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4D Low-Dose CBCT Using a Moving-Blocker

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C Zhao

C Zhao1*, Y Zhong2 , J Wang2 , M Jin1 , (1) University of Texas at Arlington, Arlington, TX, (2) UT Southwestern Medical Center, Dallas, Texas


TH-AB-601-1 (Thursday, August 3, 2017) 7:30 AM - 9:30 AM Room: 601

Purpose: To develop a low-dose 4D cone-beam computed tomography (CBCT) method using a moving blocker (“4D moving-blocker method”), which can reconstruct respiratory-motion-resolved volumetric images and hold the potential for scatter correction (SC).

Methods: A lead-stripe blocker is placed between the X-ray tube and the subject, thus part of X-ray fluence is blocked for reduced radiation dose. The respiratory gated data acquisition is performed to obtain the projection data binned into different respiratory phases. In the meantime, the blocker is moving along the axial direction. In such an acquisition, although the radiation dose is substantially reduced, each respiratory phase suffers both few view and partial projection data problems. To address the missing data problem, we adopt the total variation (TV) minimization for the spatial regularization and the simultaneous motion estimation and image reconstruction (SMEIR) 4D method to jointly reconstruct each phase image using all projection data. We tested this new 4D moving-blocker method using the simulated data of the NCAT phantom.

Results: The proposed 4D moving blocker method can accurately reconstruct respiratory phase images with 2/3 dose of a routine CBCT scan. The 4D moving-blocker reconstruction with SMEIR achieved better structural similarity index (SSIM) and root mean square error (RMSE) values than 3D TV reconstruction without blocker (Dose: 2/3 vs. 1, SSIM 0.677 vs. 0.475, and RMSE 18.3 HU vs. 19.6 HU). The results also show that the 4D moving blocker CBCT can achieve the similar reconstruction performance, if not better, to 4D SMEIR reconstruction with equivalent dose by reducing projection views.

Conclusion: We develop a new 4D low-dose CBCT acquisition and reconstruction method with a moving blocker. The simulation study demonstrated the feasibility of the proposed method. The future study will investigate the additional benefit of scatter correction and its effectiveness on real patients.

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