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At least 793 records · Page 44Linked to original sources

PubMed2002

Performance of laser-ultrasonic F-SAFT imaging.

The resolution and signal-to-noise ratio of laser-ultrasonics to detect small and buried defects can be greatly enhanced by using the synthetic aperture focusing technique (SAFT). Originally developed in the time domain, SAFT can also be implemented in the frequency domain (F-SAFT) using the angular spectrum approach for a significant reduction in processing time. In this paper, an F-SAFT based data processing method especially adapted to laser-ultrasonic data is presented. This method allows for further significant improvements towards laser-ultrasonic imaging of small defects. It includes temporal deconvolution of the waveform data, control for an optimal aperture and frequency bandwidth as well as spatial interpolation of the subsurface images. All the above operations are well adapted to the frequency domain calculations and embedded in the F-SAFT data processing. Also, the aperture control and spatial interpolation allow a reduction of sampling requirements to further decrease both inspection and processing times. The above improvements are illustrated using laser-ultrasonic data taken from an aluminum sample with flat-bottom holes.

Journal Article↗

PubMed2003

Integration of a piezoelectric transformer and an ultrasonic motor.

Ultrasonic motors are usually operated at an AC voltage higher than a regular battery. This implies the need of a voltage step-up transformer. In this paper, we report the integration of a piezoelectric transformer (PT) with an ultrasonic motor and a simple drive circuit. The stator of the ultrasonic motor and the PT were operated in the same radial vibration mode. Their dimensions were very close to each other yielding nearly matching resonance frequencies. Consequently, they could be combined together without inductor. The drive circuit was designed by using a 555 timer as an astable multivibrator, and high-speed dual MOSFET drivers as a class D half-bridge switching amplifier. This integrated PT-ultrasonic motor performed reasonably without the use of electromagnetic transformer or inductor.

Journal Article↗

PubMed2000

Ultrasonic sensor properties characterized by a PC-controlled scanning measuring system

The use of ultrasonic sensors for process control is currently widespread for flow, level or distance measurements. Recently, interest has increased, too in the application of ultrasonic sensors to concentration measurements in complex liquids. In this application there are high demands for a defined and stable quality of the properties of both the sensor transfer function and the sound field characteristic. For a detailed investigation and characterization of ultrasonic sensor propertiess, an efficient PC-controlled measuring system was developed by the Institut fur Automation und Kommunikation (IFAK). In this contribution, this high performance approach is presented to make visible the vibrating ultrasonic sensor surface as well as the sound field in front of acoustic sensors in liquids.

Journal Article↗

PubMed2000

Laser ultrasonic surface wave inspection of alumina ceramics of varying density

In this paper, the surface acoustic wave velocity results acquired from the inspection of specially manufactured and characterised alumina ceramic materials are presented. Ultrasonic velocity data of alumina-based ceramics in the range 60-100% theoretical density was generated utilising non-contacting laser-ultrasonic measurements based on laser generation and detection of surface acoustic waves with the objective of creating a routine technique for industrial advanced alumina inspection. With linear fitting the surface acoustic wave velocity data serves as a calibration graph for using laser ultrasonics for routine monitoring of alumina. A second laser ultrasonic technique based on the laser generation and foil transducer detection of surface acoustic waves was used to validate the surface acoustic wave velocities measured by the laser generation/detection technique.

Journal Article↗

PubMed1996

Ultrasonic estimation of bladder weight as a measure of bladder hypertrophy in men with infravesical obstruction: a preliminary report.

The aim of the present study was to evaluate the usefulness of ultrasonic estimation of bladder weight as a measure of bladder hypertrophy using transabdominal ultrasonography in men with infravesical obstruction. Ultrasonically estimated bladder weight (UEBW) was calculated from the thickness of the bladder wall measured ultrasonically and the intravesical volume at the ultrasonic measurement, assuming a spheric bladder. There was a statistically significant correlation (r = 0.970, P <0.001) between the actual bladder weight of cadaver bladders and the UEBW. The UEBW did not change with bladder filling. The UEBW in the obstructed group (group O, 49.7 +/- 19.5 g, mean +/- SD) was significantly greater than that in the normal control group (group NC, 25.6 +/- 5.7 g; P <0.001) or the nonobstructed group (group NO, 28.4 +/- 4.2 g; P <0.001). The greatest UEBW was 34.8 g in group NC and 35.2 g in group NO, whereas 94% (45 of 48) of group O had a UEBW greater than 35.0 g. In all 5 patients with benign prostatic hyperplasia (BPH), the increased UEBW decreased to a normal control level at 3 months after treatment of BPH. This new noninvasive method may be useful in investigation of bladder hypertrophy.

