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We investigate the feasibility of photoacoustic (PA) imaging for assessing the correlation between red blood cell (RBC) aggregation and the oxygen saturation (sO2) in a simulated pulsatile blood flow system. For the 750 and 850 nm illuminations, the PA amplitude (PAA) increased and decreased as the mean blood flow velocity decreased and increased, respectively, at all beat rates (60, 120 and 180 bpm). The sO2 also cyclically varied, in phase with the PAA for all beat rates. However, the linear correlation between the sO2 and the PAA at 850 nm was stronger than that at 750 nm. These results suggest that the sO2 can be correlated with RBC aggregation induced by decreased mean shear rate in pulsatile flow, and that the correlation is dependent on the optical wavelength. The hemodynamic properties of blood flow assessed by PA imaging may be used to provide a new biomarker for simultaneous monitoring blood viscosity related to RBC aggregation, oxygen delivery related to the sO2 and their clinical correlation.

Significance: We demonstrate the potential of probing the sO2 change under blood flow in vivo using photoacoustic (PA) imaging and sheds light on the complex relationship between RBC aggregation and oxygen delivery. Aim: To conduct in vivo assessments of the sO2 in the radial artery of healthy volunteers and simultaneously probe the relation between the sO2 and hemodynamic behavior such as red blood cell (RBC) aggregation. Approach: The effects of PA-based measurements of blood hemodynamics were studied as a function of the subjects’ age (20s, 30s, and 40s). The pulsatile blood flow in the human radial artery of 12 healthy subjects was imaged in the 700 to 900 nm optical wavelength range using a linear array-based PA system. Results: The PA power when blood velocity is minimum (Pamax) was larger than the one attained at maximum blood velocity (Pamin), consistent with predictions based on the cyclical variation of RBC aggregation during pulsatile flow. The difference between Pamin and Pamax at 800 nm (ΔPa800) increased with age (1.7, 2.2, and 2.6 dB for age group of 20s, 30s, and 40s, respectively). The sO2 computed from Pamax was larger than the one from Pamin. Conclusions: The ΔPa800 increased with participant age. The ΔPa800 metric could be a surrogate of noninvasively monitoring the age-induced changes in RBC aggregation. The sO2 change during a cycle of pulsatile blood flow also increased with age, demonstrating that RBC aggregation can affect the sO2 change.

The over-growth of phytoplankton causes harmful algal blooms (HABs) in marine ecological environments. Mobility measurement is important in understanding the action of HABs. In this study, the mobility of Amphidinium carterae Hulburt (A. carterae) was investigated using high-frequency ultrasound in the laboratory. Mobility in response to light was illustrated with M-mode images reconstructed from echoed signals. This study suggests that mobility of the swimming speed of A. carterae in response to light can be measured and calculated with M-mode images through high-frequency ultrasound. This finding may be helpful in understanding the fundamental behavior of HABs.

In this work, speckle in acoustic-resolution photoacoustic (PA) imaging systems is discussed. Simulations and experiments were used to demonstrate that PA speckle carries structural information related to sub-resolution absorbers. Numerical simulations of phantoms containing spherical absorbers were performed using Green’s function solutions to the PA wave equation. A 21 MHz linear array was simulated (256 elements, 75×165 µm resolution, bandwidth 9-33 MHz) and used to record, bandlimit and beamform the generated PA signals. The effects of absorber size (10-270 µm) and concentration (10-1000/mm3) on PA speckle were examined using envelope statistics and radiofrequency spectroscopy techniques. To examine PA speckle experimentally, a VevoLAZR system was used to image gelatin phantoms containing 3 and 15µm polystyrene beads, a tissue mimicking radial artery phantom, and murine tumour vasculature in vivo. Fully developed speckle, as assessed by Rayleigh distribution fits to PA signal envelopes, was present in all images (simulated and experimental) containing at least 10 absorbers per resolution volume, irrespective of absorber size. Changes in absorber size could be detected using the spectral slope of the normalized power spectrum (4.5x decrease for an 80 µm increase in size). PA images of flowing blood in the radial artery phantom also revealed the presence of speckle with intensity that fluctuated periodically with beat rate (4 dB per cycle). Speckle was ubiquitous to all murine tumor vasculature images. During treatment-induced vascular hemorrhaging, the spectral slope decreases by 80% compared to untreated mice. These results demonstrate that photoacoustic speckle encodes information about the underlying absorber distribution.

