Contrast T1 weighted – (MPRAGE-anatomical) T2 weighted – (fmri)

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Presentation transcript:

Contrast T1 weighted – (MPRAGE-anatomical) T2 weighted – (fmri)

Spin Relaxation Spins do not continue to precess forever Longitudinal magnetization returns to equilibrium due to spin-lattice interactions – T1 decay Transverse magnetization is reduced due to both spin-lattice energy loss and local, random, spin dephasing – T2 decay Additional dephasing is introduced by magnetic field inhomogeneities within a voxel – T2' decay. This can be reversible, unlike T2 decay

T1 decay – “spins back down” signal we “hear” V Collective Magnetic Moment of Protons end start B0 Time T1 Recovery MR Signal Typical T1 Graph 1 s Time

T2 decay – separation (dephasing) of “collective magnetic moment” Immediately after RF excitation sometime after RF excitation collective magnectic moment individual spins a little time later = separation (dephasing) MR Signal T2 Decay Typical T2 Graph Time 50 ms

Spin Echo Y X

Proton Density Contrast T2 Decay MR Signal T1 Recovery MR Signal 1 s 50 ms TE – echo time TR – repeat time

Proton Density Weighted Image

T1 Contrast 50 ms 1 s MR MR Signal Signal T2 Decay T1 Recovery time TE – echo time TR – repeat time

T1 Weighted Image

T2* and T2 Contrast 1 s 50 ms MR MR Signal Signal T2 Decay T1 Recovery TE – echo time TR – repeat time

T2 Weighted IMage

Proton Density Weighted Image T1 Weighted Image T2 Weighted Image

Properties of Body Tissues T1 (ms) T2 (ms) Grey Matter (GM) 950 100 White Matter (WM) 600 80 Muscle 900 50 Cerebrospinal Fluid (CSF) 4500 2200 Fat 250 60 Blood 1200 100-200 MRI has high contrast for different tissue types!