Electric impedance tomography for monitoring volume and size of the urinary bladder

Abstract

A novel non-invasive technique for monitoring fluid content in the human bladder is described. Specifically, a precommercial electric impedance tomograph (EIT) was applied to measure and visualize impedance changes in the lower torso due to changes in bladder volume. Preliminary measurements were conducted during routine urodynamic tests of nine male paraplegic patients, in whom a contrast agent was slowly infused into the bladder for diagnostic purposes. In some patients, a good correlation between bladder volume and EIT measurements was found, whereas in others the correlation was still good but inverted, presumably due to a poor electrode positioning. These preliminary results indicate that a sufficiently accurate finite element modeling of the impedance distribution in the abdomen, and proper electrode positioning aids, are important prerequisites to enable this technology to be used for routine measurement of bladder volume.

Impedance Ratio Method for Urine Conductivity-Invariant Estimation of Bladder Volume

“…To the knowledge of the authors, the first application of EIT for cystovolumetry has been reported by our group in 2011 [7]. In this study, nine male paraplegic patients have been monitored by EIT during regular urodynamic examination.…”

“…For EIT measurement, the set-up has been kept close to the human experiment performed in 2007 [7] incorporating an EEK1 (Dräger Medical, Lübeck, Germany) EIT device with adjacent injection and measurement pattern as well as an elastic belt with 16 conductive rubber electrodes. Solutions of demineralized water with sodium chloride concentrations of 0%, 0.9% and 1.8% accoding to conductivities of ∼0 mS/cm, ∼15 mS/cm and ∼28 mS/cm have been prepared.…”

“…Recently, both our group [7] and He et al [8] presented the extension of the extracorporal bioimpedance approach to multi-electrode electrical impedance tomography measurements (EIT). It is expected that 3D multi-electrode measurements can help to reduce distorting influences and provide more accurate bladder volume estimates than a single tetrapolar measurement could do.…”

Linear Regression for Estimating Bladder Volume with Voltage Signals

“…Methods of measuring the electrical properties of tissue at both low and high frequencies can be used to monitor the bladder volume and aid in providing clinical feedback to the clinician that can enhance decision-making with urinary incontinence [8]. To determine the bladder volume, the data can be associated with the bladder volume by metrics [9], [10] or by machine learning [10].…”

“…However, the performance of the NN was found to deteriorate when pushed outside training boundaries, such as in the extrapolating of unseen bladder volumes [10]. Bladder volume has been shown to have a 'near' linear trend with electrical properties [8]. Thus, a better machine learning algorithm may be linear regression for extrapolating bladder volume.…”