Photoacoustic (PA) imaging of blood flow can provide label free and non-invasive assessment of red blood cell (RBC) aggregation and the oxygen saturation (sO 2 ). Our group has previously demonstrated that the interrelationship between RBC aggregation and the sO 2 during a pulsatile blood flow could be potentially assessed using PA imaging. The pulsatile blood flow yields spatiotemporal changes in RBC aggregation, affecting PA imaging. A simple particle motion model was developed based on the blood flow velocity measured from the human radial artery (RA). The positions of randomly distributed, identical circular particles (2.7 um radius) in the lateral-axial plane (20 mm by 2 mm) were traced at each time step of an experimentally measured velocity profile. At each step, the time dependent PA power $(P_{PA})$ from each single cell (or particles interacting to form aggregates) was computed by modeling and accounting for the directivity of a 21 MHz (9.2 to 32.8 MHz bandwidth) linear array. In-vivo PA images of the RA of healthy volunteers were acquired using the VevoLAZR equipped with a 21 MHz linear-array probe. The measured PA images were compared to the simulated PA images. The aggregates formed a parabolic front along the axial direction and were driven to the right-hand side along the lateral direction as the simulation propagated in time. The $P_{PA}$ was also large at the parabolic front, and was also driven to the right-hand side for every time step. The spatiotemporal distribution of the computed $P_{PA}$ was comparable to the experimental $P_{PA}$. Specifically, the $P_{PA}$ increased by 12 dB along the lateral direction. These results can be used to study the label-free, non-invasive assessment of the spatiotemporal distribution of sO 2 in vivo. Furthermore, the improved particle model can provide insights into the mechanism of PA wave generation from RBC aggregation during in vivo blood flow.

We investigate the optical wavelength dependence in quantitative photoacoustic (QPA) assessment of red blood cell (RBC) aggregation and oxygen saturation (sO2 ) during pulsatile blood flow. Experimentally, the pulsatile flow was imaged with a 700 to 900 nm laser using the VevoLAZR. Theoretically, the photoacoustic (PA) signals were computed based on a Green's function integrated with a Monte Carlo simulation of radiant fluence. The pulsatile flow created periodic conditions of RBC aggregation/nonaggregation, altering the aggregate size, and, in turn, the sO2 . The dynamic range, DR (a metric of change in PA power) from 700 to 900 nm for nonaggregated RBCs, was 5 dB for both experiment and theory. A significant difference in the DR for aggregated RBCs was 1.5 dB between experiment and theory. Comparing the DR at different wavelengths, the DR from nonaggregated to aggregated RBCs at 700 nm was significantly smaller than that at 900 nm for both experiment (4.0 dB < 7.1 dB) and theory (5.3 dB < 9.0 dB). These results demonstrate that RBC aggregation simultaneously affects the absorber size and the absorption coefficient in photoacoustic imaging (PAI) of pulsatile blood flow. This investigation elucidates how QPA spectroscopy can be used for probing hemodynamics and oxygen transport by PAI of blood flow.

