for portables, they automatically engage the highest ___ available
mA
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For 100 cm (40"), average person can use
fingertip-to-opposite axilla
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From 100 cm (40"): 125 cm (50"): 150 cm (60"): 180 cm (72"):
125 cm: 1 ½ times increase in technique 150 cm (60"): Double technique 180 cm (72"): Triple technique
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For mobile chests, always check the angle of the tube from ____ perspectives, while standing back as far as possible
two
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If the anatomy of interest includes joint spaces, it is always more important to keep the CR perpendicular to the ____ rather than to the cassette or IR
anatomy
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do not ever angle CR if looking at
fluid levels
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if your pt is sitting at 20 degrees from vertical and back of bed is 10 degrees from vertical, how much angle for CR if looking for fluid levels
angle CR horizontal
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For mobile radiography of large body parts, use ___ ratio grids for wide positioning latitude when grids are used
low
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recommended approach to technique with portables is to have
manual technique chart
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fluoroscopy was developed to radiologists could view ____ images
dynamic
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image intensifier improved fluoroscopy by
• Improved fluoroscopy by increasing image brightness Dramatically reduced the mA required, saving patient dose
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fluoroscopic tubes operate between
1-5 mA
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Due to low exposure rate, fluoroscopic images are statistically inferior to overhead images and demonstrate more
noise
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ABC
automatic brightness control
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purpose of image intensifier tube
Convert the remnant radiation beam into an amplified light image
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The output phosphor (left, arrow) is always ___ cm in diameter
2.5
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Concentration of the beam from the input to the output phosphor increases ___ by thousands of times
brightness
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Increasing the physical diameter of the input phosphor results in increased
image resolution
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the input phosphor converts x-rays into
light
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Upon absorbing light energy, the photocathode emits
electrons
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Concentrating the electrons increases output intensity. This process is called
minification
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A thin photoemissive metal layer, made of a combination of antimony and cesium compounds
photocathode
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A layer of fluorescent crystals of cesium iodide
input phosphor
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A series of positively-charged metal rings that become narrower toward the anode end of the tube
The Electrostatic Focusing Lens
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Made of cesium iodide Converts the kinetic energy of the electrons striking it into light
output phosphor
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The ratio of the number of light photons emitted by the output phosphor to the number of X-rays striking the input phosphor
flux gain
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as output phosphor gets smaller, what happens to minification gain?
decreases
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The product of the minification gain and the flux gain
brightness gain
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a smaller region of the input phosphor is projected onto the output phosphor by moving the what where?
focal point of the electron beam closer to the input phosphor
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Magnification mode can be used to improve what feature in the image?
spatial resolution or sharpness in the image
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To avoid the appearance of noise from a poor SNR, the what increases the what to compensate for the loss of minification gain
Automatic Brightness Control mA
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Patient exposure increases by the ratio of the
change in area of the active input phosphor used
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Using magnification mode in fluoro has what bad quality?
increases patient dose
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As the patient rolls onto her side, the increased tissue thickness must be_____ to maintain fluoroscopic image brightness
compensated for
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brightness of a fluoroscopic is _____ to the mA
directly proportional
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brightness of a fluoroscopic image is to the what power of kvp
5th power
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Generally, what kind of technique is preferred with fluoro?
high kVp / low mA
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No form of electronic intensification can improve the image above the
statistical level of the absorbed x-ray photons
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no amount of electronic intensification can overcome the mottle or noise produced when an
insufficient amount of x-rays is reaching the image intensifier
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Small, momentary defects in the distribution of brightness ("twinkling") in a dynamic image
This noise pattern appears to be drifting across the image, creating the appearance of "crawling ants" or "snow"
scintillation
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what is the best solution to improve scintillation
raise the mA
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Image intensifiers are generally poor at
preserving high contrast in the transmitted image
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Contrast deteriorates with aging of the intensifier -deterioration can be as high as ____% per year
10
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Slight magnification and increased blur around the periphery of the image
pincushion distortion
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Scattered random light from the output phosphor
veiling glare
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Loss of brightness toward the periphery of the image
vignetting
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A contributing factor to vignetting is
pincushion distortion
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High-resolution TV cameras that use an ADC to turn the electronic signal into digital numbers
Digital Photospot Cameras
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what piece of equipment in the OR allows for significant reductions in patient exposure
Carbon fiber tables
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A series of short visual checks, rather than continuous fluoroscopy, dramatically reduces cumulative exposure to the patient
Intermittent Fluoroscopy
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This is the most important way to limit patient exposure during fluoroscopic studies
Intermittent Fluoroscopy
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Keeping the last image displayed on the monitor
"Last Image Hold" Devices:
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feature that automatically turns the x-ray beam on and off during operations
pulsed fluoroscopy
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with Pulsed-Progressive Mode, the fluoro tube is being run in
radiographic mode
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refers to the length of each pulse
pulse width
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refers to how many pulses occur per second of operation
pulse rate
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if pulse width is reduced from 6 to 3, how much is patient dose decreased?
1/2
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The _____ detector uses a cesium iodide phosphor coupled to an active matrix array (AMA) of amorphous silicon thin-film transistors (TFTs)
indirect
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The ____ detector uses an AMA of amorphous selenium TFTs
direct
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Dual-Use FPD systems convert from radiographic to fluoroscopic mode by grouping sets of 4 small pixels together to form a larger effective pixel
binning
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DFPDs can be operated either in
continuous or pulsed fluoroscopy mode
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• Changing from fluoroscopic mode to DF mode requires an increase in tube current of 20 to 100 times the mA
• Nonetheless, a net decrease in patient exposure can be achieved compared to continuous fluoroscopy because why
the extremely short pulse times for exposures
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The time it takes for the x-ray tube to be switched on
Interrogation Time:
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The time it takes for the x-ray tube to be switched off
Extinction Time
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Grids for DFPDs have their lead lines running in which direction to prevent aliasing artifacts