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J W Hunt

Publications and source records attributed to J W Hunt.

At least 55 records · Page 3Linked to original sources
PubMed1992

Accelerated gallstone dissolution in methyl tert-butyl ether by sonication. An in vitro study.

OBJECTIVES: The authors tested the effect of 195 KHz therapeutic ultrasound energy on gallstone dissolution in concert with methyl tert-butyl ether (MTBE) in vitro. METHODS: Sixteen sets of three gallstones matched for weight and appearance were selected from 16 surgically resected human gallbladders. One stone from each set was analyzed for its density pattern by computed tomography (CT) and biochemically for cholesterol content. Based on CT appearance, the stones were classified into eight noncalcified, four partially calcified, and four heavily calcified sets. The three stones were subjected to dissolution with MTBE: one with simultaneous sonication via an experimental ultrasound unit, one with manual stirring, and one acted as control without added treatment. RESULTS: Sonication reduced the dissolution time of noncalcified stones by 96% (range, 94%-98%; standard deviation [SD], 2%) relative to controls, and it was three to four times more effective than manual stirring. It was similarly effective in helping to dissolve partially calcified stones, but not heavily calcified stones. CONCLUSIONS: This study demonstrates the positive effect of sonication in accelerating gallstone dissolution with MTBE in vitro for stones without heavy calcification.

Cholelithiasis↗
PubMed1991

Measurement of the ultrasonic properties of vascular tissues and blood from 35-65 MHz.

A 50 MHz ultrasound backscatter microscope has been built to measure the acoustic properties of vascular tissues and blood over the frequency range from 35-65 MHz. High resolution (45 microns) ultrasound backscatter microscope images of nine femoral and eight common carotid human artery samples were made and compared with corresponding histological sections. Individual tissue layers were selected using these images for quantitative measurement of the frequency dependent backscatter. Backscatter measurements were made in each layer of an artery at two different angles of incidence: along the axis of the artery (axial direction) and at 90 degrees to this measurement radially out from the center of the artery (radial direction). Scattering was found to be higher in elastic arteries (carotid) than in the muscular arteries (femoral). The largest difference was found in the media where the average scatter (measured in the radial direction at 50 MHz) increased from 0.002 sr-1 mm-1 in muscular arteries to 0.4 sr-1 mm-1 in elastic arteries. Large differences in scattering between measurements made in the axial and radial direction were also found. Again, the largest differences were found in the media where scattering (at 50 MHz) in carotid arteries increased from 0.003 sr-1 mm-1 measured in the axial direction to 0.4 sr-1 mm-1 measured in the radial direction. The speed of sound and attenuation in the artery wall of each sample were measured. Speed of sound measurements were found to range between 1579-1628 ms-1. The average attenuation in the artery wall increased from 4 dB mm-1 at 30 MHz to 10 dB mm-1 at 60 mHz. This is higher than the attenuation measured in blood which increased from 1.6 dB mm-1 to 5 dB mm-1 over the same frequency range. The backscatter coefficient for flowing blood was measured for flow velocities up to 36 cms-1. At flow velocities below 18 cms-1 a level of scattering of 0.0005 sr-1 mm-1 (at 50 MHz) was found. An increase in scattering of 1.6 times was measured when the flow velocity was increased to 36 cms-1. All measurements were made at 37 degrees C. The relevance of these results to clinical imaging and image interpretation is discussed.

Arteriosclerosis↗
PubMed1990

Clinical performance of a cone/annular array ultrasound breast scanner.