Our group has previously demonstrated that lower shear rate in the pulsatile blood flow yields greater red blood cell (RBC) aggregation which in turn results in a higher oxygen saturation (sO 2 ) level and a higher photoacoustic (PA) signal. Higher shear rates led to disaggregation thereby decreasing the PA signal amplitude and the sO 2 . These results suggest that the interrelationship between the sO 2 and RBC aggregation may provide a new biomarker in the diagnosis of diseases that alter blood rheological properties. In this paper, we present a pilot study where high-frequency photoacoustic imaging (PAI) is used for the simultaneous assessment of RBC aggregation and sO 2 in vivo in the human radial artery (RA). The ultrasound (US) and PA images in the RA were acquired using a US/PA imaging system equipped with a 21 MHz linear-array probe (Vevo LAZR; LZ250, FUJIFILM VisualSonics, Canada), varying the wavelength of optical illumination (700, 750, 800, 850 and 900 nm). The blood flow velocity at the RA was assessed by pulsed wave Doppler in the same device. The PA signals inside the RA were observed at all wavelengths. The PA power increased with the illumination wavelength. At each wavelength, the PA power varied as function of time. The phase of variation in PA signals was inversely proportional to that in systolic blood flow velocity. The sO 2 is proportional to the cell surface area exposed to the surrounding media, and RBC aggregation decreases the exposed area of the aggregate. As such, the sO 2 was higher for aggregated cells (diastolic state) than single cells (systolic state). This PAI study of RA RBC aggregation and sO 2 in vivo is the first attempt to study the hemodynamics and physiological function of RBC, which can be used as a potential tool for the diagnosis of blood flow conditions in the RA.

Surface salinity in the western sea of Jeju Island in Korea becomes low due to the inflow of the Chinese coastal waters during summer. One of the characteristics of low salinity water is the formation of a surface sound channel (SSC) due to the decrease in sound speed by salinity. However, a quantitative analysis between low salinity water and SSC has not been fully investigated yet. In this paper, a temperature-salinity (T-S) gradient diagram is introduced in order to assess SSC formation and its acoustic characteristics are also investigated through a case study of low salinity waters. Maximum angles of limiting rays were less than 4.6° and low frequency cutoffs were higher than 2.0 kHz for the SSCs formed in low salinity water. When the salinity gradients were large (0.5 psu/m), a SSC was formed more efficiently than other cases whose salinity gradients were small. On the other hand, a SSC was not formed in spite of highly positive salinity gradients when the amount of temperature gradients was negatively high enough (-0.5 °C/m). However, the acoustic energy transfer in the surface ducts was dependent on frequency and position of source.

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

The mechanical scanning of a single element transducer has been mostly utilized for high-frequency ultrasound imaging. However, it requires space for the mechanical motion of the transducer. In this paper, a rotational scanning ultrasound biomicroscopy (UBM) system equipped with a high-frequency angled needle transducer is designed and implemented in order to minimize the space required. It was applied to ex vivo ultrasound imaging of porcine posterior ocular tissues through a minimal incision hole of 1 mm in diameter. The retina and sclera for the one eye were visualized in the relative rotating angle range of 270 degrees similar to 330 degrees and at a distance range of 6 similar to 7 mm, whereas the tissues of the other eye were observed in relative angle range of 160 degrees similar to 220 degrees and at a distance range of 7.5 similar to 9 mm. The layer between retina and sclera seemed to be bent because the distance between the transducer tip and the layer was varied while the transducer was rotated. Certin features of the rotation system such as the optimal scanning angle, step angle and data length need to be improved for ensure higher accuracy and precision. Moreover, the focal length should be considered for the image quality. This implementation represents the first report of a rotational scanning UBM system.

In the present paper, the optical wavelength dependence on the photoacoustic (PA) assessment of the pulsatile blood flow was investigated by means of the experimental and theoretical approaches analyzing PA radiofrequency spectral parameters such as the spectral slope (SS) and mid-band fit (MBF). For the experimental approach, the pulsatile flow of human whole blood at 60 bpm was imaged using the VevoLAZR system (40-MHz-linear-array probe, 700-900 nm illuminations). For the theoretical approach, a Monte Carlo simulation for the light transmit into a layered tissue phantom and a Green’s function based method for the PA wave generation was implemented for illumination wavelengths of 700, 750, 800, 850 and 900 nm. The SS and MBF for the experimental results were compared to theoretical ones as a function of the illumination wavelength. The MBF increased with the optical wavelength in both theory and experiments. This was expected because the MBF is representative of the PA magnitude, and the PA signal from red blood cell (RBC) is dependent on the molar extinction coefficient of oxyhemoglobin. On the other hand, the SS decreased with the wavelength, even though the RBC size (absorber size which is related to the SS) cannot depend on the illumination wavelength. This conflicting result can be interpreted by means of the changes of the fluence pattern for different illumination wavelengths. The SS decrease with the increasing illumination wavelength should be further investigated.

