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Medical ultrasound requires the coupling of skin with the transducer. Removing this requirement could make ultrasound stimulation and imaging more accessible and convenient. Synthetic setae pads are a biomimetic material that mimics the structure of a gecko’s foot, allowing it to hold substantial weight. By combining synthetic setae with an ultrasound transducer, the attenuation of existing commercial versions was measured using a 10 MHz ultrasound transducer. It was found that ShearGrip® attached to a smooth plastic surface (70.0% power loss) had notably less attenuation than to skin (86.5% power loss). The material was also examined by mounting it on the side of plastic tank, using a 5 MHz ultrasound transducer and hydrophone. In the case of the tank tests, the presence of moisture on the synthetic setae specimen was found to reduce attenuation by 0.29 dB. Otherwise, the attenuation could be 0.35 dB. However, this large attenuation was due to sample porosity and thickness, causing scattering and energy loss. Currently, work is underway to fully characterize the material. Potential improvements to the material’s acoustic conductance include uniform fiber alignment, reduced porosity, optimized thickness, and the use of lower frequency ultrasound stimulation.

The arterial structure cyclically fluctuates in three-dimensions (3-D) caused by pulsatile blood flow. The evaluation of arterial wall motion and hemodynamics contributes to early diagnosis of carotid atherosclerosis. Ultrasound is one of the most appropriate imaging modalities to evaluate arterial wall motion in real time. Although many previous studies have discussed the mechanical properties of the carotid artery bifurcation (CAB) from the two-dimensional (2-D) view, the spatio-temporal variation of carotid artery geometry in 3-D has not yet been investigated in detail. In this study, the 3-D data set of CAB from rats was acquired using a high spatio-temporal resolution ultrasound imaging system with a 40 MHz probe using mechanical sector scanning. A total of 31 slices of cross-section images were stored and a spoke scan algorithm was implemented to radially scan the lumen area in polar coordinates based on a pre-tracked seed point. The boundary of the arterial lumen was segmented using intensity-threshold-based boundary detection and fitted by polynomial regression. Two operators, who were trained with the same protocol to minimize inter- and intra-operator variability, manually segmented the lumen boundary on systolic and diastolic phase from the gray-scale images. Finally, the 3-D lumen geometries of CAB during one cardiac cycle were constructed based on the segmented lumen boundaries. From this constructed 3-D geometry, we observed that the CAB geometry favorably expanded to the anterior/posterior direction, parallel to the sagittal plane; and the manually segmented geometry also confirmed the asymmetrical change in bifurcation geometry. This is the first study on visualization and quantification on the asymmetrical variation of the CAB geometry of a rat in 3-D during a whole cardiac cycle. This finding may be useful in understanding hemodynamic etiology of various cardiovascular diseases such as arterial stenosis and its complications, and also provides reference information for numerical simulation studies on arterial wall motion.

The present study investigates cyclic variation in blood echogenicity (CVBE) in vivo using high-frequency ultrasound (HFUS). Blood echogenicity (BE) and vessel diameter (VD) were obtained from cross-sectional B-mode images of the radial artery of six volunteers (three young and three old volunteers) acquired at a frequency of 20 MHz. The magnitudes of the cyclic variations in BE and VD were 0.83 ± 0.18 dB and 0.29 ± 0.05 mm, respectively. CVBE was observed to be out of phase with the cyclic variation in VD, which is known to be in phase with blood flow velocity. This result is different from those in previous studies, which were performed in the carotid artery at lower frequencies. In addition, the magnitude of CVBE in the older group (0.96 ± 0.05 dB) was higher than that in the younger group (0.63 ± 0.06 dB, p

