_ _ _                _                                  
__      _(_) | | ___ _ __   __| |_ __ _   _ _ __   ___  _ __ __ _ 
\ \ /\ / / | | |/ _ \ '_ \ / _` | '__| | | | '_ \ / _ \| '__/ _` |
 \ V  V /| | | |  __/ | | | (_| | |  | |_| | |_) | (_) | | | (_| |
  \_/\_/ |_|_|_|\___|_| |_|\__,_|_|   \__,_| .__(_)___/|_|  \__, |
                                           |_|              |___/

Peter

Cv

Bil

Hobby
 Links
 Køretøjer
 Modeltog
 Patinering


Point Selection next up previous
Next: Parameter Estimation Up: IPS - Interactive Point Previous: Coarse Prealignment

Point Selection

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:
Figure 12: One point set entered
\includegraphics[width=0.45\textwidth]{images/ips_point_one.ps}
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).
Figure 13: 3-pane standard image window, zoom off (left) and zoom on (right).
\includegraphics[width=0.45\textwidth]{images/ips_slice3_std.ps} \includegraphics[width=0.45\textwidth]{images/ips_slice3_zoomstate.ps}
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).
Figure 14: 3-pane standard image window - zoomed view
\includegraphics[width=0.45\textwidth]{images/ips_slice3_zoomed.ps}
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 selected by
  • 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
Figure 15: One point set entered
\includegraphics[width=0.45\textwidth]{images/ips_point_value.ps}
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 window.
Figure 16: Several point sets entered
\includegraphics[width=0.45\textwidth]{images/ips_point_many.ps}

next up previous
Next: Parameter Estimation Up: IPS - Interactive Point Previous: Coarse Prealignment
Claus Svarer 2006-01-11

Last Modified: Wednesday, 11-Jan-2006 15:26:30 CET