A modified voltage changes ratio (MVCR) for in-vitro volume estimation

Electrical bioimpedance (EBI) is a non-invasive technique for monitoring bladder volume. The EBI approaches global impedance (GI), impedance ratio method (IRM), and voltage change ratio (VCR) have been successfully applied to detect changes in the volume of objects with constant but unknown conductivity. In this work, simulated and in-vitro experiments are used to compare the performance of these methods with respect to a new approach proposed by some authors and called modified VCR (MVCR). Experimental results indicated that GI, VCR, and MVCR indices increase when the volume of the object under study increases. On the other hand, no direct or inverse relationship between IRM and volume was observed. The coefficient of variation, defined as the interquartile range divided by the median of a set of measurements, was lower for MVCR, which indicates that the proposed approach is less sensitive to measurement noise than the other three methods.