Visualizing and analyzing the morphological structure of carotid bifurcations are important for understanding the etiology of carotid atherosclerosis, which is a major cause of stroke and transient ischemic attack. For delineation of vasculatures in the carotid artery, ultrasound examinations have been widely employed because of a noninvasive procedure without ionizing radiation. However, conventional 2D ultrasound imaging has technical limitations in observing the complicated 3D shapes and asymmetric vasodilation of bifurcations. This study aims to propose image-processing techniques for better 3D reconstruction of a carotid bifurcation in a rat by using 2D cross-sectional ultrasound images. A high-resolution ultrasound imaging system with a probe centered at 40 MHz was employed to obtain 2D transversal images. The lumen boundaries in each transverse ultrasound image were detected by using three different techniques; an ellipse-fitting, a correlation mapping to visualize the decorrelation of blood flow, and the ellipse-fitting on the correlation map. When the results are compared, the third technique provides relatively good boundary extraction. The incomplete boundaries of arterial lumen caused by acoustic artifacts are somewhat resolved by adopting the correlation mapping and the distortion in the boundary detection near the bifurcation apex was largely reduced by using the ellipse-fitting technique. The 3D lumen geometry of a carotid artery was obtained by volumetric rendering of several 2D slices. For the 3D vasodilatation of the carotid bifurcation, lumen geometries at the contraction and expansion states were simultaneously depicted at various view angles. The present 3D reconstruction methods would be useful for efficient extraction and construction of the 3D lumen geometries of carotid bifurcations from 2D ultrasound images.

Purpose Spontaneous echo-contrast (SEC) appears on B-mode images as moving curls of smoke in the lumen of veins. The aims of this study were to investigate the prevalence and characteristics of internal jugular vein SEC among patients with stroke, in comparison with control subjects. Methods We enrolled 97 Korean patients with acute ischemic stroke and 50 controls. Both internal jugular veins were examined for the presence and severity of SEC and measurement of flow velocity. Venous samples were obtained for laboratory evaluation of hematologic factors. Results In 294 internal jugular veins, the prevalence of SEC was 81% in stroke patients and 68% in controls (odds ratio, 2.0; 95% confidence interval, 1.1–3.6; p = 0.013). Stroke patients were more likely to have SEC on the left (p = 0.025) than on the right (p = 0.184) internal jugular vein. Overall, the association between stroke and SEC remained significant after adjustment for other variables (odds ratio, 4.3; 95% confidence interval, 1.7–10.8; p = 0.002). Conclusions Internal jugular vein SEC was found more frequently in stroke patients than in controls. However, local as well as systemic factors must be considered in the interpretation of this finding. © 2014 Wiley Periodicals, Inc. J Clin Ultrasound 43:431–437, 2015

Ultrasound speckle image of blood is mainly attributed by red blood cells (RBCs) which tend to form RBC aggregates. RBC aggregates are separated into individual cells when the shear force is over a certain value. The dissociation of RBC aggregates has an influence on the performance of ultrasound speckle image velocimetry (SIV) technique in which a cross-correlation algorithm is applied to the speckle images to get the velocity field information. The present study aims to investigate the effect of the dissociation of RBC aggregates on the estimation quality of SIV technique. Ultrasound B-mode images were captured from the porcine blood circulating in a mock-up flow loop with varying flow rate. To verify the measurement performance of SIV technique, the centerline velocity measured by the SIV technique was compared with that measured by Doppler spectrograms. The dissociation of RBC aggregates was estimated by using decorrelation of speckle patterns in which the subsequent window was shifted as much as the speckle displacement to compensate decorrelation caused by in-plane loss of speckle patterns. The decorrelation of speckles is considerably increased according to shear rate. Its variations are different along the radial direction. Because the dissociation of RBC aggregates changes ultrasound speckles, the estimation quality of SIV technique is significantly correlated with the decorrelation of speckles. This degradation of measurement quality may be improved by increasing the data acquisition rate. This study would be useful for simultaneous measurement of hemodynamic and hemorheological information of blood flows using only speckle images.

Ultrasound-based techniques have been developed and widely used in noninvasive measurement of blood velocity. Speckle image velocimetry (SIV), which applies a cross-correlation algorithm to consecutive B-mode images of blood flow has often been employed owing to its better spatial resolution compared with conventional Doppler-based measurement techniques. The SIV technique utilizes speckles backscattered from red blood cell (RBC) aggregates as flow tracers. Hence, the intensity and size of such speckles are highly dependent on hemodynamic conditions. The grayscale intensity of speckle images varies along the radial direction of blood vessels because of the shear rate dependence of RBC aggregation. This inhomogeneous distribution of echo speckles decreases the signal-to-noise ratio (SNR) of a cross-correlation analysis and produces spurious results. In the present study, image-enhancement techniques such as contrast-limited adaptive histogram equalization (CLAHE), min/max technique, and subtraction of background image (SB) method were applied to speckle images to achieve a more accurate SIV measurement. A mechanical sector ultrasound scanner was used to obtain ultrasound speckle images from rat blood under steady and pulsatile flows. The effects of the image-enhancement techniques on SIV analysis were evaluated by comparing image intensities, velocities, and cross-correlation maps. The velocity profiles and wall shear rate (WSR) obtained from RBC suspension images were compared with the analytical solution for validation. In addition, the image-enhancement techniques were applied to in vivo measurement of blood flow in human vein. The experimental results of both in vitro and in vivo SIV measurements show that the intensity gradient in heterogeneous speckles has substantial influence on the cross-correlation analysis. The image-enhancement techniques used in this study can minimize errors encountered in ultrasound SIV measurement in which RBCs are used as flow tracers instead of exogenous contrast agents.

