radiography technique - exposure factors (5)

8/18/2019 Radiography Technique - Exposure Factors (5)

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[Radiography] Technique -

[Radiography] Technique -

Exposure FactorsEx

posure Factors


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KVP = Energy of x-rays = higherKVP = Energy of x-rays = higher

penetrability, it moves through tissue.penetrability, it moves through tissue.

The energy determines the Q!"#T$ of x-The energy determines the Q!"#T$ of x-ray produ%ed.ray produ%ed.

&. in%rease in KVP = ele%trons gain high&. in%rease in KVP = ele%trons gain highenergyenergy'. higher the energy of ele%trons = greater'. higher the energy of ele%trons = greater

(uality of x-rays(uality of x-rays). greater (uality = greater penetrability). greater (uality = greater penetrability

KVP = Q!*T#T$ = in%reased +Vp =KVP = Q!*T#T$ = in%reased +Vp =more x-rays produ%ed.more x-rays produ%ed.


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! = tube %urrent = number of ele%trons! = tube %urrent = number of ele%trons

and (uantity of x-rays produ%ed.and (uantity of x-rays produ%ed.

! does not affe%t (uality of x-rays! does not affe%t (uality of x-rays

produ%ed.produ%ed.

KVP = (uality (uantityKVP = (uality (uantity

! = (uantity! = (uantity

Time = (uantityTime = (uantity


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Purpose of using ridsPurpose of using rids

&./ #n%reases %ontrast&./ #n%reases %ontrast'./ 0edu%es density'./ 0edu%es density)./ ust use more !1 2ith a grid.)./ ust use more !1 2ith a grid.

The %hoi%e to use a grid depends on3The %hoi%e to use a grid depends on3&./ KVP used&./ KVP used'./ thi%+ness of part'./ thi%+ness of partParts &4 %m or larger 2ith a KVP higherParts &4 %m or larger 2ith a KVP higherthan 54 produ%e enough s%atter tothan 54 produ%e enough s%atter tone%essitate the use of a grid.ne%essitate the use of a grid.


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Air Gap TechniqueAir Ga

p Technique33

This is li+e a grid.This is li+e a grid.

"ess s%atter on film but less detail also."ess s%atter on film but less detail also.

$ou %an in%rease 1#6 to help 2ith detail.$ou %an in%rease 1#6 to help 2ith detail.

The greater the gap the less s%atterThe greater the gap the less s%atterrea%hes film.rea%hes film.

&4 in%h air gap = &73& grid 8small body&4 in%h air gap = &73& grid 8small body

part &4%m/part &4%m/


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*eed proper balan%e of density and %ontrast*eed proper balan%e of density and %ontrast

6ensity = overall bla%+ness6ensity = overall bla%+ness

Primary %ontrolling fa%tor for density is !1Primary %ontrolling fa%tor for density is !1

TTo make a visibe change in densityo make a visibe change in density330e(uires a minimum )49 %hange in !1 or0e(uires a minimum )49 %hange in !1 or

doubledouble

KVP affe%ts density - alters amount andKVP affe%ts density - alters amount andpenetrating ability of x-ray beam, so, in%reasingpenetrating ability of x-ray beam, so, in%reasing

penetration of x-ray beam results in morepenetration of x-ray beam results in more

radiation : results into more density on x-ray.radiation : results into more density on x-ray.


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; KVP = ; (uantity of radiation ; density; KVP = ; (uantity of radiation ; density

4/

KVP affe%ts density and other aspe%ts - so, KVPKVP affe%ts density and other aspe%ts - so, KVP

is not primary fa%tor for %hanges in density.is not primary fa%tor for %hanges in density.example3 74 +Vp in%rease &4 +Vp very dar+example3 74 +Vp in%rease &4 +Vp very dar+greater %hangegreater %hange4 +Vp in%rease &4 +Vp slightly dar+er smaller4 +Vp in%rease &4 +Vp slightly dar+er smaller%hange%hange


