MRI (magnetic resonance imaging) is a fairly new technique that has been used since the beginning of the 1980s. The MRI scan uses magnetic and radio waves, meaning that there is no exposure to X-rays or any other damaging forms of radiation.

How does an MRI scanner work?

The patient lies inside a large, cylinder-shaped magnet. Radio waves 10,000-30,000 times stronger than the magnetic field of the earth are then sent through the body. This affects the body's atoms, forcing the nuclei into a different position. As they move back into place they send out radio waves of their own. The scanner 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.

Our body consists mainly of water, and water contains hydrogen atoms. For this reason, the nucleus of the hydrogen atom is often used to create an MRI scan in the manner described above.

What does an MRI scan show?

Using an MRI scanner, 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 scan is also able to provide clear pictures of parts of the body that are surrounded by bone tissue, so the technique is useful when examining the brain and spinal cord.

Because the MRI scan gives very detailed pictures it is the best technique when it comes to finding tumours (benign or malignant abnormal growths) in the brain. If a tumour is present the scan can also be used to find out if it has spread into nearby brain tissue.

The technique also allows us to focus on other details in the brain. For example, it makes it possible to see the strands of abnormal tissue that occur if someone has multiple sclerosis and it is possible to see changes occurring when there is bleeding in the brain, or find out if the brain tissue has suffered lack of oxygen after a stroke.

The MRI scan is also able to show both the heart and the large blood vessels in the surrounding tissue. This makes it possible to detect heart defects that have been building up since birth, as well as changes in the thickness of the muscles around the heart following a heart attack. The method can also be used to examine the joints, spine and sometimes the soft parts of your body such as the liver, kidneys and spleen.

How does an MRI scan differ from a CT scan?

With an MRI scan it is possible to take pictures from almost every angle, whereas a CT scan only shows pictures horizontally. There is no ionizing radiation (X-rays) involved in producing an MRI scan. MRI scans are generally more detailed, too. The difference between normal and abnormal tissue is often clearer on the MRI scan than on the CT scan.

How is an MRI scan performed?

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. It is also important for the patient to inform medical staff if they use electrical appliances, such as a hearing aid or pacemaker, or have any metal in their body such as surgical clips, but orthopaedic metalware such as artificial hips or bone screws is 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.

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What is a CT scanner?

A CT (computerised tomography) scanner is a special kind of X-ray machine. Instead of sending out a single X-ray through your body as with ordinary X-rays, several beams are sent simultaneously from different angles.

How does a CT scanner work?

The X-rays from the beams are detected after they have passed through the body and their strength is measured. Beams that have passed through less dense tissue such as the lungs will be stronger, whereas beams that have passed through denser tissue such as bone will be weaker. A computer can use this information to work out the relative density of the tissues examined. Each set of measurements made by the scanner is, in effect, a cross-section through the body. The computer processes the results, displaying them as a two-dimensional picture shown on a monitor. The technique of CT scanning was developed by the British inventor Sir Godfrey Hounsfield, who was awarded the Nobel Prize for his work.

What are CT scans used for?

CT scans are far more detailed than ordinary X-rays. The information from the two-dimensional computer images can be reconstructed to produce three-dimensional images by some modern CT scanners. They can be used to produce virtual images that show what a surgeon would see during an operation. CT scans have already allowed doctors to inspect the inside of the body without having to operate or perform unpleasant examinations. CT scanning has also proven invaluable in pinpointing tumours and planning treatment with radiotherapy.

What is the CT scanner used for?

The CT scanner was originally designed to take pictures of the brain. Now it is much more advanced and is used for taking pictures of virtually any part of the body. The scanner is particularly good at testing for bleeding in the brain, for aneurysms (when the wall of an artery swells up), brain tumours and brain damage. It can also find tumours and abscesses throughout the body and is used to assess types of lung disease. In addition, the CT scanner is used to look at internal injuries such as a torn kidney, spleen or liver; or bony injury, particularly in the spine. CT scanning can also be used to guide biopsies and therapeutic pain procedures.

How is a CT scan prepared for?

If the patient is receiving an abdomen scan, for example, they will be asked not to eat for six hours before the test. They will be given a drink containing gastrografin, an aniseed flavoured X-ray dye, 45 minutes before the procedure. This makes the intestines easier to see on the pictures. Sometimes a liquid X-ray dye is injected into the veins during the test. This also makes it easier to see the organs, blood vessels or, for example, a tumour. The injection might be a little uncomfortable, and some people also experience a feeling of warmth in their arm.

How is a CT scan carried out?

