Magnetic resonance imaging (MRI) is a type of scan that is often used to help diagnose health conditions that affect organs, tissue, and bone.
MRI scans use strong magnetic fields and radio waves to produce a detailed image of the inside of the body. The device that is used to carry out MRI scans is known as a MRI scanner. The scanner consists of a large tube that contains a series of powerful magnets. The patient lies inside the tube during the scan.
History
The scientific principles behind MRI were discovered in 1946, but it was not until the 1970s that the technology became available to make use of these principles.
At first, most MRI scanners were only available at large research centres. However, as the price of the scanners decreased, they started to become more widely available and now many NHS hospitals offer MRI facilities.
Safety
One of the main advantages of MRI is that, unlike X-rays, it does not involve exposing the body to radiation.
Extensive research has also been conducted into whether the magnetic and radio waves that are used in MRI could pose a risk to the human body. No evidence to confirm a risk has ever been found, making it one of the safest medical procedures currently available.
* show glossary terms
MRI
MRI stands for magnetic resonance imaging. It is the use of magnets and radio waves to take detailed pictures of the inside of the body.
Joints
Joints are the connection point between two bones that allow movement.
Bone marrow
Bone marrow is the soft, spongy tissue in the centre of bones that produces blood cells.
Blood vessels
Blood vessels are the tubes in which blood travels to and from parts of the body. The three main types of blood vessels are veins, arteries and capillaries.
Structures
Structure is the way something is put together and how its different parts relate to each other.
Brain
The brain controls thought, memory and emotion. It also sends messages to the body controlling movement, speech and senses.
Spine
The spine supports the skeleton, and surrounds and protects the delicate spinal cord and nerves. It is made up of 33 bones called the vertebrae.
Abdomen
The abdomen is the part of the body between the chest and the hips.
Last reviewed: 16/12/2009
Next review due: 16/12/2011
http://www.nhs.uk/conditions/MRI-scan/Pages/Introduction.aspx
Magnetic resonance imaging (MRI) can be used to look at almost all parts of the body, but it is most often used to study:
* the brain and spinal cord,
* the heart and blood vessels,
* other internal organs, such as the lungs or liver,
* bones and joints, and, in women
* breasts.
The brain and spinal cord
Due to the way that MRI works, a MRI scanner can provide very detailed images of your brain and spinal cord (the long bundle of nerves that runs from your brain down your spine).
MRI scans are often used to diagnose conditions that can affect the brain and nervous system such as:
* brain tumours,
* dementia,
* Alzheimer’s disease,
* stroke,
* Parkinson’s disease,
* multiple sclerosis,
* motor neurone disease,
* infections of the brain, such as meningitis, or encephalitis, and
* injuries to the brain and/or spinal cord.
The heart and blood vessels
MRI can be used to produce a detailed image of your heart. The image can often help to detect specific problems with the heart, such as defects with the valves or chambers.
MRI can also be used to assess whether a person’s heart has been significantly damaged after having a heart attack.
A type of MRI known as magnetic resonance angiography (MRA) can be used to study your blood vessels. MRA can help diagnose conditions that affect the blood vessels such as:
* aneurysms - a bulge in a blood vessel that is caused by a weakness in the blood vessel wall,
* atherosclerosis - hardening of the arteries, and
* narrowing of the veins (stenosis) that supply blood to important organs, such as the kidneys and lungs.
Internal organs
MRI is widely used to help diagnose cancers that affect specific organs, such as lung cancer and prostate cancer. A MRI scan is also a useful way of assessing whether a cancer has spread beyond a specific organ into near-by muscle or tissue.
MRI scans can also be used to diagnose other conditions that can affect the organs, such kidney disease.
Bones and joints
MRI scans are a very effective way of checking for damage or abnormalities to the soft tissue that is found in bones and joints such as:
* cartilage,
* tendons,
* muscles, and
* ligaments.
A MRI scan can be used to diagnose conditions that affect the bones and joints, such as arthritis and osteomyelitis (infection of the bones).
A MRI scan can also be used to assess damage to the cartilage, tendons, muscles and ligaments in cases of sports injuries, as well as other types of injuries that can damage a joint.
Breasts
MRI scans are now often used to help diagnose breast cancer. This is because they provide an effective method of checking to see how far the cancer has spread through the breast.
Functional MRI
Functional MRI is a new technique that is being used to study the workings of the brain. Rather than taking a single scan, functional MRI takes repeated scans, usually one a second, which are used to track the movement of blood through the brain.
By studying the movement of blood it is possible to tell which sections of the brain are particularly active in real time, and to see how brain activity responds to outside events and activities.
For example, a volunteer may be asked to solve a problem, or to remember a short phrase, and functional MRI will then be used to determine which parts of the brain are active during these tasks.
Functional MRI is still a relatively new technique, but it has been used by a number of specialists to help plan complex brain surgery.
http://www.nhs.uk/Conditions/MRI-scan/Pages/What-is-it-used-for.aspx
Preparing for the scan
On the day of your magnetic resonance imaging (MRI) scan, you should be able to eat and drink, and take any medication as usual.
