Po Yang Lee

Design and implementation of a smartphone-based portable ultrasound pulsed-wave doppler device for blood flow measurement

Blood flow measurement using Doppler ultrasound has become a useful tool for diagnosing cardiovascular diseases and as a physiological monitor. Recently, pocket-sized ultrasound scanners have been introduced for portable diagnosis. The present paper reports the implementation of a portable ultrasound pulsed-wave (PW) Doppler flowmeter using a smartphone. A 10-MHz ultrasonic surface transducer was designed for the dynamic monitoring of blood flow velocity. The directional baseband Doppler shift signals were obtained using a portable analog circuit system. After hardware processing, the Doppler signals were fed directly to a smartphone for Doppler spectrogram analysis and display in real time. To the best of our knowledge, this is the first report of the use of this system for medical ultrasound Doppler signal processing. A Couette flow phantom, consisting of two parallel disks with a 2-mm gap, was used to evaluate and calibrate the device. Doppler spectrograms of porcine blood flow were measured using this stand-alone portable device under the pulsatile condition. Subsequently, in vivo portable system verification was performed by measuring the arterial blood flow of a rat and comparing the results with the measurement from a commercial ultrasound duplex scanner. All of the results demonstrated the potential for using a smartphone as a novel embedded system for portable medical ultrasound applications.

Assessing the viscoelastic properties of thrombus using a solid-sphere-based instantaneous force approach.

The viscoelastic properties of thrombus play a significant role when the clot closes a leak in a vessel of the blood circulation. The common method used to measure the viscoelastic properties of a clot employs a rheometer but this might be unsuitable due to the clot fiber network being broken up by excessive deformation. This study assessed the feasibility of using a novel acoustic method to assess the viscoelastic properties of blood clots. This method is based on monitoring the motion of a solid sphere in a blood clot induced by an applied instantaneous force. Experiments were performed in which a solid sphere was displaced by a 1 MHz single-element focused transducer, with a 20 MHz single-element focused transducer used to track this displacement. The spatiotemporal behavior of the sphere displacement was used to determine the viscoelastic properties of the clot. The experimental system was calibrated by measuring the viscoelastic modulus of gelatin using different types of solid spheres embedded in the phantoms and, then, the shear modulus and viscosity of porcine blood clots with hematocrits of 0% (plasma), 20% and 40% were assessed. The viscoelastic modulus of each clot sample was also measured directly by a rheometer for comparison. The results showed that the shear modulus increased from 173 ± 52 (mean ± SD) Pa for 40%-hematocrit blood clots to 619.5 ± 80.5 Pa for plasma blood clots, while the viscosity decreased from 0.32 ± 0.07 Pa∙s to 0.16 ± 0.06 Pa∙s, respectively, which indicated that the concentration of red blood cells and the amount of fibrinogen are the main determinants of the clot viscoelastic properties.

A study of the adult zebrafish ventricular function by retrospective doppler-gated ultrahigh-frame-rate echocardiography

The zebrafish (Danio rerio) has become a preferred animal model for studying various human diseases, particularly those related to cardiovascular regeneration; therefore, a noninvasive imaging modality is needed for observing the cardiac function of zebrafish. Because of its high resolution, high-frequency ultrasound B-mode imaging has recently been used successfully to observe the heart of adult zebrafish. However, ultrahigh-frame-rate echocardiography combining Bmode imaging and color flow imaging is still needed to observe the detailed transient motions of the zebrafish ventricle. This study develops an 80-MHz ultrahigh-frame-rate echocardiography system for this purpose, based on retrospective Doppler- gated technology. B-mode and color flow images of the cardiovascular system of the zebrafish were reconstructed by two-dimensional autocorrelation at maximum frame rates of up to 40 000 and 400 fps, respectively. The timings of end diastole (ED) and end systole (ES) of ventricle can be determined by using this high-resolution image system. Two ventricular function parameters-fractional shortening (FS) and fractional area change (FAC)-were measured for evaluating the ventricular function by using ED and ES with their corresponding ventricular dimensions. The experimental results indicated that the measured FS values were 42 ± 4% (mean ± standard deviation) and 60 ± 13% for the long axis and short axis of the ventricle, respectively, and that FAC was 77 ± 9%. This is the first report of these ventricular function parameters for a normal adult zebrafish. The results showed that retrospective high-frequency echocardiography is a useful tool for studying the cardiac function of normal adult zebrafish.

