Diss. (sammanfattning) Uppsala : Uppsala universitet, 2005. / Härtill 6 uppsatser.

Thesis (M.S.)--University of Michigan, 1975.

Thesis (M.S.)--University of Michigan, 1975.

An important goal of single photon emission tomography (SPECT) is the determination of absolute regional radionuclide concentration as a function of time. Quantitative and qualitative studies of SPECT with regard to clinical application is the object of this work. Three basic approaches for image reconstruction and factors which affect the choice of a reconstruction algorithm have been reviewed, discussed and the reconstruction techniques, GRADY and CBP evaluated, based on computer modelling. A sophisticated package of computational subroutines, RECLBL, for image reconstruction and for generation of phantoms, which was fully implemented on PRIME was used throughout this study. Two different systems, a rotating gamma-camera and a prototype scanning-rig have been used to carry out tomography experiments with different phantoms in emission and transmission mode. Performance assessment and reproducibility of the gamma-camera was tested prior to the experimental work. SPECT studies are generally hampered for a number of reasons, the most severe being attenuation and scattering. The effect of scattered photons on image quality was discussed, three distinct techniques were utilised to correct the images and results were compared. Determination of the depth of the source, Am-241 and Tc-99m in the attenuating media, water and TEMEX by analysing the spectroscopic data base on the SPR and spatial resolution was studied, results revealed that both techniques had the same range of depth sensitivity. A method of simultaneous emission and transmission tomography was developed to correct the images for attenuation. The reproducibility of the technique was examined. Results showed that the technique is able to present a promising and a practical approach to more accurate quantitative SPECT imaging. A procedure to evaluate images, under certain conditions has been defined, its properties were evaluated using computer modelling as well as real data. Usefulness of the odd sampling technique to improve image quality has been investigated and is recommended.

The purpose of this study is not only to describe scintigraphy in parathyroid imaging and the results obtained but also to discuss the merits and limitations of the technique so that its role in today's climate of cost containment, may better be defined.

Poisoning is common and carries considerable morbidity and mortality. Two to three patients are admitted to the Emergency Unit at Groote Schuur Hospital every day with drug overdose. As absorption occurs in the small intestine the rates at which ingested poisons pass into and through the small bowel are important factors in determining the amount of poison potentially available for absorption. Although the effects of pharmacological doses of many drugs on gastric emptying and motility are known, information on the effects of higher doses is limited. I investigated patients who took overdoses of certain commonly used drugs to determine their effects on gastric emptying and motility and small intestinal transit. The study was divided into two parts. One hundred and four patients were studied in Part 1. These patients took overdoses of tricyclic antidepressants (n = 31), carbamazepine (n = 15), phenytoin (n = 12), paracetamol (n = 29) and opioid-paracetamol mixtures (n = 17). They received standard hospital management of which sorbitol was not a part. Part 2 consisted of sixty-one patients who had sorbitol added to their treatment. These patients had taken overdoses of the tricyclic antidepressants (n = 15), carbamazepine (n = 7), phenytoin (n = 8), paracetamol (n = 13) and opioid-paracetamol mixtures (n = 18). The effects of sorbitol on gastric emptying and small intestinal transit were evaluated. A third study-the paracetamol control test was done on 5 healthy volunteers. Each subject was studied twice; the first time after taking 1 G of paracetamol and the second time after no drug ingestion.

The adaptation of a general purpose laboratory minicomputer for nuclear medicine imaging is described. Electronic interfaces have been designed and constructed to link nucleonic equipment to a PDP 12 computer. A computer television display system has been developed to facilitate interactive processing of scintigraphic data. The main features of the television system are that it is relatively inexpensive and reliable. A domestic quality receiver has been adapted for use as a colour monitor. Any instrument that records data will produce a distorted or degraded version of the input signal. Generally, imaging equipment will produce a blurred image of the object, and in the case of scintigraphic imaging the blurs may be comparable to the size of the physiological structures being investigated. The process of refocussing the recorded data is called, in mathematical terms, deconvolution. In this study Fourier transform techniques have been developed as methods of implementing deconvolution. It is shown that the restoration of images in the presence of noise is likely to be a mathematically unstable process. Four methods of accommodating the problems associated with noise are described. Each method has built in optimisation of one form or another so that mathematically stable algorithms are used to implement deconvolution. This means that all the parameters used by the computer programs are determined automatically so that the computer operator is not required to select any parameters manually. A brief description of two dimensional digital filtering is given to enable comparison between filtering and deconvolution of scintigrams. A two dimensional lowpass filter is developed which automatically defines the passband frequency response appropriate to a particular scintigram. Finally, all the signal processing methods are tested on both simulated and clinical data. Results show that deconvolution offers advantages over digital filtering particularly for scintigrams obtained from morphic structures. Some of the problems of deconvolving certain types of scintigram are discussed.

