Physics in medicine and biology
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Clinical application of high-temperature thermal therapy as a treatment for solid tumours requires an accurate and close to real-time method for assessing tissue damage. Imaging methods that detect structural changes during heating may underestimate the extent of thermal damage. This is due to the occurrence of delayed damage manifested at tissue locations exposed to temperatures lower than those required to cause immediate structural changes. ⋯ The calculated zones were compared with the lesions seen on histopathological examination of the brains which were removed within 6-8 h of treatment. The results showed that calculated damage zones based on MR thermometry agreed well with areas of damage as assessed using histology after heating was completed. The data suggest that real-time calculations of final expected thermal damage based on an Arrhenius analysis of MR temperature data may provide a useful method of real-time monitoring of thermal therapy when combined with conventional T2-weighted images taken after treatment.
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The ingestion of I-131 by pregnant women can have consequences for the developing foetus, in particular brain function. As the foetal thyroid accumulates iodine from the twelfth week of gestation onwards, the determination of foetal brain dose resulting from such I-131 accumulation is essential. ⋯ Dose values are obtained for the foetus based on the maternal intake of I-131. It was found that the choice of biokinetic model for the mother/foetus has a large impact on the determined dose estimate.
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This paper presents the stem effect correction factors for the NE2561 and NE2571 ionization chambers calibrated in air and used at a depth in a phantom irradiated by medium-energy x-ray beams. The in air and in phantom stem effect correction factors were calculated as the ratios of the absorbed dose in the air cavity of an ionization chamber without and with a chamber stem. The 'global' stem correction factor was then calculated as the ratio of the in phantom correction factor to the in air correction factor. ⋯ For an NE2571 chamber the 'global' stem effect correction factor varies from 1.014 +/- 0.001 at 70 kV (2.9 mm A1, 0.1 mm Cu) to 1.005 +/- 0.001 at 300 kV (21.5 mm A1, 5.1 mm Cu) while for an NE2561 chamber it varies from 1.039 +/- 0.002 to 1.010 +/- 0.002 for the same kilovoltage and HVL values. In a 60Co beam the global stem correction is 1.001 +/- 0.001 for an NE2571 chamber and 1.003 +/- 0.001 for an NE2561 chamber. This is consistent with recent experimental results.
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Comparative Study Clinical Trial
Quantitative brain FDG/PET studies using dynamic aortic imaging.
Positron emission tomography (PET) measurements of cerebral glucose utilization using 18F-fluorodeoxyglucose (FDG) are a useful tool in the investigation of localized brain function in normal and disease states. A major impediment to the application of FDG/PET in clinical investigation has been the need for arterial blood sampling to quantify cerebral glucose metabolism (CMRGlc). Qualitative studies, though informative in a variety of clinical settings, are of limited value for research applications and do not utilize the inherent quantitative nature of PET. ⋯ We performed 12 studies in which both arterial blood sampling and aortic scans were obtained. We found the correlation of global metabolic rates (GMR) when comparing the two techniques to be extremely high (R2 = 0.99). This suggests that the use of dynamic aortic imaging is less invasive and a viable alternative to arterial blood sampling in quantitative FDG/PET imaging.
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Comparative Study
The evaluation of interactions between anaesthetic agent vapours and carrier gases by laser refractometry.
A measurement system and technique have been developed for the evaluation of interactions between anaesthetic agent vapours and carrier gases. The refractivities of mixtures of anaesthetic agent and carrier gas have been compared to values derived from the addition of the absolute refractivities of the individual components. These results show that there is no significant interaction between the anaesthetic agent and the carrier gas at the +/- 0.06% level of uncertainty. Results for the anaesthetic agents isoflurane, sevoflurane, enflurane, halothane, chloroform and desflurane and the carrier gases nitrogen, oxygen and dry air will be presented.