The one exception to this is if you are having a MRI scan of your bile ducts, which is known as magnetic resonance cholangiopancreatography or MRCP. In this case, you will usually be asked not to eat or drink anything for 2-3 hours before the scan.
Due to the strong magnetic fields that are used by the MRI scanner, it is important to remove any metal objects from your body including:
* watches,
* jewellery, such as rings,
* piercings, such as ear, nipple, and nose rings,
* dentures (false teeth),
* hearing aids, and
* wigs (as some wigs contain traces of metal).
Depending on which part of your body is being scanned, you may need to wear a hospital gown during the procedure. Otherwise, you should wear clothing without metal zips, fasteners, buttons, belts, or buckles.
For some MRI scans, you will be given an injection of a special dye that is known as a contrast agent. This makes certain tissues and blood vessels show up more clearly and with greater detail on the scan.
As MRI scans are painless, anaesthetic is not usually required. If you are claustrophobic, you may want to request a mild sedative during the scan to help you to relax. If this is the case, you should inform the radiographer. Also, if you decide to be sedated, you will need to arrange for a friend or a family member to drive you home after the scan because you will be unable to drive for the first 24 hours (see ‘after the scan’ below).
A general anaesthetic is often used in cases where babies and young children are to be given a MRI scan. This is because it is important to stay very still during the scan, which babies and young children are often unable to do if they are awake.
During the scan
A MRI scanner is a short tunnel which is open at both ends. During the procedure, you lie on a motorised bed which is moved inside the scanner.
A small 'receiving device' is placed behind, or around, the part of your body that is being scanned. You are moved into the scanning tube, either head-first, or feet-first, depending on which part of your body is being scanned.
A computer is used to operate the MRI scanner, which is located in a different room to the scanner. This is because the computer has to be kept away from the magnetic field that is generated by the scanner.
As the radiographer operates the computer, they will also be in a separate room to you. However, you will be able to talk to them, usually by using an intercom, and they will be able to see you at all times on a television monitor.
During your scan you may be allowed to have a friend or family member stay in the room with you.
Children are usually able to have a parent with them. Anyone who stays in the scanner room with you will be asked the same questions as you about pacemakers and metal objects in their body, and will have to follow the same guidelines about clothing and removing metallic objects.
To avoid the images being blurred, it is very important that you keep the part of your body being scanned still throughout the procedure. Depending on the size of the area being scanned and how many 'pictures' are taken, a typical scan lasts between 15-90 minutes.
At certain times during the procedure, the MRI scanner will make a loud knocking noise. Therefore, you may be given earplugs or headphones to wear. The noise is caused by the magnets in the machine being turned on and off.
After your scan has been completed, you will be moved back out of the scanner.
After the scan
MRI scans are usually performed as an outpatient procedure, so there is no need for an overnight stay in hospital. Once the scan is over, most people can resume their normal activities immediately.
However, if you have been given a sedative, you will need to be accompanied home by a friend or relative, and someone should stay with you for the first 24 hours. It is not safe to drive, operate machinery, or drink alcohol for the first 24 hours after you have had a sedative.
If you have been given an injection of a contrast agent, it is a good idea to drink a lot of water for the following 24 hours to help flush the dye out of your body.
As your MRI scan will need to be studied by the radiologist, and possibly a number of other related specialists, it is unlikely that the results of your scan will be known immediately.
The radiologist will report their findings to the doctor who arranged the scan, who will discuss the results with you. Unless they are needed urgently, it usually takes a couple of weeks for the results of an MRI scan to come through
http://www.nhs.uk/Conditions/MRI-scan/Pages/How-is-it-performed.aspx
Advantages
The main advantages of magnetic resonance imaging (MRI) scans are that:
* they do not involve exposure to radiation, so they can be safely used in people who might be particularly vulnerable to the effects of radiation, such as pregnant women and babies,
* they are particularly useful for showing soft tissue structures, such as ligaments and cartilage, and organs such as the brain, heart, and eyes, and
* they can provide information about how the blood moves through certain organs and blood vessels, allowing problems with blood circulation, such as blockages, to be identified.
Disadvantages
The main disadvantages of magnetic resonance imaging (MRI) scans are listed below.
* MRI scanners are very expensive; a single scanner can cost over a million pounds. This means that the number of scanners that a Primary Care Trust (PCT) can afford to fund is limited. Therefore, if your condition is non-urgent, you may have to wait several months to have a MRI scan.
* The combination of being put in an enclosed space and the loud noises that are made by the magnets can make some people feel claustrophobic while they are having a MRI scan.
* MRI scanners can be affected by movement, making them unsuitable for investigating problems such as mouth tumours because coughing, or swallowing, can make the images that are produced less clear.
http://www.nhs.uk/Conditions/MRI-scan/Pages/Advantages.aspx
