Chih Chung Huang

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.

Characterization of lamina propria and vocal muscle in human vocal fold tissue by ultrasound Nakagami imaging

PURPOSEnA number of ultrasound techniques have been applied to identify the biomechanical properties of the vocal folds. These conventional ultrasound methods, however, are not capable of visually mapping the concentration of collagen and elastic fibers in the vocal folds in the form of a parametric image. This study proposes to use a statistical parameter, the Nakagami factor estimated from the statistical distribution of the ultrasonic signals backscattered from tissues, as a means for parametric imaging of the biomechanical properties of the vocal folds.nnnMETHODSnThe ultrasonic backscattered signals were acquired from four larynges (eight vocal folds) obtained from individuals without vocal fold pathology for constructing the Nakagami images. The textures of the Nakagami image in the lamina propria (LP) and the vocal muscle (VM) were observed and compared. The average and standard deviation of the Nakagami parameter for the LP and the VM were also calculated.nnnRESULTSnThe results showed that the Nakagami parameter of the LP is larger than that of the VM. Moreover, the LP and the VM have different shading features in the Nakagami images. It was found that the Nakagami parameter may depend on the concentration of collagen and elastic fibers, demonstrating that the Nakagami imaging may allow visual differentiation between the LP and the VM in the vocal folds.nnnCONCLUSIONSnCurrent preliminary results suggested that the high-frequency Nakagami imaging may allow real-time visual characterization of the vocal fold tissues in clinical routine examinations.

Cyclic Variations of High-Frequency Ultrasonic Backscattering From Blood Under Pulsatile Flow

It was shown previously that ultrasonic scattering from whole blood varies during the flow cycle under pulsatile flow both in vitro and in vivo. It has been postulated that the cyclic variations of the backscattering signal are associated with red blood cell (RBC) aggregation in flowing whole blood. To obtain a better understanding of the relationship between blood backscattering and RBC aggregation behavior for pulsatile flowing blood, the present study used high-frequency ultrasound to characterize blood properties. The backscattering signals from both whole blood and an RBC suspension at different peak flow velocities (from 10 to 30 cm/s) and hematocrits (20% and 40%) under pulsatile flow (stroke rate of 20 beats/min) were measured with 3 single-element transducers at frequencies of 10, 35, and 50 MHz in a mock flow loop. To avoid the frequency response problem of a Doppler flowmeter, the integrated backscatter (IB) and flow velocity as functions of time were calculated directly using RF signals from flowing blood. The experimental results showed that cyclic variations of the IB curve were clearly observed at a low flow velocity and a hematocrit of 40% when using 50 MHz ultrasound, and that these variations became weaker as the peak flow velocity increased. However, these cyclic variations were detected only at 10 cm/s when using 10 MHz ultrasound. These results demonstrate that a high flow velocity can stop the formation of rouleaux and that a high hematocrit can promote RBC aggregation to produce cyclic variations of the backscattering signal under pulsatile flow. In addition, slight cyclic variations of the IB curve for an RBC suspension were observed at 35 and 50 MHz. Furthermore, the peak of the IB curve from whole blood led the peak of the velocity waveform when using high-frequency ultrasound, which could be explained by the assumption that a rapid flow can promote RBC aggregation under pulsatile flow. Together, the experimental results showed that the sensitivity and resolution of detecting blood properties are higher for 50 MHz ultrasound than for 10 MHz ultrasound.

High frequency ultrasonic characterization of human vocal fold tissue

Recently, endolaryngeal sonography at frequencies ranging from 10 to 30MHz has been found to be useful in diagnosing diseases of the vocal folds (VFs). However, image resolution can be further improved by ultrasound at higher frequencies, necessitating the measurement of high-frequency acoustic properties of VF tissue. The ultrasonic parameters of integrated backscatter, sound velocity, and frequency-dependent attenuation coefficient were measured in both the lamina propria (LP) and vocalis muscle (VM) of human VFs using a 47MHz high-frequency ultrasonic transducer. The integrated backscatter was −173.44±6.14 (mean±s.d.) and −195.13±3.58dB in the LP and VM, respectively, the sound velocity was 1667.68±44.9 and 1595.07±39.33m∕s, and the attenuation coefficient at 47MHz was 8.28±1.72 and 7.17±1.30dB∕mm. The difference between these ultrasonic parameters may be attributed to variations in the structure and fiber concentrations in VF tissue. These results could serve as a useful clinical reference for the fur...

