No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

A microscopy probe was developed to image small samples at 7 Tesla (300 MHz). The gradient coil set comprises two Golay coils and a Maxwell pair, generating gradients up to 2 T/m. A 3 turn solenoidal radiofrequency coil was used for excitation and signal reception. This probe was capable of imaging small samples up to 3 mm diameter. In-plane pixel sizes down to 25 m have been employed, and the images obtained have adequate quality for biological studies. This research was focused on a particular biological system: the excised mouse eye. The susceptibility-related field inhomogeneity was evaluated. Interfaces with air are the main source of field inhomogeneity, which depends strongly on the shape of the interface. Excised mouse eye images were particularly affected by susceptibility-related field inhomogeneity due to small quantities of blood and the optic nerve, which protrudes from the almost completely spherical eyeball. The signal loss and image distortion were analysed by imaging simple geometrical phantoms and comparing simulated image with the experimental results. Guidelines for imaging in the presence of magnetic field susceptibility were discussed. The measurement of diffusion coefficients by imaging techniques proved to be very sensitive to the presence of intrinsic gradients and imaging gradients. Diffusion sensitisation gradients were applied in opposite directions and the resulting images were combined to achieve sufficient accuracy. A new technique to manipulate these images was developed; this allowed the identification of the sources of error in the measurement, and the detection, of anisotropic diffusion, aiding the interpretation of diffusion weighted images and diffusion coefficient maps.

No description available.

No description available.

The thesis opens with a review of the current knowledge of the mechanisms for the repair of radiation induced damage in bacteria and mammalian cells. The experimental work is presented in Chapters 2 to 6, each chapter beginning with an introduction and concluding with a discussion pertinent to the work described. Chapter 2 is concerned with the development of the culture of the mouse lymphoma cell lines L5178Y, JL, L5178YS and AIV, together with a soft agar suspension procedure for assessment of viability. The inactivation of the four cell lines, in two stages of growth, to gamma radiation and to 254 nm, 313 nm and 365 nm ultraviolet radiation has been compared in Chapter 3. The enhanced sensitivity of L5178YS cells to gamma radiation over that of the parent, L5178Y line is shown to UV radiation of all the wavelengths, as is the increased resistance exhibited by the AIV cell line. Chapter 4 describes a preliminary investigation into the mutagenic response of L5178Y cells to 254 nm and 313 nm radiation in two mutation assay systems, ouabain resistance and 6-thioguanine resistance. The sensitisation of 313 nm radiation inactivation and mutation of L5178Y cells by the sunscreen agent, para-amino benzoic acid PABA was investigated and the results are presented in Chapter 5. The sensitisation of 313 nm radiation inactivation was found to be dependent upon PABA concentration, and 0.2% PABA was found to enhance 313 nm radiation induced resistance to both ouabain and 5-thioguanine. A method of producing mutants of L5178Y cells which are sensitive to 254 nm radiation is described in Chapter 6. The isolates were characterised in terms of their sensitivity to 254 nm radiation, with respect to the time in culture after isolation. General conclusions concerning the use of L5178Y cell line for the elucidation of mammalian cell repair mechanisms are discussed in Chapter 7.