Magnetic resonance imaging, most commonly shortened to "MRI", is a type of radiology imaging scan that is used in medicine to help with the identification and diagnosis of various diseases.
Table of Contents
- How do MRI machines work?
- Which conditions can MRIs be used to diagnose?
- What happens during an MRI?
- Are there any side effects when getting an MRI?
- Differences between MRIs and CT Scans
- What are the limitations to diagnoses via MRI?
How do MRI machines work?
MRIs are one of the most common types of scans used across the world in hospitals and private healthcare facilities. This is because they offer higher resolution imaging output than most other diagnostic imaging tests.
An MRI machine is a large scanner that looks like a long tube, inside which the patient is transferred during the scan. It uses radio waves and computer technology to produce detailed images of the inside of the body.
The radio waves create a temporary magnetic field around the patient’s body which interacts with the water inside their organs and tissues. This produces signals that are detected by receivers and fed to a computer.
The computer pieces the cross-sections together into an image, and your radiologist will interpret its results for you.
Which conditions can MRIs diagnose?
MRI scans can be used to examine any area of the body.
Most commonly, MRIs are used to assess the following areas of the body:
- Brain and spinal cord
- Bones and joints
- Heart and blood vessels
- Internal organs
- Multiple sclerosis
- Internal organs, such as the liver, kidneys, pancreas, and adrenal glands
- Lymph nodes
- Bowel conditions, such as inflammatory bowel disease (Crohn's disease and ulcerative colitis)
- Growing fetus in a pregnant woman
What happens during an MRI?
At the start of the procedure, the patient is placed on the MRI table. Most enter the MRI tube on the movable table.
During the MRI scan, the radio waves interact with the water inside the patient’s body, producing the image that will then be interpreted by the team of radiographers.
The whole procedure can take anywhere from 15 minutes to an hour and a half. In some cases, a contrast agent, such as gadolinium, is injected into the patient’s veins to enhance the resulting images.
There are no moving parts inside an MRI scanner. However, the machine may make some thumping or tapping noises as it scans the patient’s body. Patients may be given earphones to wear during the procedure so they can listen to relaxing music.
Radiographers may also perform a functional MRI (fMRI), during which the patient will be asked to perform different tasks. For example, patients may be asked to move specific fingers or pinch their thumb and forefinger together. This enables healthcare professionals to view which areas of the brain or activated upon certain movements.
Patients are asked to wear loose clothing or a hospital gown. They may also be advised on what to eat and drink before the procedure, depending on the type of MRI and their unique situation.
Jewelry, piercings, and other metal items are removed from the patient to prevent them from interfering with the magnetic field. If a patient has metal orthopedic implants, there is no extra risk but it’s important that the radiographer is aware of this.
Are there any side effects when getting an MRI?
MRIs are a low-risk procedure!
However, MRI machines use powerful magnets that may interact with metal. If a patient has metal devices or implants inside their body, there is an increased risk. The radio waves used by the MRI machine can get distorted by the metal.
Before the patient enters the MRI, the radiographer will check that they have no implants of concern. If the patient has a significant amount of metal inside their body, they may be offered an alternative type of scan.
MRI scans are generally safe unless the following is present:
- Metallic orthopedic implants
- Metal screws, plates, or stents
- Metal clips that are often used in brain aneurysm treatment
- Artificial heart valves and metal coils
- Heart defibrillators
- Vagal nerve stimulators
- Cochlear implants
- Intrauterine devices
If the patient has a lot of dark tattoos, the radiographer will assess whether or not MRI scanning is appropriate. Some dark inks that are used for tattoos can contain metals.
For women who are pregnant, they must inform the healthcare professional prior to the scan. There is currently very little evidence regarding the effects of magnetic fields on fetal development, so the doctor or radiographer may offer an alternative type of examination to assess the patient.
There is a small risk of allergic reactions if a contrast agent is used. In patients who have kidney disease or chronic kidney failure (CKD), contrast injections may not be appropriate. Although agents like gadolinium are not known to cause significant side effects, studies show that some of it may remain in the brain after the procedure.
Differences between MRIs and CT Scans
Unlike computed tomography scanning, or 'CT scans' for short, MRI machines do not use ionizing radiation to produce an image. This makes them slightly safer than CT scans or x-ray scans that do expose the body to potentially harmful radiation.
What are the limitations of an MRI?
MRI scans can be used by healthcare professionals to identify and diagnose a wide range of different diseases. They have the capability of producing high-quality, clear images that can be easily interpreted.
However, as with any other medical diagnostic tool, MRI comes with its limitations.
For a high-quality image to be produced, the patient must remain very still inside the MRI machine (unless a functional MRI is being performed where the patient needs to move certain parts of their body). Most patients find it difficult to remain still for the whole scan, which can affect the quality of the image that is produced.
MRIs, however, are not appropriate for everybody. Those who have previously had surgical implants that are made of metal may not be able to enter the MRI machine due to the metal inside their bodies. Patients who are claustrophobic may panic inside the tube of the MRI machine, and would not be good candidates to receive one.
The image that is produced during MRI can easily be distorted by a number of factors, including:
- The presence of metal
- Bowel contractions
If you've been recommended to have an MRI, have no fear. While it requires patience and calm, it is otherwise a relatively easy procedure that can produce life-saving images of what's going on inside of you!
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