How do I track when multiple objects touch in MATLAB?

I have x,y pixel coordinates of multiple objects that have been tracked from an image (3744x5616). The coordinates are stored in a structure called objects, e.g.

objects(1).centre = [1868 1236]

The objects are each uniquely identified by a numerical code, e.g.

objects(i).code = 33

I want to be able to record each time any two objects come within a radius of 300 pixels each other. What would be the best way to check through if any objects are touching and then record the identity of both objects involved in the interaction, like object 33 interacts with object 34.

Thanks!

via Chebli Mohamed