Coarse Prealignment

It is easily seen in Figure 9 that the two images are not very well aligned, especially a certain amount of rotation in the sagital and axial views make the two images differ. Since selection of the same landmarks would likely be easier if the images were roughly aligned, a method for coarse prealigment is available. Note: In principle, both images can be prealigned, however memory usage and calculation time is less if only the low resolution image is prealigned. The low resolution is typically entered into the program as the reslice image.

Figure 9: Initial orientation of the standard and reslice datasets.

To adjust the orientation of the reslice dataset, the red 'Alignment' button should be pressed, and one of the three image panes, e.g. the sagital pane clicked. A zoomed version of the image then appears (left in Figure 10). Using the keyboard and mouse

• 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 10), the window should be closed using either the keyboard x key or the close button of the window.

Figure 10: Orientation of the reslice dataset, before (left) and after (right) prealignment.

When prealignment has been applied in all panes, the images should be roughly aligned (Figure 11).

Figure 11: Orientation of the standard and reslice datasets after prealignment.