ISO-TC135-SC5 N0220 New Standards on Digital Industrial Radiology

The New Standards on Digital Industrial Radiology

ISO 16371 to replace EN 14784ISO 16371 to replace EN 14784ISO 17636 to replace EN 1435

byU. Ewert

www.bam.de [email protected]

BAM, Berlin, Germany,

1ISO 16371, ISO 17636 Ewert, June 2010

ISO/TC 135/SC 5 N 220

Available Standards on Digital Industrial RadiologyEN 13068 Radioscopy

EN 14096, ISO 14096 Film Digitisation

CR EN 14784 ISO 16371 P t 1 Cl ifi ti f S t P t 2 G lCR: EN 14784 ISO 16371 Part 1: Classification of Systems, Part 2: General principles

ASTM: CR Classification (E 2446), Long-Term Stability (E 2445), Guide (E 2007), Practice (E 2033)

ASME (BPVC, S.V, XI) CRformer Code Case 2476

Radiography (CR) with Phosphor Imaging Platesformer Code Case 2476ASTM: DDA Manufacturing Characterization (E 2597), Practice

(E 2698), Guide (E 2736), Performance Evaluation and Long Term Stability (E 2737)and Long-Term Stability (E 2737)

ISO/DIS 10893-7 NDT of steel tubes: Digital RT of the welded seam

EN 1435-2 ISO 17636-2 NDT of welds: Film Replacement (CR and DDA)35 SO 636 o e ds ep ace e t (C a d )ASTM E 2422 First digital catalogue, light alloy casting

digitized films from ASTM E 155 (BAM)


ISO 16371:Non-destructive testing Industrial computed radiography with storage phosphor imaging plates Part 1: Classification of systemsPart 2: General principles for testing of metallicPart 2: General principles for testing of metallicmaterials using X-rays and gamma rays

New Title of ISO 17636:Non-destructive examination of welds - Digital radiographic examination of welded joints part 2: X- and gamma rays techniques with digital detectors


- Proposal ISO 10893-7Standards to Consider

- Non-destructive testing of steel tubes Part 7: Digital radiographic testing of the weld seam of welded steel tubes for the detection of imperfections

- ASTM: CR - E 2445, E2446-2005: Classification, qualification, long term stability,

harmonized with EN 14784-1 but revision requested- E 2033: Standard Practice for Computed Radiology under major revision- E 2033: Standard Practice for Computed Radiology under major revision

- ASTM: DDA - E 2597-2007: Manufacturing Characterization, - E 2698-2010: Standard Practice- E 2736-2010: Guide - E 2737-2010: Performance Evaluation and Long-Term Stabilityg y

- EN ISO 17635-2010 (substitutes EN 12062) NDT, General rules, weld inspection- Non-destructive examination of welds General rules for metallic materials

R i i 14784 1 d 2 i d- Revision 14784-1 and -2 required - Non-destructive testing - Industrial computed radiography with storage

phosphor imaging plates - Part 2 : general principles for testing of metallic t i l i X d


materials using X-rays and gamma rays

Basic Requirements for Radiography

B i t d d i t f fil d di it l di l i i

g yin all National and International Standards

Basic standard requirements for film and digital radiology in comparison:

A hi i i ti l D it A hi i i SNRFilm Digital Detector (CR) Achieve minimum optical Density Achieve minimum SNRN Do not exceed maximum film system class or calibrated minimum pixel value

D t d i h C t t d

Do not exceed maximum unsharpness Correct geometry and

detector selection Prove minimum IQI perception with

Wires or Achieve minimum CNR Wires or, Achieve minimum CNRN Step holes or Use same IQIs to prove quality Plate holes Use optional unsharpness IQISNR Signal to noise ratioCNR C t t t i ti

The following formulas and measurements will prove the


CNR Contrast to noise ratiocorrectness of the requirements for digital detectors!

How to determine the Visibility of IQIs from CNR and SNR?- Now some figures and equations for those who are interested in the- Now some figures and equations for those who are interested in the

physics of IQI vision

Contrast and noise determine the visibility of indications

I

n

t

e

n

s

i

t

y

Contrast

Signal(Base material)

I

n

t

e

n

s

i

t

y

Contrast

Signal(Basematerial)

Length

(Base material)

Length

(Basematerial)

N t h i ibl ! N t h t i ibl !Notch visible!

Contrast/Noise is highSignal/Noise is high

Notch not visible!

