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Biomedical subjects

G Dougherty

Publications and source records attributed to G Dougherty.

50 records · Page 3Linked to original sources
PubMed1982

The interaction between prothidium dibromide and DNA at the molecular level.

The interactions in solution and in the fibre state of the trypanocidal drug, prothidium dibromide, with DNA have been investigated using a number of biophysical techniques. The binding parameters at 0.11 ionic strength were determined by spectroscopic means. Sedimentation studies show that the drug is able to unwind closed circular DNA in solution, but X-ray diffraction and linear dichroism experiments indicate that it is uncertain whether this unwinding can be attributed to intercalation in the classical sense. On the basis of our results, we propose that the primary mode of binding is "sideways" intercalation, supplemented by electrostatic binding along the sugar-phosphate chains and interstrand binding involving hydrogen bonding.

Animals↗
PubMed1982

Superhelical turns of closed circular DNA in solution and in a gel: evidence for a conformational difference.

We have compared the number of superhelical turns, tau, in circular covalently closed plasmid pBR beta G DNA obtained by four different methods, each based on one particular distinguishing principle. Three of the methods allow an unequivocal determination of tau under gel electrophoresis conditions, whilst the fourth enables us to determine its value in solution. We were able to detect a significant difference between the two environments, corresponding to an unwinding of the DNA duplex angle by 0.3 degrees when a sample is transferred from solution to gel. The possible existence of such an effect has been generally overlooked by previous investigators. Our result suggests that the previously reported value for the number of base-pairs per helical turn should be adjusted downwards by about 0.10, so that it applies to conditions in solution.

Animals↗
PubMedDate not supplied

Quantitative indices for ranking the severity of hepatocellular carcinoma.

A method for quantifying the severity of tumour burden based on fractional affected areas, weighted by their mean attenuation values relative to normal tissue, is presented. The procedure was applied retrospectively to routine computerized tomography (CT) scans of patients with hepatocellular carcinoma, and produced severity indices that reliably followed the ranking of an expert panel.

Adult↗
PubMedDate not supplied

Quantitative assessment of abdominal aortic atherosclerosis observed in CT scans.

Calcification of the aorta is characteristic of atherosclerotic disease. A novel numerical index for quantitating the extent of calcification observed in computed tomography (CT) scans has been developed. The index weights the fractional area of the aorta showing calcifications with the average calcium density in the plaques. It obviates the need for manual tracing of the calcifications, and avoids the arbitrary nature and lack of reproducibility of the "calcium score" system currently used in assessing CT scans. Continuously different levels of calcification were distinguished in the abdominal aortas of a group of Kuwaiti females (n = 20), with a linear correlation coefficient between index value and age of 0.914 (P < 0.0001) over three decades. The index is generally applicable to all arterial calcifications, and could be used to monitor the effect of therapeutic regimes. It could easily be modified for use with 3D reconstructions obtained from CT helical scanning or MRI.

Adult↗
PubMedDate not supplied

Computerized evaluation of mammographic image quality using phantom images.

A simple, quick and computerized method for quantitatively evaluating the image quality of mammography phantom images has been developed. Images of the American College of Radiology (ACR) mammographic accreditation phantoms were acquired under different X-ray techniques, scored and ranked subjectively by five expert readers, and digitized for quantitative analysis. The contrast and signal-to-noise (contrast-to-noise) ratios of the main nodule and microcalcification group were obtained accurately and reproducibly using an image processing protocol. The contrast values were successful at discriminating differences in image quality due to variations in scatter conditions (as a result of different kVp's, and the presence or absence of an acrylic scatterer and/or a moving Bucky grid). They were more precise, reproducible and sensitive than the ACR score. In particular, the contrast of the main nodule was highly correlated (r(s) = 0.988: p<0.001) with the ranking of image quality by our panel of expert readers.

Artifacts↗
PubMedDate not supplied

A critical review of laser Doppler flowmetry.

