basics of mri, european sales meeting, darmstadt, june 6-7 2002 basics of mri
TRANSCRIPT
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Basics of MRI, European Sales Meeting, Darmstadt, June 6-7 2002
Basics of MRI
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Basics of MRI, European Sales Meeting, Darmstadt, June 6-7 2002
NMR verses MRI
Spectrum Projection
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Basics of MRI, European Sales Meeting, Darmstadt, June 6-7 2002
Spin Warp MRI
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Basics of MRI, European Sales Meeting, Darmstadt, June 6-7 2002
Slice Selection
Gradient
RF
Selected Slice+
Excitation Spectrum
thk 2fGSlice
pos2f
GSlice
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Basics of MRI, European Sales Meeting, Darmstadt, June 6-7 2002
Slice Selection Rephasing
RF
Gradient
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Basics of MRI, European Sales Meeting, Darmstadt, June 6-7 2002
Frequency Encoding
t
GR dFOV
NMR &Sampling
Gradient
Object
Profile
dFOV 2
GRt
resolution dFOVnsamples
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Basics of MRI, European Sales Meeting, Darmstadt, June 6-7 2002
Frequency Encoding
NMR
Gradient
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Basics of MRI, European Sales Meeting, Darmstadt, June 6-7 2002
Phase Encoding
Collect a trace for each value of the phase encoding gradient
Just like 2d NMR
dFOV 2
Gpetpe
resolution dFOVnpe
npe
NMR
Gread
Gphase
Gpe
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Basics of MRI, European Sales Meeting, Darmstadt, June 6-7 2002
Contrast in MRI
Image contrast arises from differences in signals!What differences?
Signal is a function of: - Proton density T1 Spin-Lattice relaxtion time T2 - Spin-Spin relaxation time T2* - magnetic susceptibility D - diffusion flow - blood, CSF etc function - brain function, cardiac function etc
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Basics of MRI, European Sales Meeting, Darmstadt, June 6-7 2002
Basic MRI Acquisition Schemes
• Gradient Echo (Spin Warp) - GEMS– T2* dependence
• Spin Echo - SEMS– T2 dependence
• Fast Spin Echo - FSE
• Echo Planar Imaging - EPI
• Spiral MRI
• Many hybrids of above!!!
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Basics of MRI, European Sales Meeting, Darmstadt, June 6-7 2002
Gradient Echo
RF &NMR
GSlice
GRead
GPhase
TE
GEMS - Varian seqlibOther names:
FLASH, GRASS, FFE< 90° (flip angle)Contrasts:
dependent on & TRT1, proton densitySensitivity to Susceptibilitydepends on TE
Variants:RF or Gradient SpoilingTurbo FLASH (SnapShot)
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Basics of MRI, European Sales Meeting, Darmstadt, June 6-7 2002
Refocused Gradient Echo
RF &NMR
GSlice
GRead
GPhase
TE
GEMS - Varian seqlibOther names:
FAST, Refocused FLASH, GRASS, FFE, FISP
< 90° (flip angle)Steady-state preserved by rewinding phase gradient.Contrasts:
dependent on & TRT1, proton densitySensitivity to Susceptibilitydepends on TE
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Basics of MRI, European Sales Meeting, Darmstadt, June 6-7 2002
Spin Echo
RF &NMR
GSlice
GRead
GPhase
TE
2
SEMS - Varian seqlibContrasts:
T2 thru TET1 thru TRProton density
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Basics of MRI, European Sales Meeting, Darmstadt, June 6-7 2002
Fast Spin Echo
RF &NMR
GSlice
GRead
GPhase
2
Fast Spin Echo (FSE)Turbo Spin Echo (TSE)RARE
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Basics of MRI, European Sales Meeting, Darmstadt, June 6-7 2002
Echo Planar Imaging - EPI
RF &NMR
GSlice
GRead
GPhase
Images in <50-100msGradient Echo &Spin Echo variantsDisadvantages:
SusceptibilityNyquist Ghosts
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Basics of MRI, European Sales Meeting, Darmstadt, June 6-7 2002
Spiral Imaging
RF &NMR
GSlice
GRead
GRead
Images in <50-100msGradient Echo &Spin Echo variantsDisadvantages:
Very Complicated ReconVery Demanding of HW
Advantages:Motion insensitivity