How to input 100 transects in an image for the tracking of fluid flow?

I have images of an invading fluid as it is injected from the center of two parallel plates. I calculate the radial velocity of the fluid as it radially moves through the plates from the center outward. I calculate the velocity by thresholding the image, creating a binary image, inputting coordinates for a transect on the image from the center outward, calculating the pixel gradient along the transect, and tracking the max change in pixel gradient over time and using this as my position to find velocity.

Right now, I am only using one transect. I would like to use 100 transects from the center of my image outward so I can have a better average velocity value. How would I input 100 transects onto my image? I do not want to manually input coordinates for 100 transects, but I will if there is no other way. I just thought I would ask to see if someone else has any ideas on how to create 100 transects?

Thanks