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- Decay of NMV in the transverse plane in an exponential manner
- Occurs due to spin-spin interactions
- The intrinsic magnetic fields of nuclei causes loss of coherence, resulting in dephasing
- It is intrinsic to tissue
- Time taken for 63% of the transverse magnetization to be lost due to dephasing
- This dephasing occurs during TE – the time between the RF pulse and MR signal
- Depends on strength of external field. Higher the strength, longer the T2 decay
Fat
- The more closely packed the molecules in a tissue, the more efficient the T2 decay
- Fat has closely packed molecules
- As a result spin-spin interaction is very efficient
- So the T2 decay time is very short
Water
- The molecules are spaced apart
- Spin-spin interaction is poor
- T2 decay time is long
Controlling T2 decay using TE
- A short TE is insufficient to permit dephasing in fat or water. As a result tissue contrast is less
- Long TE demonstrates good tissue contrast thanks to ample time for full dephasing of fat and water