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Biomedical subjects

M F Insana

Publications and source records attributed to M F Insana.

18 recordsLinked to original sources
PubMed1992

Computers in ultrasonic imaging.

This article describes the role of computers and digital electronics in state-of-the-art diagnostic ultrasound scanners. An overview of the computational requirements is provided, and limits on color flow image frame rates are discussed. The new scanner architectures emerging may be used to extend current limitations of ultrasonography, making features such as automatic phase aberration correction, speckle reduction, and tissue characterization available.

Humans↗
PubMed1992

Identifying acoustic scattering sources in normal renal parenchyma in vivo by varying arterial and ureteral pressures.

Ultrasonic backscatter properties of normal dog kidney parenchyma are examined in vivo to determine sources of acoustic scattering. We systematically varied the renal perfusion and ureteral pressures to obtain detailed information about scattering sources that could not be seen under in vitro conditions. These data suggest that in normal parenchyma the principal sources of backscatter are Bowman's capsule at low frequencies (2.5-5.0 MHz) and glomerular arterioles at high frequencies (5.0-15.0 MHz). We found that the integrated backscatter coefficient (IBC) in normally perfused kidney cortex is approximately half that measured in the ischemic organ at all frequencies. Ischemia was found to reduce scatterer size estimates (D) by 10% at low frequencies and increase D54% at high frequencies. Acute obstruction of the kidney, under diuresis, produced an 11% increase in D at low frequencies, and no significant change in D at high frequencies. These variations in backscatter measurements are explained in terms of changes in the microscopic anatomy of the kidney.

Animals↗
PubMed1991

Identifying acoustic scattering sources in normal renal parenchyma from the anisotropy in acoustic properties.

Acoustical and histological properties of dog kidney parenchyma are examined in vitro to determine sources of acoustic scattering in the normal kidney. The speed of sound, attenuation, backscatter, effective scatterer size and scattering strength were measured within the frequency range 1-15 MHz and at eight angles of incidence with respect to the predominant nephron orientation. Significant angular dependence, or anisotropy, was observed in backscatter coefficient and scattering strength estimates; attenuation was found to be weakly anisotropic. All three parameters, each measured at 19 degrees C, exhibited values that were maximum for perpendicular incidence and minimum for parallel incidence. Speed of sound and scatterer size estimates were observed to be independent of scanning angle. Comparisons between these data for renal cortex and histological observations suggest that the glomerulus is the principal scatterer at low frequencies, and renal tubules and blood vessels at high frequencies.

Animals↗
PubMed1990

Information retrieval for teaching files: a preliminary study.

A computer algorithm for information retrieval from an electronic teaching file has been developed. This index enables the user to retrieve cases from a teaching file, based on the input of a combination of features. The algorithm is based on nearest neighbor analysis, and is programmed in the "C" language. A teaching file with this index is very easy to use as a reference resource for diagnosing unknown cases. A model was developed for a preliminary test of how likely a user would be to review a teaching file case that is the same diagnosis as an unknown case, thereby reducing uncertainty of diagnosis. The model used 110 cases of arthritis radiographs of hands scored by a skeletal radiologist. The result of the model suggests that the correct diagnosis would be reviewed 83% of the time. A standard method of reducing uncertainty of diagnosis (the maximum likelihood discriminant function) would have picked the correct diagnosis 78% of the time. The results indicate that a teaching file with the computer index is a practical tool for dealing with the uncertainty in diagnosis of unknown cases. The computer index could be included with videodisc-based teaching files (such as the American College of Radiology files). Using teaching files as a reference for interpreting unknown cases may reduce interobserver variability.

Algorithms↗
PubMed1990

Characterising the microstructure of random media using ultrasound.

This paper describes a technique of forming images of the average size and scattering strength of scatterers in a random medium using ultrasound. Quantitative ultrasound images provide a more direct interpretation of the underlying structure of the medium, e.g. size, shape, number and elastic properties of scatterers, and increased detectability for regions of varying structure. A signal-to-noise analysis was used to show quantitatively how properties of the imaging system influence low-contrast detectability in quantitative ultrasound images. In one experiment, signal-to-noise measurements using phantoms were compared with B-mode imaging for several transducer bandwidths to observe variations in image contrast and speckle noise. The findings are being used to optimise the design of quantitative imaging systems for specific diagnostic tasks.

Agar↗
PubMed1990

Describing small-scale structure in random media using pulse-echo ultrasound.

