Fernando Reiszel Pereira

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 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.

Ultrasonic wave speed measurement using the time-delay profile of rf-backscattered signals

Conventional methods determine the ultrasonic wave speed by measuring the medium path length propagated by a pulsed wave and the corresponding time-of-flight. In this study, the wave speed is determined without the need of the path length. A transmitting transducer sends a pulsed wave into the medium (constant wave speed 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 measured 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 20 mm and beam width (-6 dB) of 2 mm at the focus was used together with a PZT hydrophone, 0.8 mm in aperture. The method was applied to three phantoms (wave speed of 1220, 1501 and 1715 m/s) and, in vitro, to fresh bovine liver sample, immersed in a temperature-controlled water bath. The results vary within 3% of those obtained with a conventional method.

Evaluation of Solid Content in Petroleum and Water in Oil Emulsion by Ultrasonic Spectroscopy

The presence of inorganic solids in petroleum can result in stable emulsions and sludge formation. Thus, it is important to know the solids content in petroleum. The most applied methodology to measure solid content (ASTM 4807) is not so simple to be done in a short time. In the case of emulsions, due to the complexity of the matrix, there is no method for measuring the solids content. It is possible the application of ultrasound spectroscopy to measure solids content in petroleum and emulsions, resulting in short times analysis and allowing more accurate processes control. For petroleum, it was observed a linear relationship between the attenuation of sound and solid content, especially for concentrations above 1%. In emulsions, a tendency was also observed, but the behavior was not totally linear, probably due to complex interactions of the matrix and the wave propagated through the medium.

In vitro ultrasound characterization of coronary arteries using temperature dependent wave speed

Temperature induced time shift of backscattered ultrasound is used to probe the temperature dependence of the speed of sound, /spl part/c//spl part/T. An Ultrasound Biomicroscope (UBM), with a PVDF transducer (center frequency=50.0 MHz), and a temperature controlled micropositioning sample cell was used. RF-backscattered signals were collected at 5 fixed temperatures of the bath, starting with 36/spl deg/C and in steps of 1/spl deg/C. The experimental results for the mean (/spl plusmn/ one standard deviation) of /spl part/c//spl part/T, in m/s/spl middot//spl deg/C, from the wall of human coronary arteries obtained at autopsy of 8 different samples from 4 individuals, were 2.20 (/spl plusmn/1.95), 4.32 (/spl plusmn/0.84) and -2.26 (/spl plusmn/1.33) for intima, media and adventitia layers, respectively. At the intima layer, /spl part/c//spl part/T appeared to decrease, from 4.29 to -0.05 m/s/spl middot//spl deg/C, as the disease progressed from mild intimal thickening to a more atherosclerotic state.