Practice questions Flashcards
Where is all radiation incident?
Incident on ALL transducers
List 2 basic methods/processes of operation in radiation dectors?
- Ionize it by interacting with atoms
- Excitation
List 3 basic modes of operation of radiation detectors:
- Pulse
- Rate
- Intograte
What modes of radiation detector operation allows for the detection of raidation?
- Pulse
- Rate
- Intograte
Which of the modes of operation provides the most accurate count of raidation incident on a transducer? Why?
Integrate mode; because it counts the total amount of radiation even if the radiation if fluxuating
Why is it important to know the rate even though its not completely accurate?
Because it allows for detection of the amount of radiation to notify you on general intensity
True or false?
Integrate mode detectors require low resolving times.
True
List 2 factors that can improve the sensitivity of a radiation detector:
- Increase the size of the ion chamber/DELs
- Amplify the signal (it can also lower the dose to the patient)
List 3 ways in which accuracy of radiataion detectors can be improved:
- Increase sensitivity
- Low resolving time
- Range that it will be able to detect
What is meant by the term “intrinsic efficiency” of a transducer?
Inherent to the material itself, not other enviormental factors, it is how well the radiation is detected/the stopping power
What can affect the intrinsic efficancy of a transducer?
a. Atomic number of transducer elements
b. Mass density of transducer elements
c. Physical state of transducer material
What 2 properties of a transducer effect it’s absolute efficiancy?
1.Intrinic efficiency
2.Geometric efficiancy
What operates on the basis of saturation of a detection chamber?
Gieger muller tubes
Which is not found in a PMT and why?
a. Anode
b. Dynode
c. Photocathode
d. Air
D; we dont want air interacting with the tube photons
What is the element used in thermoulminescent phosphor TLDs?
Lithium floride
What is th primary reason LiFl is the phosphor of choice in TLDs?
It is simular in Z# and denisty to human tissue
What is the source of energy applied to LiFL to cause its luminescence?
Heat by annealing
What term is used to describe any residual latent image on the CR following processing?
Ghosting
How is ghosting resolved in CR plates?
Flooded with a very intense whhite light to give e- energy to escape the F traps
Explain the term fading with respect to CR cassettes:
The natural dropping of e- from F centers over time from not processing the latent image
List the ways in which the emmission efficancy in conventional PSP CR plates has been improved:
- Needle shaped phosphor
- Reflective layer
- Barium floride dopped with eroupium
In floro with variable mA and fixed kV, the kV setting is determined by what?
- Manually choosing KV
- Choosing the body part
In terms of conventional floro, what should the mA be?
Less than 5 mA
In the input phosphor, what gets converted into what?
X-rays, light
What is the purpose of the aluminum substrate coated on the external surface of the input phosphor?
To take any photons travelling backwards and reflect it forward to the photocathode
What is the input phosphor made of?
Cesium iodide
Why does an increase in thickness in the input phosphor layer result in reduced SR?
More diverging photons
T/F?
An increase in phosphor thickness can result in relatively reduced dose;
True, better at absorption so you can use decrease in dose
What feature ensures that all photoelectrons travel the same distance to the focal point within the II?
The curve of the IP
The pupose of the OP is what?
To turn electrons into light
The acceleration of e to a higher KE within the II contributes to what?
Fulx and brightness gain
T/F
When using mobile floro with fixed SID, geometric mag can be achieved by increasing OID.
True
With a brightness gain of 8000 in a 25 cm input phosphor, what is the flux gain if the output phospor size is 2.5 cm?
FG=80
What does magnification in floro result in?
Increase in SR
What is S distoriton due to?
External magnetic feild
What is veiling glare a result of?
Scatter
What is the conversion factor?
17 cm II tube
Flux gain=120
Output phosphor=2.5cm
55.5
