IN-VITRO VALIDATION OF RIGHT-VENTRICULAR VOLUME MEASUREMENT BY 3-DIMENSIONAL ECHOCARDIOGRAPHY

Objective-Evaluation of ability of three dimensional echocardiography to accurately assess right ventricular volumes in vitro. Methods-Silic one casts of normal human right ventricles were examined. Each was fil led with three different volumes of water to yield 15 different measur ements. The casts were examined in a waterbath with three dimensional echocardiography using a 7.5 MHz ultrasound probe mounted in a scan fr ame. It was steered by a stepper motor, which moved the probe in steps of 0.25 mm over a distance of 5.9 cm inside the frame, acquiring an i mage at each step. 236 parallel slices of the cast were thus obtained, forming the three dimensional dataset. The longest axis of the right ventricular volume was defined and the area of perpendicular 1 mm thic k slices was outlined manually to calculate the area of each slice. Th is was multiplied by the slice thickness to obtain the volume of each slice; the respective volumes were added to obtain the volume of the w hole cast. Results-The casts had a median volume of 31.1 (23) ml (rang e 15-100); three dimensional echocardiography gave a median volume of 29.0 (21.7) ml (15.7-91.7). Interobserver variability was 4.5% (0.4%-1 3.6%) and intraobserver variability 4.3% (0.2%-9.3%). Correlation betw een real cast volumes and volumes measured by three dimensional echoca rdiography was 0.99 (y = 1.08 x -0.16) with an SEE of 2.7 ml. Limits f or agreement between methods ranged from -3.1 ml to 8.3 ml. In 14 of t he 15 measurements, volume by three dimensional echocardiography was s maller than real volume, with the mean difference being 7.4% (2.8%-19. 5%). This may be due to the thickening of surfaces of structures when imaged by ultrasonography. Conclusion-Right ventricular volumes can ac curately be determined by three dimensional echocardiography.