ARRT Radiography key terms

A patient's voluntary agreement to a procedure after being told its purpose, risks, benefits, alternatives, and the consequences of refusing. It is obtained by the person who will actually perform the procedure.

Practices that lower the number of microorganisms and prevent their spread, such as hand hygiene, clean gloves, and disinfecting surfaces. It is used for every patient contact, not only invasive procedures.

Also called sterile technique: keeping objects and the immediate area completely free of microorganisms. It is required for invasive tasks such as urinary catheter insertion, wound care, or any procedure that breaks the skin.

A sudden reflex drop in heart rate and blood pressure that causes fainting. Common triggers are pain, anxiety, prolonged standing, or the sight of blood; the patient should be eased to the floor or a bed.

Leakage of injected contrast medium or fluid out of the vein and into the surrounding soft tissue. Signs include pain, swelling, and tightness at the site; the injection must be stopped right away.

A severe, rapid, whole-body allergic reaction marked by hives, swelling, wheezing, and falling blood pressure. It is a medical emergency requiring epinephrine and activation of the emergency response team.

Milliampere-seconds, the product of tube current and exposure time. It sets the number of x-ray photons produced, so it mainly controls how much radiation reaches the receptor and how much dose the patient receives.

Kilovoltage peak, the maximum voltage applied across the x-ray tube. It sets photon energy and beam penetration, so raising kVp increases penetration and scatter while lowering subject contrast.

The small area on the anode where x-rays are produced. A smaller focal spot sharpens recorded detail but limits the tube current that can safely be used.

X-ray intensity is lower on the anode side of the beam because photons are absorbed within the anode. The thicker part of the patient is therefore placed toward the cathode side of the tube.

Aluminum placed in the beam path that absorbs low-energy photons before they reach the patient. It lowers skin dose and raises average beam energy, a change described as beam hardening.

A plate of lead strips separated by spacer material, placed between the patient and the image receptor to absorb scattered radiation. It improves contrast but requires an increase in mAs.

Ionization chambers that measure radiation reaching the receptor and end the exposure once a preset amount is received. Correct chamber selection and accurate centering are needed or the exposure will be wrong.

The percentage of x-ray photons striking a detector that actually contribute to the image signal. A higher value means the system needs less radiation to produce a diagnostic image.

The distance from the focal spot to the image receptor. It affects magnification and receptor exposure, with beam intensity changing according to the inverse square law.

The gap between the part being imaged and the image receptor. A larger gap increases magnification and geometric blur, so it is kept as small as practical.

The ability of an imaging system to show two small objects that lie close together as separate. It is often measured in line pairs per millimeter and perceived as sharpness of detail.

The ability to distinguish tissues that differ only slightly in x-ray attenuation. Digital systems offer wide contrast resolution, which allows windowing to reveal subtle differences.

Graininess or speckle caused by too few x-ray photons reaching the receptor. It is reduced by increasing mAs and is a sign that the exposure was inadequate.

A number reported by a digital system that reflects how much radiation reached the receptor. Values outside the acceptable range mean the image is over- or underexposed and may need repeating.

A graph showing how many pixels carry each brightness value. In computed radiography, processing uses the histogram to set the display scale applied to the image.

Any mark or structure on an image that does not represent the patient's anatomy, such as a plate scratch, clothing snap, or grid error. Artifacts can hide disease or be mistaken for it.

Display controls on a digital image. Window width adjusts contrast and window level adjusts brightness; changing them alters how the image looks without changing the raw data.

The increase in apparent size of a structure on an image compared with its true size. It grows when object-to-image receptor distance increases or source-to-image receptor distance decreases, and it always reduces recorded detail.

The portion of the x-ray beam traveling along the middle of the collimated field and leaving the tube housing at its center. Positioning instructions specify where this ray should be aimed.

The standard reference posture: body upright, face forward, arms at the sides with palms forward, and legs together. Position terms such as supine and oblique are described relative to it.

Lying face up on the back. It is used for many abdomen, chest, and skull routines, and it changes how abdominal organs and gas sit compared with an upright view.

Lying supine with the head lower than the feet. It is used to move contrast material or air toward the upper body and is also used in some emergency situations.

A substance such as barium sulfate or an iodinated solution that attenuates x-rays more than soft tissue does, so it appears white. It is used to outline hollow structures.

A view taken with the body or body part rotated rather than straight front-to-back or side-to-side. It is described by which surface or angle faces the image receptor.

As Low As Reasonably Achievable: the principle of keeping radiation dose to patients and workers as low as practical while still obtaining the information needed for diagnosis.

A dose value in sieverts reflecting the overall cancer and genetic risk from a partial or whole-body exposure. Each tissue is weighted according to its sensitivity to radiation.

X-ray intensity decreases with the square of the distance from the source. Doubling the distance from the tube cuts the intensity to one quarter of its original value.

Limiting the x-ray field to the area of interest using shutters. Smaller fields reduce patient dose, improve contrast by reducing scatter, and are required by regulation.

A lead or lead-equivalent shield placed over the reproductive organs during an examination. It is used when the shield will not cover the area of clinical interest or interfere with the procedure.

A protective barrier designed to be struck by the useful x-ray beam, such as the wall behind the image receptor in a radiographic room. It must be thicker than a secondary barrier.

The annual limit for radiation workers, 50 mSv (5 rem) to the whole body in a year, with lower limits for the lens of the eye and extremities. It applies in addition to natural background exposure.