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Introduction to C-arm technology

7/23/2019 AOT L C-Arm Introduction

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Learning outcomes

• Identify all C-arm components and related equipment

• Describe configuration and constraints of C-arm

•Describe capabilities and clinical application of C-armfor pre-, intra-, and postoperative imaging

• Explain optimal positioning of patient, healthcare staff, and

equipment, while minimizing radiation exposure

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Outline

• hat is a C-arm!

• Image acquisition" collimation

• Image intensifier 

• C-arm movement

• #se of C-arm" pre-, intra-, and postoperatively

• C-arm attitude"

• $rotective clothing

• %echnical contributions to radiation dose reduction

• &ow much radiation is safe!

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• 'emi-circular ‘C’-shaped arm

• (-ray source fixed to one end

• Image intensifier fixed to other

end

•

Display screen shows liveimage feed

What is a C-arm?

Image courtesy of 'iemens

• Image intensifier requires

reduced amount of radiation to

produce image

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Image acquisition: collimation

• (-rays pass out of vacuum tube through a window sealed onto

vacuum envelope of x-ray tube

• 'ize of window can be controlled )collimation*

• %he smaller the window, the sharper the x-ray and the smaller the

dose of radiation

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Image intensifier 

• (-rays absorbed by image

intensifier, and thereby fluoresce

• Image intensifier allows low-

intensity x-rays to be amplified

• +agnifies intensity produced in

output image

•esult" less radiation emitted

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C-arm movement

• +obile C-arms limited in

degree of movement

&orizontal

'wivel

otation

ertical

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• .rbital rotation around /$ and lateral views 01234

• C-arm cannot rotate more than the horizontal position

• (-ray source on far side of body part being imaged

C-arm orbital rotation

.rbital rotation Image intensifier (-ray tube

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Image acquisition using the C-arm

• &igh-quality images

• 5eam of x-ray travels perpendicular to limb6bone

• Image intensifier as close to patient as possible

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Surgical application of C-arm

• 5efore surgical incision• Eg, confirm and grade degree of ligament damage

• Intraoperatively

• Eg, guide reduction and fixation

• $ostoperatively• Eg, chec7 fixation

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Surgical C-arm application: or!flo e"ample

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#reoperative application: traction films

5one overlap prevents planning %raction films

facilitate planning

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'tress view of complete rupture of ulnar collateral ligament of

metacarpophalangeal 8oint of thumb )s7i thumb*

#reoperative application: screening for ligament

instability in s!i thumb

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Intraoperative application: dynamic hip scre

$%&S'

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Intraoperative application: distal radial pinning

Do not place wrist

directly on x-ray source

during surgery

Intraarticular distal radius fracture

treated with multiple 9-wires

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#ostoperative application: assessment of

reduction(fi"ation

 /ssessment of 'chatz7er II

tibial plateau fracture fixation 

 /ssessment of femoral nailing

)showing malrotation*

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:eaded apron

 /$" 1;-fold decrease in scattered radiation

:ateral" <-fold decrease in scattered radiation

%hyroid collar 

3=>-fold decrease in scattered radiation 

Eye protection

?=1> mm lead-equivalent goggles provide @?Aattenuation of radiographic beam 

Bloves

;?;<A protection at >3> 9

)adiation: protective clothing

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• $osition x-ray tube under and close to

patient

• +ar7 C-arm on floor and beam position

on patient

• #se integrated lasers on x-ray tube and

image intensifier for positioning

• #se pulse acquisition, avoid screening

• Collimate when possible

• irtual patient anatomy selection"

correct dose for specified body area• 'elect dose rate in line with patient size

• +aintain distance from patient

C-arm *attitude* and technical contributions to

radiation dose reduction

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)educing e"posure to radiation

• +inimize duration of exposure

• 9eep beam time to minimum

• %rial screen after positioning patient

• ely on stored images when possible

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• $lace x-ray tube and

image intensifier to

minimize scatter 

• $atient as close to

image intensifier and

as far from x-ray tube

as possible

+asic C-arm positioning

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,-ray tube position

'taff exposed to

increased radiation

'taff exposed to reduced radiation

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bsorption and scatter 

• or every 1??? photons

reaching patient

• 03? reach image detector

• 01??–3?? scattered

•

remainder are absorbed bypatient )radiation dose*

• 'cattered dose is higher at

x-ray tube sideimage intensifier x-ray tube

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Dose 1>?

Dose 3??

Intensifier diameter elative patient entrance

dose m'v6h

13F )23 cm*

GH )33 cm*

;H )1; cm*

<=>H )11 cm*

Dose 1??

Dose 2??

%he smaller the image intensifier diameter,

the greater the patient entrance dose

.actors affecting patient doses

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• or staff, the further

from the patient the

lower the dose of

scattered radiation

/"ample of dose-rate around the C-arm

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adiation dosimeter 

)monitor*

• 3? m'v per year, average over

defined periods of > years

 

• &ow do you 7now how much

radiation you have received!

&o much radiation is safe?

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Summary

• +ain components of C-arm" x-ray source, image intensifier, image

display screen

• C-arm used to improve outcomes during pre-, intra, and postoperative

procedures

• %o reduce radiation exposure"

• $osition image intensifier close to patient

• 'urgeon and staff wear protective clothing and stand at safe

distance from C-arm• $ulse acquisition used as often as possible )avoid screening

unless necessary*