Part 3: Conducting the fluoro exam Flashcards
Operator radiation dose to scattered radiation is (directly/indirectly) proportional to the pt radiation dose
directly
Image brightness is directly proportional to ____
the radiation dose rate at the input phosphor
6 factors DIRECTLY influencing pt and operator dose
- mA
- kVp
- collimation
- filtration
- exposure time
- target-panel distance
3 factors INDIRECTLY influencing pt and operator dose
- lighting in the fluoro room
- poor image receptor quality
- low absorption tabletop
What is the measurement of the quantity of x-ray?
mA
mA setting for fluoroscopy is usually ___ and for cassette spot films it’s ___.
<5
> 100
Why does collimation improve image quality (and is safer)?
It reduces the scatter radiation reaching the output phosphor of the image intensifier
What happens to brightness when exposure field is enlarged?
nothing
What determines the penetrating ability of x-rays and refers to the quality of the x-rays?
kVp
___: QUANTITY of x-rays
___: QUALITY of x-rays
mA
kVp
Why does higher kVp result in reduced pt dose?
Because higher QUALITY (kVp) of x-rays means lower QUANTITY (mA) is required.
kVp technically increases what pt dose?
internal organ dose
The fluoroscopic x-ray beam collimation must be adjusted so that _____ is visible on the screen/input phosphor of image intensifier when the screen is positioned ____ inches above the tabletop and the collimators are fully open.
an unexposed border
14”
Relationship between dose rate at input phosphor and x-ray beam size
dose rate is almost independent of beam size
Radiation dose rate is “almost independent” of the x-ray beam size. What does this result in?
image won’t be brighter with larger beam size
total volume of the patient that’s exposed to radiation increases
image quality is improves with smaller x-ray beam
If exposure area is doubled by opening the collimator, the ___ will double also.
total pt integral dose
What is an integral dose?
the total energy absorbed by the pt from the beam
The integral dose to a mass of tissue is the product of ___ and ___.
the mass of tissue x the dose it receives
Integral dose unit
gram rad
(1 gm rad = 100 ergs)
What is the main purpose of a filter?
To reduce the number/amount of low-energy/long wavelength x-rays from reaching the pt
WHY is the goal of filtration to reduce the number of low-energy/long wavelength x-rays from reaching the pt?
They contribute nothing to the diagnostic image because they are not able to completely penetrate the pt to reach the image intensifier.
How many mm aluminum should be used to filter out the x-ray beam’s low-energy waves?
2.5 mm
What type of filter:
Includes the x-ray tube and its housing such as the glass envelope through which the x-ray beam passes.
Inherent filter
What type of filter?
Includes sheets of metal (usually aluminum) placed in the direct path of the x-ray beam.
Added filter
The ___ is characterized by Half Value Layer (HVL).
quality of x-rays
Definition of the HVL
the thickness of absorbing material necessary to reduce the x-ray intensity to half its original value
Fluoro equipment manufactured after 1974 and IS equipped with automatic exposure rate controls which does not allow the fluoro to be operable at any combination of tube potential and current which would result in an exposure rate in excess of ___ except during image recording or a boost.
If not equipped with auto exposure rate control, it won’t exceed ___.
10 rad/min
5 rad/min
How often must devices with ABC be monitored?
each week
Which is better: photopic visual acuity or scotopic?
photopic by about 10x
For image intensified fluoroscopy, room lighting must be ___.
dim
Where are cones vs rods located within the eye?
Cones are central, rods on the periphery
Gonad shields can’t be less than ___ mm lad equivalent.
0.5mm
Which type of gonad shield is best for fluoroscopy?
A shaped contact gonad shield
Bucky slot cover must be at least ___mm lead equivalent.
0.25mm
