Sonographic automated volume count (SonoAVC) in volume measurement of fetal fluid‐filled structures: comparison with Virtual Organ Computer‐aided AnaLysis (VOCAL)

We read with great interest the study by Kusanovic et al.1, ‘The use of inversion mode and 3D manual segmentation in volume measurement of fetal fluid-filled structures: comparison with Virtual Organ Computer-aided AnaLysis (VOCAL)’, published in the February 2008 issue of the Journal. The authors showed that volume calculations of fetal stomach and bladder may be obtained from three-dimensional volume datasets from the fetal abdomen by using either inversion mode or manual segmentation. The measurements obtained were consistent with those from VOCAL, the technique for calculating volumes that is most frequently used and extensively evaluated2-4. The main advantage of both inversion mode and manual techniques is a significant reduction in the time necessary to perform the volume calculation. We hereby report our experience in the calculation of fetal stomach volumes using the sonographic automated volume count (SonoAVC 4D View, version 7.0, GE Medical Systems, Zipf, Austria), new software developed for the automated calculation of ovarian follicular volume5. Fifty-two volume datasets were acquired from uncomplicated pregnancies from 19 to 34 weeks of gestation with a Voluson E8 (GE Healthcare Technologies, Milwaukee, WI, USA) ultrasound machine, equipped with a 4–8-MHz transabdominal transducer, starting (as reference plane) from the transverse view of the fetal abdomen at the level of the stomach, during a period of fetal quiescence. Before storing the volumes on the hard disk, color filtering and brightness/contrast adjustments were performed to optimize contrast. Each volume dataset was later analyzed for fetal stomach volume assessment using both VOCAL and SonoAVC techniques. For VOCAL we used the manual method of tracing stomach contours and a 30° rotational angle as described by Kusanovic et al.1 (Figure 1a). For SonoAVC we uploaded the volume dataset and positioned the reference point so that it was in the center of the stomach in all three orthogonal planes. The render function was activated and we selected the smallest rendering box possible that contained the entire stomach in all three orthogonal planes. The SonoAVC function was then activated and the software automatically calculated the stomach volumes (Figure 1b). The ‘separation’ parameter was set at ‘mid’ for all measurements. A high degree of reliability for volume measurements was obtained, with an interclass correlation coefficient of 0.988 (95% CI, 0.980–0.993). The Bland–Altman plot for the percentage of the mean difference and 95% limits of agreement between VOCAL and SonoAVC is shown in Figure 2. The time required to perform volume measurements, calculated from the upload of the volumes, was significantly lower for SonoAVC than it was for VOCAL (21.4 ± 14.0 vs. 76.3 ± 19.0 s; t = 16.77; P < 0.0001). Successful volume measurements were obtained in all cases with both techniques. Ultrasound images of the fetal abdomen at 20 weeks of gestation showing volume measurements performed with Virtual Organ Computer aided AnaLysis (VOCAL) (a) and with sonographic automated volume count (SonoAVC) (b) in the same fetus. The reconstructed three-dimensional image of the fetal stomach is displayed in panel D of both figures; the volume was calculated as 0.47 cm3 for VOCAL and 0.45 cm3 for SonoAVC. Bland–Altman plot for the percentage of the mean difference showing 95% limits of agreement between Virtual Organ Computer aided AnaLysis (VOCAL) and sonographic automated volume count (SonoAVC). The mean (solid line) was − 1.62 and the 95% limits of agreement (dashed lines) were − 19.07 and 15.81. The major limitation of volume measurements with SonoAVC is that its application is restricted to fluid structures with well-defined borders; it cannot be applied to solid structures. However, the results reported here suggest that volume measurements of fetal fluid-filled structures could be performed much more easily and quickly with SonoAVC than with VOCAL, a technique that may require prolonged operator training to develop the necessary expertise3. Our findings support the future use of SonoAVC in the volume calculation of fetal fluid-filled structures (e.g. cerebral ventricles, heart chambers, gallbladder), avoiding the limitations of VOCAL, including the length of time required for analysis and the difficulty and subjectivity inherent in the identification of organ borders. G. Rizzo*, A. Capponi , M. E. Pietrolucci*, D. Arduini*, * Department of Obstetrics and Gynecology, Università di Roma ‘Tor Vergata’, Ospedale Fatebenefratelli S.