All Publications

  • Distributed Aberration Correction Techniques Based on Tomographic Sound Speed Estimates. IEEE transactions on ultrasonics, ferroelectrics, and frequency control Ali, R., Brevett, T., Hyun, D., Brickson, L. L., Dahl, J. J. 2022; 69 (5): 1714-1726


    Phase aberration is widely considered a major source of image degradation in medical pulse-echo ultrasound. Traditionally, near-field phase aberration correction techniques are unable to account for distributed aberrations due to a spatially varying speed of sound in the medium, while most distributed aberration correction techniques require the use of point-like sources and are impractical for clinical applications where diffuse scattering is dominant. Here, we present two distributed aberration correction techniques that utilize sound speed estimates from a tomographic sound speed estimator that builds on our previous work with diffuse scattering in layered media. We first characterize the performance of our sound speed estimator and distributed aberration correction techniques in simulations where the scattering in the media is known a priori. Phantom and in vivo experiments further demonstrate the capabilities of the sound speed estimator and the aberration correction techniques. In phantom experiments, point target resolution improves from 0.58 to 0.26 and 0.27 mm, and lesion contrast improves from 17.7 to 23.5 and 25.9 dB, as a result of distributed aberration correction using the eikonal and wavefield correlation techniques, respectively.

    View details for DOI 10.1109/TUFFC.2022.3162836

    View details for PubMedID 35353699

  • Noninvasive estimation of local speed of sound by pulse-echo ultrasound in a rat model of nonalcoholic fatty liver. Physics in medicine and biology Telichko, A. V., Ali, R., Brevett, T., Wang, H., Vilches-Moure, J., Kumar, S. U., Paulmurugan, R., Dahl, J. J. 1800


    Objective:Speed of sound has previously been demonstrated to correlate with fat concentration in the liver. However, estimating speed of sound in the liver noninvasively can be biased by the speed of sound of the tissue layers overlying the liver. Here, we demonstrate a noninvasive local speed of sound estimator, which is based on a layered media assumption, that can accurately capture the speed of sound in the liver. We validate the estimator using an obese Zucker rat model of non-alcoholic fatty liver disease and correlate the local speed of sound with liver steatosis.Approach:We estimated the local and global average speed of sound noninvasively in 4 lean Zucker rats fed a normal diet and 16 obese Zucker rats fed a high fat diet for up to 8 weeks. The ground truth speed of sound and fat concentration were measured from the excised liver using established techniques.Main Results:The noninvasive, local speed of sound estimates of the livers were similar in value to their corresponding "ground truth'' measurements, having a slope ± standard error of the regression of 0.82 ± 0.15 (R2= 0.74 and p < 0.001). Measurement of the noninvasive global average speed of sound did not reliably capture the ``ground truth'' speed of sound in the liver, having a slope of 0.35 ± 0.07 (R2= 0.74 and p < 0.001). Decreasing local speed of sound was observed with increasing hepatic fat accumulation (approximately -1.7 m/s per 1% increase in hepatic fat) and histopathology steatosis grading (approximately -10 to -13 m/s per unit increase in steatosis grade). Local speed of sound estimates were highly correlated with steatosis grade, having Pearson and Spearman correlation coefficients both ranging from -0.87 to -0.78. In addition, a lobe-dependent speed of sound in the liver was observed by theex vivomeasurements, with speed of sound differences of up to 25 m/s (p < 0.003) observed between lobes in the liver of the same animal.Significance:The findings of this study suggest that local speed of sound estimation has the potential to be used to predict or assist in the measurement of hepatic fat concentration and that the global average speed of sound should be avoided in hepatic fat estimation due to significant bias in the speed of sound estimate.

    View details for DOI 10.1088/1361-6560/ac4562

    View details for PubMedID 34933288

  • Anisotropic regularization of ultrasound pulse-echo tomography for reconstruction of speed-of-sound and tissue heterogeneity through abdominal layers. Sanabria, S. J., Brevett, T., Dahl, J., IEEE IEEE. 2020