Laser Doppler flowmetry (LDF) is now a well-established, non-invasive technique for measuring microvascular blood perfusion. However, there are a number of factors which can seriously affect the interpretation of the laser Doppler signal which are often not considered during routine use. These include: consideration of signal processing limitations, choice of processing bandwidth, problems with motion artefact and instrument calibration, the effect of probe pressure on the skin, and the type of laser used. This paper reviews many of the problems and limitations frequently encountered using the laser Doppler technique.

Calibration↗
PubMedDate not supplied

In vivo comparison of a twin wavelength laser Doppler flowmeter using He-Ne and laser diode sources.

This paper reports the results of a preliminary in vivo investigation in which laser Doppler blood-flow measurements were made in a variety of tissues in the anaesthetized rat using a twin wavelength laser Doppler system. The aim was to assess whether there was any detectable difference in the depth response of the laser Doppler system to blood-flow in skin, muscle and brain tissue using red light (633 nm) from a He-Ne laser source and near infrared (NIR) light (780 nm) from a semiconductor diode laser source. The results show that under normalized conditions, the flow signals obtained from the near infrared laser Doppler system is consistently larger than that recorded from the red He-Ne laser Doppler system. This suggests that laser Doppler flowmetry systems based on NIR laser sources sample larger volumes of tissue than those based on red He-Ne lasers.

Animals↗
PubMedDate not supplied

Comparative study of two laser Doppler blood flowmeters.

A new infrared laser Doppler blood flow instrument (Moor MBF3D) was evaluated using an in vitro model allowing measurements over a range of flow velocities and concentrations. The responses correlated well (r = 0.96, p less than 0.01) with those obtained simultaneously using a Perimed PF3 laser Doppler instrument. The different processing bandwidths of the instruments were investigated and the wideband mode of operation is recommended for flow measurements where there may be fast moving red blood cells (rbcs). The infrared instrument is capable of dual-channel operation, and the two channels are shown to respond almost identically for similar changes in blood flow through the in vitro model (r = 0.999, p less than 0.01). The main advantage of the dual-channel instrument is that continuous measurements may be made simultaneously at two different skin sites allowing dynamic flow responses to be compared.

Equipment Design↗
PubMedDate not supplied

Design and evaluation of an instrument to measure microcirculatory blood flow and oxygen saturation simultaneously.

There are compelling clinical advantages in being able to monitor, simultaneously and continuously, blood oxygen saturation and tissue perfusion from the same volume of tissue. We describe the design of a new instrument capable of combining both functions. It uses a laser diode at 805 nm to give a blood flow index and oxygenation information at that wavelength, and a pulsed LED at 660 nm to complete the estimation of oxygen saturation. By using a compensating photodetector these readings can be made relatively insensitive to sampling site. After calibrating the instrument on forehead sites it reliably read the oxygen saturation of sites on the thigh with a bias of -0.2% and a precision of +/- 1.7% relative to an IL 282 CO-oximeter.

Calibration↗
PubMedDate not supplied

Social class and the occurrence of traffic injuries and deaths in urban children.

This paper examines motor vehicle traffic accident deaths and injuries to pedestrians and bicyclists (ICD-9 codes E813-E814) aged 0-14 years, by income quintile of area of residence. It is based on 92 deaths in urban Canada in 1981, 69 deaths in Montreal during the period 1979-1983, and 1,133 injuries which resulted in hospital care or police reports in Montreal in 1981. For injuries in Montreal, the pattern of socio-economic inequality in the annual incidence rates by quintile was very pronounced, completely regular and highly significant. The rate of injury to children living in the poorest neighbourhoods was four times that of children living in the least poor neighbourhoods. For both sexes, inequalities were much more pronounced for pedestrians compared to bicyclists. For deaths in Montreal and all of urban Canada, the inequality in the rates did not follow such a consistent pattern across the income quintiles, nor were the differences statistically significant in most cases, but the rates for each sex were consistently highest in the poorest income quintile. Socio-economic inequalities in the rates of death and injury were greater in girls than in boys. The results are discussed in the context of theories of etiology and strategies for prevention.

Accidents, Traffic↗