QC for radiology equipment

reproducibility

The same technique setting should always create the same exposure rate at any time.

reproducibility tolerance

+/- 5%

-test annually

radiation output

• he specific amount of radiation emitted by x-ray generators per unit of x-ray tube current and time.

  • this is beam quantity

  • the different xray generators should be producing similar radiation

radiation output tolerance

• Maximum variability allowed is +/- 10%.

• Test annually.

filtration

• Necessary to remove low-energy photons from the x-ray beam.

• a pt’s skin dose can increase 90% if we don't remove the low energy photos

• Best method to determine if adequate filtration exists is to measure HVL

HVL half value layer

the amount of filtration needed to reduce the intensity of the beam by half

filtration tolerance

over 70kvp, total filtration is 2.5ml aluminum equivalent

-test annually

kvp accuracy

• Has a significant effect on image contrast, optical density, and patient dose.

• kVp stated on the control panel should produce an x-ray beam with a comparable and consistent energy.

• Wisconsin Test Cassette, Ardan and Crook’s Cassette, or a digital kVp meter.

kvp accuracy tolerance

• +/- 5% or +/- 4kvp

• test annually

timer accuracy

Exposure time directly affects the total quantity of radiation emitted.

-Digital x-ray timer (most accurate), or spinning top test.

timer accuracy tolerance

• +/- 5% for exposure times greater than 10ms.

• +/- 20% for exposure times less than 10 ms.

• test annually

half wave rectified

exposure time (s) X 60

full wave rectified

 exposure time (s) X 120

three phase and high frequency

 arc size ÷ 360

reciprocity

Refers to the same mAs being selected but with different combinations of mA and exposure time.

reciprocity tolerance

• Maximum variability allowed is +/- 10%.

• Test annually or semi annually

linearity

Sequential increased in mAs should produce the same sequential increase in the exposure.

when mAs doubles, exposure should double

linearity tolerance

• Maximum variability allowed is +/- 10%.

• Test annually.

Actual focal spot

Actual rectangular surface on the target where the electrons strike.

effective focal spot

• The projected focal spot.

• effects detail in image

• increase in effective focal spot decreases detail, decrease in effective increases detaik

focal spot blooming

An increase in focal spot size, usually as a result of an increase in mA.

- Increases with age, use, and use of ma stations

-ma stations cuz it increases amount of electrons

focal spot tolerance

• Maximum variability allowed for a focal spot size of:

  •  ≤  .8 mm is 50%

  •  .8 – 1.5 is 40%

  •  ≥ 1.6 is 30%

• Test annually.

tools to test focal spot size

pinhole camera, resolution charts, focal spot test tool