Can you as a patient request an mri as opposed to a ct when going to the er with severe abdominal pain due to fear of radiation from the latter?

Well: You would be wise to follow the directions of the emergency room doctors. They know the appropriate tests to order. You can refuse a test certainly. But not the best thing to do is recommended

Not usually.: MRIs are not necessarily better for figuring out why you might have abdominal pain. In fact, MRI can miss some of the more common reasons for pain in younger patients, such as gallstones, kidney stones, and appendicitis. If you are concerned about CT radiation, you could ask your doctor to order an ultrasound instead, as a first step.

It is your right: to discuss the risks/benefits of any test or intervention, as well as alternatives, with the doctor, but in the scenario you outline, MRI would probably not be an appropriate test.