Basics of MRI

NMR verses MRI Spectrum Projection

Spin Warp MRI

Slice Selection Excitation Spectrum RF + Selected Slice Gradient

Slice Selection Rephasing RF Gradient

Frequency Encoding NMR & Sampling Object Profile Gradient GR dFOV

Frequency Encoding NMR Gradient

Phase Encoding npe NMR Gread Gphase Collect a trace for each value of the phase encoding gradient Just like 2d NMR NMR Gread Gphase npe

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

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!!!

Gradient Echo GEMS - Varian seqlib Other names: FLASH, GRASS, FFE < 90° (flip angle) Contrasts: dependent on  & TR T1, proton density Sensitivity to Susceptibility depends on TE Variants: RF or Gradient Spoiling Turbo FLASH (SnapShot) RF & NMR GSlice GRead GPhase

Refocused Gradient Echo GEMS - Varian seqlib Other names: FAST, Refocused FLASH, GRASS, FFE, FISP < 90° (flip angle) Steady-state preserved by rewinding phase gradient. Contrasts: dependent on  & TR T1, proton density Sensitivity to Susceptibility depends on TE RF & NMR GSlice GRead GPhase

Spin Echo SEMS - Varian seqlib Contrasts: T2 thru TE T1 thru TR Proton density RF & NMR GSlice GRead GPhase

Fast Spin Echo Fast Spin Echo (FSE) Turbo Spin Echo (TSE) RARE RF & NMR GSlice GRead GPhase

Echo Planar Imaging - EPI Images in <50-100ms Gradient Echo & Spin Echo variants Disadvantages: Susceptibility Nyquist Ghosts RF & NMR GSlice GRead GPhase

Spiral Imaging Images in <50-100ms Gradient Echo & Spin Echo variants Disadvantages: Very Complicated Recon Very Demanding of HW Advantages: Motion insensitivity RF & NMR GSlice GRead GRead