Salinity does not generally affect sound speed because it shows very small variations in the ocean. However, low salinity water appears in the Western Sea of Jeju Island every summer so that sound speed and sound propagation can change near sea surface. We calculated Sound Speed Profile (SSP) using vertical profiles of temperature and salinity, which were averaged over years of normal salinity and low salinity ( 2010.

An underwater transient signal is distinguished from an ambient noise. Database for the underwater transient signal is required since the underwater transient signal shows various characteristics depending on acoustic features. In the paper, hence, sound mask-filter was applied to extract the transient signals which exist temporally and locally in the ocean. The standard signal was chosen and cross-correlated with the raw signal. A mask-filter for a transient signal was obtained using the threshold which was decided by the maximum likelihood method in the envelope of the cross-correlated signal. Using the sound mask-filter, the transient signal of a sea catfish { Galeichthys felis (Linnaeus)} was extracted from the underwater ambient noise. Similarly, the man-made signal was added into the noise and it was extracted by the same method. We also have demonstrated the significance of the transient signal through comparing th e extracted signals depending on the standard signal. In the results, the proposed method, sound mask-filtering, could be utilized as a database construction of the transient signals in underwater noise. Particularly, this study would be useful to extract the wanted signal from arbitrary signals.

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.

This paper attempts to experimentally and analytically quantify the aggregation-induced changes in the photoacoustic amplitude (PAA) by simultaneously examining the effect of red blood cell (RBC) aggregate size and optical illumination wavelength. In experiments, the pulsatile flow of human whole blood at 60 bpm was imaged using the VevoLAZR system equipped with a 40-MHz-linear-array probe. The samples were illuminated every 10 nm from 700 to 900 nm. For the analytical model, the PAA from both a collection of randomly distributed RBCs of 5, 10, 15, 20, 25, and 30 cells and a single absorber as a spherical aggregate of RBCs formed by the corresponding number of RBCs. The oxygen saturation (sO2) was measured as 74% and 80% for the non-aggregated RBCs and the RBC aggregation. These values were assigned to the analytical RBC aggregates containing between 5 and 30 cells. The normalized PAA (nPAA) for the experimental results was compared to that generated by the theoretical calculations. At a given wavelength, the analytical nPAA for the collection of RBCs were identical for all numbers of RBCs, but that for the RBC aggregate increased with the number of RBCs forming the aggregate due to the increase in the effective photoacoustic absorber size. The experimental as well as analytical nPAA for both RBC aggregation and non-aggregation increased with the wavelength at a given absorber size. This was due to the fact that the PAA is mainly determined by the optical absorption coefficient (μa) which increases due to the relationship between eHbO and wavelength. In addition, the difference of PAA between RBC aggregation and nonaggregation also increased with the wavelength due to the increase in the μa induced by the hypothesized enhanced sO2 resulting from the increased size of RBC aggregates. These results can be used as a means of estimating the oxygen loading and unloading during blood flow. This investigation elucidates the quantitative relationship between the RBC aggregate size and the optical illumination wavelength for probing the physiology of flowing blood.