Adult↗

PubMed1998

Validation of displacement measurements obtained from ultrasonic images during indentation testing.

Biomechanical features of soft tissue are commonly investigated by indentation, a procedure where a blunt probe is advanced and the ensuing deformation of the tissue surface recorded. If it were possible to visualize subsurface anatomy during the indentation process, biomechanical investigation of internal tissue features might be feasible. The purpose of this experiment was to determine the accuracy of ultrasonically-derived measures of displacement obtained during indentation testing of an ultrasonic phantom. Using a 5-MHz sector transducer mounted to an automated indentation device, ultrasonic estimates of distance between a stationary target surface and the moving ultrasonic transducer were obtained and validated to a criterion. Depending on the method used to locate the target surface on the resulting B-mode image, the mean displacement error ranged from 14.37% to 22.05%. Use of this protocol for human tissue assessment, in vivo or otherwise, may be appropriate if the displacements of interest are greater than the error of the procedure.

Algorithms↗

PubMed1999

Ultrasonic backscattering from porcine whole blood of varying hematocrit and shear rate under pulsatile flow.

It was shown previously that ultrasonic scattering from whole blood varies during a flow cycle under pulsatile flow both in vitro and in vivo. It has been postulated that this cyclic variation may be associated with the dynamics of red cell aggregation because the shearing force acting on the red cell aggregates across the lumen is a function of time during a flow cycle. In all studies, the local shear rate variation as a function of time is unknown. The effect of shear rate on the red cell aggregation and, thus, on ultrasonic scattering from blood can only be merely speculated. One solution to this problem is to estimate the shear rate in a flow conduit by finite element analysis (FEA). An FEA computational fluid dynamics (CFD) tool was used to calculate local shear rate in a series of experiments in which ultrasonic backscattering from porcine whole blood under pulsatile flow was measured as a function of hematocrit and shear rate intravascularly with a 10-MHz catheter-mounted transducer in a mock flow loop. The results show that, at 20 beats per min (BPM), the magnitudes of the cyclic variation for hematocrits at 30, 40, and 50% were approximately 4 dB. However, at 60 BPM, the magnitude of cyclic variation was found to be minimal. The results also confirm previous findings that the amplitude and the timing of the peak of ultrasonic backscattering from porcine whole blood under pulsatile flow during a flow cycle are dependent upon the shear rate and hematocrit in a complicated way.

Animals↗

PubMed2000

Ultrasonic wave action upon the red blood cell agglutination in vitro.

The ultrasonic wave action upon immune red blood cell (RBC) aggregation in vitro was investigated by means of the elastic light-scattering method. The RBC agglutination process in the ultrasonic wave presence was analysed as a function of irradiation time, the antiserum series, the whole blood and antiserum dilution degree and blood group types. It was experimentally shown that the ultrasonic irradiation accelerated the agglutination reaction in the blood and antiserum mixture. The sedimentation process showed a gain in the resolution of the optical method's ability to detect the induced RBC complex formation. It revealed that the ultrasonic application led to significant diagnostic test time shortening. The results may be used to develop new diagnostic techniques and devices.

Blood Grouping and Crossmatching↗

PubMed1997

Corneal thickness measurements with the Orbscan Topography System and ultrasonic pachymetry.

