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Contour VOIs can be used for cropping image series to a sub-volume of interest. The image below shows the images reconstructed from a cardiac study with a large field-of-view and a 256x256 matrix size. The orthogonal planes are displayed with a zoom factor of 3. A sphere VOI of 10 cm diameter has been positioned around the left ventricle with the purpose of defining the volume of interest.
The data was then cropped using the Crop to VOI Bounding Box button on the Tools tab.
The resulting series is shown below with a zoom factor of 1. It still contains the full information regarding the left ventricle, but requires a factor of about 40 less space.
Image cropping is particularly useful as a pre-processing step to image registration. When matching a dynamic series to high-resolved MRI or CT images as a reference, it is highly recommended to crop the reference to the organ of interest before the registration. Hereby, the RAM requirements are reduced by factors without losing information, and processing speed is improved accordingly.