R3_image (.mat) being loaded as unit32

I am trying to load an R3_image file as follows:

load('EMCTim.mat')

However, when I do this I get the following warning message:

"Warning: Variable 'EMCTim' originally saved as a R3_image cannot be instantiated as an object and will be read in as a uint32."

Can anyone give me some advice on how to get it to load without converting it to a unit32?

[Image Analyst]

I don't even know what an R3_image data type is. What is it?