Geoffrey Dougherty

Bio: Geoffrey Dougherty is an academic researcher from Kuwait University. The author has contributed to research in topics: Imaging phantom & Medicine. The author has an hindex of 16, co-authored 43 publications receiving 1093 citations. Previous affiliations of Geoffrey Dougherty include University of Oxford & Keele University.

A critical review of laser Doppler flowmetry.

Abstract: Laser Doppler flowmetry (LDF) is now a well-established, noninvasive 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.

Measurement of thickness and density of thin structures by computed tomography: a simulation study.

Abstract: The limited spatial resolution of clinical CT systems causes difficulties in the measurement of the density and thickness of thin structures such as the vertebral cortical shell. We simulated the imaging process by convolving experimentally determined point spread functions with rectangular and Gaussian profiles, for various fields of view or pixel sizes and reconstruction kernels. The simulations successfully explained the reported overestimation of thickness and underestimation of density when imaging thin structures. Both effects are larger for Gaussian profiles. For the rectangular profiles, experimental estimates of thickness and density will only be accurate when the true thickness is greater than about 1.5 times (for the bone reconstruction kernel) or 2.0 times (for the standard kernel) the full width at half maximum of the point spread function (PSF) of the imaging system. For Gaussian profiles imaged by a system with a Gaussian PSF, there are straightforward analytical expressions for the overestimation of thickness and underestimation of density: and these are useful approximations to the simulations of Gaussian profiles with experimental (pseudo-Gaussian) PSFs. We have demonstrated that thresholding of the vertebral image cannot provide accurate estimates of cortical thickness and density because the appropriate threshold level requires foreknowledge of the cortical thickness. To circumvent such difficulties we suggest that the average value of the peak CT numbers measured along the medial axis of the cortical shell be adopted as an index of cortical shell strength, since its value depends on both the density and the thickness of the shell.

Polycyclic aromatic hydrocarbons physically intercalate into duplex regions of denatured DNA

Abstract: We have investigated the physical binding of pyrene and benzo[a]pyrene derivatives to denatured DNA. These compounds exhibit a red shift in their absorbance spectra of 9 nm when bound to denatured calf thymus DNA, compared to a shift of 10 nm when binding occurs to native DNA. Fluorescence from the hydrocarbons is severely quenched when bound to both native and denatured DNA. Increasing sodium ion concentration decreases binding of neutral polycyclic aromatic hydrocarbons to native DNA and increases binding to denatured DNA. The direct relationship between binding to denatured DNA and salt concentration appears to be a general property of neutral polycyclic aromatic hydrocarbons. Absorption measurements at 260 nm were used to determine the duplex content of denatured DNA. When calculated on the basis of duplex binding sites, equilibrium constants for binding of 7,8,9,10-tetrahydroxy-7,8,9,10-tetrahydro-benzo[a]pyrene to denatured DNA are an order of magnitude larger than for binding to native DNA. The effect of salt on the binding constant was used to calculate the sodium ion release per bound ligand, which was 0.36 for both native and denatured DNA. Increasing salt concentration increases the duplex content of denatured DNA, and it appears that physical binding of polycyclic aromatic hydrocarbons consists of intercalation into these sites.

Neither delta- nor lambda-tris(phenanthroline)ruthenium(II) binds to DNA by classical intercalation.

Abstract: Equilibrium binding studies and viscosity experiments are described that characterize the interaction of delta- and lambda-[Ru(o-phen)3]2+ with calf thymus DNA. The mode of binding of these compounds to DNA is a matter of controversy. Both isomers of [Ru(o-phen)3]2+ were found to bind but weakly to DNA, with binding constants of 4.9 (+/- 0.3) x 10(4) M-1 and 2.8 (+/- 0.2) x 10(4) M-1 determined for the delta and lambda isomers, respectively, at 20 degrees C in a solution containing 5 mM Tris-HCl (pH 7.1) and 10 mM NaCl. We determined that the quantity delta log K/delta log [Na+] equals 1.37 and 1.24 for the delta and lambda isomers, respectively. Application of polyelectrolyte theory allows us to use these values to show quantitatively that both the delta and lambda isomers are essentially electrostatically bound to DNA. Viscosity experiments show that binding the lambda isomer does not alter the relative viscosity of DNA to any appreciable extent, while binding of the delta isomer decreases the relative viscosity of DNA. From these viscosity results, we conclude that neither isomer of [Ru(o-phen)3]2+ binds to DNA by classical intercalation.

The chemistry and biochemistry of vanadium and the biological activities exerted by vanadium compounds.

Abstract: 6.1.2. Aqueous V(III) Chemistry 877 6.1.3. Oxidation State of Vanadium in Tunicates 878 6.1.4. Uptake of Vanadate into Tunicates 879 6.1.5. Vanadium Binding Proteins: Vanabins 879 6.1.6. Model Complexes and Their Chemistry 880 6.1.7. Catechol-Based Model Chemistry 880 6.1.8. Vanadium Sulfate Complexes 881 6.2. Fan Worm Pseudopotamilla occelata 883 7. Vanadium Nitrogenase 883 7.1. Nitrogenases 883 7.2. Biochemistry of Nitrogenase 884 7.3. Clusters in Nitrogenase and Model Systems: Structure and Reactivity 885

Tris(phenanthroline)ruthenium(II) enantiomer interactions with DNA: Mode and specificity of binding

Abstract: Absorbance and fluorescence methods, circular dichroism, UV melting experiments, viscosity, and competition dialysis were used to study the interaction of delta and lambda tris(phenanthroline)ruthenium(II) with DNA. The results of these studies indicated that both isomers bind to DNA by a single mode. The two isomers differ, however, in their effect on the hydrodynamic properties of DNA as measured by viscosity and, therefore, probably differ in their individual binding modes. The optical properties of the fully bound compounds differ from those of the free, but the perturbations of their visible absorbance and fluorescence emission spectra are modest when compared to changes observed for other DNA binding compounds. Binding of both isomers to DNA was found to be weak (in comparison to proven intercalators), with binding constants on the order of 10(4) M-1 determined for their binding to calf thymus DNA. A small, positive enthalpy was found for the binding of each isomer to DNA, suggesting that binding is entropically driven. Both isomers increased the melting temperature of DNA, with little quantitative difference between the two. A modest base specificity was found for each isomer, with the delta isomer preferentially binding to GC base pairs, and the lambda isomer preferentially binding to AT base pairs. Competition dialysis was used to examine the preference of delta and lambda Ru for right-handed B DNA and left-handed Z DNA. Neither isomer exhibits significant selectivity for these radically different DNA secondary structures.