In the present paper, the ultrasound blood images were measured at both the human radial artery(RA) and common carotid artery(CCA), depending on the age, and the pulsatility index of blood echogenicity(PIBE) was analyzed. In addition, the ultrasound blood images were measured at both RA and CCA of both the stroke patients and the control group, and PIBE was compared. PIBE of RA for the young group was similar with that for the old group ( and ). PIBE of CCA for the young group, however, was larger than that for the old group ( and ), and was more variable depending on the subject. Similarly, the fibrinogen concentrations of the patients ( and ) were more than that of the control group ( and ), for both RA and CCA. The results indicate the possibility of the ultrasonic test on the correlation between erythrocyte aggregation and stroke, and it is expected that the in-vivo EA measurement would be clinically useful.

High-frequency ultrasound (HFUS) signals backscattered from RBL-2H3 cell pellets prepared under different centrifugal forces were analyzed to investigate the packing effect of cell aggregates. The measurements were performed in a pulse-echo setup with a 40-MHz transducer. The changes of ultrasound signals from cell pellet in backscattered power, statistical parameter, and pellet thickness were monitored after centrifugation at between 100g and 1600g. Experimental results showed that the HFUS backscattered power from cell pellets was inversely proportional to centrifugal force and increased to a plateau within 1–2 h after centrifugation. The initial thickness of cell pellets decreased with higher centrifugal force, but the changes in thickness and time that took to reach a plateau increased at higher centrifugal force. The envelope statistics of backscattered signals with Nakagami distribution indicates that the centrifugal force and elapsed time after centrifugation affected the backscattering characteristics. The present study suggests that centrifugal force and data acquisition time after cell pellet formation should be considered in in vitro cell packing method with centrifugation to emulate the tissue in vivo.

To better understand the characteristics of erythrocyte aggregation in flowing blood, echogenicity variation in blood was observed both in vitro and in vivo. However, few noninvasive observations of blood echogenicity variation during the cardiac cycle in human arteries have been reported. In the present study, to reduce the dynamic range between the blood vessel lumen and the surrounding tissue, coded harmonic images were acquired from human carotid arteries using a GE LOGIQ 700 Expert system (GE, Milwaukee, WI, USA) with an M12L probe, which enabled the noninvasive detection of the cyclic and radial variation of echogenicity in arterial vessels. It was found that blood echogenicity increased during systole, reaching a maximum at peak systole and then decreased to a weak level during diastole. The echogenicity profiles of blood along the vessel diameter were found to be approximately parabolic in the cardiac cycle, except for the hypoechoic zone near the center of the vessel at peak systole. The present results for human carotid arteries corroborate previous in vitro observations that showed a cyclic and radial variation of blood echogenicity, which was thought to be caused by the enhancement of erythrocyte aggregation due to the combined effects of flow acceleration and shear rate during systole.

Ultrasonic backscatter from flowing and static rat red blood cells (RBCs) in autologous plasma and in 360 kDa polyvinylpyrrolidone (PVP 360) solution was measured as a function of hematocrit. The flow speed was varied by a stirring magnet in a cylindrical chamber. The radio-frequency (RF) signals backscattered by RBC samples were measured over 5 min in a pulse-echo setup with a 5 MHz focused transducer. Although the intact rat blood has poor RBC aggregability, RBC aggregation of rat blood was enhanced by replacing its plasma with a higher molecular weight polymer solution. The experimental results showed that the nonlinear relationship between hematocrit and ultrasonic backscatter from rat RBCs in plasma and aggregating media is affected by flow speed, which may provide a unified insight into hematocrit dependence of RBC aggregation under flowing and static conditions.

