Biomedical Engineering Reference
In-Depth Information
to the resolution. To carry the registration parameters to different resolution,
the parameters are also scaled down before entering the optimization loop and
scaled up after leaving the loop. Only translation offsets need scaling. When
the sampling is not 1,
s
−
1 pixels are skipped over when the pixel pairs are
binned. In the inner simplex optimization, the “reference image” and “original
floating” image should be understood as the down-scaled reference image and
down-folded floating image at each resolution.
4.2.6
Object-Oriented Software Implementation
and Architecture
The MVC framework is adopted to facilitate the software design [37]. Models rep-
resent the information, views present information, and controllers interpret user
manipulation. Since the algorithm is automatic and there are not many user inter-
actions, the control and view can be combined, which is similar to the document-
view pattern used in Microsoft Foundation Class Doc-View Framework.
In our case the model has the information on the two images to be registered,
i.e., the reference image and the floating image and the current registration
parameters. Both images are stored as Buffered Image. The view object gets
two images as well as the registration parameters from this model and displays
the images properly. The registration object also gets two images from the model
object and sets the registration parameters after a solution is found.
The iterative optimization is implemented with two classes. Simplex is an ab-
stract base class and implements the logic of simplex optimization. The method
to calculate the objective function (mutual information in this case) is not im-
plemented in the class and thus is abstract. Its subclass should implement the
objective function calculation method. The subclass, MIMax, extends the Sim-
plex abstract class and provides all necessary methods to compute the mutual
information.
4.3
Registration Results and Discussion
4.3.1
Description of the Image Files
The retinal images used in this study were provided by Dr. Nicola Ritter of the
Lions Eye Institute of Perth and the Glaucoma Foundation of Perth. The images
