weekchapter 18,19 radio graph exposure

7/25/2019 WeekChapter 18,19 Radio Graph Exposure

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Chapter 18 Radiographic Exposure

Exposure Factors influence and determine

the quantity and quality of the x-radiation

to which the patient is exposed.

Radiation quantity refers to the radiation

intensity referred to as mR or mR m!s.

Radiation "uality refers to the #eam

penetra#ility and measured in $%&.


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Radiographic Exposure

'he radiographic exposure factors are

under the control of the operator except for

those fixed #y the design of the x-ray

machine.

'here are two choices for focal spot.

(ith the exception of compensating filters)

added filtration is fixed.

'he type of high *oltage power is also fixed.


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Exposure Factors Controlled #y

the +perator ,%p

m! times Exposure 'ime m!s

etermines the quality and quantity of theexposure

/0) Focal /pot and Filtration are

secondary factors


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,%p

!s we ha*e discussed in the la#oratory)

,%p controls radiographic contrast.

,%p determines the a#ility for the #eam topenetrate the tissue.

,%p has more effectthan any other factor

on image receptor exposure #ecause it

affects #eam quality.


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,%p

2 ,% 345 is photoelectric) 615 Compton) 7 15no interaction

82 ,%p 95 is photoelectric) 65 Compton 65

no interaction 112 ,%p 6:5 photoelectric) 325 Compton) 35

no interaction

!s no interaction increases) less exposure is

needed to produce the image so patientexposure is decreased.


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m!

1 !mpere 1 Cs 9.: x 1218electrons second.

'he m! selected for the exposure determines

the num#er of x-rays produced.

'he num#er of x-rays are directly proportional tothe m! assuming a fixed exposure time.

122 m! produced half the x-ray that 622 m!

would produce.


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m!

;atient dose is also directly proportional to

the m! with a fixed exposure time.

! change in m! does not affect ,ineticenergy of the electrons therefore only the

quantity is changed.


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m!


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m!

eneral Electric


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Exposure 'ime

'he exposure time is generally always

,ept as short as possi#le.

'his is not to reduce patient exposure #ut

to minimi?e motion #lur resulting from

patient mo*ement.

'his is a much greater pro#lem with

weight #earing radiography.


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Exposure 'ime

+lder machine express time as a fraction.

@ewer machines express exposure time

as milliseconds AmsB

0t is easy to identify the type of high

*oltage generation #y loo,ing at the

shortest exposure time.


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Exposure 'ime

/ingle phase half wa*e rectified fasted

exposure time is 192 second 13 ms.

/ingle phase full wa*e rectified fastest

exposure time is 1162 second or 8 ms

'hree phase and high frequency can

pro*ide exposure time down to 1 ms.


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m!s

m! and exposure time is usually

com#ined and used as one factor

expressed as m!s.

m!s controls radiation quantity) optical

density and patient dose.

m!s determine the num#er of x-rays in the

#eam and therefore radiation quantity.

m!s does not influence radiation quality.


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m!s

!ny com#ination of m! and time that will

gi*e the same m!s should pro*ide the

same optical density on the film. 'his is

referred to as the reciprocity law.

!s noted earlier for screen film

radiography) 1 ms exposure and exposure

longer than 1 seconds do not follow thisrule.


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m!s

+n many modern machines) only m!s can

#e selected. 'he machine automatically

gi*es the operator the highest m! and

shortest exposure time.

'he operator may #e a#le to select m! #y

what is referred to as ;ower le*el.


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m!s

0f we ,now the mRm!s) multiply that

figure times the m!s. or

0f we ,now the mR for a gi*en exposure

at a gi*en ,%p) we can di*ide the

exposure #y the m!s to get the mR m!s.

'o compute exposure we need to ,now

what the mRm!s is for the ,%p used and

the /0.


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istance

istance affects the exposure of the

image receptor according to the in*erse

square law.

istance affects the intensity of the x-ray

#eam at the film #ut has no effect on

radiation quality.


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0n*erse /quare &aw

m!s Asecond exposureB /066nd

exposure

---------------------------- -------------------------

m!s Afirst exposureB /061st exposure


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istance

'he most common source to image

distances are 2D A122 cmB and 36DA186

cmB

/ince /0 does not impact the quality of

the #eam) adustments to the technical

factors are made with the m!s.

'o go from 2D to 36D increase the m!s

:. time.


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istance

0ncreasing the distance will impact the

geometric properties of the #eam.

