Chapter 11 Equipment Design for Radiation Protection Flashcards
What kind of radiation does the tube housing protect the patient and personnel from?
off focus or leakage radiation
What does the tube housing prevent?
electrical shock, damage to rough handling, helps with cooling of the tube
What is the tube housing lined with?
lead
Off focus radiation creates what?
ghosting
The limit of off focus radiation for the tube housing is to not exceed ____ one meter away at highest voltage
.88 mGya/hr (100 mR/hr)
Who required an audible sound and visible radiation symbol?
Radiation Control for Health and Safety Act of 1968
What is required of radiographic tables and why?
must be as radiolucent as possible so that it will absorb only a minimal amount of radiation reducing the patients radiation dose
What are the radiographic tables made of?
carbon fiber material
The _____ to IR is the source to image receptor distance indicator
anode focal spot
The accuracy of the indicator must be accurate within ____ of the indicated SID and centering must be within _____ of SID indicator
2%
1%
How large should the primary beam be?
collimated to no larger than the size of the IR
Image quality is increased when collimating by _____ the amount of ______ radiation
decreasing
scatter
What were earlier collimation devices made of?
Cones and cyllinders
This is the automatic or manual collimator that is used on digital units today
light localizing variable aperture rectangular collimator
The first set of shutters is ____ to the tube window and ____ off focus radiation but ______ do anything to reduce primary beam
close
reduces
does not
The second set of shutters is the ____ ____ type and is _____ on the underside of the collimator head when looking at the light
variable aperture
visible
The patient skin surface should be at least _____ below the collimator head on fixed units and _____ on mobile units
15cm
30cm
______ refers to the brightness of a surface and quantifies the intensity of light source
luminance
The unit of measure is ____ for luminance
nit - candela per square meter, intensity measured at 40” should be 15 foot-candles = 161 nit
Coincidence between radiographic beam and localizing light beam must be within ____ of SID
2%
This must ensure that the collimation is adequate by collimating the radiographic beam so that it is no larger than the IR
positive beam limitation
The state requirements for the positive beam limitation is _____ of the SID
2-3%
______ reduces exposure to patient skin and superficial tissue by absorbing most lower-energy photons, increases beam quality and test rid of soft rays
filtration
Filtration is also referred to as
hardening the beam
reducing exposure to the skin ______ absorbed dose
decreases
What are the two types of filtration?
inherent and added
Where is inherent filtration?
glass envelope, insulating oil, glass window
What is the normal aluminum equivalency, light localizing collimator equivalency and minimum aluminum filtration?
.5mm
1mm
1.5mm
1.5mm equivalent aluminum filtration is also called
intrinsic filtration
Added filtration is located _____ the glass envelope but _____ the collimator shutters
outside
above
inherent + added = ______
total filtration
70 kVp and above is ____ AI Eq
50-70 kVp is _____ AI Eq
below 50 kVp is _____ AI Eq
2.5mm
1.5mm
.5mm
Aluminum has an atomic number of
13
Aluminum ______ low energy photons from a poly energetic beam without severely _____ the intensity of the beam
removes
decreasing
Why is aluminum used?
lightweight, sturdy, inexpensive, easily available
Quality assurance test to check filtration, thickness of absorber to decrease the intensity of the primary beam by 50%, measure of beam quality
half value layer
The _____ act of _____ required to have adequate filtration in all tubes
Radiation Health and Safety Act of 1968
kVp _____ determines the amount of required filtration
potential
Compensating filters help with dose _____ and provides ______, made up of aluminum or lead acrylic
reduction
uniformity
What are the two types of compensating filters and where do they go?
wedge - foot
trough - chest
The thick part of the compensating filter goes over the ____ part of the body
thin
The function of a compensating filter is to even out ______ of the body part with different _______, helps with dose reduction and uniformity
densities
thicknesses
Consistency of exposures of same technique set throughout the day, variance of _____ or less is acceptable
exposure reproducibility
5%
must be less than .1 (10%), consistency in output radiation intensity at selected kVp settings when generator settings are changed from one mA and time setting to another
exposure linearity
Radiographic grids are used to _____ image quality and _____ scatter
improve
reduce
Grids use _____ dose
more
_____ grid ratios increase the patient dose
higher
Virtual grids work in post processing by the system removing _____
scatter
In mobile radiography at least _____ source to skin distance is required
30cm (12”)
When the SSD is small, the patient entrance exposure is significantly ______ than exit exposure
greater
The larger the image matrix and smaller the individual units the ______ the resolution
better
The size of a pixel is about ____micrometers
50
What are the three materials used for image receptors
amorphous silicon - scintillator that converts x-ray energy to visible light
charge coupled device - converts visible light into electrical signals
amorphous selenium - converts x-ray directly into electrical signals
What are advantages to digital imaging
lower dose
ease of use and faster exams
immediate images
image manipulation
What are disadvantages to digital imaging
more costly
one IR size
The computed radiography plate is made of _____
europium activated barium fluorohalide phosphors
_____ ______ is the process of using automatic settings leading to an increased dose because you are not paying attention to exposure index numbers
dose creep
____ is more sensitive to scatter so grids should be used ____ often
CR
more
_____ produces the greatest patient exposure rate in diagnostic radiology
fluoroscopy
What are three benefits of fluoroscopy
brighter image
low mA
image intensifier tubes
How much brighter are fluoroscopy tubes
10,000 times
how low can mA settings go during fluoro
new systems 1-1.5 mA
old systems 3-5 mA
What are the two multi field or magnification phosphors and what are they made of?
input phosphor - cesium iodide
output phosphor - zinc cadmium sulfide
magnification produces a smaller area but causes it to be more magnified which ______ the mA
increases
magnified images have more of an ____ appearance so there is _____ noise
even
less
the ____ _____ _____ feature should be used to reduce patient and personnel dose
last image hold
for pulsed and interrupted fluoroscopy the kVp increases, the tube SSD should for fixed units should be no less than _____ and ____ for mobile units
38cm
30cm
The half value layer for pulsed and interrupted fluoroscopy should be ____ aluminum for 80-100 kVp
3mm-4.5mm
_____ ______ _____ is an alarm that is sounded after 5 minutes of Fluoro time, all fluoroscopy time should be documented at the end for physician and radiologist
cumulative timing device
The exposure rate limitations for entrance skin exposure should be ______ per minute at 30cm
88 mGya (10 R)
The fluoroscopy exposure control switch is what type of switch
dead man
The image intensifier should be _____ to the patient to reduce scatter
as close as possible
Weakest scatter is _____ in relation to the patient
on top of the patient
What is used in vascular imaging
digital subtraction angiography
reference image of the same area before contrast is administered
mask
remove of overlying structures to view vessels more clearly
roadmapping
When are high level control interventional procedures done
catheters, vascular type studies, fluid drainage, occlusions
visualization of smaller and lower contrast objects requires a ______ exposure rate
higher
When did the FDA issue warnings about high level control fluoro
1974
in 1994 the FDA limited table top exposure rates to _____
100 mGy/minute (10 R/min)