In this paper, a Bayesian classifier based on PCA (principle component analysis) is proposed to classify underwater transient signals using order LPC (linear predictive coding) coefficients as feature vector. The proposed classifier is composed of two steps. The mechanical signals were separated from biological signals in the first step, and then each type of the mechanical signal was recognized in the second step. Three biological transient signals and two mechanical signals were used to conduct experiments. The classification ratios for the feature vectors of biological signals and mechanical signals were 94.75% and 97.23%, respectively, when all 16 order LPC vector were used. In order to determine the effect of underwater noise on the classification performance, underwater ambient noise was added to the test signals and the classification ratio according to SNR (signal-to-noise ratio) was compared by changing dimension of feature vector using PCA. The classification ratios of the biological and mechanical signals under ocean ambient noise at 10dB SNR, were 0.51% and 100% respectively. However, the ratios were changed to 53.07% and 83.14% when the dimension of feature vector was converted to three by applying PCA. For correct, classification, it is required SNR over 10 dB for three dimension feature vector and over 30dB SNR for seven dimension feature vector under ocean ambient noise environment.

The acoustic integrated backscattered power (IBP) of the phytoplankton Cochlodinium polykrikoides, which causes red tides in Korean waters, was measured in the laboratory and in the sea in situ to investigate the feasibility of observing red tides using high frequency ultrasound at 5 and 10 MHz. The IBP was measured with cultured C. polykrikoides at abundance levels of 90, 110, 200, 260, 300, 340, 360, 600, 700 and 850 cells/mL in the laboratory. Using the same high frequency acoustic transducers that were attached to the side of a research vessel, the IBP was measured in situ over a 9 km ship track near the Gumo Islands in Yeosu in the Southern Sea of Korea during the red tide season. The IBP was also measured simultaneously with positional information obtained from global positioning system data and by sampling the seawater in which C. polykrikoides was counted to survey the C. polykrikoides distribution in the study area. The IBP in situ was in agreement with that in the laboratory depending on the C. polykrikoides abundance. Consequently, we suggest that it is feasible to use underwater ultrasonic methodology for the observation of red tides in real time in situ.

In this paper, we investigate the feasibility of high-frequency photoacoustic (PA) imaging to study the shear rate dependent relationship between red blood cell (RBC) aggregation and oxygen saturation (SO2) in a simulated blood flow system. The PA signal amplitude increased during the formation of aggregates and cyclically varied at intervals corresponding to the beat rate (30, 60, 120, 180 and 240 bpm) for all optical wavelengths of illumination (750 and 850 nm).The SO2 also cyclically varied in phase with the PA signal amplitude for all beat rates. In addition, the mean blood flow velocity cyclically varied at the same interval of beat rate, and the shear rate (i.e. the radial gradient of flow velocity) also cyclically varied. On the other hand, the phase of the cyclic variation in the shear rate was reversed compared to that in the PA signal amplitude. This study indicates that RBC aggregation induced by periodic changes in the shear rate can be correlated with the SO2 under pulsatile blood flow. Furthermore, PA imaging of flowing blood may be capable of providing a new biomarker for the clinical application in terms of monitoring blood viscosity, oxygen delivery and their correlation.

In this paper, high-frequency photoacoustic (PA) imaging is proposed to simultaneously measure erythrocyte aggregation (EA) and oxygen saturation (SO 2 ). EA is a reversible phenomenon where red blood cells aggregate under flowing conditions and it becomes pathological when enhanced in a number of circulatory disorders. Here we investigate the feasibility of PA imaging in detecting EA-induced changes in SO 2 in a simulated circulatory flow system. For all optical wavelengths of illumination (750 and 850 nm), the mean PA amplitude inside the region of interest cyclically varied at intervals corresponding to the beat rate (30, 60, and 90 bpm). The vessel diameter also cyclically varied at the same time interval, but the phase of its variation was reversed compared to the PA amplitude variations. This was expected: as the blood velocity decreased, the shear rate in the radial direction also decreased, resulting in increased EA thus enhancing the PA amplitude due to the increased effective absorber size. When the velocity is increased, the aforementioned process is reversed, resulting in decreased EA and PA amplitude. The cyclic variation in SO 2 was evident for the highest beat rate, and differences in the mean PA amplitude at 750 and 850 nm were detected for all beat rates. This indicates that the SO 2 was varying while blood was flowing with the different beat rates. The temporal variation in SO 2 can be correlated to EA, since it has been reported that oxygen release is inhibited by EA.