A method for estimating structural properties of random media is described. The size, number density, and scattering strength of particles are estimated from an analysis of the radio frequency (rf) echo signal power spectrum. Simple correlation functions and the accurate scattering theory of Faran [J.J. Faran, J. Acoust. Soc. Am. 23, 405-418 (1951)], which includes the effects of shear waves, were used separately to model backscatter from spherical particles and thereby describe the structures of the medium. These methods were tested using both glass sphere-in-agar and polystyrene sphere-in-agar scattering media. With the appropriate correlation function, it was possible to measure glass sphere diameters with an accuracy of 20%. It was not possible to accurately estimate the size of polystyrene spheres with the simple spherical and Gaussian correlation models examined because of a significant shear wave contribution. Using the Faran scattering theory for spheres, however, the accuracy for estimating diameters was improved to 10% for both glass and polystyrene scattering media. It was possible to estimate the product of the average scattering particle number density and the average scattering strength per particle, but with lower accuracy than the size estimates. The dependence of the measurement accuracy on the inclusion of shear waves, the wavelength of sound, and medium attenuation are considered, and the implications for describing the structure of biological soft tissues are discussed.

Models, Theoretical↗
PubMed1990

Parametric ultrasound imaging from backscatter coefficient measurements: image formation and interpretation.

A broadband method for measuring backscatter coefficients sigma b and other acoustic parameters is described. From the sigma b measurements, using a commercially-available imaging system, four high-resolution parametric ultrasound images are formed in a C-scan image plane. Scatterer size images are computed from the frequency dependence of sigma b and a correlation model function that describes the structure and elastic properties of the medium. Scattering strength images are computed from the absolute magnitude of sigma b. Chi-square images are generated to display how well the correlation model represents the interrogated medium. Integrated backscatter coefficient images are formed over the transducer bandwidth. All four images are generated simultaneously and compared with the corresponding B-mode image. Test samples with known physical properties were used to demonstrate experimentally that accurate parametric images are possible if an accurate correlation model is used. Local variations in attenuation, the center frequency and bandwidth of the transducer, and the distribution of scatterer sizes greatly influence the accuracy of estimates and the appearance of the image, thus demonstrating the importance of these factors in parametric image interpretation.

Agar↗
PubMed1989

New contrast-detail phantoms for improved precision in lesion detection measurements.

The previous design of our ultrasound contrast-detail (C-D) phantom is limited in its ability to evaluate the quality of diagnostic ultrasound imaging systems. There is uncertainty in the contrast-detail measurements due to the single available viewing angle for each target and the resulting single realization of the ultrasound speckle pattern. Two new contrast-detail phantom designs are described which enable many independent realizations of the speckle noise for observer C-D experiments of improved precision. In the first design, a single tissue-mimicking cone is located on the axis of a tissue-mimicking cylinder. Cross-sectional images of the cone which simulate focal lesions can be obtained from any orientation by rotating the cylinder under the transducer. In the second new design, a tissue-mimicking cone is positioned in a tissue-mimicking slurry of agar/graphite spheres. Gentle stirring of the slurry and rotation of the cone produce many independent realizations of the speckle. In both new phantoms, the lesion contrast can be specified and is frequency/transducer independent.

Equipment Design↗
PubMed1989

Quantitative ultrasonic detection and classification of diffuse liver disease. Comparison with human observer performance.

A multiparameter ultrasonic tissue characterization system has been developed and tested on several types of diffuse liver disease. The four tissue characterization parameters used are based on the first and second order statistics of the B-scan image. Performance of the system was evaluated using receiver operating characteristic (ROC) analysis and was compared with the performance of experienced human observers viewing B-scan images. The machine-based multiparameter system achieved an area under the ROC curve (Az) of 0.88 for detection of chronic hepatitis in more than 100 proven cases of the disease. This was dramatically better than the performance of human observers (Az = .64, P less than .05) and compares favorably to the performance of other accepted diagnostic tests such as head CT and the PAP smear. For detection of Gaucher's disease, the Az for the system was .92, whereas for separating hepatitis from Gaucher's disease Az was .84. Human observers also did well at these tasks (P greater than .8) using organomegaly as their major criterion for diagnosing Gaucher's disease. For primary biliary cirrhosis the system Az was .80, for glycogen storage disease Az was .94. These results suggest that use of multiparameter tissue characterization can significantly increase the usefulness of ultrasound for evaluation of diffuse liver disease.

Gaucher Disease↗
PubMed1989

Quantitative ultrasonography.

A perspective on quantitative techniques in diagnostic ultrasound is presented. The method involves the use of multiple tissue characterization features, pattern recognition methods, and imaging techniques to extract diagnostic information beyond that available with conventional imaging techniques. The information that each acoustic property and characterization feature reveals about physical properties of the tissues is discussed, and examples of clinical and laboratory data are summarized. The emphasis is on features that describe the composition, microscopic structure, and flow characteristics of normal and diseased soft tissues.

Discriminant Analysis↗
PubMed1988

A modified color display for computed tomography.

An algorithm for color assignment of computed tomography (CT) scans is presented. The intention is to produce color images similar to illustrations in anatomy atlases. There are three major advantages to the use of this color assignment algorithm. A single color image may replace the multiple monochrome density range pictures now used for portraying CT information. Perception of low spatial frequencies is improved, which may improve detection of soft tissue tumors. Finally, there are economic advantages for using color displays and printed color copies.

