplished by means of a subtraction CBCT (CTs) added to the full CBCT (CTm). CTs is obtained as follows: i) we sort the CBCT projections into each phase bin k according to the known motion trace; ii) compute the digitally reconstructed radiographs (DRR) from the full reconstruction at the gantry angles correlated to bin k; iii) generate a set of subtraction projections for phase k by subtracting the DRR from the original projection at the same gantry angle; v) reconstruct CTs from this single‐phase subtraction projection set; vi) add CTs to CTm to obtain CTnm. A qualitative assessment of the image quality improvement was performed using a simple shapes phantom. To quantitatively study the method, we used the image quality modules of a Catphan phantom, evaluated in a static scan and under anterior‐posterior motion. Results: The single phase CBCT reconstruction generated by our method successfully isolates the desired motion phase from the full motion CBCT, effectively reducing motion blur. It also shows improved image quality, with reduced streak artifacts with respect to the reconstructions from unprocessed phase‐sorted projections only. Conclusions: A novel CBCT motion de‐blurring algorithm has been developed and tested with phantom data. The algorithm allows to improve visualization of a single phase motion extracted from a standard CBCT dataset. NIH R01CA133539