The scanner looks like a large doughnut. During the scan the patient lies on a bed, with the body part under examination placed in the round tunnel or opening of the scanner. The bed then moves slowly backwards and forwards to allow the scanner to take pictures of the body, although it does not touch the patient. The length of the test depends on the number of pictures and the different angles taken.

Does a CT scan hurt?

The examination does not hurt but some people find it uncomfortable to lie in the tunnel. As there is little room inside the tunnel, people who suffer from severe claustrophobia sometimes have problems with CT scans. Let the doctors and radiographers know if this might be a problem. Other people get slightly nervous because of the whirring noise the machine makes while working.

Is a CT scan dangerous?

Far more X-rays are involved in a CT scan than in ordinary X-rays, so doctors do not recommend CT scans without a good medical reason. Some patients may experience side effects due to allergic reactions to the liquid dye injected into the veins. In very rare cases, this dye has been known to damage already weakened kidneys. It is important to let the X-ray doctors or technicians know if you have any allergies, asthma or kidney trouble, prior to having the X-ray dye injected.

How is a CT scan read?

A CT scan can give the doctor a much clearer picture of the inside of the body than an ordinary X-ray. For example, different types of tissue such as bone, muscle and fatty tissue are easy to see on a CT scan. When looking at the abdomen, the scan shows various organs such as the pancreas, spleen and liver. When it is necessary to look at the brain, the areas containing liquid - the ventricles - are also clearly defined. Very small shadows on the lungs can also be detected using CT and there are now studies looking into using it as a screening test for lung cancer.

X-rays

X-rays were first discovered in 1895 when, during experiments with electric currents passed through a vacuum tube, Wilhelm Conrad Röntgen noted that a nearby fluorescent screen glowed when the current was being passed. When the current was switched off the screen stopped glowing. He attributed this effect to previously unknown rays which, X being the symbol for an unknown quantity, he called X-rays.

We now know that these rays are, like light and radio waves, a form of electromagnetic radiation. X-rays have high energy and short wavelength and are able to pass through tissue. On their passage through the body, the denser tissues, such as the bones, will block more of the rays than will the less dense tissues, such as the lung.

A special type of photographic film is used to record X-ray pictures. The X-rays are converted into light and the more energy that has reached the recording system, the darker that region of the film will be. This is why the bones on an X-ray image appear whiter (less energy passes through) than the lungs (more energy passes through).

In the early days of X-rays, images, such as that of Mrs Röntgen's hand, were produced differently: the bones appeared dark rather than white.

Within two months of their discovery X-rays were being used both in Europe and North America, not just to take pictures of the internal organs of living people but also to treat a wide variety of diseases. The energy that does not pass through the body is deposited within it and it is this energy that causes the biological effects of radiation.

The machines used to take X-ray pictures produce X-rays with energies of around 120,000 electron volts. The X-rays used for cancer treatment are much more powerful, with energies of between 2 million and 20 million electron volts.

Staff involved in X-ray tests and treatment

A radiographer is a trained professional concerned with the operation of X-ray equipment and the care of patients during radiological examinations or X-ray treatment. Radiographers who operate equipment used for taking X-ray pictures are known as diagnostic radiographers: those who operate equipment used for treatment are known as therapy radiographers.

A radiologist is a qualified doctor who is concerned with interpreting X-ray pictures and performing certain types of investigation and treatment that rely on imaging techniques.

A radiotherapist (sometimes known as a clinical oncologist) is a doctor who specialises in the treatment of disease using X-rays and/or cell-killing medicines.

Cancer is the group of diseases most commonly treated in this way but radiation is sometimes used to treat benign diseases such as an overactive thyroid. In the UK both radiologists and radiotherapists usually belong to the Royal College of Radiologists (http://www.rcr.ac.uk/enquiries) which is responsible for setting examinations and maintaining professional standards.

X-ray tests

A simple X-ray image can be extremely informative. For example it can show whether or not a bone is broken or whether or not there is a shadow on the lung.

Special X-ray techniques can also be used to investigate other problems with the soft tissues of the body. By injecting special dye into arteries and/or veins the blood vessels can be made visible. By swallowing special dye the gullet and stomach can be examined. Similar dye can be introduced via an enema to examine the back passage and the rest of the large bowel.

CT scanning is a further development of the use of X-rays. By using a sophisticated scanner connected to a computer, it is possible to construct a series of pictures that look at the living body in cross-section.

What happens during an X-ray test?

The X-rays are produced by an electrical machine and the patient stands between the machine and a special screen used for obtaining the image. Patients are asked to remove any metal objects, such as watches and jewellery, that might appear on the picture and cause confusion.

The patient is asked to keep as still as possible for the few seconds it takes for each image to be obtained. The procedure is entirely painless and there are no side effects. The pictures are checked for technical quality by the radiographer and then sent off to the radiologist for reporting.

