Tae-Hoon Bok

Simultaneous assessment of red blood cell aggregation and oxygen saturation under pulsatile flow using high-frequency photoacoustics.

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.

Acoustic Channel Formation and Sound Speed Variation by Low-salinity Water in the Western Sea of Jeju during Summer

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.

Diel variation in high-frequency acoustic backscatter from Cochlodinium polykrikoides

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.

Quantitative photoacoustic assessment of red blood cell aggregation under pulsatile blood flow: experimental and theoretical approaches

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.

High-frequency photoacoustic imaging of erythrocyte aggregation and oxygen saturation: probing hemodynamic relations under pulsatile blood flow

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.

Simultaneous measurement of erythrocyte aggregarion and oxygen saturation under in vitro pulsatile blood flow by high-frequency photoacoustics

In this paper, high-frequency photoacoustic (PA) imaging is proposed to simultaneously measure erythrocyte aggregation (EA) and oxygen saturation (SO2). 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 SO2 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 SO2 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 SO2 was varying while blood was flowing with the different beat rates. The temporal variation in SO2 can be correlated to EA, since it has been reported that oxygen release is inhibited by EA.

Extraction of an Underwater Transient Signal Using Sound Mask-filter

ABSTRACT: 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.

Mobility of Amphidinium carterae Hulburt measured by high-frequency ultrasound

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.

Effect of optical wavelength on photoacoustic investigations of pulsatile blood flow

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.

Low-salinity-induced surface sound channel in the western sea of Jeju Island during summer

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.