The integrated backscatter power (IBP) from Cochlodinium polykrikoides was measured every 15 min by a 5-MHz acoustic system during a 5-day cultivation with an irradiation cycle. IBP increased by 0.6 dB in 5 days, but varied by 0.83 dB during the irradiation cycle. The daily increase and diel variation in IBP were postulated to be affected by an increase in cell numbers and a diel variation in cell biovolume or density via photosynthesis, respectively. Cell division/separation might also affect a total variation in IBP. This study suggests that high-frequency acoustics may be a potential tool for investigating phytoplankton cell functions.

The dynamic phenomena of erythrocyte aggregation (EA) need to be analyzed statistically since EA varies spatially and temporally. In the present study, the cross-sectional B-mode images were acquired from a mock circulatory system with varying blood flow velocity (BFV) under steady flow, and the human radial artery using an ultrasound biomicroscopy system at 20 MHz. The kurtosis (K) and skewness (S) coefficients, and the Nakagami parameter (m) were computed for each image. For the in-vitro experiment, both K and S increased about 0.87±0.18 and 0.63±0.09 with increasing BFV from 12 to 44 cm/s, respectively; while m decreased about 0.90±0.20. In-vivo experimental results also showed that K, S, and m varied during a cycle. When BFV varied from 5 to 15 cm/s during a cardiac cycle, K and S increased about 0.36±0.14 and 0.13±0.06 for subject 1, and 0.60±0.24 and 0.15±0.07 for subject 2, respectively; while m was estimated as large as 4.73±0.14 and 2.74±0.09. The in-vivo results seemed to be consistent with the in-vitro results in the sense that K and S increased with BFV despite large m. This study suggests that the statistical analysis of blood echogenicity can be useful for in-vivo hemorheology and blood characterization.

The geometry of carotid artery bifurcation is of high clinical interest because it determines the characteristics of blood flow that is closely related to the formation and development of atherosclerotic plaque. However, information on the dynamic changes in the vessel wall of carotid artery bifurcation during a pulsatile cycle is limited. This pilot study investigated the cyclic changes in carotid artery geometry caused by blood flow pulsation in rats. A high-resolution ultrasound imaging system with a broadband scanhead centered at 40 MHz was used to obtain longitudinal images of the rat carotid artery. A high frame rate retrospective B-scan imaging technique based on the use of electrocardiogram to trigger signal acquisition was used to examine precisely the fast arterial wall motion. Two-dimensional geometry data obtained from nine rats showed that the rat carotid artery asymmetrically contracts and dilates during each cardiac cycle. Systolic/diastolic vessel diameters near the upstream and downstream regions from the bifurcation were 0.976 ± 0.011/0.825 ± 0.015 mm and 0.766 ± 0.015/0.650 ± 0.016 mm, respectively. Their posterior/anterior wall displacement ratios in the radial direction were 41.0 ± 14.9% and 2.9 ± 1.6%, respectively. These results indicate that in the vicinity of bifurcation, the carotid artery favorably expands to the anterior side during the systolic phase. This phenomenon was observed to be more prominent in the downstream region near the bifurcation. The cyclic variation pattern in wall movement varies depending on the measurement site, which shows different patterns at far upstream and downstream of the bifurcation. The asymmetric radial expansion and contraction of the rat carotid artery observed in this study may be useful in studying the hemodynamic etiology of cardiovascular diseases because the pulsatile changes in vessel geometry may affect the local hemodynamics that determines the spatial distribution of wall shear stress, one of important cardiovascular risk factors. Further systematic study is needed to clarify the effects of wall elasticity, branch angle and vessel diameter ratio on the asymmetric wall motion of carotid artery bifurcation.

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.

