Unit 3: Grids Flashcards
Function of a grid
to absorb a large amount of scattered radiation before it reaches the IR
Transmission is responsible for:
dark areas
Absorption responsible for
light areas
The absorption of x-rays in the patient, occurs from?
Photoelectric Interaction
Scattered x-rays
Creat noise
Lower image contrast and overall quality
Image forming x-rays
- photons that reach IR
- transmission
- compton scatter
Scatter definition
X rays in the primary beam that interact within the patient which cause them to change direction and lose energy.
Each time an xray photon scatteres, what happens to its energy?
Decreases
Are scattered x-rays in the primary beam?
No
X-rays only scatter when:
they interact w/ the pt or other matter
Primary beam is made up of:
Brems
Characteristic
Stem (off focus)
(no scattered xrays)
Off focus radiation
Radiation that escapes the collimators (this will image things not w/in the collimated field)
When do x-rays scatter
When interacting w/ tissues in the pt., compton interactions, and some from classical interactions
Scattered x rays reaching the IR are produced almost entirely from
Compton Interactions
Things that increase the intensity (quantity) of scattered radiation
- Higher kVp techniques create more scatter. (bigger beam = higher energy = more forward scatter)
- Thicker body parts create more scatter.
- Increasing field size (decreasing collimation) creates more scatter.
- Higher tissue density body parts create more scatter.
- Water rich tissues produce a greater amount of scatter.
What is tissue (mass) density?
the number of atoms in a specific volume of tissue.
“ how tightly packed” atoms are in certain tissues.
tissue (mass) density
Compton Scatter is just as likely to occur in an atom soft tissue and bone.
The increased presence of water in soft tissue makes it just as likely that scatter will occur in bone and soft tissue, despite the density of bone vs. soft tissue.
a muscular, or obese, or hypersthenic body build creates ____ scattered radiation compared to a hyposthenic, asthenic, or emaciated body build, with all other factors remaining constant.
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