João Carlos Machado

An ultrasonic method to measure human plasma coagulation time

An ultrasonic method to measure coagulation time for prothrombin time (PT) is discussed. This method is based on the measurement of ultrasonic scattering from spherical glass particles of 200-microns diameter kept in motion, inside of a holder containing 0.1 ml of plasma, by ultrasonic energy. The incident wave (2.7 MHz) not only keeps the particle in motion but also is the source for the scattered waves. A receiving transducer captures part of the scattered wave and generates at its electrical output a signal containing amplitude and phase fluctuations. The motion of the particles are strongly influenced by the rheological changes during the process of coagulation. When the clot is formed, the amplitude of the motion of these particles is significantly reduced and so the fluctuations on the received signal stop. The time from the start of the coagulation process until the end of the fluctuations at the received signal is the coagulation time. Experimental results demonstrate that the ultrasonic method has precision and accuracy compatible to those provided by the manual tilt-tube method when PT is measured with normal and abnormal samples of human plasma.

Ultrasound characterization of coronary artery wall in vitro using temperature-dependent wave speed

Temperature dependence of the speed of sound, /spl part/c//spl part/T, is examined as a parameter to characterize tissue-equivalent phantoms and coronary artery tissue in vitro. The experimental system comprises an ultrasound biomicroscope, operating at center frequency of 50 MHz, and a temperature controlled micropositioning sample cell. Radio frequency (RF) backscattered signals were recorded, with a digital oscilloscope, from 64 independent positions and at 5 temperatures starting at 31/spl deg/C (phantom) and 36/spl deg/C (tissue) in steps of one degree. Time shift per degree Celsius (/spl part/t//spl part/T) was obtained with a correlation technique applied between gated sections of two RF-signals collected with one degree temperature difference from the same location in the sample. The average , calculated for every position of the gated sections along the propagation axis of the ultrasound beam, has the slope proportional to the difference between the linear coefficient of thermal expansion and the thermal sensitivity of the speed of sound. Calibration measurements of /spl part/c//spl part/T, made with single- and three-layer tissue equivalent phantoms, correlated well (r/spl ges/0.91) with those measured by the time-of-flight substitution method. The /spl part/c//spl part/T was estimated for the three layers on the wall of eight samples of human coronary arteries, obtained at autopsy from four individuals. The /spl part/c//spl part/T for the intima layers decreases as the disease progresses from mild intimal thickening to a more advanced atherosclerosis.

Ultrasonic integrated backscatter coefficient profiling of human coronary arteries in vitro

A theoretical formulation for the profile of the integrated backscatter coefficient (IBC) is derived. This new formulation is based on a theoretical treatment. It includes correction for the diffraction of the ultrasonic beam and correction for the non-ideal nature of the reference signal. The inclusion of these correction factors permits accurate quantitative profiling of the IBC over the transducer focal zone. Experimental measurements are first performed on well-calibrated vessel-equivalent phantom materials and subsequently on human coronary arteries in vitro. A spherically focused 50.0 MHz f/1.83 transducer is used. IBC profiles are shown for three samples that are representative of early, mid, and advanced atherosclerotic coronary disease. The IBC profiles clearly differentiate the arterial tissues. However, variation between samples with histologically confirmed intimal thickening (N=24) was large. The mean IBC (/spl plusmn/1 standard deviation), in (Sr.mm)/sup -1/, for media, adventitia, and thickened intima were 3.86/spl times/10/sup -3/, 1.53/spl times/10/sup -2/, and 2.24/spl times/10/sup -2/, respectively. The mean IBC of thickened intima is larger than previous measurements obtained from femoral arteries, and the mean IBC for media and adventitia layers are lower, reflecting differences in tissue composition between coronary and femoral vessels.

Measurement of plasma clotting time using ultrasonic shear waves

This work presents a method that employs ultrasonic shear waves in the determination of prothrombin time (PT) and activated partial thromboplastin time (APTT), two plasma tests, during the coagulation process. Two AT-cut quartz crystal transducers are used as transmitter and receiver, with a frequency of 2.0 MHz. During the coagulation process there are random fluctuations in the amplitude of the wave transmitted through the sample of plasma that cease once the clot is formed. The time interval during which these fluctuations occur is used to indicate the coagulation time for the plasma. The method, repeated 35 times over the same plasma sample, provided for the mean of PT and APTT 12.7 s and 23.4 s with standard deviations of 0.8 s and 2.1 s, respectively. These results are in accordance with those obtained for normal plasma by means of other clinical tests.

Ultrasonic wave speed measurement using the time-delay profile of rf-backscattered signals: Simulation and experimental results

Conventional methods determine the ultrasonic wave speed measuring the medium path length propagated by a pulsed wave and the corresponding time-of-flight. In this work, the wave speed is determined without the need of the path length. A transmit transducer sends a pulsed wave into the medium (wave speed constant along the beam axis) and the backscattered signal is collected by a hydrophone placed at two distinct positions near the transmitted beam. The time-delay profile, between gated windows of the two rf-signals received by the hydrophone, is determined using a cross-correlation method. Also, a theoretical time-delay profile is determined considering the wave speed as a parameter. The estimated wave speed is obtained upon minimization of the rms error between theoretical and experimental time-delay profiles. A PZT conically focused transmitting transducer with center frequency of 3.3 MHz, focal depth of 30 mm, and beam full width (-3 dB) of 2 mm at the focus was used together with a PZT hydrophone (0.8 mm of aperture). The method was applied to three phantoms (wave speed of 1220, 1540, and 1720 m/s) and, in vitro, to fresh bovine liver sample, immersed in a temperature-controlled water bath. The results present a relative speed error less than 3% when compared with the sound speed obtained by a conventional method.

