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Hi all,

I'm curious at to why T1 and T2 relaxation are represented as they are. T1 relaxation is usually represented as logarithmic increase in Mz, but isn't the measurement really the magnitude of the excited samples moment in the transverse plane over time?

Maybe my mental model is incomplete. Over time the excited magnetic vector will relax back to longitudinal field. We measure the magnetic vector's energy level with a coil that is only able to measure in the transverse plane. Therefore, over time the signal intensity will be decreasing.

It might be that the disentanglement of transverse and longitudinal relaxation is easiest to describe when one is separated into the Mz and the other is described in x,y plane. Also, Bloch originally described the T1 relaxation in the Mz plane so it has probably just stuck from the theoretical side rather than the experimental side.

Please let me know if this makes any sense and if I am misunderstanding anything.

Thank you!

Dear Krimsonking:

I think you have this right. Don't make it too complicated.

T1 relaxation describes how the longitudinal (z-axis) magnetization (Mz) regrows with time. However, Mz cannot be measured directly. Its value at each time point is determined by tipping it into the transverse plane where immediately after the tip Mz=Mxy. By plotting successive points at various time intervals after the initial excitation, T1 can be calculated by fitting to an exponential curve.

ADE