Validation study of ultrasound bladder wall thickness measurements

The aim was to validate ultrasound bladder wall thickness measurements. We scanned at three frequencies (5 MHz, 7 MHz and 9 MHz), using two techniques described in clinical practice and compared them with direct micrometre calliper measurements.

Bladder dome cadaver specimens were dissected from male and female cadavers. The direct micrometre calliper measurement under direct vision was used as the gold standard. We imaged using a Voluson E8 ultrasound scanner at three frequencies, using three probes: AB27D (2-7 MHz), RAB25D (2-5 MHz) and RIC50D (5-9 MHz). The specimens were scanned on two different occasions for intra-observer variability. A second operator, measured the samples again independently for the interobserver agreement. The specimens were gently placed onto a sheathed and gelled probe to avoid deformation. The method of scanning was the same for all the specimens, probes and operators.

Twenty-five bladder dome specimens were assessed. The correlation of the ultrasound measurement to the direct measurement improved at higher ultrasound frequencies. Measuring from the inside of the serosal hyperechogenicity also increased the accuracy correlation with the direct measurement for all the frequencies tested.

This is the first study validating BWT ultrasound measurements against cadaveric bladder wall calliper measurements. Technology and technique affect accuracy, which is important in clinical practice. The use of 5-MHz probes is not recommended. The most accurate measurement was obtained using high-frequency ultrasound, where the measurement did not include the serosal brightness. These data suggest that high-frequency ultrasound should be used to assess BWT.