rpdir-p18 qc for ct web
TRANSCRIPT
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IAEA
18: Optimization of protection in CT scanner 2
Contents
Quality control tests
CT accuracy, uniformity, linearity. an noise,
!o" an #i$# contrast resolution
%-axis sensiti&ity
'li$nment, ta(le top tra&el accuracy
)antry tilt measurement
*osimetry
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IAEAInternational Atomic Energy Agency
Part !"# O$timi%ation o& $rotection in CTscanner
Topic 1: Quality Control
IAEA Training Material on Radiation Protection in Diagnostic and Interentional Radiology
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18: Optimization of protection in CT scanner +
P'ysical $arameters o& CT image
ma$e uality
ay (e expresse in terms of p#ysical parameters suc#as uniformity, linearity, noise, spatial resolution, lo"
contrast resolution
ma$e uality epens on t#e tec#nical c#aracteristics oft#e CT scanner, t#e exposure factors use an ima$e
&ie"in$ conitions.
Quality may (e assesse (y uantitati&e measurementusin$ test p#antoms, an (y t#e appearance of artifacts.
easurements s#oul (e conucte re$ularly
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IAEA
18: Optimization of protection in CT scanner /
Scanner $er&ormance# tec'nical
$arameters (I)
Test P#antoms: Test p#antoms of a stanarize #uman s#ape
or test o(0ects of a particular s#ape, size an
structure, are use for t#e purposes ofcali(ration an e&aluation of t#e performancesof CT scanners
P#antoms s#oul allo" for e&aluation of CT
num(er uniformity noise spatial resolutionslice t#icness ose positionin$ of ta(le top
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IAEA
18: Optimization of protection in CT scanner 3
Scanner $er&ormance# tec'nical
$arameters (II)CT 4um(er 'ccuracy
CT num(er epens on tu(e &olta$e, filtration, o(0ect t#icness
CT num(er of "ater is (y efinition eual to 5
easure CT num(er s#oul (e 6 7 + 9 in t#e central O
CT 4um(er !inearity T#e linear relations#ip (et"een t#e calculate CT num(er an t#e linear
attenuation coefficient of eac# element of t#e o(0ect
*e&iations from linearity s#oul (e 6 7 / 9
CT 4um(er 9niformity T#e CT num(er of eac# pixel in t#e ima$e of an #omo$eneous o(0ect
s#oul (e t#e same o&er t#e ima$e area
T#e ifference in t#e CT num(er (et"een a perip#eral an a centralre$ion of an #omo$eneous test o(0ect s#oul (e 6 8 9
*ifferences are lar$ely ue to (eam #arenin$
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IAEA 18: Optimization of protection in CT scanner ;
4oise T#e local statistical fluctuation
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IAEA 18: Optimization of protection in CT scanner 8
Scanner $er&ormance# tec'nical
$arameters (IV)
@patial esolution
T#e #i$# contrast resolutionetermines t#e minimumsize of etails &isualize in t#e plane of t#e slice "it# a
contrast A15>.
t is affecte (y:
t#e reconstruction al$orit#m
t#e etector "it#
t#e effecti&e slice t#icness
t#e o(0ect to etector istance
t#e x-ray tu(e focal spot size
t#e matrix size.
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IAEA 18: Optimization of protection in CT scanner B
Scanner $er&ormance# tec'nical
$arameters (V)
@patial esolution
T#e lo" contrast resolutionetermines t#e sizeof etail t#at can (e &isi(ly reprouce "#en
t#ere is only a small ifference in ensity relati&eto t#e surrounin$ area
!o" contrast resolution is limite (y noise.
T#e perception t#res#ol in relation to contrast anetail size can (e etermine (y creatin$ contrast-
etail cur&e.
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IAEA 18: Optimization of protection in CT scanner 15
Scanner $er&ormance# tec'nical
$arameters (VI)
@lice T#icness
T#e slice t#icness is etermine int#e center of t#e fiel of &ie" as t#e
istance (et"een t#e t"o points on
t#e sensiti&ity profile alon$ t#e axis
of rotation at "#ic# response #as
fallen to /5>.