Red blood cells (RBCs) stick together to form rouleaux at lower shear rate and the rouleaux break up at higher shear rate. This reversible phenomenon is known to RBC aggregation, which is responsible for a non-Newtonian fluid. This erythrocyte aggregation is also related to several pathological diseases, such as hyperlipidemia, arteriosclerosis, diabetes, obesity, and other cardiac vascular diseases. However, there are not many ways to measure and monitor this RBC aggregation noninvasively in real time. Ultrasound is a possible tool for this. In this study, a commercialized GE LOGIQ 700 Expert ultrasonic system with an M12L linear transducer was used in several in vitro and in vivo experiments for investigation of blood under pulsatile flow using B-mode and harmonic imaging. In in vitro experiments in a mock flow loop with porcine blood, two interesting phenomena, “Black Hole” (BLH) and “Bright Collapsing Ring” (BRCR), were observed in B-mode cross-sectional images. BLH is a lower echoic zone at the center stream of a tube, and BRCR refers to the appearance of a hyper-echoic ring at the periphery and its collapse to the tube center during a pulsatile flow cycle. These phenomena were investigated under well-controlled hemodynamic conditions at different flow speeds and stroke rates. Radial distribution of rouleaux was also studied at different transducer beam angles. In in vivo experiments on human carotid arteries, the BRCR was also observed from harmonic images of not 1 but 10 human subjects.

Ultrasonic scattering by blood has been studied both theoretically and experimentally for a better characterization of the performance of ultrasonic devices. In the course of these investigations it became clear that ultrasonic scattering from blood is critically related to the hematological and hemodynamic properties of blood, including hematocrit, plasma protein concentration, flow rate, and flow cycle duration, to name a few parameters. An unexpected conclusion from this work is that ultrasound appears to be a totally unexplored and ignored tool for blood flow visualization and hemodynamic measurements. Two unique hemodynamic phenomena have been observed: the black hole, a low echogenic zone in the center stream of a blood vessel, and the collapsing ring, an hyperechogenic ring converging from the vessel periphery toward the center, and eventually collapsing during pulsatile flow. They seemed to be resulted from the spatial and temporal variations of the shear rate and acceleration in the vessel.

The "black hole," a hypo-echoic hole at the center of the bloodstream surrounded by a hyper-echoic zone in cross-sectional views, has been observed in ultrasound backscattering measurements of blood with red blood cell aggregation in in vitro studies. We investigated whether the phenomenon occurs in the in vivo arterial bloodstream of rats using a high-frequency ultrasound imaging system. Longitudinal and cross-sectional ultrasound images of the rat common carotid artery (CCA) and abdominal aorta were obtained using a 40-MHz ultrasound system. A high-frame-rate retrospective imaging mode was employed to precisely examine the dynamic changes in blood echogenicity in the arteries. When the imaging was performed with non-invasive scanning, blood echogenicity was very low in the CCA as compared with the surrounding tissues, exhibiting no hypo-echoic zone at the center of the vessel. Invasive imaging of the CCA by incising the skin and subcutaneous tissues at the imaging area provided clearer and brighter blood echo images, showing the "black hole" phenomenon near the center of the vessel in longitudinal view. The "black hole" was also observed in the abdominal aorta under direct imaging after laparotomy. The aortic "black hole" was clearly observed in both longitudinal and cross-sectional views. Although the "black hole" was always observed near the center of the arteries during the diastolic phase, it dissipated or was off-center along with the asymmetric arterial wall dilation at systole. In conclusion, we report the first in vivo observation of the hypo-echoic "black hole" caused by the radial variation of red blood cell aggregation in arterial bloodstream.

Blood echogenicity is highly susceptible to hemodynamic conditions mainly due to the variation of erythrocyte aggregation. The purpose of the present study is to investigate the echogenicity variation in arterial blood flow to better understand hemodynamics and erythrocyte aggregation in in vivo rat arteries. Blood echogenicity in the carotid artery and the abdominal aorta of rats was measured using a high-frequency ultrasound imaging system with a 40 MHz probe. The ECG-based kilohertz visualization reconstruction technique was employed to obtain high temporal and spatial resolution images. Experimental results show that blood echogenicity increased at systole and decreased at diastole. Complex changes in the distribution of blood echogenicity, such as the 'black hole' or the 'bright collapsing ring' phenomena, were observed in some rats treated with dextran 500 or skin incision. The present in vivo study using rats and a high-frequency ultrasound imaging system corroborates the previous observations of cyclic and radial variations of blood echogenicity in in vitro studies.

