Focused Impedance Measurement

The Focused Impedance Measurement is a recent technique for measurement of tissue impedance in the human body with improved zone localization compared to conventional methods. This method was proposed and developed at the Biomedical Physics Laboratory of University of Dhaka.

Use of electrical impedance in medical diagnosis

Electrical impedance is a measurement of how electricity travels though a given material. Every tissue has different electrical impedance determined by its molecular composition. Some materials have high electrical impedance while others have low electrical impedance. For example, breast tissue which is malignant (cancerous) has a much lower electrical impedance – or conducts electricity much better – than normal tissue and benign (non-cancerous) tumours.Impedance is the measure of the degree to which an electric circuit resists electric current when a voltage is impressed across its terminals. Impedance, expressed in ohms, is the ratio of the voltage impressed across a pair of terminals to the current between those terminals. In direct-current (DC) circuits, impedance corresponds to resistance. In alternating current (AC) circuits, impedance is a function of resistance, inductance, and capacitance. Inductors and capacitors build up voltages that oppose the current. This opposition, called reactance, must be combined with resistance to find the impedance. The reactance produced by inductance is proportional to the frequency of the alternating current, whereas the reactance produced by capacitance is inversely proportional to the frequency.Electrical impedance measurements exploit the differences in the electrical properties of materials to detect inhomogeneities. Electrodes placed on the surface of an object are used to determine the electrical characteristics of the volume of that object. By injecting known amounts of current and measuring the resulting electrical potential field at points on the boundary of the body, it is possible to "invert" such data to determine the conductivity or resistivity of the region of the body probed by the currents. Since this method is often used in principle to image changes in dielectric constant at higher frequencies, the term "impedance”, is used instead of "conductivity" or "resistivity".

What is Focused Impedance Measurement?

The Focused Impedance Measurement (FIM) is a measurement technique with improved zone localization which is chiefly contributing to various physiological measurements. This method, the brainchild of Dr. K. S. Rabbani, was first introduced at the biophysics laboratory of the University of Dhaka. For its simplicity and accuracy it may prove to be a potential replacement of other earlier methods like Four Electrode Impedance Measurement (FEIM) and Electrical impedance Tomography (EIT) in many practical measurement situations as described in the next section. In fact FIM can be considered as the technique that bridges FEIM and EIT.

Computerized Focused Impedance Measurement

For efficient experimentation and medical use of this new technique, computerization was felt to be a necessity. The first computerization of Focused Impedance Measurement was done by Saiful Arefin Khaled of Biomedical Research Lab of University of Dhaka. A user friendly, windows-based software for data acquisition, storage and display of FIM data was developed. Using this software a large amount of experimental data could be analyzed very easily in a short time. Furthermore using this software, real time graphical presentation of data could be viewed in any microcomputer. This development immensely helped further researches in this field.

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