Hi Julie,
Immedia have a bed ladder, it could be looped on the bottom of the table (if there is something to secure it around or through) the patient can use that to hand over hand self assist to sit. Low cost simple solution, might be worth a look. Easy to take on and off so can be well away for the actual imaging.
Meg Ransley
Physiotherapist Morton&Perry
megan@mortonperry.co.nz