Algorithms↗
PubMed1987

Quantitative estimation of liver attenuation and echogenicity: normal state versus diffuse liver disease.

A method based on broad-band amplitude for obtaining attenuation and echogenicity estimates from homogeneous phantoms and tissues is described. Although a number of assumptions about the beam and scattering properties must be made, the attenuation results are as accurate as those obtained by the spectral-difference method and show less variability. The method was applied to the livers of 18 healthy volunteers and 76 patients with liver disease, including 29 patients with chronic hepatitis and 30 patients with Gaucher disease. Patients with chronic hepatitis formed a bimodal distribution, with one group having lower than normal attenuation and echogenicity values and another having elevated values. Six patients with type I glycogen storage disease and fatty infiltration of the liver had highly attenuating, echogenic livers as did patients with fatty livers from other causes. This finding confirms the subjective impressions already reported in the literature. In contrast to previous literature reports, patients with cirrhosis had normal attenuation and echogenicity values. Reasons for this discrepancy are discussed.

Gaucher Disease↗
PubMed1987

Statistical properties of radio-frequency and envelope-detected signals with applications to medical ultrasound.

Both radio-frequency (rf) and envelope-detected signal analyses have lead to successful tissue discrimination in medical ultrasound. The extrapolation from tissue discrimination to a description of the tissue structure requires an analysis of the statistics of complex signals. To that end, first- and second-order statistics of complex random signals are reviewed, and an example is taken from rf signal analysis of the backscattered echoes from diffuse scatterers. In this case the scattering form factor of small scatterers can be easily separated from long-range structure and corrected for the transducer characteristics, thereby yielding an instrument-independent tissue signature. The statistics of the more economical envelope- and square-law-detected signals are derived next and found to be almost identical when normalized autocorrelation functions are used. Of the two nonlinear methods of detection, the square-law or intensity scheme gives rise to statistics that are more transparent to physical insight. Moreover, an analysis of the intensity-correlation structure indicates that the contributions to the total echo signal from the diffuse scatter and from the steady and variable components of coherent scatter can still be separated and used for tissue characterization. However, this analysis is not system independent. Finally, the statistical methods of this paper may be applied directly to envelope signals in nuclear-magnetic-resonance imaging because of the approximate equivalence of second-order statistics for magnitude and intensity.

Humans↗
PubMed1986

Tests of the accuracy of a data reduction method for determination of acoustic backscatter coefficients.

The accuracy of a new method for measuring ultrasonic backscatter coefficients was tested, using narrow-band pulses and well-defined media having scatterers randomly distributed in space. Experimentally determined values agree very well with theoretical values for wide ranges of experimental parameters, these ranges being applicable in measurements made on human soft tissues. An important outcome is that the method yields accurate results for scattering media positioned anywhere from the nearfield through the farfield of the nonfocused transducers employed. In addition, backscatter coefficients can be determined for a broad range of gate durations.

Humans↗
PubMed1986

Pattern recognition methods for optimizing multivariate tissue signatures in diagnostic ultrasound.

Described is a supervised parametric approach to the detection and classification of disease from acoustic data. Statistical pattern recognition techniques are implemented to design the best ultrasonic tissue signature from a set of measurements and for a given task, and to rate its performance in a way that can be compared with other diagnostic tools. In this paper, we considered combinations of four ultrasonic tissue parameters to discriminate, in vivo, between normal liver and chronic active hepatitis. The separation between normal and diseased samples was made by application of the Bayes decision rule for minimum risk which includes the prior probability for the presence of disease and the cost of misclassification. Large differences in classification performance of various tissue parameter combinations were demonstrated using the Hotelling trace criterion (HTC) and receiver operating characteristic (ROC) analysis. The ability of additional measurements to increase or decrease discriminability, even measurements from other diagnostic modalities, can be evaluated directly in this manner.

Humans↗
PubMed1984

Method of data reduction for accurate determination of acoustic backscatter coefficients.

In previous methods of data reduction used to determine ultrasonic backscatter coefficients, various approximations were made. One frequently used is that there is an abrupt cutoff in the lateral extent of the scattering volume interrogated. Another approximation in all previous methods is that the effect of time gating the received echo signals can be written as a function of the distance along the axis of the interrogating beam. In the present paper we show that the backscatter coefficient can be derived from experimental data without making such approximations. The cases of narrow-band and broadband pulses are treated, and the method is applicable whatever the distance between the interrogated volume of scatterers and the transducer face. It is shown that, for a given pulse form, the gate duration must be sufficiently long in order to attain a specified accuracy for the measured backscatter coefficient. A test of the method was done using a phantom with well-defined scattering properties. Very good agreement was found between measured values of backscatter coefficients and those calculated using a first-principles theory.

Humans↗