Assessment of Blood Coagulation Under Various Flow Conditions With Ultrasound Backscattering

Several in vitro studies have employed ultrasonic techniques to detect varying properties of coagulating blood under static or stirred conditions. Most of those studies mainly addressed on the development and feasibility of modalities and however were not fully considering the effect of blood flow. To better elucidate this issue, ultrasonic backscattering were measured from the coagulating porcine blood circulated in a mock flow loop with various steady laminar flows at mean shear rates from 10 to 100 s-1. A 3 ml of 0.5 M CaCl2 solution for inducing blood coagulation was added to that of 30 ml blood circulated in the conduit. For each measurement carried out with a 10-MHz transducer, backscattered signals digitized at 100-MHz sampling frequency were acquired for a total of 20 min at temporal resolution of 50 A-lines per s. The integrated backscatter (IB) was calculated for assessing backscattering properties of coagulating blood. The results show that blood coagulation tended to be increased corresponding to the addition of CaCl2 solution: the IB was increased approximately 6.1 plusmn 0.6 (mean plusmn standard deviation), 5.4 plusmn 0.9, and 4.5 plusmn 1.2 dB at 310 plusmn 62, 420 plusmn 88, and 610 plusmn 102 s associated with mean shear rates of 10, 40, and 100 s-1, respectively. The rate of increasing IB for evaluating the growth of clot was estimated to be 0.075 plusmn0.017,0.052 plusmn0.027, and 0.038 plusmn 0.012 DeltadB Deltas-1 corresponding to the increase of mean shear rates. These results consistently demonstrate that higher shear rate tends to prolong the duration for the flowing blood to be coagulated and to decrease the rate of IB. Moreover, the laminar flow was changed to turbulent flow during that the blood was clotting discerned by spatial variations of ultrasound backscattering in the conduit. All these results validate that ultrasound backscattering is feasible to be utilized for detecting and assessing blood coagulation under dynamic conditions.

Characterization of Blood Properties from Coagulating Blood of Different Hematocrits Using Ultrasonic Backscatter and Attenuation

The influence of hematocrit on the change of blood properties during coagulating was extensively investigated using ultrasonic integrated backscatter and attenuation. Measurements were performed with porcine blood at hematocrits ranging from 25 to 55% using a 10 MHz transducer. Results showed that both integrated backscatter and attenuation are able to sensitively differentiate various stages of blood properties during coagulating. The slopes of integrated backscatter (Sr, dB/S) and attenuation (αr, dBcm-1MHz-1mS-1) are increased relative to hematocrit. The best fits for Sr and αr as a function of hematocrit (H) equal to Sr=0.0357+1.62e-0.108H and αr=0.0281+0.003H, respectively. Variations of clotting time (Ts) and reaction time (Tα), estimated respectively from ultrasonic integrated backscatter and attenuation, associated with clot formation are also increased with hematocrit. This study demonstrates that blood hematocrit is a substantial factor affecting viscosity and backscattering properties of blood during coagulation capable of being discerned by ultrasonic backscattering and attenuation.

Quantitative assessments of burn degree by high-frequency ultrasonic backscattering and statistical model

An accurate and quantitative modality to assess the burn degree is crucial for determining further treatments to be properly applied to burn injury patients. Ultrasounds with frequencies higher than 20 MHz have been applied to dermatological diagnosis due to its high resolution and noninvasive capability. Yet, it is still lacking a substantial means to sensitively correlate the burn degree and ultrasonic measurements quantitatively. Thus, a 50 MHz ultrasound system was developed and implemented to measure ultrasonic signals backscattered from the burned skin tissues. Various burn degrees were achieved by placing a 100 °C brass plate onto the dorsal skins of anesthetized rats for various durations ranged from 5 to 20 s. The burn degrees were correlated with ultrasonic parameters, including integrated backscatter (IB) and Nakagami parameter (m) calculated from ultrasonic signals acquired from the burned tissues of a 5 × 1.4 mm (width × depth) area. Results demonstrated that both IB and m decreased exponentially with the increase of burn degree. Specifically, an IB of -79.0 ± 2.4 (mean ± standard deviation) dB for normal skin tissues tended to decrease to -94.0 ± 1.3 dB for those burned for 20 s, while the corresponding Nakagami parameters tended to decrease from 0.76 ± 0.08 to 0.45 ± 0.04. The variation of both IB and m was partially associated with the change of properties of collagen fibers from the burned tissues verified by samples of tissue histological sections. Particularly, the m parameter may be more sensitive to differentiate burned skin due to the fact that it has a greater rate of change with respect to different burn durations. These ultrasonic parameters in conjunction with high-frequency B-mode and Nakagami images could have the potential to assess the burn degree quantitatively.

