X-ray
Introduction
An X-ray is a widely used diagnostic test to examine the inside of the body. X-rays are a very effective way of detecting problems with bones, such as fractures. They can also identify problems with soft tissue, such as pneumonia or breast cancer.
What are X-rays?
X-rays are a type of radiation. Radiation is a general term that refers to any sort of energy that can travel through space as either a wave or particle . Examples of other types of radiation include:
- light,
- radio waves, and
- microwaves.
X-rays are similar to light, except that they have a much higher frequency, which makes them invisible to the naked eye.
Due to their high frequency, X-rays can pass through the human body. This makes X-rays ideal for looking inside the body.
Safety
X-rays consist of a type of radiation known as ionising radiation. Ionising radiation is high-energy radiation. It can damage the cells of the body and cause mutations in the DNA (deoxyribonucleic acid), which can trigger cancer in later life. DNA is a type of acid that contains all human genetic material.
However, ionising radiation is only a threat to health when a person is exposed to a significantly high dose, such as after the disaster that occurred in the nuclear plant at Chernobyl in the former Soviet Union in 1986.
The doses that are used in medical X-rays are very low and are thought to be very safe. They are similar in strength to other sources of natural radiation that people are exposed to every day.
For example, brazil nuts contain a tiny trace of a radioactive substance called radium, so are slightly radioactive. The radiation that you are exposed to during a typical chest X-ray is the same dose that you would receive if you ate four bags of brazil nuts.
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What is it used for?
Examining bones
As bone is made out of calcium, which is a very hard and tough material, it shows up very clearly on X-rays. This makes X-rays very useful in diagnosing may different conditions and other problems related to bones, such as:
- fractures and breaks,
- problems with your teeth, such as tooth decay,
- osteoporosis (thinning and weakening of your bones),
- osteomyelitis (a bone infection),
- scoliosis (abnormal curvature of the spine), and
- cancers of the bone, such as osteosarcoma and Ewing’s sarcoma.
Examining the chest
Although major organs and blood vessels do not show up as clearly on X-rays as bones, they are visible. Therefore, chest X-rays are a good way of looking for changes or abnormalities in your heart, lungs and major arteries.
In particular, chest X-rays can be used to help diagnose:
- lung conditions, such as pneumonia, lung cancer and chronic obstructive pulmonary disease (COPD), and
- heart conditions, such as heart failure, congenital heart disease and pericarditis (inflammation of the lining of the heart).
X-rays and contrast fluids
X-rays are often used in combination with contrast fluids to produce a more detailed picture of certain organs and blood vessels.
Most contrast fluids are ‘radio-opaque’, which means they block the passageway of X-rays. When a contrast fluid coats the lining of organs and blood vessels, they show up clearly in white. Barium is a widely used contrast fluid.
The different ways that X-rays can be used in combination with contrast fluids are described below.
Barium swallow
A barium swallow is a procedure where you are given some barium solution to drink. Once the barium moves down into your upper digestive system, a series of X-rays is taken. The test is often used to diagnose problems with your upper digestive system, such as problems swallowing (dysphagia), or persistent symptoms of abdominal pain.
Barium enema
A barium enema involves having barium solution pumped through your anus (back passage) into your bowel. Barium enemas are used to diagnose bowel problems, such as persistent constipation and blood in your faeces (stools).
Angiogram
An angiogram is a detailed way of looking inside blood vessels to check for problems, such as blocked or narrowed vessels or weakness in the walls of a blood vessel (aneurysm). A small tube, called a catheter, is inserted into your groin and guided to the site of the vessel using X-ray.
Contrast fluid is then pumped through the catheter and a series of X-rays is taken to show how the fluid moves through the blood vessel. Studying the movement of the fluid through a blood vessel can often highlight problems, such as a blockage.
Intravenous urogram (IVU)
An intravenous urogram (IVU) is where a contrast fluid (usually an iodine solution) is injected into your veins, before it moves into your kidneys and bladder. X-rays are then taken of your kidneys and bladder. The procedure is often used to diagnose problems with your urinary system.
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How does it work?
Photon absorption
X-rays are similar to visible light, in that they are both waves of energy that are made up of tiny particles (photons). The difference is that the photons in X-rays have a higher energy level than those found in light (in other words, X-rays have a higher frequency and a lower wavelength than light).