PURPOSE: To compare corneal thickness measurements obtained with a new instrument, the Orbscan Topography System, with those obtained with the DGH ultrasonic pachymeter and to assess the agreement and repeatability of the two devices. SETTING: LSU Eye Center, New Orleans, Louisiana, USA. METHODS: Measurement agreement was assessed in 51 eyes of 26 normal volunteers using both Orbscan and ultrasonic pachymetry. Repeatability for the instruments was measured in 10 eyes of 5 additional volunteers. Corneal thicknesses were compared using the analysis of variance (ANOVA). The relationship between the devices was assessed by analysis of regression (ANOR). RESULTS: In the measurement agreement experiment, the mean corneal thickness was 571.3 microm +/- 6.21 SEM with the Orbscan system and 543.3 +/- 7.49 microm with ultrasonic pachymetry; these values were significantly different (F test, ANOVA, P = .0048). In the repeatability experiment, the mean thickness was 561.1 +/- 8.42 microm with the Orbscan system and 537.4 +/- 5.84 microm with ultrasound pachymetry; these values were also significantly different (F test, ANOVA, P = .0003). Analysis of regression showed a significant linear regression between the values obtained with the devices (P = .0001, F test, ANOR). CONCLUSIONS: In both studies, the Orbscan system obtained statistically significantly different and higher values for corneal thickness. Regression analysis suggests that over the range of values in this study, the two devices differ by a constant amount (intercept and slope). The nonzero intercept of this regression shows that the values from the devices differ and cannot be directly substituted for each other. We therefore conclude that in this study, Orbscan system measurements of corneal thickness were 23 to 28 microm greater than ultrasonic pachymeter measurements. Linear regression equations may be developed for the results of measurements from the two devices and used as a precise transformation factor for the values obtained with the two devices.

Adult↗

PubMed1997

Standardizing constants for ultrasonic biometry, keratometry, and intraocular lens power calculations.

PURPOSE: To provide a method and values that facilitate standardization of constants for ultrasonic biometry, keratometry, and intraocular lens (IOL) power calculations. SETTING: University of Texas Medical School, Houston, Texas, USA. METHODS: Keratometry and ultrasonic biometry provide the two measured input variables for the six variable vergence equations used to calculate the appropriate IOL power for a specific patient with a cataract. A review of the literature reflecting the past 156 years of research and development reveals the appropriate index of refraction to be used with the keratometer for net optical corneal power, the location of the principal planes of the cornea, the nominal value for retinal thickness, and the appropriate velocities for ultrasonic measurement of the axial length. The relationship of the thick IOL to the thin IOL is derived along with the physical location of the thick lens. Two methods are described that provide the best IOL constant to be used by a manufacturer to minimize the prediction error for a surgeon using the lens for the first time. The formulas for phakic IOLs and secondary piggyback IOLs are also derived and applied to methods described above for standard IOLs. RESULTS: Using a standardized net index of refraction of 4/3 for the cornea eliminates a variability of 0.56 diopter (D) in the predicted refraction. Using a standardized 1532 m/s velocity for axial length measurements and adding a value of 0.28 mm reduces the tolerance of axial length measurements to +/-0.03 mm for any length eye. The physical location of the thick IOL's secondary principal plane must be anterior to the thin lens equivalent by approximately the separation of the principal planes of the thick lens. For biconvex poly(methyl methacrylate) IOLs, the separation in the principal planes is approximately 0.10 mm. Using these relationships, the physical position of the thick lens within the eye can be used to confirm the lens constant for any IOL style. CONCLUSIONS: Standardizing the constants for keratometry, ultrasonic biometry, and IOL power calculations can significantly improve the predictability of refractive outcomes. Back-calculating and physically measuring the position of the lens within the eye can provide surgeons with an initial lens constant known to have a standard error of the mean of +/-0.05 mm (+/-0.10 D). Other parameters such as the cardinal points of a lens, the shape factor, the lens-haptic plane, and the center lens thickness would allow further refinement of IOL power calculations.

Adult↗

PubMed1998

Accuracy of ultrasonic pachymetry and videokeratography in detecting keratoconus.

PURPOSE: To compare the accuracy of ultrasonic pachymetry measurements and videokeratography-derived indices in distinguishing keratoconus patients from those with normal eyes. SETTING: A subspecialty cornea practice (Los Angeles, California, USA) and the Keratoconus Genetics Research Project. METHODS: Corneal thickness was measured by ultrasonic pachymetry at the center and inferior margins of the pupil of 142 normal and 99 keratoconus patients The corneal surface topography of patients was studied with the Topographic Modeling System (TMS-1). The videokeratographs obtained were analyzed with a computer program that automatically calculates two indices derived from data points in the central and paracentral cornea: central K and I-S values. Linear discriminant analysis was used to determine the correct classification percentages using pachymetry measurements and indices derived from videokeratography as the independent variables. RESULTS: The range of corneal thickness in normal and keratoconic eyes overlapped considerably. In the discriminant analysis, videokeratography indices provided a 97.5% correct classification rate and pachymetry data, an 86.0% rate (P < .01, McNemar's test). CONCLUSION: Keratoconus is more accurately distinguished from the normal population by videokeratography-derived indices than by ultrasonic pachymetry measurements. This may be due to the large variation in corneal thickness in the normal population or the inability of ultrasonic pachymetry to accurately detect the location of corneal thinning in keratoconus by measuring standard points on the cornea. Pachymetry should not be relied on to exclude or diagnose keratoconus because the false-negative and false-positive rates are unacceptably higher than those obtained by videokeratography.

