5/26/2009. Magnetization Preparation and Other Pulse Sequence Options. Outline. The Anatomy of Basic MR Pulse Sequences.

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1 The Anaomy o Basic MR Pulse Sequences Magneizaion Preparaion and Oher Pulse Sequence Opions Chen Lin, PhD Indiana Universiy School o Medicine & Clarian Healh Parners Magneizaion Preparaion Secion Chemical Shi Selecive Sauraion & Exciaion Spaial Selecive Sauraion Magneizaion Transer () Inversion Recovery (IR) Daa Acquisiion Secion Slice/Slab Selecive Exciaion Phase Encoding(s) Echo Generaion Spin Echo (SE), Fas/Turbo SE (TSE), Single-sho FSE (HASTE) Gradien Recalled Echo (GRE), Single-sho GRE (EPI) Diusion Weighing (DWI/DTI) and Gradien Momen Nulling (GMN) Frequency Encoding Filling o K-space Magneizaion Recovery Secion End o Sequence Spoiling Driven Equilibrium Incremen Phase Encoding Ouline Magneizaion Preparaion: Based on Spaial Locaion Based on Chemical Shi Based on Magneizaion Transer () Based on Relaxaion Time T1 (Inversion recovery) T2 Based on Moion and Flow (Diusion, Perusion, Flow) Spoiler Gradien Large uni-polar gradien pulse (G s ) Dephase ransverse magneizaion in every voxel (M xy -> 0) Maybe on muliple gradien axis (, and ). Selecive Daa Acquisiion Exciaion G s G s Selecive pre-sauraion Imaging Spaial Selecive Sauraion (Sa. Band) Slab selecive 90 0 exciaion + spoiling Til M z o - plane and desroy. Muliple sa bands can be applied, bu laer ones are more eecive. Increase min. TR and SAR Non-ideal proile Need gap beween sa and imaging slices Traveling or concaenae sa band mainains consan gap. Spaial Selecive Sauraion Applicaions Reduce low/moion ariacs. Eliminae arerial/venous blood signal. Avoid phase-warp wih small FOV. Reine volume selecion (i.e. Ouer Volume Suppression [OVS] in MRS) 1

2 Universiy Munich (LMU), 5/26/2009 Parallel Sa. Bands Grid Tagging Example Modulae Sa RF pulse o creae wo sidebands. Produce wo parallel sa bands wih one pulse. Shorer ime han wo independen sa bands Same SAR. RF Gradien Tagging (SPAMM) Tagging (DANTE) RF 90 +x 90 +x RF GRAD G ag G spoil GRAD G ag G spoil M The phase accumulaion depends on he locaion along G ag Chemical Shi Selecive Sauraion Fa Sauraion Specrally selecive exciaion (Narrow BW) wih no gradien applied + spoiling. Suppress signal wihin cerain resonance requency range. i.e. FaSa Improve conras and conspicuiy. Suppress chemical shi ariacs (i.e. in EPI) T1 FLASH, FaSa, Pos T1w T1w + FS T2 TSE, FaSa 2

3 Chem Sa Consideraion B 0 and B 1 homogeneiy is very imporan Consider IR based a sa echniques Check cener requency. Increase min. TR and SAR. Fa peak, Waer Peak Fa Sa Opions Srong (more opimized) vs Weak (ixed) Quick FaSa (Inerleaved) Field Srengh F/W Separaion 1.5T 220 Hz 3.0T 440 Hz PD PD + Fa Sa Quick FaSa in Breas Imaging T2w 3D SPC o 3T 3D Shim Volume T1 VIBE Dynamic T1 VIBE + Fa Sa Use Quick FaSa o mainain emporal resoluion Adjus 3D shim volume ( Green box ) o include breas region only. T2 SPC w. FaSa T2 SPC w. SPAIR Complee a suppression more challenging or TSE due o J-coupling Composie RF Pulse Concaenaion o sub pulses o improve perormance (i.e. insensiive o B 0 and B 1 inhomogeneiy) Composie ChemSa Pulses: CHEmical Shi Selecive (CHESS) Band Selecive Inversion wih Gradien dephasing (BASING) MEGA MELV 90x 90y 90x Gs Gs Gs Specral Spaial (SpSp) pulse RF pulse Gradien Waveorm 3

4 hou e al MRM 60:842 (2008) 5/26/2009 SpSp Pulse Consideraion Shorer and less sensiive o B 1 inhomogeneiy han ChemSa. May no be very spaially selecive wih shor sub-pulses. Maybe more sensiive o B 0 inhomogeneiy when he # o sub-pulses is limied. Require accurae alignmen o RF and gradien waveorms. SpSp Waer Exciaion Convenional Fa Sa Magneizaion Transer () O-resonance non-selecive RF + spoiling Eec: RF power & requency ose Frequency ose (D = Hz) Long (pulse widh = 5-20ms) -> narrow BW High SAR (FA = ) Macromolecule proon Waer proon D Magneizaion Transer () Eec: Type and concenraion o macromolecules Muscle 60% WM 40% GM 30% Blood 15% CSF 0% C = Signal( On)/Signal( O) Avoid undesired eec rom imaging RF pulses 3DTOF MRA wih 3.0T P3 3DTOF (12:06) 3DTOFEC (7:11) Full k-space acq. wihou P3 Ellipical k- space acq. wih cenral Chemical Exchange Sauraion Transer (CEST) Sauraion ranser rom speciic chemical groups (i.e. amide proon, 8.3ppm) o waer (@ 4.3ppm). Allows deecion o cerain molecules or conras agen T2w Preparaion Inroduce ransverse (T 2 ) relaxaion by lipping magneizaion o - plane 180 y 90 -x 90 x Spoiling T2 Relaxaion Period Imaging Sequence 4

5 T2 Prep or Coronary MRA Driven Equilibrium (Fas Recovery, Resore) Add 180 y x RF pulses o reocus and lip he M xy back o axis. Allow shorer TR ( ~2000ms) while mainaining T2w or PDw. MELV Adiabaic 90 x 180 y 90 -x W/O T2 Prep W. MELV W. Adiabaic Nezaa e al MRM 55: (2006) Resore Example Flow compensaion (FC) Minimizes phase shi (moion ariacs) caused by slow-moving blood and CSF Gradien Momen Nulling (GMN): TSE 4 minues TSE wih Resore 2.4 minues Sequence Family +0 +Dx Moving Spins +0-3Dx +Dx +2Dx Flow Comp Consideraions Flow Comp direcion: FC can be implemened in slice and req direcion. No easily or phase encoding direcion Only correcs or phase shi a a given ime poin (i.e. echo ime) Only compensaes or low wih consan velociy. Increase min. TE and min. TR Flow Comp Applicaions Reduces low ariacs rom he vessels. Improve CSF conras in T2w spine imaging. Improve vessel signal in TOF MRA. Used in low quaniicaion reerence image acquisiion. 5

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