  Motion correction of dynamic contrast enhanced magnetic resonance images
(DCE-MRI) is a challenging task, due to changes in image appearance. In this
study a groupwise registration, using a principle component analysis (PCA)
based metric,1 is evaluated for clinical DCE MRI of the liver. The groupwise
registration transforms the images to a common space, rather than to a
reference volume as conventional pairwise methods do, and computes the
similarity metric on all volumes simultaneously. This groupwise registration
method is compared to a pairwise approach using a mutual information metric.
Clinical DCE MRI of the abdomen of eight patients were included. Per patient
one lesion in the liver was manually segmented in all temporal images (N=16).
The registered images were compared for accuracy, spatial and temporal
smoothness after transformation, and lesion volume change. Compared to a
pairwise method or no registration, groupwise registration provided better
alignment. In our recently started clinical study groupwise registered clinical
DCE MRI of the abdomen of nine patients were scored by three radiologists.
Groupwise registration increased the assessed quality of alignment. The gain in
reading time for the radiologist was estimated to vary from no difference to
almost a minute. A slight increase in reader confidence was also observed.
Registration had no added value for images with little motion. In conclusion,
the groupwise registration of DCE MR images results in better alignment than
achieved by pairwise registration, which is beneficial for clinical assessment.