Contrast/Noise is lowSignal/Noise is low


Signal/Noise is high Signal/Noise is low

Image Quality Parameters in Digital Radiography

IQI visibility (wires plate holes of given size)

g y g g p y

IQI-visibility (wires, plate holes of given size)Specific Contrast

effISNRCNR Material, keVScatter protection{

Contrast

effITotalw Scatter protectionScreens and filters{

Exposure timeExposure timeTube currentDetector efficiencyDetector efficiencySource Detector Distance

Specific Contrast-to-Noise Ratio


Contrast-to-Noise Ratio

Equivalence Value for Optical Density and Film System ClassThe measured SNRN is independent on unsharpness and is used as equivalent value for a required film system class and given optical density.Grey values cannot be used as equivalent values without qualification for the y q qused system and its settings because different digital systems (DDA or IP scanner) read out the detectors with different grey values in response to the same exposure dose and efficiency.y

Influence of Noise in RadiographyFilm system C1 (Agfa D2) C4 (Agfa D5) C6 (Agfa D8)

C t tNoise

Contrast

Indications vanish in the noise at higher film system classes


Noise SourcesTypical noise sources in digital radiography:

1 EXPOSURE CONDITIONS: Photon noise depending on1. EXPOSURE CONDITIONS: Photon noise, depending on exposure dose (e.g. mAs or GBqmin). This is the main factor! SNR increases with higher exposure dose.g p

2. Limitation for the maximum achievable SNR:1 DETECTOR: Structural noise of DDAs and Imaging Plates1. DETECTOR: Structural noise of DDAs and Imaging Plates

also called fixed pattern noise (due to variations in pixel to pixel response and inhomogeneities in the phosphor layer). p p g p p y )

2. OBJECT:1 Crystalline structure of material (e g nickel based steel1. Crystalline structure of material (e.g. nickel based steel,

mottling)

2 Surface roughness of test object9ISO 16371, ISO 17636 Ewert, June 2010

2. Surface roughness of test object

Verification of the Visibility Equations by Measurement and CalculationMeasurement and Calculation

- The numeric calculation of the just visible IQI diameter depends on the qualification data SNR and Eff as well as on SNR (PV)the qualification data SNRmax and EffIP as well as on SNRmeasured(PV) and SRb_measured. For calculation of the just visible IQI diameter the visibility equation and the qualification equation are applied:

Visibility equation II Qualification equation

)(*

PVSNRSRPTd

eff

bvisible 2max /)/( IPmeasuredmeasured

measured

EffPVSNRPVPVSNR

4,719/2100)19( visiblevisible dmmdmmFeEPSEPS conversion

PT* for wires is about 1,5 (depends on operator)eff for 200 kV and 19 mm Fe is about 0,05 mm-1SRb shall be used in mm


Verification of the Visibility Equations by Measurement and Calculation

Calculated visible wire diameters from pixel value, , SRb and SNRN

- The numeric conversion of the qualification data SNRmax and EffIP as well as SNR (PV) and SR for calculation of the just

0,400Justvisiblewirediameter

largefocalspotcalcwirediameterFujiSTVI

value, , SRb and SNRN

well as SNRmeasured(PV) and SRb_measured for calculation of the just visible IQI diameter needs the combination of the visibility equation and the qualification equation after normalization with SR by:

0,300

0,350

r

VI

largefocalspotcalcwirediameterFujiUR1

largefocalspotcalcwirediameterDrrUR1

largefocalspotcalcwirediameterDrrST

Calculated and measured visible wire diameter in comparison

SRb by:

0,150

0,200

0,250

v

i

s

i

b

l

e

w

i

r

e

d

i

a

m

e

t

e

r VI

largefocalspotmeasuredwirediameterDrrSTVI

largefocalspotmeasuredwirediameterDrrUR1

large focal spot measured wire diameter

W 12

W 13

W 14

0,050

0,100

0, 50

v

largefocalspotmeasuredwirediameterFujiSTVI

largefocalspotmeasuredwirediameterFujiUR1

PT* for wires = 1,49 (depends on operator)

0,000

0 10000 20000 30000 40000 50000 60000 70000GV

The visibility equation (II) and the qualification equation were PT for wires 1,49 (depends on operator)eff for 200 kV and 19 mm Fe is 0,05 mm-1Measured with scanner DynamIx HR and Drr HD35 Imaging plates UR 1 and ST VI

used to calculate the wire visibility. The solid lines in the graph are the result of calculation.The points in the diagram show the just visible wire diameters of EN 462-1 IQIs on a inch plate (19 mm) with 1,74 m SDD and


Imaging plates UR 1 and ST VI EN 462 1 IQIs on a inch plate (19 mm) with 1,74 m SDD and 200 kV of a 320 kV X-ray tube of Seifert, Isovolt.