T#e use of post-patient collimationto reuce t#e "it# of t#e ima$e
slice leas to &ery si$nificant
increasesin t#e patient ose
Positionin$ of couc#
T#e accuracy of positionin$ of t#epatient couc# is e&aluate (y
mo&in$ t#e loae couc# a efine
istance an mo&in$ it (ac to t#e
start position
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IAEA 18: Optimization of protection in CT scanner 11
Minim*m re+*irements# CT scanner (I)
ma$e noiseT#e @tanar *e&iation of CT num(ers in t#e central /55mm2O for a "ater or tissue eui&alent p#antom s#oulnot e&iate more t#an 25> from t#e (aseline.
CT num(er &alues
T#e e&iation in t#e CT num(er &alues for "ater or tissueeui&alent material an materials of ifferent ensitiess#oul 67 25 9 or />.
CT num(er uniformity
T#e @* of t#e CT num(er o&er a /55 mm2
re$ion ofinterest for "ater or tissue eui&alent material at t#e centeran at t#e perip#ery of p#antom s#oul &ary (y less t#an1./> of t#e (aseline
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Minim*m re+*irements# CT scanner
(II)
Compute tomo$rap#y ose inex
from t#e (aseline.
rraiate slice t#icness
T#e D of t#e ose profile s#oul not iffer more t#an 7 25> from(aseline.
i$# contrast resolution from (aseline.
!o" contrast resolution
Polystyrene pins of 5.E/ cm iameter inserte in a uniform (oy "ater
p#antom s#oul (e &isi(le in t#e ima$e.
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IAEAInternational Atomic Energy Agency
Part !"# O$timi%ation o& $rotection in CTscanner
Topic 2: 4oise
IAEA Training Material on Radiation Protection in Diagnostic and Interentional Radiology
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IAEA 18: Optimization of protection in CT scanner 1+
Imaging $er&ormance (Noise)
4oise is assesse usin$ cylinricalp#antoms, "#ic# are eit#er fille "it# "ateror mae of a tissue eui&alent material
Once an axial ima$e of t#e p#antom #as
(een acuire, noise is measures as t#e
stanar e&iation in CT num(er in a re$ionof interest
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e$ion ofe$ion ofinterestinterest
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IAEA 18: Optimization of protection in CT scanner 13
Imaging $er&ormance (Noise)
4oise &alues are $i&en in manufacturersFspecifications are uote for a specific p#antom
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IAEA 18: Optimization of protection in CT scanner 1;
Imaging $er&ormance (Noise)
Gaseline noise &alues s#oul (e o(tainefor se&eralscan protocols t#at "ill (e useclinically, usin$ t#e routine QC noise
p#antom
To ensure t#at noise fi$ures are (ot#
accurate an representati&e, it is essential tofin t#e mean &alue from se&eral scans
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IAEAInternational Atomic Energy Agency
Part !"# O$timi%ation o& $rotection in CTscanner
Topic E: CT uniformity an linearity
IAEA Training Material on Radiation Protection in Diagnostic and Interentional Radiology
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IAEA 18: Optimization of protection in CT scanner 1B
CT n*m,er *ni&ormity
CT num(er uniformity can (e assesse at t#esame time as measurin$ noise, (y placin$ fouraitional O
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IAEA 18: Optimization of protection in CT scanner 25
'xial ima$e of'xial ima$e of
a #omo$enousa #omo$enous
p#antomp#antom
CT n*m,er *ni&ormity
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IAEA 18: Optimization of protection in CT scanner 21
CT n*m,er *ni&ormity
CT num(er linearity is assesse usin$ ap#antom containin$ inserts of a num(er ofifferent materials
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CT n*m,er *ni&ormity
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IAEAInternational Atomic Energy Agency
Part !"# O$timi%ation o& $rotection in CTscanner
Topic +: !o" an #i$# contrast resolution
IAEA Training Material on Radiation Protection in Diagnostic and Interentional Radiology
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IAEA 18: Optimization of protection in CT scanner 2+
Lo- contrast resol*tion
!o" contrast resolution
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IAEA 18: Optimization of protection in CT scanner 2/
TypicalTypicalima$e of t#eima$e of t#e
Catp#an !CCatp#an !C
insertinsert
Lo- contrast resol*tion
