title: Triphasic MRI of pelvic organ descent: sources of measurement error.
abstract: OBJECTIVE
  To identify sources of error when measuring pelvic organ displacement during straining using triphasic dynamic magnetic resonance imaging (MRI).
  
  
  METHODS
  Ten healthy nulliparous woman underwent triphasic dynamic 1.5 T pelvic MRI twice with 1 week between studies. The bladder was filled with 200 ml of a saline solution, the vagina and rectum were opacified with ultrasound gel. T2 weighted images in the sagittal plane were analysed twice by each of the two observers in a blinded fashion. Horizontal and vertical displacement of the bladder neck, bladder base, introitus vaginae, posterior fornix, cul-de sac, pouch of Douglas, anterior rectal wall, anorectal junction and change of the vaginal axis were measured eight times in each volunteer (two images, each read twice by two observers). Variance components were calculated for subject, observer, week, interactions of these three factors, and pure error. An overall standard error of measurement was calculated for a single observation by one observer on a film from one woman at one visit.
  
  
  RESULTS
  For the majority of anatomical reference points, the range of displacements measured was wide and the overall measurement error was large. Intra-observer error and week-to-week variation within a subject were important sources of measurement error.
  
  
  CONCLUSIONS
  Important sources of measurement error when using triphasic dynamic MRI to measure pelvic organ displacement during straining were identified. Recommendations to minimize those errors are made.
authors.affiliation: The Bowel and Digestion Centre, The Oxford Clinic, 38 Oxford Terrace, Christchurch, New Zealand. geert_morren@hotmail.com
authors.forename: Geert L
authors.initials: GL
authors.lastname: Morren
authors.forename: Adrian G
authors.initials: AG
authors.lastname: Balasingam
authors.forename: J Elisabeth
authors.initials: JE
authors.lastname: Wells
authors.forename: Anne M
authors.initials: AM
authors.lastname: Hunter
authors.forename: Richard H
authors.initials: RH
authors.lastname: Coates
authors.forename: Richard E
authors.initials: RE
authors.lastname: Perry
mesh_terms: D000293:Adolescent; D000328:Adult; D000704:Analysis of Variance; D003951:Diagnostic Errors / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D015588:Observer Variation; D010388:Pelvis / Q000033:anatomy & histology*; D011391:Prolapse; D012007:Rectum / Q000033:anatomy & histology; D012016:Reference Values; D001743:Urinary Bladder / Q000033:anatomy & histology; D014621:Vagina / Q000033:anatomy & histology