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D J Watmough

Publications and source records attributed to D J Watmough.

54 records · Page 3Linked to original sources
PubMed1977

A constant-flow calorimeter for the measurement of acoustic power at megahertz frequencies.

The calorimeter absorbs, in a flow of castor oil, a fraction of the acoustic power output of an ultrasound transducer. It has been used to measure powere of between 1 mW and 10 W at frequencies from 1-5 to 3 MHz. Examples are given of results obtained for an ultrasound therapy unit and an ultrasonic pulse--echo scanner. Sources of inaccuracy are defined. It appears that constant-flow calorimetry offers a potentially very sensitive method for the absolute measurement of acoustic power.

Calorimetry↗
PubMedDate not supplied

Local hyperthermia induced by focussed and overlapping ultrasonic fields--an in vivo demonstration.

Axial temperature distributions were measured in living and post mortem porcine tissues during sonication with plane, focussed and overlapping ultrasonic fields. With the focussed field it was always possible to induce the temperature maxima at depths up to 50 mm, although the actual temperatures achieved varied from animal to animal. The plane 0.75 MHz transducer produced a maximum temperature close to the skin surface. With 7 overlapping plane fields a relatively uniform temperature distribution was produced in a large tissue volume. The blood perfusion in tissue has a significant effect not only on the magnitude of the temperature increase, but also on the temperature distribution.

Animals↗
PubMedDate not supplied

Observations of ultrasound-induced effects in the fish Xiphophorous maculatus.

Tails of the fish Xiphophorous maculatus have been studied by transmission light microscopy during irradiation with continuous wave ultrasound (frequencies 0.78-3 MHz, spatial average intensities 0.01-3 Wcm-2). Blood flow started to increase a few minutes after the start of an irradiation, reaching a maximum after 5-10 min. Periodic variations in blood flow rate were often seen, and the response varied considerably among individual specimens. Acoustic microstreaming, which resulted in rapid rotation of clusters of cells, was observed in blood vessels adjacent to cartilaginous rods in the tail. The threshold average spatial intensities to initiate this were a few hundred mW cm-2 at 0.78, 1.5 and 3 MHz. The microstreaming resembled that occurring around ultrasonically stimulated microbubbles, but no evidence of any association was found. Microbubbles, possibly originating in water, were sometimes seen in the tissue of the fish following treatment with ultrasound.

Animals↗
PubMedDate not supplied

The construction and assessment of lenses for local treatment of malignant tumours by ultrasound.

A simple method to build ultrasound lenses from araldite has been developed. The focussing properties of these lenses as a function of sonic frequency and lens diameter were studied using a computer model. The optimum frequency and diameter of these lens were found to be around 1 MHz and between 40 and 60 mm respectively, for deep tissue heating. The stability of the power output as well as the temperature distributions produced in vitro and in vivo have also been studied. It appears to be possible to produce larger temperature elevations near the acoustical focus than near the skin surface in vivo. Therefore the lenses seem to be suitable for local cancer treatment.

Animals↗
PubMedDate not supplied

Measurement of ultrasound energy density distributions in vivo.

Thermocouple junctions coated with absorbing material have been used for measurement of ultrasound energy density distribution in vivo. The response of this type of probe has been measured in tumours implanted in rats, in ox liver, and in a water bath, using 1 and 3 MHz focussed ultrasound, and these measurements are reported in this paper. The initial rapid rate of temperature rise during the first 60 ms after the ultrasound is switched on provides a reliable index of ultrasound energy density. The coating material increases the magnitude of the temperature rise and reduces variations caused by differences in tissue properties and changes in blood flow. The response is a linear function of ultrasound energy density over the range of interest for therapeutic applications. Thus probes calibrated in known ultrasound fields in water tanks can be used to estimate energy densities in tissue directly.

Animals↗
PubMedDate not supplied

Combined effects of hyperthermia (to 45 degrees C) and ultrasound irradiation on the surface ultrastructure of HeLa cells.

Hyperthermic treatment of HeLa cells in suspension combined with ultrasound irradiation produced alterations to the cell surfaces. The changes induced were related to ultrasound intensity in the standing wave and to heat treatments between 37 and 45 degrees C. Two transducers were used, driven at resonant frequencies of 0.75 and 1.5 MHz, and producing peak intensities up to 7 W/cm2. These intensities produced a negligible rise in temperature of the cell suspension medium. Ultrastructural damage in standing wave fields, as seen by scanning electron microscopy, progressed through stages. The first stage was characterized by the loss of microvilli and smooth appearance of the cell surface, e.g. after insonation at 41.5 degrees C for 10 min; damage increased to a final stage where the surface appeared heavily pitted and porous, with the cells showing signs of disintegration, e.g. after insonation at 45 degrees C for 10 min. The monitoring of ultrasound-induced cavitation suggested that damage was caused by bubble oscillations, not collapse cavitation. Shearing stresses accentuated by hyperthermia were considered the probable cause of such damage. Coulter counter studies of cell size distribution showed that the extent of cell damage depended on the geometry of the vessel in which insonation was carried out.

Cell Membrane↗