Shyh Hau Wang

Interlaboratory comparison of ultrasonic backscatter, attenuation, and speed measurements.

In a study involving 10 different sites, independent results of measurements of ultrasonic properties on equivalent tissue‐mimicking samples are reported and compared. The properties measured were propagation speed, attenuation coefficients, and backscatter coefficients. Reasonably good agreement exists for attenuation coefficients, but less satisfactory results were found for propagation speeds. As anticipated, agreement was not impressive in the case of backscatter coefficients. Results for four sites agreed rather well in both absolute values and frequency dependence, and results from other sites were lower by as much as an order of magnitude. The study is valuable for laboratories doing quantitative studies.

An approach for measuring ultrasonic backscattering from biological tissues with focused transducers

When the standard substitution method is used with a focused transducer to measure the backscattering coefficient from biological tissues including blood, it yields erroneous results. Extending the backscattering measurements to frequencies beyond 15 MHz necessitates the use of focused transducers because of the worsened signal-to-noise ratio-caused by the increased attenuation and the smaller transducer aperture size-in order to make the measurements close to the transducer. An approach which allows the use of focused transducers in backscattering measurements has been developed. It has been used to measure the backscattering coefficient of red cell suspensions of hematocrit ranging from a few percent to 30% in the frequency range from 5 MHz to 30 MHz. The results at hematocrits below 20% agree well with those obtained with the standard substitution method, although they differ as the hematocrit is increased beyond 20%. The experimental results also show that the fourth-power dependence of backscatter on frequency is in general approximately valid for suspended erythrocytes of hematocrit between 6% and 30%.

Feasibility study of using high-frequency ultrasonic Nakagami imaging for characterizing the cataract lens in vitro.

A cataract is a clouding of the crystalline lens that reduces the amount of incoming light and impairs visual perception. Phacoemulsification is the most common surgical method for treating advanced cataracts, and determining the optimal phacoemulsification energy is dependent on measuring the hardness of the lens. This study explored the feasibility of using an ultrasonic parametric image based on the Nakagami distribution to quantify the lens hardness. Youngs modulus was measured in porcine lenses in which cataracts had been artificially induced. High-frequency ultrasound at 35 MHz was used to obtain the B-mode and Nakagami images of the cataract lenses. The averaged integrated backscatter and Nakagami parameters were also estimated in the region of interest. The experimental results show that the conventional B-scan and integrated backscatter are inadequate for quantifying the lens hardness, whereas Nakagami imaging allows different degrees of lens hardening to be distinguished both globally and locally based on the concentration of fiber coemption therein.

A linear relation between the compressibility and density of blood

By considering the blood as a mixture of ultrafiltrate and protein concentrate, the additive nature of compressibility and density from the components is utilized to deduce a linear relation between the compressibility and density for blood. This deduction also indicates that the intercept and slope of the linear relation are independent of the hematocrit, plasma protein concentration, and hemoglobin concentration of red blood cells. To verify experimentally this linear relation, saline and plasma dilutions on porcine or canine blood flowing in an extracorporeal circuit were carried out. The hematocrit of the experiments ranges from 0% to 55% and the plasma protein concentration ranges from 10 to 90 g/l. A resonance device in the circuit measured the density rhob of blood at 37 degrees C and an ultrasound system measured the sound velocity cb. The range of density is from 1,010 to 1,060 g/l and that of sound velocity is from 1,530 to 1,580 m/s. The linear relation that best fits the data of compressibility [computed as (rhob cb(2))-1] and density has a correlation coefficient of 0.9978. The linear relation is found to fit well the dependence of compressibility on density derived from the sound velocity data of human, horse, and porcine blood in the literature.

In vivo measurements of ultrasonic backscattering in blood

Ultrasonic backscattering in blood including its dependence on the hematocrit, plasma proteins, shear rate, and flow disturbance, has been studied extensively theoretically and experimentally in vitro. However, much of the result has never been validated in vivo. To do so, backscattering measurements were made on pigs using a 10-MHz non-focused intravascular transducer in direct contact with blood. The probe was placed in either the abdominal aorta or the inferior vena cava. The backscattering coefficient (BSC) of blood flowing in these vessels as well as downstream from a stenosis was measured using an approach that was originally developed for measurements with focused transducers. With this approach, 6% porcine red cell saline suspensions prepared immediately after each in vivo measurement were used as the reference medium. Result from seven pigs at hematocrits ranging from 29 to 36% (31.9/spl plusmn/2.5%) demonstrated that BSC of blood in the vena cava, (4.62/spl plusmn/2.06)/spl times/10/sup -5/ cm-sr/sup -1/, is consistently higher than that in the aorta, (2.65/spl plusmn/1.22)/spl times/10/sup -5/ cm-sr/sup -1/. The difference has been attributed to the lower shear rate and the formation of red cell aggregation in venous blood. These in vivo results are in agreement with those obtained in vitro. In response to stenoses created by ligating the aorta, backscattering of the blood measured downstream from the stenosis showed that the closer the site of measurement relative to the stenosis, the higher the backscatter, presumably resulting from the higher degree of flow disturbance. In vitro backscattering results on porcine whole blood were also acquired at 20 MHz with a Diasonics intravascular scanner.

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.

Some considerations on the measurements of mean frequency shift and integrated backscatter following administration of albunex

Ultrasonic contrast agents have been of heightened interest in recent years. More success has been achieved by agents consisting of micro bubbles, since only a few of these agents are capable of producing very strong ultrasonic backscattered signals for the enhancement of certain tissue structures. Recent investigations also demonstrate that an analysis of the radio frequency (RF) backscattered echoes by the contrast agents may lead to quantitative means for assessing tissue perfusion. In these studies, a parameter, mean frequency shift (MFS) of the RF signal, along with integrated backscatter (IB) has received the most attention. In an effort to better understand the physical mechanisms responsible for the observed mean frequency shift, we have performed experiments on 10 dogs following injections of Albunex (Molecular Biosystems, Inc.) into the left atrium, coronary artery and abdominal aorta, respectively, for investigations in the heart and kidney. The integrated backscatter and mean frequency (MF) of a region of interest (ROI) were calculated from the RF signal acquired with a modified real-time ultrasonic scanner. The results show consistently that the RF signals acquired from all regions of interest are greatly affected by the presence of the contrast agent in the path between the transducer and the ROI, which can cause either an upward or a downward shift of the MF. This could not be observed by video densitometry or a measurement of the IB alone. The MFS is the result of the resonant behavior of the micro bubbles, which is related to the frequency, ambient pressure, and physical properties of the bubbles including size distribution, surface tension and concentration. On the other hand, when there is no contrast agent present in the path, a downward frequency shift is seen.

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.