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Basics of MRI

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. G R. d FOV. Frequency Encoding.

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Basics of MRI

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  1. Basics of MRI

  2. NMR verses MRI Spectrum Projection

  3. Spin Warp MRI

  4. Slice Selection Excitation Spectrum RF + Selected Slice Gradient

  5. Slice Selection Rephasing RF Gradient

  6. Frequency Encoding NMR & Sampling Object Profile Gradient GR dFOV

  7. Frequency Encoding NMR Gradient

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

  9. 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

  10. 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!!! Basic MRI Acquisition Schemes

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

  12. 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 Susceptibilitydepends on TE RF & NMR GSlice GRead GPhase

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

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

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

  16. 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

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