How does an MRI scan work?
The MRI is a large, cylindrical (tube-shaped) system that generates a powerful magnetic field around the patient and sends radio wave pulses from a scanner. The intense magnetic field allows the body’s hydrogen atoms to align themselves around the same axis. Out of this balanced location the radio waves knock the nuclei of the atoms in your body. They send out radio signals as the nuclei realign back into proper position. A device that analyzes and translates these signals into an picture of the part of the body being studied receives those signals. This picture will appear on a display for viewing. You can get cross-sectional views to show additional information. Some MRI machines look like narrow tunnels, and others are more widespread.
In cases where organs or soft tissue are being examined, magnetic resonance imaging ( MRI) can be used instead of computed tomography ( CT), since MRI is better at telling the difference between different types of soft tissue and the difference between normal and abnormal soft tissue. There is no chance of exposure to ionizing radiation during an MRI operation since ionizing radiation is not used.
MRI can not be done on most patients with implanted pacemakers, older intracranial aneurysm films, cochlear implants, some prosthetic devices, implanted drug infusion pumps, neurostimulators, bone growth stimulators, some intrauterine contraceptive devices, or any other type of iron-based metal implants, due to the usage of the powerful magnet. Also, MRI is not approved for people who have internal metal items such as bullets or shrapnel and certain surgical sticks, pins, plates, screws, metal sutures or wire mesh in their bodies. Colouring used in tattoos may contain iron and can heat up during an MRI, but this is an uncommon occurrence.
Newer MRI uses, and signs have helped improve new magnetic resonance technology.
Magnetic resonance angiography (MRA) is a non-invasive (the skin is not pierced) technique used to measure blood flow across arteries. MRI can also be used to diagnose brain aneurysms and vascular malformations (blood vessel defects within the brain, spinal cord, or other parts of the body).
Magnetic resonance spectroscopy (MRS) is another non-invasive technique used in the assessment of chemical anomalies in body tissues, including the brain. MRS may be used to evaluate disorders such as brain HIV infection, stroke, headache, coma, Alzheimer’s disease, tumours, and multiple sclerosis.
Functional brain magnetic resonance imaging (fMRI) is used to determine the specific place within the brain where there is a specific function, such as speech or memory. The general areas of the brain where such functions occur are known, but the exact location can vary from individual to individual. You may be asked to perform a particular task during functional resonance imaging of the brain, such as reciting the Pledge of Allegiance while the scan is being performed. Doctors may prepare Surgery or other therapies for a particular brain condition by determining the precise position of the functional core within the brain.
The “accessible” MRI is yet another development in MRI technology:
- Standard MRI units are equipped with a closed cylinder-shaped tunnel into which the patient is put. Open MRI units do not cover the patient entirely, and certain units may be open on all sides.
- Open MRI units are especially useful for procedures which involve children. Parents or other caregivers may stay with a child during the procedure to provide comfort and security.
- Claustrophobia: Before the development of open MRI units, persons with severe claustrophobia often required a sedative medication prior to the procedure.
- Very large or obese persons. Almost anyone can be accommodated in most open MRI units.
How is an MRI performed?
An MRI can be done on an outpatient basis, or as part of hospital treatment. Although each facility may have unique protocols in place, this method usually follows an MRI procedure:
- The patient has to remove all jewelry and metal items, such as hairpins or barrettes, hearing aids, eyeglasses, and dental bits, because of the strong magnetic field.
- If an intravenous line (IV) is to deliver a contrast drug and/or sedative, an IV line is initiated in the hand or arm. If the contrast is to be taken by mouth, then the contrast to swallow is offered to the patient.
- The patient will be lying on a table in the scanner, which slides into a tunnel.
- The MRI team will be in another room where the controls of the scanner are stored. The patient would also be through a window in constant sight of the workers. Speakers inside the scanner enable the staff to communicate with the patient and listen to him. The patient will have a call bell to let the staff know if he or she is having any concerns during the operation.
- A clicking noise can sound during the scanning process, as the magnetic field is generated and radio wave signals are transmitted from the scanner. To help block the sounds from the MRI scanner and hear any signals or orders from the technologist, the patient may be given headphones to wear.
- During the examination, it is necessary for the patient to remain very still.
- At intervals, depending on the part of the body being examined, the patient may be advised to hold his or her breath, or not breathe, for a few seconds. When he or she can breathe the patient will then be told. The patient should have no more than a few seconds to catch his or her breath, so this should not be painful.
- The technologist will always observe the patient and will be in continuous contact.