Ultrasound is a useful adjunctive imaging modality to x-ray mammography for the detection and management of breast disease. A high resolution (0.3 mm at -6 dB) transducer consisting of co-axially aligned cone and annular array transducers has been incorporated into a prototype breast imaging system. The prototype scanner had an operating frequency of 4 MHz and scanning was performed in the prone position. We hypothesized that the increased resolution of this system would lead to improved detection of smaller, nonpalpable lesions and would thus contribute to the early detection of breast cancer. Results of a four year clinical study of the prototype involving 1743 patients are reported. The overall true positive (TP) fraction for the detection of malignancy was 52.5% compared with 86.6% for x-ray mammography. Improved performance of ultrasound approaching that of mammography is demonstrated for the youngest age group (less than 34 years) and for women whose breasts are predominantly dysplastic. However, the detection of nonpalpable tumours is disappointing with a TP fraction of only 22%. Causes for the failure of the prototype breast scanner to detect early breast lesions are presented and general conclusions on the use of large aperture transducers for automated breast imaging are discussed.

Adolescent↗
PubMed1989

A ray tracing method for calculating the speed of sound in a nonparallel layered model using pulse echo ultrasound.

A method of calculating the speed of sound in a nonparallel layered model is presented. A focussed ultrasound source and receiver are used to locate the angle and position of an incident pulse and the reflected pulses at the surface of the model. Triangulation is used to calculate the speed of sound in the first layer and points on the first interface for a number of source positions and angles. For subsequent layers, ray tracing is used to eliminate the effect of the overlying layers. A computer simulation in which images of the speed of sound are reconstructed from data generated by ray tracing through two models is presented. Ways in which this method could be implemented are proposed.

Computer Simulation↗
PubMed1988

A comparison of the rate of clearance of xenon (133Xe) and pertechnetate ion (99mTcO4-) in murine tumors and normal leg muscles.

Xenon-133 is a widely used tracer for clearance measurements to estimate nutritive blood flow. There are however certain difficulties in handling and obtaining the radionuclide. Pertechnetate ion, 99mTcO4-, is used extensively as a radiotracer in nuclear medicine studies and is easily available. To assess the usefulness of pertechnetate ion for blood flow studies, we have measured the rate of clearance following a local injection of pertechnetate ion and xenon simultaneously in normal mouse leg muscle and in murine tumors (fibrosarcoma and mammary carcinoma) of different sizes. The partition coefficients for the two tracers were also measured. The results indicated that the clearance halftime for pertechnetate ion was consistently greater than that for xenon in the tumors but similar in normal resting muscle. The estimated blood flow values assessed using the two tracers were similar in all cases except for large tumors (greater than 1.5 g). In this case, pertechnetate ion gave lower values than xenon. The difference could be explained by the large intracapillary distances which occur in poorly vascularized regions of large tumors since pertechnetate is a charged ion and hence might be expected to have limited diffusion capacity. The results indicate that caution is warranted when pertechnetate ion is used as a tracer for measurements of blood flow and for other biological determinations which depend on tissue transport for properties.

Animals↗
PubMed1988

Ultrasonographically defined parenchymal patterns of the breast: relationship to mammographic patterns and other risk factors for breast cancer.

We have used ultrasound of the breast to define four parenchymal patterns in which increasing proportions of the breast are replaced by densely echogenic tissue. A series of 452 symptomatic women examined by both ultrasound and conventional X-ray mammography was reviewed to determine whether these ultrasonographic images could predict the breast parenchymal pattern defined mammographically. A very strong correlation was demonstrated between the breast pattern on ultrasound and the volume of the breast replaced by either dysplasia (Kendall's tau-b = 0.731 +/- 0.026, p less than 0.0001) or ductal prominence (Kendall's tau-b = 0.641 +/- 0.049, p less than 0.0001). This was seen both on initial reporting and on a blind re-reading of a random sample of 100 cases. The strength of correlation was similar for subgroups defined by family history of breast cancer, age, menopausal status, and history of benign breast disease, and the breast parenchymal pattern assessed by mammography or ultrasound showed similar associations with these variables. Ultrasonographic parenchymal patterns of the breast can predict the tissue patterns defined mammographically and may therefore be useful as a marker of breast cancer risk.

Adult↗
PubMed1986

Quantitative contrast measurements in B-mode images comparison between experiment and theory.

