No description available.

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No description available.

There is still much information to be gained on the pharmacokinetics of platinum based chemotherapy agents such as cisplatin, and its second generation analogue, carboplatin. A <SUP>99m</SUP>Tc based XRF system in backscatter geometry has been re-introduced in Swansea, for the <I>in vivo</I> measurement of platinum uptake in head and neck tumours. The minimum detection limit (MDL) was found to be 21 ppm for a tumour depth of 10 mm, increasing to 40 ppm for a depth of 20 mm, for a skin dose of 9 mGy. <I>In vivo</I> measurements were therefore limited to superficial tumours only. Eight patients underwent a total of fifteen measurements using the <SUP>99m</SUP>Tc system. The MDL was exceeded in five of these measurements. Replacing the <SUP>99m</SUP> Tc source with <SUP>133</SUP>Xe, and optimising the collimator-to-skin distance, improved the sensitivity of the system for tumour depths less than 15 mm. The MDL was reduced to 15 ppm at a depth of 10 mm, for the same skin dose. The sensitivity of the Swansea <I>in vivo</I> XRF system was significantly improved by the introduced of a polarised x-ray source. A clinical orthovoltage x-ray unit (Pantak DXT-300), which is routinely used for radiotherapy treatments, was adapted for this purpose. Experimental investigation into the effect of varying the operating voltage, polarising material and additional filtration on the system sensitivity, showed that the optimum combination consisted of a copper polariser, 0.25 mm of additional tin filtration in the primary beam and an operating voltage of 220 kV. The MDL at a depth of 20 mm was 8 ppm for the optimised system, with a corresponding skin dose of approximately 3 mGy. This represents more than an 80% reduction in the MDL compared to the <SUP>99m</SUP>Tc based system, enabling the measurement of deeper tumours, with increased sensitivity.

This thesis describes the construction, development and clinical use of a mobile neutron activation analysis facility which was designed specifically to measure, in-vivo, renal cadmium levels in environmentally exposed populations. The experimental method involved irradiating the left kidney with a collimated beam of neutrons from a radioisotopic neutron source and measuring on-line, from outside the body, the chaxacteristic 559 keV capture gvmma-rays from TT3Cd, using a high efficiency Ge(Li) detector. The irradiation facility was based on a 200µg (4.6xI08ns-I) californium-252 neutron source, which was housed in a cylindrical steel vessel, 90 cm high and 90 cm in diameter, containing borated paraffin wax. The combined activation and detection response of the system was dependent on kidney size and position and these were determined prior to the neutron irradiation using ultrasonography. The apparatus could detect (2S.D.s of the background), 3.2 mg of cadmium in the left kidney for an organ dose of 0.3 rem (skin dose e 0.8 rem), which was delivered in 33 minutes. The apparatus has been used to measure renal cadmium burdens in a group of 30 hypertensive patients undergoing treatment and in a group of 30 carefully matched controls, both groups being volunteers selected at random from a non-occupationally exposed population. The aim of this clinical study was to investigate the possible involvement of cadmium in the aetiology of hypertension at the chronic low levels of environmental exposure. The results showed that the mean cadmium level in the hypertensive croup, 3.3± 2.3mg(tI S.D.), was not significantly different from that in the normotensive group, 4.4t2.7 mg. Therefore, this work does not implicate environmental cadmium exposure as a risk factor in hypertensive disease.

No description available.

No description available.

This Thesis covers the investigation into the feasibility of monitoring blood glucose non-invasively. The work carried out involved the development of an <I>in-vitro</I> instrument through a series of four stages, each stage of development being an improvement on the previous one. Using these instruments it was shown that by using an appropriate wavelength, glucose could be detected down to 156 mg/dL repeatedly in distilled water, saline and a non-opaque blood analogue. It was also demonstrated that this wavelength could be used to detect the difference between blood samples with different glucose levels. The instruments were also used to demonstrate that a appropriate wavelength could be used as a reference wavelength. In addition to the <I>in-vitro</I> instrument, a basic <I>in-vivo </I>instrument was developed so that physiological data could be taken from either a person's ear or little finger non-invasively. It was clearly demonstrated that the instrument could detect a physiological change in a person whilst the person carried out a 75 g oral glucose to tolerance test.

The technique of X-ray fluorescence of heavy elements is widely used in medical physics and has been used for tracing the platinum-based drugs administered for the treatment of malignant tumours. A method is developed for analyzing an <i>in vivo</i> XRF system and optimizing the system for measuring the absorption of platinum in the target. The nature of the emitted radiation and its interaction with materials are explained. The general principles of the Monte Carlo method are described. A flexible program for an annular source/collimator and back-scattering geometry is developed. Several techniques are employed to improve the statistics and the program calculates the XRF spectrum for several heavy elements simultaneously. The dimensions and shielding materials of the source collimator are investigated in detail. The results support the choice of tungsten with a thin lining of tin or copper. The background spectrum contains a prominent Compton peak, the region above this containing mainly singly-scattered photons and the region below mainly multiply-scattered photons (plus the target element K-line). Very few of these multiply-scattered photons originate in the phantom, and the high background observed experimentally in the low-energy region is therefore attributed to scattering on the surface of the detector collimator. A design is proposed which would reduce this scattering considerably. A matrix of detection sensitivity versus depth and radius of the field is obtained. To calculate the response due to the tumour one can integrate the sensitivity over the volume of the tumour using data obtainable from tomographic images (like CT or MRI). It is also found that the regions of producing the greatest number of K-photons are not directly visible from the detector. A design is proposed which corrects for this deficiency and should therefore greatly improve the detection limit.

Previous investigations have focused on the development of bidirectional reflectance distribution function (BRDF) models and the implementation of computationally-efficient procedures for model inversion. The present study explores the operational use of BRDF models since little is known about producing BRDF at an operational level. Earlier work indicated that the angular sampling regimes of sensors influenced the accuracy of albedo estimated from BRDF models and multiple view angle (MVA) data. This work takes this a stage further by attempting to quantify the albedo error from present and future sensors, like SPOT VEGETATION, ATSR2, MODIS and MISR. The simulations demonstrated that the solar zenith angles (SZA) and the number of samples influences the accuracy of albedo derived. These findings suggest albedo can be accurately derived from the sensors studied. Contemporary work has shown the problem of residual mis-registration between images acquired by fine resolution MVA data, but this work shows new advances by examining mis-registration for coarse resolution AVHRR data. The results, even at these coarse scales, show similar mis-registration sensitivity curves to previous work. The implications of this result are that images needed to produce operational BRDF products will need sub-pixel registration accuracy and that mis-registration effects could swamp out the directional component of MVA data. Inversion of BRDF models against remotely sensed data has been used to derive biophysical parameters. Little is known, however, about the issues of mixed pixels and the derivation of biophysical parameters. A linear mixture model (LMM) is used in this study to unmix pixels <I>before</I> model inversion. The findings suggest the unmixing of pixels could improve the quality of BRDF products produced by sensors.