In principle you can get as many MRI as you want , so image quality is no big deal. However, the machine as a maximal weight (and a maximal diameter). If the patient break the couch (which can happen over the maximal weight) it will likely break the machine cover too. under the cover you have magnets, in these magnets you have high voltage.  Better being sued for denying a treatment non possible due to the machine design. than being sued for killing a patient and being fired for breaking a million dollar machine.