Korean J Radiol.  2016 Feb;17(1):103-110. 10.3348/kjr.2016.17.1.103.

Quantitative Analysis of Disc Degeneration Using Axial T2 Mapping in a Percutaneous Annular Puncture Model in Rabbits

• Chai JW
• Kang HS
• Lee JW
• Kim SJ
• Hong SH

• KMID: 2351169
• DOI: http://doi.org/10.3348/kjr.2016.17.1.103

Abstract

OBJECTIVE
To evaluate T2 relaxation time change using axial T2 mapping in a rabbit degenerated disc model and determine the most correlated variable with histologic score among T2 relaxation time, disc height index, and Pfirrmann grade.
MATERIALS AND METHODS
Degenerated disc model was made in 4 lumbar discs of 11 rabbits (n = 44) by percutaneous annular puncture with various severities of an injury. Lumbar spine lateral radiograph, MR T2 sagittal scan and MR axial T2 mapping were obtained at baseline and 2 weeks and 4 weeks after the injury in 7 rabbits and at baseline and 2 weeks, 4 weeks, and 6 weeks after the injury in 4 rabbits. Generalized estimating equations were used for a longitudinal analysis of changes in T2 relaxation time in degenerated disc model. T2 relaxation time, disc height index and Pfirrmann grade were correlated with the histologic scoring of disc degeneration using Spearman's rho test.
RESULTS
There was a significant difference in T2 relaxation time between uninjured and injured discs after annular puncture. Progressive decrease in T2 relaxation time was observed in injured discs throughout the study period. Lower T2 relaxation time was observed in the more severely injured discs. T2 relaxation time showed the strongest inverse correlation with the histologic score among the variables investigated (r = -0.811, p < 0.001).
CONCLUSION
T2 relaxation time measured with axial T2 mapping in degenerated discs is a potential method to assess disc degeneration.

Keyword

MRI; T2 mapping; Degeneration; Intervertebral disc; Rabbit

MeSH Terms

Animals
Disease Models, Animal
Intervertebral Disc/injuries/*pathology
Intervertebral Disc Degeneration/*pathology
Lumbar Vertebrae/*pathology
Magnetic Resonance Imaging/*methods
Male
Punctures
Rabbits

Figure

• 

  Fig. 1 Fluoroscopic guided annular puncture of lumbar intervertebral disc in rabbit. A. Fluoroscopic image showing needle placement on anteroposterior projection. Note needle tip reaches middle 1/3 to ensure full thickness puncture of annulus fibrosus. B. Route of annular puncture is demonstrated by black arrow on axial MR T2-weighted image.

• 

  Fig. 2 Pfirrmann grade 1 to grade 4 discs assessed with MR T2-weighted sagittal scan. A. Grade 1 disc shows homogenous bright high signal intensity in nucleus pulposus and inner annulus fibrosus. B. Grade 2 disc shows inhomogeneous high signal intensity in nucleus pulposus with less distinct margin between nucleus pulposus and annulus fibrosus. C. Grade 3 disc shows intermediate signal intensity in nucleus pulposus and slightly decreased disc height. D. Grade 4 disc shows moderately decreased disc height and intermediate to low signal intensity in nucleus. Note focal disc herniation (open arrow) to central zone.

• 

  Fig. 3 Typical histologic grades of disc degeneration. Hematoxylin and eosin stained sections of normal (A and B, histologic score 4), moderately degenerated (C and D, histologic score 10), severely degenerated (E and F, histologic score 12) discs show obliteration of border between nucleus pulposus (N) and annulus fibrosus (A), more fibrous, less cellular nucleus pulposus with increasing severity. Note annular tear (open arrowheads) and disc herniation (open arrow) in severely degenerated disc as shown in E (A, C, E at 30 x and B, D, F at 200 x).

• 

  Fig. 4 Mean T2 relaxation time at each time point. Significant decrease in T2 relaxation time for injured discs is observed with time (p < 0.001). Error bars represent standard deviation from mean.

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  Fig. 5 Number of discs in different Pfirrmann grades of degenerative disc models are demonstrated in different columns according to severity of injury, 2 weeks and 4 weeks after annular puncture.

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