Evaluation of the Canine Intervertebral Disc Structure in Turbo Spin Echo-T2 and Fast Field Echo-T1 Sequences in Magnetic Resonance Imaging.

Katarina Kunze,Andrea Tipold,Veronika Maria Stein

doi:10.3389/fvets.2019.00068

Abstract

In the current study the hypothesis should be proven that T1 weighted Fast Field Echo (FFE) sequence is a useful method to visualize intervertebral disc degeneration, respectively changes of the expected disc appearance. Medical records of 208 dogs were reviewed and images of 781 intervertebral discs were evaluated by two blinded examiners using a modified Pfirrmann classification system in two MRI sequences: FFE and Turbo-Spin-Echo T2-weighted sequence (T2W). The patients were allocated to three categories based on body conformation: (1) brachycephalic and chondrodystrophic breeds, (2) non-chondrodystrophic and non-brachycephalic breeds with a body weight of < 25 kg, and (3) non-chondrodystrophic and non-brachycephalic breeds with a body weight greater or equal 25 kg. In brachycephalic and chondrodystrophic dogs 340 intervertebral discs were evaluated, the majority of them presented a mild change of the normal disc structure, 53% in the FFE sequence and 41% in T2W images. High discrepancies were observed between mild and moderate degeneration: in the FFE-sequence 15% (n = 50) of the discs had signs of mild degeneration, whereas in T2W the same discs were graded as moderately degenerated. In non-chondrodystrophic and non-brachycephalic breeds under 25 kg body weight 320 intervertebral discs were assessed. In the FFE-sequence 52% (n = 166) of the intervertebral discs were judged as having a mild degeneration. In contrast, these same discs were graded as healthy discs (22%), mildly degenerated (33%), moderately degenerated (37%), and severely degenerated (8%) in T2W. In non-chondrodystrophic and non-brachycephalic breeds greater or equal 25 kg 121 intervertebral discs were assessed. The grading was equal in 43%, but differed in one grade (47%) and in two grades (10%) between the two sequences. In both sequences intervertebral disc herniations were equally well-diagnosed. The Kappa coefficient revealed a high discrepancy between the two MRI-sequences. In conclusion, FFE cannot replace the well-established T2W sequence for grading disc degeneration.

Highlights

Degeneration of the intervertebral disc occurs during physiological aging processes and pathological events [1, 2]
For the classification of the extent of intervertebral disc degeneration the Pfirrmann classification system was used and evaluated for the dog by Bergknut et al [15] In this classification system, the intervertebral disc is evaluated in T2 weighted images and this sequence can currently be considered as gold standard
Modic et al [25] confirmed that the decrease of the signal intensity in T2-weighted sequence (T2W) correlates with the progression of intervertebral disc degeneration

Summary

Introduction

Degeneration of the intervertebral disc occurs during physiological aging processes and pathological events [1, 2]. T2W images are used to evaluate disc degeneration and can be viewed as gold standard for this evaluation Further sequences such as preand post-contrast T1-weighted (T1W) images, gradient echo sequence or short tau inversion recovery (STIR) are applied to better delineate disc diseases or to rule out paraspinal soft-tissue pathology [9, 10]. In T1 weighted FFE images, the sequence used in the current study, the intervertebral disc has a homogenous signal intensity isointense to adjacent muscle tissue. In the present study the hypothesis should be proven that the FFE sequence is a useful method to visualize intervertebral disc degeneration or changes of the expected disc appearance and could give additional information to conventional T2W images, the proposed gold standard. More than 700 single intervertebral discs were evaluated by two blinded examiners

Methods

Results

Conclusion