No description available.

No description available.

This thesis reports an investigation of soil erosion problems associated with maize cultivation in England. To place the investigation into a broader context, the study commences with a review of soil erosion problems more generally, before focusing on the specific on-site and off-site problems associated with maize cultivation. Agricultural statistics are used to quantify the recent expansion of maize cultivation in England and attention is directed to both the temporal trends and spatial patterns involved. A major expansion of maize cultivation occurred in England between 1990 and 2000. Particular attention is then directed to the expansion of maize cultivation in Southwest England, since this is a very important area for cultivation of forage maize. Against this general background, a more detailed investigation of soil erosion associated with maize fields and its impact on the local streams and rivers was undertaken. This focused on two river catchments, namely the River Culm above Cullompton, Devon, and the River Tone above Taunton, Somerset. These two basins were selected as having a high density of maize fields within their catchments. A detailed field survey was undertaken to identify all the fields used for maize cultivation in the two catchments during 2004 and the previous two years and to provide a map of their location. More detailed work, aimed at quantifying both gross and net rates of soil loss, was undertaken on six fields selected to be representative of maize fields in the two catchments. Beryllium-7 measurements were used to estimate the erosion associated with a period of heavy rainfall in late December 2004 and early January 2005, when the harvest fields were left in a bare compacted conditions, with little or no vegetation cover and field observations indicated that significant erosion occurred. The results obtained from the beryllium-7 measurements which related only to the short period in late 2004 and early 2005 were complemented by caesium-137 measurements in the same fields which were used to obtain an estimate of the longer-term (i.e. ca. 45 years) mean annual erosion rates associated with the more traditional land use that had characterized these fields prior to the introduction of forage maize cultivation. These results indicated that the introduction of maize cultivation increased gross and net rates of soil loss by ca. 4 and 8 times, respectively and significantly increased sediment delivery ratios, resulting in more efficient delivery of sediment from the eroding fields to the streams. An assessment of the likely impact of sediment mobilised from the maize fields within the catchments of the River Culm and River Tone during winter 2004-5 was made by establishing a sediment monitoring and sampling programme at the downstream gauging stations on these two rivers over the period November 2004 to March 2005. Estimates of the suspended sediment loads of both rivers were obtained for this period and these were compared with an estimate of the total amount of sediment delivered to the water courses in the two catchments from maize fields based on an upscaling of the results obtained from the beryllium-7 measurements undertaken on the six representative fields. Uncertainties regarding both field to channel and within channel and floodplain conveyance losses precluded definitive comparison of the estimates of the amounts of sediment delivered to the water courses from maize fields with the measured sediment loads. However, the results obtained demonstrated the likely importance of the contribution from eroding maize fields to the suspended sediment loads of the Rivers Culm and Tone during winter 2004-5. The geochemical properties of suspended sediment collected from the two rivers were also compared with the equivalent properties of soil collected from the surface of maize fields within the two study catchments, in order to provide further evidence of the impact of maize cultivation on their suspended loads. The available geochemical data confirmed that much of the sediment transported by the Rivers Culm and Tone could have been mobilized from maize fields, but the lack of detailed geochemical data, precluded a definitive conclusion regarding its source. The results obtained from the field-based component of the study have been combined with the information on the regional and national patterns of maize cultivation and synthesized to provide a general assessment of the likely environmental impact of maize cultivation in England. This information has in turn been used to consider the potential for developing improved land management practises to reduce the environmental impact of maize cultivation within the context of the EU Common Agricultural Policy (CAP) and the Water Framework Directive (WFD). Finally, recommendations for the further development and extension of the study are provided.