Human: What are the different types of MRI's? Assistant: 

1. Magnetic resonance imaging (MRI) is a medical imaging technique that uses magnetic fields to visualize the internal structures of the body.
2. Ultrasound is a diagnostic medical imaging technique that uses high-frequency sound waves to create images of the body.
3. Computed tomography (CT) is an imaging technique that uses X-rays to produce cross-sectional images of the body.
4. Positron emission tomography (PET) is a nuclear medicine imaging technique that produces 3D images of the body.
5. Single photon emission computed tomography (SPECT) is a nuclear medicine imaging technique that creates 2D images of the body.