Free Induction Decay, Relaxation, Decay T1 and T2 in Tissues

  1. What is relaxation
    the process by which hydrogen loses energy caused by an rf pulse being switched off and the NMV tries to realign with Bo
  2. what is the amount of time of magnetization in the longitudinal plane takes to grsdually increase called
  3. At the same time but independently the amount of magnetization in the the transverse plane that gradually decreases is called
  4. AS the magnitude of transverse magnetization decreases so does the magnitude of the voltage induced in the receiver coil. The induction of reduced signal is called
    FID signal
  5. the recovery of longitudinal magnetization is caused by a process called
    T1 recovery
  6. the decay of the transverse magnetization is caused by a process called
    t2 decay
  7. what is another term for t1 recovery
    spin lattice
  8. what is spin lattice known as and explain the term
    known as t1 recovery and is caused by the nuclei giving up their energy to the surrounding environment lattice
  9. MAgnetization always occurs in what plane in t1 recovery
  10. what is t1 relaxation time
    the rate at which it takes the nuclei to recover their longitudinal magnetization which is an exponential process
  11. what percentage of time does it take the tissue to recover along the longitudinal axis
  12. t2 decay is also termed what
    spin spinrelaxation
  13. what is spin spin relaxtion
    is caused by the decay or loss of coherent transverse magnetization in the transverse plane
  14. what is the precentage of decay in tissue and how much remains
    37 % remains and takes 63% of transverse magnetization to be lost
  15. what is TR time
    it is the time from one application of RF pulse to the application of the next RF pullse for each slice and is measured in milliseconds
  16. What determines the amount of longitudinal relaxation that is allowed to occur between the end of one RF pulse to the application of the next
  17. TR thus determines what amount of relxation that has occurred when the signal is read
    T1 relaxation
  18. what is echo time
    TE is the time from the application of the RF pulse to the peak of signal induced in the coil and is also measured in milliseconds
  19. what measures how much DECAY in the transverse magnetization is allowed to occur
    TE time
  20. what controls the amount of T2 relaxation that has occurred when the signal is read
  21. what are intrinsic and extrinsic contrast parameters
    intrinsic are those that cannot be changed because they are inherent to the bodys tissue

    extrinsic are those that can be changed
  22. give examples of intrinsice parameters
    • T1 recovery and T2 decay time 
    • proton density 
    • flow
  23. list some extrinsic parameters
    • TR 
    • TE 
    • Flip angle TI 
    • Turbo factor 
    • B value
  24. why does fat have short t1 and t2 relaxtion time
    because fat has a low inherent energy and can easily absorb energy into its lattice from hydrogen. fat recovery is relatively fast because it matches the larmor frequency and allows for efficient energy exchange from hydrogen nuclei to the surrounding molecular tissue. Fat is able to relax and regain longitudinal magnetization quickly
  25. In t1 weighted images fat and water is bright or dark
    • fat is bright because it recovers magnetization faster than water 
    • water is darker because it take longer to regain longitudinal magnetization
  26. what color is fat and water in t2 decay or t2 weighted
    • fat is dark 
    • water is bright
  27. the TR must be short in t1 weighting to produce a bright fat and dark water image because?
    if the TR was long the contrast would be the same at a short TR magnetization occurs at different rates between fat and water thus creating the contrast differences
  28. what happens if the T2 weighted time is too short
    the image will look the same no contrast because in t2 weighting fat and water require longer time to decay which is also at differenct rates thus showing the contrast of fat being dark and water being bright
  29. what is the spin echo sequence
    sequences that use 180 deg pulse to REGENERATE signal
  30. spin echo sequences uses what degree excitation pulse to flip the NMV into the transverse plane
    90 deg
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Free Induction Decay, Relaxation, Decay T1 and T2 in Tissues