MAKE SURE TO KNOW ABOUT THE GENERATOR PHASES AND RIPPLE EFFECTS
What are the 2 types of mobile units?
fluoroscopic c-arm unit and radiographic unit
Mobile units are classified by ___
generator type
What are the generator types for mobile units?
direct power (wall outlet)
battery driven/operated
capacitor discharge
high frequency
Define generator
device used to convert mechanical energy to electricity
Define rectifier
system of electrified gates to force current to flow in one direction
Explain the capacitor discharge unit
light weight and maneuverable
not battery operated (must be plugged in to use)
capacitor stores charge
charge is released before each exposure
kV drops during exposure
1 kV per mAs
up to 30% drop
Explain radiation leakage for capacitor discharge units
residual x-rays may be present after exposure is terminated
shock hazard - kV may not return to 0 immediately
minimize leakage by:
grid biased/controlled tube
metal wire mesh acts like a focusing cup
negative charge runs to grid to stop exposure
tube collimation
Explain battery operated units
energized by powerful storage batteries
sealed, lead acid, batteries
won’t leak if punctured
10-16 12 volt packs connected in a series
some are used to create x-rays
some are used to drive the unit
similar current to high frequency generator
efficient energy with nearly constant potential
can use lower kVp
~0.75mm focal spot (cannot change size in mobile units)
thermal capacity of 275,000 HU
Explain the battery of battery operated units
power drive
“dead man” switch
can drive up to 10 miles when fully charged
light goes on when charge is needed
Explain digital mobile units
battery operated
exams selected directly from worklist
fast image viewing
no wait time between exposures
storage of 3,000+ exposures
no cassette processing
Explain flat panel detectors
(the mobile unit IR)
tethered or wireless
7-10 lbs
Explain the speed and accuracy of digital mobile units
QA image before removing IR
can remain at bedside until exam is “truly done”
post processing
annotation, window level, etc.
send to PACS immediately
faster result times
Explain pediatric mobile radiography
turn a possible fearful experience into a FUN experience
pediatric patients may remain more relaxed during exam
obtain a quality image
Explain the c-arm mobile unit
fluoro unit
x-ray tube and ii suspended on c-arm
maneuverable/flexible
utilized in many departments
2 monitors: live imaging and saved images
Explain mobile unit technical factor selection
most have single mAs control (ma and s not selected separately)
high, fixed mA
short exposure times
reduced amount of mAs needed
wider exposure latitude (more forgiveness)
Explain mobile unit AEC
can have a paddle ionization chamber
positioning challenges
most techs prefer to set manual technique
must place paddle under the anatomy of interest but BEHIND the IR
Explain grid selection for mobile units
low grid ratio = wide positioning latitude (6:1 or 8:1)
high frequency, short dimension, wide focal range (SID)
off centering to a focused grid by as little as 5o can cause cut-off
Explain distance challenges with mobile units
estimating distance is a bad idea
estimates must be within 15% to avoid significant exposure differences
measure whenever possible!
from 40” to 56” you need to double mAs
from 56” to 72” you need to double mAs
When are air/fluid level best visualized?
patient 90o upright and horizontal beam (when not possible, semi-erect may be enough)
Explain radiation safety with mobile units
YOU are responsible for protecting the patient, visitors, staff, and yourself
time
high mA, short s
don’t hold patients
distance
exposure cord minimum of 6 feet
ask visitors and staff to leave room
shielding
min of .5 mm lead
collimate
Explain radiation exposure with a c-arm
primary source of tech exposure = scatter from patient
vertical position (tube below patient) has less dose to neck and face
30o tilt increases dose by a factor of 4
tech should stand minimum of 6 feet from tube
minimum source to skin distance of 12”
exposure rate should not exceed 10 R/min at tabletop
What should you do (in terms of compassionate care) when going into a patient room for a portable exam?
knock and enter
introduce yourself
explain what you are doing (communicate)
return the room to the way it was
give patient call light
ask if they need anything else before you leave