<p>Accurate knowledge of the frequency- and temperature-dependent dielectric properties of biological tissues is crucial in the development of ultra-wideband diagnostic and therapeutic technologies such as microwave breast cancer detection and hyperthermia treatments. This work examines the temperature dependence of the dielectric properties of the five tissue phantom-types developed by our group as well as porcine fat, muscle and liver tissues for the frequency range from 3 GHz to 10 GHz and for the temperature range from 5 °C to 45 °C. A systematic and simple measurement procedure is developed to measure the continuous temperature dependence of the dielectric properties of the various phantom and tissue types. The temperature trends of the dielectric properties of the different phantoms and tissues are investigated.</p> <p>Linear temperature coefficients at discrete frequencies are impractical and insufficient in ultra-wideband applications when realistic, non-linear numerical models of the dielectric properties are required. Therefore, a compact one-pole Cole-Cole model is used to model the frequency dependence of the dielectric properties of the measured samples at every temperature point. A second- or third-order polynomial is used to model the temperature dependence of the Cole-Cole parameters. The final model is a one-pole Cole-Cole model whose parameters are polynomial functions of temperature. This model enables the estimation of the relative permittivity and the conductivity of the measured phantom and tissue types at any temperature and frequency.</p> / Master of Applied Science (MASc)

The relationship between post-mortem state and changes of biological tissue impedance has been investigated to serve as a basis for developing an in-vitro measurement method for monitoring the freshness of meat. The main challenges thereby are the reproducible measurement of the impedance of biological tissues and the classification method of their type and state. In order to realize reproducible tissue bio-impedance measurements, a suitable sensor taking into account the anisotropy of the biological tissue has been developed. It consists of cylindrical penetrating multi electrodes realizing good contacts between electrodes and the tissue. Experimental measurements have been carried out with different tissues and for a long period of time in order to monitor the state degradation with time. Measured results have been evaluated by means of the modified Fricke-Cole-Cole model. Results are reproducible and correspond to the expected behavior due to aging. An appropriate method for feature extraction and classification has been proposed using model parameters as features as input for classification using neural networks and fuzzy logic. A Multilayer Perceptron neural network (MLP) has been proposed for muscle type computing and the age computing and respectively freshness state of the meat. The designed neural network is able to generalize and to correctly classify new testing data with a high performance index of recognition. It reaches successful results of test equal to 100% for 972 created inputs for each muscle. An investigation of the influence of noise on the classification algorithm shows, that the MLP neural network has the ability to correctly classify the noisy testing inputs especially when the parameter noise is less than 0.6%. The success of classification is 100% for the muscles Longissimus Dorsi (LD) of beef, Semi-Membraneous (SM) of beef and Longissimus Dorsi (LD) of veal and 92.3% for the muscle Rectus Abdominis (RA) of veal. Fuzzy logic provides a successful alternative for easy classification. Using the Gaussian membership functions for the muscle type detection and trapezoidal member function for the classifiers related to the freshness detection, fuzzy logic realized an easy method of classification and generalizes correctly the inputs to the corresponding classes with a high level of recognition equal to 100% for meat type detection and with high accuracy for freshness computing equal to 84.62% for the muscle LD beef, 92.31 % for the muscle RA beef, 100 % for the muscle SM veal and 61.54% for the muscle LD veal. / Auf der Basis von Impedanzspektroskopie wurde ein neuartiges in-vitro-Messverfahren zur Überwachung der Frische von biologischem Gewebe entwickelt. Die wichtigsten Herausforderungen stellen dabei die Reproduzierbarkeit der Impedanzmessung und die Klassifizierung der Gewebeart sowie dessen Zustands dar. Für die Reproduzierbarkeit von Impedanzmessungen an biologischen Geweben, wurde ein zylindrischer Multielektrodensensor realisiert, der die 2D-Anisotropie des Gewebes berücksichtigt und einen guten Kontakt zum Gewebe realisiert. Experimentelle Untersuchungen wurden an verschiedenen Geweben über einen längeren Zeitraum durchgeführt und mittels eines modifizierten Fricke-Cole-Cole-Modells analysiert. Die Ergebnisse sind reproduzierbar und entsprechen dem physikalisch-basierten erwarteten Verhalten. Als Merkmale für die Klassifikation wurden die Modellparameter genutzt.

