STEP WEDGE

Typical Number in Hospital: 1

Cost Bands: 1,2

References: 7

Sometimes known as a penetrometer or penetrameter, it consists of an aluminium block or laminate of several strips of aluminium forming a staircase. It is used to test X-ray sets (and film processors). It is placed on the film or cassette such that the increasing thickness of each step of the wedge causes different amounts of X-ray absorption so that the film is exposed to a different extent under each step of the wedge. The step wedge is placed over different portions of the film as X-rays of different kilovoltage (kV) and milliampere-seconds (mAs) are delivered. Any marked differences or irregularities in strip density indicate malfunction of the X-ray set or processor.

Special X-ray test cassettes exist which include copper step wedges and are used for calculations of the kVp of X-ray beams.

The print on the X-ray film created by exposure under a step wedge is also called a step wedge, even if created by a sensitometer, or simulated on a video screen.