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what are the two types of mobile radiography units
Fluoroscopic C-arm unit and radiography mobile unit
how much voltage ripple is present in each generator:
single phase: _____
3 phase 6 pulse: _______
3 phase 12 pulse: _______
high frequency: ________
battery operated: _______
single phase: 100%
3 phase 6 pulse: 14%
3 phase 12 pulse: 4%
high frequency: <1%
battery operated: <1%
pro of capacitor discharge unit?
con of capacitor discharge unit?
lightweight and maneuverable
not battery operated and must be plugged into outlet before using
what is a capacitor
stores a charge for each exposure and releases the charge during exposure
how much does kV drop during an exposure from a capacitor
1kV per mAs, up to 30%
radiation leakage
residual x-rays may be present after an exposure is terminated, shock hazard
what are some strategies to minimize leakage
-grid biased/controlled tube
-metal wire mesh, actually the focusing cup itself, negative charge runs to grid to stop exposure
-collimation
battery operated units:
energized by powerful storage batteries
10-16, 12 volt packs of sealed, lead acid, batteries
battery operated units produce a current similar to what generator
high frequency
battery operated units have a typical focal spot size of ______ and a thermal capacity of ________heat units
0.75mm, 275,000 heat units
what are all battery operated units equipped with
“dead man” switch and special circuitry to monitor battery strength
characteristics of digital mobile units
battery operated
patient exams selected from worklists
fast imaging viewing
no wait time between exposures
onboard storage of 3,000 exposures
no more cassette processing
exposures immediately transmitted or printed within seconds
image data can be transferred to the hospital IT system for archival and documentation
pediatric mobile radiography
stickers on machines to make a fearful experience into fun experience, patients may remain more relaxed during an exam and obtain a high quality image
characteristics of a c-arm unit
fluoro unit
tube and image intensifier on c-arm
maneuverable and flexible
utilized in many departments
have 2 monitors (live imaging and static/saved images)
technical factor selection:
mobile units have single mAs control, mA and time not selected seperately
designed to operate at a high, mixed mA
provides a wider exposure latitude
what does a high mA allow for
shorter exposure time
AEC:
mobile units
paddle ionization chamber
positioning challenges
where is the paddle placed for AEC
behind the IR
what type of grid ratio do we want to use for mobile radiography? Why?
low grid ratio (6:1, 8:1) for a wider positioning latitude
what type of grid frequency do we want for mobile radiography
higher frequency, short dimension, and wide focal range (SID)
off centering to a focused grid by as little as _____ can cause cut-off
5 degrees
of how much can estimates be for distance to avoid significant exposure differences
15%
Time: high mA enables ______ exposure time
Distance: exposure cord must be min. of ____ ft.
Shielding: min. of _____ mm lead
Time: high mA=short exposure time
Distance: cord at minimum of 6 ft.
Shielding: minimum of 0.5 mm lead
where is the primary source of tech exposure
the patient
when c-arm is in a vertical position the tube is ______ the patient and there is less dose to the _____ and _____
below, neck and face
what does a 30% tilt of c-arm increase
dose by a factor of 4
minimum source to skin distance is ____ per federal regulation of c-arm mobile unit
12”
the exposure rate for a c-arm unit should not exceed ________ at tabletop
10 R/min
when using a high frequency generator the tech has to use ______ exposure factors
higher