Ultrasound blood imaging can be used to the clinical applications including the in-vivo measurement of erythrocyte aggregation (EA). In the present paper, the ultrasound blood images were measured at both radial (RA) and common carotid artery (CCA) of the stroke patients and the control group. The pulsatility index of blood echogenicity (PIBE) was computed from the images, and PIBE from the patient group were higher than those from the control group, in RA (0.22±0.02 and 0.16±0.03) but not in CCA (0.35±0.02 and 0.32±0.01). Similarly, the fibrinogen concentrations of the patients were higher than those of the control group in RA (336±61 and 264±38 mg/dl) but not in CCA (340±126 and 257±43 mg/dl) except for a patient (555 mgIdl). The glucose concentrations of the patients were higher than those of the control group for CCA (129±32 and 92±16 mg/dl) but not for RA (128±39 and 98±13 mg/dl) except for a patient (210 mg/dl). Based on the present research, we suggest that EA can be estimated using ultrasound imaging in the RA and CCA, and that the in-vivo EA estimation would be contributed to the clinical applications for stroke patients.

An optically transparent tissue-mimicking (TM) phantom whose acoustic properties are close to those of tissue was constructed for visualizing therapeutic effects by high intensity focused ultrasound (HIFU). The TM phantom was designed to improve a widely used standard bovine serum albumin (BSA) polyacrylamide hydrogel (PAG), which attenuated ultrasound far less than tissue and, unlike tissue, did not scatter ultrasound. A modified recipe has been proposed in the study by adding scattering glass beads with diameters of 40–80 μm (0.002% w/v) and by raising the concentration of acrylamide (30% v/v). The TM BSA-PAG constructed has an acoustic impedance of 1.67 MRayls, a speed of sound of 1576 m/s, an attenuation coefficient of 0.52 dB/cm at 1 MHz, a backscattering coefficient of 0.242 × 10−3 1/sr/cm at 1 MHz and a nonlinear parameter (B/A) of 5.7. These parameters are close to those of liver. The thermal and optical properties are almost the same as the standard BSA-PAG. The characteristic features of the thermal lesions by HIFU were observed to be more accurately visualized in the TM BSA-PAG than in the standard BSA-PAG. In conclusion, the proposed TM BSA-PAG acoustically mimics tissue better than the standard BSA-PAG and is expected to be preferentially used for assuring if a clinical HIFU device produces the thermal lesion as planned.

The objective of this research is to study the cyclic variations in echogenicity (CVE) as an acute response to smoking. CVEs, caused by the aggregation of red blood cells (RBC) were measured from the cross-sectional images of the common carotid artery using coded harmonic imaging of a commercial ultrasound system. The amplitude of the CVE (A(cve)) was analyzed among 28 smokers before and after smoking. A(cve) was increased in 22 smokers and decreased in six smokers after 1-2 cigarettes were smoked. Heart rate (HR) was also estimated from the ultrasonic images before and after smoking. The smokers were optimally divided into two clusters with respect to the change in A(cve) and the intrinsic characteristics of smokers (i.e., daily consumed cigarettes and smoking years) through a two-step cluster analysis (TSCA). The increase in A(cve) after smoking was significantly higher in the heavy smoker cluster compared with the light smoker cluster. The results suggest that the acute changes in A(cve) in response to smoking are different between heavy smokers and light smokers. This preliminary study demonstrates the potential application of coded harmonic ultrasound imaging to detect or characterize RBC aggregation. In addition, the results may be useful for understanding the acute physiologic changes caused by smoking.

High frequency ultrasound over 40 MHz has been used to image the anterior segment of the eye, but it is not suitable for the posterior segment due to the frequency dependent attenuation of ultrasound and thus the limitation of penetration depth. This paper proposes a novel scan method to image the posterior segment of the eye with an angled high frequency (beyond 40 MHz) ultrasound needle transducer. In this method, the needle transducer is inserted into the eye through a small incision hole (approximately 1 mm in diameter) and rotated around the axial direction to form a cone-shaped imaging plane, allowing the spatial information of retinal vessels and diagnosis of their occlusion to be displayed. The feasibility of this novel technique was tested with images of a wire phantom, a polyimide tube, and an excised pig eye obtained by manually rotating a 40-MHz PMN-PT needle transducer with a beveled tip of 45 degrees . From the results, we believe that rotational scan imaging will help expand the minimally invasive applications of high frequency ultrasound to other areas due to the capability of increased closeness of an angled needle transducer to structures of interest buried in other tissues.

