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Myth vs. Realityin Digital ImageQualityand SystemPerformanceSteve MangoWW Technical Manager
Carestream Health Inc.!DT Solutions
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The $%&#'&.() Question*
What do users +ant,
-r
What do users think they +ant,
-r
What do users need,
What is the real requirement??
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".
Is it/.
X Lp/mm resolution?
Nth duplex wire pair?
X Micron laser spot size?
X Micron pixel size?
20% MT o! X Lp/mm?
" ma#ic super duper $ &' (ma#in# )late?
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".0
"*
None o! those parameters +speci!ications,- .themsel es- can #uarantee a s stem will achie e theradiographic sensitivity required !or a particular
examination tas1
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".&
&ontrast 3N' MT
&N'
(ma#e 4ualit )erception
12ray Scatter
Scanner 3lare
12ray 45"osure
Scanner 6aser 45"
Imaging Plate7eg. Structure noise8
9ac:ground !oise
6aser 45"osureS"ot ;itter
6uminescent decay
4lectronic <and+idth
6aser S"ot Si=e
Imaging Plate
Scanner !oise
12ray 4nergy 7:>"8
P< Screen
Scanner?Screen gain
12ray 4nergy 7:>"8P< Screen
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Image Quality Perce"tion
".%
&ontrast 3N' MT
&N'
Tas1 .ased ima#e perception
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Contrast and !oise 3actors
".'
&ontrast 3N' MT
&N'
Tas1 .ased ima#e perception
12ray energy 7:>8
12ray scatter
P< screen
scanner flare
12ray e5"osure
Scanner?screen gain
Scanner laser e5"osure
Imaging "late7eg. Structure noise8
9ac:ground noise
Scanner noise
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Contrast and !oise 3actors
".)
&ontrast 3N' MT
&N'
Tas1 .ased ima#e perception
12ray energy 7:>8
12ray scatter
P< screen
scanner flare
12ray e5"osure
Scanner?screen gain
Scanner laser e5"osure
Imaging "late7eg. Structure noise8
9ac:ground noise
Scanner noisecan <e o"timi=ed <y
techni@ueA
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Modulation Transfer 3unction
It is customary to characteri=e s"atial resolution of systems using the MT3. TheMT3 re"resents the ma5imum a<ility of a system to transfer su<Bect contrast to thefinal image as a function of s"atial fre@uency.
".(
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45am"le System MT3 Com"onents
".
C # 0 &. C
.C
C
EP Screen F 6aser 45"osureG C. 5
System MT3 7 F !y@uist G #.(0C cy?mm 8
9eam 7d<GC µ m8
Screen 7hGC.08
Pream" 72 d<F #H!y@uist8 3ilter 72d<
F CH!y@uist8 Decay 7 of τ c
G&.C8 System
M T 3
S"atial 3re@uencyS"atial 3re@uency 7cycles?mm8
MT3
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The CR ReaderJs Role in System MT3
".
&ontrast 3N' MT
&N'
Tas1 .ased ima#e perception
6aser e5"osure
S"ot Bitter
6uminescent decay
4lectronic <and+idth6aser s"ot si=e
Imaging "late
12ray energy 7:>8
P< screen
can <e o"timi=ed <y <etterdesign choices or <y
o"timi=ation of scan "arameters
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Image Quality Perce"tion
". #
&ontrast 3N' MT
&N'
Tas1 .ased ima#e perception
6aser e5"osure
S"ot Bitter
6uminescent decay
4lectronic <and+idth6aser s"ot si=e
Imaging "late
12ray energy 7:>8
P< screen
can <e o"timi=ed <y design or o"timi=ation of thic:ness "hos"hor grain
si=e use of a<sor<er dyes etc.
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".
Imaging Plate MT3
KThe "resam"ling MT3 descri<es the system res"onse u" to <ut not includingthe stage of sam"ling. The figure <elo+ sho+s the "resam"ling MT3 curves for<oth imaging "lates.
KThe im"roved shar"ness of the I!DLSTR41 HR imaging "late comes from
smaller "hos"hor "articles and a thinner "hos"hor layer.
0
10
20
30
40
50
60
70
80
90
100
0 1 2 3 4 5 6
Spacial Frequency (cycles/mm)
Sharpness(MTF%)
HR imaging plates
GP imaging plates
" 0
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ey Contri<utors to CR Image Quality
6etJs ta:e a closer loo: at the effects of*
K 6aser "o+er
K S"ot si=e
K Pi5el si=e
K 45"osing energy
K 45"osure dose
". 0
" &
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". &
4ffect of laser "o+er
$i#her laser power penetrates deeper into thephosphor la er- de#radin# MT
Hi Po+er 6o+ Po+er
" %
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Imaging Plate MT3 as a function of 6aserPo+er
". %
S"atial 3re@uency 7cycles?mm8
MT3
" '
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6aser S"ot Si=e N What is it,
". '
O laser does not ma:ea "erfect s"ot +ith ashar"ly defined <oundary.
Instead it has a gaussiandistri<ution +ith highintensity in the center and
falling off gradually a+ayfrom the center.
3o- how is it measured or characterized?
0
500
1000
1500
2000
2500
3000
3500
4000
" )
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. )
Common S"ot Si=e Criteria
The t+o most common +ays of Characteri=ing s"ot si=e are*
5 ull Width $al! Max6
and
7/e 2
But there isNo standard!
