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Biomedical subjects

F E Barber

Publications and source records attributed to F E Barber.

12 recordsLinked to original sources
PubMed1991

The scanning acoustic microprobe: I. Analysis and synthesis of a spherically symmetric point spread function.

The scanning acoustic microprobe is a novel system which probes and characterizes, from a limited acoustic window, the fine-scale structural features of an object, point-by-point, using a multiplicity of acoustic pulses all aimed and focused at that point. Spherically symmetric, three-dimensional Gaussian pulses are synthesized to measure the backscatter diffraction pattern of the least-resolvable volume of scatterers centered at the point in question. The size and distribution of the scattering volume is forced to be constant, independent of frequency and angle. This method is analytically simple, compared with other pulse-echo techniques, and is applicable to scatterers ranging continuously in size from Rayleigh scatterers to specular reflectors. This is the first of a number of papers describing the development and application of systems based on these concepts. The analytical principles will be described herein for examination of one point at a time. In a companion paper appearing in this issue [F. E. Barber, J. Acoust. Soc. Am. 90, 11-19 (1991)], application to measurement and characterization of a discrete, flat, circular "piston" will be presented. Application to human tissue imaging and tissue characterization will be described in a subsequent third paper. The primary features detected experimentally are the strength of nondirective patterns, and the strength, orientation, and directivity of angle-dependent echo functions associated with planar or layered structures. Fine-scale structural features of a scattering center are obtained either by pattern recognition in k(data) space or inverse Fourier transformation. It is shown that when the bandwidth criteria are met to produce a spherically symmetric point spread function, scattering phenomena are completely described by only two parameters, namely the center frequency of the pulse-echo system and the characteristic diameter of the Gaussian point spread function.

Computer Simulation↗
PubMed1991

The scanning acoustic microprobe: II. Application to the measurement and characterization of a piston reflector.

In a pulsed ultrasound beam, echoes detected from a flat, circular piston of arbitrary size depend on the time-space characteristics of the entire pulse-echo measurement system, being a function of as many parameters as it takes to accurately define the system. In the limiting case of a target that is small relative to the spatial extent of an interrogating plane wave, an echo pattern is known to be a relatively simple function of the dimensionless product k0b, where k0 is the wave number and b is the radius of the target. In a companion paper preceding this one [F. E. Barber, J. Acoust. Soc. Am. 90, 8-17 (1991)], the author has described the scanning acoustic microprobe, a pulse-echo system in which the time-space properties of the interrogating waves are specified completely by k0 and a single additional parameter s0, which is the characteristic radius of a spherically symmetric, Gaussian-distributed scattering volume. In this system, the reflection pattern of a flat, circular piston of any arbitrary size is thus a function of two dimensionless parameters, namely k0b and b/s0. In this paper, this functional relationship is derived, a physical system is described, and analytical and experimental results are reported. It is shown that the diameter, orientation, and impedance mismatch properties of this simple target can be measured unambiguously over a range of target sizes from about a wavelength (2 pi/k0) to a beam diameter (about 3s0). For a typical ultrasound system, this is about a 5-1 range; i.e., a range extending to target sizes about five times smaller than can be detected in a simple B-mode imaging system.(ABSTRACT TRUNCATED AT 250 WORDS)

Computer Simulation↗
PubMed1987

An improved ultrasound simulation model: use in evaluating log versus linear processing for lesion detection.

This paper reports the development of an improved three-dimensional computer simulation model for evaluation of ultrasonic imaging systems. This model was used to successfully evaluate a signal processing method for improving lesion detection in ultrasound imaging. Linear processing of the rf signal amplitudes from a limited region of tissue was compared with the logarithmic compression employed by most commercial scanners. Two lesions were simulated by spherical distributions of scatterers having backscatter coefficients greater than the scatterers in the surrounding medium. Linear processing improved the differential contrast by a factor of about two. The simulation is based on the three-dimensional distribution of acoustic frequency spectra in a transducer beam and integration of scattered pulses from a corresponding three-dimensional array of scatterers. The simulation reported in previous papers depended upon physical measurement of the impulse response of a transducer. An original contribution described briefly herein, and in more detail in a companion article, is the addition of a model of the transducer's pulse waveform generation. Another new addition is the definition of a specific lesion detection task for objective assessment of a change in image quality following perturbation of some system parameter.

Computer Simulation↗
PubMed1987

Digital simulation of pulsed ultrasonic waveforms.

