Mobile Radiography

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 5^o 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 90^o 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

• 30^o 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