Dr. Xinhua Li Profile

Dr. Xinhua Li

at Massachusetts General Hospital

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Publications (4)

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Proceedings Article | 6 March 2013 Paper

Multi-resolution analysis of scatter in digital breast tomosynthesis imaging

Da Zhang, Xinhua Li, Bob Liu

Proceedings Volume 8668, 86685L (2013) https://doi.org/10.1117/12.2007315

KEYWORDS: Digital breast tomosynthesis, Breast, Wavelets, Monte Carlo methods, Mammography, X-rays, Lead, Tissues, Signal attenuation, Prototyping

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The influence of large x-ray scatter components in projection images remains a problem for digital breast tomosynthesis, especially when anti-scatter grids may not be used because of dose limitation and possible source/detector geometric limitations. Monte-Carlo simulation of scatter fits better in this situation, but the heavy computational cost hinders its clinical application. To simplify scatter estimation, scatter is often assumed to be smooth. However, scatter is not spatial invariant across a projection image, and where and to what degree the smoothness could be claimed and utilized is unclear. In this study, we investigated this question via multi-resolution analysis based on two experiments: one with direct measurements of scatter profiles in the projection images of an anthropomorphic breast phantom; the other with scatter map obtained from Monte-Carlo simulation that used a voxelized breast model as input. We applied 1D and 2D wavelet-based multi-resolution analyses to the scatter profiles and maps. The first experiment indicated that a reduced number of scatter data points that matches the true data can be extracted from densely sampled but noisy scatter profiles: a data reduction rate of 64-128 was achieved at the inner region of the phantom, suggesting that the slowly changing scatter may be obtained at lower sampling distances of 9.0-17.9 mm. Near the edge of the phantom a data reduction rate of 8 was achieved, corresponding to a sampling distance of 2.2 mm. Similar observations were made from the second experiment.

Proceedings Article | 3 March 2012 Paper

Characterization of adaptive statistical iterative reconstruction (ASIR) in low contrast helical abdominal imaging via a transfer function based method

Da Zhang, Xinhua Li, Bob Liu

Proceedings Volume 8313, 83133S (2012) https://doi.org/10.1117/12.911082

KEYWORDS: Image filtering, Spatial frequencies, Denoising, Image processing, Computed tomography, Reconstruction algorithms, Statistical modeling, Imaging systems, Physics, Optical filters

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Since the introduction of ASiR, its potential in noise reduction has been reported in various clinical applications. However, the influence of different scan and reconstruction parameters on the trade off between ASiR's blurring effect and noise reduction in low contrast imaging has not been fully studied. Simple measurements on low contrast images, such as CNR or phantom scores could not explore the nuance nature of this problem. We tackled this topic using a method which compares the performance of ASiR in low contrast helical imaging based on an assumed filter layer on top of the FBP reconstruction. Transfer functions of this filter layer were obtained from the noise power spectra (NPS) of corresponding FBP and ASiR images that share the same scan and reconstruction parameters. 2D transfer functions were calculated as sqrt[NPSASiR(u, v)/NPSFBP(u, v)]. Synthesized ACR phantom images were generated by filtering the FBP images with the transfer functions of specific (FBP, ASiR) pairs, and were compared with the ASiR images. It is shown that the transfer functions could predict the deterministic blurring effect of ASiR on low contrast objects, as well as the degree of noise reductions. Using this method, the influence of dose, scan field of view (SFOV), display field of view (DFOV), ASiR level, and Recon Mode on the behavior of ASiR in low contrast imaging was studied. It was found that ASiR level, dose level, and DFOV play more important roles in determining the behavior of ASiR than the other two parameters.

Proceedings Article | 23 March 2010 Paper

Quantifying breast density with a cone-beam breast CT

Xinhua Li, Bob Liu

Proceedings Volume 7622, 762245 (2010) https://doi.org/10.1117/12.844369

KEYWORDS: Breast, Signal attenuation, Tissues, Sensors, Computed tomography, Calibration, Mammography, Image restoration, Image filtering, Reconstruction algorithms

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Volumetric breast density was evaluated using a simulated cone beam breast CT with 80 kVp. The breast was modeled as a cylinder with background tissue composition of 20% glandular and 80% adipose. Various objects with different sizes and tissue compositions were embedded. Ray-tracing algorithm was utilized to obtain projection images in a full rotation without considering scatter, beam hardening and imaging noise. Filtered backprojection was adopted for image reconstruction with high quality. Reconstructed images had flat profiles except at large cone angle of 8.6° to 10°. They were calibrated using known linear attenuation coefficients of two image contrast objects. A 3D mapping of tissue densities could be directly computed within 5% error. Tissue volumes were obtained by counting voxels in appropriate attenuation coefficient ranges. Results of contrast objects were consistent with true volumes within 10% error. However, cone angle artifact decreased pixel values, and a reduction algorithm was required for accurate tissue assessment at large cone angles. This study indicates the possibility of excellent quantitative breast density measurements and volume assessments with cone-beam breast CT.

Proceedings Article | 14 March 2009 Paper

Effects of scatter radiation on reconstructed images in digital breast tomosynthesis

Bob Liu, Xinhua Li

Proceedings Volume 7258, 72585Y (2009) https://doi.org/10.1117/12.814130

KEYWORDS: Breast, Radiation effects, Digital breast tomosynthesis, Lead, X-rays, Tissues, Reconstruction algorithms, Signal attenuation, Sensors, Chest

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We evaluated the effects of scatter radiation on the reconstructed images in digital breast tomosynthesis. Projection images of a 6 cm anthropomorphic breast phantom were acquired using a Hologic prototype digital breast tomosynthesis system. Scatter intensities in projection images were sampled with a beam stop method. The scatter intensity at any pixel was obtained by two dimensional fitting. Primary-only projection images were generated by subtracting the scatter contributions from the original projection images. The 3-dimensional breast was reconstructed first based on original projection images which contained the contributions from both primary rays and scattered radiation using three different reconstruction algorithms. The same breast volume was reconstructed again using the same algorithms but based on primaryonly projection images. The image artifacts, pixel value difference to noise ratio (PDNR), and detected image features in these two sets of reconstructed slices were compared to evaluate the effects of scatter radiation. It was found that the scatter radiation caused inaccurate reconstruction of the x-ray attenuation property of the tissue. X-ray attenuation coefficients could be significantly underestimated in the region where scatter intensity is high. This phenomenon is similar to the cupping artifacts found in computed tomography. The scatter correction is important if accurate x-ray attenuation of the tissues is needed. No significant improvement in terms of numbers of detected image features was observed after scatter correction. More sophisticated phantom dedicated to digital breast tomosynthesis may be needed for further evaluation.

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