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biac:analysis:topup_correction [2019/09/04 20:25] cmp12 |
biac:analysis:topup_correction [2021/08/24 18:23] cmp12 |
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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 ). | 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: | ||
- | < | + | **For singleband images :** |
+ | < | ||
+ | readout = (echospacing * (acquisitionmatrix[0] * (percentsampling/ | ||
echospacing in the BXH header is in microseconds | echospacing in the BXH header is in microseconds | ||
+ | < | ||
+ | |||
+ | |||
+ | **For mutli-band images the readout calculation is more complex: | ||
+ | < | ||
+ | readout = ( ( ceil ((1/ | ||
+ | |||
+ | EffectiveEchoSpacing = TotalReadoutTime/ | ||
+ | |||
+ | AcquisitionMatrixPE = the acquisition size of the data ( acquisitionmatrix[0] ) | ||
+ | reconMatrixPE = the size of the reconstructed data ( may be different from acquisition because of FFT rules ) | ||
+ | Round_factor = 4 if partial fourier ( PFF is in scanoptions ), 2 if full fourier. | ||
+ | Asset_R_factor = the reciprocal of the first value of dcm tag (0043,1083) | ||
</ | </ | ||
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< | < | ||
- | dwipre | + | dwifslpreproc |
- | proc dwi.mif dwi_corr.mif -rpe_pair -se_epi bud.nii.gz -pe_dir AP -readout_time 0.10656 | + | |
-rpe_pair specifies you're providing a pair of B0s ( regular, reversed ) | -rpe_pair specifies you're providing a pair of B0s ( regular, reversed ) | ||
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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 | + | - rpe_all signals that you've replicated |
- | A | + | - pe_dir is the phase encode direction of your regular acquisition |
- | LL the directions with a rpe acquisition | + | - readout_time from above |
- | -pe_dir is the phase encode direction of your regular acquisition | + | |
- | -readout_time from above | + | |
</ | </ | ||