# ITK metrics direct application

**URL:** https://discourse.itk.org/t/itk-metrics-direct-application/2495
**Category:** Engineering
**Tags:** registration
**Created:** [December 9, 2019, 2:46pm UTC](https://discourse.itk.org/t/itk-metrics-direct-application/2495 "2019-12-09T14:46:15Z")
**Posts on this page:** 1
**Showing post:** 5

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### Author: ![dzenanz](https://discourse.itk.org/user_avatar/discourse.itk.org/dzenanz/32/1093_2.png) [@dzenanz](https://discourse.itk.org/u/dzenanz)
#### Post date: [December 9, 2019, 4:19pm UTC](https://discourse.itk.org/t/itk-metrics-direct-application/2495/5 "2019-12-09T16:19:08Z")

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> [@Image registration metric derivative](https://discourse.itk.org/t/image-registration-metric-derivative/1200):
>
> I am using image registration for some time now but I am still trying to understand things in more deep. It seems tracing ITK code is not that easy. What is the math behind the metric derivative and where can I find the implementation part i.e the update function of the transform parameters? it would be nice if someone provide explanation or some simple-to-read references. Assuming a 2D rigid transformation with only 3 parameters translation in x and y, and a rotation angle; assuming also a me…

> [@Metric to evaluate the registration accuracy on 3D MRI](https://discourse.itk.org/t/metric-to-evaluate-the-registration-accuracy-on-3d-mri/2426):
>
> Hello, I am a newbie to ITK registration. Currently, I am implementing intra-subject registration of 3D PET (moving image) into 3D MRI (fixed image) using ITK. I want to check the registration accuracy which is the error in distance between transformed PET and fixed MRI images. How can I do that in ITK C++? Are there any available examples? Thanks in advance.

> [@New to ITK - moving from ImageJ macros - SimpleITK arithmetic Q](https://discourse.itk.org/t/new-to-itk-moving-from-imagej-macros-simpleitk-arithmetic-q/2101/5):
>
> Thanks for the reply Dženan, When I take a single image and translate/rotate a copy, then run registration, the mean square reported goes from a high at the start of 650,000 to a fitted value of 300,000. You can see this in the images below, showing the metric as well as the fitted image overlaid the “original”. So these images are identical - except for translation/rotation. So I would expect that a mean squares metric would be essentially zero. (assuming its a mean squared difference that…

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