Mr. Alexandre H. Ba Profile

Alexandre H. Ba

at Ctr Hospitalier Univ Vaudois

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Author

Publications (9)

SPIE Journal Paper | 24 July 2020 Open Access

Search of low-contrast liver lesions in abdominal CT: the importance of scrolling behavior

Alexandre Ba, Marwa Shams, Sabine Schmidt, Miguel Eckstein, Francis Verdun, François Bochud

JMI, Vol. 7, Issue 04, 045501, (July 2020) https://doi.org/10.1117/12.10.1117/1.JMI.7.4.045501

KEYWORDS: Electromagnetic coupling, Liver, Computed tomography, Scanners, Eye, Visualization, Signal detection, Medical imaging, Lung

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Purpose: Visual search using volumetric images is becoming the standard in medical imaging. However, we do not fully understand how eye movement strategies mediate diagnostic performance. A recent study on computed tomography (CT) images showed that the search strategies of radiologists could be classified based on saccade amplitudes and cross-quadrant eye movements [eye movement index (EMI)] into two categories: drillers and scanners. Approach: We investigate how the number of times a radiologist scrolls in a given direction during analysis of the images (number of courses) could add a supplementary variable to use to characterize search strategies. We used a set of 15 normal liver CT images in which we inserted 1 to 5 hypodense metastases of two different signal contrast amplitudes. Twenty radiologists were asked to search for the metastases while their eye-gaze was recorded by an eye-tracker device (EyeLink1000, SR Research Ltd., Mississauga, Ontario, Canada). Results: We found that categorizing radiologists based on the number of courses (rather than EMI) could better predict differences in decision times, percentage of image covered, and search error rates. Radiologists with a larger number of courses covered more volume in more time, found more metastases, and made fewer search errors than those with a lower number of courses. Our results suggest that the traditional definition of drillers and scanners could be expanded to include scrolling behavior. Drillers could be defined as scrolling back and forth through the image stack, each time exploring a different area on each image (low EMI and high number of courses). Scanners could be defined as scrolling progressively through the stack of images and focusing on different areas within each image slice (high EMI and low number of courses). Conclusions: Together, our results further enhance the understanding of how radiologists investigate three-dimensional volumes and may improve how to teach effective reading strategies to radiology residents.

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SPIE Journal Paper | 20 May 2019

Channelized Hotelling observer correlation with human observers for low-contrast detection in liver CT images

Alexandre Ba, Craig Abbey, Damien Racine, Anaïs Viry, Francis Verdun, Sabine Schmidt, François Bochud

JMI, Vol. 6, Issue 02, 025501, (May 2019) https://doi.org/10.1117/12.10.1117/1.JMI.6.2.025501

KEYWORDS: Computed tomography, Liver, Image quality, Signal detection, Performance modeling, Spatial frequencies, Medical imaging, Barium, Reconstruction algorithms, Data modeling

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Proceedings Article | 12 March 2018 Presentation + Paper

A resampling comparison of CHO's detectability index bias and uncertainty

Francesc Massanes, Alexandre Ba, François Bochud, Jovan Brankov

Proceedings Volume 10577, 105770V (2018) https://doi.org/10.1117/12.2297689

KEYWORDS: Statistical analysis, Image quality, Medical imaging, Data modeling, Performance modeling, Diagnostics, Optimization (mathematics), Barium, Medical research, Physics

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Proceedings Article | 10 March 2017 Presentation + Paper

Low contrast detection in abdominal CT: comparing single-slice and multi-slice tasks

Alexandre Ba, Damien Racine, Anaïs Viry, Francis Verdun, Sabine Schmidt, François Bochud

Proceedings Volume 10136, 101360S (2017) https://doi.org/10.1117/12.2254237

KEYWORDS: Computed tomography, Image analysis, 3D image processing, 3D modeling, Signal detection, Liver, Image quality, Mathematical modeling, Medical imaging, Diagnostics, Databases

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Proceedings Article | 10 March 2017 Paper

Characterization of a CT unit for the detection of low contrast structures

Anais Viry, Damien Racine, Alexandre Ba, Fabio Becce, François Bochud, Francis Verdun

Proceedings Volume 10136, 101361C (2017) https://doi.org/10.1117/12.2250529

KEYWORDS: Computed tomography, Reconstruction algorithms, Denoising, Infrared imaging, Image quality, Detection and tracking algorithms, Physics, Diagnostics

