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types of mobile unit
-C-arm unit
-Radiographic mobile unit
portable generator types
-direct power (outlet)
-battery driven and operated
-capacitor discharge
-high frequency
generator
device used to convert mechanical energy to electricity
rectifier
system of electrified gates to force current to flow in one direction
fill in gnereator pulses and ripples*
capacitor discharge unit
pros:
-light weight, movable
cons:
-needs to be plugged in, not motor driven
-kV drops immediately during exposure, one kV per mAs, so a 30% drop*
-radiation leakage risk (kV doesnt go to zero immediately)
-shock hazard
define capacitor
a piece of equipment that stores the charge until its needed to be used
Define Grid bias/controlled tube
-metal wire mesh that acts as focusing cup
-completely insulated
-stops or minimizes radiation leakage
Battery Operated Units
energized by large battery packs]
sealed, lead acid batteries, wont leak if puncture
self-propelled and energizing units to take exposure
produces current similar to high frequency, so lower kVp can be used, increased avg. energy, .75 mm focal spot
thermal capacity of 275,000 HU
pros:
-power drive with deadman switch
-can drive up to 10 miles
-special circuitry to track battery percent
cons:
-
Digital Mobile units
high fequency as well and battery operated
pros:
no wait time between exposures or sending images
large storage capacity
flat panel detectors used with DR
-tethered or wireless
-7-10 lbs
pediatric mobile radiography
-make images less frightening
-good quality image
C-arm
Fluoro unit
tube on one end, ii on another
2 monitors, one is live one is static
Pros:
-maneuverable and flexible
-utilized in many departments
technical factor selection
have a single mAs control (mA and time not seperate)
Pros:
-at high fixed mA for short exposure times
-reduces mAs needed
-more exposure latitude/forgiveness
Automatic Exposure Control (AEC)
paddle ionization chamber
Pros:
Available for mobile units
Cons:
positioning challenge
manual technique
paddle is behind image receptor
grid selection
-low grid ratio= wide positionig latitude (6:1, 8:1)
-higher frequency, short dimesnion, and wide focalrange (SID)
-off centering to a focused grid by as little as 5* can cause grid cut off
room challenges
-distance issues must be within 15%
mAs conversion rule of thumb:
double mas for=
40-56 in
56-72 in
positioning challenges
use critical thinking for angulation and how patient is seated
radiation safety
time-
high mA for short exposures
don’t hold PTs
distance-
min of 6ft- cord
ask visitors and staff to leave room
shielding-
min .5mm lead
radiation exposure with c arms
PT is primary radiation source
verticle position: tube below patient= less dose to neck and face
30* tilt increases dose by a factor of 4
12 in minimum source to skin distance
10R/min should not be exceeded