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IAEA 18: Optimization of protection in CT scanner 23
S$atial resol*tion ('ig' contrast)
T#ere exist t"o (roa cate$ories of measurin$tec#niues : analysis of t#e point sprea function, usually (y
calculation of t#e moulation transfer function
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IAEA 18: Optimization of protection in CT scanner 2;
S$atial resol*tion ('ig' contrast)
T#e num(er of linepairs per cm 0ust&isi(le in t#e ima$e isapproximately
eui&alent to t#e 2>&alue of t#e T
T#is result can t#en (ecompare "it# t#e 2>
T, as uote in t#emanufacturerFsspecifications
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IAEAInternational Atomic Energy Agency
Part !"# O$timi%ation o& $rotection in CTscanner
Topic /: %-axis sensiti&ity
IAEA Training Material on Radiation Protection in Diagnostic and Interentional Radiology
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IAEA 18: Optimization of protection in CT scanner 2B
./Sensitiity (Imaged slice -idt')
'xial measurements
P#antoms use for axial measurements may containt#in metal plates, "ires or arrays of air #oles, incline atan an$le to t#e ima$e plane
anufacturers s#oul (e a(le to supply an appropriatep#antom or, alternati&ely, t#e Catp#an contains an insertsuita(le for t#is test
4ote:to o(tain meanin$ful measurements, t#e t#icnessof t#e plates, "ires or #oles cannot (e $reater t#an t#e
nominal slice "it# concerne. T#is may createpro(lems for t#e su(-millimetre slice "it#s offere onmulti-slice scanners.
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IAEA 18: Optimization of protection in CT scanner E5
./Sensitiity (Imaged slice -idt')
'xial measurements
P#antoms manufacturers may uote t#e tolerancefor eac# nominal slice "it# settin$ in t#eirspecification ocumentation
%-sensiti&ity measurements in axial moe can (euse to c#ec t#at ima$e slice "it#s are "it#int#e tolerances $i&en
T#is can also (e use in con0unction "it# irraiateslice "it# measurements to assess t#e accuracy ofpost patient collimation an to calculate t#e$eometric efficiency for t#e scanner
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IAEA 18: Optimization of protection in CT scanner E1
Plan &ie" of a test o(0ect use to measure ima$e
slice "it#s for axial scans
./Sensitiity (Imaged slice -idt')
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IAEAInternational Atomic Energy Agency
Part !"# O$timi%ation o& $rotection in CTscanner
Topic 3: 'li$nment
IAEA Training Material on Radiation Protection in Diagnostic and Interentional Radiology
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IAEA 18: Optimization of protection in CT scanner EE
Alignment o& indicating lig'ts -it'
scan0 coronal and sagittal $lanes
@e&eral met#os can(e use to perform
t#ese tests
T#e tec#niuesescri(e #ere are
strai$#tfor"ar to
implement an reuire
minimal testeuipment.
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IAEA 18: Optimization of protection in CT scanner E+
Agreement ,et-een internal and
e1ternal scan $lane lig'ts
9se an en&elope-"rappe film
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Co/incidence o& internal scan $lane
lig'ts and scan $lane
Pin prics are mae in a piece of t#erapy&erification film
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IAEA 18: Optimization of protection in CT scanner E3
Co/incidence o& internal scan $lane
lig'ts and scan $lane
or multi-slice scanners, pin prics
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IAEA 18: Optimization of protection in CT scanner E;
%
M
Pin $ric2s made in
&ilm at $osition o&
scan $lane lig't
3/ray ,eam
e1$os*re
Co/incidence o& internal scan $lane
lig'ts and scan $lane
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IAEA 18: Optimization of protection in CT scanner E8
Coronal and Sagital $lane lig'ts
' lon$, t#in o(0ect, "it# a #i$# CT num(er relati&e toair, suc# as t#e NleaF in a pencil or a strai$#tenepaper clip, can (e use as a marer to perform t#istest
T#e marer is supporte a(o&e t#e patient ta(le anali$ne, usin$ t#e inicatin$ li$#ts, so t#at it ispositione at t#e isocentre, parallel to t#e z-axis anperpenicular to t#e scan plane
f inicatin$ li$#ts are accurately ali$ne to t#e coronal
an sa$ital planes, t#e marer s#oul appear as a otat exactly x 5, y 5 on t#e axial ima$e.