Cornea↗

PubMedDate not supplied

Dobutamine stress ultrasonic myocardial tissue characterization in patients with dilated cardiomyopathy.

Although acoustic properties of the myocardium are different between patients with cardiomyopathy and normal subjects, the frequency of the abnormal properties in patients with cardiomyopathy is unknown. We assessed the frequency of abnormal acoustic properties of the myocardium detectable with integrated backscatter in patients with cardiomyopathy and attempted more sensitive ultrasonic tissue characterization by combining dobutamine stress testing in patients with cardiomyopathy with apparently normal acoustic properties of the myocardium at rest. The magnitude of cyclic variation of integrated backscatter and calibrated myocardial integrated backscatter at end diastole were measured in 36 normal subjects and 40 patients with dilated cardiomyopathy. Either one of the integrated backscatter parameters was abnormal in 30 of 40 patients with cardiomyopathy. Dobutamine stress ultrasonic tissue characterization was performed in 10 patients with cardiomyopathy with normal values of both integrated backscatter parameters and 10 normal subjects. Calibrated myocardial integrated backscatter did not change during dobutamine infusion in any subject. The magnitude of cyclic variation in integrated backscatter increased in normal subjects but did not change in patients with cardiomyopathy despite a comparative associated increase in the systolic wall thickening during dobutamine infusion. Abnormal acoustic properties are detectable at rest with myocardial integrated backscatter about in three quarters of patients with cardiomyopathy. A combination of dobutamine stress testing would provide more sensitive ultrasonic myocardial tissue characterization and may make it possible to detect subtle changes in the acoustic properties of the myocardium in patients with dilated cardiomyopathy. Therefore dobutamine stress ultrasonic tissue characterization may detect mild dilated cardiomyopathy.

Adult↗

PubMed2000

Mechanical properties of bovine aortic endothelial cells in suspension studied by ultrasonic interferometry.

OBJECTIVE: Cell adhesion phenomenon has been extensively studied in the last decade and was shown to be mediated by specialized molecules and driven by physical forces. Cohesion of the vessel wall cells is also dependent on adhesion molecules but less is known about the physical forces involved. To investigate endothelial cell/endothelial cell interaction from a mechanical point of view, we have used an ultrasonic interferometry device, named EchoCell, which has been previously designed to study red blood cell-red bood cell (RBC-RBC) interaction. METHODS: Bovine aortic endothelial (BAE) cells were cultured, detached, then suspended in buffer and their mechanical and geometrical properties studied with the EchoCell system. The ultrasonic apparatus measures both the accumulation rate of cells in suspension on a solid plate and the acoustical impedances of the suspension and the sediment. RESULTS: In suspension, BAE exhibited, in our experimental conditions (3x10(6) cells per ml), a spherical size evaluated by calculation at a mean radius of 7+/-2 microm. Moreover, no BAE aggregation occurred at the concentrations used. The acoustical impedance of the BAE suspensions calculated from all the samples studied, in the cell concentration range from 1.5x10(6) to 6x10(6) cells per ml, was 1.52x10(6) Rayl (kg m(-2) s(-1)). Furthermore, the acoustical impedance of the cell sediment was found to be independent on the initial cell suspension concentration and equal to 1.63x10(6) Rayl (kg m(-2) s(-1)). Estimation of the volume fraction of BAE inside the sediment allows to evaluate the ultrasonic velocity and the elastic bulk modulus of cells. CONCLUSION: The ultrasonic interferometry method appears particularly interesting to study geometrical and mechanical (acoustical impedance, sound velocity, elastic bulk modulus) properties of BAE cells.

Animals↗

PubMed1998

Stereoscopic visualization of three-dimensional ultrasonic data applied to breast tumours.