The relationship between post-mortem state and changes of biological tissue impedance has been investigated to serve as a basis for developing an in-vitro measurement method for monitoring the freshness of meat. The main challenges thereby are the reproducible measurement of the impedance of biological tissues and the classification method of their type and state. In order to realize reproducible tissue bio-impedance measurements, a suitable sensor taking into account the anisotropy of the biological tissue has been developed. It consists of cylindrical penetrating multi electrodes realizing good contacts between electrodes and the tissue. Experimental measurements have been carried out with different tissues and for a long period of time in order to monitor the state degradation with time. Measured results have been evaluated by means of the modified Fricke-Cole-Cole model. Results are reproducible and correspond to the expected behavior due to aging. An appropriate method for feature extraction and classification has been proposed using model parameters as features as input for classification using neural networks and fuzzy logic. A Multilayer Perceptron neural network (MLP) has been proposed for muscle type computing and the age computing and respectively freshness state of the meat. The designed neural network is able to generalize and to correctly classify new testing data with a high performance index of recognition. It reaches successful results of test equal to 100% for 972 created inputs for each muscle. An investigation of the influence of noise on the classification algorithm shows, that the MLP neural network has the ability to correctly classify the noisy testing inputs especially when the parameter noise is less than 0.6%. The success of classification is 100% for the muscles Longissimus Dorsi (LD) of beef, Semi-Membraneous (SM) of beef and Longissimus Dorsi (LD) of veal and 92.3% for the muscle Rectus Abdominis (RA) of veal. Fuzzy logic provides a successful alternative for easy classification. Using the Gaussian membership functions for the muscle type detection and trapezoidal member function for the classifiers related to the freshness detection, fuzzy logic realized an easy method of classification and generalizes correctly the inputs to the corresponding classes with a high level of recognition equal to 100% for meat type detection and with high accuracy for freshness computing equal to 84.62% for the muscle LD beef, 92.31 % for the muscle RA beef, 100 % for the muscle SM veal and 61.54% for the muscle LD veal. / Auf der Basis von Impedanzspektroskopie wurde ein neuartiges in-vitro-Messverfahren zur Überwachung der Frische von biologischem Gewebe entwickelt. Die wichtigsten Herausforderungen stellen dabei die Reproduzierbarkeit der Impedanzmessung und die Klassifizierung der Gewebeart sowie dessen Zustands dar. Für die Reproduzierbarkeit von Impedanzmessungen an biologischen Geweben, wurde ein zylindrischer Multielektrodensensor realisiert, der die 2D-Anisotropie des Gewebes berücksichtigt und einen guten Kontakt zum Gewebe realisiert. Experimentelle Untersuchungen wurden an verschiedenen Geweben über einen längeren Zeitraum durchgeführt und mittels eines modifizierten Fricke-Cole-Cole-Modells analysiert. Die Ergebnisse sind reproduzierbar und entsprechen dem physikalisch-basierten erwarteten Verhalten. Als Merkmale für die Klassifikation wurden die Modellparameter genutzt.

