nearpod Flashcards
In a fluoroscopy system with variable mA and fixed kV, the kV setting is determined by:
- the operator manually adjusting the kV values
- selecting the body part being examined, which in turn selects the appropriate kV
In terms of mA values used in conventional fluoroscopy, which of the following is true?
mA < or = 5
What purpose does the aluminum substrate coated on the external surface of the input phosphor serve?
reflective layer - pushes any light emitted backwards and pushes it forwards
List 2 functions of the lead-lined metal housing surrounding the glass envelope of the image intensifier:
help support
protect and maintain vacuum seal
stops scatter
The input phosphor in modern day image intensifiers is made of:
Cesium Iodide
Why does an increase in input phosphor layer thickness result in reduced spatial resolution?
Light photons are scattered laterally within the phosphor layer, reducing spatial resolution
An increase in. input phosphor layer thickness can result in relatively reduced patient dose. True or false?
true
in ALL radiation detectors, radiation is incident on the ________ of the device?
Transducer
List 2 basic methods (processes) of operation in radiation detectors
- the ionization of atoms, which frees up electrons that can be measured as a charge or as a current or a circuit
- the basis of excitation of electrons, as the electrons return to the pre-excitation stage, they release energy which is captured and transferred into an electrical current
list 3 basic modes of detection of radiation detectors
pulse, rate and integrate modes
which mode of operation provides the most accurate count of radiation incident on a transducer?
integrate mode - electronic devices can count these events at extremely high speed and with great accuracy
true or false, integrate mode detectors require low resolving times
true, need low resolving times to increase accuracy
list 2 factors that can improve the sensitivity of a radiation detector
- larger surface area
- increased electronic amplification of incoming signal
list 3 ways in which accuracy of radiation detectors can be improved
- increased sensitivity
- range within what we’re looking for
- faster resolving time
What is meant by the term “intrinsic efficiency” of a transducer?
the stopping power of the transducer
- the chemical composition of the transducer and how likely it is to absorb the radiation (higher atomic number is better)
what can affect the intrinsic efficiency of a transducer?
- Z of the transducer
- mass density of the transducer
- physical state of the transducer
what 2 properties of a transducer affect its absolute detection efficiency?
intrinsic and geometric efficiency
which detector operates on the basis of saturation of the detection chamber?
geiger-muller tube
what is not found in a photo multiplier tube?
air, the tube is a vacuum
what is the thermoluminescent phosphor used for in TLDs?
Lithium fluoride, it is a tissue equivalent
what is the primary reason LiF is the phosphor of choice in TLDs?
because it is tissue equivalent (similar Z and density)
what is the source of energy applied to LiF to cause it to luminesce?
heat (thermoluminescence) annealing oven
What feature ensures that all photoelectrons travel the same distance to the focal point within the image intensifier?
the curved anode
what is the purpose of output phosphor?
phosphors will create light so it turns electrons into light
the acceleration of electrons to a higher kinetic energy within the image intensifier contributes to?
Flux gain and brightness gain
When using a mobile fluoroscopic machine with a fixed SID, geometric image magnification can be achieved by increasing the OID, Tru or false?
true, any time you increase OID you get geometric magnification
If the brightness gain of a 25cm II tube is 8000, what is the flux gain of the system with an output phosphor size of 2.5cm?
brightness gain = flux gain x minification gain
8000 = F x (25/2.5)^2
F = 80
A 17cm II tube has a flux gain of 120 and a 2.5 cm output phosphor. If the conversion factor of an II os equal to 0.01 times the brightness gain, what is this II’s conversion factor?
Brightness gain = flux gain x minification gain
BG = 120 (17/2.5)^2
BG = 5548.8
Conversion factor = BG(0.01)
CF = 55.488
What is conversion factor?
how much light you get out of it compared to the rate of dose that’s hitting it
magnification during a fluoroscopic procedure result in?
Increased spatial resolution
veiling glare in II’s is the result of/
Scatter inside the image intensifier
How is patient dose affected, and by what factor does it change when IP size is changed from 25 cm to 10 cm?
increases
patient dose = (ip old/ip new)^2 = (25/10)^2
= 6.25
