Accuracy of post-void residual urine volume measurement using a portable ultrasound bladder scanner with real-time pre-scan imaging

To evaluate whether the bladder scanner with real-time pre-scan imaging (RPI) is superior to the conventional bladder scanner in measuring post-void residual urine (PVR) volume.

Sixty-seven patients with voiding dysfunction were subjected to PVR volume measurements. The PVR volume was measured three times by two experienced examiners using bladder scanners with (BioCon-500, Mcube Technology, Seoul, Korea) or without (BVI-3000 BladderScan, Verathon, WA) RPI. Immediately after the procedure, urethral catheterization was performed to obtain true volume. The accuracy and variability of measurements were compared between the two devices and correlation coefficients were obtained.

The Pearson correlation coefficients between the PVR volume measured by each device and the true volume were 0.932 for the bladder scanner without RPI and 0.950 for the bladder scanner with RPI. The bladder scanner without RPI tended to overestimate the true volume in moderate volume ranges (>100 ml) by a mean percentage of differences of volume (PDV) of 16.3%, while the bladder scanner with RPI underestimated the true volume in the whole volume range by a mean PDV of -14.1% (P<0.001). Repeated measures ANOVA showed no significant interobserver variability (P=0.977 for the bladder scanner without RPI and P=0.853 for the bladder scanner with RPI) or intraobserver variability (P=0.660 for the bladder scanner without RPI and P=0.271 for the bladder scanner with RPI).

Our results showed that exact pointing to the bladder prior to actual measurement of bladder volume with RPI seems to reduce the variability of the measured values.