When modeling or simulating an ultrasonic pulse-echo system it is necessary to know the transducer waveforms that are the input to the system. In general, accurate transducer modeling is complex and waveform calculation is computationally intensive. Because of this, investigators often assume these waveforms to be simple sinusoids, modulated by Gaussian or exponential envelopes. However, these latter type pulses do not properly represent the complex response of modern piezoelectric transducers. In this paper, a simple set of equations is presented which can approximate the behavior of a number of common transducer configurations. In the first step of the procedure, a simple but accurate model is employed to calculate the step responses of quarter-wave-matched and backed piezoelectric transducers, assuming open circuit conditions. Effects of electrical terminations and transmit/receive bandwidth limitations are accounted for, approximately, by cascaded filtering. Emitted pressure waveforms and echo voltage waveforms synthesized by this simple procedure are very similar to measured waveforms from real transducers. Under most conditions, the method is only an approximation because the model erroneously assumes isolation between the electrical and acoustic networks. However, under many conditions the model is sufficiently accurate to predict actual transducer performance.

Computer Simulation↗
PubMed1983

Sonography of thickened gallbladder wall: causes in children.

A review of 793 consecutive abdominal sonograms in children aged 1 day to 16 years disclosed 453 patients in whom the gallbladder was clearly visible on at least two perpendicular views. Twenty had a gallbladder wall more than 3 mm thick. The following diseases were associated with gallbladder wall thickening; hypoalbuminemia (13 cases), ascites (five, three with concomitant hypoalbuminemia), physiologic thickening because of partial wall contraction (one), and systemic venous hypertension (one). None of 26 patients with gallstones and one of 14 with sludge had a thickened gallbladder. (The latter patient had concomitant hypoalbuminemia). Five patients with surgically proven acute cholecystitis during this same interval of time had sonograms. In four, the gallbladder wall was of normal thickness. In the fifth patient, the gallbladder wall could not be visualized because of densely shadowing stones. In this population, thickening of the gallbladder wall was not associated with acute cholecystitis and thus was not an indication for cholecystectomy.

Adolescent↗
PubMed1982

Sonographic pseudoasymmetry of the prenatal cerebral hemispheres.

The ultrasonographic image of the fetal head at the appropriate level for determination of the biparietal diameter reveals an apparent asymmetry of the cerebral hemispheres. This was confirmed and analyzed in 49 sequential fetuses who had no neurologic deficits at birth and in the autopsy specimen of an 8-month-old infant without any anatomic abnormalities of the head. In the hemisphere farthest from the transducer, a crescent-shaped echo-poor region was visualized abutting the calvarium. This resembles an abnormal fluid collection but represents normal anatomy. High-amplitude reflections were observed on the medial side of the crescent and were produced by the combination of the sylvian fissure and the choroid plexus of the lateral ventricle. The fine echo pattern of the near hemisphere, which appeared to represent normal anatomy, was artifactual. The cerebral asymmetry seen by conventional ultrasonographic imaging after the 15th gestational week should not suggest an underlying pathologic process. The studies suggest that a higher-quality examination of the near hemisphere of the fetal cranium can be performed with properly focused transducers.

Adolescent↗
PubMed1970

Dental enamel: detection of surface changes by ultrasound.

Evidence indicates that the tooth surface differs in structure from the enamel immediately beneath it, and particularly that the enamel rod type structure is minimal in the true natural surface. Furthermore, the rod ends appear to disappear with age after the eruption of the tooth. The thickness of the surface layer may be as much as 25 micrometers. Studies of caries incidence show a peak in the attack curve 2 to 4 years after eruption and a decline thereafter for all teeth. This information indicates that the mechanical structure of the tooth surface should be carefully studied. A highly useful means appears to be ultrasound since the specific acoustic impedance of highly mineralized tissue like enamel is strongly dependent on fraction volume mineralization and since non-destructive test techniques can be based on ultrasonics. An experimental demonstration of ultrasonic detection in vitro of tooth surface demineralization is given.

Collagen↗
PubMed1968

Looking into teeth with ultrasound.

Ultrasound is readily conducted across a boundary when the specific acoustic impedances of the two media are about equal. The specific acoustic impedance of dental enamel is about that of aluminum. A longitudinal sonic pulse, less than 250 nanoseconds in duration, conducted to the tooth through an aluminum rod, has positively detected the enamel-dentin junction as well as the dentin-pulp interface.

Aluminum↗