Felix Bloch
Nobel Prize in Physics lecture, 11th December 1952:
“To follow the analogue of mechanical resonance we must now come back to relaxation, which can be seen to act like a friction, and which counteracts the tilt produced by the alternating field.”
Since the net magnetisation of a sample is the vector sum of many protons, and since there is a constant interaction growth rate of the protons with the lattice, we can write
where M0 is the equilibrium magnetisation, T1 is the longitudinal, or spin-lattice relaxation time, which is the time constant of the exponential recovery of Mz.†
The transmission of energy to the local environment of a magnetic moment in a magnetic field which mediates this relaxation is primarily due to its thermal “contact” with that environment (fluctuating magnetic fields).
It is possible to perceive why Bloch likened relaxation to friction.
†Take the general Bloch equation (dM/dt=γMxB, derivation), and rewrite it in terms of parallel and perpendicular components of M to the external, static main magnetic field: dMz/dt=0 and dMxy=γ(MxyxB). From the former we may write the equation in the post above, and from the latter, dMxy/dt=γ(MxyxB)-(1/T2)Mxy (or simply dMxy/dt=-(1/T2)Mxy in the rotating frame).
can you explain what the T1, T2 and PD mean? Because I always see, in the scientific papers, that the authors state that they use the MRI images of T1, or they use the images of T2. Thanks a lot!
and if possible, could you email me?
May 28th, 2008, at 1:54 am #Hi kang,
Short answer: people rarely image T1 or T2. Images are T1-weighted or T2-weighted or PD-weighted. T1, T2 and PD are properties of tissues.
This is a question for the Forum. Why don’t you ask it there?
Dave
May 28th, 2008, at 11:18 am #1. What is the operative system used by Philips Medical Company in operating a clinical MRI.
January 2nd, 2009, at 10:35 am #2. What are the components of the Menu Bar.
3. What sequence is good for an MRI scan of the PELVIC?
1. Please sent me a protocol ( soft ware instruction procedure)that allows me to make MRI Scans.
January 2nd, 2009, at 10:42 am #Beginning with the power ON of the machine through patient preparation to selection of sequence and obtention of the image.
HI paul
if you go to the philips website mriforum
http://netforum.medical.philips.com/Home.aspx
you can find philips protocols
however, i think you have to register first
Kostas
June 25th, 2009, at 1:33 pm #