How to find the inner contour of the myocardium

Dear Sir/Madam: Wish you have a good day!

Here is my orignal image:

And what I want is:

This is the image after Thresholding:

Could you please give me some methods? Is there any problem about the threshold? And actually my final image should like the third image(c):

And I know how to find edema and outer contour except the inner contour.

[A-J KHAN]

hi can you plz help me how to segment the oedema