Biomedical subjects

C M Sehgal

Publications and source records attributed to C M Sehgal.

32 records · Page 2Linked to original sources

PubMed1994

Three-dimensional sonographic imaging of the equine superficial digital flexor tendon.

In a feasability study, a technique for constructing 3-dimensional sonographic images of the superficial digital flexor tendon (SDFT) was established in 6 clinically normal horses and applied to 7 horses with injured SDFT. Two-dimensional B-mode sonographic images were recorded on videotape as the sonographic transducer was manually moved along the palmar aspect of the metacarpal region. Selected videofields were digitized, and 3-dimensional images were constructed, using a computer work station and dedicated software program. The 3-dimensional images were of high quality and presented qualitative clinical information in unique fashion. Indication of the extent of SDFT injuries was excellent. Such 3-dimensional images would be especially useful in explaining to owners and trainers the importance of the injury to their horse and would have a role in monitoring tendon healing and in the assessment of various treatments.

Animals↗

PubMed1993

Ultrasound-assisted thrombolysis.

RATIONALE AND OBJECTIVES: Current use of thrombolytic agents to lyse thrombus, though safe, is complicated by stroke, bleeding, and clot embolization. Therapy may be protracted, resulting in further ischemia and possible tissue loss. Peripheral arterial and graft occlusions often require several hours of thrombolytic therapy, which may occasionally exceed 48 hours and may also require expensive intensive care monitoring. It is desirable to accelerate clot lysis and to thereby reduce the risks and costs associated with the procedure and minimize morbidity. In this article, the authors propose the use of intravascular ultrasound in conjunction with thrombolytic agents to increase the rate of thrombolysis. METHODS AND RESULTS: In-vitro thrombolysis of fresh human blood clots was studied with and without urokinase by using continuous wave, 20-KHz ultrasound at the power levels 1-2 watts. Loss in weight of each clot was used to measure the extent of thrombolysis. Clot lysis was observed when ultrasound and thrombolytic agents were used alone. At modest power levels of 1.0 to 1.5 watts of ultrasonic energy a significant increase in lysis was observed in conjunction with 5,000 units of urokinase. CONCLUSIONS: In the short treatment duration of this in-vitro study, 5,000 units of urokinase combined with 20-KHz ultrasound energy at 1.0 and 1.5 watts was associated with a greater percentage thrombolysis by weight than either urokinase or ultrasound alone.

Humans↗

PubMed1993

Quantitative relationship between tissue composition and scattering of ultrasound.

This study establishes quantitative laws by which the magnitude of ultrasonic scatter is related to the gross chemical composition of tissues, viz., water, fat, and collagen. Tissues are modeled as immiscible mixtures, the constituents of which are uniformly dispersed over the volume. Each component of the mixture causes the ultrasonic velocity of the medium to fluctuate about the mean value. Such localized variations in the refractive index of a medium cause propagating sound waves to scatter. It is proposed that the contribution of each component to the total fluctuation is in proportion to its volume fraction. The analysis shows that the scatter of ultrasound exhibits a complex nonlinear dependence on the concentrations of the individual components. From the knowledge of sound speed of individual components, total velocity fluctuations are determined for binary and three-component models of the tissue. Comparison of these values, with those estimated from scatter measurements, shows a close correlation between the two sets. Collagen, although present in relatively small amounts in soft tissues, contributes a significant portion of the total scatter. However, both fat and collagen fractions must be taken into consideration to account for the major fraction of the observed scatter. In conclusion, there is a direct relationship between tissue composition and scatter from tissues. Such dependence must also be taken into consideration, in addition to the correlation function and correlation lengths to explain backscatter or loss in a transmitted signal due to scatter from tissues.

Acoustics↗

PubMed1993

Sonographic brightness of the flexor tendons and ligaments in the metacarpal region of horses.

Sonographic observations were made of the image mean gray scale (MGS) of the flexor tendons and ligaments in the left and right metacarpal regions of each of 10 clinically normal horses. In images made in the dorsal and sagittal planes, the MGS was measured at multiple sites in the superficial digital flexor tendon (SDFT), deep digital flexor tendon (DDFT), accessory ligament (AL), and suspensory ligament (SL), and at single sites in the medial and lateral limbs of the SL, and the palmar ligament. Relative sonographic brightness of each tendon and ligament was calculated by dividing the value of its MGS by the mean value for the MGS of images of 3 soft tissue equivalent phantoms. When a multivariate repeated-measures of ANOVA of the relative brightness values was statistically significant (P < or = 0.05), Tukey's method of multiple comparisons was used to determine which values were significantly different from each other. In the dorsal plane, the SL was significantly brighter than the DDFT, SDFT, and AL; relative brightness of the DDFT and SDFT were similar, as were those of the SDFT and AL. In the sagittal plane, the SL again was the significantly brightest structure, followed by the AL, and similar brightness of the DDFT and SDFT. In dorsal images made 25 cm distal to the accessory carpal bone, relative brightness of the SDFT, DDFT, and the medial and lateral limbs of the SL were similar.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1990

Ultrasonic imaging of the nonlinear parameter B/A: simulation studies to evaluate phase and frequency modulation methods.

