No, but de-oxygenated hemoglobin is paramagnetic, and therefore detectable using what's called T2*-weignted scan sequences.

http://casemed.case.edu/clerkships/neurology/Web%20Neurorad/...

No, that's why MRI has an undeniable advantage if it's what's important. What I was hoping, was that if the brain is somehow "opening" the various valves to bring more juice to certain area then that would be useful info (regardless of whether or not there is O2 in the blood, and where this O2 is consumed).

I see, so you are proposing a way to infer capillary expansion/contraction as a way to measure blood flow.