Ch 15 & Tube/Target Interactions Flashcards
What factors contribute to Compton scatter
KVp
Volume of irradiated material (part size)
What is occupational dose
Compton scatter
What does increased kVp do to pt interactions
Less photoelectric absorption
More scatter
Less dose
As long as it goes with decreased MAs
How does increased kVp effect image quality
Lower amount of contrast
What does decreased kVp do to pt interaction
More photoelectric absorption
More dose
Less scatter
How does decreased kVp effect Pt dose
Increased photoelectric absorption meaning Increased dose
Decreased kVp effect on image quality
Higher image contrast
Increased field size increases the volume of tissue irradiated, what also does this increase
Scatter
Decreased field size decrease beam quantity which also
Decreases scatter
Decreases amount of remnant radiation hitting the receptor
What is quantum mottle
IR does not receive the correct amount of exposure & causes a greying/grainy effect
What do you increase if you decrease the field size to maintain image quality
Mas
More photons make the image look less grainy
Is barium/contrast dense or not dense
Dense
Atomic number 74
Tungsten
Atomic number 56
Barium
Atomic number 20
Bone
What does beam restriction do for the pt and workers
Decrease scatter
Increase detail
Decrease dose
Decrease scale of contrast
What are the types of beam restrictors
Collimator
Aperture diaphragm
Cones
Cylinders
What’s the most common beam restrictor
Collimator
How many sets of shutters do the Collimator have
Two
What type of collimation does the Collimator allow
Rectilinear collimation
What do the bottom shutters reduce
Penumbra
What is penumbra
Geometric unsharpness
What does the upper shutters reduce
Off focus radiation
What is off focus radiation
Image shadows - ghosting
What percent of accuracy does the light field need to be within
+/- 2% of SID
What is PBL
Positive beam limitation
What does PBL do
Automatically collimate the light field to the size of the IR - you can reduce the light field still but not increase it bigger than IR
What does scatter create on the IR
Fog
What does a grid do
Cleans up scatter - soft photons
How are the shutters in the Collimator positioned
At right angles of each other. That shutter in opposing directions
Example of Lead blocker
Shield
When xray photons interact with matter and lose energy through those interactions, it is called
Attenuation
Scattered photons that are deflected back towards the X-ray source is called
Back scatter
What can coherent scatter also be called
Classical scatter
Thompson scatter
Unmodified scatter
What is coherent scatter
Very low energy xray (10kev or lower) - non diagnostic
The atom is excited and releases energy by producing a secondary photon equal to the incident photon - just moving in a different direction.
What is photoelectric absorption
Patient dose
Xray photon interacts with inner shell electron & ejects it, which gets absorbed by the pt. The atom is now ionized & a photoelectron is produced.
What is Compton scattering
Occupational dose - AKA Compton effect
Incident photon interacts & removes a loosely bound outer electron, loses 1/3 its energy & proceeds in a new direction as a scattered photon. It can continue to interact with more matter or exit the body
What is pair production
Does not occur in diagnostic xray
Very high energy photons (1.02 MeV or higher) gets close to the nucleus causing it to lose all of its energy. The result is production of a negatron & positron
What is photo-disintegration
Does not occur in diagnostic xray
Extremely high energy photons (10 MeV or higher)
Photon strikes the nucleus & energy is absorbed, the nucleus gets excited & emits a nuclear particle
Will increased kVp increase scatter or decrease scatter
Increase - more power behind the photons, the more chance it will act as a pin ball & go in all directions
When will photoelectric absorption happen
When lower kVp is used
When contrast agents are used
Low kVp does what to contrast
High contrast
High kVp does what to contrast
Decreased contrast
