3T Multiband: Difference between revisions
From SpinozaWiki
No edit summary |
|||
| Line 9: | Line 9: | ||
== Sequence-parameter considerations == | == Sequence-parameter considerations == | ||
* Shimming | * Shimming | ||
** Shimbox: inside brain? Is bottomline shimbox wrt OFC / air transition most important? | ** Shimbox: inside brain? Is bottomline shimbox wrt OFC/air transition most important? | ||
** What is a good shim?LINEWIDTH | ** What is a good shim? Check LINEWIDTH before start EPI? Log values | ||
** Acquire extra B0-scan as check to avoid large B0-gradient? | ** 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 | ** Use Maarten's patch for image based shimming: this patch applies shim to B0-prescan | ||
* TR: | * TR: | ||
** for physiological noise correction, aim for 750ms | ** for physiological noise correction, aim for 750ms or less | ||
** minimal TR: to be adjusted on-scanner (not realistic in VM) | ** 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) | * 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 | * Water Fat Shift: minimal. Increase to reduce TR | ||
* TE | * 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 | * Acquired/Reconstructed Matrix size should match | ||
* Multiband factor * SENSE ~= 6 | * Multiband factor * SENSE ~= 6 | ||
* Half scan: no. Unless minimal TR deviates more than 10% from shortest. But: see Gradient mode | * Half scan: no. Unless minimal TR deviates more than 10% from shortest. But: see Gradient mode | ||
* Dynamic Stabilization: regular ( | * Dynamic Stabilization: regular (enhanced optional for longer runs, ~100ms penalty. May give distortion) | ||
* Offc/Ang: free rotatable Yes | * Offc/Ang: free rotatable Yes | ||
* PNS moderate or low | * PNS moderate or low | ||
* Flip angle --> [http://www.mritoolbox.com/ErnstAngle.html Ernst angle] A typical T1 value for gray matter @ 3T: 1330 ms (Kruger, et al, 2001). | * Flip angle --> [http://www.mritoolbox.com/ErnstAngle.html Ernst angle] A typical T1 value for gray matter @ 3T: 1330 ms (Kruger, et al, 2001). | ||
* Planning: | * Planning: angulate in parallel to OFC. Change read-out direction? (AP-->PA? | ||
* Equidistant dynamic sampling | * Equidistant dynamic sampling | ||
== distortion correction == | == distortion correction == | ||
Create two SE-EPIs for distortion correction (better unwarping | * 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 == | == Data-export == | ||
Revision as of 08:48, 24 January 2018
Multiband
Overview sequences
All have 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?
- 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