Biomedical subjects
J Ophir
Publications and source records attributed to J Ophir.
Attenuation estimation with the zero-crossing technique: phantom studies.
Global and local attenuation coefficient estimations were performed in a phantom using a pulse echo method based on the rate of decay of zero crossing density. Focussed and unfocussed 3.5 MHz transducers were used. It was found that good global estimates could be made with either transducer over a 2:1 range of attenuation coefficient. Local estimates exhibit large bias errors and a high degree of variability. This variability diminishes in the focal zone of the focussed transducer and in the far field of the unfocussed transducer.
Quantitative assessment of in vivo backscatter enhancement from gelatin microspheres.
Experimental work using a quantitative C-scan technique to measure in situ enhancement of hepatic backscatter resulting from the administration of gelatin microspheres to dogs is reported. We have found that reproducible enhancement of hepatic backscatter on the order of 2 dB followed the peripheral administration of gelatin within minutes, the magnitude of the effect was not sensitive to the rate of infusion, but was likely to be dose dependent, changes in the overlying tissue attenuation had a pronounced effect on the measurement, and the effect was sustained for up to one half hour or longer.
[Allergic reaction to oral clindamycin given after topical application].
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The attenuation of ultrasound in biological fluids.
We have measured the ultrasonic attenuation parameters alpha o and n of several biological fluids in vitro in the frequency range 2.8-6.8 MHz, using frequency shift and/or a sinc (.) sidelobe ratio technique. The parameters alpha 0 and n describe the frequency-dependent attenuation via a power-law model, i.e., alpha(f) = alpha 0 fn, where f is frequency. The samples investigated were blood, pus, cyst fluid, bile, and infected hematoma. It was found that the values of alpha o span approximately the range between 0.03-0.3 dB cm-1 MHz-n, and values of n range from about 1.1-1.3.
Attenuation of ultrasound in normal liver and diffuse liver disease in vivo.
Preliminary results of in vivo attenuation measurements of the liver have been obtained in 39 normal patients and in 35 patients with diffuse liver disease. A modified real-time sector scanner incorporating an online attenuation measurement method was used. The value of attenuation in normal liver was estimated as 0.52 +/- 0.03 dB/cm/MHz, measured at 3 MHz. Significantly higher attenuation values were obtained from patients with alcoholic and cardiac cirrhosis, and following hepatic artery infusion with chemotherapeutic agents. Lower values were obtained from patients with biliary cirrhosis, chronic active hepatitis, and diffuse infiltration by lymphoma or leukemia. Fatty infiltrated livers showed a wide range of values of 0.37-0.66 dB/cm/MHz. The results suggest that estimates of attenuation coefficients are useful in detecting the presence of diffuse liver disease.
Attenuation estimation in reflection: progress and prospects.
This monograph presents a tutorial review of the current state-of-the-art in ultrasonic attenuation estimation in reflection. Clinical indications which provide the motivation for attempting in vivo attenuation estimation are discussed. Frequency and time domain techniques and their respective tradeoffs and problems are presented. Finally, current clinical results obtained with the various techniques are summarized and further areas of study are suggested.
Thickness of basal cell epithelioma measured preoperatively by ultrasonography.
A new approach to the diagnosis and measurement of the thickness of basal cell epithelioma (BCE) by ultrasonography is described. The advantages and efficacy of the new technique are presented.
[Photosensitivity due to combined hydrochlorothiazide and amiloride].
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Pediculid. An unusual -id reaction to pediculosis capitis.
We describe a pruritic rash that appears to be associated with pediculosis capitis. We suggest calling it ' pediculid ' since it appears to be an -id reaction to pediculosis capitis.
Miconazole treatment for cutaneous leishmaniasis.
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Effect of half-wavelength membranes on the axial resolution of real-time ultrasonic scanners.
The effect of interposing a half-wavelength membrane between the transducer and the load in mechanically sectored ultrasonic scanners was investigated. In particular, the effects of impedance mismatch and detuning on broadband spectra were theoretically and experimentally studied. These studies indicate that for certain common cases, a bandwidth reduction of 20%-30% can be anticipated, resulting in a proportional decrease in the axial resolution.
A closed form method for the measurement of attenuation in nonlinearly dispersive media.
A closed form solution of the equation describing the spectrum of a Gaussian pulse propagating in a medium with nonlinear frequency dependence of attenuation is presented. This solution suggests that in general the spectrum remains Gaussian, subject only to center frequency downshift and bandwidth reduction. The possibility of experimentally determining the two nonlinear material parameters from the measurement of the center frequency downshift and the reduced bandwidth is proposed.
Spectral shifts of ultrasonic propagation: a study of theoretical and experimental models.
The theoretical relationship between center frequency downshift and the spectral bandwidth was investigated for pulses with a sinc(x) spectrum propagating through lossy media. Power law and exponential models for frequency dependence of attenuation were used. Six target materials encompassing a range of attenuation parameters were used to verify the theoretical model. The frequency downshift data from these materials was used to calculate their respective attenuation parameters. It was shown theoretically and verified experimentally that for small frequency downshifts, the sinc(x) model yields the same material parameters as the Gaussian model. The choice of the model for the attenuation of the material was found to be inconsequential.
Aqueous solutions as contrast agents.
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Echo detection and lipid particle size.
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A ternary solution for independent acoustic impedance and speed of sound matching to biological tissues.
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