I have tried a few techniques to register pelvic bones rigidly from MRI to CT image of one patient. For all I put the CT as the fixed image.
First tried Mutual Information registration with cropping the dark areas with this ROI for both CT and MRI (elastix setting: 1000 iteration and 3000 samples)
Second MI (last settings) on original images after a fiducial registration and third with multi metric registration with three MI on original images. For three techniques the result was the same and is shown with the segmented bone from CT over MRI which is not completely correct
I also used a mask for the above ROI but the result is not much different:
on another try did the MI registration with cropped images after the cropped MRI was hardened with a fiducial registration transform and also used masking
Forth tried Normalized MI (5 resolution levels, recursive pyramid, 10000 samples, (NumberOfHistogramBins 16 32 64) and (MaximumNumberOfIterations 4096 2048 1024 512 256) for which the result is this, right side is off:
Fifth was piecewise registration on only left femur as white crop ROI shows, default setting but 2000 iteration and 5000 samples in elastix, still a bit off as shows on the axial and sagittal views :
Fiducial-Model registration for which the result is very similar to fiducial registration only:
Now I have a few questions:
1- why does Mutual Information registration messes up the fiducial registration result, doesn’t fiducial initialization supposed to increase the accuracy?
2- Can the result of piecewise registration be used for further analysis? I mean is this result considered a good registration?
3- I followed the tutorial for surface registration from SlicerIGT to do the fiducial-model registration, there they wanted to register the stylus on the segment but here I want to register the MRI on the CT segmented bone. Because the 30-40 points that I specify on the segment and register with fiducial-model registration module are completely separate from the fiducials used for the fiducial registration wizard makes me wonder if it make sense to use this technique?
4- Overall am I missing something ? is there anything that I can improve?
Thank you very much in advance.