Cl ifi ti Q lifi ti L T St bilitClassification, Qualification, Long Term Stability


Basic Requirements for Radiography Classification, Qualification, Long Term Stability TestsClassification, Qualification, Long Term Stability Tests

- The Drr scanner provides linearAll CR systems are linear in the photo stimulated luminescence with radiation dose but may

70000

GVResponsetomAsIP 1 UR1IP 2 ST VI

The Drr scanner provides linear pixel values with the exposure dose of the IPs.

- The FujiFilm scanner provides

yprovide non linear numeric data

y=0,0001x2 +8,7975x 338,47

y=8E05x2 +5,1652x+173,24

y=0,0005x2 +48,745x 56,281

50000

60000

70000 Scanner 1 DynamIx HRScanner 2 Drr HD35

j pnonlinear values with the exposure dose of the IPs.

- The data of the DynamIx HR y=6E06x2 +1,7255x 167,22

30000

40000

50000

G

r

e

y

V

a

l

u

e

IP1scanner1IP2scanner1

scanner were read as 12 bit raw data and linearized with a look up table (LUT) to linear 16 bit grey values:Th d t d t f th

10000

20000

IP1scanner2IP2scanner2Poly.(IP1scanner1)Poly.(IP2scanner1)Poly.(IP1scanner2)Poly.(IP2scanner2)

- The read out data of the scanner change depending of the used IP.

- Minor offset and nonlinearity effects can be seen from the figure

No saturation observed

0

0 5000 10000 15000 20000 25000

mAs

can be seen from the figure.

320 kV-X-ray tube,


320 kV X ray tube, Seifert, Isovolt

Validation of Correlation of SNR and Grey values by Measurements and Calculations for

Q lifi i f i i lQualification of imaging plate - scanner systems- The qualification is based on the correlation of SNR and Pixel Values

of a CR system with fixed scanner settingsof a CR system with fixed scanner settings.- Scanner parameters as gain, scan speed, laser intensity, scan pixel

resolution and others shall not be modified for qualification.

y=4x0,5 y=1,2x0,5

SNRMethod The IPs UR 1 and ST VI were

exposed at different kVs and with different objects (Al and Fe plates) of different thickness (10 and 20SNR = 215

Straight lines in the graph represent the grey efficiency as calculated from photon statistic without considering

100,00

10mmFeSTVI

10mmALSTVI

20mmAlUR1

20mmALUR1

20mmALUR1

of different thickness (10 and 20 mm) and scanned with the DynamIx HR with standard settings.

SNRmax =215STVI

gSNRmax.

S

N

R

10mmFeUR1

UR1medianSNRFe19mm200kV

STVI200kV19mmFe

SNRcalcSTVI

SNRcalcUR1

SNR photo calc ST VI

All measured SNR values are always about the same for a corresponding pixel value.

S f

SNRmax =165UR1

10,00

10 100 1000 10000 100000

Greyback

SNRphotocalcSTVI

SNRcalcphotoUR1

Pot.(SNRphotocalcSTVI)

Pot.(SNRcalcphotoUR1)

measuredPVSNR

measuredIPPhoto PVEffSNR All SNR vs. PV curves can be fitted

with one SNRmax value and one grey efficiency EffIP value per IP.

Q lifi ti ti


y

2max /)/( IPmeasuredmeasuredmeasured

EffPVSNRPVPVSNR Qualification equation:ODD = 25 cm

SNRD vs. Normalized SNRN

mSNRSNR 6,88b

N SRSNRSNR

SR 0 5 USRb = 0.5 Ui

SNR Signal to noise ratio at detectorSNRN normalized SNR

SNRN is the normalized detector SNR It is normalized to the standard pixel size of X-ray

film in accordance to EN 584-1 (classification).SNRN normalized SNRSRb Basic spatial resolutionUi inherent detector unsharpness

film in accordance to EN 584 1 (classification). The normalized SNRN considers the basic spatial

resolution SRb (also called: effective detector pixel size) of the detector, measured with the duplex wire IQI (EN 462-5).

The detector SNR of unsharp detectors is reduced to the value which is typically measured

ith fil


with films.

