A method for measuring the cross sectional area of the anterior portion of the optic nerve in vivo using a fast 3D MRI sequence.
OBJECTIVE
To investigate the three-dimensional (3D) fast-recovery fast spin-echo accelerated (FRFSE-XL) sequence as a new application for measuring the intraorbital optic nerve (ION) mean cross-sectional area in vivo and to determine its value within a commonly used high resolution imaging protocol.


METHODS
The entire ION was scanned in nine healthy volunteers (mean age 32 +/- 4 years) using the 3D FRFSE-XL sequence and a commonly used high resolution short-echo fast fluid-attenuated inversion-recovery (sTE fFLAIR) sequence with identical slice locations at 1.5T. The mean cross-sectional area from both sequences was measured on a slice-by-slice basis from 3 mm behind the globe to the orbital apex. The reproducibility of both techniques was assessed from repeated scans (scan-rescan) and repeated image analysis (intraobserver).


RESULTS
Measurement of the mean cross-sectional area of the anterior 9 mm segment of the ION was only possible using the 3D FRFSE-XL sequence with a mean area of 11.6 +/- 2.2 mm(2) (scan rescan COV = 3.3 +/- 1.5, intraobserver COV = 2.4 +/- 0.02) whereas the remainder segment of the ION (i.e., 9 mm behind the globe to the orbital apex) could only be measured with the use of the sTE fFLAIR with a mean area of 8.5 +/- 1.7 mm(2) (scan rescan COV = 4.9 +/- 2.5 and intraobserver COV = 3.70 +/- 0.03).


CONCLUSIONS
The 3D FRFSE-XL allows fast and reproducible measurement of the cross-sectional area of the anterior 9 mm segment of the ION, which is not possible using commonly used imaging sequences due to image degradation from motion, and is of complementary value to the existing imaging protocol for ION atrophy quantification.
Department of Neuroinflammation, UCL Institute of Neurology, Queen Square, London, WC1N 3BG, UK. m.yiannakas@ion.ucl.ac.uk
Marios C
MC
Yiannakas
Claudia A M
CA
Wheeler-Kingshott
Alaine M
AM
Berry
Karyn
K
Chappell
Andrew
A
Henderson
Madhan
M
Kolappan
David H
DH
Miller
Daniel J
DJ
Tozer
D000328:Adult; D000465:Algorithms; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008953:Models, Anatomic; D009896:Optic Atrophy / Q000175:diagnosis* / Q000473:pathology; D009900:Optic Nerve / Q000033:anatomy & histology* / Q000473:pathology*; D012984:Software