Magnetic resonance imaging (MRI) is a dynamic and flexible imaging technique used primarily to produce high quality images of the inside of the human body. MRI is
based on the principles of nuclear magnetic resonance (NMR), a spectroscopic technique used by scientists to obtain microscopic chemical and physical information about molecules. The technique was called magnetic resonance imaging rather than nuclear magnetic resonance imaging (NMRI) because of the negative connotations associated with the word nuclear in the late 1970’s. MRI started out as a tomographic imaging technique, that is it produced an image of the NMR signal in a thin slice through the human body. MRI has advanced beyond a tomographic imaging technique to a volume imaging technique.
Magnetic resonance imaging is based on the absorption and emission of energy in the radio frequency range of the electromagnetic spectrum. That is, the technique uses a magnetic field and pulses of radio wave energy to form images of the body.
The human body is primarily fat and water. Fat and water have many hydrogen atoms which make the human body approximately 63% hydrogen atoms. Hydrogen nuclei have an NMR signal. For these reasons magnetic resonance imaging primarily images the NMR signal from the hydrogen nuclei.
For an MRI examination, the area of the body being studied is placed inside the gantry containing
a strong magnet. The digital images acquired can be saved and stored on a computer for more study. The images also can be reviewed remotely, such as in a clinic or an operating room. In some cases, contrast material may be used during the MRI scan to show certain structures more clearly.
Indications for MRI examination include:
Detecting problems such as tumors, bleeding, injury, blood vessel diseases, or infection, to confirm or rule out a problem seen on radiograph, ultrasound scan, or CT scan. Other indications include:
- Head: brain tumors, aneurysms, haemorrhages, nerve injury, cerebrovascular accidents, ophthalmic and ocular lesions, optic nerves lesions, ears and auditory nerves lesions.
- Chest: the heart, the valves, and coronary blood vessels, lungs or cardiac lesions, breast or lung cancer.
- Blood vessels: in MRA to find aneurysm, vascular occlusions, or dissection.
- Abdomen and pelvis: To examine the liver, gallbladder, pancreas, kidneys, and bladder, tumors, bleeding, infection, and blockage. In women, it can be used to examine the uterus and ovaries. In men, the prostate.
- Bones and joints: arthritis, problems with the temporomandibular joint, bone marrow problems, bone tumors, cartilage problems, torn ligaments or tendons, or infection: MRI may also be used to tell if a bone is broken when X-ray results are not clear.
- Spine: for conditions such as spinal stenosis, disc bulges, and spinal tumors