Previous studies have found that ultrasound backscatter from blood in vascular flow systems varies under pulsatile flow, with the maximum values occurring during the systolic period. This phenomenon is of particular interest in hemorheology because it is contrary to the well-known fact that red blood cell (RBC) aggregation, which determines the intensity of ultrasound backscatter from blood, decreases at a high systolic shear rate. In the present study, a rat model was used to provide basic information on the characteristics of blood echogenicity in arterial blood flow to investigate the phenomenon of RBC aggregation under pulsatile flow. Blood echogenicity in the common carotid arteries of rats was measured using a high-frequency ultrasound imaging system with a 40-MHz probe. The electrocardiography-based kilohertz visualization reconstruction technique was employed to obtain high-temporal-resolution and high-spatial-resolution time-course B-mode cross-sectional and longitudinal images of the vessel. The experimental results indicate that blood echogenicity in rat carotid arteries varies during a cardiac cycle. Blood echogenicity tends to decrease during early systole and reaches its peak during late systole, followed by a slow decline thereafter. The time delay of the echogenicity peak from peak systole in the present results is the main difference from previous in vitro and in vivo observations of backscattering peaks during early systole, which may be caused by the very rapid heart rates and low RBC aggregation tendency of rats compared with humans and other mammalian species. The present study may provide useful information elucidating the characteristics of RBC aggregation in arterial blood flow.

The cyclic variation in echogenicity (CVE) was observed from the cross-sectional images of the common carotid artery using coded harmonic imaging of a GE ultrasound system. The objective of this research is to study the smoking acute effects on the amplitude of the CVE (A cve ). A cve was analyzed among the 28 smokers before and after 1–2 cigarettes were smoked. 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 relative change of A cve after smoking was significantly higher in the heavy smoker cluster compared with the light smoker cluster. However, there is no significant difference in the absolute value of A cve between before and after smoking for both two clusters. The effect of tissue attenuation on A cve was compensated with body mass index (BMI). The compensated parameter, A' cve , is significantly increased in heavy smoker group after smoking (BS: 0.47±7.4; AS: 5.4±8.0; p cve . Furthermore, after smoking, A' cve is significant higher in heavy smoker group (5.4±8.0), compared with light smoker group (−1.3±6.7; p cve is help to reduce the interference from tissue attenuation and is good for the comparison among individuals.

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.

The importance of phytoplankton contributing more than 50% of the global amount of photosynthesis has been emphasized for a long time. Sometimes, the over-growth of phytoplankton causes the negative influence such as red-tide phenomenon on marine ecological environments. Therefore, the measurement of the mobility of phytoplankton is important. In this study, the mobility of the benthic dinoflagellate, Amphidinium carterae Hulburt (A. Carterae) incubated by f/2 medium was investigated using high-frequency ultrasound. Backscattering signal from A. Carterae was measured for 2 s in every 2 min by a 40-MHz ultrasound transducer, and the integrated backscattering power calculation was followed. The mobility of A. carterae in response to the light was illustrated by M-mode image of the echoed signals. The mobility of A. carterae was estimated to about 0.4 mm/s for the upward movement in response to light, while its sedimentation rate was measured to about 0.1 mm/s in a dark environment. This study suggests that mobility of benthic dinoflagellates responding to light can be measured by M-mode imaging of high-frequency ultrasound. (This research was a part of the project titled “Measurement of cells division and photosynthesis of phytoplankton using ultrasound”, funded by the Ministry of Oceans and Fisheries, Korean.)

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.]

Phytoplankton is a primary producer in the ocean, and its vegetative activity plays an important role in controlling the global environment. In this study, the high-frequency acoustic signals were collected to evaluate the photosynthetic activity of phytoplankton during a day. The integrated backscatter power (IBP) from a dinoflagellate Cochlodinium polykrikoides was measured by a 5 MHz acoustic system during a 5-day cultivation period with a 14 h:10 h light:dark cycle. IBP increased by 0.6 dB in five days, but varied by 0.83 ± 0.1 dB during an irradiance cycle. The daily increase in IBP was a result of an increase in the number of cells during cultivation, while the diel variation was partly resulted from the variation of volume of cells by photosynthesis. In addition, cell division and separation might affect IBP. IBP of another dinoflagellate Amphidinium carterae Hulburt was also measured by a 10MHz transducer during a 3-day cultivation period while cell volume and photosynthetic capacity were measured four times a day (07:00, 12:00, 19:00, 24:00). This study suggests that high-frequency acoustics may be a meaningful tool to investigate the photosynthetic metabolism of a phytoplankton cell. [This work was supported by Defense Acquisition Program Administration and Agency for Defense Development under the contract UD130007DD.]