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IAEAInternational Atomic Energy Agency
Part !"# O$timi%ation o& $rotection in CTscanner
Topic ;: Ta(le tra&el accuracy
IAEA Training Material on Radiation Protection in Diagnostic and Interentional Radiology
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IAEA 18: Optimization of protection in CT scanner +5
Ta,le trael acc*racy
' ruler or tape measure place alon$sie t#e ta(le,can (e use to c#ec t#at t#e amount of ta(le
mo&ement inicate on t#e $antry a$rees "it# t#e
actual istance mo&e.
' loa of approximately ;5- 85 $ s#oul (eplace on t#e ta(le in orer to simulate t#e "ei$#t
of a patient.
T#e test s#oul (e performe t"ice: (y ri&in$ t#eta(le top (ot# a"ay from an to"ars t#e $antry.
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IAEA 18: Optimization of protection in CT scanner +1
Assessment o& distance indicator acc*racy
Ta,le trael acc*racy
A i l i i
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IAEA 18: Optimization of protection in CT scanner +2
A1ial scan incrementation acc*racy
erification of incrementation accuracy (et"eensuccessi&e axial slices can (e ac#ie&e (y placin$
t#erapy &erification film on t#e couc#
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IAEA 18: Optimization of protection in CT scanner +E
Ta,le trael acc*racy &or 'elical scans
n #elical scannin$, it is not sufficient to use a simplemec#anical test (ecause t#e istance ima$e epens oncouc# spee an scanner soft"are
One met#o of assessin$ istance accuracy is to use an
acrylic test o(0ect containin$ t"o small raio-opauemarers, separate (y a fixe istance
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IAEA 18: Optimization of protection in CT scanner ++
Co*c' trael acc*racy &or 'elical
scans
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IAEAInternational Atomic Energy Agency
Part !"# O$timi%ation o& $rotection in CTscanner
Topic 8: )antry tilt measurement
IAEA Training Material on Radiation Protection in Diagnostic and Interentional Radiology
G t Tilt
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IAEA 18: Optimization of protection in CT scanner +3
Gantry Tilt
T#e accuracy of isplaye $antry tilt can (eassesse (y supportin$ t#erapy &erification
film at t#e $antry en of t#e patient ta(le
T#e film must (e #el &ertically
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Gantry Tilt
T#ree axial exposures are mae usin$ t#e samefilm:
one for t#e maximum superior $antry tilt,
one for t#e maximum inferior $antry tilt
one at 5 $antry tilt
T#e t#ree scan planes s#oul t#en (e &isi(le ont#e e&elope film
T#e an$les Jan -(et"een scan planes atmaximum tilt relati&e to t#at at 5 tilt s#oul eual
tilt an$les isplaye on t#e $antry.
