Since the images have now been roughly aligned, it is time to select a
number of landmark points in both images. To add a point set, we
must click the 'Add Point' button of the IPS main
window. This modifies the appearance of the
point list window:
One point set entered
Entering data into the program now happens by interaction with the two
3-pane windows. Adjustment of e.g. a point set in the standard image
can happen in several ways:
By clicking on either of the three panes.
By adjusting the sliders of the window.
By entering numbers into the x,y and z boxes of the window.
The effect of clicking on a pane depends on the zoom state of
the 3-pane window. The zoom state is toggled on/off by pressing the
keyboard ctrl key, when the window has focus. The state is
indicated by the background color of the window (Figure 13).
3-pane standard image window, zoom off (left) and zoom on (right).
When the window is not in zoom mode, clicking the panes will adjust
the white crosshair and the two other panes, i.e. clicking the axial
pane will modify the x,y values of the crossing planes, and readjust
the coronal and sagital views. When the window is in zoom state, a
zoomed version of the clicked pane will appear on screen (Figure 14).
3-pane standard image window - zoomed view
The currently selected coordinates are indcated by the dashed, white
crosshair, and the modified coordinate set by the green dot. A
landmark, e.g. the central point of the left eye, can now be
Clicking the zoomed window using the mouse.
Pressing the keyboard arrow keys, translation stepsize
selectable by the + and - keys.
The standard Matlab zoom function can be utilised to zoom further when
selecting a new landmark point. When coordinates of a landmark point
are updated, the currently selected pointset on the
point list interface
is updated (Figure 15). By pressing the 'undo'
buttons, point changes made in error can be un-done.w
One point set entered
By entering text into the description field of the
point list interface,
the landmark can be given an anatomical label. The entire process of
point selection should now be repeated for a suitable number of
landmark points. The litterature2 indicates that this number should be at least 6 point
sets and preferably 12 pointsets. Note: If the reslice 3-pane window
has undergone the Coarse Prealignment procedure, the numbers indicated
on the point list interface will differ from those shown on the 3-pane