L3-NMR signal

L3-NMR signal - 3000 Fat T2 84 White matter T2 92 94 50...

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Physics of MRI why should we care?
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because …
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Nuclear spins
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Spins within Magnetic field
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Magnetic moment and spin
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RF excitation Robert Cox
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Signal reception
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Three relaxation mechanisms T1 – time constant for the recovery of the longitudinal magnetization. T2 – time constant for the reduction of the transverse magnetization due to spin-spin interaction. T2* -- time constant for the reduction of the transverse magnetization due to a combination of spin-spin interaction and non-homogeneity of the local field. T1>T2>T2* -- always!!
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Bloch equation 1 0 2 2 , , T M M T M T M dt d z y x - - × = B M M γ precession at Larmor freq. ν spin-spin (transversal) relaxation spin-lattice (longitudinal) relaxation 0 2 B π ν=
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T1 & T2 for different tissue types Tissue 1.5T 3.0T 4.0T Fat T1 >240 ms White matter T1 640 860 1040 Gray matter T1 880 1200 1410 CSF T1
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Unformatted text preview: 3000 Fat T2 84 White matter T2 92 94 50 Gray matter T2 101 110 50 CSF T2 1400 Relaxation time and image contrast T1-weighted T2-weighted T2*-weighted Free Induction Decay Spin-Echo next 90 pulse TR 180 refocusing pulse Robert Cox TR & TE Signal equation for basic Spin Echo 90 wait TE/2 180 wait TE/2 measure wait TR-TE ) 2 1 ( 1 1 2 / / ) 2 / ( / T TR T TE TR T TE se e e e M S----+-= T1 contrast T2 contrast Gradient Echo Signal equation for Gradient Echo (flip angle) wait TE measure wait TR-TE 1 1 * 2 / / / cos 1 1 sin T TR T TR T TE ge e e e M S-----= For the that leads to max signal: 1 / cos T TR E e-= Higher leads to a signal that is more dependent on T1....
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This note was uploaded on 02/07/2009 for the course PSYC 425 taught by Professor Lu during the Spring '08 term at USC.

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L3-NMR signal - 3000 Fat T2 84 White matter T2 92 94 50...

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