What are the uses and relative advantages to other imaging modalities, relative disadvantages as compared to other imaging modalities, hazards posed and evaluation of these hazards, and control methods used to minimize hazards and risks for the following imaging methods: Gamma Camera Imaging, MRI, X-rays, Ultrasound?

Gamma cameras use gamma particles produced by radioactive materials to penetrate through layers of the body and embed an image on a negative plate made of a sodium iodide crystal to create images. The advantage is that these are very accurate and give detailed pictures, but exposure to gamma radiation is very harmful over time. To prevent this, such cameras are used infrequently, and typically shielding materials are used to limit exposure.
Magnetic Resonance Imaging (MRI) uses high-power magnetic fields to map the body based on the varying frequencies different materials resonate with when exposed to that field. These are relatively safe, but they require high electric currents and are cumbersome.
An x-ray works much the same way gamma cameras do; however, they are less powerful and therefore penetrate less and generate less clear images. X-rays are a very cheap and quick imaging method, but prolonged or frequent exposure to them can still cause damage. Once again, shielding (typically lead-lined sheets) is used to prevent harm.
An ultrasound works similar to an MRI, except that instead of magnetic fields, it uses sonic vibrations to test the density of materials and create images. Ultrasounds require less energy and are safer, but they are less clear and cannot penetrate as deeply as an MRI. Also, they have been known to cause irritation to the patient.