The estimation of bladder volume by sonocystography.

Real-time ultrasonography was used to measure bladder volumes. Volumes were calculated as the product of 3 internal bladder diameters (height, width and depth). The true bladder volume was obtained from the voided volume or by catheterization. There was a good correlation between calculated and true volumes provided a correction factor of 0.6 was applied. It also was found that a simpler method using only 2 diameters and a correction factor of 0.15 was nearly as reliable. The accuracy of this quantitative method was shown to be limited to an average error of plus or minus 25 per cent for bladder volumes between 100 and 500 ml. Smaller volumes could be assessed only qualitatively. False negative readings were common for bladder volumes less than 50 ml.