ewert wcndt standards 2012 04
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Outline
- New standards on Computed Radiography and radiography with DigitalDetector Arrays have been developed and partly published.
- Some key requirements are discussed for the major standard organizations:
ASME, ASTM, EN ISO.
- The proof of minimum image quality by image quality indicators in radiographyis the basis for technical safet and contractual a reements in industr and willnot be changed.
- The essential parameters for optimization and prediction of step hole visibility.
- Three essential parameters for image quality in Digital Radiology (DR) are:
- Signal to noise ratio (SNR)- pec c con ras eff- Basic spatial resolution (SRb).
- Discussion of the requirements for detector qualification and selection.- Information on the implementation of the essential parameter concept in the new
standard practice EN ISO/DIS 17636-2: NDT of welds RT Part 2: X- andgamma ray techniques with digital detectorsand in the ASTM E 2033 (draft: CR
April 2012,
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practice) and E 2597 (DDA qualification) and E 2698 (DDA practice).
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Overview of Standards on Digital Industrial Radiology
EN 14096, ISO 14096 Film Digitization
EN 14784 CR 2005 Part 1: Classification of S stems, Part 2: General
Goes to ISO, revision required principles, becomes ISO 16371
ISO 10893-7 (2010) Steel tubes NDT of welds with DDA and (CR)New ISO/DIS 17636-2 NDT of welds: CR and DDA to substitute EN 1435
New ISO draft: corrosion and
wall thickness measurement
Practice with film, CR and DDA for double wall and
tan ential techni ue
ASME (BPVC, S.V, XI) CR Radiography (CR) with Phosphor Imaging Plates
ASTM CR (2005) Classification (E 2446-05), Long term stability (E2445-Revision required 05), Guide (E 2007-10), Practice (E 2033-06)
ASTM DDA (2010) Characterization (E 2597-07), Guide (E 2736-10),Practice E 2698-10 Lon Term Stabilit E 2737-10
ASTM DICONDE (2010)
(data format)
Standard Practice for Digital Imaging and Communication
Non-destructive Evaluation (DICONDE)
April 2012,
Ewert et al. Standards in Digital Radiology
- , - , - , - , -
ASTM E 2422-05, E 2660-
10, E 2669-10Digital reference image catalogues,
light alloy, titanium and steel castings
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Basic Requirements for Film Radiography
in all National and International Standards
All film based standards require: Minimum optical Density (e.g. D > 2.0)
ax mum m sys em c ass e.g. Maximum unshar ness < 0.1 mm FFD/FOD
Minimum IQI perception (e.g. > W14, < H3)What are the correct requirements for film replacement by
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ASME BPVC Section V (NDE)
Mandatory Appendices
I In-Motion Radiography
II Real-Time Radioscopic Examination
III Digital Image Acquisition, Display, and Storage for Radiography and Radioscopy
IV Interpretation, Evaluation, and Disposition of Radiographic and Radioscopic Examination
Test Results Produced by the Digital Image Acquisition and Display ProcessV Glossary of Terms for Radiographic Examination
VI Digital Image Acquisition, Display, Interpretation, and Storage of Radiographs forNuclear Applications
VII Radiographic Examination of Metallic Castings
VIII Radio ra h Usin Phos hor Ima in Plate
IX Application of Digital Radiography
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ASME Section V Article 2 Radiographic Examination 2007
W 13
W 12
W 11
W 10
W 09
W 08W 07
W 06
W 05
W 04
W 02
W 01
CEN wires
ASME requires basically the
April 2012,
Ewert et al. Standards in Digital Radiologyminimum IQI-Visibility for digital radiography only!
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Basic Requirements for IQI Visibility of
y = 17,687x-0,483 Ste Holes ISO/DIS 17636-2 EN 1435y = 15,711x-0,48
y = 11,112x-0,505
n[%
]Plate Holes,ASMEBPVC SC V Ar. 2
Plate Holes,ASTME 1742, E 2104,
3,00R
esoluti
hicknes
, . ,
EN 1435-class A andISO 17636-class A are
about equivalent
y = 5,851x-0,402
y = 4,2561x-0,406
Wall
ASTM E1742, E 2104,
EN 1435-class B and
-
0,30
1,00 10,00 100,00
res 7 - , 5
about equivalent below
t=12 mm (1/2)
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Influence of Image Noise on
etail Visibilityetail Visibility
Intensity
Contrast
Signal Intensity
Contrast
Signal
Length
Length
Notch visible!