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.

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...

Communication environments vary with time in the context of underwater channel because multipaths are affected by the sound speed profile (SSP) in the ocean. In this paper, the average SSPs for 10 years (2000–2009) were calculated in the Yellow Sea so that the eigen‐ray paths with the channel impulse responses were determined. The computer simulation was conducted to compare the performance of underwater communication near the surface according to the variation of season. The performance of underwater communication was analyzed using the BPSK modulation and time reversal method. The significant differences of bit error rate (BER) were shown according to the change of season. In many cases, the received signals were distorted by the multi‐path channel whose features are frequency selected fading. The time reversal method was applied to compare the BER without frequency selected effect. It turns out that the good performance was shown in the autumn because of the direct path through the mixed layer channel ...

Salinity is one of variables in the empirical formula of the sound speed (SS) of seawater. Its effects on the SS are generally neglected because the average salinity is 34 psu and varies within a few psu seasonally and spatially in the ocean. Recently, low‐salinity water around 25 psu flows into the western sea of Jeju Island in Korea due to the Yangtze River flood in China during summer. In this paper, it was analyzed how the low‐salinity water affected the SS profile (SSP) and the underwater communication. The SSP was calculated with and without the low‐salinity layer, and the communication channel was estimated by the simulated acoustic eigen‐rays. The bit error rate (BER) was computed using binary phase‐shift keying modulation, and the effects of the low‐salinity water on the BER were investigated. The SSP was changed to a positive slope by the low‐salinity layer at the sub‐surface up to 20 m of depth, forming the acoustic wave guide which mostly resulted in the decrease of the BER. Consequently, this...

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

Pulsatile flow generated by the cardiac motion results in the complicated hemorheological phenomena in the artery. The pulse wave in the radial artery is utilized for the measurement of tonometry and the diagnosis of various diseases by the oriental medical doctors. In this paper, the pulse wave obtained from the three‐dimensional (3‐D) pulse wave analyzer was compared with the blood echogenicity and vessel diameter in the radial artery using an ultrasound biomicroscopy system. The ultrasonic data were acquired for five subjects and the left wrist of each subject was put on the wrist‐rest of the 3‐D pulse wave analyzer measuring the pulse waves for 25 s. The repetitive measurement was performed eight times for one of the subjects. The blood vessel motion and the blood echogenicity were calculated from the cross sectional B‐mode images of the radial artery. The cyclic variation of the vessel diameter and the blood echogenicity was measured during cardiac cycles. The phases between both of them were opposit...

This research is to measure the volume backscattering strength, Sv, of the Cochlodinium polykrikoides (the main species of red tide in Korea) in order to investigate the possibilities of early detection of red tide using high‐frequency transducers (5, 10 MHz). First, the Sv from the cultured C. polykrikoides was measured with the population density in the laboratory. Next, ultrasonic transducers were attached to the side of a research vessel, and the Sv was measured over 9‐km ship track near Yeosu in the Korean southern sea. Seawater at three stations was sampled, and the number of C. polykrikoides was counted to compare the theoretical Sv with the measured one. The results show that the measured Sv was in agreement with the theoretical one. The Sv when the light was on was measured to be higher than that when the light was off in the laboratory, probably due to the increase of size and density of C. polykrikoides during photosynthesis. In the field experiment, the Sv was measured in real time with the position information from the Global Positioning System data. This research proposes the use of underwater ultrasonic technology for early detection of red tide in real time.