Diagnostic X-Ray

The use of x-rays in medicine dates back to their discovery by Wilhelm Conrad Roentgen of Austria in 1895. Roentgen took the first known radiograph (an x-ray picture on film or paper) of his wife's hand in December 1895. Two months later, x-rays were found to be in use for medical imaging at Columbia University, in New York. Today, x-rays are the most commonly used tool in diagnostic medicine.

X-rays are produced in the tube of an x-ray machine when a source of electrons (the cathode, or filament) is placed in a high voltage-accelerating field and directed toward a high-density absorber (the anode, or target). In the process of electron absorption by the target, x-rays are emitted. The x-rays produced by this process are emitted in all directions, however, the tube housing prevents most of the radiation from escaping, except through a small window in one direction. In this manner, an x-ray machine can emit a beam of radiation toward the patient without needlessly exposing other persons present. Of course, in reality, some radiation reaches the persons involved in taking the picture, and precautions must be taken to prevent unnecessary exposure to workers.

Primary radiation (Figure 1) is the direct beam from an x-ray machine. This beam is limited to the region of interest on the patient by adjustment of movable shutters on the machine, a process called collimation.

Figure 1. Primary Radiation from an X-Ray Machine

Secondary radiation (Figure 2) is the x-ray radiation scattered from the patient and equipment. Secondary, or scatter, radiation is emitted in every direction from the patient and is not limited to a defined beam. For most workers in an x-ray room, or around a portable x-ray machine, scattered radiation from the patient is the main source of exposure.

Figure 2. Secondary Radiation

It is important to note that in the use of diagnostic x-ray equipment, radiation is produced only when the beam is on. No residual radiation is present after an exposure.

The dose from scattered radiation to workers at a distance of one meter (approximately three feet) from the patient is approximately 1000 times less than the patient dose. When many exposures to a large number of patients are taken, the dose to an individual worker can add up significantly. Several requirements have been implemented to reduce employee exposure:

• Shielding is required to enclose fixed (stationary) x-ray equipment. Lead shielding is added to the walls as appropriate to reduce exposure to surrounding areas. The control booth in an x-ray suite is also shielded.
• Personnel who are inside the x-ray room during an exposure are required to wear leaded aprons of at least 0.25 mm lead equivalent. The integrity of aprons is checked annually.
• Only personnel essential to patient care are allowed into the x-ray room during an exposure.
• A visible and audible indicator is required to alert personnel when the equipment is operating.
• In the use of portable x-ray equipment, personnel are to remain at least six feet from the patient and out of the direct beam.
• Personnel are not allowed to hold a patient during an exposure, except in emergencies. Personnel who are used in this capacity must not routinely perform this duty.

There are several different types of x-ray equipment in use in the hospital environment. It is important to recognize the function of each, since radiation protection methods must be appropriate for the individual machine.

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