Motion Correction; Difference Between Ep2D_Pace And Ep2D_Bold Sequences; Analyzing Data Acquired Using Motion Correction - Siemens fMRI User Manual

fMRI User Guide
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3.2.4 Motion Correction

MoCo checkbox controls motion correction in general. In the ep2d_pace sequence, if MoCo is not checked, no
motion correction is performed. Only the original EPI images are generated. If MoCo is selected, the following
functions are performed in MotionCorrDecorator (ICE):
• DetectMotion3D
• SendPACEFeedback (controlled by m_iPACE, set by sequence)
• CorrectMotion3D (write MoCo parameters to DICOM and log file)
If MoCo is not selected, then none of the above methods will be invoked. No motion correction takes place,
neither prospective nor retrospective.
ep2d_bold sequence:
MoCo ON: Retrospective motion correction, two series generated, original EPI series and MoCo series.
MoCo OFF: No motion correction, only original EPI series generated.
ep2d_pace sequence:
MoCo ON: Prospective motion correction, two series generated, original EPI series (if motion is detected in a
volume, all future volumes are prospectively corrected in this series) and a MoCo series (with those volumes in
which motion is detected, being corrected).
MoCo OFF: No motion correction, only original EPI series generated.

3.2.5 Difference between ep2d_pace and ep2d_bold sequences

The difference between ep2d_pace and ep2d_bold is mainly in the sequence. ep2d_pace retrieves the detected
motion parameters in DetectMotion3D() and uses it to turn the gradients with the head (so called prospective,
PACE). This now affects the original images, but only prospectively, i.e. only for the succeeding volumes.
Example:
Let's say motion occurred in volume 23. Using PACE (ep2d_pace), volume 24 and following are turned with the
motion, but volume 23 is NOT affected in the original series. In the MoCo series, volume 23 is corrected using
CorrectMotion3D(). The following series do not need correction, since they are already acquired in the new tilted
patient frame.
Not using PACE (ep2d_bold), volume 24 and following still remain tilted in the original series. In the MoCo series,
volumes 23 and all the following are corrected.

3.2.6 Analyzing data acquired using Motion Correction

If the ep2d_pace sequence is used for acquiring data, and motion correction is checked ON, then one must use
the MoCo series (e.g. bas_MoCo, act_MoCo) for data analysis, not the EPI series.
If the ep2d_bold sequence is used, one may use the original EPI series or the MoCo series, depending on whether
one wants to use the original data or retrospectively corrected data.