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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.

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 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 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.