- T1 Relaxation time, also known as longitudinal relaxation, refers to the process where the magnetization of spins recovers along the longitudinal axis after being disturbed by a magnetic pulse. This process is also known as Spin-Lattice relaxation.
- The other options refer to different aspects of spin behavior or signal decay in MRI but are not related to T1 relaxation.
Conclusion:
T1 relaxation time refers to Spin-Lattice relaxation, making option (a) the correct answer.