Hello!

I'd like to understand the application of quadrupolar effects in MRI. I read different materials on this topic but I met a problem - either only facts without explanation why it is so, or very deep explanation with usage of quantum mechanics. I will be very appreciate if someone explains me following points (or maybe advises some scecific literature): 1) Why do nuclei with spin higher than 1/2 have non-spherical nuclear charge distribution and thus quadrupolar moment? 2) Let's consider nucleus 23Na. Why does its quadrupolar interaction with electric field gradient causes biexponential T2 relaxation in semi-solid substances (for instance, biological tissues)? I read that quadrupolar interaction in pure liquids is absent and it is the reason of monoexponential T2 relaxation in pure liquids - why? 3) What is correlation time (usually designated as tau with sub-index "c")? I saw this parameter while reading publications but I don't understand how it is connected with question number 2. 4) I also met the term "residual quadrupolar interaction". What does it mean? 5) What is single quantum coherence and multiple quantum coherence? I encountered two methods: multiple quantum coherence MRI and multiple quantum filtered MRI? Are they mean the same?

Thanks in advance! Best regards, Philipp