T2 decay

photo of thunderstorm
  • 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
  • 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
  • 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