Measurement of Basic Spatial ResolutionDuplex wire IQIEN 462-5ISO 19232-5

Determination of the basic spatial resolution in each

ASTM E 2002

spatial resolution in each production radiograph is not required.

SNR controls sufficiently SNRN controls sufficiently the image quality at a given pixel size.

SNR is a sufficient SNR is a sufficient parameter, if a maximum detector unsharpness is not exceedednot exceeded.

The detector unsharpness shall be controlled by reference exposures withreference exposures with the duplex wire IQI.


SNR method for determination of minimum PV

- Make a reference exposureMake a reference exposure- Determine the GVmean and SNR as a graph

- Do one exposure with a step wedge orDo one exposure with a step wedge or- Do different exposures of the IP without object but with

prefilterp- Determine the duplex wire reading for determination of the

basic spatial resolution SRbp b - Determine the SNRN values as function of grey value or

dose and determine the maximum achievable SNRN max and N max classify

- Determine for the specified SNRN the corresponding IP

17ISO 16371, ISO 17636 Ewert, June 2010system class and add the basic spatial resolution

Proposed reference exposure with step wedgeAlternatively a step exposure can be taken under the same conditions as described in the standard.


Calibration graph for SNR in dependence on PV

The following graph should be generated:

180

The SNR number in the graph are examples.

120

140

160 SNR=150

g p pThe corresponding GVs can also be used in the standard practice

60

80

100

S

N

R

SNR=70

SNR=100standard practice

The following table may be used to obtain

0

20

40be used to obtain recommended minimum SNR values for IP-systems with different0 1000 2000 3000 4000 5000

GreyvaluePixel valuesystems with different SRb in equivalence to film system classes.SRb = 88,6 m


Proposedtable6intheoriginalproposalof2033,Annex5,fordefinitionofminimumSNRvalues

Measurements have shown that higher SNRN values are required than for films. The new European values are 180, 120, 100, 70 (see revision of EN 14784-2 and ISO 17636 2)

System parameter High definition system Standard system

17636-2)

Duplex wire value 13+ 13 12 11 10 9 8 7

Detector-scanner unsharpness 80 m 100 m 125 m 160 m 200m 260 m 300 m 400 munsharpness

Basic spatial CR system resolution 40 m 50 m 63 m 80 m 100m 130 m 160 m 200 m

SNR levels Minimum SNR

IP Special 70 85 110 135 170 220 270 340

IP Level I 45 60 75 90 115 150 180 230

SNRN150100IP Level I 45 75 90 150 230

IP Level II 35 40 50 65 80 105 130 160

IP Level III

10070


Verification from measured data for low SNR

StepwedgeexposurewithTAMIQIsofE1742.

i

l

t

e

r

e

d

H

i

g

h

p

a

s

s

f

i

H

CR of a step wedge with IQIs Taken at 80 kV and 10 mAmin, 1 m.At SNR = 36 the 2-2T is clearly visible.


Classification in EN 14784-1 (also ASTM E 2446) by SNRN and Basic spatial resolution SRb

Where do the SNR values come from for CR ?- Equivalence to film systems was used as defined in ISO 11699-1 for the film

t lsystem classes.- Films systems have the following minimum SNR values at 88.6 m square

aperture and optical density of 2 above fog and base (see table below)

Minimum gradient-noise Signal to Noise Ratio for

Table for film system classification of international standards:

Minimum gradient noise ratio for film at

Signal to Noise Ratio for film and CR

D=2 above D0 D=2 above D0ISO 11699-1 CEN 584-1

USA ASTM

E181 01 GD SNRC1 Special 300 130C2 270 117C3 180 78

CEN 584 1 E1815-01

IC4 150 65C5 II 120 52C6 III 100 43

W-A 135W-B 110


W-B 110W-C 80

Classification in EN 14784-1 (also ASTM E 2446) by SNRN and Basic spatial resolution SRb

Where do the SNR values come from for CR ?- Minimum normalized SNRN and SRb requirements for CR classification

Y basic spatial resolution SR in mmresolution SRb in mm

In the mean time allIn the mean time all commercial NDT CR systems fulfill all IP classes withclasses with different SRb


Annex for Classification in EN 14784-1 (also ASTM E 2446) by SNRN and Basic spatial resolution SRb

SNRN SNRN_max should be added for a next revision after finalization of

IP 1

development of ISO 17636.