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.

Estimating the viscoelastic modulus of a thrombus using an ultrasonic shear-wave approach.

PURPOSEnMeasurements of the viscoelastic properties of a thrombus can be used to assess whether blood clots are likely to become occlusive or to break apart and leak into the blood circulation and block smaller vessels. An accurate method for estimating both the shear elasticity and viscosity of a blood clot in vivo is still lacking, which prompted us to use a novel shear-wave approach to measure the viscoelastic modulus of blood clots.nnnMETHODSnThe shear-wave dispersion ultrasound vibrometry was used to measure both the elasticity and viscosity of blood clots. The experimental system was verified by measuring the viscoelastic modulus of phantoms containing gelatin at different concentrations. Blood-clot experiments were carried out using porcine whole blood with hematocrits ranging from 3% to 40%. The measured values for both clots and gelatin phantoms were compared to those obtained using an embedded-sphere method in order to validate the accuracy of the viscoelastic modulus estimations.nnnRESULTSnThe shear elastic modulus increased from 406.9 ± 15.8 (mean ± SD) Pa for 3% gelatin to 1587.2 ± 28.9 Pa for 7% gelatin, while the viscosity increased from 0.12 ± 0.02 Pa s to 0.86 ± 0.05 Pa s, respectively. The shear modulus increased from 196.8 ± 58.4 Pa for 40%-hematocrit clots to 641.4 ± 76.3 Pa for 3%-hematocrit clots, while the viscosity increased from 0.29 ± 0.02 Pa s to 0.42 ± 0.01 Pa s, respectively.nnnCONCLUSIONSnThe results from the statistical analysis indicated that both the embedded-sphere and shear-wave approaches can provide accurate estimations of the shear elasticity for clots and gelatin phantoms. In contrast, the shear-wave approach as well as other methods of rheological measurements does not provide accurate viscosity estimations for blood clots. However, the measured viscosity range of 0.29-0.42 Pa s is reasonable for blood clots.

High-Resolution Acoustic-Radiation-Force-Impulse Imaging for Assessing Corneal Sclerosis

In ophthalmology, detecting the biomechanical properties of the cornea can provide valuable information about various corneal pathologies, including keratoconus and the phototoxic effects of ultraviolet radiation on the cornea. Also, the mechanical properties of the cornea can be used to evaluate the recovery from corneal refractive surgeries. Therefore, noninvasive and high-resolution estimation of the stiffness distribution in the cornea is important in ophthalmic diagnosis. The present study established a method for high-resolution acoustic-radiation-force-impulse (ARFI) imaging based on a dual-frequency confocal transducer in order to obtain a relative stiffness map, which was used to assess corneal sclerosis. An 11-MHz pushing element was used to induce localized displacements of tissue, which were monitored by a 48-MHz imaging element. Since the tissue displacements are directly correlated with the tissue elastic properties, the stiffness distribution in a tiny region of the cornea can be found by a mechanical B/D scan. The experimental system was verified using tissue-mimicking phantoms that included different geometric structures. Ex vivo cornea experiments were carried out using fresh porcine eyeballs. Corneas with localized sclerosis were created artificially by the injection of a formalin solution. The phantom experiments showed that the distributions of stiffness within different phantoms can be recognized clearly using ARFI imaging, and the measured lateral and axial resolutions of this imaging system were 177 and 153 μm, respectively. The ex vivo experimental results from ARFI imaging showed that a tiny region of localized sclerosis in the cornea could be distinguished. All of the obtained results demonstrate that high-resolution ARFI imaging has considerable potential for the clinical diagnosis of corneal sclerosis.