OBJECTIVE: This paper presents a technique for stereoscopic visualization applied to three-dimensional (3D) ultrasonic breast data. METHODS: A motorized acquisition system has been designed to translate regularly a linear-phased array transducer, in order to provide a series of parallel echographic slices of the breast. During acquisition, the breast is compressed between a plane support and a plexiglass plate to avoid breast motion. A window in this plate provides access for ultrasonic exploration. From the series of cross-sectional scans, a 3D volume is formed by interpolation between the successive ultrasonic images. A stereoscopic computer-graphic method has been developed to visualize these 3D ultrasonic data. Two conical transparent projections of the volume are computed from two slightly different viewpoints. These two projections make up the stereoscopic pair. This pair is displayed on a stereoscopic monitor for the visualization of the 3D data with the depth dimension. RESULTS: The acquisition system and the method for computing the stereo-echograms were validated using an agar gel phantom. In vivo breast experiments were also performed. CONCLUSION: Visualization of stereo-echographic projections improves the perception of depth and shape of breast tumours.

Breast Diseases↗

PubMed2000

Ultrasonic parameters and relationship between compressive strength, microstructure of gall bladder stones.

Patients with symptomatic stones are at a great risk for complications and these complications are a major cause of morbidity. The gall bladder stones may have a complex structure and variable composition. In the present investigation stones have been grouped into three categories namely cholesterol, bilirubinate and mixed, and a correlation between the surface structure, ultrasonic parameters and compressive strength is estimated. A double-probe through-transmission technique was used for the ultrasonic parameters study, a universal testing instrument for hardness and a scanning electron microscope (SEM) for microstructure study. Gall bladder stones of mixed type with higher ultrasonic velocity, less attenuation and higher crushing strength were found to be more difficult to break in comparison to other types of stones. SEM of mixed type stones showed rough surface as compared to bilirubinate and cholesterol stones. The results obtained as well as the relationship might be useful in the design of a focussed ultrasonic 0lithotripter.

Cholelithiasis↗

PubMed2000

Phase-transfer catalysis and ultrasonic waves. I. Cannizzaro reaction.

The aim of this work is to study the effect of an ultrasonic wave on the Cannizzaro reaction catalyzed by a phase-transfer catalyst. The reaction of benzaldehyde with potassium hydroxide was chosen as the reference reaction. The kinetics of the reaction was followed by the amount of benzoic acid which is well characterized and easily isolatable. Investigations were made on variables such as the kind of aldehyde, the phase-transfer catalyst, the temperature and the frequency of ultrasonic wave. As the phase-transfer catalyst depends strongly on mass transfer between two phases, it is well understood that ultrasonic waves have a greater efficiency of interface mixing than conventional agitation. The results showed that an ultrasonic wave of 20 kHz dramatically accelerates on the reaction.

Journal Article↗

PubMed2000

A comparative study between classical stirred and ultrasonically-assisted dead-end ultrafiltration.

The aim of this work was to determine mass transfer coefficients in the cases of ultrasonically-assisted and classical stirred dead-end ultrafiltration. A comparative study was then performed, and mass transfer coefficients obtained under ultrasonic conditions are described by an empirical model. This correlation results from an analogy with what is observed using a stirred cell and involves the ultrasonic power as the main parameter. The hydrodynamics are assumed to depend on the intensity of the ultrasound effects illustrated by the agitation arising within the cell. This agitation is due to convective currents as well as physical effects due to cavitation. The concentration polarization phenomenon is therefore affected by this action of ultrasonic waves.

Journal Article↗

PubMed2003

Ultrasonic-induced nucleation of ice in water containing air bubbles.

Cavitation induced by ultrasonic vibrations can cause nucleation of ice in supercooled water. In this study, the time required for ultrasonic-induced nucleation of ice was measured for water containing two different size distributions of air bubbles. When the water was supersaturated with air bubbles, there was a time lag of about 0.5 s between the onset of ultrasonic irradiation and the onset of ice nucleation, and the probability of ice nucleation was unusually high within 0.5-1.1 s after the onset of ultrasonic irradiation. These results cannot be explained by conventional models alone, in which the collapse of a cavitation bubble triggers the nucleation of ice. Secondary effects appear to also influence ice nucleation.

Journal Article↗