Definition and Overview
An MRI (magnetic resonance imaging) scan is a device used to closely assess the internal structure of the body, especially the bones, tendons, and soft tissues. It can be used in determining problems affecting the head, including the brain, and to a certain extent spinal cord.
The MRI, unlike other advanced imaging scans such as CT scan, uses magnetic fields and radio waves to create a detailed image of the head. The body is composed of at least 65% water, which is made up of molecules and atoms. In hydrogen atom, for example, is an ion known as proton. Proton is very sensitive to magnetic field as it reacts and “follows” where the magnetic field is. In an MRI, a radio wave is used to “throw” these protons off from their alignment with the magnetic field. If these radio waves are off, the protons then realign and send back radio signals. All these will then help create a more accurate, clearer image of the organ or tissue.
Radiologists, who are trained and are experts in imaging and interpreting results, can distinguish organs and tissues since protons react differently in terms of speed and signals based on what part of the body they are found.
Who Should Undergo and Expected Results
An MRI of the head is requested by the patient’s general physician or a specialist such as a neurologist typically to make a diagnosis or to confirm or rule out any suspicion. It is recommended when patients are having head and even spinal cord issues, such as:
- Frequent or recurrent headaches
- Headaches that get worse in time
- Loss of control of certain body movements
- Vision loss or blurred vision
- Balance problems
A person who suffered an injury that involves the head may also require an imaging test such as an MRI. The scan may be helpful in diagnosing a traumatic brain injury and in assessing its extent. It can also spot internal bleeding or buildup of intracranial pressure that can cause death to the nerves of the brain.
MRI can also be utilized to diagnose or detect the presence of tumors and other anomalies to the head. It may complement other tests that detect any developmental problems of both adults and children. It can also spot problems with blood vessels such as weakened ones that may result in aneurysm.
The scan may be undertaken as a form of monitoring. The doctor may request it to check if the present treatment or medication is working, or whether a disease has already progressed.
The test is not recommended for people who have certain implants such as pacemakers or aneurysm clips. This is because they may react to the magnetic field and radio waves used in the test. For anyone who likes to know whether the implant is MRI safe, they can contact the manufacturer of the device.
Although some pregnant and breastfeeding women are allowed to undergo MRI, the test is conducted only when it’s absolutely necessary. Moreover, women may have to avoid breastfeeding for at least 24 hours if they are provided with a contrast dye, which can help create a clearer image during the scan.
MRI alone doesn’t help doctors give the correct diagnosis and doesn’t produce a complete picture of the concerns of the patient. Therefore, it’s undertaken along with other tests and consultations that involve interviews, review of the medical records, and physical examination.
How Does the Procedure Work?
The MRI scan is a big machine with a large opening on both ends. There’s a huge dome, where the head goes in during the procedure. Usually, there’s no preparation needed, and the patient may continue taking his medications or other treatments before the exam. Nevertheless, the doctor should be able to brief the patient on the dos and don’ts before the exam.
If a contrast medium has to be used, an IV line is placed on the patient’s arm, and it will be used to deliver the agent. It may take around an hour before the exam can begin to make sure that the agent is absorbed well by the body. All metallic objects such as jewelry should be removed from the body before the procedure.
The scanning room is divided into two sections. In the middle is the scanning device while there’s another room where the radiologist stays. In front are computer screens that receive the images picked up by the scan.
The patient wears a hospital gown or any loose-fitting clothing and lies down comfortably on the table that goes into the machine slowly. Once ready, the scan then moves around the body taking pictures of the head. The entire process may take around 20 to 45 minutes since MRI is generally slow. The patient may also hear some noise as it works.
The patient receives any instruction from the radiologist through an intercom. In the same manner, the patient can provide feedback or communicate concerns to the radiologist through the system. Once done, the patient can return to normal activities unless advised not to do so by the radiologist.
The scanned images with interpretations are then forwarded to the patient’s doctor. They may be available within a few days.
Possible Risks and Complications
In general, MRI of the head is a safe procedure, especially since it doesn’t expose the patient to any radiation that can potentially damage or alter the DNA. However, some people may develop a high level of anxiety especially if they are claustrophobic. If this happens, the patient may be administered a sedative to help calm the nerves.
Some patients may also be allergic to the contrast dye. Prior to the administration, the technician will first ask the patient if he’s allergic to the ingredients.
It’s necessary for patients to have a good kidney function if the scan requires a contrast dye. This is because the dye has to be expelled by the body properly after the procedure.
Broder J, Preston R. Imaging of the head and brain. In: Broder J, ed. Diagnostic Imaging for the Emergency Physician. Philadelphia, PA: Elsevier Saunders; 2011:chap 1.
Wilkinson ID, Graves MJ. Magnetic resonance imaging. In: Adam A, Dixon AK, Gillard JH, Schaefer-Prokop CM, eds. Grainger & Allison's Diagnostic Radiology: A Textbook of Medical Imaging. 6th ed. Philadelphia, PA: Elsevier Chuchill Livingstone; 2014:chap 5.