implement of Simpson’s biplane method to calculate volume

Hello, I’m trying to calculate left ventricle volume at end-diastole and end-systole. After googling, I fould this article describe the method for detail. However, I still have some issue to implement it. According to eq 1 in the article, I think I need to do Simpson integrate, which I could use scipy.integrate.simps method.
I have extract the label contour using sitk.LabelContour. I don’t know how I could get the length of the green line in the fig (coressponding to dA4C/dA2C in eq 1). Any suggestion?