Magnetic resonance imaging (MRI Scans) uses a large magnet and radio waves to look at organs and structures inside your body.
Magnetic Resonance Imaging (MRI) produces images of the body’s internal structures by passing radio waves through a powerful magnetic field. Differing frequencies of radio waves are produced by the different body structures, in return, and these are mapped and converted into digital images by a computer. MRI is especially good for imaging soft tissues in the body, including the brain, nerves, muscles and organs.
Visual Therapy
At Radiology Affiliates Imaging the ceilings of our CT and MRI suites resemble the skies of spring, transforming the rooms into spaces of natural beauty and freshness. This idea of nature imagery, also known as visual therapy, helps patients relax during imaging procedures. The minute patients enter the suite, they feel at ease, making them more relaxed and helping to eliminate anxiety.
The MRI scaner uses magnetic and radio waves to create pictures of tissues, organs and other structures within the body, which can then be viewed on a computer.
Unlike some other modes of medical imaging, there is no exposure to X-rays or any other damaging forms of radiation.
The pictures produced by an MRI scan, when compared to other imaging modalities, are much more detailed and therefore are of higher diagnostic quality when compared to more frequently used X-ray scans for example.
How does an MRI scan work?
The patient lies inside a large, cylinder-shaped magnet.
Radio waves 10,000 to 30,000 times stronger than the magnetic field of the earth are then sent through the body. This strong magnetic field causes the alignment of particles, called protons which are found naturally within the body, mostly in hydrogen atoms.
Hydrogen, together with oxygen and carbon, make up 99 per cent of the average human body, and therefore almost all the protons found within the body are affected by the strong magnetic field.
This allows detailed MRI images to be created Once the magnetic field is switched off, the protons begin to lose their alignment, and go back to the position they were in before the magnetic field was applied.
As they move back into their original positions, they send out radio waves of their own. The scan picks up these signals and a computer turns them into a picture. These pictures are based on the location and strength of the incoming signals.
Different protons send out different signals, depending on which tissue the proton can be found in. For example, a proton found in bone will emit a very different radio wave signal when compared to a proton found in blood.
It is these signal differences which allow a picture to be created, and allow different tissues or structures to be distinguished from one another.
What does an MRI scan show?
Using an MRI scan, it is possible to make pictures of almost all the tissue in the body.
The tissue that has the least hydrogen atoms (such as bones) turns out dark, while the tissue that has many hydrogen atoms (such as fatty tissue) looks much brighter.
By changing the timing of the radiowave pulses it is possible to gain information about the different types of tissues that are present.
An MRI of the brain and spinal cord can be done to look at a multitude of different abnormalities, as it can provide clear pictures of these structures even though they are surrounded by bone tissue.
Changes within the tissues of the brain, whether subtle or gross, can help with a diagnosis and so determine treatment.
For example, an MRI of the brain can be done to look for the changes associated with bleeding or when the brain has been starved of oxygen after a stroke.
It can be used to investigate a traumatic brain injury, and also help diagnose developmental abnormalities.
It can be used to characterise tumours (benign or malignant abnormal growths) and check their progression, for example if they have changed in size and whether there has been spread to nearby tissues.
Within the heart, an MRI scan can give very detailed imaging of the thickness and size of the chamber walls. Damage occurring to the heart tissue after a heart attack or in association with valvular disease can also be assessed.
Other structures, such as the large blood vessels within the surrounding tissue can also be examined, for example to check for the build up of plaques, which can predispose the patient to having a heart attack in the future.
Congenital cardiovascular conditions can more accurately be assessed with MRI, along with changes to the heart which have occurred as a consequence of these conditions.
MRI is the imaging modality of choice for assessing joint problems. This is because joints are typically made up of a number of very different tissues, for example muscle, bone and ligaments, and MRI is very effective at giving clear images of these individual tissues.
The method can also sometimes be used to image other parts of your body such as the liver, kidneys, spleen and breasts.
How does an MRI scan differ from a CT scan?
There’s no ionizing radiation (X-rays) involved in producing an MRI scan. MRI scans are generally more detailed, too.
This is because they are more capable of illustrating all soft tissues and higher density tissues, such as bone.
For this reason an MRI is preferred over a CT scan for imaging structures such as joints, the brain, and the spinal cord, where clearer and more anatomically detailed images are required. CT scans should therefore not be used if fine detail of soft tissues is needed.
The difference between normal and abnormal tissue is often clearer on the MRI scan than on the CT scan, because the anatomical differences between these types of tissues is seen more clearly.
It is also possible to differentiate cystic lesions from malignant tumours, to identify areas of infection and inflammation and for assessment of joint tendon tears.
MRI scans are also more costly than CT scans, and take longer to complete. The length of the MRI scan depends on the region of the body being imaged. MRI scans may be indicated in those patients who are not able to have a CT scan.
For example patients with surgical clips, metallic fragments, cardiac pacemarkers, and for female patients who are pregnant.
It is also possible to produce images in any plane without having to move the patient when using an MRI scan.
The scan is usually done as an outpatient procedure, which means that the patient can go home after the test. During the scan it is important to lie completely still. For this reason it might be necessary to give a child an anaesthetic before they are tested.
Since you are exposed to a powerful magnetic field during the MRI scan, it is important not to wear jewellery or any other metal objects.
An MRI scan is not suitable for the patient if they have electrical appliances, such an a ear implant, implantable cardioverter defibrillator or pacemaker, or have any metal in their body such as surgical clips.
But orthopaedic metal ware, such as artificial hips or bone screws, are not normally a problem.
Is an MRI scan dangerous?
There are no known dangers or side effects connected to an MRI scan. The test is not painful; you cannot feel it. Since radiation is not used, the procedure can be repeated without problems. There is a small theoretical risk to the foetus in the first 12 weeks of pregnancy, and therefore scans are not performed on pregnant women during this time.
Because patients have to lie inside a large cylinder while the scans are being made some people get claustrophobic during the test. Patients who are afraid this might happen should talk to the doctor beforehand, who may give them some medication to help them relax.
The machine also makes a banging noise while it is working, which might be unpleasant.
Health care professionals use MRI scans to diagnose a variety of conditions, from torn ligaments to tumors. MRIs are very useful for examining the brain and spinal cord.
During the scan, you lie on a table that slides inside a tunnel-shaped machine. Doing the scan can take a long time, and you must stay still. The scan is painless. The MRI machine makes a lot of noise. The technician may offer you earplugs.
Before you get a scan, tell your doctor if you
- Are pregnant
- Have pieces of metal in your body. You might have metal in your body if you have a shrapnel or bullet injury or if you are a welder
- Have electronic devices in your body, such as a cardiac pacemaker
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