[Insight-users] Jumps or spikes in metric values

[Karthik Krishnan]

Try using the ExhastiveSearchOptimizer to plot the metric space.
You can define a region in which to plot the metric...
This optimizer (its really not an optimizer :) ), will also report the 
min and max metric values in the space.
You can also set the grid spacing along each dimension. (this will 
evaluate the metric at every nth point).

In the end, for a 3D image, you should be able to extract a 3D volume of 
metric values, for all possible overlaps of the fixed and moving image. 
Once you do that, you can throw contours or cut a plane etc, to see how 
the metric values look like in the volume..

Most likely you need smoothing prior to registration.

-karthik

Steven Boyd wrote:

> Hello,
>
> When tracking the registration metrics at each iteration, I see there 
> are periodic jumps in the metric value.  I'm using a gradient descent 
> optimizer, and testing with three different metrics: normalized 
> correlation, mattes mutual information and mean squares.
>
> Am I correct to assume that these jumps are due to the changes in the 
> step size of the optimizer?  If so, why would a step size change lead 
> to a spike in the metric value?  Why are these spikes more prevalent 
> with the mean squares metric than the normalized correlation or mattes 
> mutual information metrics?
>
> A sample plot of the metrics can be seen here:
>
> http://www.enme.ucalgary.ca/~skboyd/download/data/Metrics.jpg
>
> Regards,
>
> Steve
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