Advanced Editing of Irregular ROIs

Joining Irregular ROIs

When you have more than one Irregular ROI selected, the Irregular region joining tool becomes active in the ROI Toolkit frame: waisted_join .

Click this button to combine two or more Irregular ROIs into a single Irregular ROI. The ROIs will be joined by a small "bridge" that connects them at their nearest point.

Suppose we have three irregular ROIs selected, as shown below:

irregular_before_join

After the join, a single ROI results:

irregular_after_join

Note how there are two bridges that form the join: a close-up of one of these bridges is shown below:

irregular_bridge

Once Irregular ROIs are joined in this way, they can be edited as any other Irregular ROI.

Smoothing Irregular and Curved Line ROIs

Irregular and Curved Line ROIs can be smoothed, by setting a minimum radius of curvature of the line that defines the shape of the ROI. For Irregular ROIs, this radius of curvature only affects concave sections of the ROI, and is intended for use in finding the brain parenchymal fraction, as part of brain atrophy measurement.

The default minimum radius of curvature is 20.0 mm; to set a new value, select Set Smoothing Radius ... from the Edit menu of the ROI Toolkit:

roi_edit_menu

This brings up the following dialog:

smooth_radius

Type in the desired minimum radius of curvature, and then click on the

button.

To smooth either a Curved Line or Irregular ROI, select Smooth Outline from the Edit menu of the ROI Toolkit (keyboard accelerator: Control-T).

The figure below illustrates the effect of smoothing on an ROI that was used to outline the brain: before smoothing, the contour follows all the sulci of the brain; after smoothing the contour follows the brain as if it were "shrink-wrapped".

**The effect of smoothing on an Irregular ROI**

Before	After

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