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To maintain density 2ith KVp use the &79To maintain density 2ith KVp use the &79

rule3rule3%hange KVP by &79 and you 2ill have the%hange KVP by &79 and you 2ill have the

same effe%t on density as doubling !1same effe%t on density as doubling !1

example3 KVP ?' %hange to @ 8&79/example3 KVP ?' %hange to @ 8&79/

same assame as

!1 &4 %hange to '4 8double/!1 &4 %hange to '4 8double/


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!atient thickness!atient thickness

#n general, for every @%m of thi%+ness of patient,#n general, for every @%m of thi%+ness of patient,you need to adAust !1 by ayou need to adAust !1 by afa%tor of 'fa%tor of '

example3example3thin pt. &? %m use @4 !1thin pt. &? %m use @4 !1thi%+er pt. '' %m use ?4 !1 to maintainthi%+er pt. '' %m use ?4 !1 to maintaindensitydensity

@4 B ' = ?4 for the additional @%m of thi%+ness@4 B ' = ?4 for the additional @%m of thi%+ness


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KVP 8penetrating po2er/ is the %ontrolling fa%torKVP 8penetrating po2er/ is the %ontrolling fa%tor

for %ontrast.for %ontrast.

Cigh KV = more densities but fe2er differen%esCigh KV = more densities but fe2er differen%es

= lo2 %ontrast= lo2 %ontrast

"o2 KV = fe2er densities but greater differen%es"o2 KV = fe2er densities but greater differen%es= high %ontrast= high %ontrast

"# aso a$$ects amount o$ scatter "# aso a$$ects amount o$ scatter

Cigh KV = in%rease in s%atter - only addsCigh KV = in%rease in s%atter - only adds

un2anted density 8fog/ on film. 1o, in%reasingun2anted density 8fog/ on film. 1o, in%reasingfog al2ays de%reases %ontrast.fog al2ays de%reases %ontrast.

"o2 KV = de%reases s%atter - redu%es fog, so,"o2 KV = de%reases s%atter - redu%es fog, so,

in%reases %ontrast.in%reases %ontrast.


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%n$uencing Factors o$ &ontrast%n$uencing Factors o$ &ontrastThe most influen%ing fa%tor for %ontrast isThe most influen%ing fa%tor for %ontrast is

%ontrolling the amount of s%atter.%ontrolling the amount of s%atter.less s%atter 8fog/ = in%reases %ontrastless s%atter 8fog/ = in%reases %ontrast

&./ rids - absorption of s%atter that exits patient&./ rids - absorption of s%atter that exits patient

'./


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@./ Dody Part - %omposition, thi%+ness,@./ Dody Part - %omposition, thi%+ness,

%ompa%tness.%ompa%tness.

These differen%es ma+e the range of densitiesThese differen%es ma+e the range of densities

8%ontrast/8%ontrast/

Tissues 2ith higher atomi% number absorb moreTissues 2ith higher atomi% number absorb more

radiation - bone, %ontrastradiation - bone, %ontrastTissues 2ith lo2er atomi% number absorb lessTissues 2ith lo2er atomi% number absorb less

radiation - air radiation - air

ide range of tissue %omposition = high %ontrastide range of tissue %omposition = high %ontrastsimilar types of tissue = lo2 %ontrastsimilar types of tissue = lo2 %ontrast

Thi%+er tissue = more s%atter = less %ontrastThi%+er tissue = more s%atter = less %ontrast


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1#* ! C#CE0 KV FG0 ! TC#%reates fog 2hi%h de%reases the %ontrast.%reates fog 2hi%h de%reases the %ontrast.

