Study Of Laser-Generated SAW Spectroscopy And Its Application To Human Skin Irregularities Detection

In medicine the diagnosis and treatment of any skin disease is largely carried outon a visual basis by a trained dermatologist. A dermatologist is required to havecompleted many years of training and clinical expertise in the field. There arehowever some conditions where a visual diagnosis does not give the dermatologistenough quantitative information and where it would be useful to have a more accuratemethod to resolve any ambiguities.The aim of this research project is to evaluate an innovative non-damage systemusing laser ultrasonics that allows the rapid functional characterization of skin withcancer, by utilising the properties of laser generated ultrasonic surface waves tocharacterise the layers in human skin and to monitor changes in the mechanical andgeometrical changes of these layers due to skin disease.Unlike traditional ultrasonic methods laser ultrasonics uses a pulsed laser beamas a remote ultrasonic input source, which generates ultrasonic waves in the material.When a solid surface is illuminated by a very short laser pulse, the absorption of laserradiation results in a localised thermal expansion and hence results in the generationand propagation of bulk and surface waveforms. The characterisation of lasergenerated waves depend strongly on the optical penetration of the laser beam, thermaldiffusion and the elastic and geometrical feature of the material under study alongwith the parameters of the exciting laser pulse including the shape, focus spot andpulse width. The main advantages of using a laser ultrasonic system are due to itsremote generation and detection without physical contact with the material, thecoupling constraint is suppressed and there is almost no sensitivity to surfaceorientation.By the use of Finite Element Modelling techniques the project aims to obtain anunderstanding of the way in which the laser source interacts with tissues of differenttypes and the resulting signals generated by the tissues. The analysis involves thestudy of dispersion characteristics of the generated surface waveforms in a variety ofskin models with varying sizes of the melanoma and mesh.The main tasks developed and main results were the following: Introduce the properties of human skin and the individual layers that make uphuman skin. We will also introduce some of the diseases and conditions that affect theskin and discuss the effects that the diseases have on the mechanical and geometricalproperties of the individual layers of skin. Presents an overview of ultrasound theoryand surface acoustic wave motions in elastic solids. The theory of laser basedultrasonics will also be introduced along with some applications used today inindustry and medicine. We will also discuss the method of simulating the generationand propagation of laser generated ultrasound which will form the basis of thisresearch. Provide an overview of the finite element method and the simulationprocedure used in this research which is developed to simulate the generation andpropagation of ultrasonic waves generated by a laser pulse. Provide a basis of thedevelopment of a simulation procedure in skin models. Utilise the properties of lasergenerated ultrasonic surface waves to characterise the layers in human skin and tomonitor changes in the mechanical and geometrical changes of these layers due toskin disease. By using the results of the finite element modelling of the tissue and skinmodels, use a Matlab program to do the digital signal processing and calculate thedispersion curves. By comparing the dispersion curves we could figure out thechanges of the skin. The minimum detection size of melanoma is0.03mm and theinfluence of mesh size to the simulation is discussed. We will present the conclusionsof the feasibility to use laser ultrasound for melanoma detection along with somesuggestions for further study.