What are the units of MSE and Standard Deviation in case of Medical Image Fusion?

Mean Square error and Standard Deviation Units

eg: units of PSNR are decibels and entropy are bits per pixel

Answer 1

[Image Analyst]

I don't know. Probably pixels, but could be gray levels, depends on what you're comparing.

[Daljit Kaur]

I am comparing two jpeg images. I have searched internet it says MSE has square the units of the quantity we are calculating for. So can can the units of MSE be pixel square and SD as pixels