Biomedical Engineering Reference
In-Depth Information
information is incorporated into a subsequent re-reconstruction of the whole
data set. The lines of response are adjusted according to the motion field which
implies time-varying system matrices, see [
46
,
80
,
111
,
112
] for respiratory motion
correction approaches. Motion compensated re-reconstruction is also used in
Sect.
3.2.3
in connection with the simplified motion correction pipeline.
3.1.4
Event Rebinning
The acquired list mode data is gated and each gate is reconstructed. Motion is
estimated based on these reconstructed images. The initial list mode data is rebinned
in a subsequent step by applying the transformation gained from the motion
estimation step [
79
]. As only affine transformations are allowed, such methods can
correct for respiratory motion (which is primarily locally rigid) to a certain extent
but not for non-linear cardiac motion.
3.1.5
Joint Reconstruction of Image and Motion
In joint reconstruction, motion is estimated simultaneously to the reconstruction
of the image [
13
,
14
,
20
,
68
,
89
,
121
]. An objective function is optimized in two
arguments: image and motion. Hence, only
one
image with the full statistics is
reconstructed. A drawback of these approaches is the relatively high computational
cost.
3.2
Motion Correction Pipelines for Dual Gated PET
As we have seen with the motion correction approaches discussed so far, motion
is typically estimated between each gate and a certain reference gate (based on the
motion estimation methods presented in Chap.
2
) and eliminated subsequently in a
gate-by-gate manner. This intuitive motion correction procedure is further described
with the serial pipeline in Sect.
3.2.1
specifically for dual gated PET. However,
dual gated PET offers more advanced opportunities for the correction step. In
Sects.
3.2.2
and
3.2.3
we present pipelines for motion correction which efficiently
combine motion estimation and motion correction. The key feature is thereby the
decoupling of respiratory and cardiac motion. This means that respiratory and
cardiac motion are estimated separately with intermediate correction steps. As
a result, the presented simplified pipelines feature a reduced number of motion
estimation steps with an increased robustness towards noise in each step.
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