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Biomedical subjects

J Ophir

Publications and source records attributed to J Ophir.

At least 19 recordsLinked to original sources
PubMed1992

On the feasibility of pulse-echo speed of sound estimation in small regions: simulation studies.

Computer simulations are used to study the feasibility of the estimation of sound speed in small regions with precision better than 1% using the Beam Tracking method. The speed of sound is estimated in a 10-mm by 10-mm region by considering a number of parallel tracks confined to the small region. The transducer focusing and the step sizes for the tracking and tracked transducers required to extract the maximum amount of uncorrelated data from the 10-mm by 10-mm region is evaluated. The results show that the speed of sound can be estimated with error less than 1% in a small region using a typical medical transducer. The statistical comparison of estimates in small areas with different speed of sound is also considered.

Acoustics↗
PubMed1992

Axial stress distributions between coaxial compressors in elastography: an analytical model.

We describe an analytical model to study the behavior of stress along the compression axis for different configurations of opposing circular compressors, as applied to elastography. The method is based on a hypothesis that the axial stress at any point on the axis is the superposition of the individual components of the stresses derived from the boundary conditions at either end. The determination of the axial stress behavior according to the model permits the correction of certain elastograms for depth-dependent stress. Experimental results have been presented to corroborate the model.

Elasticity↗
PubMed1992

Correction of diffraction errors in attenuation estimation with Dynamic Beam Translation.

We describe computer simulations for the estimation of the attenuation coefficient in scattering media using the Dynamic Beam Translation (DBT) method. DBT refocuses a variable aperture transducer to maintain the focal characteristics of the transducer at different depths in order to reduce diffraction errors. The efficacy of DBT is evaluated for transducers with different focal powers and under the influence of phase aberration due to the body wall. DBT shows robustness in the elimination of diffraction errors and resistance to the effects of aberration.

Computer Simulation↗
PubMed1992

Nonbullous bullous pemphigoid.

Three patients had a rare form of bullous pemphigoid, clinically similar to the erythematous type of bullous pemphigoid without vesiculobullous lesions. All the patients displayed immunofluorescence features of bullous pemphigoid. This form of the disease presents a substantial diagnostic problem because it lacks the principal morphologic feature of bullous pemphigoid, namely the vesicles and bullae.

Aged↗
PubMed1992

Squamous cell carcinoma--70 years after irradiation.

The rare event of invasive squamous cell carcinoma 70 years after irradiation to the scalp for tinea capitis, occurred in a 75-year-old Caucasian male. The clinical, histological, roentgenologic and magnetic resonance imaging picture are described, and the literature is reviewed.

Aged↗
PubMed1992

Systemic amyloidosis secondary to chronic leg ulcers.

Chronic leg ulcers due to any cause are almost invariably associated with an inflammatory process. As with any long-standing inflammation, leg ulcers may be complicated by systemic amyloidosis, which occurs in rheumatoid arthritis, cystic fibrosis, tuberculosis, and other disorders. There are, however, very few reports on the association between these two conditions. We report a patient with severe leg ulcers of twenty years' duration in whom reactive systemic amyloidosis presented as a nephrotic syndrome.

Aged↗
PubMed1991

Pemphigus gestationis (herpes gestationis): a case report.

Pemphigus gestationis is a rare disease, probably of immunologic origin, that causes the placenta to absorb immunoglobulins and deposit them in its basement membrane. The resulting placental insufficiency leads to increased morbidity and mortality among the offspring of such patients. A case of pemphigus gestationis is presented, and the importance of early diagnosis is discussed.

Adult↗
PubMed1991

Pulse-echo ultrasound speed measurements: progress and prospects.

The data on the relationship of sound speed to tissue condition, and the development of methods for measurement of sound speed in vivo, are outlined. The methods developed by the authors are discussed. These include methods which use the spatial shift in images of targets viewed from different directions, time-of-flight measurements along incrementally tracked beams and echo tracking during transaxial compression of tissue. The reported sound-speed values are discussed, discrepancies noted and suggestions made on the potential clinical applications of in vivo sound-speed estimation.

