
- Conventional MRI units have long, closed bores that surround most of the patient’s body during imaging.
- Short-bore MRI units were developed in response to patient claustrophobia and to retain the image-quality benefits of conventional systems, and have bore lengths that allow patients of average height to have much of their body outside the bore during imaging. The patient’s head can then be outside the bore for exams not involving the brain and neck, thereby reducing claustrophobic reactions.
- Open MRI units were also developed in response to patient claustrophobia and to facilitate interventional procedures. They have bores that are open on most sides (sometimes columns are used to support the gantry). Open MRI units usually have low-field strengths.
- Dedicated extremity/head/breast MRI units have very small bores designed to accommodate imaging of limbs, joints, or the head, and are primarily used for orthopedic applications. A dedicated breast MRI system is also available.
- Mobile MRI units are installed in a specially designed trailer and driven to hospitals that do not have an MRI unit. Mobile MRI services are used frequently in rural areas.
- Functional MRI is an imaging technique that rapidly acquires images that display changes in cerebral blood flow in response to visual or auditory stimuli or motor tasks. This technique is used primarily for research to map the functional organization of the brain.
- Interventional and intraoperative MRI is a developing field that involves performing interventional procedures such as catheterization or guidewire insertion, and intraoperative guidance such as during neuro-surgery, using a specially designed MRI unit. Open MRI units are being used for these applications due to their open-bore design, which facilitates patient access.
- MRI spectroscopy is an imaging technique used primarily in research that measures metabolites in the brain to evaluate brain tissue.
- Echoplanar MRI is an imaging technique that uses rapidly oscillating magnetic field gradients for image acquisition in less than 30 milliseconds. It is used to evaluate real-time cardiac and brain function, as well as muscle activity.
- MRI angiography is an imaging technique used to evaluate the blood vessels, for example, to detect aneurysms or atherosclerosis. Injection of a contrast agent is required.
- Diffusion tensor MRI is a relatively new imaging technique that tracks water molecules in the brain to detect abnormalities associated with stroke, multiple sclerosis, and other conditions.