0ncreased /0 reduces magnification

distortion and focal spot #lur.

(ith the need to increase the m!s :.

times for the 36D /0) tu#e loading

#ecomes a concern.


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istance

36D /0 is used for Chest radiography and

the lateral cer*ical spine to reduce

magnification.

36D /0 used for the full spine to get a :9D

#eam.


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0maging /ystem Characteristics

+perator has limited control.

'he following will impact the technical

factors #ased upon the type of machine.

Focal /pot /i?e

Filtration

$igh-*oltage >eneration


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Focal /pot /i?e


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Focal /pot /i?e

'he focal spot si?e limits the tu#es

capacity to produce x-rays. 'he electrons

and resulting heat are placed on a smaller

portion of the x-ray tu#e.

'he m! is therefore limited for the small

focal spot. 'his results in longer exposure

times with greater chance of patientmo*ement.


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Focal /pot /i?e

For single phase machines) the small focal

spot use is limited to extremities and the

cer*ical spine.

(ith high frequency) most *iews can #e

done on the small focal spot except for

larger patient and ones that cannot hold

still.


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Focal /pot /i?e

0f the m! is properly cali#rated) the focal

spot will ha*e no impact on the quantity or

quality of the #eam.


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Filtration

!ll x-ray #eams are affected #y the

filtration of the tu#e. 'he tu#e housing

pro*ides a#out 2. mm of filtration.

!dditional filtration is added in the

collimator to meet the 6. mm of

aluminum minimum filtration required #y

law.

6. mm is required for 32 ,%p.


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Filtration

:.2 mm is required for at 122 ,%p.

:.6 mm is required for operations at 162

,%p.


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Filtration

Chiropractic radiography is a leader in the

use of compensating filters. (e ha*e total

control o*er compensating filtration.

0n areas of the #ody with high su#ect

contrast or wide differences in density)

compensating films impro*e image quality

and reduce patient exposure.


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$igh-*oltage >eneration

Gou will determine the type of high-*oltage

generation when you purchase your x-ray

machine.

'he type of generator will determine the

efficiency of the generator or the amount

of ripple in the wa*e form.

/ingle phase has 1225 ripple.


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'hree ;hase >eneration

'hree phase has a 15 so it is significant

impro*ement in efficiency increasing #oth

quality and quantity of the #eam.


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$igh Frequency >eneration

%irtually no ripple A less than 15.B

0nexpensi*e and can use normal incoming

power.

;ro*ides significant reduction is m!s or

,%p compared to single phase. Reduction

of m!s #y 25 compared to single phase

techniques.


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Chapter 14 Radiographic

"uality Radiographic "uality refers to the fidelity

with which the anatomic structures #eing

examined are images on the film.

'hree main factorsH

Film Factors

>eometric Factors

/u#ect Factors


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Radiographic "uality

Characteristic of radiographic qualityH

/patial Resolution ARecorded etailB

Contrast Resolution A%isi#ility of etailB

@oise A%isi#ility of etailB

!rtifacts


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/patial Resolution

/patial Resolution is the a#ility to image

small structures that ha*e high su#ect

contrast such as #one-soft tissue

interface.

(hen all of the factors are correct)

con*entional radiography has excellent

spatial resolution.


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Contrast Resolution

Contrast resolution is the a#ility to

distinguish structures with similar su#ect

contrast such as li*er-spleen) fat-muscle.

Computed tomography and


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Film >raininess

Film graininess refers to the distri#ution in

si?e and space of the sil*er halide grains

in the film emulsion.

/imilar to photographic film. 22 !/! film

is more graininess than 122 !/! film.

/imilar to structure mottlethat refers to

the si?e and shape of the phosphors in the

intensifying screens.


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"uantum


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"uantum


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/peed

Resolution and noise are intimately

connected with speed.

(hile the speed of the images receptor is

not apparent on the image) it influences

#oth resolution and noise.


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Radiographic "uality Rules

Fast 0mage receptors ha*e high noise and

low spatial and contrast resolution.

$igh spatial and contrast resolution

require low noise and slow image

receptors.

&ow noise accompanies slow image

receptors with high spatial and contrast

resolution.


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Film Factors of "uality

Characteristic cur*e

ensity

Contrast

&atitude

;rocessing

'ime

'emperature


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/ensitometry

/ensitometry is the study of the

relationship #etween the intensity of

exposure of the film and the #lac,ness

after the film is processed.

=nexposed film is clear with a #lue tint

after processing.

