Very recommended:

The virtual family by IT'IS:

http://www.itis.ethz.ch/itis-for-health/virtual-population/human-models/

http://iopscience.iop.org/0031-9155/55/2/N01/

http://www.itis.ethz.ch/itis-for-health/virtual-population/human-models/

http://iopscience.iop.org/0031-9155/55/2/N01/

The Diffusion Imaging Group (part of the Danish research centre for MR) have made available several types of high resolution diffusion data (brain and spine):

http://dig.drcmr.dk/about-dig#Resources

Hope that this helps!

check ADNI  initiative

You may check these:

http://braintumorsegmentation.org/

http://neobrains12.isi.uu.nl/index.php

http://mrbrains13.isi.uu.nl/index.php

http://www.litislab.fr/?projet=1rvsc

http://smial.sri.utoronto.ca/LV_Challenge/Home.html

http://promise12.grand-challenge.org

http://www.osirix-viewer.com/resources/dicom-image-library/

YOU CAN TRY THIS

I suggest openfMRI:

https://openfmri.org/

you can use these datasets:

http://fcon_1000.projects.nitrc.org/indi/adhd200/

I suggest :

https://www.openfmri.org/

https://www.kaggle.com/navoneel/brain-mri-images-for-brain-tumor-detection

Best regards