1+inny person - good %ontrast1+inny person - good %ontrast

Ceavy person - fog, one density, not a lotCeavy person - fog, one density, not a lot

of %ontrast on filmof %ontrast on film


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Exposure 'odi$icationsExposure 'odi$ications33

Pediatri% %hest = use fast exposure timesPediatri% %hest = use fast exposure timesto stop motion.to stop motion.inimum KVP to Penetrate


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!dapting exposure fa%tors for %hildren !dapting exposure fa%tors for %hildren

based on exposure fa%tors for adults,based on exposure fa%tors for adults,

ex%luding %hest and s+ull examsex%luding %hest and s+ull exams

Age Exposure $actor adaptationAge Exposure $actor adaptation

4-7 years H '79 of !1 that is indi%ated4-7 years H '79 of !1 that is indi%ated

for adultsfor adults

5-&' H 749 of !1 that is indi%ated for5-&' H 749 of !1 that is indi%ated for

adultsadults


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Pathology3 #f %hanges are needed toPathology3 #f %hanges are needed to

%ompensate for diseases it is 8generally/ best to%ompensate for diseases it is 8generally/ best to

adAust the KVP be%ause this affe%ts theadAust the KVP be%ause this affe%ts thepenetrating ability. 8minimun of &79 rule/penetrating ability. 8minimun of &79 rule/

!dditive %onditions - may need to add KVP !dditive %onditions - may need to add KVP

!bdomen - aorti% aneurysm, as%ites, %irrhosis, !bdomen - aorti% aneurysm, as%ites, %irrhosis,

hypertrophy of some organs 8splenomegaly/hypertrophy of some organs 8splenomegaly/


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6estru%tive %onditions - may need to6estru%tive %onditions - may need tode%rease KVPde%rease KVP

!bdomen - bo2el obstru%tion, free air !bdomen - bo2el obstru%tion, free air


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(o$t Tissue(o$t Tissue33GbAe%ts in soft tissue3 if less density isGbAe%ts in soft tissue3 if less density isre(uired - !1 should be de%reasedre(uired - !1 should be de%reased#mportant to +no2 2hether %ontrast should#mportant to +no2 2hether %ontrast shouldbe in%reased or de%reasedbe in%reased or de%reased

e.g. air2ay for soft tissue ne%+ - %ontraste.g. air2ay for soft tissue ne%+ - %ontrastshould be in%reasedshould be in%reasedForeign body - de%rease %ontrast toForeign body - de%rease %ontrast tovisualiJe both bone and soft tissuevisualiJe both bone and soft tissue

1oft tissues that re(uire a de%rease in1oft tissues that re(uire a de%rease indensity should use a de%reased !1density should use a de%reased !11oft tissues that re(uire a higher or lo2er1oft tissues that re(uire a higher or lo2er

%ontrast should use a %hange in KVP%ontrast should use a %hange in KVP


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#ariabes and their e$$ect on the photographic#ariabes and their e$$ect on the photographic

properties o$ the x-ray imageproperties o$ the x-ray image33

0adiographi% variables0adiographi% variables 6ensity6ensity


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sing &44 m!8small fo%al spot/ station forsing &44 m!8small fo%al spot/ station forextremity has better detail thanextremity has better detail thansing the same m!s and same +V 2ith highersing the same m!s and same +V 2ith higher

ma stationma station

1%atter radiation is detrimental to the (uality of1%atter radiation is detrimental to the (uality offilm and adds un2anted density to the filmfilm and adds un2anted density to the film2ithout adding any patient information.2ithout adding any patient information.

1%atter de%reases %ontrast and using grids1%atter de%reases %ontrast and using grids

in%rease the %ontrast.in%rease the %ontrast.

Deam restri%ting devi%es and grids are used toDeam restri%ting devi%es and grids are used tolimit s%atter radiation.limit s%atter radiation.


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T2o maAor fa%tors that affe%t the amount ofT2o maAor fa%tors that affe%t the amount of

s%atter radiation - KVP and the volume of tissues%atter radiation - KVP and the volume of tissue

irradiated 8opening %ollimation and largerirradiated 8opening %ollimation and largerpatient/.patient/.

&./ sing higher KVP produ%e more s%atter as&./ sing higher KVP produ%e more s%atter as

%ompared 2ith a lo2er KVP.%ompared 2ith a lo2er KVP.

