Ultrasound Obstet Gynecol 2008; 32: 111–114 Published online in Wiley InterScience (www.interscience.wiley.com).
Letters to the Editor
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 threedimensional 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.
Copyright 2008 ISUOG. Published by John Wiley & Sons, Ltd.
Figure 1 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.
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. 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 .
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ultrasound with spatio-temporal image correlation compared with two-dimensional and Doppler ultrasonography. Prenat Diagn 2007; 27: 1147–1150. 5. Raine-Fenning N, Jayaprakasan K, Clewes J. Automated follicle tracking facilitates standardization and may improve workflow. Ultrasound Obstet Gynecol 2007; 30: 1015–1018.
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Prepartum sonographic demonstration of ‘to-and-fro’ motion in fetal intestinal obstruction: a novel sign for immediate postnatal surgery
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Figure 2 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.
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† and D. Arduini† †Department of Obstetrics and Gynecology, Universita` di Roma ‘Tor Vergata’, Ospedale Fatebenefratelli S. Giovanni Calabita, Isola Tiberina 89, 00186, Rome and ‡Department of Obstetrics and Gynecology, Ospedale GB Grassi Roma, Rome, Italy *Correspondence. (e-mail:
[email protected]) DOI: 10.1002/uog.5387 Published online 6 June 2008
References 1. Kusanovic JP, Nien JK, Gon¸calves LF, Espinoza J, Lee W, Balasubramaniam M, Soto E, Erez O, Romero R. The use of inversion mode and 3D manual segmentation in volume measurement of fetal fluid-filled structures: comparison with VirTM tual Organ Computer-aided AnaLysis (VOCAL ). Ultrasound Obstet Gynecol 2008; 31: 177–186. 2. Farrell T, Leslie JR, Chien PF, Agustsson P. The reliability and validity of three dimensional ultrasound volumetric measurements using an in vitro balloon and in vivo uterine model. BJOG 2001; 108: 573–582. 3. Raine-Fenning NJ, Clewes JS, Kendall NR, Bunkheila AK, Campbell BK, Johnson IR. The interobserver reliability and validity of volume calculation from three-dimensional ultrasound datasets in the in vitro setting. Ultrasound Obstet Gynecol 2003; 21: 283–291. 4. Rizzo G, Capponi A, Cavicchioni O, Vendola M, Arduini D. Fetal cardiac stroke volume determination by four-dimensional
Copyright 2008 ISUOG. Published by John Wiley & Sons, Ltd.
Small bowel atresia can be visualized clearly on ultrasound from the second trimester of pregnancy onwards1 . The sonographic features are usually dilated hypoperistaltic bowel loops, with or without polyhydramnios. Fetuses with this condition are usually allowed to progress to term delivery, with subsequent postnatal evaluation. Surgery may be postponed for several hours or days to allow optimal operative and anesthetic conditions. Ten percent of babies born with atresia will have meconium peritonitis (MP) due to an intrauterine intestinal perforation2 . The diagnosis of MP is based on finding intra-abdominal calcifications, with or without ascites, and cases may present with the sudden onset of ascites. Cases are divided into those with simple MP, in which there is a gradual absorption of the fluid, and those with complex MP, with the accumulation of fluid and/or the development of a meconium pseudocyst3 – 6 . Management of pregnancies with either simple or complex MP should be expectant until term or fetal lung maturation because extensive bowel ischemia with ensuing perforation and necrosis usually starts after birth when the bowel fills with air7 . Signs of impending bowel ischemia and ongoing perforation in complex MP may prompt a planned delivery at a tertiary center in order to allow earlier neonatal surgical intervention3,6 . The prognosis for neonatal bowel obstruction with or without MP is good, with survival rates of between 80% and 100% when properly diagnosed and treated if there is no associated cystic fibrosis. New modalities in fetal imaging have increased the rate and accuracy of prenatal diagnosis, with vast improvements in the visualization and understanding of the fetal abdomen. The chronically obstructed gut, such as in an atresia, is usually hypoperistaltic and thickened. In the field of general radiology, the presence of ‘to-and-fro’ motion of intraluminal contrast material is a sign of a complete obstruction in an acute setting, indicating potentially salvageable bowel8,9 . This sign has not been described in fetal sonography, perhaps because ultrasound equipment previously was not sufficiently advanced. We describe a case in which small bowel atresia developed into simple MP, and in which there was also an acute obstruction caused by an inborn internal hernia. Retrospective examination of the fetal sonograms showed to-and-fro motion in a bowel segment that was found to be incarcerated and ischemic at surgery. A 24-year-old primigravida had a routine fetal ultrasound examination at 30 weeks’ gestation that
Ultrasound Obstet Gynecol 2008; 32: 111–114.
