MRI/CT scan body positioning

I had a contrast dye ct scan and contrast dye mri last week, ct scan was whole upper body, mri was just liver. I had to hold my arms above my head, with elbows pointing outwards, for the ct only 5 mins. But the mri was in this position for 20 minutes. I found it quite painful on my arms and neck muscles. Is this a standard positioning for a liver mri scan? Someone I know said they had a liver mri and they didnt have to do this positioning.