"Free" means not constrained to an orthogonal view; in free mode the slice can be rotated to any angle. You can drag the image while in free mode; however, you must be in free mode to rotate the image; in fact, the Volume Browser places you in free mode when you select the Rotate button.
To rotate the image, select the Rotate button from the Volume Browser window (the yellow menu button in the example below). The Free button is then also activated (the green menu button):
There is a small delay between starting rotation with the mouse and the display rotating on the screen, intended to help you rotate about a single axis when you can't move the mouse exactly the distance you want.
The tick marks provide a guide for your rotation angle.
- Click the left mouse button on the top or bottom tick to rotate your current x-axis by 45 degrees.
- Click the left mouse button on the left or right tick to rotate your current y-axis by 45 degrees.
- Drag the right mouse button from the center cross to any of the tick marks to rotate your view about the x-axis. Dragging the right mouse button from the tick mark on one edge of the window to a tick mark on an adjacent edge rotates the view 90 degrees.
As an instance of why arbitrary rotation is important, the optic nerve cannot be completely seen in the coronal, transverse, or sagittal views. However, if you rotate a transverse view a few degrees you'll be able to see the optic nerve completely:
A transverse view of
the optic nerve.
A rotated view so the
entire optic nerve appears.