Regional T₁ mapping of the whole cervical spinal cord using an optimized MP2RAGE sequence

Abstract

While T1 measurements present multiple challenges (robustness, acquisition time), the recently proposed MP2RAGE sequence (magnetization‐prepared two rapid acquisition gradient echoes) has opened new perspectives to characterize tissue microstructure changes occurring in a pathological or developmental context. Extensively used for brain studies, it was herein adapted to investigate the cervical spinal cord (SC) at 3 T. By integrating Bloch equations, the MP2RAGE sequence parameters were chosen to optimize SC gray matter/white matter (GM/WM) T1 contrast with sub‐millimetric resolution, a scan time less than 10 min and a reliable T1 determination with minimal B1+ variation effect, within a range of values compatible with different pathologies and surrounding structures. The residual B1+ effect on T1 values was corrected using a look‐up‐table approach and B1+ mapping. The accuracy of B1+‐corrected T1 measurements was assessed on a phantom with respect to conventional inversion recovery. In vivo MP2RAGE acquisitions were performed on five young (28.8 ± 4.3 years old) and five elderly (60.2 ± 2.9 years old) volunteers and analyzed using a template‐based approach. Phantom experiments led to high agreements between inversion‐recovery spin‐echo and MP2RAGE‐based T1 values (R2 = 0.997). In vivo T1 values for cervical WM, anterior GM (aGM), posterior sensory tracts (PSTs) and lateral motor tracts (LMTs) were 917 ± 29 s, 934 ± 33 ms, 920 ± 37 ms and 877 ± 35 ms, respectively, with all subjects and cervical levels considered. Significant differences were observed between aGM and LMTs, and between LMTs and PSTs, in agreement with the literature. Repeated T1 measurements demonstrated high reproducibility of the MP2RAGE in the SC (variation coefficient < 5% in all regions of interest). Finally, preliminary assessment of age‐related SC tissue microstructure variation additionally showed evidence of SC atrophy and slight trends of T1 decrease with age in all regions. Overall, this study shows that fast, robust and accurate sub‐millimetric resolution T1 mapping in the cervical SC using the MP2RAGE sequence is possible, paving the way for future multi‐centric and longitudinal clinical studies investigating the pathological cord.

T1 Mapping for Microstructural Assessment of the Cervical Spinal Cord in the Evaluation of Patients with Degenerative Cervical Myelopathy

“…Another difficulty is the variable performance of the semi-automated detection and projection of the cervical SC in the compressed levels of the DCM (here performed with PropSeg 33 but also tried with DeepDeg 47 ) involving mandatory visual checking and manual correction in the postprocessing phase, which are sometimes time-consuming. Nonetheless, due to the feasibility and reproducibility of the protocol on the one hand 27 and partial correlation of the T1 values with the clinical severity on the other, this study confirms the already encouraging results of previous experiences. 18,28 Consequently, orthcoming attention to T1 mapping in DCM will have to focus on diverse key points, starting with selecting the optimal technique of measurement to standardize it.…”

“…The protocol included a 3D T2 sagittal sampling perfection with application-optimized contrasts by using different flip angle evolution (SPACE sequence; Siemens) and MP2RAGE acquisitions. The MP2RAGE 31 sequence was optimized for the SC as in Rasoanandrianina et al 27 (TE ¼ 2.48 ms, TR ¼ 4 seconds, generalized autocalibrating partially parallel acquisition ¼ 2, isotropic resolution ¼ 0.9 mm) and covered both brain and C1-C7 vertebral levels (Fig 1). This sequence provided both anatomic imaging and quantitative T1 mapping.…”

“…This sequence provided both anatomic imaging and quantitative T1 mapping. In fact, normally the MP2RAGE sequence acquires two 3D gradient-echo volumes at 2 different TIs (T1 inv1 and T1 inv2 , here 65 and 2000 ms) with 2 different flip angles (a 1 and a 2 , here 4°and 5°) that are combined to obtain a composite "uniform" T1WI contrasted volume, called T1 UNI, 27 from which a T1 map is subsequently derived.…”

“…T1 UNI and B 1 1 maps were first combined to offset bias fields, generating the adjusted T1 Q. 27 Denoising of T1 Q was achieved by Block-matching 4D filtering (BM4D). 32 The next stage consisted of cervical SC segmentation using the semi-automated processing pipeline PropSeg, 33 included in the Spinal Cord Toolbox.…”

“…[22][23][24] Used in the brain to study alterations in white and gray matter in both lesions and tissue with a normal appearance, T1 values demonstrated an interesting clinical correlation with cognitive dysfunction. 25,26 Although it has been rarely used in the SC until recently, studies have now outlined fast and reproducible methods to measure T1 in cervical SC in healthy subjects using 3D-MP2RAGE, 27 2D multisection inversion recovery zonally oblique-magnified multislice EPI, 18 or 2D single-section inversion recovery radial gradient-echo 28 sequences. This latter procedure, recently applied in patients presenting with mild and moderate cervical spinal canal stenosis, 28 demonstrated decreased T1 values in the SC at the compression site, with a more pronounced decrease in the higher-grade stenosis.…”