For more complex examinations this process may take a few hours so the official result of the test is not usually available immediately.

Is X-ray radiation dangerous?

It is one of the ironies of radiological practice that X-rays can both cause cancer and be used to treat it. Nowadays, with the use of very small doses of radiation to produce high quality X-ray images, the risk of cancer after properly supervised X-ray examinations is extremely small; so small as to be of no consequence to any individual.

Because staff in the X-ray department work with X-rays all the time they would, if they stayed beside every patient, over the course of time, be exposed to quite a high dose of radiation. This is why they go behind a screen when the X-ray beam is switched on. The cumulative effect would be significant for them in a way that it is not significant for an individual patient.

Radiation can cause damage to a foetus, which is why, as far as possible, the use of X-rays during pregnancy is kept to the absolute minimum. Any woman who suspects that she is pregnant, and who has been referred for an X-ray examination, should make sure that the radiographers and doctors caring for her know about her condition.

Paracetamol

This medicine contains the active ingredient paracetamol, which is a medicine used to relieve mild to moderate pain. It is also useful for reducing fever. It is not fully understood how paracetamol produces these effects.

Paracetamol can be used to relieve mild to moderate aches and pains associated with conditions such as headaches, migraine, toothache, teething, colds and flu. It is also useful for reducing fever and discomfort associated with colds and flu and following vaccinations.

The legal category of paracetamol ranges from prescription only, to pharmacy only, to general sales list (available from outlets such as supermarkets and garages) depending on the quantity and strength of paracetamol supplied in a container or packet.

What is it used for?

Fever (pyrexia)
Mild to moderate pain

Warning!

Alcohol increases the risk of liver damage that can occur if an overdose of paracetamol is taken. The hazards of paracetamol overdose are greater in persistant heavy drinkers and in people with alcoholic liver disease.
If symptoms persist for more than three days consult your doctor.
Do not take this medicine with any other paracetamol containing products.
An overdose of paracetamol is dangerous and capable of causing serious damage to the liver and kidneys. You should never exceed the dose stated in the information leaflet supplied with the medicine. Immediate medical advice should be sought in the event of an overdose with this medicine, even if you feel well, because of the risk of delayed, serious liver damage.
Some products containing paracetamol are not recommended for use in children under certain ages. Consult the package literature or information leaflet supplied with the product for further information.

Use with caution in

Decreased kidney function
Decreased liver function

Not to be used in

An inherited disorder of protein metabolism called phenylketonuria (Calpol Fast Melts only)
Known sensitivity or allergy to any ingredient

This medicine should not be used if you are allergic to one or any of its ingredients. Please inform your doctor or pharmacist if you have previously experienced such an allergy.

If you feel you have experienced an allergic reaction, stop using this medicine and inform your doctor or pharmacist immediately.

Pregnancy and Breastfeeding

Certain medicines should not be used during pregnancy or breastfeeding. However, other medicines may be safely used in pregnancy or breastfeeding providing the benefits to the mother outweigh the risks to the unborn baby.Always inform your doctor if you are pregnant or planning a pregnancy, before using any medicine.

There are no known harmful effects when this medicine is used during pregnancy.

• Small amounts of this medicine may pass into breast milk, however there are no known harmful effects when it is used by breastfeeding mothers.

Label warnings

Do not take this medication with any other products containing paracetamol.

• Refer to the printed instructions for maximum daily intake.

Side effects

Medicines and their possible side effects can affect individual people in different ways. The following are some of the side effects that are known to be associated with this medicine. Because a side effect is stated here, it does not mean that all people using this medicine will experience that or any side effect.

Blood disorders

• Skin rashes

The side effects listed above may not include all of the side effects reported by the drug's manufacturer.

For more information about any other possible risks associated with this medicine, please read the information provided with the medicine or consult your doctor or pharmacist.
 

How can this medicine affect other medicines?

You should avoid taking other medicines that contain paracetamol while taking this medicine, as this can easily result in exceeding the maximum recommended daily dose of paracetamol. Many cold and flu remedies and over-the-counter painkillers contain paracetamol so be sure to check the ingredients of any other medicines before taking them with this one.

Cholestyramine may reduce the absorption of paracetamol from the gut.

Metoclopramide and domperidone may increase the absorption of paracetamol from the gut.

Long-term or regular use of paracetamol may increase the anti-blood-clotting effect of warfarin and other anticoagulant medicines, leading to an increased risk of bleeding. Regular monitoring of blood clotting times should be performed if paracetamol is used regularly with these medicines. This effect does not occur with occasional pain-killing doses.

Non-steroidal anti-inflammatory drugs (NSAIDs)