Determination of organ volume by means of ultrasonic B‐mode scanning

The volume of the urinary bladder was measured in 23 nonpregnant females, 18 males and 8 pregnant females—49 patients in all. Measurement of organ volume was accomplished to an accuracy of ± 20% in over 90% of cases in bladders between 40 cc and 800 cc in volume. Multiple parallel B‐mode sections were taken at 1 cm intervals where cross‐sectional area changed slowly, and at intervals of 1 / 2 cm where cross‐sectional area changed rapidly. The area of each cross section was measured with a polar planimeter, and then multiplied by the distance between adjacent scans to give an approximate estimate of the volume between successive sections. The total of these volumes represents the volume of the organ (planimeter volume). A further increase in accuracy was obtained by applying the regression equation: true volume = 25cc + planimeter volume. The calculated volume was compared with voided urine volume. Patients with residual urine were exlucded. The method does not require the use of computer techniques. In organs where there is significant respiratory motion, such as the liver, the spleen and the kidneys, suspension of respiration in the same phase during each scan is mandatory to achieve an accurate result.