A t & & t tilt
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IAEA 18: Optimization of protection in CT scanner +8
Assessment o& acc*racy o& gantry tilt
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IAEAInternational Atomic Energy Agency
Part !"# O$timi%ation o& $rotection in CTscanner
Topic B: *osimetry
IAEA Training Material on Radiation Protection in Diagnostic and Interentional Radiology
D i t CTDI i i
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IAEA 18: Optimization of protection in CT scanner /5
Dosimetry / CTDI in air
T#e Compute Tomo$rap#y *ose nex
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IAEA 18: Optimization of protection in CT scanner /1
Ioni%ationc'am,er
Ta,le
Dosimetry / CTDI in air
Dosimetry CTDI in air
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IAEA 18: Optimization of protection in CT scanner /2
Dosimetry / CTDI in air
t is important to measure t#e CT* in airuner t#e follo"in$ conitions D#en
commissionin$ a CT scanner:
or all (eam s#apin$ filters or all nominal slice "it#s
or all clinical settin$s
or a ran$e of scan times or a ran$e of m' settin$s
Dosimetry CTDI in air
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Dosimetry / CTDI in air
Dosimetry CTDI in air
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Dosimetry / CTDI in air
Dosimetry CTDI in air ('elical)
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'xial slice positions'xial slice positions
elical scan
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IAEA 18: Optimization of protection in CT scanner /3
Dosimetry / CTDI in Acrylic P'antoms
T#e (oy p#antom is place on t#e patient ta(lean t#e #ea p#antom is supporte in t#e #ea
rest
P#antoms are ali$ne an centre at t#e scanisocentre
T#e ion c#am(er is inserte into eit#er t#e centralor one of t#e perip#eral #oles of t#e p#antom
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IAEA 18: Optimization of protection in CT scanner /;
Dosimetry / CTDI in Acrylic P'antoms
*ose measurements at t#e center are use tocalculate t#e central CT*
Perip#eral CT* is measure in at least four
positions aroun t#e p#antom, so as to ac#ie&e atrue a&era$e
4ote:f $antry rotation is initiate from ifferent
an$ular positions for successi&e scans it may (e
necessary to tae a num(er of measurements ateac# position in orer to $et a representati&e mean
ose
Dosimetry / CTDI in Pers$e1
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4ead $'antom4ead $'antom5ody $'antom5ody $'antom (or ann*l*s(or ann*l*s
to &it oer 'ead $'antom)to &it oer 'ead $'antom)
Insert to $l*g 'olesInsert to $l*g 'oles
Dosimetry / CTDI in Pers$e1
P'antoms
Dosimetry / CTDI in Pers$e1
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IAEA 18: Optimization of protection in CT scanner /B
Central an perip#eral CT*Fs are use tocalculate "ei$#te CT*, CT*":
CT*"
s can (e compare a$ainst ia$nosticreference le&els for stanar scan
examinations
Dosimetry / CTDI in Pers$e1
P'antoms
)( CTDI32+CTDI31C1=CTDI p100,c100,wn
E1am$le o& CTDI Val*es &or some CT
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IAEA 18: Optimization of protection in CT scanner 35
E1am$le o& CTDI Val*es &or some CT
*nitsMODEL 6V 7AD S nCDTI (mGy8mAs)
Air -eig'ted4ead 5ody
Siemens4I9
!:: ;
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IAEA 18: Optimization of protection in CT scanner 31
Dose Pro&iles (Irradiated slice -idt')
easurement of irraiate slice "it#s, for allnominal slice "it#settin$s, pro&ies a irect testof pre-patient (eam collimationan allo"s$eometric efficiencies to (e calculate for t#e
scanner )eometric efficiency
Dose Pro&iles (Irradiated slice -idt')
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IAEA 18: Optimization of protection in CT scanner 32
Dose Pro&iles (Irradiated slice -idt')
irst met#o : expose t#erapy &erification film, supporte inair at t#e isocentre, at eac# of t#e slice "it# settin$s
Once e&elope, optical ensity profiles may (e plotteusin$ a i$itizer or t#e "it# measure usin$ a ruler
To pro&ie an accurate ose profile, a cali(ration cur&e can(e applie to con&ert optical ensity profiles into ose
profiles, from "#ic# irraiate slice "it#s
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IAEA 18: Optimization of protection in CT scanner 3E
Meas*rement o&Meas*rement o&irradiated sliceirradiated slice
-idt's &or a range-idt's &or a range
o& nominal sliceo& nominal slice
-idt' settings-idt' settings
Dose Pro&iles (Irradiated slice -idt')
9*ality control $rogram
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9*ality control $rogram
E1am$le o& a +*ality control $rogram &or a CT *nit#
Gaseline 7 25>1 yGi$# contrast resolution
A 7 25> or 1 mm1 yGma$e slice t#icness
A 7 25> or 1 mm1 yGrraiate slice t#icness
Gaseline 7 25>1 y'CT*
A 7 1./>1 yGCT num(er uniformity
Dater: 7 15 9
Ot#er materials 7 25 9
Rmore scansKparameters
*KD
1 IR
'
G
CT num(er &alues
Gaseline 7 25>
Rmore scansKparameters
*KD
1 yR
'
G
ma$e noise
emeial le&elPriorityreuency!e&el ofexpertise
P#ysical parameter