Contrast/Noise is high
Notch not visible!
Contrast/Noise is low
April 2012,
Ewert et al. Standards in Digital RadiologySignal/Noise is high Signal/Noise is low
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Effect of System Class in Film Radiography
Lost of information / perception of flaws
D
Fine grained film,
slow Imaging plates
Coarse grained film,
fast imaging plates
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Film system C1 C5 C6
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Noise Sources in Radiographic Images
Typical noise sources in digital radiography:
1. EXPOSURE CONDITIONS: Photon noise, depending on
exposure dose (e.g. mAs or GBqmin). This is the main factor!SNR increases with higher exposure dose.
2. Limitation for the maximum achievable SNR:
1. DETECTOR: Structural noise of DDAs and Imaging Platesalso called fixed pattern noise (due to variations in pixel topixel response and inhomogeneities in the phosphor layer).
2. OBJECT:
1. Crystalline structure of material (e.g. nickel based steel,mottling)
2. Surface roughness of test object
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Noise in Dependence on Exposure Time
CNR and SNR increase with increasing exposure time due to
Normalized at constant contrast
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improved photon statistics
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Human Observer Model: Perception Threshold PT
a o you seeNoise = 1000
=
or magnification technique
CNR = 2.5
.visible than small ones at
same Contrast-to-NoiseA
CNR = 1.25 Each row has indications
=
CNR = 0.625
ep
Each column has holes
with same diameterFlat bottom holes of different de th and diameter2T = 0.5 mm / 0.02SRb image = 50 mCalculated CNRmin = 1
b
depthlateral
constSR
PT -
Alateral area of just visible indication
Cdepth mean contrast of just visible indication
- noise of image (N)
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SRb basic spatial resolution (effective pixel size)Rose approach, 1946
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Image Quality in Digital Radiology- -
The 3 essential parameters:
gna o no se ra o Specific contrast (eff)
ratio (CNR)
Basic spatial resolution (SRb)
noise ratio (SNRN)
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Essential Parameters for Calculation of JustVisible IQI 1 T Hole Diameter
The essential parameters are: eff, SNR and SRb?
New Formula
Depends on Hardware: effective pixel sizeMagnification
Focal spot size, source size
SRPTd
image
b
SNR - Signal to noise ratio
eff specific contrast,
SNReff
SRb effective pixel size in the image,basic spatial resolution of image
a er a ,keV, Source typeScattered radiation
Exposure timeTube current, Activity
Detector efficiency
-
ource- o- e ec or s ance
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,
viewing conditions and operator14
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Comparison of Calculated and Measured Image Quality
0,17Berechnete und gemessene Bildqualitt
d = PT*/square_root((kV,w) SNR(GV))
Calculated and Measured Image Quality
Dependence on tube kV
0,15
s(m
m)
Calculated IQI visibility from measured CNR
Diameter of Visible wires
Diameter of visible wires (digital fil ter)
W 14d
ntinmm
0,13
barenDrahte
Diameter of Visible hole normalised by 2.5
Diameter of Visible hole normalised by 2.5 (digital filter)W 15
IQIeleme b .
0,09
0,11
serdessicht
W 16Calculated just visible wire
ustvisibl
0,07Durchmes
W 17
Just visible wire diameter and
of the just visible1T-hole,
ame er
terofthej
132 mAmin
1 m SDD
0,05
60 80 100 120 140 160 180 200 220 240kV
,
(high pass filter)Diam
19 mm FeUR 1, DynamIx HR
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Qualification of Imaging Plate Systems by the Visibility ofIQIs and/or EPS calculation from eff, SNR and SRb10
25)
EPS Procedure is proposed for CR qualificationin the new ASTM E 2033 draft and the Draft on Practice for the Use of Computed Radiology for Aerospace Casting Inspections (USA: MAI group)6,
E747,
- The EPS (equivalent penetrameter sensitivity) measurement is based on E 746
- A smooth inch (19 mm) steel plate with a set of plate holes is radiographed at 200kV in 1 m distanceASTME7
- Other IQIs are on the plate
to increase the information
on image response.sitivity(se
The exposure is performedwith different mAs settings
metersen
,
see next page
Verification of equation:
len
tpenetr
SNR
SRPTd
eff
mage
bvisible
E 746S=equiva
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eff for 200 kV and 19 mm Fe is about 0,05 mm-1
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Example: EPS test with DRR HD CR scanner at20 m pixel size
Do you see the holes?
