Basic principles of radiographic practice

Radiation

Energy that travels in high energy electromagnetic waves

ALARP

As Low As Reasonably Practicable

Three functions of ALARP

Identifying the risk vs benefit to the patient

Getting it right the first time

Optimising radiation dose

Production of x-ray imaging

Requires the right amount of x-ray beams with the right amount of energy

Kilovoltage peak

Amount of energy of the x-ray beam

Contrast

Affected by kVp because energy of the x-ray beams must be high enough

Milliampereseconds

Amount of x-ray photons in the x-ray beams

Density

Affected by mAs because the greater the amount of x-ray photons, the greater the density of the x-ray subject

Image noise

Scattered x-ray photons increasing the graininess of the image

Attenuation

When energy is lost due to obstacles

Source Image Distance (SID)

Instance from the x-ray tube to the imaging detector

110cm for most imaging

180cm for chest x-rays

Source Object Distance

The larger it is and closer it is to the detector, the less magnified the image

Grids and Bucky mechanism

Grids used between detector and patient to absorb scattered radiation and reduce image noise

Absorbs more primary radiation so requires a greater dose

Automatic Exposure Chambers

Used when radiation dose is uncertain

Used when a large area with different densities is being image

Radiation cuts out once detector has received a given density

Located between patient and detector

Light Beam Diaphragm

Cross light produced where the centering point is aimed

Collimation

Size of the field imaged

Three reasons for limiting collimation

Reduces radiation dose to patient

Improves image quality

Reduces scatter

Anatomical side markers

Mark which side of the body has been scanned

Allows for radiographer identification