" (
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. (
4ffect of laser s"ot si=e
" 2X impro ement in spot size does not ield a&orrespondin# 2X impro ement in ima#e qualit 8
microns"ot
& microns"ot
" #
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.#
45am"le Eaussian 9eam MT3s
# 0 % ) C.C
C
Eaussian 9eam Mtfs
M t f
S"atial 3re@uency cy?mmQ
&%.&µ micron (). µ micron Im"rovement 3actor
" #
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45am"le System MT3 Com"onents
.#
C # 0 &. C
.C
C
EP Screen F 6aser 45"osureG C. 5
System MT3 7 F !y@uist G #.(0C cy?mm 8
9eam 7d<GC µ m8
Screen 7hGC.08 Pream" 72
d<F #H!y@uist8
3ilter 72d<
F CH!y@uist8 Decay 7 of τ
cG&.C8
System
M T 3
S"atial 3re@uency
MT3
S"atial 3re@uency 7cycles?mm8
Im"roving the laser 9eam 7s"ot8 MT3
9y /
/ +ould im"rove theSystem MT3 <y
-nly
" ##
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.##
4ffect of "i5el si=e
6arge "i5el*3aster scan shorterd+ell time
Small "i5el*Slo+er scanlonger d+ell time
" smaller pixel can ha e acounterproducti e e!!ect on MT 8
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.#
4ffect of 45"osing 4nergy
Increasing :>
3 stem 9
3 stem X
3 stem :
Resol ution
With increasin# ener# - theper!ormance capa.ilities o!
arious &' s stems .e#in to5con er#e68
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The 4ffect of Dose
# # Carestream Health
Increasing DoseIncrea sing!oise
;lectronicnoise
X<'anoise
() 3tructurenoise
5Noise6 is impro ed withincreasin# dose
".#&
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S!R vs Pi5el >alue 7Dose8
Normalized 3N' s (N%=3T';X )ixel (ntensit/ +&>, !or "&' 2000iand $' (ma#in# )lates
D
#D
0D
%D
)D
CDD
C#D
C0D
C%D
C)D
#DD
D &DD CDDD C&DD #DDD #&DD
(N%=3T';X )ixel >alue +&>,
N o r m a
l i z e d 3 N ' () 7
() 2
() ?
() @() A() B
".#%
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O Simulation
An input targetcontaining2% contrastpatches
5% contrast bars
0 1 2 3 4 5 6 7 8 9 100
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Spatial Frequency [cy/mm]
M t f
System Mtfbased onh-value
0 1 2 3 4 5 6 7 8 9 100.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Spatial Frequency [cy/mm]
M t f
System Mtf basedon h-value
And two differentMTFs
LetCs illustrate a couple o! the pre ious pointsD +ith a simulation in +hich e5"osure
is varied using*
".#'
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The 4ffect of MT3
0 1 2 3 4 5 6 7 8 9 100
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
SpatialFrequency [cy/mm]
M t f
System Mtfbased onh-value
1 mr50 um pixelGain 10
1 mr50 um pixelGain 10
0 1 2 3 4 5 6 7 8 9 100.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
SpatialFrequency [cy/mm]
M t f
System Mtfbased onh-value
".#)
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The 4ffect of Dose
0 1 2 3 4 5 6 7 8 9 100
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Spatial Frequency [cy/mm]
M t f
SystemMtfbasedon h-value
10 mr50 umpixelGain !
0 1 2 3 4 5 6 7 8 9 100
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Spatial Frequency [cy/mm]
M t f
System Mtfbased on h-value
1 mr50 um pixelGain !
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O 3e+ Practical45am"les
".
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Ho+ Much Resolution is 4noughU,
CR Scan at ' Micron "i5el si=e
".
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MT3* 9e Careful What Vou Os: 3orA
Ty"ical HR Plate) Microns 9SR
S"ecial 9lueU Plate
% Microns 9SR
". #
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Ta:e a closer loo:*
HR Plate 9lueU "late
".
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S"ot si=e* not a <ig factor <y itself
& Micron Micron
##& :>" & micron "i5el .& mW :H=
Eoth laser spots produced similar results 8
". 0
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Pi5el Si=e* See any difference,
Eoth samplin# pitches produce similar results8
)' micron "i5el & micron "i5el
". &
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Onother e5am"le* .'& U 7 (mm8 3e "late
;ither pixel size meets the required sensiti it
'& micron s"ot' micron "i5el
'& micron s"ot& micron "i5el
". %
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The 9ottom 6ine*
&' System per!ormance is a !unction o! man competin# parameters Thereis no sin#le 5ma#ic .utton68
KCR system "erformance is a function of many "arameters.
K O num<er of these factors com"ete +ith each other and are traded off against each other.
On im"rovementU in one "arameter can degrade another resulting in degraded"erformance.
KThe radiogra"hic techni@ue is a critical com"onent in gaining @uality image out"ut.
K4ven a very im"ressive shar"ness 7MT38 +ill not result in a good image +ithout good C!Rand S!R.
". '
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Than: Vou
Man than1s to m collea#ues at&arestream $ealth !or their contri.utions tothis wor1*
Eo. Fulpins1iCarestream Health Inc.Research X Innovation 6a<s
Gacques 'oussilheCarestream Health 3rance!DT Solutions
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