Multi-Echo EPI
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Numaris/4 VA21B
1.2 Image contrast of Multi-Echo EPI
The signal intensity of the single echo images of the Multi-Echo EPI sequence is
simply given by:
*)
2
/
exp(
0
T
TE
S
S
−
=
where
S0
is the signal intensity at echo time 0, which corresponds to the proton
density for long repetition times
TR
, and
TE
is the echo time. Therefore, the echo
times of the different echo-images should be on the order or less than the tissue T2*.
Parametric images of the proton density and T2* can be obtained by fitting a model
function to the signal intensities at the different echo times (3). Please see the
processing options described below.
Figure 2
– Head images acquired on Magnetom TRIO with the Multi-Echo EPI
sequence with 4 different echo times in a single shot.
1.3 Processing options
Several processing options are given in the method. The different echo images are
always saved separately as the original images and optionally parametric maps can
be calculated in the reconstruction. In addition, online 3D-motion correction (even
prospective – PACE) and t-test can be performed. Please see sequence and
protocols for details.
1.4 References
1. P. Mansfield, A.A. Maudsley. Planar Spin Imaging. J. Magn. Reson. 27, 101
(1977)
2. O. Speck, J. Hennig. Functional Imaging by I
0
- and T
2
*-Parameter Mapping
using Multi-Image-EPI. Magn. Reson. Med. 40(2), 243-248 (1998)