Implementation of a novel high frequency ultrasound device for guiding epidural anesthesia-in vivo animal study

Epidural anesthesia has been used widely for anesthesia surgery in many clinical applications. However, the risk of epidural anesthesia may be occurred as the puncture needle was inserted too deeper to cause the dural puncture. In most cases, the anesthetists finish the anesthesia operation according to their clinical experiences. In our previous study, a novel idea of combining the ultrasound needle transducer and epidural catheter has been proposed for guiding the epidural anesthesia insertion. In present study, the implementation of this novel ultrasonic device was performed, and the animal experiments were also carried out for verifying the system performance. The portable device including a high frequency ultrasound pulser/receiver, 40-MHz high frequency needle transducer, high speed analog-to-digital converter, LCD monitor, and a FPGA chip was used to control the pulse signal by adjusting the pulse repetition frequency and pulse frequency. The distance between the tip of the epidural needle, ligamentum flavum, and dura mater can be measured in real-time by monitoring the reflected ultrasound signal in A-mode image display.

40 MHz high-frequency ultrafast ultrasound imaging

Purpose Ultrafast high‐frame‐rate ultrasound imaging based on coherent‐plane‐wave compounding has been developed for many biomedical applications. Most coherent‐plane‐wave compounding systems typically operate at 3–15 MHz, and the image resolution for this frequency range is not sufficient for visualizing microstructure tissues. Therefore, the purpose of this study was to implement a high‐frequency ultrafast ultrasound imaging operating at 40 MHz. Methods The plane‐wave compounding imaging and conventional multifocus B‐mode imaging were performed using the Field II toolbox of MATLAB in simulation study. In experiments, plane‐wave compounding images were obtained from a 256 channel ultrasound research platform with a 40 MHz array transducer. All images were produced by point‐spread functions and cyst phantoms. The in vivo experiment was performed from zebrafish. Since high‐frequency ultrasound exhibits a lower penetration, chirp excitation was applied to increase the imaging depth in simulation. Results The simulation results showed that a lateral resolution of up to 66.93 μm and a contrast of up to 56.41 dB were achieved when using 75‐angles plane waves in compounding imaging. The experimental results showed that a lateral resolution of up to 74.83 μm and a contrast of up to 44.62 dB were achieved when using 75‐angles plane waves in compounding imaging. The dead zone and compounding noise are about 1.2 mm and 2.0 mm in depth for experimental compounding imaging, respectively. The structure of zebrafish heart was observed clearly using plane‐wave compounding imaging. Conclusions The use of fewer than 23 angles for compounding allowed a frame rate higher than 1000 frames per second. However, the compounding imaging exhibits a similar lateral resolution of about 72 μm as the angle of plane wave is higher than 10 angles. This study shows the highest operational frequency for ultrafast high‐frame‐rate ultrasound imaging.

Implementation of a smart-phone based portable Doppler flowmeter

Blood flow measurement by using Doppler ultrasound has become a useful tool for diagnosing cardiovascular diseases and as a physiological signal monitor. Recently, a couple of pocket-sized ultrasound scanners have been introduced for portable diagnosis. However, it is not convenient to apply Doppler measurements by commercial duplex scanner during exercise or sleeping due to the shape of handheld probe. In addition, most devices use the digital integrated circuits to process the Doppler signals from flowing blood. However, some attached components are needed such as RF and/or audio ADC, on board memory, programmable timer, and LCD graphic display module and its control circuit. In order to simplify these complex circuits, an implementation of a smartphone based portable ultrasound pulsed-wave (PW) Doppler flowmeter is reported in this study. A 10-MHz ultrasonic surface transducer was designed for the dynamic monitoring of blood flow velocity. The directional audio Doppler shift signals were obtained using a portable analog circuit system. After hardware processing, the Doppler signals were fed directly to an Android-based smartphone for Doppler spectrogram analysis and display in real-time. In order to verify the portable device, a Couette flow phantom was used to simulate the flowing blood for in vitro verification. Doppler spectrograms of porcine blood flow were measured using this stand-alone portable device under the pulsatile condition. Finally, the arterial blood flow of a volunteer carotid was measured in vivo to verify the performance of the smartphone-based portable PW Doppler ultrasound device. All of the results demonstrated the potential of using a smartphone as a novel embedded system for portable medical ultrasound applications.

