Add PET volume processing: SUVR, ROI masking, projection to surface, SPM-petpve plugin

[DiellorBasha]

PET processing functionalities, extending the previously integrated PET import pipeline.

Features:

• Atlas-based ROI masking, using existing '_volatlas' files in Brainstorm
• Intensity rescaling (SUVR)
• Volume-to-surface projection
• GUI/dialog for collecting user input for PET processing
• PETPVE plugin as an SPM toolbox

New functions:

• process_pet.m: scriptable entry point for PET processing - used to chain together PET processing functions
• panel_process_pet.m: GUI for collecting user input for PET processing - works with process_pet.m
• mri_rescale.m: rescale intensity values (e.g. SUV/SUVR) using the mean value of a reference regions - works with panel_process_pet.m and mri_mask.m
• mri_mask.m: bilateral ROI-based volume masking using atlas labels from supported atlases: "aseg", "Desikan-Killiany" and so on.
• mri_interp_vol2tess.m: interpolates 3D PET volumes onto cortical surfaces

Please let me know if further modularization or code cleanup is needed. Thanks for reviewing!

[rcassani]

Ping @DiellorBasha

[DiellorBasha]

Thank for the review @rcassani and apologies for the delay. I've made the requested changes - see e10d74789b0e05dd1abf3617273fd0ea8c305ea5

[rcassani]

@DiellorBasha, the code PR is good to be merged. The documentation is missing. Please complete: https://neuroimage.usc.edu/brainstorm/Tutorials/PetProcessing

After that we can merged to master