Basics of MRI, European Sales Meeting, Darmstadt, June 6-7 2002

Basics of MRI

Basics of MRI, European Sales Meeting, Darmstadt, June 6-7 2002

NMR verses MRI

Spectrum Projection

Basics of MRI, European Sales Meeting, Darmstadt, June 6-7 2002

Spin Warp MRI

Basics of MRI, European Sales Meeting, Darmstadt, June 6-7 2002

Slice Selection

Gradient

RF

Selected Slice+

Excitation Spectrum

thk 2fGSlice

pos2f

GSlice

Basics of MRI, European Sales Meeting, Darmstadt, June 6-7 2002

Slice Selection Rephasing

RF

Gradient

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

Basics of MRI, European Sales Meeting, Darmstadt, June 6-7 2002

Frequency Encoding

NMR

Gradient

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

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

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!!!

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)

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

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

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

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

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