Abnormalities that can be diagnosed using X-rays

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Wednesday February 16, 2011

By DR MILTON LUM

Most X-ray photons pass through the body and are absorbed by the body parts at different rates during their passage. This absorption pattern is shown as images on the X-ray film.

RADIATION is a term used to describe energy that traverses space as a wave or particle. They include light, radio waves, microwaves, and X-rays, which is an abbreviation for x-radiation.

There are various sources of natural radiation (sometimes termed background radiation) that humans are exposed to throughout their lives. They include cosmic rays, which is radiation from space, e.g. the sun and some common foods.

X-rays are similar to light but have a higher frequency, making them invisible. They have longer wavelengths than gamma rays and shorter wavelengths than ultra-violet rays. X-rays have different wavelengths that impact on their ability to penetrate solid objects. “Soft” X-rays do not penetrate matter, but “hard” X-rays do. The latter can pass through the human body, making it possible to take images of the inside of the body as well as other solid objects in industry.

Telling images: Abnormalities that can be diagnosed from a chest X-ray include heart conditions like heart failure, an enlarged heart (cardiomegaly) and congenital heart diseases, and lung conditions like infection (pneumonia), tuberculosis, chronic obstructive airway disease and lung cancer.

The discovery of X-rays is attributed to Wilhelm Roentgen, a German physicist, who published a paper on the ability of X-rays to identify bone structure. The use of X-rays in diagnostic medical imaging followed within a month of his publication. Roentgen gave X-rays their name, but they are still called “Roentgen rays” today in some countries, including Germany.

How it works

X-rays, like visible light, comprise of tiny particles called photons. The X-ray photons, which are energy waves, have a higher energy level than light, i.e. a higher frequency and shorter wavelength.

The majority of X-ray photons pass through the body and are absorbed by the body parts at different rates during their passage. This absorption pattern is shown as images on the X-ray film.

Bone, which is thick and dense, absorbs a large amount of photons, and appears as white on the X-ray film. Softer body structures, e.g. heart and lungs, which absorb a smaller amount of photons, appear darker on the X-ray film.

The X-rays are produced by a machine which comprises an X-ray tube, lead shielding and a photographic plate. The X-ray tube produces X-rays with high voltage electricity. The lead shielding directs the X-rays towards a specific body structure and prevents the X-rays from indiscriminate spread at the same time. The photographic plate takes images of the X-rays during its passage through the body.

Until recently, the photographic plate produced films just like film cameras do. However, the photographic plates in X-ray machines in many healthcare facilities today are connected to a computer, thereby producing digital images.

How it is done

When an X-ray is taken, the patient will be asked by a radiographer — a healthcare professional who has been trained in the use of imaging, to lie on a table or stand against a firm and even surface. This ensures that the body structure being examined lies between the X-ray tube and the photographic plate.

X-rays are produced by the machine for a fraction of a second. The X-rays pass through the body structure being examined to reach the photographic plate producing image(s), just like the film in a camera produces a photograph.

The patient has to be still when an X-ray examination is being done to ensure that the images formed are clear and not blurred, as the latter would pose difficulties in interpretation. One or more X-ray films may be taken depending on the request made by the attending doctor, e.g. lung examination usually involves X-rays from front to back and from the side.

The X-ray images are either printed out immediately or transferred to a computer from which it can be reviewed and then, the relevant films printed. The review is usually done by a radiologist in most hospitals. However, plain X-rays of long bones and the chest are reviewed by general practitioners or medical officers in hospitals.

X-ray examinations are usually painless.

Myriad uses

There are several uses of X-rays in assisting doctors to make or confirm a diagnosis.

A common use is a chest X-ray, which is useful in the diagnosis of conditions affecting the heart, lungs and major blood vessels. The heart and lungs appear grey or dark in the film. Abnormalities that can be diagnosed from a chest X-ray include heart conditions like heart failure, an enlarged heart (cardiomegaly) and congenital heart disease, and lung conditions like infection (pneumonia), tuberculosis, chronic obstructive airway disease and lung cancer.