Efficiency is correctlyIP 1IP 2IP 3IP 4

Exposure Geometry for t f SNR G

Efficiency is correctly considered for measurement of ISO speed

IP 4IP 5IP 6

measurement of SNRN vs. Grey values or exposure dose

Log (mAs or GV)Annex A of EN 14784-1Annex A of EN 14784 1


High Definition CR SYSTEMD HD CR 3 NDT & HD IP

Detailed BAM qualification reports are available for Carestream, Duerr, FujiFilm and GE S&IT

Drr HD-CR 35 NDT & HD-IP pentaprism speed: 2000 RPM PMT Voltage: 620 HV operating pixel size: 20 moperating pixel size: 20 m

IP Scanner SystemHi h D fi iti I i Pl t


IP Scanner SystemHigh Definition Imaging Plates

Result of Classifications of Different Computed Radiography Systems

350

400

250

300

e

d

200

250

R

n

o

r

m

a

l

i

z

e

100

150

S

N

R

D2, DR, IX25

D3, M100D4, MX125

FujiFilm CR XG1, ST VI

0

50 D7, AA400D5, T200

D8, H800

00 1 2 3 4 5 6 7 8 9 10

SQRT (Dose / mGy)

Normalized SNR vs square root of Exposure Dose


Normalized SNR vs. square root of Exposure Dose

Measurement of long term stability for quality assurance in EN 14784-1 (also ASTM E 2445)

Test phantom with a variety of IQIs and test yobjects

The test phantom or its IQIs shall be exposed and the results shall be documented periodicallydocumented periodically.

Deviations in the measured values will indicate changes , aging or malfunction.

The frequency of the testThe frequency of the test shall be part of the quality assurance system of the manufacturer.


Documentation of long term stability for quality assurance in EN 14784-1 (also ASTM E 2445)

The results of the tests can be documented as demonstrated by the following template


New Features for Standard Practice in ISO 16371-2 and ISO 17636-2

CR and DR with DDA is proposed in one standard document for ISO 17636-2. SNRN or grey value as equivalent value for film system class and opt. density

and ISO 17636 2

N g y q y p y No mandatory requirement of SNRN and duplex wire for production radiographs Usage of duplex wire for system qualification and system selection only Mandatory usage of duplex wire for magnification technique onlyMandatory usage of duplex wire for magnification technique only Usage of flat cassettes and DDAs for curved objects with new formula for

calculation of SDD New revised unsharpness tables New revised unsharpness tables 3 compensation principles (3rd one for DDAs only) No lead back screens but back scatter protection

L d f t l b 250 kV d t f CR t b l 250kV Lead front screens only above 250 kV mandatory for CR, not below 250kV (values can be discussed)

New part on DDAs with calibration and bad pixel discussion in ISO 17636-2 Annex C for conversion of SNR and SNRN requirements to gray values (for CR)

as equivalent for opt. density. No use of EPS plates as in ASTM E 2033-2010 proposal.


New Requirement for Minimum SNRNRadiation source Penetrated wall Minimum SNR_D Type and thickness in mm of metal

Class A

Class B

X-ray < 50 kV 100 180

thickness w in mm

yscreen

IP classes are not mentioned X-ray 50 kV to 150 kV 70 120

X-ray > 150 kV to 250 kV 70 100

w < 50 70 100 X-ray > 250 kV to 350 kV

in the standard proposal anymore

New SNR values wereX ray > 250 kV to 350 kV w > 50 70 70 w < 50 70 100

X-ray > 350 kV to 450 kV w > 50 70 70

5 70 120

New SNRN values were taken due to experiences over years with DDAs and CR

w < 5 70 120Yb 169

w > 5 70 100

w < 50 70 100 Ir 192, Se 75

w > 50 70 70w > 50 70 70

w < 100 70 100 Co 60b

w > 100 70 70

w < 100 70 100X 1 MVbX-ray > 1 MVb

w > 100 70 70

a


Selection of Radiation Quality vs. Exposure Dose

Compensation Principle (I)


Compensation Principle (I)Visibility of IQIs in dependence on exposure dose andexposure dose and tube voltage for steel

- Increasing tube voltage reduces the specific contrast b tcontrast eff but increases the exposure dose on the detector

- The increase of SNR by the improved quantum statisticquantum statistic compensates the loss of contrast

SNRCNR IQI-perception (wires, plate holes)


effITotalSNR

w

Compensation Principle (I)

The diagram limiting the maximum tube voltage is not mandatory anymoreanymore

The used tube voltage should be higher for application of DDAsg pp

The tube voltage should be lower (about 20%) for application of i i l t ( di dimaging plates (medium and coarse grained) for class B inspection in comparison to film

Compensation principle (I):

A reduction of contrast by increased tube voltage can be compensated by increasedA reduction of contrast by increased tube voltage can be compensated by increased detector SNR. Reduced detector SNR shall be compensated by contrast increase (e.g. by reduced tube voltage).


