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biac:analysis:topup_correction [2019/02/22 14:03]
cmp12
biac:analysis:topup_correction [2019/09/04 20:25] (current)
cmp12
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 There will be two series of single timepoint EPI images. ​ You can grab relevant info to create the acq_params.txt files from your XML header. There will be two series of single timepoint EPI images. ​ You can grab relevant info to create the acq_params.txt files from your XML header.
  
-You need to calculate readout time in seconds ( the physical time it takes to get the acquisition matrix of a single slice ) and get the polarity direction ( phase encode direction ).+You need to calculate readout time in seconds ​of the PEPOLAR images ​( the physical time it takes to get the acquisition matrix of a single slice ) and get the polarity direction ( phase encode direction ).
  
 the readout time in seconds for the parameter file will be: the readout time in seconds for the parameter file will be:
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 </​code>​ </​code>​
  
 +unfortunately at this point the polarity of the images will have to be determined from visual inspection. we aren't provided enough information in the metadata to give an entry into the BXH file ( yet ).
 +
 +Here is a rough guide to help with inspection. ​ Take note of the eyeballs being crushed in for AP and stretched out for PA.  Below shows the PEPOLAR images in red/blue on top of a mean functional.
 +{{:​biac:​analysis:​connneuro_func.png?​800|}}
  
-the polarity for the entry will have to be determined from the **seriesdescription**,​ which is typically "field map reverse polarity"​ or "field map regular"​ 
  
 reverse will be "​-1"​ in the acq_params.txt and regular will be "​1"​ reverse will be "​-1"​ in the acq_params.txt and regular will be "​1"​
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 applytopup --imain=../​bia6_00186_009_01.nii.gz --inindex=1 --method=jac --datain=acq_params.txt --topup=rs_topup --out=run009 --verbose applytopup --imain=../​bia6_00186_009_01.nii.gz --inindex=1 --method=jac --datain=acq_params.txt --topup=rs_topup --out=run009 --verbose
 applytopup --imain=../​bia6_00186_010_01.nii.gz --inindex=1 --method=jac --datain=acq_params.txt --topup=rs_topup --out=run010 --verbose applytopup --imain=../​bia6_00186_010_01.nii.gz --inindex=1 --method=jac --datain=acq_params.txt --topup=rs_topup --out=run010 --verbose
 +</​code>​
 +
 +If you have the scenario where the functional data was acquired with acceleration,​ but the PEPOLAR images were not.  You can create an additional acq_params file with a modified readout time to help prevent over correction. ​ You will need to divide the echospacing by the sensefactor from your BXH header of the functional run.  If your functional data and PEPOLAR images have the same sensefactor,​ this compensation is not needed.
 +
 +<​code>​readout = ((echospacing/​sensefactor) * (acquisitionmatrix[0] * (percentsampling/​100))) / 1e6 
 +echospacing in the BXH header is in microseconds
 </​code>​ </​code>​
  
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 there are 2 scenarios that typically apply here there are 2 scenarios that typically apply here
-1) a short acquisition with RPE B0s +1) DWI and a short acquisition with RPE B0s 
-2) an entire ​acquisition ​with the same gradient table and reverse phase encoding ​+2) entire ​acquisitions ​with the same gradient table and reverse phase encoding ​
  
 In both scenarios it is important to create your data with normal phase encoding direction first, followed by reversed. In both scenarios it is important to create your data with normal phase encoding direction first, followed by reversed.
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 ==== Prepare your input datasets ==== ==== Prepare your input datasets ====
 +
 +Specify that a set of images (typically b=0 volumes) will be provided for use in inhomogeneity field estimation only
  
 For scenario 1, create your blip up / blip down B0 data the same way as above. For scenario 1, create your blip up / blip down B0 data the same way as above.
 <​code>​ <​code>​
-bxhselect --timeselect 0 bi +bxhselect --timeselect 0 bia6_00197_012.bxh bu 
-a6_00197_012.bxh bu +
 bxhselect --timeselect 0 bia6_00197_013.bxh bd bxhselect --timeselect 0 bia6_00197_013.bxh bd
 fslmerge -t bud bu.nii.gz bd.nii.gz fslmerge -t bud bu.nii.gz bd.nii.gz
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 <​code>​ <​code>​
 #concat the 2 series ( regular, reversed )  #concat the 2 series ( regular, reversed ) 
-bxh_concat ​bia6_00260_007_LAS.bxh bia6_00260_008_LAS.bxh both+bxh_concat ​bia6_00260_00 
 +7_LAS.bxh bia6_00260_008_LAS.bxh both
  
 #extract the gradients #extract the gradients
-extractdiffdirs --fsl both bvecs bvals+extractdiffdirs --fsl both.bxh bvecs bvals
  
 #convert to mif #convert to mif
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 dwipreproc dwi.mif dwi_corr.mif -rpe_all -pe_dir AP -readout_time 0.10656 -debug dwipreproc dwi.mif dwi_corr.mif -rpe_all -pe_dir AP -readout_time 0.10656 -debug
  
--rpe_all signals that you've replicated ​ALL the directions with a rpe acquisition+-rpe_all signals that you've replicated ​ 
 +
 +LL the directions with a rpe acquisition
 -pe_dir is the phase encode direction of your regular acquisition -pe_dir is the phase encode direction of your regular acquisition
 -readout_time from above  ​ -readout_time from above  ​
 </​code>​ </​code>​
  
 +
 +{{ :​biac:​analysis:​trace_raw_corr.png?​800 |}}
  
biac/analysis/topup_correction.1550844201.txt.gz · Last modified: 2019/02/22 14:03 by cmp12