Another common use is the examination of bones. The calcium in the bone appears white in the film(s). Many conditions affecting the bones of the body can be diagnosed, e.g. broken bones (fractures), loss of bone resulting in its thinning (osteoporosis), infections of the bone (osteomyelitis), abnormal curvatures of the spine from side to side (scoliosis) or back to front (kyphosis), bone cancers, and tooth decay.

X-rays are often used with substances called “contrast media” to examine in detail certain organs and blood vessels. The media are radio-opaque, i.e. they block the passage of X-rays though the body structure being examined and appear white on the films.

There are various examinations in which X-rays are used with contrast media. Some examples are described below.

A barium enema assists in the diagnosis of conditions affecting the lower intestinal tract, e.g. polyps, cancers, diverticula. It involves emptying the bowels and the pumping of a solution of barium into the lower intestinal tract via the anus, followed by the taking of a series of X-ray films.

A barium swallow assists in the diagnosis of conditions affecting the upper digestive tract, e.g. polyps, cancers, diverticula. It involves drinking a barium solution followed by the taking of a series of X-ray films.

An intravenous pyelogram (IVP) assists in the diagnosis of conditions affecting the urinary tract, e.g. cysts, blockage by stones within the tract or other abdominal or pelvic organs outside the tract, and cancers. After the bowels have been emptied, a contrast medium containing an iodine solution is injected into the veins. It travels to the kidneys through the blood stream, passes down the ureters to the bladder and is excreted from the body through the urethra.

As the iodine is radio-opaque, the whole urinary tract can be visualised through the series of X-ray films taken.

An angiogram assists in the diagnosis of conditions affecting the blood vessels, e.g. blockage, narrowing, and weakness of the vessel wall (aneurysm). A coronary angiogram involves the insertion of a small tube called a catheter into a blood vessel in the groin or arm. The catheter is then guided to the heart vessels under X-ray control. A contrast fluid is then injected into the catheter and a series of X-rays taken. The films will provide information about the movement of the contrast fluid through the blood vessels of the heart.

Similar examinations can be made of the blood vessels supplying the head, e.g. carotid angiogram.

A venogram involves injecting contrast fluid into veins to assist in the diagnosis of conditions affecting the veins, e.g. dilated (varicose) veins or blocked ones (thrombosis).

There are more sophisticated uses of X-rays like CT scans which will be described in a subsequent article.

Risks

It is not uncommon for a patient to be concerned about the health risks of X-rays. One should remember that everyone is exposed to background radiation throughout our lives, e.g. rays from the sun and common foods like nuts, bananas and potatoes.

There is a theoretical long term risk of the development of cancer, just as there is a similar risk from exposure to background radiation. Such a risk is, however, very low.

The estimates from Britain’s Health Protection Agency provide perspective, that is:

> An X-ray of the chest, teeth, arms or feet is equivalent to a few days of exposure to background radiation with a less than one in a million chance of causing cancer.

> An X-ray of the skull or neck is equivalent to a few weeks of exposure to background radiation with a 1 in 100,000 to 1,000,000 chance of causing cancer.

> An X-ray of the breasts (mammogram), hip, spine, abdomen or pelvis is equivalent to a few months to a year of exposure to background radiation with a 1 in 10,000 to 100,000 chance of causing cancer.

> An X-ray with contrast media is equivalent to a few years exposure to background radiation with a 1 in 1,000 to 10,000 chance of causing cancer.

It has also been estimated that everyone has a one in three to five chance of developing cancer during one’s lifetime.

Another common concern is the use of X-rays in pregnancy. Scientists believe that the amount of radiation used in X-rays do not harm the developing foetus.

It is, however, precautionary not to take X-rays directed at the uterus unless there is a well-founded medical reason for doing so. Ultrasound is a useful alternative diagnostic tool.

Panic buttons need not be pressed if an X-ray is inadvertently taken in early pregnancy as X-rays with contrast media have not been reported to have an adverse effect on pregnancy outcome.

Nevertheless, it must be emphasised that X-rays should only be taken for genuine medical reasons.

Category: Milton's Corner
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