Measurements of urinary bladder volume: comparison of five ultrasound calculation methods in volunteers

To assess the precision of five different calculation methods in real-time bladder volume measurement.

Bladders from 10 medical staff volunteers were examined. Two examinations of each subject were performed by one examiner using the same ultrasound scannet Five different calculation algorithms were used on the frozen ultrasound pictures: the prolate ellipsoid method based on the formula: volume = length x width x heigth x 0.52 on two dimensions; the double area method based on the formula: volume = ex [C1 + C2 x ln(A1) + C3 x ln(A2)] on two dimensions; The double ellipsoid method on two dimensions; the method of one dimension of the shape of the bladder outlined manually with the maximal longitudinal diameter; the method of one dimension of the shape of the bladder outlined by smooth ellipsoid with the maximal longitudinal diameter After registration of the voided volume the subjects were scanned again in order to assure complete emptying.

Voided volumes ranged from 120 ml to 465 ml. The precision of each method was equal. Errors were not more than 25% of the voided volume. No significant improvement in accuracy for any of the methods was found.

Ultrasound bladder volume calculation is an easy method for estimation of bladder volume. Errors can be reasonably accepted. Large variation, irrespective of methods, from the true bladder volume, indicates that the clinical evaluation of ultrasound bladder measurement must be interpreted with great care in some patients.