The arterial structure experiences cyclic pulsation in three-dimension (3-D) by pulsatile blood flow. Here we reconstruct the 3-D carotid artery bifurcation (CAB) geometry from three rats to observe the pulsatile variation of the carotid artery geometry by a high-resolution ultrasound imaging system (Vevo 770, VisualSonics, Canada). Two experienced observers manually segmented the cross-sectional ultrasound images to outline the arterial lumen. From the constructed geometry of three subjects, we observed that the CAB geometry favorably expanded to anterior/ posterior direction which parallel to sagittal plane. Furthermore, an in vitro blood flow experiment using an anthropomorphic flow phantom was implemented to more clearly understand the asymmetric pulsation phenomenon. Finally we confirmed the elastic bifurcation geometry favorably expands in a direction of bifurcation, both in vivo and in vitro measurements, which derived by bifurcated flow. This finding, the asymmetrical pulsation phenomenon of carot...

The computational simulation of the interaction between blood flow and arterial wall motion during a cardiac cycle is complicated and requires high quality information of the vessel wall motion in space and time. In this study, a set of cross-sectional ultrasound images was acquired using an electrocardiogram-gated kilohertz visualization mode, which provides 1000 frame images per second, by an ultrasound imaging system (Vevo 770, VisualSonics, Canada) with a probe of 40-MHz central frequency (RMV 704). The three dimensional (3D) geometry of carotid artery bifurcation was reconstructed at systolic and diastolic phases during a cardiac cycle using the cross-sectional ultrasound images, and a block meshing method was applied to the reconstructed 3D geometry. Then, an appropriate hexahedral mesh was constructed for the computational simulation. The 3D geometry measured by high-frequency ultrasound imaging provides high temporal and spatial information on the vessel wall motion during a cardiac cycle, which is important for accurate computational simulation of hemodynamics in the bifurcation area of the carotid artery. The fluid-structure interaction simulation of blood flow in the carotid artery bifurcation during a cardiac cycle is in progress using the meshes of 3D geometry of vessel wall. [Work supported by NIPA-2013-H0401-13-1007 and 2013R1A1A2043478.]

A pulse‐echo system was used in a cylindrical chamber with a stirring magnet and a 5‐MHz focused transducer for studying erythrocyte aggregation from human, horse, and rat blood. The highest backscattering power was measured from horse blood and followed by human and rat blood both at stasis and under shear forces. In human and horse blood, the backscattered power (BP) was decreased with stirring speed and saturated within 1 min. The BP was increased to 20 dB when blood flow was stopped. Since the aggregation of rat erythrocytes in autologous plasma is very low and barely detectable by the ultrasound BP, rat plasma was replaced by phosphate buffered saline containing polyvinylpyrrolidone 360 in order to enhance the aggregation. In conclusion, this simple in vitro ultrasound measurement system requires a small amount of blood, which may provide an alternative method to investigate the mechanisms and physiological roles of erythrocyte aggregation. Furthermore, the rat erythrocytes in polymer solution may be useful for an automatic measurement system to examine the bioactive materials that affect aggregation in preclinical studies.

Ultrasound (US) is known to enhance thrombolysis when thrombolytic agents and/or microbubbles are injected into the targeted vessels. In this research, high-intensity US (1 MHz, 7 W/cm2, 30 % duty cycle) was applied in vivo to the ear marginal vein of three rabbits which was occluded by either laser photothrombosis or thrombin, right after the injection of 0.3~0.6 cc of microbubbles (13 × 108 bubbles/ml of concentration) through the other ear vein without using any thrombolytic agent. To determine the effect of the sonothrombolysis, the blood flow velocity near the occlusion site in the vein was measured by a custom-made 40-MHz US needle transducer and its corresponding Doppler US system. The Doppler spectra show that the blood flow velocity recovered from total occlusion after three 10-minute high-intensity US treatments. Fluorescein angiography was employed to confirm the opening of the vessel occlusion. A control study of three rabbits with only the microbubble injection showed no recovery on the occlusion in 3 hours. The results show that the sonothrombolysis in the rabbit ear marginal vein can be achieved with microbubbles only. The results of cavitation measurements indicate that the mechanism of sonothrombolysis is probably due to the cavitation induced by the microbubbles. Without the need of applying any thrombolytic agent, high-intensity US has high potential for therapies targeting on small blood vessels.

