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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.
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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