'./ "arger field siJe and the thi%+er the patient'./ "arger field siJe and the thi%+er the patient

the greater amount of s%atter produ%ed from thethe greater amount of s%atter produ%ed from thepatient.patient.

$ou should use appropriate KVP and limit x-ray$ou should use appropriate KVP and limit x-ray

beam to limit s%atter.beam to limit s%atter.


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Deam restri%tion serves t2o purposes -Deam restri%tion serves t2o purposes -

this in%reases %ontrast, alsothis in%reases %ontrast, also

&./ limits patients exposure&./ limits patients exposure

'./ redu%es s%atter './ redu%es s%atter

De%ause %ollimation de%reases x-ray field,De%ause %ollimation de%reases x-ray field,less s%atter is produ%ed 2ithin theless s%atter is produ%ed 2ithin the

patient, so, less s%atter and %ontrastpatient, so, less s%atter and %ontrast

in%reases.in%reases.


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Exposure fa%tors may need to be %hanged 2henExposure fa%tors may need to be %hanged 2hen

in%reasing %ollimation. 8less density/ 1o, asin%reasing %ollimation. 8less density/ 1o, as

%ollimation in%reases 8smaller area/, density%ollimation in%reases 8smaller area/, densityde%reases, as %ollimation de%reases 8largerde%reases, as %ollimation de%reases 8larger

area/, density in%reases.area/, density in%reases.

hen %ollimating a lot you must in%reasehen %ollimating a lot you must in%rease

exposure to %ompensate for loss of density. Theexposure to %ompensate for loss of density. TheKVP should not be in%reased be%ause it resultsKVP should not be in%reased be%ause it results

in de%reased %ontrast. To %hange density only,in de%reased %ontrast. To %hange density only,

!1 should be %hanged.!1 should be %hanged.

#t is re%ommended 2ith a lot of %ollimation#t is re%ommended 2ith a lot of %ollimationre(uires an in%rease in as mu%h as )49 to 749re(uires an in%rease in as mu%h as )49 to 749

of the !1 to %ompensate for the loss of density.of the !1 to %ompensate for the loss of density.


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%ncreases Factor)%ncreases Factor) E$$ectE$$ect


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Purpose of using grids3Pur pose of using grids3&./ in%reases %ontrast&./ in%reases %ontrast

'./ redu%es density'./ redu%es density)./ must use more !1 2ith a grid)./ must use more !1 2ith a grid

The %hoi%e to use a grid depends on3The %hoi%e to use a grid depends on3&./ KVP used&./ KVP used'./ thi%+ness of part'./ thi%+ness of part

GridsGrids --#mprove %ontrast, using a grid re(uires additional#mprove %ontrast, using a grid re(uires additional

!1 resulting in a higher patient dose.!1 resulting in a higher patient dose.rids are typi%ally used only 2hen the patientrids are typi%ally used only 2hen the patientpart is &4 %m 8adult +nee siJe/or greater andpart is &4 %m 8adult +nee siJe/or greater and2hen using more than 54 KVP.2hen using more than 54 KVP.


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Air gap technique)Air gap technique)

This is li+e using a grid. "ess s%atter onThis is li+e using a grid. "ess s%atter on

film but also less detail. $ou %an in%reasefilm but also less detail. $ou %an in%rease

1#6 to help 2ith the detail. The greater the1#6 to help 2ith the detail. The greater the

gap the less s%atter.gap the less s%atter.

sing an in%reases G#6 is ne%essary forsing an in%reases G#6 is ne%essary for

the air gap te%h. Co2ever, this de%reasesthe air gap te%h. Co2ever, this de%reases

(uality. To de%rease unsharpness and(uality. To de%rease unsharpness andin%rease detail, you must in%rease 1#6.in%rease detail, you must in%rease 1#6.


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Accurate measurement o$ part thickness isAccurate measurement o$ part thickness is

critica to the e$$ective use o$ exposurecritica to the e$$ective use o$ exposure

technique chartstechnique charts..