Exposed film is #lac, after processing.


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/ensitometry

'wo principles in*ol*ed.

Exposure of the film

!mount of light transmitted through the

processed film of optical density.

=sed to descri#e the relationship of

radiation exposure and #lac,ness or

density on the film.


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Characteristic Cur*e

'his relationship is

called the

characteristic cur*e or

$ I cur*e of thefilm.

$ I stands for

$urter and riffield.

; t f th Ch t i ti


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;arts of the Characteristic

Cur*e Toeand shoulder

where large changes

in exposure results in

small changes in +. %ery high and *ery

low *ariations of

exposure ma,e *ery

small changes indensity.

; t f th Ch t i ti


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;arts of the Characteristic

Cur*e 'he straight line or

intermediate area is

where *ery small

changes in exposureresults in large

changes in density.

'his is the important

part of the cur*e inradiography.


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&og Relati*e Exposure A&REB

J-ray films responds

to a wide range of

exposure from 1 mR

to 1222 mR. Exposure is

represented on

logarithmic manner.


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+ptical ensity Range

'he optical density

range is from 2.2 for

no density to .2 for

a#solute #lac,. =seful range in

general radiography

is from 2. to 6.6.

0mage range is 2. to

1.6 +


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Kase fog or #ase density

'he tint of the #ase of

the film and the

inad*ertent exposure

of the duringprocessing.

Range is from 2.1 to

2.:. /hould #e ne*er

a#o*e 2.:2 most is .61 +


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0tems that 0mpact Kase Fog

Film storage

Film exposure to wrong spectrum of light

or light intensity.

Chemical contamination.

0mproper processing.

$igh Kase fog le*els reduce contrast.


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Contrast

Radiographic Contrast is the com#ined

result of image receptor contrastand

subject contrast.

Image receptor contrastrefers to the

contrast inherent in the film and influenced

#y the processing of the film.


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Contrast

/u#ect contrast is determined #y the si?e)

shape and x-ray attenuating

characteristics of the su#ect #eing

examined and the energy A,%pB of the x-ray #eam.


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0mage Receptor Contrast

0nherent to the film and screen

com#ination #ut is influenced #yH

Range of +ptical ensity

Film ;rocessing 'echnique

Film type is determined #y the type of

intensifying screens used #ut many

dealers sell off #rands of film.


58/70

0mage Receptor Contrast

'he slope of the

straight line portion of

the $ I cur*e is the

receptor contrast. 'he a*erage gradient

is a straight line

drawn #etween the

densities of 2.6 and6.22 L #ase fog.


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!*erage >radient

'he a*erage gradient

is a straight line

drawn #etween 2.6

+ and 6.2 +a#o*e #ase plus fog.

'his is the normal

range of density in a

radiograph


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/peed

/peed is the a#ility of

the receptor to

respond to low x-ray

exposure. 'he $ I curse is

useful in comparing

speed when selecting

film or screens.


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/peed

! relati*e num#er of 122 gi*en to ;ar

/peed Calcium 'ungstate /creens.

$igh /peed Calcium 'ungstate has a

speed of 622. $alf of the exposure is

needed to produce the same image.

Rare earth screen film com#inations range

is speed from 82 to 1922.


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/peed

Ky ,nowing the /peed) sometimes

referred to as the Relati*e /peed %alue) it

is easy to con*ert the technical factors for

one speed to another speed.


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&!'0'=E

&atitude can #e

o#ser*ed on the $ I

cur*e.

&atitude refers to therange of exposure

that will produce a

diagnostic range +.


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&atitude

&atitude and Contrast

are in*ersely

proportional.

(ide latitude has awide gray scale or low

contrast. AKB

@arrow latitude has a

short scale or highcontrast. A!B


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&atitude

&atitude is designed into some screen and

film com#inations. (ith wide latitude) the

error factor in technique is wider.

&atitude can also #e impacted #y the

technical factors.


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Film ;rocessing

Radiographic "uality

is impacted #y film

processing

parameters. 'he de*eloper must

#e at the proper

concentration and at

the correcttemperature.


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Film ;rocessing

'he film must also

spend the correct

amount of time in the

de*eloper. This is the time &

temperature

relationship.


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;rocessing

/peed and #ase fog increase with the

temperature.

Contrast will increase to a point and then

drop with the #ase fog increase.


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;rocessing

0n 4th "uarter we will discuss processor

quality control in detail.


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End of &ecture

weekchapter 18,19 radio graph exposure

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