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X-ray

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What is it?

X-rays are part of the electromagnetic spectrum, a range of low to high energies in waveform around us. Waves have peaks and troughs, and the wavelength is the distance between two peaks. The shorter the wavelength the more energy the wave has, and therefore the more it can penetrate the body. Most of the electromagnetic energy is at a wavelength which is beyond our senses, such as radio waves (104 cm), but we do make use of them. Visible light is an example of a wavelength (10-5 cm) of which we are aware, unlike X-rays, which at a wavelength of 10-8 cm are not detectable by our senses. While light energy can cause damage to the skin and eyes if given enough exposure, the higher energy of X-rays are potentially more dangerous.

How does it work?

X-rays can be generated in machines by using a very high voltage electric current to accelerate electrons to very high speeds inside a vacuum tube. The source of the electrons is usually a heated filament, not unlike the filament in an electric light bulb. These high velocity electrons are then directed at a target, which is often made of tungsten, and the target discharges X-rays in response to the electron bombardment. The X-rays are then directed at the body part under examination with as much precision as possible to reduce X-ray scatter to a minimum.

X-rays penetrate soft tissues with ease, but are blocked by harder tissues like bone, in the same way that an object blocks sunlight and therefore casts a shadow. The X-ray ‘shadows’ are captured on film. Different tissue densities allow different amounts of X-ray to pass through, creating a picture on the film of varying ‘shadows’ of the body’s interior. Air in the body allows X-rays to pass with no resistance and therefore appears black on the film (this is why lungs are dark in chest X-rays). Fat causes a dark grey shadow, whilst water is a lighter grey on the film. Bones show up as white areas on the film since this is the tissue through which least X-rays can pass.

What is it used for?

X-rays are used to form an image of the interior of the body, called a radiograph. They assist in the diagnosis of:

-Fractures, dislocations and joint erosions;

-Organ collapse (e.g. Lungs) or enlargement (e.g. The heart);-Solid tumour location;

-Gas distribution (e.g. digestive system).

With the introduction of a contrast medium (a substance that shows up well on X-ray films) into part of the body, X-rays can be used to demonstrate:

-Blood flow along an artery or vein;

-Organ function, e.g. the kidney (pyelogram);

-The patency of a tube or canal, e.g. the digestive tract (using barium), or a myelogram.

How is it done?

The patient is carefully positioned so the body part to be examined is lying on or against an X-ray film with the X-ray tube pointing at the chosen area and the film. Sometimes this involves the patient laying on a hard and somewhat uncomfortable X-ray table, and the nurse may be required to help with the positioning, and sometimes the maintenance of the patient in that position (see safety). The patient must remain stationary during the few seconds of the exposure otherwise, as in ordinary photography, the picture will be blurred. This need for the patient to remain still is emphasised in chest X-rays, where the patient must even hold their breath during the exposure. This requires patient co-operation, and difficulties may arise with confused people, small children or those mental health problems. In these circumstances, nurses may be required to assist the radiographer in the positioning and maintenance of the patient.

The X-ray film is developed and the patient may be required to wait in the department until this is done to check to see if a repeat film is necessary or not.

Measurements of X-ray radiation

X-ray exposures are measured using the term ‘rad’ (radiation-absorbed dose) or millirad (one thousandth of a rad). The Standard International (SI) equivalent of the rad is the Gray (Gy) - the unit for measuring the X-ray energy absorbed per unit mass of body tissue. One Gray is one joule of absorbed energy per kilogram of body tissue. This has to be estimated because different tissues absorb different amounts of X-ray. The term ‘effective dose’ is also used to indicate the dose averaged over the entire body. The unit sometimes used for measuring the effective dose is the millisievert (mSv). A single standard chest X-ray delivers a dose of about 0.1-0.17 mSv, which is about as much radiation as we all receive from natural sources (background radiation) in about 10 days. More extensive X-ray procedures increase this dosage many times.

Safety

X-ray radiation is cumulative and therefore repeated exposure to X-rays will continuously increase the risk of harm to the body. The risks include increased chance of cancers and genetic mutations, reduced bone marrow function, sterility (if ovary or testes are exposed) or damage to a developing fetus during pregnancy. The risk associated with a single uncomplicated X-ray film is minimal and not a reason for concern. There is a need, however, for all those involved to take precautions against unnecessary exposure.

Patients should:-Not demand an X-ray. This is a decision for the doctor who will balance the benefit of such an examination against the risk of radiation exposure. The doctor will take into account the need for the films and all recent previous X-ray exposures.

-Keep a record of all their previous X-rays, especially recent ones.

-Question the doctor to check if the X-ray is really necessary, and ask for information on any aspects that are not clear.

-Tell the doctor, nurse and radiographer if they are, or suspect they may be pregnant.

Nurses should:

-Ensure their own safety when assisting the patient during an X-ray examination by:

1.Leaving the room during X-ray exposures whenever possible;

2.Keep the time they are exposed to X-rays as short as possible;

3.Use protective lead shielding while inside the X-ray theatre if they cannot leave, by standing behind a lead screen or wearing a lead apron.

4.Nurses, and other staff working continually in the X-ray department should wear a safety dose exposure badge and have this monitored regularly.

Remember, gonads (ovaries and testes) are extremely vulnerable to radiation exposure, and excessive dosage may seriously alter ovarian or sperm production, with potential consequences on any future offspring.

Nursing considerations

For standard X-ray examinations there is little nursing preparation required. Many such X-rays are performed on outpatients who care for themselves. However, some points may need to be considered:

-Nurses may need to reduce anxiety in some patients, particularly in those who are very young or confused. Some may be anxious about the exposure to radiation, and need to be given as much information as possible about the test, and to be reassured that the benefits of having the test far out way the very small risk involved.

-Some physical preparation is sometimes required, especially for more extensive investigations involving contrast media.

-Simple, loose clothing is important to gain access to that part of the body under examination. This may mean a loose fitting gown for hospital patients. The patient may need a dressing gown and footwear for privacy and warmth while away from bed.

-If the investigation involves contrast medium, check to see if the patient has any allergies, particularly to iodine or seafood (which may indicate an iodine allergy). Report any allergies the patient has to the radiography staff.

-Some specialised X-ray investigations may require nothing by mouth for a few hours before the test, or a particular bowel preparation. Often, the radiography department will issue specific instructions when the appointment is made. Nurses should ensure these instructions are carried out for all hospital patients.

-Check that the patient has emptied the bladder before the test commences.

-Check to see if a female patient is, or could be pregnant. Exposure of the unborn fetus to X-rays can be damaging to the child.

-After the test, the patient should be returned to their normal activities if these have been disturbed, i.e. eating and drinking, as quickly as possible.

-Whilst most contrast medium allergies are instantaneous, nurses should be aware of possible longer-term reactions over the next few hours or days, and observe patients accordingly.

Future developments

-T-rays (terahertz rays) are another form of energy on the electromagnetic spectrum between microwaves and infrared. These can be used to form images rather like X-rays but are said to be sharper and clearer with less radiation risk.

-Mini X-ray machines are another development. Being much smaller they will be cheaper and therefore much more portable.

-The development of an aluminium lens could focus X-rays far more accurately, hitting only the exact spot required and reducing the risks to others from X-ray scatter.

Useful reading

Foss, M., Farine, T. (2000) Science in Nursing and Health Care. London: Prentice Hall.

Useful website

NASA: The Electromagnetic Spectrum. http://imagers.gsfc.nasa.gov/ems/xrays.html

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