title: Reproducibility and accuracy of optic nerve sheath diameter assessment using ultrasound compared to magnetic resonance imaging.
abstract: BACKGROUND
  Quantification of the optic nerve sheath diameter (ONSD) by transbulbar sonography is a promising non-invasive technique for the detection of altered intracranial pressure. In order to establish this method as follow-up tool in diseases with intracranial hyper- or hypotension scan-rescan reproducibility and accuracy need to be systematically investigated.
  
  
  METHODS
  The right ONSD of 15 healthy volunteers (mean age 24.5 ± 0.8 years) were measured by both transbulbar sonography (9 - 3 MHz) and 3 Tesla MRI (half-Fourier acquisition single-shot turbo spin-echo sequences, HASTE) 3 and 5 mm behind papilla. All volunteers underwent repeated ultrasound and MRI examinations in order to assess scan-rescan reproducibility and accuracy. Moreover, inter- and intra-observer variabilities were calculated for both techniques.
  
  
  RESULTS
  Scan-rescan reproducibility was robust for ONSD quantification by sonography and MRI at both depths (r > 0.75, p ≤ 0.001, mean differences < 2%). Comparing ultrasound- and MRI-derived ONSD values, we found acceptable agreement between both methods for measurements at a depth of 3 mm (r = 0.72, p = 0.002, mean difference < 5%). Further analyses revealed good inter- and intra-observer reliability for sonographic measurements 3 mm behind the papilla and for MRI at 3 and 5 mm (r > 0.82, p < 0.001, mean differences < 5%).
  
  
  CONCLUSIONS
  Sonographic ONSD quantification 3 mm behind the papilla can be performed with good reproducibility, measurement accuracy and observer agreement. Thus, our findings emphasize the feasibility of this technique as a non-invasive bedside tool for longitudinal ONSD measurements.
authors.affiliation: Department of Neurology, University Medical Center Freiburg, Breisacher Str, 64, 79106 Freiburg, Germany. jochen.baeuerle@uniklinik-freiburg.de.
authors.forename: Jochen
authors.initials: J
authors.lastname: Bäuerle
authors.forename: Florian
authors.initials: F
authors.lastname: Schuchardt
authors.forename: Laure
authors.initials: L
authors.lastname: Schroeder
authors.forename: Karl
authors.initials: K
authors.lastname: Egger
authors.forename: Matthias
authors.initials: M
authors.lastname: Weigel
authors.forename: Andreas
authors.initials: A
authors.lastname: Harloff
mesh_terms: D000328:Adult; D064368:Healthy Volunteers; D006801:Humans; D008279:Magnetic Resonance Imaging; D009186:Myelin Sheath / Q000000981:diagnostic imaging*; D015588:Observer Variation; D009900:Optic Nerve / Q000033:anatomy & histology* / Q000000981:diagnostic imaging*; D015203:Reproducibility of Results; D012189:Retrospective Studies; D017585:Ultrasonography, Doppler, Transcranial; D055815:Young Adult