Imaging methods that can be used to study the lower spinal cord have potential to provide new insights in to the pathophysiology of symptoms such as bladder and sexual dysfunction, which are often associated with neurological conditions including multiple sclerosis¹, spinal cord injury² and multiple system atrophy³. Using magnetic resonance imaging (MRI), it has recently been possible to depict grey matter (GM) and white matter (WM) in the lumbosacral enlargement (LSE) using clinical systems⁴. Quantitative MRI methods such as diffusion tensor imaging (DTI) could provide measures that reflect tissue microstructure at that level, hitherto unreported. In this pilot study, we investigated the feasibility of obtaining tissue-specific (i.e. GM and WM) DTI metrics within the LSE in vivo in healthy volunteers using reduced field-of-view echo planar imaging (ZOOM-EPI^5,6) on a clinical 3T MRI system.A) Participants: Six healthy subjects were recruited (mean age 27 years, 5 female). The local institutional review board approved the study and informed consent was obtained from all participants. B) MR Imaging: A 3T Philips Achieva system with RF dual-transmit technology (Philips Healthcare, Best, Netherlands) and the product 15-channel SENSE spine coil were used. A sagittal T2-weighted image of the lumbar spine was first obtained and used to facilitate prescription of subsequent scans perpendicular to the cord at the T11 - L1 level, to ensure coverage of the LSE⁴. For identifying the LSE, a 3D fast field-echo (3D-FFE) sequence was used with fat suppression: TR = 22 ms, TE = 4.4 ms, flip angle a =10°, FOV = 180 x 180 mm², voxel size = 0.5 x 0.5 x 5 mm³, NEX = 8, slices = 10, acquisition time ~ 9, 5 mins. For calculating the DTI metrics, a cardiac-gated ZOOM-EPI was used with identical slice geometry as the 3D-FFE, 60 diffusion directions at b = 1000 s/mm² interleaved with 7 b = 0 measurements: TR = 6000 ms, TE = 40 ms, flip angle a = 90°, number of slices = 10; FOV = 64 x 48 mm², voxel size = 1 x 1 x 5 mm³, acquisition time ~ 15 mins (depending on heart rate). C) Image analysis: Using the 3D-FFE, three slices (i.e. 15 mm) through the widest section of the lumbar cord (i.e. the LSE) were identified, using the active surface model (ASM) segmentation method in JIM 6.0 (http://www.xinapse.com)⁴. The diffusion-weighted (DW) images were firstly corrected for motion using slice-wise linear registration implemented in FSL (http://www.fmrib.ox.ac.uk/fsl/), with registration transformations estimated among non-DW images⁷. DTI fitting was performed using CAMINO (http://cmic.cs.ucl.ac.uk/camino/) and maps of axial, radial and mean diffusivity (AD/RD/MD) and fractional anisotropy (FA) were obtained. Using the mean b = 0 volume, the three slices corresponding to the LSE, previously identified from the 3D-FFE, were segmented using ASM to obtain the whole cord outline. GM was manually outlined on an image obtained by averaging DW images^7,8. Binary masks were subsequently created and eroded prior to their application to the DTI maps. To examine the impact of the number of diffusion directions on the quality of DTI indices, the DTI model was retrospectively fitted to gradually reduced sets of measurements optimally spread over the sphere (60 to 10, with steps of 10), extracted with CAMINO. D) Reproducibility assessment: All volunteers had a repeated scan on a different occasion, and the reproducibility of all DTI metrics obtained with all diffusion protocols within GM, WM and the whole cord was assessed by calculating the intra-class correlation coefficient (ICC) and the coefficient of variation (%COV).High-resolution images through the LSE and corresponding DTI maps are shown in Figure 1. Tissue-specific values (mean ± SD) of AD, RD, FA and MD in 6 healthy subjects are shown in Table 1. ICC and %COV results from the reproducibility assessment are shown in Table 2 and Table 3, respectively. The effect of using a different number of diffusion directions on the %COV of the DTI metrics within each tissue-type is demonstrated in Figure 2.This study has shown that tissue-specific DTI metrics within the LSE can be obtained reliably using a commercially available 3T MR system. This allows characterisation of microstructural features at lumbar level, which show some differences compared to other levels, such as lower FA in WM than in the upper cervical spinal cord. Future studies will be focused on developing the most time-efficient acquisition protocol (i.e. minimum number of diffusion directions), refining the image segmentation method further and assessing the value of the final protocol in the investigation of neurological disease.