IIO - Interactive Image Overlay

This section describes the usage of the NRU developed registration module for the Interactive Image Overlay (IIO) approach to coregistration. The method is inspired by that of Pfluger et al.³.

The basis of the method is the assumption that the human eye is good at detecting differences in shapes. Once the module has been initiated using the main program, the user interface of the method appears (Figure 20).

Figure 20: The main interface of the IIO module.

On the interface, the reslice image is shown as it directly appears within the space of the standard image⁴

Next, adjustment of the reslice and standard Min/Max values should be made, to adjust the colormaps to the value ranges of the images. The value of the reslice threshold (which determines the position of the overlayed green contour should also be adjusted, e.g. to a value corresponding to the cranial surface.

A first order registration can be done by pressing the 'CM alignment' button on the IIO interface, which will register the centres of mass of the two images (Figure 21).

Figure 21: IIO - centres of mass aligned.

Clicking the three lower panes, will navigate the standard image space. Clicking the coronal pane will update the corresponding axial an sagital view ports. Clicking one of the three upper panes will make a zoomed version of that pane visible (left in Figure 22)

Figure 22: Zoomed pane before (left) and after (right) transformation.

By using the keyboard and mouse, the overlayed image and the overlayed image can now be aligned visually with the underlying standard image:

• The pointer keys adjusts the image orientation by translation.
• Translation stepsize is adjustable through + and - keys.
• The , and . keys adjusts the image orientation by rotation, in positive/negative direction.
• Rotation stepsize is adjustable through * and / keys.
• The centre of rotation is selectable using mouse clicking.

Once the image orientation is satisfactory (right in Figure 22), the window should be closed using either the keyboard x key or the close button of the window. Repeating this process on all viewports and navigating the standard image space will register the two images (Figure 3.2.5).

Figure 23: 5

Once registration is satisfactory, the IIO interface should be closed, returning the user to the main interface of MARS, where registration parameters can be saved.