Did the doctors say that? And why would you have to be institutionalized for them to provide medical help for you? This is incredibly unjust, unfair, and wicked to force someone to stay within the confines of a psychiatric ward in order to get a scan. If this is true they’re truly manipulating you and holding you hostage. While treating you like you’re not fit to live day to day life. This is bad, if the test results come back and it’s negative they could inform the judge that you aren’t fit for everyday life anymore and need assistance. Which could mean a plethora of things and ultimately land you in a nursing home or somewhere of sorts you don’t wanna be.
You need to be extremely careful dealing with these people and if you go back in you need some legal consultation on what’s going on. There’s no way you should be comfortable for being held at the crazy/looney bin for a month. Then expect these people to actually come through for you, when I got my MRI scan in America it took half a day for them to approve of it. While a PET scan is much more complex and a serious look into your brain, it’s ridiculous waiting a month in a psychiatric ward just for them to hope they may approve of you.