Numerical modelling of skin tumour tissue with temperature-dependent properties for dynamic thermography.

Dynamic thermography has been clinically proven to be a valuable diagnostic technique for skin tumour detection as well as for other medical applications, and shows many advantages over static thermography. Numerical modelling of heat transfer phenomena in biological tissue during dynamic thermography can aid the technique by improving process parameters or by estimating unknown tissue parameters based on measurement data. This paper presents a new non-linear numerical model of multilayer skin tissue containing a skin tumour together with thermoregulation response of the tissue during the cooling-rewarming process of dynamic thermography. The thermoregulation response is modelled by temperature-dependent blood perfusion rate and metabolic heat generation. The aim is to describe bioheat transfer more realistically. The model is based on the Pennes bioheat equation and solved numerically using a subdomain BEM approach treating the problem as axisymmetrical. The paper includes computational tests for Clark II and Clark IV tumours, comparing the models using constant and temperature-dependent properties which showed noticeable differences and highlighted the importance of using a local thermoregulation model. Results also show the advantage of using dynamic thermography for skin tumour screening and detection at an early stage. One of the contributions of this paper is a complete sensitivity analysis of 56 model parameters based on the gradient of the surface temperature difference between tumour and healthy skin. The analysis shows that size of the tumour, blood perfusion rate, thermoregulation coefficient of the tumour, body core temperature and density and specific heat of the skin layers in which the tumour is embedded are important for modelling the problem, and so have to be determined more accurately to reflect realistic skin response of the investigated tissue, while metabolic heat generation and its thermoregulation are not.

Application of Lagrangian particle transport model to tuberculosis (TB) bacteria UV dosing in a ventilated isolation room.

The aim of this work is to define the basis for design guidelines that will minimise the risk of exposure from airborne organisms in hospital isolation rooms. This research employs an algorithm that combines an understanding of the interaction between the room airflow and the ultra violet (UV) system. The airflow in such a room is complex and therefore cannot easily be accounted for by existing design guidance. The main findings were firstly, the mean lifetime of the ventilated particles does not reduce in proportion with increasing ventilation rate. Secondly, an increase in the ventilation rate reduces the effectiveness of ultra violet germicidal irradiation (UVGI) with only a limited increase in the number of particles that are ventilated. Finally, there is a social benefit attached to this project from the point of view of helping people who are vulnerable as well as reducing their risk of being exposed to possible tuberculosis infection. The significance of these findings is to provide the engineer and the architect with an essential tool to ensure good design practice. It is also important to ensure that the methodology can be applicable to most isolation room uses.