Prescan normalize (Siemens), high b value multi-shell diffusion data, and CSD

Dear MRtrix community,

I am working with the following multi-shell diffusion data acquired using a 64-channel RF coil on a 3T Siemens Prisma. High resolution 1 mm isotropic diffusion MRI data of the hippocampus was acquired with 20 1 mm slices, no gap, single shot 2D EPI (GRAPPA R2; 6/8 PPF; A/P phase encode), FOV 220 x 216 mm2, matrix 220 x 216, BW 1420 Hz/px, 1x1x1 mm3 with no interpolation, TE 85 ms, TR 3100 ms, b = 500 s/mm2 with 64 monopolar gradient directions, b = 2000 s/mm2 with 64 monopolar gradient directions, and 20 non DWIs (b = 0 s/mm2) in 7:50 min.

Prescan normalize was used to minimize B1-inhomogeneity across the slice, and in a similar version of this acquisition (single shell, b = 500 s/mm2, 10 averages of 10 monopolar gradient directions for 100 DWIs, and 10 non DWIs; Treit, NeuroImage, 2018), comparisons to non-normalized data showed no difference in tensor parameter quantification and improved visualization of the hippocampus on mean DWIs with normalization.

We want to test single and multi-shell CSD approaches for the hippocampus using the multishell data that I initially described above in a comparison to the tensor model for examining intra-hippocampal connections.

My questions are as follows:

(1) what may be the effects of Siemens prescan normalize for the b2000 images and the resultant fODFs?

(2) What may be the effect of using a low b value shell (64dir at b500) with a high b value shell (64dir at b2000) in a multi-shell multi-tissue CSD approach?

Thank you,
Kevin
PhD Candidate
University of Alberta

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