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The Impedance Measurement Technique, in the last several decades of 20th century, has earned the recognizable reputation in terms of its technological accomplishment. In the meantime, this methodology has been applied to certain physiological measurements. Those physiological knowledge gained from various biological impedance measurements, provide us better understanding toward many unknown biological medical areas.
The purpose of this study is mainly the investigation of applying the Electrical Impedance Tomography(EIT) as a noninvasive and non-ionized-radiative method, in order to reconstruct the outline of the bladder tomography and realize the physiological estimation of the bladder cross-section area empty ratio with respect to the bladder volume. The EIT could be used to observe continuous graphs of the change of bladder urine impedance. Its basic principle is applying the Impedance Plethysmography to compare the difference of urine impedance before and after urination and then use the results to investigate the dynamical graphs and time for its corresponding change of bladder empty. The EIT method, we will focus in this study, is utilizing the optimal adaptive method. By switching method, we place twelve electrodes in a circular array around the lower abdomen to gain the distribution density of electrical field which is generated evenly by the organ rings of the scanned cross-section. Meanwhile, the design of receiver is based on the proposal of Bhat in 1990. In that proposal, he suggest placing matrix-arranged point electrodes between symphysis pubis and umbilicus, then use this orthogonal arranged style sensors to measure the impedance change picked up from the skin around the bladder, Since such change is due to the bladder volume change, further information can be rebuilt by computational methods and the bladder cross-section graph could then be obtained. The volume of urine in bladder could be estimated by using Plethysmography to calculate the ratio change of the area of the cross-section graph with respect to the time axis.
In order to prove the feasibility of this technique, we have designed a dummy and animal experiment to simulate human's abdomen. First of all, we utilize pig's bladder in the oval perspex tank to calibrate the area alteration, then we apply to the result △Z=-0.34667△ A±0.00081 to dog experiment. Besides, The linear correlation is more than 0.986609. We can also use the relation of the area to volume transform function to calculate dog's bladder capacity with R=0.9971, guantizing error ±13ml. If we make experiments on more animals, a noninvasive calibration way will be developed. So We can confirm, the rehability of applying such a system to measure human's body directly.
The research of EIT are currently interesting by many investigators in Europe and USA. However, the performance and results still need to be improved. If similar research were conduct in Taiwan, they have to be done independently. We believe the result of our study will help the urinologist to use impedance tomography in clinic. In that way, there will be more room for applying the biological impedance measurement technique in clinical urine function diagnostics.
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