contrast Mechanisms

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Author:
mriregistry
ID:
130991
Filename:
contrast Mechanisms
Updated:
2012-01-27 15:24:31
Tags:
contrast
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Description:
factors that affect image contrast
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  1. What type of contrast are those that cannot be changed because they are inherent to the body's tissue?
    Intrinsic contrast parameters
  2. Areas of high signal and areas of low signal are appear how on the image?
    • White on image are high signal
    • Dark on image are areas of low signal
  3. What molecules contain atom hydrogen arranged with carbon and oxygen?
    Fat molecules
  4. What molecules are closely packed together and whose molecular tumbling rate is relatively slow?
    Fat molecules called lipids
  5. What molecules contain 2 hydrogen atoms arranged with one oxygen atom?
    Water molecules (H2O)
  6. What molecules are spaced apart and their molecular tumbling rate is relaively fast?
    Water molecues
  7. In T1 recovery, the magnectic moment of _____ takes LONGER to relax and regain their longitudinal magnetizations.
    The NMV of WATER takes longer to realign with B0 and so the T1 time of WATER is long.
  8. If The inherent energy of the tissue is low, then the the Molecular lattice how does that affect absorption?
    More able to absorb energy form the hydrogen nuclei. Tissue with low inherent energy are like sponges that can easily absorb energy from hydrogen nuclei during relaxaion.
  9. What has a low inherent energy and can easily absorb energy into its lattice from hydrogen nuclei; this slow molecular tumbling allows the recovery pocess to be relatively rapid.
    T1 recovery in fat
  10. The T1 of fat is long or short?
    • short
    • low inherent energy can easily absorb energy into is lattice from hdrogen nuclei.
    • means that the manetic moment of fat nuclei are able to relax and regain their magnetization quickly.
    • NMV of fat realign rapidly with Bo, so the
    • T1 time of fat is short
  11. T1 recovery in water is long or short?
    long
  12. What has a high inherent energy and cannot easily absorb energy into its lattice from hydrogen nuclei.
    • - Water
    • - Magnetic moment of water takes longer to relax and regain their longitudinal magnetization.
    • - NMV of water takes longer to realign with Bo and so the T1 time of water is long.
  13. T1 recovery occurs in fat how?
    due to nuclei giving up their energy to the surrounding environment.
  14. T1 recovery in water occurs how?
    due to nuclei giving up the energy acquired form the RF excitation puls to the surrounding lattice.
  15. T2 time of fat is long or short?
    short
  16. T2 time of water is long or short?
    long
  17. T2 decay in fat occus how?
    as a result of magnetic fields of nuclei interaticng with each other. Fat molecules are packed closely together and therefore spin-spin interactions are more likely to occur. Dephasing quickly and the loss of transverse magnetization is Rapid.
  18. T2 Decay in Water occurs how?
    Molecules are spaced Apart and spin-spin mineractions are LESS lkely to occur. SPin dehase slowly and the loss of transverse magnetizations is GRADUal.
  19. Discribe how water and fat look on a T2 weighed image?
    • Fat has low signal and apperars dark
    • Water has a signal and apperars Bright on a.
  20. Describe how fat and water appear on a T1 weighted image?
    • Fat has a high signal and apperears Bright
    • Water has a Low signal and appereaars Dark
  21. Proton densiy weighted images are characterized by areas with
    • high proton density (bright)
    • low proton density (dark)
  22. Spin echo pulse sequences produce?
    • T1
    • T2
    • Proton Density
  23. T1 weighting is controled by?
    • Short TR
    • 300-700
    • Short TE
    • 10-25
  24. T2 weighted is controlled by?
    • long TR 2000ms
    • long TE 60ms+
    • For T2 weighting the TE must be long
  25. Proton Density is controlled by?
    • Long TR 2000
    • Short TE 20
    • long TR maximizes proton density weighting

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