The balloon option lets you choose a particular tissue and highlight it by inflating a balloon within it.
1. Define the tissue to be highlighted.
2. From the Tissue Definition toolbar, click Semi-Automatic Expansion Seed 
.
3. Click anywhere in the tissue you wish to highlight.
4. Keep the left mouse button pressed to inflate the balloon.
Release the mouse button to stop inflating. To reduce the inflated balloon, click Backspace.
NOTE: Once the balloon begins inflating, the other toolbar buttons are grayed out and cannot be used.
5. To delete an inflated area, click on it, then press Delete on the keyboard.