Unlike light, which is absorbed by your skin, most of the photons in X-rays pass through your body due to their higher energy level. As they pass through your body, the photons are absorbed at different rates. This pattern of absorption shows up on the X-ray images. An X-ray image is produced in a similar way to how a shadow is cast, but X-rays are used rather than visible light.
Parts of your body that are made up of thick and dense material, such as your bones, absorb lots of photons, so show up as clear white areas on the X-rays. Other parts that are made of softer material, such as your lungs and heart, absorb only a small amount of photons, so show up as darker patches on the X-ray image.
The X-ray machine
An X-ray machine consists of:
- an X-ray tube,
- lead shielding, and
- a photographic plate.
The X-ray tube is like a giant light bulb that uses high-voltage electricity to generate the X-rays. The lead shielding is used to direct the X-rays towards a specific part of your body while preventing them from escaping in all directions. The photographic plate captures the image of the X-rays as they pass through your body.
In the past, the photographic plate used the same type of film as traditional cameras. Nowadays, the photographic plate in most X-ray machines is directly connected to a computer so that a digital image can be taken.
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How is it performed?
If you have an X-ray, you will be asked to lie on a table or stand against a surface so that the part of your body being X-rayed is between the X-ray tube and the photographic plate.
An X-ray is usually carried out by a radiographer, a healthcare professional who specialises in using imaging technology, such as X-rays and ultrasound scanners.
The part of your body being investigated is exposed to X-rays for a fraction of a second. As the X-rays hit the photographic plate, the plate captures a snapshot of the image, in a similar way that the photographic film in a camera captures a photograph. The image will usually be transferred to a computer where it can be studied on a screen and, if necessary, printed out.
During the procedure, you will need to keep still so the image is clear and not blurry. The X-ray is painless and you will not be able to see or feel it. More than one X-ray may be taken from different angles to give more information. For example, when examining the lungs, both the front and side of the body will be X-rayed.
A radiologist will study the image. A radiologist is a doctor who specialises in interpreting images of the body, such as X-rays and ultrasound scans. Depending on the reasons for your X-ray, the radiologist may discuss their findings with you on the day of your X-ray or they may send a report to your GP.
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Risks
Radiation
People are often concerned about being exposed to radiation during an X-ray. However, everyone is exposed to natural sources radiation throughout their life. Natural radiation is sometimes referred to as background radiation.
Sources of background radiation include:
- radon, a naturally occurring radioactive gas that is found in the UK,
- cosmic rays, a type of radiation that originates from space and is caused by sources of energy, such as the sun and other stars, and
- foods, many of which, such as nuts, bananas, red meat and potatoes, contain tiny traces of radiation.
The doses that are used in X-rays carry a theoretical risk of triggering cancer at a later date (as does your exposure to background radiation), but the risk is very low.
The Health Protection Agency (HPA) has calculated that:
- an X-ray of your chest, teeth, arms or feet is the equivalent to a few days' worth of background radiation and has a less than one in a million chance of causing cancer,
- an X-ray of your skull or neck is the equivalent to a few weeks' worth of background radiation and has 1 in 100,000 to 1,000,000 chance of causing cancer,
- an X-ray of your breasts (mammogram), hip, spine, abdomen or pelvis is the equivalent of a few months' to a year’s worth of background radiation and has a 1 in 10,000 to 100,000 chance of causing cancer, and
- an X-ray that uses a contrast fluid, such as a barium meal, is the equivalent of a few years' worth of background radiation and has a 1 in 1,000 to 10,000 chance of causing cancer.
It is important to put the risk of cancer in perspective as everyone has a one in three chance of developing cancer at some point.
X-rays and pregnancy
The doses of radiation that are used in X-rays are not thought to pose a risk to an unborn baby if used during pregnancy.
However, as a precaution, X-rays that directly target your womb, such as an X-ray of your abdomen, are not usually recommended unless there is a clear clinical need. Sometimes, an alternative method that does not involve radiation, such as an ultrasound scan, may be recommended instead.
Also as a precaution, you will usually be asked for the date of your last period before you have an X-ray. This is to check that there is no chance you could be pregnant.
If you have an X-ray and later discover you are pregnant, do not panic.
Even the most powerful types of X-rays, such as a barium enema, are not thought to adversely affect the outcome of pregnancy.
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