[Insight-users] Registration Problem

[Fischer, Sven]

Dear all,

I want to do an registration between CT and MRI images. I use RegularStepGradientDescentOptimizer with MutualInformationImageToImageMetric for that task. I begin with loading the DICOM images with vtk and transform it to an ITKImage with VTKImageToImage filter, I register the images and transform them with ResampleImageFilter and  AffineTransform and transform them back to VTK to display them.
Now when I display the images I find that they aren´t registered. I tried different settings on the optimizer and metric but nothing worked. I even found that two images that are already registered will be misregistered afterwards. When I display the MI value during the iterations I find that it is geting worse sometimes and the final is not always the best that was found in an earlier iteration step. Shouldn't it go back into direction of the best value if it finds a worse? Is that a mistake in the Optimizer? Could you give me an advice which Optimizer to use and how to set the settings for Optimizer and Metric?
Could it be up to transforming the images between VTK and ITK? Is it important which ImageTypes/PixelTypes I use for Transforming, registration and transform between VTK/ITK?

Regards
Sven