Proximity, distance measuring in 2 channels

[dmerwe]

Hi everyone,
I'm quite new to ImageJ/Fiji and have a straight forward problem that I which someone can help me solve. I've not found a similar topic in the Archives.

I have blobs and particles in 2 channels (fluorescent images taken with a Confocal microscope). I would like to calculate the distance in µM of the particles (beads) to the 'surface' of my blobs. I have an example of what I mean. I did a threshold, and particle count in the 2 channels.