BAM 5, 8mm steel

Maximum Achieved Contrast EnhancementFuji IX25SNRnorm~ 265

DDA Technology provides betterprovides better image quality than film with a

Best (slowest) NDT filmt a

special calibration procedure!

Images high pass filtered for better presentation

PerkinElmer 1620

presentation

34ISO 16371, ISO 17636 Ewert, June 2010SNRnorm~ 1500

DDA exposure

Testing with flat Detectors and flat Cassettes is required for ff ti t ti ith DDA d I i Pl teffective testing with DDAs and Imaging Plates

DDA flat and

Film and CR in contactb

Cassettest

3/1tba

df Class A: a = 7,5Class B: a = 15

f source object distance (SOD)d focal spot sozet wall thickness (nominal)


tdt wall thickness (nominal)

The correct selection of magnification shall be proven by usage of the duplex wire IQI on the object

Magnification TechniqueThe correct selection of magnification shall be proven by usage of the duplex wire IQI on the objectin all production radiographs. The duplex wire IQI shall be positioned at the object side near to the detector, if 2SRb > d (d - source size or focal spot size). Otherwise the duplex wire shall be positioned at the sorce side of the object. It is recommended that a duplex wire is positioned at both object sides for selection of the mangnification value but only one needs to be seen in theboth object sides for selection of the mangnification value, but only one needs to be seen in the final production radiographs after selection of the correct magnification factor and source size or focal spot size. The suitable magnification v can be estimated by the following equation:The suitable magnification v can be estimated by the following equation:

333

Im

)2()(1 bG SRuU

Im

(5) with

)1( SODSSDduG SOD

(6) SRb basic spatial resolution of the detector SDD source detector distanceSDD source detector distanceSOD source object distance uG geometrical unsharpness d focal spot size or source size in accordance with EN 12544 or EN 12579 UI required image unsharpness in accordance with table B13 or B14 for class A or B testing


UIm required image unsharpness in accordance with table B13 or B14 for class A or B testing

Magnification Technique The magnification factor is typically different for source and detector side of the object. Therefore, the magnification v should be calculated for the object center. The variation of the magnification

l t id d d t t id h ld t b hi h th 25% S ll ifi ti

g q

value at source side and detector side should not be higher than 25%. Smaller magnification values may be choosen if compensation principle (II) as described in 6.3.3 is used.

L tiFDD LocationFOD

FDD

Collimator

Real focal spot

Object

IntensityDetector


Partial presentation of ptable 1, class A ofISO DIS 10893-7

Minimum requirements for IQI visibility

SO SIn ISO DIS 10893-7 is the usage of the duplex wire IQI mandatory.

In prEN 1435-2 the usage of the duplex wire shall be mandatory onlyshall be mandatory only for system selection, system qualification and magnification techniquemagnification technique.


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.

That means achieves a digital system not the required visibility of theThat means, achieves a digital system not the required 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) can be seen clearly in the digital image for one or two missing duplex wire pairsin the digital image for one or two missing duplex wire pairs.

For instance, is a digital detection system used, which achieves the duplex wire pair D11 (first unsharp wire pair) for inspection of a 5 mm thick object and class B testing (required is D12 and W16), single wire W17 shall be clearly visible in the image for acceptable quality.

Compensation principle (II):Compensation principle (II): High detector unsharpness can be compensated by increased SNR


Compensation Principle (II) Test sample BAM 58 mm steelDetection of fine flaws with subpixel resolution

highpass highpass filtered

13 14 15 16 17 18 19 Draht O3 5 6 8 9

13 14 15 16 17 18 19C1 film:wire ~16 visible

DDA ( ifi ti 1)

Draht O EN 462-1

W13 200mW14 160m

200m pixel size!

100m contrast resolution DDA (magnification = 1):W19 = 50m contrast resolution

W15 130mW16 100mW17 80mW18 63mclass B


200m pixel size!W18 63mW19 50m

class B

Compensation Principle (III)Management of Bad Pixels

The appearance of certain detector elements, which do not perform as required has initiated a controversial discussion about the acceptance of DDAs for NDT. p

ASTM E 2597 describes the different types and groups of bad pixels and provides a recommendation for interpolation.