This paper presents a method for imaging the nonlinear parameter B/A. It is based on measuring phase shift and frequency shift of a high frequency acoustic probe wave by a low frequency acoustic pump wave. These measurements yield the real and the imaginary parts of the Fourier component of the distribution B/A at the wave number of the pump wave. We also derive the necessary set of wave numbers of the pump wave which must be employed to accurately image the B/A parameter. We show that these wave numbers are a function of sampling period and sampling number. Simulations of the imaging method show that the proposed method in this paper leads to more accurate imaging of B/A than the earlier method.

Animals↗

PubMed1988

Measurement of ultrasonic nonlinear parameter in excised fat tissues.

This paper reports sound speed co, adiabatic acoustic nonlinear parameter B/A, and isothermal nonlinear parameter (B/A)' of 33 samples of excised human and animal fats and some simple mixtures, e.g., skim milk and powdered milk. Tissues were obtained from different parts of the body and the measurements were made in the temperature range of 20 degrees C to 37 degrees C. All the fats were highly nonlinear. Although there was a considerable overlap in the values of acoustic nonlinearity of different body fats, in general their values followed the order: mesenteric fat greater than subcutaneous fat greater than omentum fat greater than breast fat. Temperature coefficients of co and B/A, and the difference between adiabatic and isothermal nonlinearity, correlated highly with water/fat content of tissues. A reciprocal relationship between B/A and co, similar to that proposed for liquids, was observed for soft tissues but not for solutions of powdered milk in skim milk. No significant correlation was observed between acoustic measurements and the age of human subjects from which fat tissues were obtained.

Adipose Tissue↗

PubMed1987

Dependence of ultrasonic nonlinear parameter B/A on fat.

This study deals with the relationship between the magnitude of acoustic nonlinearity, sound speed of tissues and the amount of fat present in them. A two-component model, i.e., nonfat and fat, has been assumed and equations that relate the nonlinear parameter (B/A) of a medium to the properties of its components have been derived for two cases. In the first case, the density and sound speed are the same for the two components; B/A is a linear function of fat concentration. To represent this case, mixtures of egg white and yolk were studied. Even though the differences in density and sound speed of the two egg components were within 1 percent of each other, B/A showed a deviation from linearity. In the second case, i.e., when the density and sound speed of the two components are not equal, a quadratic equation has been derived using mixture laws. Livers, fats, egg mixtures, and oil data were used to represent this case. B/A increased quadratically with fat concentration. The presence of proteins on the binary aqueous/fat mixtures modified the quadratic rule.

Adipose Tissue↗

PubMed1986

Correlative study of properties of water in biological systems using ultrasound and magnetic resonance.

Ultrasonic and nuclear magnetic resonance properties of media rich in water are investigated. The chemical shift of the water proton in pure water, aqueous solutions of tertiary butanol, and sodium chloride is shown to be linearly correlated to the reciprocal of sound speed in these media. A new method of determining the self-diffusion coefficient of water by using acoustic nonlinearity and sound speed is proposed. The method is tested on a variety of media that include pure water, aqueous solutions of glycerol, serum albumin, egg constituents, plant tissues, frog muscle and liver, and excised human tissues. In all the cases the results are found to compare closely to diffusion coefficients measured by magnetic resonance. The results presented here indicate that the acoustic and magnetic resonance modalities, though inherently different in their origin, can provide closely related information on the properties of water.

Animals↗

PubMed1986

Measurement and use of acoustic nonlinearity and sound speed to estimate composition of excised livers.

The acoustic nonlinearity parameter B/A and sound speed c have been determined for excised normal and abnormal human livers at 20-37 degrees C. These values are compared with analytic measurements of fat and water content of tissues. The results show that normal liver containing 71.0% water and 2.9% fat by weight has a B/A value of 6.75 and sound speed of 1592 m/s at 37 degrees C. Both these parameters increase at an average rate of 0.026 degrees C and 1.5 m/s/degrees C, respectively, as the temperature is raised from 20 to 37 degrees C. Fatty liver (24% fat by weight) exhibits highest B/A (9.12) and lowest c (1522 m/s) of all the livers studied. In contrast to normal livers sound speed in such a liver was found to decrease with temperature. Based on the acoustic and composition measurements, quantitative correlations of B/A and c with fat-water composition have been developed. Inversion of these relationships provide a simple method to determine composition of a tissue sample from B/A and c measurements.

