Intra-tissue pressure measurement in ex vivo liver undergoing laser ablation with fiber-optic Fabry-Perot probe

We report the first-ever intra-tissue pressure measurement performed during 1064 nm laser ablation (LA) of an ex vivo porcine liver. Pressure detection has been performed with a biocompatible, all-glass, temperature-insensitive Extrinsic Fabry-Perot Interferometry (EFPI) miniature probe; the proposed methodology mimics in-vivo treatment. Four experiments have been performed, positioning the probe at different positions from the laser applicator tip (from 0.5 mm to 5 mm). Pressure levels increase during ablation time, and decrease with distance from applicator tip: the recorded peak parenchymal pressure levels range from 1.9 kPa to 71.6 kPa. Different pressure evolutions have been recorded, as pressure rises earlier in proximity of the tip. The present study is the first investigation of parenchymal pressure detection in liver undergoing LA: the successful detection of intra-tissue pressure may be a key asset for improving LA, as pressure levels have been correlated to scattered recurrences of tumors by different studies

Sensores de fibra ótica como tecnologia não-invasiva para avaliação da pressão arterial central

Doutoramento em Engenharia FísicaCom o presente trabalho pretendeu-se explorar soluções de fibra ótica na aquisição da onda de pulso na artéria carótida, para análise da sua morfologia e cálculo da pressão arterial central. Foram desenvolvidos três sistemas, dois baseados em redes de Bragg, gravadas em fibra de sílica, e outro em modulação de intensidade, usando fibra ótica de plástico. O primeiro sensor foi desenvolvido com o objetivo de testar a exequibilidade da utilização de fibra ótica nesta aplicação. Após resultados promissores da sua caracterização e testes em sujeitos, o desenvolvimento dos dois sensores consequentes teve por objetivo o aumento da sensibilidade e facilidade de utilização das sondas, pela melhoria da sua forma, portabilidade e autonomia. A solução baseada em intensidade mostrou-se ainda como um sistema que coligava desempenho a baixo custo, tendo por isso sido submetida a um estudo pré-clínico, comparando o seu desempenho ao de um dispositivo comercial, de natureza eletromecânica, numa pequena coorte de indivíduos saudáveis. Este estudo teve como objetivo investigar a correlação dos resultados obtidos com a sonda de fibra ótica e o dispositivo comercial. Tendo-se obtido uma correlação muito forte entre as duas técnicas, o dispositivo foi proposto para avaliação clínica. O desempenho da sonda foi assim comparado a um dispositivo comercial, numa coorte de indivíduos hipertensos. Foram também levados a cabo testes invasivos, usando como referência ondas de pressão obtidas no lúmen da artéria aorta em contexto de cateterismo cardíaco. Em ambos os estudos clínicos foram obtidos coeficientes de correlação muito fortes e diferenças de pressão média na gama obtida para dispositivos comerciais. Conclui-se assim que o dispositivo baseado em modulação de intensidade surge como uma promissora alternativa de baixo custo aos dispositivos eletromecânicos de avaliação de pressão arterial central disponíveis no mercado.The present study aimed to explore fibre optic solutions in the acquisition of the pulse wave in the carotid artery, to its morphology analysis and central arterial pressure calculation. Three systems were developed, two based on Bragg gratings, engraved in silica fibre, and another on intensity modulation, using plastic optical fibre. The first sensor was developed in order to test the feasibility of the fibre optics use in this application. After promising results in the characterization and small tests in subjects, the development of the consequent two sensors had as main goals increasing the probes sensitivity and user-friendliness, by improving its shape, portability and autonomy. The intensity-based solution proved to be the system that best combined performance to low cost, and thus was subjected to a pre-clinical study, comparing its performance to a commercial device in a small cohort of healthy individuals. This study aimed to investigate the correlation between the results obtained with the fibre optic probe and the commercial device. Having been obtained a very strong correlation between the two techniques, the device was proposed for clinical evaluation. The probe’s performance was therefore compared to a non-invasive commercial device, in a cohort of hypertensive individuals. Invasive testing was also performed, using as reference pressure waves obtained in the lumen of the aortic artery in cardiac catheterization context. In both trials very strong correlation coefficients were obtained, as well as medium pressure differences in the range verified for commercial devices. It is concluded that the device based on intensity modulation arises as promising low cost alternative to central arterial pressure assessment electromechanical devices available in the market

