# CT to optical image registration

**URL:** <https://discourse.slicer.org/t/ct-to-optical-image-registration/514>\
**Category:** Support\
**Created:** [June 16, 2017, 2:28am UTC](https://discourse.slicer.org/t/ct-to-optical-image-registration/514 "2017-06-16T02:28:20Z")\
**Posts on this page:** 1\
**Showing post:** 11

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**Author:** ![lassoan](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/lassoan/32/13_2.png) [@lassoan](https://discourse.slicer.org/u/lassoan)\
**Post date:** [June 30, 2017, 1:53pm UTC](https://discourse.slicer.org/t/ct-to-optical-image-registration/514/11 "2017-06-30T13:53:56Z")

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> [@Niousha\_Aflatouni](#):
>
> There was however no documentation for  
> this feature that I could find

I think the only help is in the tooltips. Let us know if anything is unclear.

> [@Niousha\_Aflatouni](#):
>
> I was wondering is this something that I  
> can reliably use for calculating the MI

Yes.

> [@Niousha\_Aflatouni](#):
>
> I was wondering how can one interpret these numbers

It is the metric that is minimized during registration. Read about the metric in journal papers, such as [https://www.researchgate.net/publication/222899257\_BRAINSFIT\_Mutual\_information\_registrations\_of\_whole-brain\_3D\_Images\_using\_the\_insight\_toolkit](https://www.researchgate.net/publication/222899257_BRAINSFIT_Mutual_information_registrations_of_whole-brain_3D_Images_using_the_insight_toolkit).

> [@Niousha\_Aflatouni](#):
>
> what is the  
> suggested histogram bin number to use?

Usually registration is not very sensitive to the number of bins. You can probably use the default value or slightly change it and see if it makes results better. See more details of mutual information metric in journal papers.

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