Ensure spatial is same in multiple runs of imnoise

Hello I am performing tests on an image after adding increasing the noise in the image each time. I am using the function imnoise for this purpose. However, in order to ensure integrity of my tests, I require that the spatial locations of the noise pixels remains the same as I keep increasing the variance of the noise. I am initially trying to get this working for Gaussian noise. Can anybody suggest on what I can do.