An optical fibre point temperature sensor for investigation of 3,4-methylenedioxymethamphetamine (MDMA, ‘ecstasy’) induced hyperthermia in the rat brain

3,4-methylenedioxymehtamphetamine (MDMA, ‘ecstasy’) is an illegal stimulant drug that can produce life-threatening hyperthermia following consumption in humans. Administration of MDMA also produces similar effects in experimental animals and it can lead to death usually through multi-organ failure, and vasogenic brain oedema. Despite the danger acute MDMA-induced hyperthermia poses, current treatments for these adverse effects in a clinical setting are limited and do not address hyperthermia’s central origins. Due to ethical reasons, the investigation of these MDMA-induced changes in humans are restricted, therefore animal models are relied on to investigate the real-time thermoregulatory effects of MDMA and their underlying pharmacological mechanisms. This being considered, it is important to investigate MDMAs adverse effects in animals and potential pharmacological therapeutics using advantageous techniques in order to effectively relate these findings from animals to humans. The aim of this thesis was to develop a novel portable optical fibre temperature sensor for the monitoring of brain temperature in awake freely-moving rats, and to use this sensor in conjunction with radiotelemetry to investigate the effects of MDMA on thermoregulation and its related physiological parameters. We also aimed to investigate the brain hyperthermia-attenuating effects of the tetracycline antibiotic drug minocycline, as well as its effects on body temperature, heart rate, and locomotor activity. The first part of this thesis aimed at optimizing a portable optical fibre temperature sensor based on rare-earth thermometry for long-term temperature measurements in vivo. Initial in vitro tests revealed measurement instabilities in the original configuration and therefore changes were made to the optical equipment aimed at increasing its long-term stability. The susceptibility of the previous probe to signal bend-loss and breakage during animal movement following MDMA administration was also reduced through numerous physical changes to the sensor design. The second study aimed to provide proof-of-concept for this portable optical fibre-tip sensor capable of recording brain temperature in conscious freely-moving rats. This study was successful in demonstrating that accurate and spatially precise brain temperature recordings could be performed by the probe while utilising a portable optical setup. These brain temperature measurements also showed a good correlation with body temperature recorded with radiotelemetry throughout the experiment. The third study made further improvements to the probe structure which increased probe durability, reusability and ease of use for in vivo experiments. These changes significantly increased experimental throughput and reduced time and resource costs associated with probe fabrication. Brain temperature measurements made with this probe showed that MDMA (10 mg/kg) induced a significant hyperthermia in the brains of Sprague-Dawley rats. The fourth study looked at the effects of MDMA administered at differing ambient temperatures, as well as the hyperthermia attenuating effects of minocycline. Administration of MDMA (10 mg/kg) induced both a significant hypothermia and hyperthermia when administered at normal, and high ambient temperature respectively, and significantly increased heart rate, and locomotor activity irrespective of environmental conditions. Pretreatment with minocycline (50 mg/kg) was able to significantly attenuate MDMA-induced brain and body hyperthermia at high ambient temperature and reduce MDMA-induced increases in heart rate and locomotor activity. In conclusion, we have developed and validated an optical fibre point temperature sensor based on rare-earth thermometry that accurately records rat brain temperature in vivo. We also combined optical fibre brain temperature measurements with body temperature monitoring to investigate the thermoregulatory, and physiological effects of MDMA and minocycline in freely-moving rats.Thesis (Ph.D.) -- University of Adelaide, Adelaide Medical School, 201