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P P Dendy

Publications and source records attributed to P P Dendy.

At least 19 recordsLinked to original sources
PubMed1998

Characterization and use of a commercial n-type diode system.

The characteristics of n-type diodes (linearity, temperature, dose rate, radiation damage response, directional dependence, output factors, wedge factors and percentage depth dose determinations) were investigated. Subsequently, the diodes were used clinically for in vivo dose verification during external megavoltage photon beam therapy. It has been shown that n-type diodes are easy to use and the results obtained are comparable to those reported for p-type diodes. On most occasions, n-type diodes can be used without any additional correction factors apart from regular monthly calibration. There is good agreement between the uncertainty limits estimated from the diodes' characteristics and those obtained on the basis of 2261 patient measurements.

Equipment Failure↗
PubMed1990

A search for sonoluminescence in vivo in the human cheek.

In a previous experiment, sonoluminescence was observed in aerated water, especially at the pressure antinodes in the standing-wave field of a physiotherapeutic ultrasound device (Therasonic 1030). Mammalian cells in vitro showed growth inhibition when placed at the pressure antinodes but not at adjacent pressure nodes. In the light of these results, we looked for sonoluminescence in vivo when a similar standing-wave field was set up. To detect luminescence, a light guide was held against the inner surface of the human cheek. This would channel any luminescence photons to a cooled, red-sensitive photomultiplier which would quantify the light. Direct insonation of the cheek produced no detectable luminescence. Similarly when a water bag was placed against the outer surface of the cheek, and the latter was insonated through the bag, no luminescence was detected. Sonoluminescence from the water bag was, however, detected when the bag was placed against the inner surface of the cheek, showing that absorption of sound by the cheek tissue was not preventing cavitation. Further analysis showed that if cavitation had been occurring in the cheek without detection using the system employed, then the resulting sonoluminescence would have to be at most 0.025 times as intense as that produced by an equivalent volume of aerated water.

Acoustics↗
PubMed1989

Studies of the cavitational effects of clinical ultrasound by sonoluminescence: 4. The effect of therapeutic ultrasound on cells in monolayer culture in a standing wave field.

In previous work the phenomenon of sonoluminescence (SL) has been used to find the conditions in which transient cavitation during exposure to ultrasound is likely to be maximum. This paper reports the effect of therapeutic ultrasound on growth of mouse tumour cells in monolayer culture when the cells are insonated either at a pressure antinode or at a pressure node in a standing wave ultrasound field that is known to produce strong bands of SL at the pressure antinodes. Reduced cell numbers 72 h after insonation were recorded when the cells were insonated at an antinode but not when they were at a node. The possibility that this effect might be an artefact of the experimental system, and further experiments that could elucidate the nature of the damage, are discussed.

Animals↗
PubMed1989

Sites of deposition of aqueous aerosols: a study of efficiency of delivery systems for lung ventilation imaging in man.

A study was made of the deposition of 99Tcm-DTPA aerosol in the components of a jet nebulizer-based aerosol production system. Three impaction devices were compared: a ball-bearing separator, a virtual impactor and a step separator. In addition a comparison was made of two types of tubing which carried aerosol from nebulizer to mouthpiece: corrugated and smooth-walled tubing. The retention of aerosol following inhalation was measured in five normal volunteers using different patterns of breathing. Using an aerosol production system which included a ball-bearing separator only a mean of 11% of the radioactivity loaded into the nebulizer was emitted as an aerosol. Some 18% remained in the ball-bearing separator. The ball-bearing and step separators produced similar total outputs (7% and 6% minimum), the step separator producing marginally higher mean output/min. The virtual impactor produced a lower output than the other two impactors studied, only 1%. A larger proportion of the aerosol output was deposited on corrugated tubing (7%) compared with smooth-walled tubing (1%). The retained fraction of the aerosol inhaled by subjects ranged from 16% to 43%. A higher fraction was retained when subjects inhaled deeply and held their breath for 10 s between each breath. The efficiency of radionuclide deposition from aerosol generator to patient ranged from 1.1% to 6% and was determined more by the retention in the subject than by choice of separator or tubing.

Aerosols↗
PubMed1988

An experimental study of the relationship between image quality and spatial resolution for the gamma camera.

Many centres make regular measures of gamma camera performance as part of routine quality assurance programmes. Such measures may detect gradual deterioration in the camera but provide no basis on which to decide when corrective action should be taken. It is necessary to know when changes in camera performance are significant in terms of perceived image quality. In this work, one index of performance, the full width half maximum (FWHM) of the line spread function, was degraded in a controlled manner and the ability of observers to detect this change in the images produced was examined. Both simple and complex objects were investigated. A suitable decision criterion was suggested which indicated that changes of about 0.3 mm in the FWHM of the camera could be detected in the image. This figure was essentially independent of the complexity of the image, the initial FWHM of the camera and, above 300 k, the number of counts in the image. The way in which this type of experiment can help to establish a rational basis for gamma camera quality assurance programmes is discussed.

Bone and Bones↗
PubMed1985

Texture analysis in radionuclide tomographic liver imaging.

In clinical trials assessing the value of radionuclide tomographic liver imaging there has been no significant increase in diagnostic accuracy when conventional views have been viewed with tomographic images. In an effort to increase the diagnostic value of tomography, we have applied some simple methods of texture analysis to both phantom and patient tomograms in order to quantify different uptake patterns. Three algorithms were used which look at the differences between a pixel and its near neighbours. In phantom experiments, the variation of image texture with image noise was quantified. Accurate values of texture were obtained for images of the phantom containing various sizes of cold spots. Detection limits were then calculated for the different sizes of cold spots. It was found that 1.5 cm cold spots could be detected with a collection time of approximately 25 min, the usual collection time for livers being 20 min. The theoretical detection limits were checked experimentally and found to agree well with experimental values. A preliminary clinical survey was made applying texture analysis to eight images from normal livers and eight from abnormal (metastatic) livers. Although the sample was small, good separation between normals and abnormals was obtained.

Humans↗
PubMed1983

Relationship between objective and subjective assessment of gamma camera image sharpness.

In order to relate the performance of the human observer to the objective specifications of a gamma camera system, images of a test object were taken under various conditions that could be expected to cause changes in resolution. Observers were asked to put the images in the order of increasing/decreasing sharpness. For the same physical conditions, objective measurements were made from which the resolution parameters FWHM and FWTM could be derived. By looking for significant differences in ordering of the images, it was possible to show that, within the limitations of the specific system investigated, a fractional change in FWHM of about 10% caused a significant change in image quality. Further experiments to test the universality of this figure are suggested.

Humans↗
PubMed1983

Value of tomographic section views in identifying liver abnormalities by scintigraphy.

A previously published prospective trial to assess the value of tomographic transverse section images provided by the Aberdeen Section Scanner has been repeated using gamma camera images. Reports for 192 patients were analysed and compared with the final independent clinical diagnosis. The results were also compared with those of the previous investigation. When the latest results were plotted in the form of receiver operating characteristic curves, they showed some improvement for the 'with tomography' reports. Furthermore, introduction of a diagnostic classification rating showed that for cases with a high level of independent diagnostic evidence that the liver was abnormal, reporting confidence was higher with tomography. However, a simplified analysis of abnormality ratings suggested that the differences were not statistically significant for the numbers of patients examined.

False Negative Reactions↗