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spine-generic / protocols

Generic acquisition protocol for quantitative MRI of the spinal cord
MIT License
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MT protocol #12

Open mjt320 opened 3 months ago

mjt320 commented 3 months ago

Hello,

Thanks for sharing these protocols! I'm implementing the Siemens version and have a comment/query about the MT GRE acquisitions.

The original MTSat paper by Helms assumes non-selective excitation, such that the MT and excitation pulse flip angles are both proportional to B1+. As a result, there is (some) cancellation of B1+ inhomogeneity effects. The generic protocol uses slab-selective excitation, so the spatial flip angle profiles of the two pulses are different. I wondered if you'd looked at the implication for accuracy of MTSat measurements?

Thanks, Michael

jcohenadad commented 2 months ago

Hi Michael,

Great question! It's been many years since the genesis of this protocol, but if I remember correctly the reason we went for the slab-selective was to reduce the amount of artifacts (I forgot exactly what kind of artifacts we were trying to get rid of-- possibly S-I wrapping).

We have not looked at the implication for accuracy of MTSat measurement, but if you'd be willing to acquire with/without slab-selective and compare, that would be awesome. We could assist with the analysis script.

Cheers

mjt320 commented 2 months ago

Hello,

Thanks for replying so quickly! Yes, I agree it makes sense to use slab-selective to avoid wrap without needing masses of oversampling. We'd like to scan all/most of the spine so we might need to change the orientation anyway. We'll try it with/without slab-selective if possible. I'll let you know if we do.

Cheers, Michael