The interpolation causes local unsharp regions in the digital image. The detection of small flaws can be achieved if the SNR is increased.

Compensation principle (III) :

Local unsharpness due to bad pixel interpolation can be compensated by increases SNR.


Bad pixel Types and ClassificationsDead Pixel Pixels that have no response, or that give a constant response independent ofradiation dose on the detector.Over responding pixel Pixels whose gray values are greater than 1.3 times the mediangray value of an area of a minimum of 2121 pixels This test is done on an offset correctedgray value of an area of a minimum of 2121 pixels. This test is done on an offset correctedimage.Under responding pixel Pixels whose gray values are less than 0.6 times the median grayvalue of an area of in a minimum of 2121 pixels. This test is done on an offset correctediimage.Noisy pixel Pixels whose standard deviation in a sequence of 30 to 100 images withoutradiation is more than 6 times the median pixel standard deviation for the complete DDA.Non-uniform pixel Pixel whose value exceeds a deviation of more than +/-1 % of themedian value of its 99 neighbor pixel. The test should be performed on an image where theaverage gray value is at or above 75% of the DDAs linear range. This test is done on anoffset and gain corrected image.Persistence / Lag pixel Pixel whose value exceeds a deviation of more than a factor of 2Persistence / Lag pixel Pixel whose value exceeds a deviation of more than a factor of 2of the median value of its 99 neighbors in the first image after X-ray shut downBad neighborhood pixel Pixel, where all 8 neighboring pixels are bad pixels, is alsoconsidered a bad pixel.

Single bad pixel Cluster bad pixelsLine of bad pixels

CKP

Cluster kernel pixel (CKP) are pixels which only


Line of bad pixelsCluster kernel pixel (CKP) are pixels, which only have four or less good neighborhood pixels

Measurement of Bad PixelBad Pixel EvaluationASTM E2597 Manufacturers measure bad pixels and their natureASTM - E2597 Manufacturers measure bad pixels and their nature

Some classifications of Bad Pixels ...

single dead line (without signal)

cluster (2x3 pixel)

single non uniform line (signal level varies differently to dose thansignal level of the other lines)

single dead pixel (without signal)

single noisy pixel (> 6 sigma in dark image)

single non uniform pixel(signal level varies differently with dose thansignal level of the neighboring pixels)

detail from the complete image

signal level of the neighboring pixels)

single lag pixel(pixel with factor 3 higher lag compared

di l f h l 9 % )


to median lag of the central 95% area)

Bad Pixels, Relevant and Irrelevant Clusters, and Bad Lines


Bad Pixel Correction

How Bad Pixels are corrected:

Bad Pixels do not avoid the detection of flaws, if the SNR is high enough

Grid of the detector

The defect pixel is substituted by theThe defect pixel is substituted by the 8 neighborhood pixels

one pixel


one pixel

Worst case scenario - Interpolation

Bad pixels do not look like defects-Defects have some blur, bad pixels are discrete

A Defect in Material, size of 1.5 pixel

Example:An area of material with grayvalue 10000.Th d f t h 2% l d it th thThe defect has 2% less density than the rest.The defect covers ~ of the pixel (100).

1010010038

The substituted Pixel will be:(3*10100 + 5*10000) / 8 = 10038 == 0.38%and well visible with SNR>265.

Pixel Grid of the Detector

10000

Bad Pixel


Pixel Grid of the Detector

Guidance for bad pixel specifications based on CNR and defect size

Bad pixel considerations

Bad pixel considerationsLimited number of bad pixels allowed in area of interest

Detectability: positive (best practice)

area of interest

isolated bad pixels allowed, but no clusters allowed

isolated bad pixels and irrelevant clusters allowed but

clusters allowed

clusters allowed but relevant clusters not allowed.

impact of different

Defect size (as number of pixels)

impact of different types of bad pixels on detectability is minimal


Defect size (as number of pixels)

6.9.2 Calibration of DDAs

If using DDAs the detector calibration procedure as recommended by th f t h ll b li dthe manufacturer shall be applied.

The detector shall be calibrated with a background image (without radiation) and at least with one gain image (X-Rays on and ) g g ( yhomogenously exposed).

Multigain calibration will increase the achievable SNR and linearity but takes more time All calibration images shall be taken at least with 2takes more time. All calibration images shall be taken at least with 2 times longer exposure dose (mAmin or GBq min) as finally used for the production radiographs to minimise the noise introduction of the

lib ti dcalibration procedure. Calibrated images may be treated as unprocessed raw images for

quality assurance if the procedure has been documented. qua ty assu a ce t e p ocedu e as bee docu e ted The calibration and a bad pixel interpolation shall be performed

periodically and if the exposure conditions are changes significantly.


