I'm looking for a segmentation algorithm to extract the middle part of the mouse spine from MRI image shown below. I thought about extracting the part by thresholding intensity but the intensity is too similar to other parts in the image. I was also told (by my supervisor) to look into semi-automated segmentation algorithms where you would click on a pixel in the region of interest and the algorithm would consider pixels spreading from the one you clicked. Any additional advice on this would also be appreciated.
I'm new to this field so a simple explanation and/or links to additional resources are welcome.
MRI image of mouse spine:
Same as above with highlighted region that needs to be segmented:
P.S. - I'm working in matlab so if you know of a good toolbox, please let me know.
My background: Undergrad in Physics, starting Medical Physics MSc, and trying to get into image analysis / computer vision.