title: High-Resolution Axonal Bundle (Fascicle) Assessment and Triple-Echo Steady-State T2 Mapping of the Median Nerve at 7 T: Preliminary Experience.
abstract: The aims of this preliminary study were to determine the number of axonal bundles (fascicles) in the median nerve, using a high-resolution, proton density (PD)-turbo spin echo (TSE) fat suppression sequence, and to determine normative T2 values, measured by triple-echo steady state, of the median nerve in healthy volunteers and in patients with idiopathic carpal tunnel syndrome (CTS), at 7 T.
  
  
  
  This prospective study was approved by the local ethics committee and conducted between March 2014 and January 2015. All study participants gave written informed consent. Six healthy volunteers (30 ± 12 years) and 5 patients with CTS (44 ± 16 years) were included. Measurements were performed on both wrists in all volunteers and on the affected wrist in patients (3 right, 2 left). Based on 5-point scales, 2 readers assessed image quality (1, very poor; 5, very good) and the presence of artifacts that might have a possible influence on fascicle determination (1, severe artifacts; 5, no artifacts) and counted the number of fascicles independently on the PD-TSE sequences. Furthermore, T2 values by region of interest analysis were assessed. Student t tests, a hierarchic linear model, and intraclass correlation coefficients (ICCs) were used for statistical analysis.
  
  
  
  Proton density-TSE image quality and artifacts revealed a median of 5 in healthy volunteers and 4 in patients with CTS for both readers. Fascicle count of the median nerve ranged from 13 to 23 in all subjects, with an ICC of 0.87 (95% confidence interval [CI], 0.67-0.95). T2 values were significantly higher (P = 0.023) in patients (24.27 ± 0.97 milliseconds [95% CI, 22.19-26.38]) compared with healthy volunteers (21.01 ± 0.65 milliseconds [95% CI, 19.61-22.41]). The ICC for all T2 values was 0.97 (95% CI, 0.96-0.98).
  
  
  
  This study shows the possibility of fascicle determination of the median nerve in healthy volunteers and patients with CTS (although probably less accurately) with high-resolution 7 T magnetic resonance imaging, as well as significantly higher T2 values in patients with CTS, which seems to be associated with pathophysiological nerve changes.
authors.affiliation: From the *MR Centre of Excellence, Department of Biomedical Imaging and Image-Guided Therapy, Medical University of Vienna, Vienna, Austria; †Division of Radiological Physics, Department of Radiology, University of Basel Hospital, Basel, Switzerland; and ‡Department of Neurology, Medical University of Vienna, Vienna, Austria.
authors.forename: Georg
authors.initials: G
authors.lastname: Riegler
authors.forename: Gregor
authors.initials: G
authors.lastname: Drlicek
authors.forename: Claudia
authors.initials: C
authors.lastname: Kronnerwetter
authors.forename: Rahel
authors.initials: R
authors.lastname: Heule
authors.forename: Oliver
authors.initials: O
authors.lastname: Bieri
authors.forename: Gerd
authors.initials: G
authors.lastname: Bodner
authors.forename: Doris
authors.initials: D
authors.lastname: Lieba-Samal
authors.forename: Siegfried
authors.initials: S
authors.lastname: Trattnig
mesh_terms: D000328:Adult; D016477:Artifacts; D000071448:Axon Fasciculation / Q000502:physiology*; D002349:Carpal Tunnel Syndrome / Q000000981:diagnostic imaging* / Q000503:physiopathology; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008475:Median Nerve / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D008875:Middle Aged; D011446:Prospective Studies; D014953:Wrist / Q000000981:diagnostic imaging; D055815:Young Adult