Volume overload is a common feature in patients on haemodialysis (HD). This contributes significantly to the cardiovascular disease burden seen in these patients. Clinical assessments of the volume state are often inaccurate. Techniques such as interdialytic blood pressure, relative blood volume monitoring, bioimpedance are available to improve clinical effectives. However all these techniques exhibit significant shortcomings in their accuracy, reliability and applicability at the bed side. We evaluated the usefulness of a dual compartment monitoring technique using Continuous Segmental Bioimpedance Spectroscopy (CSBIS) and Relative Blood Volume (RBV) as a tool to assess hydration status and determine dry weight. We also sought to evaluate the role of Atrial Natriuretic Peptide (ANP) and B-type Natriuretic Peptide (BNP) as a volume marker in dialysis patients. The Retrospective analysis of a historical cohort (n = 376, 55 Diabetic) showed a significant reduction in post-dialysis weights in the first three months of dialysis (72.5 to 70kg, p<0.027) with a non-significant increase in weight between months 6-12. The use of anti-hypertensive agents reduced insignificantly in the first 3 months, increased marginally between months 3-6 and significantly increased over the subsequent 6 months. The residual urea clearance (KRU) fell and dialysis times increased. The cohort was very different to that dialysing at Tassin and showed a dissociation between weight reduction and BP control. This may relate to occult volume overload. CSBIS-RBV monitoring in 9 patients with pulse ultrafiltration (pulse UF) showed distinct reproducible patterns relating to extra cellular fluid (ECF) and RBV rebound. An empirical Refill Ratio was then used to define the patterns of change and this was related to the state of their hydration. A value closer to unity was consistent with the attainment of best achievable target weight. The refill ratio fell significantly between the first (earlier) and third (last) rebound phase (1.97 ± 0.92 vs 1.32 ± 0.2). CSBIS monitoring was then carried out in 31 subjects, whilst varying dialysate composition, temperature and patient posture to analyse the effects of these changes on the ECF trace and to ascertain whether any of these interventions can trigger a change in the slope of the ECF trace distinct to that caused by UF. Only, isovolemic HD caused a change in both RBV and ECF in some patients that was explained by volume re-distribution due to gravitational shifts, poor vascular reactivity, sodium gradient between plasma and dialysate and the use of vasodilating antihypertensive agents. This has not been described previously. These will need to be explored further. The study did demonstrate a significant lack of comparability of absolute values of RECF between dialysis sessions even in the same patient. This too has not been described previously. This is likely to be due to subtle changes in fluid distribution between compartments. Therefore a relative changes must be studied. This sensitivity to subtle changes may increase the usefulness of the technique for ECF tracking through dialysis. The potential of dual compartment monitoring to track volume changes in real time was further explored in 29 patients of whom 21 achieved weight reductions and were able to be restudied. The Refill Ratio decreased significantly in the 21 patients who had their dry weights reduced by 0.95 ± 1.13 kg (1.41 ± 0.25 vs 1.25 ± 0.31). Blood pressure changes did not reach statistical significance. The technique was then used to examine differences in vascular refill between a 36oC and isothermic dialysis session in 20 stable prevalent patients. Pulse UF was carried out in both these sessions. There were no significant differences in Refill Ratios, energy removed and blood pressure response between the two sessions. The core temperature (CT) of these patients was close to 36oC and administering isothermic HD did not confer any additional benefit. Mean BNP levels in 12 patients during isovolemic HD and HD with UF did not relate to volume changes. ANP concentrations fell during a dialysis session in 11 patients from a mean 249 ± 143 pg/ml (mean ± SD) at the start of dialysis to 77 ± 65 pg/ml at the end of the session (p<0.001). During isolated UF levels did not change but fell in the ensuing sham phase indicating a time lag between volume loss and decreased generation. (136±99 pg/ml to 101±77.2 pg/ml; p<0.02) In a subsequent study ANP concentrations were measured throughout dialysis and in the post-HD period for 2 hours. A rebound in ANP concentration was observed occurring at around 90 min post-HD. The degree of this rebound may reflect the prevailing fluid state and merit further study. We have shown the utility of dual compartment monitoring with CSBIS-RBV technique and its potential in assessing volume changes in real time in haemodialysis patients. We have also shown the potential of ANP as an independent marker of volume status in the same setting. Both these techniques merit further study.