Quantitative measurements of image contrast were carried out for B-mode images of anechoic spheres (cysts) embedded in a random scattering medium. Four transducer geometries were used: (a) f/5.7 spherical transducer in pulse echo mode, (b) f/2.4 spherical transducer in pulse echo mode, (c) f/2.4, 30 degrees cone (hybrid transducer), (d) f/5.7, 30 degrees cone (hybrid transducer). The image contrast was also calculated via two methods; (i) a three-dimensional computer simulation and (ii) a relatively simple numerical convolution which relates the image of a small point-like scatterer [point spread function (PSF)] to image contrast. Generally, good agreement was found between the experimental measurements and the values calculated via both theoretical methods. The results indicate that image contrast is not determined solely by the full width at half maximum (FWHM) of the PSF. In particular, the results demonstrate the importance of far off-axis contributions of the ultrasound beam to the significant degradation of contrast in images obtained with high resolution (low f-number) axicons.

Computers↗
PubMed1986

Speckle reduction in pulse echo imaging using phase insensitive and phase sensitive signal processing techniques.

In conventional B-scan imaging, speckle often distorts the true representation of small structures and lesions and hence reduces the diagnostic potential of the technique. Considerable speckle reduction has been achieved with an f/2.4, cone hybrid system by cutting the large aperture transducers into sectors, and using either phase insensitive sector addition (PISA), phase insensitive sector multiplication (PISM), or an rf multiplicative processing technique. We have compared two modes of operation with the hybrid system. In the first, the cone acts as transmitter, and each sector of the f/2.4 spherical aperture is a receiver. In the second mode, the f/2.4 sphere acts as transmitter, and each sector of the cone is a receiver. Quantitative assessment using the contrast to speckle ratio developed by Patterson et al, indicates that processing under both modes results in reduced speckle noise and improved image quality, with the cone sector receive (rx) geometry offering the greatest improvement.

Breast↗
PubMed1983

Computer simulations of speckle in B-scan images.

The granularity or speckle in medical ultrasound images tends to mask the presence of small lesions. As well, artifactual filling in of anechoic regions such as cysts, reduces the diagnostic potential of the images. These effects depend not only on the acoustic properties of the tissue but also are strongly influenced by the imaging system, especially the transducer geometry. To study the effect of the transducer on the final B-scan image, a computer model has been developed simulating the interaction of ultrasound with a simple scattering medium. This model, incorporating the position dependence of the point response of the transducer, is based on single scattering from a collection of points positioned randomly in a three-dimensional volume. Using this approach, B-scan images showing speckle have been generated for different transducer geometries. Inclusion of a 2.6 mm void mimicking a cyst within the three-dimensional scattering volume has allowed us to predict the cyst contrast in the image for the different transducer systems. Experimental B-scan images of a scattering phantom were obtained using the different pulse echo systems. Quantitative assessment using first and second order statistics of the images shows good agreement between experiment and theory.

Acoustics↗
PubMed1982

Applications of microwave, ultrasound, and radiofrequency heating.

Different needs must be considered in the control of localized tumors or disseminated disease when deep heating techniques are used. For localized disease, various electromagnetic microwaves, radiofrequency currents and high-powered ultrasound sources are being used. At the present time, each approach has its own strengths and limitations. Microwave and inductive approaches appear to be useful only for surface lesions. Radiofrequency currents, generated by pairs of plates, give more deeper heating in the body, but excessive heating occurs in fatty layers related to high resistivity of the tissue and sometimes near the edge of the applicators. In an invasive approach, needles are implanted into the tumor and excited by a radiofrequency source. Considerable clinical successes are claimed for local heating of the lesion with this approach, but it is only useful for specific sites of the body. Ultrasound has special advantages for both surface or deep-seated soft tissues due to its flexibility and its ability to focus the beam onto the lesion. However, ultrasound cannot be used in the chest cavity or near bone, and the dosimetry is not defined at present. For disseminated disease, much larger regions, particularly in the chest cavity, can be heated, with the hope that the reduced blood circulation in some tumors can achieve a preferential heating in the lesion. Several microwave and inductive heating approaches are being used or considered in the achievement of this goal.

Humans↗