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Comparing several series of images is not always easy as the corresponding slices often need
to be selected manually. In times where series contain an ever-increasing number of slices this
can mean manual work when moving several series to the corresponding slice. Particularly two
situations were identified in this context: (1) patients with a large number of image series over
time (such as patients with cancers that are monitored) frequently need to compare the series,
for example to compare tumor growth over time. Manually adapting two series is possible but
with four or more series this can mean loosing time. Having automatically the closest slice
by comparing visual similarity also in older series with differing slice thickness and inter slice
distance can save time and synchronize the viewing instantly. (2) analyzing visually similar
image series of several patients can profit from being viewed in a synchronized way to compare
the cases, so when sliding through the slices in one volume, the corresponding slices in the other
volumes are shown. This application could be employed after content-based 3D image retrieval
has found similar series, for example. Synchronized viewing can help finding or confirming the
most relevant cases quickly.
To allow for synchronized viewing of several image volumes, the test image series are first
registered applying affine transformation for the global registration of images followed by diffeomorphic
image registration. Then corresponding slices in the two volumes are estimated based
on a visual similarity. Once the registration is finished, the user can subsequently move inside
the slices of one volume (reference volume) and can view the corresponding slices in the other
volumes. These corresponding slices are obtained after a correspondence match in the registration
procedure. These volumes are synchronized in that the slice closest to the original reference
volume is shown even when the slice thicknesses or inter slice distances differ, and this is automatically
done by comparing the visual image content of the slices. The tool has the potential to
help in a variety of situations and it is currently being made available as a plugin for the popular
Osirix image viewer.
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