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.
JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 146(4) 2335-2349 2019年10月 査読有り
In this report, a method is proposed to quantify the translation of ultrasound contrast agent (UCA) microbubbles driven by acoustic radiation for the detection of channels filled with stationary fluid. The authors subjected UCA microbubbles in a channel with diameters of 0.1 and 0.5mm to ultrasound pulses with a center frequency of 14.4MHz. The translational velocity of the UCA microbubbles increased with the sound pressure and pulse repetition frequency (PRF) of the transmitted ultrasound. The mean translational velocity reached 0.75 mm/s at a negative peak sound pressure of 2.76 MPa and a PRF of 2 kHz. This trend agreed with the theoretical prediction, which indicated that the translational velocity was proportional to the square of the sound pressure and the PRF. Furthermore, an experiment was carried out with a phantom that mimics tissue and found that the proposed method aided in detection of the channel, even in the case of a low contrast-echo to tissue-echo ratio. The authors expect to develop the proposed method into a technique for detecting lymph vessels. (C) 2019 Acoustical Society of America.
INTERNATIONAL FORUM ON MEDICAL IMAGING IN ASIA 2019 11050 2019年 査読有り最終著者責任著者
In this study, the examination results of speed of sound of sliced rat organs analyzed with multi-frequency ultrasound (80 and 250 MHz) from the acquiring radiofrequency (RF) echo signals observed by our self-made scanning acoustic microscopy (SAM) system is reported. The frequency dependence of SoS was evaluated by analysis method involving filtering considering spatial resolution at each frequency.
2019 IEEE INTERNATIONAL ULTRASONICS SYMPOSIUM (IUS) 2019-October 2299-2302 2019年 最終著者
This study proposed a method for visualizing lymph channels filled with stationary fluid, named contrast-enhanced active Doppler ultrasonography (CEADUS). CEADUS can quantify the translation of ultrasound contrast agent (UCA) due to the acoustic radiation force by Doppler method. In this report, we attempted to visualize a cylindrical channels with a diameter of 0.28 and 0.1-mm filled with a suspension of Sonazoid (TM) as UCAs in a tissue mimicking phantom containing acoustic scatterers. The single element concave transducer with 14.4-MHz center frequency was scanned at the step of 10 mu m in the lateral direction, and ultrasound was emitted with pulse repetition frequency of 2 kHz at each scan line. We obtained two-dimensional images using dynamic information of the UCAs by analyzing for several seconds exposure duration in echo signals at each scanning line. As a result, the CEADUS image could be detected with high sensitivity even when the channel diameter was below the resolution.
Takashi Ohnishi, Shu Kashio, Kazuyo Ito, Stanislav S. Makhanov, Tadashi Yamaguchi, Yasuo Iwadate, Hideaki Haneishi
2018 INTERNATIONAL WORKSHOP ON ADVANCED IMAGE TECHNOLOGY (IWAIT) 2018(IWAIT) 1-2 2018年
In order to analyze the relationship between ultrasonic signal and tissue structure, accurate image registration is required. However, spatial resolution and image features are different between pathological and ultrasonic images. Thus, this paper proposed an image feature conversion method including downscale process using convolutional neural network. The proposed method was applied to the pathological images and we confirmed that the converted pathological images were similar to the ultrasonic images from visual assessment and image registration was also successfully conducted.
2018 IEEE INTERNATIONAL ULTRASONICS SYMPOSIUM (IUS) 2018-October(IUS) 1‐4 2018年 査読有り
We have proposed an evaluation method for liver fibrosis using an ultrasound B-mode image. We proposed a multi-Rayleigh (MRA) distribution model to express a probability density function of ultrasound echo envelope obtained from a fibrotic liver tissue. The MRA model enabled us to estimate quantitative liver fibrosis parameters such as amount of fibrotic tissue and fibrosis progressive ratio, and to quantitatively visualize the fibrotic tissue in the B-mode image. In previous studies, we addressed several challenges to quantitatively and correctly evaluate liver fibrosis using the MRA model in clinical condition. In the present study, we integrated past achievements as the optimized MRA model and evaluated the clinical ultrasound B-mode image of fibrotic liver. Using the optimized MRA model, the change of estimated fibrotic tissue characteristics according to the liver fibrosis stage well reflected the tissue structural change caused by liver fibrosis. We concluded that the fibrotic tissue characteristics can be quantitatively and correctly estimated in clinical condition by using the optimized MRA model.
2018 IEEE INTERNATIONAL ULTRASONICS SYMPOSIUM (IUS) 2018-October(IUS) 1‐9 2018年 査読有り
Applying the autoregressive (AR) model in exponential to separate echoes is known as one of the practical methods to analyze the speed of sound (SoS) using scanning acoustic microscopy. However, the accuracy of SoS analysis with AR model in ultra-high frequency (> 100 MHz) is unknown. AR model requires the number of echo components separated in and optimizing this parameter is essential to analyze SoS in high accuracy. Also, the condition of the tissue is one of the elements that can have the influence on the SoS analysis. There, we investigated the relationship between the shape of sliced samples (thickness and surface shape), analysis parameter (AR order) and the accuracy of SoS analysis through the simulations using the Finite-difference time-domain (FDTD) method. Echo simulations were performed with flat samples with thickness varied and sample imitating the actual surface shape of sliced rat liver. From the result, it was suspected that to analyze SoS in high accuracy is difficult if the thickness of the sliced sample is not enough thick. In addition, we found that the surface roughness of sliced samples can occur the disturbance of wave propagation and not only make the accuracy of SoS analysis worse but also make the optimal AR order higher.