4D cone-beam computed tomography (CBCT) using a moving blocker for simultaneous radiation dose reduction and scatter correction

Abstract

Four-dimensional (4D) x-ray cone-beam computed tomography (CBCT) is important for a precise radiation therapy for lung cancer. Due to the repeated use and 4D acquisition over a course of radiotherapy, the radiation dose becomes a concern. Meanwhile, the scatter contamination in CBCT deteriorates image quality for treatment tasks. In this work, we propose the use of a moving blocker (MB) during the 4D CBCT acquisition ('4D MB') and to combine motion-compensated reconstruction to address these two issues simultaneously. In 4D MB CBCT, the moving blocker reduces the x-ray flux passing through the patient and collects the scatter information in the blocked region at the same time. The scatter signal is estimated from the blocked region for correction. Even though the number of projection views and projection data in each view are not complete for conventional reconstruction, 4D reconstruction with a total-variation (TV) constraint and a motion-compensated temporal constraint can utilize both spatial gradient sparsity and temporal correlations among different phases to overcome the missing data problem. The feasibility simulation studies using the 4D NCAT phantom showed that 4D MB with motion-compensated reconstruction with 1/3 imaging dose reduction could produce satisfactory images and achieve 37% improvement on structural similarity (SSIM) index and 55% improvement on root mean square error (RMSE), compared to 4D reconstruction at the regular imaging dose without scatter correction. For the same 4D MB data, 4D reconstruction outperformed 3D TV reconstruction by 28% on SSIM and 34% on RMSE. A study of synthetic patient data also demonstrated the potential of 4D MB to reduce the radiation dose by 1/3 without compromising the image quality. This work paves the way for more comprehensive studies to investigate the dose reduction limit offered by this novel 4D MB method using physical phantom experiments and real patient data based on clinical relevant metrics.

A weighted rebinned backprojection‐filtration algorithm from partially beam‐blocked data for a single‐scan cone‐beam CT with hybrid type scatter correction

“…The scatter distribution can be estimated from the x‐ray partially beam‐blocked projection data using an interpolation method . Established schemes in this category revolve around a central idea that measured data in the blocker shadow regions can be considered as scatter signals because the primary x‐ray photons are almost completely attenuated by the beam‐blocker.…”

“…The convolution‐based method is computationally efficient, but the kernel must be predefined to be used and the results are sensitive to the kernel parameters . The measurement‐based methods typically use x‐ray beam‐blockers or beam stopper array . The measurement‐based methods are simple and efficient, and can achieve accurate scatter estimation without a prior knowledge of the target object.…”

“…However, secondary effects due to modulator penumbra and beam hardening may influence the scatter distribution. Recently, object model‐based approaches were introduced for scatter correction using energy‐resolved reprojection technique . Nevertheless, segmentation involving complex materials and structures may become a very challenging work.…”

“…[12][13][14][15] The measurement-based methods typically use x-ray beam-blockers or beam stopper array. [16][17][18][19][20][21][22][23][24][25] The measurement-based methods are simple and efficient, and can achieve accurate scatter estimation without a prior knowledge of the target object. However, they usually end up with a problem of insufficient primary signals for accurate image reconstruction.…”

“…Recently, object model-based approaches were introduced for scatter correction using energy-resolved reprojection technique. [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] Nevertheless, segmentation involving complex materials and structures may become a very challenging work.…”