Combine Helvetica text and Latex equation in an axis label

Hi, when creating a figure label (e.g. 'Outer radius, r (m)'), I would like to format it so that the text parts (i.e. 'Outer radius, ' and ' (m)') use the MATLAB default font, Helvetica, and the symbol (i.e. 'r') is interpreted by Latex. What would be the command for this? Thank you.