Commonly used medical imaging techniques are X-Ray Computed Tomography (CT), nuclear imaging techniques called nuclear medicine or Emission computed tomography (ECT) like single photon emission tomography (SPECT) and positron emission computed tomography (PET), X-Ray Mammography, Magnetic Resonance Imaging (MRI), Ultrasound and Thermal imaging. All these techniques either use harmful radiations which may cause side effects to body tissues or the cost is not affordable. SPECT and PET are invasive and CT, SPECT, PET uses ionizing radiations which imposes a limit on their usage especially for pregnant women and children. Ultrasound provides very low resolution images .CT and MRI gives better resolution than nuclear imaging techniques but it is quite expensive and the patients with metal implants, pacemakers and other medical implants are not allowed to go for MRI .Thermograph can help in diagnosis of advanced abnormality but has the limitation that the change in surface temperature occurs only if the impurity is near to the surface. Human body is a complex structure composed of several tissues constructed by the three dimensional arrangement of cells. Tissue exhibits two important electrical properties: Conductivity or Resistivity (how easily free charges move, like a conductor) and Permittivity (how bound charges respond, like in a capacitor). In tissue and living cells, there is an inseparable relationship between physiology, electricity, and chemistry. Conductivity of cancerous and non-cancerous cell is different and we are using this property to locate cancer . Our aim is to design a Non- invasive diagnostics device using electrical impedance which is low cost, energy efficient ,wireless and no ionizing , portable, medically safe, compact diagnostic tool to give the geometrical anatomy functional information of the tumour.
I . INTRODUCTION
Electrical impedance tomography (EIT) is an imaging modality wherein the spatial map of conductivity and permittivity inside a medium is obtained from a set of surface electrical measurements. Electrodes are brought into contact with the surface of the object being imaged and a set of currents are applied and the corresponding voltages are measured. These voltages and currents are then used to estimate the electrical properties of the object using an image reconstruction algorithm which relies on an accurate model of the electrical interaction. Reconstruction of the electrical properties distribution is an under-determined problem requiring a regularization method. EIT has been researched extensively in the medical field, as well as in other technological areas, such as industrial process control, chemical engineering and geotechnical research. The technique has become an independent, fully-featured stream in the biomedical engineering field, and has high clinical potential as an investigation tool. The objective of this Project is to develop a device for EIT imaging, which will be convenient, non-invasive, easily programmable,portable and relatively inexpensive. In this direction a simple EIT system and its hardware and software parts have been developed. A set of16-electrodes probes in circular were built for treating two dimensional samples. Probes and a circuit board, comprehending a serial programmable interface and a switch based multiplexer, have been built to be used as an acquisition system. As the object of EIT is a human body part, the current must be limited within the range regulated by Medical Electrical Safety Regulations in order to ensure safety the system was therefore designed to apply low AC currents (12 to 22 mA ) to the samples. Matlab code for electrode switching, acquisition and reconstruction were developed. The effects of noise and of systematic error coming from the channels crosstalk was analysed. Preliminary studies on a model system consisting of a saline solution have been performed in order to estimate the electric behavior of a physiological sample, for...Read more »