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--- biac:analysis:topup_correction [2021/03/19 15:37]
cmp12
+++ biac:analysis:topup_correction [2021/08/24 18:23]
cmp12
@@ Line 8: / Line 8: @@
 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:
-<code>readout = (echospacing * (acquisitionmatrix[0] * (percentsampling/100))) / 1e6
+**For singleband images :**
+<code>
+readout = (echospacing * (acquisitionmatrix[0] * (percentsampling/100))) / 1e6
 echospacing in the BXH header is in microseconds
+</code>
+**For mutli-band images the readout calculation is more complex:**
+<code>
+readout = ( ( ceil ((1/Round_factor) * AcquisitionMatrixPE / Asset_R_factor ) * Round_factor) - 1 ) * EchoSpacing * 0.000001
+EffectiveEchoSpacing = TotalReadoutTime/ (reconMatrixPE - 1)
+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.  most all scans will be 4
+Asset_R_factor = the reciprocal of the first value of dcm tag (0043,1083)
 </code>
@@ Line 297: / Line 313: @@
 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 ALL the directions with a rpe acquisition
-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
 </code>

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