mobile radiography- (POI2) Sem. 2

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