How to find the inner contour of the myocardium

Dear Sir/Madam I am trying to find the contour and edema of the myocardium, and here is the last step. I do not know how to automatically detect the inner contour of the myocardium, could you please tell me some methods? The inner contours are just like the inner blue lines:

Thank you ! Best regards

Answer 1

[Image Analyst]

Assuming you can start with that cropped image, just threshold for that gray scale range, then get rid of blobs touching the border with imclearborder(), then fill with imfill(), then extract the largest blob using the function in my attached demo.

[Neil Liu]

Thank you very much! Yes,actually I have successfully cutted the region so that I can start with the cropped image.

[Neil Liu]

I am sorry, could you please teach me how to threshold for that gray scale range? Use im2bw? Or other functions?