mean_value_in_region
=======================================

.. py:function:: petpal.utils.stats.mean_value_in_region(input_img: ants.ANTsImage, seg_img: ants.ANTsImage, mappings: int | list[int]) -> float

   Calculate the mean value in a 3D PET image over a region based on one or more integer
   mappings corresponding to regions in a segmentation image.

   :param input_img: 3D PET image over which to calculate the mean.
   :type input_img: ants.ANTsImage
   :param seg_img: Segmentation image in same space as `input_img`.
   :type seg_img: ants.ANTsImage
   :param mappings: One or more mappings to mask input_image over.
   :type mappings: int | list[int]

   :returns: *region_mean (float)* --

             Mean PET value over voxels in the regions corresponding to
                 `mappings`.