Table of Contents
Load any volume.
Place it into a window.
Click on of this window.
Select the RoiManagement panel.
Session => New.
Region => New and provide a name.
Change the brush: Paint => Disk, Bush Radius = 7.
Draw your region on the window.
Session => Save As.
Click Ok.
See the ROI drawing toolbox chapter in Anatomist manual for more details about the ROI drawing toolbox.