Visualization of the background and foreground image together

Hi, I have a related question. I want to overlay US images onto MRI images. The problem is that the empty (black) part of the US images obscures the MRI image. It looks like this:

Is there a way to deal with this issue? For example by making black foreground pixels transparent?

(I know I can choose ‘Add’ as the blending option, but this is not what I’m trying to achieve as it changes the appearance of the foreground)

Thanks for your help in advance