Exposure Variables and Image Characteristics

Flashcards covering X-ray attenuation, exposure variables, and image characteristics.

What is attenuation in the context of X-rays?

A measure of how easily a material can be penetrated by an X-ray beam

How are X-ray photons attenuated?

Absorbed, transmitted with lower energy, or scattered.

How does an increase in kV and tissue density affect attenuation?

Increases probability of PEA and Compton scatter, resulting in greater attenuation of X-ray photons.

How does an increase in X-ray photon energy affect attenuation?

Decreases the probability of PEA and increases probability of Compton scatter, resulting in a reduction of total attenuation

What are the two types of filtration?

Inherent and additional filtration

What is the effect of filtration on an X-ray beam?

Creates a more homogenous X-ray beam by attenuating lower energy photons

Name 3 ways filtration affects photons

• Creates lower energy photons

• Decreases the total number of photons

• Increases the average energy of photons

How does exposure time affect image quality?

Longer exposures increases the probability patient will move a create motion blur

What determines the amount of X-ray photons produced?

Current (mA) and exposure time (s)

How does a higher mAs affect image appearance?

Higher mAs means more x-ray photons are produced and therefore more can hit the detector, resulting in a darker image

Define radiolucent and radioopaque in the context of X-ray imaging.

Radiolucent refers to substances through which a large amount of the X-ray beam passes unobstructed, appearing darker (e.g., air, fat, soft tissue)

Define radioopaque in the context of X-ray imaging.

Radioopaque refers to substances that absorb or scatter X-ray photons, appearing white (e.g., bones).

What is the purpose of an Automatic Exposure Control (AEC) device?

An AEC device terminates exposure when a preset amount of radiation reaches the detector, achieving optimum exposure and reducing dose creep

What is Exposure Index in digital imaging?

A measure of the exposure by the image receptor providing feedback about the accuracy of the exposure utilised

List three factors that increase scatter radiation.

Field size, patient thickness, and higher kV.

How does increasing the Source to Image Distance (SID) affect magnification and patient dose?

Increasing the SID reduces magnification and patient dose.

How does increasing the thickness of area exposed affect image quality and patient dose?

Minimises dose and reduces scatter radiation which improves image quality

What are the benefits of limiting the size of the primary X-ray beam?

Less tissue is exposed, less scatter radiation is produced, image contrast is improved and the patient dose is lowered.

How does air gap technique reduce scatter radiation?

Scattered x-rays have low energy and are absorbed by air, not reaching the detector

How do grids improve image quality?

By absorbing scatter radiation and allowing primary X-rays to penetrate to the image receptor

What are the limitation of using grid?

Grid lines and cut-off can interfere with image formation

How can you resolve issues with grid lines?

Using an oscillating grid