@kathleenmkastrup When I had Pet Scans they said it was from chin to thigh so your head doesn’t have to go all the way in and sit there like during an MRI. I seem to recall going feet first for one of my scans ( I don’t recall if it was PET or some other reason) so my head wasn’t in the tube very far; maybe you can ask if they can scan you feet first.
I don’t get claustrophobic however I found the MRI machine a bit too close. I found that by closing my eyes before I went into the tube made me more comfortable. I only opened my eyes once I was inside, but felt more comfortable just keeping my eyes closed. Maybe you can try keeping your eyes closed before you go into the tunnel and don’t open them at all. Although you know you are in a close space, not seeing it might help you stay calm…… maybe they will let you wear a sleep mask?