It's not ideal. You'll have to add scanner as a covariate. Also, you'll need to make sure that you are not scanning one group on one scanner and another group on another scanner. If at all possible, try and scan everyone on the same scanner. If that not possible, try and scan everyone on the same type of scanner. Multiple type of scanners is the last resort and you must be careful that there is no bias in the groups that are scanned on each scanner. You'll also need a lot more subjects to account for scanner interactions with your covariates such as age and gender.
You could also scan some people on both scanners to see if there is a difference in the scanners as well. I suspect that you will find that the Prisma is much better.
You'll want to make sure that the acquisition parameters are the same, not just the task paradigm.