(19 mm) steel plate, 200 kV
CNR 0.81 mm steel step formeasuremen o eff
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Visibility of EPS holes (E 746)
Do you see the holes?
CNR 0.8
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New Formula for Conversion of SNRN Measurements toEPS Values and Working Range for CR (ASTM Draft E 2033)
PT is about 2100 for visibility of the 2 T hole of IQIs corr. to ASTM E 1025
EPS by ASTM E 746 with 200 kV, t = 19 mm Fe plate and eff = 0.05 mm-1
Plateau area defines theSRPT
EPSimage
b
'
PT EPSmax
wor ng range etestp ate
ASTM
EPS = 15%Level I
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EPS= equivalent penetrameter sensitivity (see ASTM E 746, E 747, E 1025)
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Requirements for Digital Detector Arrays
Exceeding Film Quality withHigh Contrast Sensitivity Technique
HCS-RT
DDA
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Qualification of Digital Detector Arrays- -
6.2.1 Definition and Test of Bad Pixels:
A bad pixel can be corrected if it has at least 5 good neighbors. . .
6.2.1.2 Over Responding Pixel
6.2.1.3 Under Responding Pixel
6.2.1.4 Noisy Pixel
6.2.1.5 Non-Uniform Pixel
6.2.1.6 Persistence/Lag Pixel
6.2.1.7 Bad Neighborhood Pixel
6.2.2 Types or Groups of Bad Pixels:
. . .
6.2.2.2 Cluster of Bad Pixels
6.2.2.3 A cluster without an CKP is wellcorrectable.
6.2.2.4 A cluster with CKP is labeled a
relevant cluster.
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. . .
special irrelevant cluster.
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Qualification of Digital Detector Arrays
DDAs are qualified by different tests of ASTM E 2597.Five relevant parameters shall be provided: Basic spatial resolution (SRb)
Specific Material Thickness Range
Efficiency
Image lag Contrast sensitivity
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Measurement of Contrast to Noise Ratio in DDA Practice
CNR shall be measured in theNoise
y
4T hole or proo o image quality.
A minimum CNR of 2.5 is
required by ASTM E 2698. This value needs to be revised!
= .C = I = 473
Noise = 71
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SNR = 155
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Verification of CNRmin for ASTM Standard Practice
ASTM Draft, Practice for the Use of Digital Detector Arrays and ComputedRadiology for Aerospace Casting Inspections and E 2698 Standard
for digital images with DDAs in the 2T IQI hole:
But CNRmin for all digital images can be described more accurate by the
.min
equation:image
SR10
holeIQIdiameter
min
The ASTM E 2698 value (CNR = 2.5) is optimized for testing of thin objects with
thickness < and typical DDAs in the range of 0.1 mm < SRb < 130 m.
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BAM 5, 8mm steel
FujiFilm IX25SNRN ~ 265
DDA Technology
quality than fi lm with a
s ecial calibrationBest (slowest) NDT film
procedure!
Images high pass
filtered for better
PerkinElmer 1620
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SNRN ~ 1500Magn. = 3.5
DDA exposure 25
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Requirements of ISO/DIS 17636-2
NDT of welds RT Part 2: X- and gamma ray
techni ues with di ital detectors
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Computed Radiography (CR) with storage
phosphor imaging plates
CR DDA
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S
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New Standard Proposal
-Radiographic testing of welds with digital detectors.