B d i l d f i d t t l t f DDA Th d fi d d

6.9.3 Bad pixel interpolation

Bad pixels are underperforming detector elements of DDAs. They are defined and described in ASTM 2597.

If using DDAs the detector shall be mapped to determine the bad pixel map in d ith th f t id li Thi b d i l h ll b d t daccordance with the manufacturer guideline. This bad pixel map shall be documented.

The bad pixel interpolation is acceptable and an essential procedure of radiography with DDAs. It is recommended to apply only detectors which have no cluster kernel pixels (CKP, definition see in ASTM E 2597) in the region of interest (ROI). All cluster kenel(CKP, definition see in ASTM E 2597) in the region of interest (ROI). All cluster kenel pixels shall be documented.

DDAs without CKPs and CR shall be applied for inspection of flaws which are larger than 3x3 pixels for spot like indications and larger than 2x6 pixels for linear indications in the3x3 pixels for spot like indications and larger than 2x6 pixels for linear indications in the digital image.

If using DDAs or Imaging plates for inspection of smaller flaw sizes, the required SNR shall be increased significantly. The inspection shall be performed on the basis of anshall be increased significantly. The inspection shall be performed on the basis of an agreement between the contracting parties. The image quality shall be proven as described above.

Note 3: ote 3

In analogy to the compensation principle (II) the increased SNR compensates also for the local unsharpness caused by bad pixel interpolation. This is considered as compensation principle (III).


p p p ( )

Minimum Requirement for SNR and Lead Screen ThicknessRadiation source Penetrated wall Minimum SNR_D Type and thickness in mm of metal

Class A

Class B Front Back

X-ray < 50 kV 100 180 None None

thickness w in mm

yscreen

X-ray 50 kV to 150 kV 70 120 Pb 0 - 0,1 Fe 0,5+ Pb

X-ray > 150 kV to 250 kV 70 100 Pb 0 - 0,1 Fe 0,5+ Pb

w < 50 70 100 Pb 0 - 0,2 Fe 0,5+ PbX-ray > 250 kV to 350 kVX ray > 250 kV to 350 kV

w > 50 70 70 Pb 0,1 - 0 ,3 Fe 0,5+ Pb

w < 50 70 100 Pb 0,1 - 0 ,3 Fe 0,5+ PbX-ray > 350 kV to 450 kV

w > 50 70 70 Pb 0,1 - 0 ,3 Fe 0,5+ Pb

5 70 120 Pb 0 0 1 F 0 5 Pbw < 5 70 120 Pb 0 - 0,1 Fe 0,5+ PbYb 169

w > 5 70 100 Pb 0 - 0,1 Fe 0,5+ Pb

w < 50 70 100 Pb 0,1 - 0 ,3 Fe 0,5+ PbIr 192, Se 75

w > 50 70 70 Pb 0 1 - 0 4 Fe 0 5+ Pbw > 50 70 70 Pb 0,1 - 0,4 Fe 0,5+ Pb

w < 100 70 100 Fe 0,5+Pb 1,5 Fe 0,5+PbCo 60b

w > 100 70 70 Fe 0,5+Pb 2,0 Fe 0,5+Pb

w < 100 70 100 Fe 0,5+Pb 1,5 Fe 0,5+PbX 1 MVbX-ray > 1 MVb

w > 100 70 70 Fe 0,5+Pb 2,0 Fe 0,5+Pb

a.

b In case of multiple screens (Fe+Pb) the steel screen shall be located between the IP and the lead screen. InsteaFe or Fe+Pb also copper tantalum or tungsten screens may be used if the image quality can be proven


Fe or Fe+Pb also copper, tantalum or tungsten screens may be used if the image quality can be proven.

Edge Profiles220 kV, no Pb back screen

Effect of Scatter UnsharpnessEffect of Scatter UnsharpnessScatter Effects at

sharp edges:

- Internal scatter in the

220 kV 4 mm Pb back screen

layer

- Internal scatter of the back screen support Long range 220 kV, 4 mm Pb back screenback screen, support and cassette

- Object scatter

unsharpness effect from lead back screen, cassette and support


ENDEND

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ISO-TC135-SC5 N0220 New Standards on Digital Industrial Radiology

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