3T Multiband
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Multiband
Overview sequences
All h 10% gap, fat suppression SPIR offset 175Hz
- 3mm, TR=600ms, MB4 S1.8, FOV 240x240x132mm, WFS12pix (36mm), PNS moderate. Max dyns/time ???
- 2.5mm, TR=800ms, MB4 S1.8, FOV 240x240x140mm, WFS 14pix (35mm), PNS moderate. Max time ???
- 2mm, TR=1400ms, MB3 S2, FOV=224x224x125, (min TR=1337ms), WFS 21 pix (42mm), PNS low, Gradient Mode Maximum, Dyn stabilization Regular. Max ~1100 dyns, 26 min.
Sequence-parameter considerations
- Shimming
- Shimbox: inside brain? Is bottomline shimbox wrt OFC/air transition most important?
- What is a good shim? Check LINEWIDTH before start EPI? Log values
- Acquire extra B0-scan as check to avoid large B0-gradient?
- Use Maarten's patch for image based shimming: this patch applies shim to B0-prescan
- TR:
- for physiological noise correction, aim for 750ms or less
- minimal TR: to be adjusted on-scanner (not realistic in VM)
- Gradient mode: Set to Enhanced if duty cycle is limiting factor (enormous difference on AMC-wide bore scanner)
- Water Fat Shift: minimal. Increase to reduce TR
- TE not phase: not important as fat signal is already dispersed at this TE. TE30-32, 27 to short.
- Slice gap optional for voxel sizes <3mm, set to sefault (10%)
- Acquired/Reconstructed Matrix size should match
- Multiband factor * SENSE ~= 6
- Half scan: no. Unless minimal TR deviates more than 10% from shortest. But: see Gradient mode
- Dynamic Stabilization: regular (enhanced optional for longer runs, ~100ms penalty. May give distortion)
- Offc/Ang: free rotatable Yes
- PNS moderate or low
- Flip angle --> Ernst angle A typical T1 value for gray matter @ 3T: 1330 ms (Kruger, et al, 2001).
- Planning: angulate in parallel to OFC. Change read-out direction? (AP-->PA?)
- Perhaps not include dummies and use one of the pre-saturation scans for registration as it has better grey/white matter contrast (see Multiband data registration
- Equidistant dynamic sampling
distortion correction
- Create second GE-EPI with opposite fatshift direction, set preparation to auto (so it won't perform a second B0 shim) and group the sequences
- Alternatively create two SE-EPIs for distortion correction (better unwarping around regions with dropout)
Data-export
- enhanced dicom does not work for >16k images
- export nifti
- export PAR/REC or XML/REC to store sequence parameters