I. Minimum score for wire type or step-hole type Image Quality
Indicators (IQIs) in function of test technique (similar to ASME)
II. Maximum image unsharpness requirements (SRb = Basic Spatial
Resolution, determined using a duplex wire gauge)
III. Choice of tube voltage or gamma source in function of objectcomposition, penetrated thickness and detector
. - - N
Determine SNR (Signal-to-Noise Ratio) and SRb
Anti-scatter filter t e & thickness Source-to-Detector Distance requirements
New testing geometries
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V. New compensation principles
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Minimum IQI score for wire type or step-hole
IQI scores taken
from EN1435
Potential Issues
Same re uirements for
wire type and step hole
IQIs as in EN 1435 and
ISO 19232-3
New exceptions for
isotopes for doublewall inspections
1 wire or step-holevalue less for Ir192
5 mm < w 12 mm:-
value less for Se75
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New European standard proposal
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New European standard proposal
ISO 17636-2
n mum N an an -sca er er
Concept SNRN was taken
from EN14784-1. Minimum values are
tabulated in function of
radiation ener and
object thickness, similar totable 2 of EN14784-2.
reduced to maximum
values only except for
g energy.
April 2012,
Ewert et al. Standards in Digital RadiologyHigher SNRN requirements than in EN14784-2
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New European standard proposal ISO 17636-2Maximum detector or image unsharpness (SRb)
0.030
0.030
.
0.040
0.063
April 2012,
Ewert et al. Standards in Digital RadiologySRb concept taken from EN14784-1IQI scores relaxed compared with EN14784-2
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Measurement of Interpolated Basic Spatial Resolution
Duplex wire IQIEN 462-5
-
ASTM E 2002
Determination of the basicspatial resolution in each
production radiograph is not
required but recommended.
N con ro s su c en y
the image quality at a givenpixel size.
I,90k
V,
lfocus
udetectorshall be controlled
by reference exposures with
the duplex wire IQI. x
Wire
I
D,
sma
l
The interpolated basic
spatial resolution is
1
Dup
l
1m
S
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totalb 2
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Compensation Principle (II)
Compensation of high detector unsharpness by increased SNR
Unsharp digital systems may be applied for NDT if they enable
to compensate the missing sharpness by increased SNR.
at means, ac eves a g ta system not t e requ re
visibility of the separated duplex wires, it can be used for
NDT, if one or two single wires more than required (see
tables B.1 B.12 of ISO/DIS 17636-2) can be seen clearly in
the digital image for one or two missing duplex wire pairs.
Com ensation of 3 wires vs. wire airs re uires a reement
of contracting parties.
Compensation principle (II):
High detector unsharpness can be compensated by
increased SNR 34
April 2012,
Ewert et al. Standards in Digital RadiologyCompensation Principle II
Compensation for Higher Unsharpness by Increased SNR
New European standard proposal
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New European standard proposal
ISO/DIS 17636-2
Example : new compensation principle II
Compensate missing spatial resolution by increased singlewire sensitivity:
A lower spatial resolution i.e. a lower double wire score (D)
. .
higher single wire score (W). Max. two (or three) single/double wire scores may be exchanged.
Required:Not OK: OK OK
D12
W14D13
W13
D11
W15D10
W16
D9
W17
Duplex wire score
Single wire score
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Conclusions
New standards were developer for digital industrial radiography for detector qualification, quality
assurance and standard practices.
Image quality depends on the essential parameters: (specific) contrast eff, achieved SNR and
b.
For practical application further parameters have been included for DDAs, as contrast sensitivity,
efficiency, image lag and material thickness range.
max
value which is limited by the design of the imaging plate (fixed pattern noise) or DDA calibration.
The operator increases the contrast sensitivity by the exposure time and tube current up to a
certain EPS lateau, which defines the recommended re value workin ran e for CR ASTM E
2033, new draft).
DDAs achieve a significant better contrast sensitivity with correct detector calibration than film
radiography. The prove of image quality requires CNR measurements (ASTM practice E 2798).
New standard practices have been developed for CR and Radiography with DDAs. Basic
requirements are defined by EPS, SNR, SRb and CNR depending on the technology.
ISO/DIS 17636-2 defines additionally compensation principles for the standard practice and
.
3 compensation principles (3rd one for DDAs only) are described in the standard.
ISO/DIS 17636-2 defines minimum requirements for detector SRb, depending on the material
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.
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www.filmfree.eu.comAcknowledgement
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g
European Projects:
with 33 Partners, 11 countries2005 2009
HEDRad
2009 2011
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End
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uwe.ewer am. e
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