Which term refers to the time it takes for 63% of transverse magnetisation to be lost?

The term that refers to the time it takes for 63% of transverse magnetization to be lost is T2 time. This decay is related to the process of spin-spin relaxation, where the magnetic moments of nuclei lose coherence among themselves due to interactions with neighboring spins. As T2 time progresses, the signal strength decreases, and the transverse magnetization diminishes. The time constant T2 quantifies this decay; specifically, after one T2 time, approximately 63% of the transverse magnetization has been lost, illustrating the exponential nature of the decay process.

T1 time, in contrast, relates to the time it takes for longitudinal magnetization to recover, reflecting the process of spin-lattice relaxation. TR time is the repetition time, which is the time between successive pulse sequences applied to the same slice, and TE time is the echo time, indicating the time between the excitation pulse and the peak of the signal received. These other terms are important in MRI, but they pertain to different aspects of the imaging process rather than the loss of transverse magnetization.