Mr. Luo Ouyang Profile

Luo Ouyang

at UT Southwestern Medical Ctr

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Proceedings Article | 19 March 2014 Paper

An experimental study on the noise correlation properties of CBCT projection data

Hua Zhang, Luo Ouyang, Jianhua Ma, Jing Huang, Wufan Chen, Jing Wang

Proceedings Volume 9033, 90332R (2014) https://doi.org/10.1117/12.2043151

KEYWORDS: Sensors, Data acquisition, Data modeling, Data processing, Imaging systems, X-rays, Reconstruction algorithms, Denoising, Statistical analysis, Image analysis

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In this study, we systematically investigated the noise correlation properties among detector bins of CBCT projection data by analyzing repeated projection measurements. The measurements were performed on a TrueBeam on-board CBCT imaging system with a 4030CB flat panel detector. An anthropomorphic male pelvis phantom was used to acquire 500 repeated projection data at six different dose levels from 0.1 mAs to 1.6 mAs per projection at three fixed angles. To minimize the influence of the lag effect, lag correction was performed on the consecutively acquired projection data. The noise correlation coefficient between detector bin pairs was calculated from the corrected projection data. The noise correlation among CBCT projection data was then incorporated into the covariance matrix of the penalized weighted least-squares (PWLS) criterion for noise reduction of low-dose CBCT. The analyses of the repeated measurements show that noise correlation coefficients are non-zero between the nearest neighboring bins of CBCT projection data. The average noise correlation coefficients for the first- and second- order neighbors are 0.20 and 0.06, respectively. The noise correlation coefficients are independent of the dose level. Reconstruction of the pelvis phantom shows that the PWLS criterion with consideration of noise correlation results in a lower noise level as compared to the PWLS criterion without considering the noise correlation at the matched resolution.

Proceedings Article | 6 March 2013 Paper

A moving blocker system for cone-beam computed tomography scatter correction

Luo Ouyang, Kwang Song, Timothy Solberg, Jing Wang

Proceedings Volume 8668, 86681P (2013) https://doi.org/10.1117/12.2008095

KEYWORDS: Imaging systems, Reconstruction algorithms, Computed tomography, X-ray computed tomography, Signal detection, Image restoration, Image quality, Lead, Scatter measurement, X-rays

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Scatter contamination in cone-beam computed tomography (CBCT) degrades the image quality by introducing shading artifacts. In our previous study, a moving-blocker-based approach was proposed to simultaneously estimate scatter and reconstruct the complete volume within field of view (FOV) from a single CBCT scan. Promising results were obtained from simulation studies. In this work, we implemented the moving blocker system on a LINAC on-board kV CBCT imaging system. A physical attenuator (i.e., "blocker") consisting equal spaced lead strips was mounted on a linear actuator. A step motor connected to the actuator drove the blocker to move back and forth along gantry rotation axis during CBCT acquisition. Scatter signal was estimated from the blocked region of imaging panel, and interpolated into the un-blocked region. A sparseness prior based statistical iterative reconstruction algorithm was used to reconstruct CBCT images from un-blocked projections after the scatter signal was subtracted. Experimental studies were performed on both a Catphan phantom and an anthropomorphic pelvis phantom to evaluate performance of the moving blocker system. The scatter-induced shading artifacts were substantially reduced in the images acquired with the moving blocker system. CT number error reduced in selected regions of interest of the Catphan phantom from 318 to 17. It also decreased in those of the pelvis phantom from 239 to 10. We demonstrated for the first time that the moving blocker system could successfully estimate the scatter signal in projection data, reduce the imaging dose and obtain complete volumetric information within the FOV using a single scan.

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