T2o types of te%hni(ue %harts3T2o types of te%hni(ue %harts3

&./ Variable KVPfixed !1 &./ Variable KVPfixed !1

'./ Fixed KVPvariable !1 './ Fixed KVPvariable !1

&./ Variable KVPfixed !13 8Dest 2ith small&./ Variable KVPfixed !13 8Dest 2ith small

extremities/extremities/KVP in%reases as part siJe in%reases. DaselineKVP in%reases as part siJe in%reases. Daseline

KVP is in%reased by ' for every &%m in%rease inKVP is in%reased by ' for every &%m in%rease in

part thi%+ness, and !1 stays the same.part thi%+ness, and !1 stays the same.


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!%%urate measurement of part thi%+ness is %riti%al !%%urate measurement of part thi%+ness is %riti%al

to use this type of %hart.to use this type of %hart.

#n general %hanging the KVP for variations in part#n general %hanging the KVP for variations in partthi%+ness is ineffe%tive throughout the entire rangethi%+ness is ineffe%tive throughout the entire range

of x-rays. This +ind of %hart is most effe%tive 2ithof x-rays. This +ind of %hart is most effe%tive 2ith

small extremities su%h as hands and feet. !t lo2small extremities su%h as hands and feet. !t lo2

KVP levels, small %hanges in KVP may be moreKVP levels, small %hanges in KVP may be moreeffe%tive than %hanging the !1.effe%tive than %hanging the !1.


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*+, Fixed "#!variabe 'A(*+, Fixed "#!variabe 'A(

This uses an Gptimal KVP 2hi%h is theThis uses an Gptimal KVP 2hi%h is the

KVP value that is high enough to ensureKVP value that is high enough to ensure

penetration of the part but not too high topenetration of the part but not too high to

diminish x-ray %ontrast. Then the !1 isdiminish x-ray %ontrast. Then the !1 isvaried to the part thi%+ness.varied to the part thi%+ness.

#n general, for every @-7 %m %hange in part#n general, for every @-7 %m %hange in part

thi%+ness, the !1 should be adAusted bythi%+ness, the !1 should be adAusted bya fa%tor of '. 8double !1/a fa%tor of '. 8double !1/


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!%%urate measurement of part thi%+ness !%%urate measurement of part thi%+ness

is important but less %riti%al %ompared 2ithis important but less %riti%al %ompared 2ithvariable KVP.variable KVP.

!n advantage of using this %hart is that !n advantage of using this %hart is that

patient groups %an be formed around @-7patient groups %an be formed around @-7%m %hanges. $ou %an use patient%m %hanges. $ou %an use patient

thi%+ness groups. #t is easier thi%+ness groups. #t is easier

to use, more %onsisten%y on films,to use, more %onsisten%y on films,standardiJation of %ontrast.standardiJation of %ontrast.


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8&79 rule/ &44 KV up to &&7 KV =8&79 rule/ &44 KV up to &&7 KV =doubling !1doubling !1

To ma+e a visible %hange in density itTo ma+e a visible %hange in density itre(uires at least )49 %hange in !1 orre(uires at least )49 %hange in !1 or749.749.


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To maintain density 2ith KVP use &79To maintain density 2ith KVP use &79

rulerule

so &79 in%rease in KVP = doubling !1so &79 in%rease in KVP = doubling !1

maintains densitymaintains density

KVP ?' %hange to @ 8&79/ is same asKVP ?' %hange to @ 8&79/ is same as!1 &4 %hange to '4 8double/!1 &4 %hange to '4 8double/

For ea%h additional @%m thi%+ness youFor ea%h additional @%m thi%+ness youneed to double !1 to maintain density.need to double !1 to maintain density.


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&79 rule&79 rule

54 = 554 = 5

5' =>&.)5' =>&.)

57 = >@.>757 = >@.>75? = >?.'5? = >?.'

>4 = ?4.7>4 = ?4.7

>' = ?'.?>' = ?'.?>7 = ?5.'7>7 = ?5.'7

radiography technique - exposure factors (5)

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