• phantom;
  • reliability;
  • technique;
  • three-dimensional ultrasound;
  • validity;
  • VOCAL;
  • volume;
  • water bath



The primary aim of this validation study was to determine the interobserver reliability and validity of measurements of phantom objects of known volume using conventional and rotational techniques of volume calculation according to measurement technique.


Two observers each acquired a single three-dimensional ultrasound dataset of three water-filled objects of different size and shape. The same two observers measured all six datasets using both the conventional technique and the newer rotational technique (Virtual Organ Computer-aided AnaLysis, VOCAL) of volume calculation. Reliability was assessed by calculating intraclass correlation coefficients (ICC) and validity by examining the percentage difference from the ‘true’ volume, as determined by a water displacement technique, by the limits of agreement method.


All of the techniques were highly reliable (ICC: 0.9962–0.9997) and valid to within 4% of the ‘true’ volumes. There were no significant differences in reliability according to measurement plane or between observers. Measurements made with the 6° rotation step were significantly more reliable than those made by all other techniques with the exception of the 9° rotation step (P < 0.05) and significantly more valid than those made with the 30° rotation step or conventional technique (P < 0.05).


Volume calculation in the in vitro setting is both reliable and valid but is dependent upon the technique applied, with rotational measurements of volume proving superior to conventional techniques. Copyright © 2003 ISUOG. Published by John Wiley & Sons, Ltd.