I want to understand MRI and what exactly is T2. I have read the November issue of Sci-am and I'm still confused what exactly is T2 as it has different descriptions. The article "The Incredible Shrinking Scanner" by Bernhard Blumich: "The system can also monitor the precessing spins as they fall randomly out of sync (T2 graph)" "The synchronous precession of magnetic spins induces an oscillating voltages in the coil that decays with a characteristic T2 time constant for each spin type as the spins fall out of synchrony." Can you give in your own worlds what you think is T2 for MRI in particular and NMR in general? Also I guess in MRI, they only deal with Hydrogen atoms in water while NMR handle the rest of the elements beside Hydrogen? What are the best references or web sites about MRI out there (I have read the wiki but it is not so good). Thank you.