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Biomedical subjects

J Ophir

Publications and source records attributed to J Ophir.

At least 91 records · Page 5Linked to original sources
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↗
PubMed1989

Correlation artifacts in speed of sound estimation in scattering media.

A recently described method for speed of sound estimation in tissues in pulse-echo mode involves reception of echoes generated by an ultrasonic pulse by means of a linearly tracking transducer. When the peaks of echo amplitudes are used as markers of arrival time, stairstep-like artifacts appear in the echo arrival time vs. transducer position plots. We postulate that these artifacts are a consequence of the speckle phenomenon commonly encountered in ultrasonic imaging. To test this hypothesis, we report computer simulations and water tank experiments which demonstrate similarities between the behavior of the stairsteps and the properties of ultrasonic speckle. Additionally, equations describing the precision of the speed of sound estimation in terms of the second order statistical properties of the stairstep artifact are derived.

Computer Simulation↗
PubMed1989

Correction of refraction and other angle errors in beam tracking speed of sound estimations using multiple tracking transducers.

The beam tracking approach to the estimation of the speed of sound has shown potential for making unbiased estimates in tissues. The speed of sound in a medium can be found from the arrival times of echoes as a function of the position of a tracking transducer. There is a problem in this approach if the angle between the direction of tracked beam and the direction of tracking translation is not zero due to refraction or other effects. An angle error as small as 1 degree would result in an error that is too large for diagnostic applications. A modified technique using three or more tracking transducers is described. This yields a corrected speed of sound estimate, and calculates the angle error. A simulation program has shown that this modified technique could indeed correct for the angle errors.

Computer Simulation↗
PubMed1989

Atenolol-induced cutaneous vasculitis.

We present a case of cutaneous vasculitis apparently due to an adverse reaction to atenolol. The causal relationship between the drug and the eruption was based mainly on circumstantial evidence. It has been further strengthened by positive results of the indirect rat mast cell degranulation test. The number of published cases of reaction to atenolol is limited. Cutaneous vasculitis has, to the best of our knowledge, never been reported as an adverse reaction to atenolol, although it is not a rare side effect of other beta blocker drugs including propranolol and practolol. Atenolol should be added to the list of beta blocker medications that may produce cutaneous vasculitis.

Atenolol↗
PubMed1988

Correlation of ultrasonic attenuation with pathologic fat and fibrosis in liver disease.

The attenuation coefficient in two groups (n1 = 70; n2 = 59) of pathologically graded in vitro human liver specimens was measured over a frequency range from 1.25-8.0 MHz and fitted to a power law model. The slopes of the power law curves at 5 MHz were correlated with pathological scores for fat in Group I, which consisted of normal and fatty livers (no fibrosis); they were also correlated with the pathological score for fibrosis in Group II, which consisted of normal and fibrotic livers (no intracellular fat). Significant (p less than 0.002) differences were found between the two groups. The fatty liver group exhibited approximately a 0.23 +/- 0.06 dB cm-1 MHz-1 (fat grade)-1 behavior (mean +/- s.d.), while the fibrotic liver group exhibited approximately a 0.11 +/- 0.01 dB cm-1 MHz-1 (fibrosis grade)-1 behavior. These results may explain some of the conflicting literature in this area, and suggest that attenuation may in principle be used for screening for liver disease, but not for differentiation between fatty and fibrotic conditions.

Fatty Liver↗
PubMed1988

Products of class II major histocompatibility complex gene subregions are differentially expressed on keratinocytes in cutaneous diseases.

Aberrant expression of class II major histocompatibility complex (MHC) subregion antigens by keratinocytes was examined immunohistochemically in a range of cutaneous disorders. Although cell surface expression of human lymphocyte antigen (HLA)-DR was observed, HLA-DQ and HLA-DP were not expressed in any disorder investigated except for allergic contact dermatitis. Epidermal Langerhans cells expressed antigens of all three subregions on the cell surface. Differential expression of class II MHC subregion antigens may be related to tissue levels of gamma-interferon or to different functions of each subregion.

Adult↗
PubMed1988

Elimination of diffraction error in acoustic attenuation estimation via axial beam translation.

Optimized wideband attenuation estimations were performed on a tissue mimicking phantom in a water tank with and without axial beam translation (ABT), and the results were compared to those from standard substitution measurements. A -17 percent discrepancy between the results of the substitution method and the optimized estimation without ABT was noted in the far field. This discrepancy was eliminated when ABT was utilized.

Models, Structural↗
PubMed1988

The hair follicle mites (Demodex spp.). Could they be vectors of pathogenic microorganisms?

The hair follicle mites Demodex folliculorum and D. brevis are the most common permanent ectoparasites of Man. Ordinarily they are harmless to their human host and appear to be of no medical significance. We present, however, an unusual finding regarding this mite, namely, that in a potassium hydroxide mount of a skin scraping from a mycotic plaque we found numerous Demodex mites containing inside them spores of Microsporum canis. This could mean that the putatively inoffensive Demodex has the potential to ingest various microorganisms that are found in its niche and transport them to other areas of the skin or possibly to other individuals.

Acari↗
PubMed1987

Frequency-dependent ultrasonic differentiation of normal and diffusely diseased liver.

The attenuation coefficient in 38 pathologically graded in vitro liver specimens was measured over a frequency range from 1.25-8 MHz and fitted to the power law model. The attenuation in the normal group (n = 17) exhibited a frequency dependence of the form 0.399f1.139; in the mild disease group (n = 13), it exhibited a dependence of the form 0.395f1.212; and in the moderate/severe disease group (n = 8), it exhibited a dependence of the form 0.391f1.325. Using a Student's t test, it is shown that, due to these differences in the frequency dependence, the statistical significance level at which the null hypothesis regarding the difference between the mean attenuation slopes of any two of these categories is rejected, is a strong function of frequency in the range of 1-4 MHz. The significance level relating to the difference between the normal and moderate/severe disease group is more than one order of magnitude better than the other categories. In all cases, no substantial improvement occurs beyond 4 MHz. It is also shown that attenuation slope values at 3 MHz confirm in vivo literature results obtained via different techniques.

Fatty Liver↗
PubMed1987

Correlations of sound speed with tissue constituents in normal and diffuse liver disease.

The speed of sound in normal and diffusely-diseased liver specimens was measured. There were four experimental groups, consisting of normal (n = 21), fatty (n = 7), fibrotic (n = 7) and mixed fatty and fibrotic (n = 9). These classifications were based on histological grading. We found that the results corroborate and extend most of the results of Bamber and coworkers. Specifically, no significant correlation was found between speed of sound and fibrosis score; a moderate correlation was found between speed of sound and tissue water content; and a relatively good correlation (r = -0.670, p less than 0.1%) was found between the speed of sound and the histological fat score, which increased to r = -0.819 (p less than 0.1%) when a correction for variations in water content was used.

Fatty Liver↗