Evaluation of electrical impedance tomography for determination of urinary bladder volume: comparison with standard ultrasound methods in healthy volunteers.

BACKGROUND: Continuous non-invasive urinary bladder volume measurement (cystovolumetry) would allow better management of urinary tract disease. Electrical impedance tomography (EIT) represents a promising method to overcome the limitations of non-continuous ultrasound measurements. The aim of this study was to compare the measurement accuracy of EIT to standard ultrasound in healthy volunteers. METHODS: For EIT of the bladder a commercial device (Goe MF II) was used with 4 different configurations of 16 standard ECG electrodes attached to the lower abdomen of healthy participants. To estimate maximum bladder capacity (BCmax) and residual urine (RU) two ultrasound methods (US-Ellipsoid and US-L × W × H) and a bedside bladder scanner (BS), were performed at the point of urgency and after voiding. For volume reference, BCmax and RU were validated by urine collection in a weight measuring pitcher. The global impedance method was used offline to estimate BCmax and RU from EIT. RESULTS: The mean error of US-Ellipsoid (37 ± 17%) and US-L × W × H (36 ± 15%) and EIT (32 ± 18%) showed no significant differences in the estimation of BCmax (mean 743 ± 200 ml) normalized to pitcher volumetry. BS showed significantly worse accuracy (55 ± 9%). Volumetry of RU (mean 152.1 ± 64 ml) revealed comparable higher errors for both EIT (72 ± 58%) and BS (63 ± 24%) compared to US-Ellipsoid (54 ± 25%). In case of RU, EIT accuracy is dependent on electrode configuration, as the Stripes (41 ± 25%) and Matrix (38 ± 27%) configurations revealed significantly superior accuracy to the 1 × 16 (116 ± 62%) configuration. CONCLUSIONS: EIT-cystovolumetry compares well with ultrasound techniques. For estimation of RU, the selection of the EIT electrode configuration is important. Also, the development of an algorithm should consider the impact of movement artefacts. Finally, the accuracy of non-invasive ultrasound accepted as gold standard of cystovolumetry should be reconsidered.

Unobtrusive and comprehensive health screening using an intelligent toilet system.

Home monitoring is a promising technology to deal with the increasing amount of chronically ill patients while ensuring quality of medical care. Most systems available today depend on a high degree of interaction between the user and the device. Especially for people relying on advanced levels of care, this scheme is impracticable. In this paper, we are presenting an "intelligent toilet" performing an extensive health check while being as simple to use as a conventional toilet. The main focus of the system is to support the treatment of diabetes and chronic heart failure, but additional applications are possible.

Simulation of a current source with a Cole-Cole load for multi-frequency electrical impedance tomography.

An accurate current source is one of the keys in the hardware of Electrical impedance Tomography systems. Limitations appear mainly at higher frequencies and for non-simple resistive loads. In this paper, we simulate an improved Howland current source with a Cole-Cole load. Simulations comparing two different op-amps (THS4021 and OPA843) were performed at 1 kHz to 1 MHz. Results show that the THS4021 performed better than the OPA843. The current source with THS4021 reaches an output impedance of 20 MΩ at 1 kHz and above 320 kΩ at 1 MHz, it provides a constant and stable output current up to 4 mA, in the complete range of frequencies, and for Cole-Cole (resistive and capacitive) load.

Bladder volume estimation from electrical impedance tomography.

Ubiquitous knowledge of bladder volume is of great interest to patients whose perception of bladder volume is impaired. A promising approach to provide frequent bladder volume estimates to the patient are automatic and noninvasive measurements by electrical impedance tomography (EIT). Previous studies have shown a linear correlation of abdominal electrical impedance and bladder volume. In this article, we present two methods to extract a volume estimate from EIT measurements. One method is based on the global impedance from a reconstructed image, the second method is based on a singular value decomposition of the raw voltage measurement vector. A performance evaluation in presence of noise is performed.