Multi-Echo EPI
Page 9 of 9
Numaris/4 VA21B
t-Test
: The online t-test and display work as in the original EPI sequence. However,
the
t-test only works properly when motion correction is selected
! Alternatively,
T2*-Maps can be processed within the BOLD-card.
3.3 Remarks on reconstruction performance
The number of images that can be acquired with the Multi-Echo EPI method is very
high (up to 30 images per second for 64*64 matrix). The processing (especially T2*-
Fit and Motion Correction) requires computationally intensive calculations and may
required slower acquisition speeds (increased TR) to be performed online. If the
reconstruction system lags behind the acquisition, the raw data is saved to disk
during acquisition and reconstructed afterwards. Therefore, long reconstruction times
after the scan are possible. The scan is not aborted! However, no new scan can be
started during reconstruction!
Do not move the patient table to the home position
during reconstruction, otherwise the reconstruction will stop and data is lost!
The number of images that can be processed online depends on the reconstruction
hardware. Up to 20 slices with 4 echoes and a TR of 3s can be acquired without
motion correction and without long reconstruction delays.
3.4 Protocols
When the default protocol is created, motion correction and t-test are selected!
Please adjust to your needs. Remember, t-test only works correctly when motion
correction is enabled (due to inflexibility in the BOLD task card t-test could not be
disabled for this condition).
As in the standard EPI sequence, the sequence automatically introduces ‘dummy
scans’ at the beginning if more than one measurement is specified! The number of
dummy scans depends on the TR.