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D J Watmough

Publications and source records attributed to D J Watmough.

At least 19 recordsLinked to original sources
PubMed1996

Case report: tuberculosis of the parotid gland--diagnosis by CT.

A case of parenchymal and intraparotid lymph node tuberculosis is reported in a young Asian male. The diagnosis was suggested pre-operatively by the contrast enhanced CT (CECT) appearance. There were no systemic symptoms of tuberculosis and this is a characteristic feature of the 100 cases reported in the literature. The presence of thick walled rim enhancing lesions with a central lucency on CECT should suggest the diagnosis. Filling defects with or without thin walls are non-specific findings and are seen in tumours and other inflammatory processes. In an appropriate clinical setting, thick walled round rim enhancing lesions with a central lucency are characteristic of tuberculosis.

Adult↗
PubMed1994

Role of ultrasonic cleaning in control of cross-infection in dentistry.

The dye/paper method of mapping ultrasound fields has been used to demonstrate the non-uniform distribution of energy density and cavitational activity in an ultrasonic cleaning bath. It is also shown that removal of a layer of artificial contaminant from a surface proceeds at rates which vary considerably with position because of standing waves set up by reflections in the walls of the bath and at the liquid surface. In view of the use of such baths as part of the process of controlling cross-infection in dentistry, it is suggested that manual cleaning of reusable instruments may be necessary as well.

Colloids↗
PubMed1993

Breast compression: a preliminary study.

X-Ray mammography is the technique employed to image breast tumours; it is the gold standard for both diagnosis and screening. To increase the sensitivity of the test and to reduce the dose of X-radiation, breast compression is used. The effect of squeezing a simple model of a breast in which there is an idealized spherical tumour volume is investigated; the cases where the lesion has both a smaller, and a larger compressibility than the surrounding tissues are considered. Surface strain is computed as a function of the deformation of the lesion from its spherical shape. Evidence from earlier studies is adduced to show that when the lesion is malignant care should be exercised to avoid the possibility of disseminating cancer cells by the application of compressive forces.

Breast Neoplasms↗
PubMed1993

The effect of gas bubbles on the production of ultrasound hyperthermia at 0.75 MHz: a phantom study.

Transparent phantoms, made of bovine hide gelatine, have been constructed in order to study the consequences of the occurrence of cavitation in tissues. Gas pockets of about resonant size, physically introduced into the gel, lead to a mean temperature rise of 41 +/- 15 degrees C in 1 min, when the gel of concentration 11.4% (w/v) is sonicated in the continuous-wave (cw) mode at 1 W cm-2 (spatial average) and 0.75 MHz. Nyborg (1965) has shown that gas bubbles in a sound field can act as acoustic amplifiers and the observations reported here may be connected with this feature. A layer of gelatine foam was also used to introduce gas into the gel and in this case the temperature rise was about 12 +/- 5 degrees C under similar conditions. Without gaseous inclusions, the mean temperature rise in gel in 1 min was 2.3 +/- 0.2 degree C. At a gel/air interface, the rise per unit intensity per minute was 4.4 degrees C. It is concluded that in clinical situations, cavitation (or degassing due to supersaturation), when it does occur, is likely to be an undesirable consequence of ultrasound treatment. This finding, of large temperature rises in proximity to gas bubbles, is in broad agreement with the report by Hynynen (1991) of an excess temperature elevation of 60 degrees C in dogs' muscle in vivo during a 1 s pulse at 250 W cm-2 and 0.56 MHz. Other studies, by ter Haar and Daniels (1981) and Daniels and ter Haar (1986), of sonicated animal tissues in vivo, have found thresholds for bubble inception but no consequent temperature rise greater than 0.3 degrees C was observed.

Gases↗
PubMed1992

Study of tissue compression in breast phantoms: possible implications for the use of X-ray mammography as a method of imaging breast carcinoma.