Body Composition↗

PubMed1986

Ultrasonic nonlinear parameters and sound speed of alcohol-water mixtures.

Changes in the nonlinear parameter B/A caused by the addition of monohydric alcohols to water have been investigated. The measurements, made by using an aqueous solution of n-propanol, isopropanol, and t-butanol, show that as the alcohol concentration is increased, B/A decreases to a minimum at approximately 10% concentration (by volume). Further increase in alcohol concentration raises B/A rapidly to a maximum at about 80% by volume. This complex variation in B/A is attributed to solute-solvent interaction which is believed to be due to an enhancement of water structure in the water-rich region. These results suggest that the magnitude of B/A may be closely related to the quasilattice structure of water, which to a first approximation can be expressed by relative amounts of bound and unbound water.

Acoustics↗

PubMed1984

Measurement of the acoustic nonlinearity parameter B/A in human tissues by a thermodynamic method.

A thermodynamic method for measuring the acoustic nonlinearity parameter B/A in tissues is presented. It is based on the measurement of change in phase velocity as a function of time as the hydrostatic pressure of the sample is quickly reduced from a known value. This technique circumvents the effect of the attenuation in the medium and does not require a prior knowledge of the thermodynamic parameters of the tissues. The method is used to estimate nonlinearity parameters for normal and malignant tissues in the temperature range 20 degrees to 37 degrees C. The values and the temperature dependence of these parameters are found to vary with the nature of the tissues.

Adipose Tissue↗

PubMed1984

Scattering of ultrasound by tissues.

Scattering of ultrasound by biological tissues (continuous-inhomogeneous media) is discussed. An analytical expression for the attenuation due to scattering (alpha Tsc) and backscatter coefficients (sigma T) of tissues are obtained. The results explain the variation of alpha Tsc and sigma T with frequency for a number of tissues. The study also provides two statistical parameters, velocity fluctuation coefficient and correlation length, in terms of which the scattering of tissues can be defined quantitatively.

Animals↗

PubMedDate not supplied

Catheter-delivered ultrasound potentiates in vitro thrombolysis.

PURPOSE: To develop a catheter-directed method to enhance urokinase- mediated thrombolysis with use of ultrasound. MATERIALS AND METHODS: A prototype catheter was constructed by using a 9-F piezoelectric crystal capable of producing 640-kHz pulsed ultrasound energy. Clots formed in vitro from whole blood were trace-labeled with iodine-125 fibrinogen, and the release of radiolabeled fibrin degradation products was measured in the presence of urokinase, ultrasound, or a combination of urokinase and ultrasound. RESULTS: By 30 minutes, clot lysis was more complete with urokinase plus ultrasound (78.7% +/- 5.3 [mean +/- SD]) than with ultrasound alone (19.3% +/- 10.0) or urokinase alone (47.9% +/- 10.0) (P < .001 for ultrasound and urokinase vs either alone). The time to 50% clot lysis was shortened by 46% on average with the application of urokinase and ultrasound compared with urokinase alone (P < .03). CONCLUSIONS: Catheter-based ultrasound enhances enzymatic thrombolysis in vitro and may be a practical means to reduce the dose of enzyme and the time needed to achieve clot lysis in vivo.

Adult↗

PubMedDate not supplied

Proton MR chemical shift imaging using double and triple phase contrast acquisition methods.

Conventional chemical shift magnetic resonance (MR) imaging with the phase contrast technique has a number of limitations with respect to quantitative accuracy. The hypothesis of this study is that the accuracy of phase contrast chemical shift MR may be improved by increasing the number of basis images from two to three. Water and fat images were obtained from phantoms and volunteers with a 1.5 T MR system using double and triple acquisition phase contrast chemical shift methods. Longitudinal relaxation time and relative water and fat content were calculated from these basis images. The T1 relaxation times of the aqueous component of composite phantoms were determined more accurately using the triple acquisition method than with the double acquisition method. In vivo studies demonstrate that the triple acquisition method separated fat and water signals more accurately and showed less field inhomogeneity dependence than the modified double acquisition method. The new method also provided a map of static field magnetic inhomogeneity and tissue magnetic susceptibility. The triple acquisition phase contrast chemical shift imaging technique should improve the prospect for quantitative tissue characterization in clinical MR.

Adipose Tissue↗