A FPGA-based home-care ultrasound device for measuring the flow volume of arteriovenous fistula in dialysis patients

In general, kidney patients often have hemodialysis three to four times a week, and need to take few hours once. Before hemodialysis, the medical staff must often measure the flow volume within the vessel for the patient. If blood flow is found to be insufficient, it denotes that the blood vessels are blocked for some reasons. However, it is a very serious event for the patient, which means that patients cannot be hemodialysis and must be done the repair surgery of arteriovenous fistula immediately, otherwise it will cause the patients life risk. In order to reduce this occurrence, the surgeon suggested that could develop a device for the patients who can measure the blood flow volume by himself or families at home. In this study, we developed a FPGA-based home-care ultrasound device for measuring the flow volume of arteriovenous fistula in dialysis patients.

Implementation of a Wearable Ultrasound Device for the Overnight Monitoring of Tongue Base Deformation during Obstructive Sleep Apnea Events

Obstructive sleep apnea (OSA) is a breathing disorder characterized by the repeated collapse of the pharyngeal airway during sleep. Previous studies have reported that tongue base deformation may be a major contributing factor. However, overnight monitoring of tongue motion in patients with OSA has previously been impracticable. We developed a wearable ultrasound device for prolonged recording during natural sleep of the changes in tongue base thickness (TBT) in patients with OSA. The maximum TBT was fed into a polysomnography system so that physiologic signals and TBT data were simultaneously monitored. Subject trials revealed that TBT increased significantly during snoring, hypopnea and apnea events during natural sleep in patients with OSA. Moreover, the data revealed that the location of the maximum TBT during normal breathing was significantly different compared with the location during obstructive respiratory events, which implies a posterior or inferior displacement of the tongue base during sleep apnea.

In vivo analysis of adult zebrafish cardiac functions by Doppler-gated ultrahigh frame rate 80 MHz high frequency retrospective ultrasound imaging

The zebrafish has become a preferred animal model for studying cardiovascular developments. Recently, the high frequency ultrasound B-mode imaging has been utilized successfully to observe the heart of adult zebrafish. However, an ultrahigh frame rate echocardiography is needed in order to observe the detailed transient motions of zebrafish ventricle. In this study, the retrospective Doppler-gated technology was developed for this purpose. The frame rates of reconstructive B-mode and color flow images can respectively up to 40000 and 400 fps. Since the echocardiography exhibits high spatial and temporal resolutions, the transient motions of endocardium can be monitored for analyzing the ventricular functions of zebrafish. The timing of end diastole (ED) and end systole (ES) for ventricle were found by measuring the ventricular blood flow. Two ventricular function parameters, fractional shortening (FS) and fractional area change (FAC), were measured for evaluating the ventricular functions by using ED and ES with its corresponding ventricular dimension, respectively. The results indicated that the measured FSs were approximately 17% and 35% for long axis (LAx) and short axis (SAx), respectively, and the FAC was approximately 47%. All the results showed that retrospective high frequency echocardiography is an useful tool for studying the cardiac functions of normal adult zebrafish.

High frequency Doppler flow triggering for 75 MHz ultra-high frame rate 3D ultrasonic zebrafish echocardiography

The ultra-high frame rate 3D high frequency ultrasound zebrafish heart image was reconstructed by using the Doppler triggering method in this study. The detailed changes of zebrafish cardiac volume were monitored during the cardiac cycle. A 40 MHz pulsed wave Doppler flowmeter was built for measuring the Doppler spectrogram from zebrafish artery, and the timing of peak flow velocity was selected by analog circuits as a trigger signal to synchronize the 3D 75 MHz high frequency ultrasound imaging system. The high frame rate 2D and 3D echocardiographs were reconstructed by acquired A-line signals at different cardiac positions with high pulse repetition frequency (PRF). The imaging frame rate was independent from the speed of scan motor. However, it was determined by the PRF of ultrasonic pulser. The boundary between heart and other tissues was detected using a matching similarity processing which used the correlation algorithm to calculate the shift at each pixel window for 3D dynamic image reconstruction. A median filter was applied to move the noise before the image reconstruction. The adult zebrafish experimental results showed that the volume size of heart was changed approximately 12-14% between diastole and systole. Even though the single element transducer was used for scanning the zebrafish heart, this technology still can be applied to array system for high frame dynamic 3D imaging.