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Novel Application of the Pfirrmann Disc Degeneration Grading System to 9.4T MRI

Higher Reliability Compared to 3T MRI

Sher, Idrees B.App.Sc.-MRS(DR), B.Med.Sc, MBBS. (Hons)∗,†,‡; Daly, Chris MBBS, MPhil∗,†,‡; Oehme, David MBBS, PhD, FRACS§; Chandra, Ronil V. MBBS, FRANZCR†,¶; Sher, Mustafa B.Med.Sc||; Ghosh, Peter DSc, PhD, FRSC‡,∗∗; Smith, Julian MBBS, MS, M.Surg, Ed, FRACS, FACS; Goldschlager, Tony MBBS, PhD, FRACS∗,†,‡

doi: 10.1097/BRS.0000000000002967
DIAGNOSTICS
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Study Design. Reliability study.

Objective. To evaluate the applicability and reliability of 9.4T magnetic resonance imaging (MRI) in the assessment of degenerative disc disease compared with 3T MRI.

Summary of Background Data. MRI is a reliable indicator of biochemical changes in the intervertebral disc (IVD) including hydration status, proteoglycan content, and disc degeneration compared with anatomical and histological studies. High-field 9.4T MRI has been shown to provide superior resolution and anatomical detail. However, it has not been tested against current standard MRI techniques.

Methods. Disc degeneration was initiated in 36 skeletally mature ewes 6 months prior to necropsy via validated surgical IVD injury models using either scalpel injury or drill-bit injury techniques at lumbar spine levels L2/3 and L3/4 with L1/2, L4/5, and L5/6 serving as control discs. All ex vivo IVDs were examined with 9.4T MRI and 3T MRI. All scans were analyzed using the Pfirrmann grading system by four independent observers. Intra- and interobserver reliability was assessed using kappa statistics and Spearman correlation.

Results. Inter- and intraobserver agreement for 9.4T MRI was excellent, both at κ 0.91 (P < 0.001). Comparatively, 3T interobserver reliability demonstrated substantial agreement at κ 0.61 (P < 0.001). Complete agreement was obtained in 92.7% to 100% of discs at 9.4T compared with 69.7% to 83.1% at 3T. A difference of one grade or more occurred in 6.7% at 9.4T and 39.3% at 3T. 9.4T MRI scored 97.3% of discs as grade 1 to 2 compared with 71.3% at 3T. 3T MRI tended to over-score the extent of disc degeneration with 28.6% of discs scored as grade 3 or higher compared with 2.7% at 9.4T MRI.

Conclusion. 9.4T MRI study of IVD degeneration using the Pfirrmann grading system demonstrated excellent inter- and intraobserver reliability. Comparatively, 3T MRI demonstrated a tendency to over score the extent of disc degeneration. This improved reliability of 9.4T MRI holds great potential for its clinical applications.

Level of Evidence: 3

MRI is an important tool in the assessment of disc degeneration. High-field MRI such as the 9.4T magnet provides superior resolution and excellent reliability compared with low-field MRI. 3T MRI demonstrates reduced levels of agreement among observers compared with 9.4T MRI and only substantial interobserver reliability.

Department of Neurosurgery, Monash Medical Centre, Clayton, Victoria, Australia

Department of Surgery, Monash University, Clayton, Victoria, Australia

The Ritchie Centre, Hudson Institute of Medical Research, Monash University, Clayton, Victoria, Australia

§Department of Neurosurgery, St Vincent's Hospital, Fitzroy, Victoria, Australia

Department of Imaging, Monash Medical Centre, Clayton, Victoria, Australia

||Faculty of Medicine, Griffith University, Gold Coast, Queensland, Australia

∗∗Proteobioactives, Pty Ltd, Brookvale, New South Wales, Australia.

Address correspondence and reprint requests to Idrees Sher, B.App.Sc.-MRS(DR), B.Med.Sc., MBBS (Hons), Department of Neurosurgery, Monash Medical Centre, 246 Clayton Road, Clayton, Victoria, Australia 3168; E-mail: idrees.sher@monash.edu

Received 20 August, 2018

Revised 23 October, 2018

Accepted 3 December, 2018

The manuscript submitted does not contain information about medical device(s)/drug(s).

No funds were received in support of this work.

Relevant financial activities outside the submitted work: board membership, consultancy.

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