Images produced using high-energy radiation; especially suitable for looking at bone and some soft tissues
X-rays have been used in imaging since they were discovered in 1895. Ordinary X-rays, called plain X-rays, are mainly used for imaging bones and certain soft tissues, such as the breasts. Structures that are hollow or fluid-filled, such as the digestive tract or blood vessels, do not show up well on ordinary X-rays and are more successfully imaged using contrast X-rays.
Ordinary X-rays are still commonly used in imaging, despite the development of more sophisticated techniques, such as CT scanning and MRI. This is because X-rays are inexpensive, quick, simple to perform, and usually provide the doctor with sufficient information to make a diagnosis.
How do they work?
X-rays are a form of radiation similar to light waves but with a higher energy. This high energy enables X-rays to pass through body tissues. The ability of X-rays to penetrate structures depends on the tissue’s density. X-rays easily penetrate soft tissues but pass less readily through dense tissue, such as bone.
X-rays blacken photographic film. If a single beam of X-rays is focused on to the body, the parts that allow X-rays through, such as air in the lungs, appear black on the film. Soft tissues, such as skin, fat, and muscle, appear as varying shades of grey. Dense substances, such as bone, are seen as white. As a result of these differences, the final image of the body created by the X-rays on the film looks like a photographic negative. Instead of photographic film, some modern X-ray machines use a special plate that detects the X-rays and converts them into a signal, which is then processed by computer into a digital image that is displayed on a monitor.
X-rays only create two-dimensional images, which means that occasionally two or more X-rays must be taken from different angles to pinpoint a condition. For example, to determine the position of a tumour in the lung, X-rays would be taken of the body from the front and from the side or at a slanting angle.
What are they used for?
Ordinary X-rays produce clear images of bone and are often used to look for fractures (see Having an X-ray). Chest X-rays may be performed to look for an enlarged heart or damaged lung tissue in a person with symptoms, such as chest pain, that may be due to heart or lung disease.
At lower doses, X-rays are useful for examining soft tissues, such as those of the breast, in detail, and they are widely used to screen for breast cancer (see Mammography). Bone densitometry uses low-dose X-rays to measure bone density. This technique is used to screen for and diagnose osteoporosis, a common condition in postmenopausal women.
What are the risks?
There are no immediate risks from having ordinary X-rays, but there is some risk that radiation may cause damage to body cells, possibly leading to cancer later in life. This risk increases if you are repeatedly exposed to X-ray radiation. The earlier in life you are exposed to radiation, the greater the risk. Radiographers always try to use the minimum amount of radiation when taking X-rays, and modern equipment makes it possible to produce good-quality images with lower doses of radiation than in the past.
During X-ray procedures, areas that are not being imaged may be shielded. For example, when X-raying the pelvis, special care is often taken to shield the reproductive organs to avoid damage to sperm or eggs. The amount of radiation used in ordinary X-rays is not thought to pose a risk to a fetus. However, women are asked if they may be pregnant before having an X-ray and, if so, X-rays that target the uterus are not usually recommended unless they are essential; in some cases, an alternative form of imaging that does not use radiation, such as ultrasound scanning, may be possible. Radiographers are always protected by a lead apron or screen to avoid repeated exposure to radiation.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.
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