Ch. 15 Beam Restriction (Exp II) Flashcards
Scatter radiation in radiography is produced during…
Compton interactions
Scattered photons will…
- Impair image quality
- Add density to image receptor exposure
- Not be considered part of the useful beam
A radiographer can best reduce the amount of scatter radiation from reaching the receptor by…
- Collimating
- Beam restriction
- Utilizing a grid
What can be placed between the patient and the image receptor to absorb scatter radiation?
Radiographic grid
A key factor that affects the amount of scatter produced is…
Kilovoltage
A factor that affects the amount of scatter produced is…
The irradiated material
As the kilovoltage increases, the percentage of x-rays that undergo _____ interactions will increase.
Compton
As the kilovoltage increases, the percentage of photons that undergo a ____ interaction will decrease.
Photoelectric
As more photons pass through the irradiated material unaffected, the resulting image receptor exposure has…
Greater radiographic image density
When more photons are absorbed photoelectrically, the resulting radiograph has…
Less radiographic image density
As the volume of irradiated tissue ____, the amount of scatter produced _____.
Increases; increases
The volume of the irradiated tissue increases as…
Field size and patient thickness increase.
The _____ the atomic number o the irradiated material, the ____ the number of photoelectric absorption interactions will be, and the _____ the scatter produced.
Higher; higher; less
When a beam-restricting device is used to limit field size, technical factors may need to ____ to compensate for the change in image receptor exposure.
Be increased
All off the following are considered beam-restricting devices EXCEPT:
a. Aperture diaphragm
b. Beam filter
c. Positive beam limitation (PBL) device
d. Collimator
b. Beam filter
Penumbra is _____ when the beam restrictor is at an ____ distance from the port.
Reduced; increased
An effective method for reducing scatter radiation production is the…
15% rule of kVp change
Cones and cylinders would be commonly employed for the following examinations EXCEPT:
a. Orbits
b. L5-S1 spot
c. Skull
d. AP thoracic spine
d. AP thoracic spine
The shutters of a collimator…
- Regulate field size
- Reduce penumbra
- Reduce stem radiation
All of the following are true of PBL EXCEPT:
a. PBL automatically collimates the beam
b. PBL senses the size and orientation of the receptor
c. PBL is possible with portable radiography
d. PBL may be overridden by the radiographer in select instances
c. PBL is possible with portable radiography
When collimating down from a 14”x17” field size to an 8”x10” field size…
mAs must be increased to maintain radiographic image density.
The collimation assembly of a radiographic unit…
Employs an upper and lower set of shutters.
Placing a lead blocker adjacent to an obese patient’s anatomy during a lateral lumbar spine radiograph…
Will improve image quality.
