1/ To assess the feasibility of a qualitative, semi-quantitative and multi-parametric quantitativemagnetic resonance imaging (MRI) evaluation using 3-dimensional ultrashort echo-time (3D-UTE), 2D-T2and 3D-T1 mapping sequences to evaluate normal and pathological disco-vertebral complex (DVC) onmature and immature rats at 4.7 T, with assessment of its different portions e.g. disc (nucleuspulposus (NP) and annulus fibrosus (AF)), vertebral endplate (cartilage endplate (CEP) and growthplate (GP)) and subchondral bone (SB), in a rat model of degenerative disc disease (DDD) withhistological correlation.2/ To assess whether this complete MRI cartography can help monitoring DDD in pathologicalconditions.

Eight rats (4 mature and 4 immature rats) were induced with a DDD model by percutaneous disctrituration and collagenase injection of the tail, and imaged at 4.7T. The adjacent disc served ascontrol. MRI protocol included 3D-UTE, 2D-T2 and 3D-T1 mapping sequences performed at baseline(day 0, n = 8 animals /16 DVC) and each week (W) postoperatively for 2 weeks. Visual analysis andsignal intensity measurements on the 3D-UTE images as well as T2 and T1 measurements wereperformed in all DVC portions. Following sacrifice at 2 weeks, histological analysis with Hematoxylin-eosine and Masson trichrome was performed with comparison to MR findings.

3D-UTE sequence allowed the qualitative complete identification of normal DVC zonal anatomyincluding AF, CEP and GP. GP and CEP appeared thicker in immature compared with mature rats.SNR and CNR quantitative measurements in the AF and NP enabled to distinguish healthy DVC fromsurgery-induced DDD through a significant increase in these values 1-week post-surgery (p<.001).

2D-T2 mapping showed a significant increase in T2 values for AF and a decrease for NP betweenbaseline and both W1 and W2 post-operatively (p<.001).3D-T1 mapping showed a significant decrease in T1 values for both AF and NP between baseline andW1 and W2 post-operatively (p<.001).These T1 and T2 variations over time in the pathological rats are coherent with what was observedwith the 3D-UTE sequence.

3D-UTE sequence enables complete, robust and reproductible visualization of DVC anatomy innormal and pathological conditions on both immature and mature rats, confirmed quantitatively byT2 and T1 mapping sequences and histologically. This sequence is of prime interest in spine imagingand should be performed systematically.