Abstract
This study investigates the dependence of the translational velocity of lipid-coated microbubbles in an ultrasound field on the viscosity of the surrounding Newtonian fluid. Plane burst waves with a center frequency of 7.34 MHz were used to uniformly drive microbubbles with a radius of 1.4 ± 0.3 m (mean ± standard deviation) in a flow channel. Bubbles were detected using the Doppler method using pulse waves with a center frequency of 5.2 MHz, and the velocities of individual bubbles were analyzed by tracking them in consecutive images. Examinations were conducted at various viscosities from 1 to 3 mPa∙s. The experimentally determined velocity–viscosity relationship qualitatively agreed with numerical simulations. This was written as a power-law dependence and used as a calibration curve to evaluate the local viscosity coefficient for the trajectories of individual bubbles. We succeeded in demonstrating viscosity imaging by multiplying the obtained viscosity coefficient with the bubble trajectories, convoluted with the point spread function of ultrasound imaging.
Japanese Journal of Applied Physics 2025年2月14日 査読有り最終著者責任著者
Abstract
We conducted a fundamental study to elucidate the relationship between acoustic and electrical properties in the context of liver steatosis. The speed of sound, attenuation coefficient, conductivity, and relative permittivity were measured in rat livers with varying degrees of fat deposition. Fat deposition result in a decrease in the speed of sound, an increase in the attenuation coefficient, and reductions in conductivity and relative permittivity. However, no linear correlation was observed between these properties and fat content or droplet size individually. However, a notable correlation between changes in acoustic and electrical properties was identified when the structural and organizational effects of fat were considered in combination. Especially, attenuation changes were found to correlate with corresponding changes in electrical properties. These findings underscore the importance of comprehensively considering structural factors, such as fat droplet size and distribution, to better understand the physical mechanisms underlying the relationship between acoustic and electrical properties.
Hemorheological properties, such as erythrocyte aggregation can be assessed by ultrasonic backscatter coefficient analysis. In this study, a data-acquisition sequence with dual-frequency (dual-f) excitation was proposed to expand the ultrasonic frequency bandwidth with high-frame-rate imaging. The approach was experimentally validated using ex vivo porcine blood measurements and in vivo human imaging. The center frequency of the excitation wave was alternated between 7.8 (f1) and 12.5 (f2) MHz in the frequency spectral analysis using the reference phantom method. The frequency spectra revealed that the dual-f sequence achieved a bandwidth of 4.5-15 MHz at -20 dB, almost equivalent to those achieved with conventional single-frequency excitation (5.0-15 MHz) with a short-duration wave at 10 MHz (mono-f) in reference media with the sufficient condition of signal-to-noise ratio. The aggregation and disaggregation states of porcine blood suspended in high-molecular-weight dextran were determined by the isotropic diameter and packing factor using the structure factor size estimator. The discrimination performance of the dual-f approach increased, owing to the broadband frequency responses, in contrast with the limited performance of mono-f due to a low signal-to-noise ratio. This approach incorporating dual-f sequence is beneficial for obtaining robustly frequency spectra of hemorheological properties from in vivo scenarios.
Journal of Medical Ultrasonics 52(1) 5-15 2024年11月23日 査読有り
Abstract
Purpose
Early detection and quantitative evaluation of liver steatosis are crucial. Therefore, this study investigated a method for classifying ultrasound images to fatty liver grades based on echo-envelope statistics (ES) and convolutional neural network (CNN) analyses.
Methods
Three fatty liver grades, i.e., normal, mild, and moderate-to-severe, were defined using the thresholds of the magnetic resonance imaging-derived proton density fat fraction (MRI-PDFF). There were 10 cases of each grade, totaling 30 cases. To visualize the texture information affected by the deposition of fat droplets within the liver, the maps of first- and fourth-order moments and the heat maps formed from both moments were employed as parametric images derived from the ES. Several dozen to hundreds of regions of interest (ROIs) were extracted from the liver region in each parametric image. A total of 7680 ROIs were utilized for the transfer learning of a pretrained VGG-16 and classified using the transfer-learned VGG-16.
Results
The classification accuracies of the ROIs in all types of the parametric images were approximately 46%. The fatty liver grade for each case was determined by hard voting on the classified ROIs within the case. In the case of the fourth-order moment maps, the classification accuracy of the cases through hard voting mostly increased to approximately 63%.
Conclusions
The formation of parametric images derived from the ES and the CNN classification of the parametric images were proposed for the quantitative diagnosis of liver steatosis. In more than 60% of the cases, the fatty liver grade could be estimated solely using ultrasound images.
Jungtaek Choi, Jeffrey A. Ketterling, Jonathan Mamou, Cameron Hoerig, Shinnosuke Hirata, Kenji Yoshida, Tadashi Yamaguchi
Sensors 24(22) 7118-7118 2024年11月5日 査読有り最終著者責任著者
The objective of this work is to address the need for versatile and effective tissue characterization in abdominal ultrasound diagnosis using a simpler system. We evaluated the backscattering coefficient (BSC) of several tissue-mimicking phantoms utilizing three different ultrasonic probes: a single-element transducer, a linear array probe for clinical use, and a laboratory-made annular array probe. The single-element transducer, commonly used in developing fundamental BSC evaluation methods, served as a benchmark. The linear array probe provided a clinical comparison, while the annular array probe was tested for its potential in high-frequency and high-resolution ultrasonic observations. Our findings demonstrate that the annular array probe meets clinical demands by providing accurate BSC measurements, showcasing its capability for high-frequency and high-resolution imaging with a simpler, more versatile system.
2016 IEEE INTERNATIONAL ULTRASONICS SYMPOSIUM (IUS) 2016年 IEEE
A quantitative diagnostic method for liver fibrosis using ultrasound echo signals is highly required. A probability density function (PDF) of echo envelope from a normal liver can be approximated by a Rayleigh distribution; however, the PDF of echo envelope from liver fibrosis deviates from the Rayleigh distribution. To evaluate tissue characteristics in the ultrasound B-mode image, several amplitude distribution models have been proposed. We proposed a multi-Rayleigh distribution model and evaluation method of liver fibrosis using the multi-Rayleigh model. In this study, we evaluated the modeling accuracy of the multi-Rayleigh model and other amplitude distribution models using the KL divergence. From the evaluated results for the 120 clinical data, it was found that the multi-Rayleigh model with three components is more suitable model than other amplitude distribution models for approximating the PDF of echo envelope from the liver fibrosis.
K. Ito, S. Irie, J. Mamou, H. Maruyama, K. Yoshida, T. Yamaguchi
2015 IEEE INTERNATIONAL ULTRASONICS SYMPOSIUM (IUS) 2015年 IEEE
Early diagnosis of non-alcoholic steatohepatitis (NASH) is highly desired because NASH can lead to cirrhosis or even to hepatocellular carcinoma in some severe cases. Towards non-invasive diagnosis with ultrasound, we studied free fatty acids (FFAs) present in the liver, which is the organ most likely to be affected by the disease. As a preclinical study, we performed acoustic-impedance measurements of five kinds of FFAs in solvent or in cultured Huh7 cells. To measure the acoustic impedance, a concave transducer with an 80-MHz center frequency was incorporated in a scanning acoustic microscopy system. One-way ANOVA showed statistically-significant differences (p<0.05) in acoustic impedance among the FFAs in FFA solvent and with cultured Huh7 cells. These results suggest that each of the FFAs, especially PA, OA and PAOA could be distinguished from each other regardless of whether they were in solution or in absorbed by cells.