X-ray basics

Formation:

X-rays are formed in an X-ray tube when:

1. A high-energy electron (an accelerated electron) knocks and displaces an inner shell low-energy electron (from tungsten nuclei in the tube anode).
2. This causes an outer shell electron (from same tungsten nuclei) to take the place of the inner shell electron.
3. The resultant energy loss as a result of this electron's shift from the outer shell to the inner shell is in the form of the X-ray itself.

Principles:

• X-rays travel in straight lines
• Body parts further away from the detector are magnified compared with those that are closer
• Magnification can be helpful in localising abnormalities
• Relevance to AP, PA, Lateral etc. (Left Lateral means that the Left is closer to detector and is hence LESS magnified than the right)

Tissue densities:

• An X-ray image is a map of X-ray attenuation (greater attenuation = more blockage of the beam)
• Attenuation is variable depending on the density and thickness of tissues
• Descriptions can be done in terms of density
• Less dense = Darker
• More dense = Brighter
• In increasing density (Darker to Brighter)
• Air
• Fat
• Soft tissue
• Bone
• Metal

X-ray safety:

• X-rays are potentially harmful
• Requests for radiological examinations should be clinically justified
• The inverse square law
• The strength of the X-ray beam is inversely proportional to the square of the distance from the source
• Standing back double the distance will therefore quarter the dose of radiation