Analytical Low-Dose CBCT Reconstruction Using Non-local Total Variation Regularization for Image Guided Radiation...

Area of Science:

• Medical Imaging
• Image Reconstruction
• Radiotherapy Technology

Background:

• Conventional iterative Cone Beam CT (CBCT) reconstruction is slow and can over-smooth images.
• Low-dose CBCT is desirable for patient safety but suffers from noise and reduced image quality.
• Existing methods struggle to balance noise reduction with preservation of image details.

Purpose of the Study:

• To develop a fast, non-iterative analytical method for low-dose CBCT reconstruction.
• To improve image quality by restoring noisy low-dose projections to high-dose quality.
• To enhance the clinical applicability of low-dose CBCT in radiotherapy.

Main Methods:

• Modeled low-dose CBCT reconstruction as restoring noisy projections using non-local total variation (NLTV).
• NLTV minimizes an energy function penalizing gray-level differences between noisy and denoised projections.
• Applied the standard FDK method after NLTV restoration for final image reconstruction.

Main Results:

• Achieved significant noise reduction while maintaining image quality comparable to high-dose CBCT.
• Demonstrated robust noise restoration and improved overall image quality with NLTV.
• Showed noticeable improvements in normalized mean square error (NMSE) and peak signal-to-noise ratio (PSNR).
• Observed comparable contrast-to-noise ratios (CNRs) to high-dose CBCT.

Conclusions:

• The proposed NLTV method successfully restores low-dose CBCT projections to high-dose quality.
• This approach offers considerable improvement over standard FDK-based methods.
• Significant reduction in reconstruction time makes the algorithm attractive for clinical radiotherapy.