title: Reliability of three-dimensional sonographic measurements in early pregnancy using virtual reality.
abstract: OBJECTIVE
  To establish the reliability of three-dimensional (3D) ultrasound measurements in early pregnancy using a virtual reality system (the Barco I-Space).
  
  
  METHODS
  The study included 28 pregnancies with gestational ages ranging from 6 to 14 (median, 10) weeks. 3D volumes were acquired and offline measurements were made, where possible, of the yolk sac diameter, crown-rump length, biparietal diameter, head circumference and abdominal circumference, using specialized 3D imaging software (4D View). The datasets were then transferred to the Barco I-Space, a virtual reality system that allows the observer to perceive depth and interact with volume-rendered (ultrasound) data. The 3D rendered volumes were measured using a virtual pointer, controlled by a wireless joystick. For intraobserver variability, 3D and virtual reality volumes were measured twice by one operator. For interobserver variability, another operator performed the same measurements once. All measurements were repeated three times and their mean values were used for comparisons.
  
  
  RESULTS
  All intraclass correlation coefficients (ICCs) comparing 4D View measurements with I-Space measurements were > 0.97. Intra- and interobserver ICCs for the 4D View measurements were > 0.96 and for the I-Space ones were > 0.98, representing good agreement.
  
  
  CONCLUSIONS
  The application of virtual reality is a novel method of visualizing 3D ultrasound data and perception of the depth in the I-Space offers possibilities for measuring non-planar structures. We have demonstrated that early pregnancy measurements in the I-Space are reliable. New areas of embryonic and fetal biometry can now be explored using this technique, which we tentatively name 'virtual embryoscopy'.
authors.affiliation: Department of Obstetrics and Gynaecology, Division of Obstetrics and Prenatal Medicine, Erasmus MC, University Medical Centre Rotterdam, Rotterdam, The Netherlands. c.verwoerd@erasmusmc.nl
authors.forename: C M
authors.initials: CM
authors.lastname: Verwoerd-Dikkeboom
authors.forename: A H J
authors.initials: AH
authors.lastname: Koning
authors.forename: W C
authors.initials: WC
authors.lastname: Hop
authors.forename: M
authors.initials: M
authors.lastname: Rousian
authors.forename: P J
authors.initials: PJ
authors.lastname: Van Der Spek
authors.forename: N
authors.initials: N
authors.lastname: Exalto
authors.forename: E A P
authors.initials: EA
authors.lastname: Steegers
mesh_terms: D000005:Abdomen / Q000000981:diagnostic imaging; D018568:Crown-Rump Length; D005260:Female; D005333:Fetus / Q000033:anatomy & histology*; D006257:Head / Q000000981:diagnostic imaging; D006801:Humans; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D016216:Ultrasonography, Prenatal / Q000379:methods*; D015017:Yolk Sac / Q000000981:diagnostic imaging