title: Early pregnancy volume measurements: validation of ultrasound techniques and new perspectives.
abstract: OBJECTIVE
  To investigate accuracy and reliability of four different ultrasound-related volume-measuring methods.
  
  
  METHODS
  Observational study.
  
  
  METHODS
  Both in vitro and in vivo.
  
  
  METHODS
  Ten phantoms for in vitro measurements and 28 pregnancies with gestational ages ranging from 6 to 11 weeks for in vivo measurements were included.
  
  
  METHODS
  Three-dimensional (3D) ultrasound images of phantoms (with known variable contents) and yolk sacs were used to calculate volumes using four different methods: Virtual Organ Computed-Aided AnaLysis (VOCAL), inversion mode, Sono Automatic Volume Calculation (SonoAVC) and V-Scope. V-Scope is a newly developed 3D volume visualisation application using a Barco I-Space virtual reality system. Intra- and interobserver agreement was established by calculating intraclass correlation coefficients (ICC).
  
  
  METHODS
  Evaluation of accuracy and reliability by comparing the different techniques with true volumes (in vitro) and with each other (in vitro and in vivo).
  
  
  RESULTS
  In the in vitro study, volume measurements by VOCAL, inversion mode and V-Scope proved to be accurate. SonoAVC measurements resulted in a substantial systematic underestimation. Correlation coefficients of measured versus true volumes were excellent in all four techniques. For all techniques, an intra- and interobserver agreement of at least 0.91 was found. Yolk sac measurements by the different techniques proved to be highly correlated (ICCs>0.91).
  
  
  CONCLUSIONS
  We demonstrated that VOCAL, inversion mode and V-Scope can all be used to measure volumes of hypoechoic structures. The newly introduced V-Scope application proved to be accurate and reliable.
authors.affiliation: Department of Obstetrics and Gynaecology, Division of Obstetrics and Prenatal Medicine, Erasmus MC, University Medical Center, Rotterdam, Rotterdam, The Netherlands. m.rousian@erasmusmc.nl
authors.forename: M
authors.initials: M
authors.lastname: Rousian
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: 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: D000465:Algorithms; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D021621:Imaging, Three-Dimensional; D015588:Observer Variation; D019047:Phantoms, Imaging; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D012680:Sensitivity and Specificity; D016216:Ultrasonography, Prenatal / Q000379:methods / Q000592:standards* / Q000639:trends; D015017:Yolk Sac / Q000000981:diagnostic imaging*