They can't do an MRI with a bullet in them. It would tear the guts apart. It was explained in a previous thread by some brave father with a daugher in an accident. There is a point where they can do so much in an operation then have to back off temporarilly because of life signs and body pressure.
I know a basketball player that played for Pitt in the last few years that has a bullet in his head. They don't want to mess with it because it is too close to some vitals. I mean, this is touchy stuff when you mess with the vitals in the body. I understand now, there are some things better off just left alone.
Assume bullet is metal. Magnetic Resonance Imaging cannot be done when metal is present, as metal resonates too much in the magnetic field, like you can't put metal in a microwave.
CAT scan (computerized axial tomography) would be okay as it is just a bunch of Xray slices coordinating by a computer.
However, I suspect the simple Xrays they took in the ER have probably told them most of what they need to know for the moment.