Ultrasound biomicroscopy for biomechanical characterization of healthy and injured triceps surae of rats

SUMMARY This work describes the use of ultrasound biomicroscopy (UBM) to follow up the degeneration–regeneration process after a laceration injury induced in the lateral gastrocnemius (LG) and soleus (SOL) muscles of rats. UBM (40 MHz) images were acquired and used for biomechanical characterization of muscular tissue, specifically using pennation angle (PA) and muscle thickness (MT). The animals were distributed in three groups: the variability group (VG; N=5), the gastrocnemius injured group (GG; N=6) and the soleus injured group (SG; N=5). VG rats were used to assess data variability and reliability (coefficients of variation of 9.37 and 3.97% for PA and MT, respectively). GG and SG rats were submitted to the injury protocol in the LG and SOL muscles of the right legs, respectively. UBM images of muscles of both legs were acquired at the following time points: before and after injury (immediately, 7, 14, 21 and 28 days). We observed an increase in PA for the non-injured leg 28 days after injury for both GG and SG rats (GG=10.68 to 16.53 deg and SG=9.65 to 14.06 deg; P<0.05). Additionally, MT presented a tendency to increase (GG=2.92 to 3.13 mm and SG=2.12 to 2.35 mm). Injured legs maintained pre-injury PA and MT values. It is suggested that a compensatory hypertrophic response due to the overload condition imposed to healthy leg. The results indicate that UBM allows qualitative and quantitative muscle differentiation among healthy and injured muscle at different stages after lesion.

Study of cutaneous cell carcinomas ex vivo using ultrasound biomicroscopic images

Background: The ultrasound biomicroscopy (UBM) technique generates high‐resolution echographic images using acoustic frequencies between 20 and 200 MHz. In dermatology, it enables non‐invasive visualization of cutaneous structures. In this sense, several studies are being conducted for the measurement of cutaneous tumor sizes and for the evaluation of their response to therapeutic procedures. The present work was conducted to analyze the ability of UBM to identify diverse histological structures associated with cutaneous carcinomas ex vivo regarding the evaluation of the technique as a diagnostic tool that could, eventually, improve the patients healthcare protocol.

Structural adaptations of rat lateral gastrocnemius muscle-tendon complex to a chronic stretching program and their quantification based on ultrasound biomicroscopy and optical microscopic images.

BACKGROUND A chronic regimen of flexibility training can increase range of motion, with the increase mechanisms believed to be a change in the muscle material properties or in the neural components associated with this type of training. METHODS This study followed chronic structural adaptations of lateral gastrocnemius muscle of rats submitted to stretching training (3 times a week during 8weeks), based on muscle architecture measurements including pennation angle, muscle thickness and tendon length obtained from ultrasound biomicroscopic images, in vivo. Fiber length and sarcomere number per 100μm were determined in 3 fibers of each muscle (ex vivo and in vitro, respectively), using conventional optical microscopy. FINDINGS Stretching training resulted in a significant pennation angle reduction of the stretched leg after 12 sessions (25%, P=0.002 to 0.024). Muscle thickness and tendon length presented no significant changes. Fiber length presented a significant increase for the stretched leg (8.5%, P=0.00006), with the simultaneous increase in sarcomere length (5%, P=0.041) since the stretched muscles presented less sarcomeres per 100μm. INTERPRETATION A stretching protocol with characteristics similar to those applied in humans was sufficient to modify muscle architecture of rats with absence of a sarcomerogenesis process. The results indicate that structural adaptations take place in skeletal muscle tissue submitted to moderate-intensity stretching training.

Evaluation of an ultrasonic method applied to the measurement of blood coagulation time

Clinical assessment of the blood clotting mechanism is usually made by measuring the time necessary for a sample of plasma to clot. In this work a semi-automatic method for measuring coagulation time is evaluated. It employs ultrasound, at 2.7 MHz, for monitoring variations of the viscosity in a plasma sample undergoing coagulation. The evaluation is performed by comparing measurements obtained by two well-known methods, the manual tilt tube and the fibrometer, with those obtained using the ultrasonic method. A total of 330 plasma samples from individuals with normal and altered homeostatic process were analysed. The experimental protocol follows two standard tests: the prothrombin time (141 samples) and the activated partial thromboplastin time (189 samples). The agreement between the three different methods is estimated statistically and it is shown that all the three can be used interchangeably for clinical purposes.

Statistical Analysis of High Frequency Ultrasonic Backscattered Signals from Basal Cell Carcinomas

A statistical approach was implemented in the study of histologic characteristics from ex vivo basal cell carcinomas, based on the properties of backscattered acoustic waves, for the purpose of evaluating the method as a diagnostic tool. The study was developed using an ultrasound biomicroscope working at a frequency of 45 MHz. The parameters examined were signal-to-noise ratio (SNR), and shape parameters from the Weibull (b(W)) and generalized gamma (c(GG) and υ(GG)) probability density functions. Twenty-seven carcinomatous skin samples were obtained from volunteer patients and classified into two groups (BCC1 and BCC2) based on the distribution patterns of their tumor nests; also, seven non-tumoral samples were used for comparative purposes. Significant differences between groups were obtained for all studied parameters. The successful differentiation between some tissue groups suggests its potential use for carcinoma characterization.