Biomedical subjects

D K Nassiri

Publications and source records attributed to D K Nassiri.

8 recordsLinked to original sources

PubMed1986

Tissue characterization from ultrasound B-scan data.

An approach to ultrasonic tissue characterization, using textural features of the B-scan image, is described. Portions of a B-scan image, 64 X 64 pixels spatially by 8 bits deep, are acquired from regions of interest and subjected to computer analysis. A systematic approach to defining a set of 93 textural features of a B-scan is described and methods and criteria for selecting optimum combinations of these are discussed. As a test of its power, the approach has been applied to the discrimination between the B-scan textures corresponding to livers and spleens of normal humans and various measures of "success" have been quantified both on a "training set only" and on a "training set plus test set" basis. The overall test probability of success of 82% on a single image and 94% on a subject yielding multiple images indicates the potential of the techniques for conditions where a subtle but uniform change in parenchymal texture may be present.

Computers↗

PubMed1986

Ultrasonic study of in vivo kinetic characteristics of human tissues.

A method is described for quantifying tissue movement in vivo from the computation of correlation coefficient between pairs of A-scans with appropriate time separation. The method yields quantifiable and repeatable secondary patterns of soft tissue movement in response to primary cardiac movement in a given subject, shows consistently different results as between normal livers and a variety of abdominal tumours, and is sensitive to either progress or therapeutically-induced regression of malignant disease. While the results reported here have been obtained using somewhat simple and crude equipment, the method is well suited to implementation on a commercial real-time scanner.

Abdominal Neoplasms↗

PubMed1986

The differential and total bulk acoustic scattering cross sections of some human and animal tissues.

This paper describes methods that have been developed for the accurate measurement of total and differential bulk acoustic scattering cross sections. Analysis is made of the sources of uncertainty entailed in measurements of this kind and a complete derivation is developed for the angular variation of the interrogated scattering volume. Experimentally determined values of differential scattering cross sections are reported for specimens of skeletal muscle, blood, liver, and secondary tumors arising in liver, obtained in the frequency range 4-7 MHz for scattering angles in the practically attainable range 60 degrees-150 degrees and also at 180 degrees (backscatter). A basis for extrapolating these results to other scattering angles can be derived from a combination of theoretical and experimental considerations, as presented in a companion paper [J. Acoust. Soc. Am. 79, 2048-2054 (1986)]. Based on such extrapolation, values for total scattering cross sections are estimated for the above tissues, the values are compared with determinations by different techniques as reported by other authors, and corresponding estimates are derived for the contribution of scattering processes to total attenuation in the tissues.

Acoustic Stimulation↗

PubMed1986

The use of angular acoustic scattering measurements to estimate structural parameters of human and animal tissues.

Theoretical formulations are developed, based on mathematical models of inhomogeneous continua for the expected angular variation of bulk scattering from human and animal tissues. These results are compared with experimental data on angular scattering from liver, muscle, and blood, reported in a companion paper [J. Acoust. Soc. Am. 79, 2034-2047 (1986)], and deductions are drawn as to the appropriateness of the various models for representing the mechanical structure of the different tissues. On this basis, the experimental data and theoretical formulations are used to derive estimates, appropriate to the frequency range of observation (4-7 MHz), of correlation distance (or effective scatterer spacing) d, the local variabilities of density and compressibility, gamma rho = delta rho/rho and gamma kappa = delta kappa/kappa 0, and their ratio gamma rho/gamma kappa. For blood, liver, and skeletal muscle, the values derived at 6 MHz for d are approximately 5, 55, and 75 microns and for gamma rho/gamma kappa are 0.5, 0.15, and 0.28, respectively. These results are, in particular, at variance with the commonly made assumption, based on evidence from low-frequency measurements, that the ratio gamma rho/gamma kappa is sufficiently small that density terms can be ignored in calculations of human tissue scattering.

Acoustic Stimulation↗

PubMed1983

B-scan texture classification: a study using physical and theoretical models.

Recent clinical trials, in our own centre and elsewhere, have demonstrated the ability of A- and B-scan texture analysis techniques to provide useful in vivo separation of certain disease conditions. The present paper reports studies, using physical and theoretical models of tissues, aimed at identifying the particular sets of textural features which are most effective in achieving such separations. Using a 3.5 MHz, single element manual scanner, a total of 300 B-scans have been collected from four physical models consisting of gel-embedded 'point' scatterers, with differing mean separations. Additionally, computer modelling has been used to obtain a further 500 B-scans from 14 statistically different scattering situations. The total set of B-scans thus obtained has been subjected to a variety of texture classification procedures which have previously been developed for application in other imaging fields, such as cytology and aerial photography. The results are discussed in terms of: i) the features which are best suited to the classification of B-scans, and ii) the manner in which the resulting classification schemes are sensitive to variables of the ultrasonic scanning instrumentation.

Biometry↗

PubMed1979

Attenuation of ultrasound in skeletal muscle.

Ultrasonic attenuation in fresh and 5% formalin fixed beef skeletal muscle has been measured, as a continuous function of frequency, in the range 1-8 MHz, for muscle fibre orientations both parallel and normal to the direction of propagation. Good agreement was found in all cases between two independent sets of measurements employing transmission and reflection techniques respectively. The data are consistent with a power law dependence of attenuation coefficient on frequency, with an exponent that is not significantly different from unity. For propagation normal to the fibres attenuation values are found as 1.1 +/- 0.15 and 1.6 +/- 0.15 dB cm-1 MHz-1 for fresh and fixed tissue respectively, the corresponding values for parallel propagation being 2.9 +/- 0.23 and 4.1 +/- 0.25 dB cm-1 MHz-1.

Animals↗

PubMedDate not supplied

Effect of gaseous inclusions on the frequency dependence of ultrasonic attenuation in liver.

The greatest variation in published data of the attenuation of ultrasound in mammalian liver in vitro occurs at the lower end of the 0.5 to 7 MHz frequency range and gives rise to some departure from a linear or simple power law dependence of attenuation on frequency. These effects do not appear to be highly dependent on the method of measurement. It is suggested that they are due to a varying presence of small gas bubbles distributed throughout the tissue--a suggestion based on calculated estimates of the attenuation due to microscopic bubbles and on the measured frequency dependence of attenuation in water loaded sponges containing varying amounts and distribution of gas. We now believe that preferred methods of tissue specimen preparation, for in vitro measurement of ultrasonic attenuation or scattering, should involve either pressurization as described elsewhere (Frizzell et al., 1979) or storage under refrigeration.

Animals↗

PubMedDate not supplied

The diaphragmatic echo complex: an in vitro study.

The brightly echogenic appearance of the diaphragm on routine clinical scans is not easily reconciled with the well-documented echo-poor appearance of muscle elsewhere in the body. A series of specimens of normal human diaphragm freshly excised at autopsy were suspended in a water bath. Articulated arm scans were done varying the angle of the incident beam to the specimen by 5-degree increments and recording the maximum attenuation which allowed visualization (ie, an extinction point). This was accomplished for intact diaphragm, peritoneal membrane alone, and diaphragmatic muscle alone with both membranes stripped. The bright specular echoes seen are due almost exclusively to the membranes (parietal pleura and peritoneum) and the diaphragmatic muscle itself produces only low-level scattered echoes as elsewhere. However, these scattered echoes account for persistent visualization of the diaphragm at steep angles of the incident beam. A considerable portion of the in vivo thickness of the diaphragmatic echo complex is, therefore, produced by diaphragm-lung interface.

Diaphragm↗