World J Urol (2009) 27:747–753 751 Fig. 2 Comparison of bladder wall thickness measurements with conventional ultrasound and bladder scan based on Wrst urodynamic investigation measurements at 150 ml (a) and 250 ml (b); n = 46 pairs of measurements. Mean diVerence between paired measurements and their variation (mean § 2SD) are indicated by respective lines. 95% CI of the mean (not shown) are ¡0.27 to +0.74 mm (a), ¡0.39 to +0.61 mm (b). The presence of one outlier is indicated in a and b (patient 17). The exact position of the outlier in relation to x–y axes (not shown) is (6.90, +8.60 mm) in a and (6.80, +9.60 mm) in b. There is an obvious positive trend of the distribution of diVerences across the range of BWT measurements (diVerences increase for higher BWT values). There is evidence of agreement between the two modalities at both bladder Wlling volumes since no systematic diVerences are observed between paired measurements; mean diVerences do not diVer signiWcantly from zero (p > 0.05) Fig. 3 Bladder wall thickness measurements of a patient with conven- tional ultrasound (a) in comparison to the corresponding image of the BVM 6500 device (b). The patient had a thick bladder wall due to uro- dynamically conWrmed severe bladder outlet obstruction (patient 17, Wrst measurement at 250 ml). Bladder wall thickness measured with conventional ultrasound was greater in comparison to the measurement with the BVM 6500 device which measured only the inner part of the anterior bladder wall (double wavy line). The double arrow head in Fig. 3b indicates the true bladder wall thickness which is comparable with the measurement value of conventional ultrasound 250 ml, respectively). However, there was a trend towards a higher diVerence of BWT at higher BWT values which was as high as 11.7 and 11.0 mm at 150 and 250 ml, respectively (concerning a patient with severe bladder outlet obstruction). Direct comparison of the US images with automatically obtained images in patients with thicker anterior bladder walls showed that the BVM 6500 device did not capture the entire anterior bladder wall and measured the inner part of the anterior bladder wall only (Fig. 3). Discussion The BVM 6500 device has to be positioned on the skin of the lower abdomen and aims to measure bladder volume and anterior BWT. The correct position on the lower abdo- men and a measurement of good quality are immediately indicated on the display of the BVM 6500 device. If the device is improperly positioned, arrows on the display indi- cate the direction towards which the device has to be moved to receive images and measurements of good 123