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Proceedings Article | 24 March 2016 Paper

Impact of large x-ray beam collimation on image quality

Damien Racine, Alexandre Ba, Julien Ott, François Bochud, Francis Verdun

Proceedings Volume 9787, 978714 (2016) https://doi.org/10.1117/12.2217018

KEYWORDS: Collimation, Spatial resolution, LCDs, Image quality, X-ray imaging, Computed tomography, X-ray computed tomography, Image quality standards, 3D image processing

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Proceedings Article | 22 March 2016 Paper

Design, fabrication, and implementation of voxel-based 3D printed textured phantoms for task-based image quality assessment in CT

Justin Solomon, Alexandre Ba, Andrew Diao, Joseph Lo, Elianna Bier, François Bochud, Michael Gehm, Ehsan Samei

Proceedings Volume 9783, 978328 (2016) https://doi.org/10.1117/12.2217463

KEYWORDS: Image quality, 3D printing, X-ray computed tomography, 3D modeling, Liver, 3D image processing, Image segmentation, Matrices, Genetics, Optimization (mathematics), Reconstruction algorithms, Printing, Computed tomography

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In x-ray computed tomography (CT), task-based image quality studies are typically performed using uniform background phantoms with low-contrast signals. Such studies may have limited clinical relevancy for modern non-linear CT systems due to possible influence of background texture on image quality. The purpose of this study was to design and implement anatomically informed textured phantoms for task-based assessment of low-contrast detection. Liver volumes were segmented from 23 abdominal CT cases. The volumes were characterized in terms of texture features from gray-level co-occurrence and run-length matrices. Using a 3D clustered lumpy background (CLB) model, a fitting technique based on a genetic optimization algorithm was used to find the CLB parameters that were most reflective of the liver textures, accounting for CT system factors of spatial blurring and noise. With the modeled background texture as a guide, a cylinder phantom (165 mm in diameter and 30 mm height) was designed, containing 20 low-contrast spherical signals (6 mm in diameter at targeted contrast levels of ~3.2, 5.2, 7.2, 10, and 14 HU, 4 repeats per signal). The phantom was voxelized and input into a commercial multi-material 3D printer (Object Connex 350), with custom software for voxel-based printing. Using principles of digital half-toning and dithering, the 3D printer was programmed to distribute two base materials (VeroWhite and TangoPlus, nominal voxel size of 42x84x30 microns) to achieve the targeted spatial distribution of x-ray attenuation properties. The phantom was used for task-based image quality assessment of a clinically available iterative reconstruction algorithm (Sinogram Affirmed Iterative Reconstruction, SAFIRE) using a channelized Hotelling observer paradigm. Images of the textured phantom and a corresponding uniform phantom were acquired at six dose levels and observer model performance was estimated for each condition (5 contrasts x 6 doses x 2 reconstructions x 2 backgrounds = 120 total conditions). Based on the observer model results, the dose reduction potential of SAFIRE was computed and compared between the uniform and textured phantom. The dose reduction potential of SAFIRE was found to be 23% based on the uniform phantom and 17% based on the textured phantom. This discrepancy demonstrates the need to consider background texture when assessing non-linear reconstruction algorithms.

SPIE Journal Paper | 29 December 2015

Anthropomorphic model observer performance in three-dimensional detection task for low-contrast computed tomography

Alexandre Ba, Miguel Eckstein, Damien Racine, Julien Ott, Francis Verdun, Sabine Kobbe-Schmidt, François Bochud

JMI, Vol. 3, Issue 01, 011009, (December 2015) https://doi.org/10.1117/12.10.1117/1.JMI.3.1.011009

KEYWORDS: 3D modeling, Performance modeling, 3D image processing, Reconstruction algorithms, Infrared imaging, Interference (communication), Data modeling, Computed tomography, Signal detection, X-ray computed tomography

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Proceedings Article | 17 March 2015 Paper

Low contrast detectability in CT for human and model observers in multi-slice data sets

Alexandre Ba, Damien Racine, Julien Ott, Francis Verdun, Sabine Kobbe-Schmidt, Miguel Eckstein, Francois Bochud

Proceedings Volume 9416, 94160F (2015) https://doi.org/10.1117/12.2082009

KEYWORDS: Data modeling, 3D modeling, Performance modeling, Reconstruction algorithms, Computed tomography, Signal detection, Signal to noise ratio, Image quality, Molybdenum, Infrared imaging

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Showing 5 of 9 publications

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