Humans↗
PubMed1991

Elastography: a quantitative method for imaging the elasticity of biological tissues.

We describe a new method for quantitative imaging of strain and elastic modulus distributions in soft tissues. The method is based on external tissue compression, with subsequent computation of the strain profile along the transducer axis, which is derived from cross-correlation analysis of pre- and post-compression A-line pairs. The strain profile can then be converted to an elastic modulus profile by measuring the stresses applied by the compressing device and applying certain corrections for the nonuniform stress field. We report initial results of several phantom and excised animal tissue experiments which demonstrate the ability of this technique to quantitatively image strain and elastic modulus distributions with good resolution, sensitivity and with diminished speckle. We discuss several potential clinical uses of this technique.

Abdomen↗
PubMed1991

A single transducer transaxial compression technique for the estimation of sound speed in biological tissues.

In this paper we report an extension to the TACT method for the estimation of sound speed with a single transducer to any depth. This method is based on the hypothesis that the displacement of the tissue caused by transaxial compression follows a theoretical function which we derive analytically. In this method, as in the original TACT, a transducer imparts an accurate transaxial compression to the tissue, and the corresponding change in the arrival time of an echo at a range of interest is measured. This procedure results in a biased speed estimate whose value is range dependent. The theoretical function is fitted to the experimental estimates, from which the unbiased sound speed is then computed.

Biophysical Phenomena↗
PubMed1991

Atopic dermatitis provoked by AL721 in a patient with acquired immunodeficiency syndrome.

A 40-year-old patient with acquired immunodeficiency syndrome (AIDS) had an atopic dermatitis-like skin eruption and elevated serum IgE levels after therapy with AL721. This agent is a mixture of egg yolk lipids used for the treatment of AIDS. The relationship between the drug and the eruption has been based on circumstantial evidence and confirmed by the positive results of skin tests. Although an almost unlimited amount of materials have been reported to be responsible for atopic manifestations, cases of drug-induced atopic dermatitis are rare. AL721, however, can be regarded as a food product; therefore, the appearance of the eruption following intake of this agent should not be considered exceptional.

Acquired Immunodeficiency Syndrome↗
PubMed1990

Diffraction correction methods for pulse-echo acoustic attenuation estimation.

We describe computer simulations and water tank experiments for the estimation of the attenuation coefficient in scattering media. The efficacies of the Axial Beam Translation (ABT) and Inverse Diffraction Filtering (IDF) methods in reducing diffraction errors in such estimates are compared throughout the radiation field of a plane transducer. The effect of phase aberration due to the body wall and the effect of the scattering properties of the media are considered. Consistent improvement in the estimation due to ABT is demonstrated as well as unreliable improvement due to IDF which is sensitive to the presence of phase aberration and to changes in scattering.

Computer Simulation↗
PubMed1990

A transaxial compression technique (TACT) for localized pulse-echo estimation of sound speed in biological tissues.

We describe a new method for the estimation of the speed of sound in soft tissues in the pulse-echo mode. A transducer imparts an accurate transaxial compression to the tissue, and the corresponding change in the arrival time of an echo feature is measured. The ratio between the compressed depth and the difference in arrival time is taken as the estimate of the speed of sound. A second, noncompressing transducer is used to correct for distal tissue movement. We show theoretically and experimentally that accurate speed of sound estimations can be made in overlying and underlying tissue mimicking layers.

Biophysical Phenomena↗
PubMed1989

Contrast agents in diagnostic ultrasound.

We review the field of contrast agents in diagnostic ultrasound. The progress in the development of various classes of contrast agents such as free and encapsulated gas bubbles, colloidal suspensions, emulsions, and aqueous solutions is described. The mechanisms for production of backscatter contrast, as well as attenuation contrast and speed of sound contrast are explained. Finally, the potential advantages and disadvantages of various classes of contrast agents are compared.

Animals↗