Getting all images sizes via ajax

Hi there, I am trying to get all image sizes for all attachments of a post via ajax. I’m very close but just stuck on one little php issue.

I have posted my question over here as it was php:
http://stackoverflow.com/questions/17738638/concatenate-arrays-from-foreach-loop-into-single-variable-of-nested-arrays

However it relates to wordpress so I was hoping someone here can answer.

Thanks,

Nicole