An optically transparent tissue mimicking (TM) phantom whose acoustic properties are close to those of tissue was constructed for visualizing therapeutic effects by high intensity focused ultrasound (HIFU). The TM phantom was designed to improve a prevalent polyacrylamide hydrogel (PAG) which attenuates ultrasound far less than a tissue and does not scatter ultrasound unlike any other tissue. A modified recipe has been proposed in the study by adding scattering glass beads with diameters of 40 ~ 80 μm (0.002 % in w/v) and by raising the concentration of acrylamide (30% in v/v). The constructed TM PAG has an acoustic impedance of 1.66 Mrayls, a speed of sound of 1,573±5 m/s, an attenuation coefficient of 0.53±0.04 dB cm-1MHz-1, a backscattering coefficient of 0.23×10-3 cm-1sr-1 MHz-1 and a nonlinear parameter (B/A) of 5.5±0.2. These parameters are close to those of liver. The thermal and optical properties are almost the same as the prevalent PAG. The TM PAG was tested to visualize the thermal lesions by H...

Blood echogenicity is changed by red blood cell aggregation due to hemodynamic and hematological factors depending on a person. A stroke is known as a cerebrovascular accident due to lack of the blood flow. Hence, an ultrasound blood imaging could be the preliminary diagnosis for the stroke patient. In this paper, ultrasound images were acquired from the common carotid artery of stroke patients and the control group by the ultrasound imaging system (Voluson e, GE Healthcare, USA). The numbers of subject were 6 stroke patients and 5 healthy people for the control group, and their ages were 67±17 and 68±3 years old, respectively. The average of blood echogenicity of the stroke patients (54±8) was lower than that of the control group (96±8). The amplitudes of the cycle variation of blood echogenicity were similar for both of the stroke patient (18±6) and the control group (23±6). The preliminary experimental results showed the statistical difference of blood echogenicity between the stroke patients and the c...

Previous studies have demonstrated that blood echogenicity is highly variable depending on blood flow velocity and pulsatility mainly due to the variation of red blood cell (RBC) aggregation. However, most of the studies were performed in a mock-flow loop using porcine blood and the results were not fully validated in vivo. Rat was rarely used for investigation of RBC aggregation due to its low aggregation tendency. But high-frequency ultrasound may detect the RBC aggregation from rat blood. The purpose of the present study is to investigate the cyclic and radial variation of blood echogenicty in rat arteries using a high-frequency ultrasound system with a 40-MHz scanner. B-mode images of blood were acquired from various arteries, including carotid artery and abdominal aorta. Blood echogenicity increased at systole and decreased at diastole. The cyclic variation was larger at the vessel center than near the vessel wall. The central hypoechoic zone ('black hole' phenomenon) was observed in carotid arteries...

The dynamic changes of echogenicity in common carotid artery was observed from coded harmonic images by GE ultrasound systems. The observed variation in echogenicity was related with the dynamic change of red blood cell (RBC) aggregation during a cardiac cycle. In this research, the cyclic variation in echogenicity (CVE) was observed in the harmonic images of the carotid artery from 28 smokers before and after smoking using a GE Voluson e ultrasound system. The amplitude of CVE (Acve) was significantly increased after smoking in the heavy smokers compared with the one in light smokers (4.98±4.26 vs −0.3±3.01, P

It is already known that the ultrasound speed and attenuation coefficient are increasing during the blood clotting process. A pulse echo system was set up to measure the sound speed and attenuation coefficient of human blood at 37 C. From ten healthy volunteers, the blood was taken to measure sound speed and attenuation coefficient during blood coagulation without and with heparin. For ten stroke patients, sound speed and attenuation were measured with aPTT or PT for comparison. The variation of sound speed and attenuation coefficient of blood after adding heparin was small. Sound speed of plasma from healthy volunteers was increased to 7 from 1535 m/s over 50 min without heparin, but to 1 m/s during the first 5 min for heparin‐added blood. Sound speed of plasma from stroke patients was changed little compared to that from healthy volunteers without heparin. Attenuation coefficient was increased linearly during plasma coagulation for both volunteers and stroke patients, but its temporal slopes were much smaller for stroke patients. The blood samples from the stroke patients that investigated how heparin affects sound speed and attenuation as a function of time before and after taking the heparin and the results will be discussed.