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Regional and structural integrity of the whole cervical spinal cord using 3D-T1 MP2RAGE and multi-slice multi angle DTI and ihMT sequences at 3T: preliminary investigations on age-related changes.
Henitsoa RASOANANDRIANINA1,2,3, Guillaume DUHAMEL1,2, Thorsten FEIWEIER4, Manuel TASO1,2,3, Aurélien MASSIRE1,2,3, Olivier GIRARD1,2, Maxime GUYE1,2, Jean-Philippe RANJEVA1,2, and Virginie CALLOT1,2,3

1Aix Marseille Univ, CNRS, CRMBM, Marseille, France, 2AP-HM, Pôle d'Imagerie Médicale, Hopital de La Timone, CEMEREM, Marseille, France, 3iLab-Spine International Associated Laboratory, Marseille, France, 4Siemens Healthcare GmbH, Erlangen, Germany

Synopsis

In this study, we present a 3T multi-parametric MR protocol allowing structural and diffuse evaluation of the whole cervical spinal cord (SC), within a clinically acceptable scan-time. The MRI protocol includes high-resolution anatomical T2*-weighted images allowing WM/GM atrophy evaluation, a MP2RAGE sequence allowing T1-mapping, a Multi-Slice Multi-Angle (MSMA) DTI sequence allowing evaluation of tissue structural organization and, last but not least, a MSMA inhomogeneous Magnetization transfer (ihMT) sequence allowing myelin-content evaluation in whole cervical SC. This protocol was combined with a template-based automated post-processing pipeline in a preliminary study investigating age- and region-related microstructural differences in specific regions along the cervical SC.

Introduction

Quantitative MRI techniques offer tremendous perspectives for normal aging and pathological spinal cord (SC) tissue characterization [1-7]. However, limited scan time with regards to patients’ discomfort and motion artifacts usually leads to reduced spatial coverage (e.g. C2-C4), or precludes multi-parametric MRI (mp-MRI) investigations yet useful to comprehensively characterize progression and different pathophysiological patterns as encountered in amyotrophic lateral sclerosis [8, 9] or multiple sclerosis [10-12]. In this feasibility study, we present a multi-parametric MRI protocol at 3T including a prototype multi-slice-multi-angle (MSMA) Diffusion Tensor Imaging (DTI) and inhomogeneous Magnetization Transfer (ihMT) acquisitions covering C1 to C7, along with a quantitative bias-free MP2RAGE T1-mapping sequence and a high-resolution T2*-weighted imaging providing optimal GM/WM contrast for automatic segmentation purposes. As compared to promising earlier studies based on DTI and the emerging ihMT [5, 13], the total scan time (30 minutes) was greatly reduced using single-shot EPI read-outs, while offering a better spatial coverage (whole cervical cord) using MSMA, with high-spatial resolution, and an additional structural-related quantitative information (T1 relaxation time).

Material and Method

As a preliminary application of this new multi-slice mp-MRI protocol, five young (<35yo, 28.8±4.3yo, range: [22 - 34]) and five elderly (>50yo, 60.2±2.9, range: [57 - 64]) healthy subjects were scanned on a 3T system (MAGNETOM Verio; Siemens Healthcare, Erlangen, Germany) with standard coils. Main sequence parameters and post-processing are presented in Figure 1.

Results and Discussion

Figure 2 shows the added values of MSMA acquisitions as compared to previous single-slab single-orientation acquisitions. Figure 3 presents anatomical (GM, WM and SC CSA) metrics whereas Figure 4 summarizes mp-MRI metrics (T1, DTI and MT/ihMT) within whole WM, in the two age groups.

Interestingly, all metrics were found altered in elderly subjects. First, CSA values were significantly lower suggesting GM and WM atrophies (cf. Figure 3). Second, T1 values also exhibited a significant decrease in elderly subjects. It is worth noting that T1-values extracted from GM/WM in this study are in line with previous report investigating C3 level [23], hence adding further information on T1 distribution along the whole SC. An overall decrease tendency was observed for FA and axial diffusivity along with non-significant ADC variation. Finally, radial diffusivity was significantly increased (p<0.05), along with a significant decrease of ihMT ratios (p<0.005) and a moderate decrease of MTR, significant in lower cervical levels (p<0.005)(cf. Figure 4). All together, these variations suggest axonal loss and demyelination occurring with age consistent with previous study results [1, 4, 5].

Additionally, we also found differences when comparing mp-MRI metrics within CST and PST in young subjects (cf. Figure 5): PST exhibited higher FA, ADC, axial diffusivity and T1-values and lower MT/ihMTratios and radial diffusivity as compared to CST, suggesting a higher myelination and lower axonal density of motor CST tracts as compared to posterior sensory tracts, which is consistent with previous studies [5, 24, 25].

Conclusion

In this preliminary study, we performed in vivo quantitative measurements of T1 values in the whole cervical spinal cord at 3T for the first time, compared to previous study reports on a single vertebral level [23]. We also used multi-slice multi-angle ihMT sequence for the first time, along with MSMA DTI, and were able to preliminarily characterize diffuse and regional changes of the SC microstructure related to aging or white matter pathways. Methodological improvements are under consideration in order to correct for B1 inhomogeneities and T1 relaxation effects on ihMT acquisitions. Further longitudinal follow-ups on larger cohorts are expected to confirm these preliminary but promising results. The proposed MR protocol argues for the feasibility of whole cervical SC investigation in short scan-time and its added value to future clinical investigations on degenerative SC pathologies.

Acknowledgements

No acknowledgement found.

References

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Figures

Main sequence parameters and Post-processing.

Comparison between MR images of an healthy subject scanned using previous single slab MR protocol and another age-matched healthy subject scanned with the proposed fast multi-slice multi-angle MR protocol showing spatial coverage and scan-time gain and allowing diffuse microstructural age-related and pathological changes in SC tissues.

Cross-Sectional Area values extracted in young (dark blue) versus elderly (light blue) subjects showing gray matter atrophy (left), white matter atrophy (middle) and whole spinal cord atrophy (right) occurring in SC of elderly subjects. Each apex of the hexagon corresponds to the mean CSA value at the each cervical level from C1 to C6. Standard deviation bars are not shown for visibility concerns.

Multi-parametrics results extracted in whole White Matter from young (dark blue) and elderly (light blue) subjects showing differences at each cervical level (corresponding to the pentagon’ s apexes) suggesting SC tissue degeneration and demyelination occurring with age, especially at lower cervical level (C4 to C6, 14% average decrease for ihMTR and 9% average increase for radial diffusivity). Standard deviation bars are not shown for visibility concerns.

Multi-parametrics results extracted in corticospinal tracts (CST, light red) and in posterior sensitive tracts (PST, dark red) in young subjects showing microstructural differences between the WM tracts at each cervical level from C2 to C6 (corresponding to the pentagon’s apexes). Standard deviation bars are not shown for visibility concerns.

Proc. Intl. Soc. Mag. Reson. Med. 25 (2017)
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