Table of Contents
Discuss the spin-lattice relaxation time constant (T1) and relevance in Magnetic Resonance Imaging:
T1 relaxation is called longitudinal relaxation and spin-lattice interactions. It is a result of the nucleus interacting with the surrounding jiggling spins and undergoes recovery energy to the environment (lattice). T1 relaxation increases with magnetic field strength. Gadolinium causes T1 to be shortened.
Longitudinal magnetisation grows exponentially from zero to the equilibrium value of Mz with a time constant of T1. Mz is parallel to the direction of the external magnetic field.
- T1 is the time it takes for Mz to recover to 63% of its maximum value.
- Full magnetisation occurs at 4 x T1
- Liquids have long T1 relaxation
- T1 depends on the surrounding molecules and lattice.
- T1 weighted images have a short TR to emphasise the T1 differences
- Short TR times less than 300ms in 1.5T // 450ms in 3.0T
*** T1 is always longer than T2 (except water in which T1 = T2) ***
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