A method is described of constructing a simple phantom breast containing an idealised tumour with elastic properties. The transparent tissues are compressed and evidence is adduced to show that with tissue compression the tumour boundary is subjected to a degree of strain the magnitude of which is dependent on the degree of deformation. Excessive compression can lead to fracture of the tumour. A literature survey reveals that malignant tissues are more delicate than normal tissues. The study underlines the need for care when using X-ray mammography with compression to image a cancer bearing breast, in order to avoid disseminating cancer cells via the circulation.

Breast Neoplasms↗
PubMed1991

Imaging microbubbles and tissues using a linear focussed scanner operating at 20 MHz: possible implications for the detection of cavitation thresholds.

B-Scan images have been used as a means of detecting the onset of cavitation in tissues. New echoes appearing during simultaneous sonication with therapeutic ultrasound have often been attributed to bubble formation. In this study temperature rises up to 15 degrees C W-1 cm2 in guinea pig leg (post-mortem) were found, which would itself increase the rate of growth of gas bubbles. It is also hypothesized that a temperature dependent attenuation coefficient predicted by Bamber and Hill may, at least in part, account for new echoes appearing in tissues. Possible artefactual echoes in the B-scan images arising from acoustically induced gas bubbles in the coupling medium are also discussed.

Animals↗
PubMed1991

Theoretical considerations in relation to the treatment of brain tumours by means of local hyperthermia generated by ultrasound fields.

Brain tumours comprise a significant fraction of all tumours in the human body. Despite the development of technology in clinical oncology, these tumours still present a difficult challenge. The margin between destruction of tumour and damage to normal tissue is narrow in the brain. The price paid for producing tissue damage outside the tumour is high in terms of quality of survival. Results of many experiments with ultrasound hyperthermia show that this new technique is successful for treating certain types of malignant tumours. In the case of brain tumours, applying focused fields should have the advantage of selectively destroying the tumour and leaving surrounding tissues intact. Previous attempts at applying ultrasound to the field of neurosurgery are reviewed. Those factors which have effects on the generation of thermal fields in brain tissues are considered in relation to the possible treatment of human brain tumours. Calculated thermal fields in a 2-D brain model generated by an applicator built in our laboratory are also presented.

Brain↗
PubMed1990

Some of the factors involved in the Sarvazyan method for recording ultrasound field distributions with special reference to the application of ultrasound in physiotherapy.

The mapping of ultrasound fields using the dye paper method is described. The mode of action by which the dye concentration is increased has been investigated. Microbubbles on the paper surface and microstreaming of dye solution seem to be essential features of the mapping method. The streaming is thought to inhibit the formation of a dye depletion layer near the paper to an extent dependent on local sound intensity A linear relation between streaming velocity and intensity is derived.

Coloring Agents↗
PubMed1990

Possible explanation for the unexpected absence of gross biological damage to membranes of cells insonated in suspension and in surface culture in chambers exposed to standing and progressive wave fields.

Quoted values of cavitation thresholds reported in the literature vary over several orders of magnitude. This paper describes an investigation of the threshold in a chamber with acoustically transparent windows, situated around the last axial maximum of a 0.75 MHz standing wave field. The chamber, the transducer and the reflector are submerged in a tank containing distilled water which also fills the chamber. The formation of bubbles outside the chamber, both above and below it, occurred at lower intensities than those needed to generate bubbles in the chamber. This unexpected finding led to a theoretical study of streaming patterns in progressive and standing wave fields. These showed that there is a region around the last axial maximum in which there is no gradient of energy density. Therefore if this region is enclosed by an acoustically transparent chamber, no significant bulk streaming occurs within it. We speculate on how this lack of streaming raises the cavitation threshold. The cavitation phenomenon is also examined by Doppler ultrasound of frequency 8 MHz. This confirms the occurrence of increased intensity thresholds within the chamber. It also shows that the time between filling the chamber and the start of sonication strongly influences the magnitude of the cavitation threshold. We expect that the effects described here may have consequences for sonication of cells in suspension culture when the samples are held in chambers situated around the last axial maximum of an ultrasound beam from a plane transducer.

Acoustics↗