CR UweZ BAM - Shield · PDF file- The CR procedure is different from the film radiography procedure - The optical impression of digital radiographic images is not different ... CR_UweZ_BAM.ppt

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Computed Radiography April 2007Zscherpel, Ewert

Computed Radiography

- INDE 2007, Kalpakkam, India -

Computed Radiography

- INDE 2007, Kalpakkam, India -

Requests and information to:Dr. U. Zscherpel / BAMe-mail [email protected]

Requests and information to:Dr. U. Zscherpel / BAMe-mail [email protected]

Uwe Zscherpel, Uwe EwertBAM Berlin, Division VIII.3

BerlinBAM

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New Technologies and Film ReplacementNew Technologies and Film Replacement

ImagingPlates

Scannerfor Imaging Plates

Hard CopyGrayscalePrinterAgfa

CR: Mobile Orex Scanner

CR:FujiFilm XG1 NDT

Radiographywith

Imaging Plates(CR)

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Erasure

Re-usage

Read-out

Exposure

• high sensitivity• medium resolution• high dynamic range• re-usable

Laser

Lumisys ACR2000

Imaging Plate CycleComputed RadiographyImaging Plate CycleComputed Radiography

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Storage Principle of Luminescence Imaging PlatesStorage Principle of Luminescence Imaging Plates

BaFCl:Eu scintillator BaFBr:Eu storage phosphor

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Comparison of step wedge exposures

Comparison of step wedge exposures

X-ray tube

BAS 2000

IP

Film

a) Imaging plate system with log.amplifier.The grey level is proportional to the wall thickness.

b) Digitized film.The grey level is proportional tothe light intensity behind the film.

a) Imaging plate system with log.amplifier.The grey level is proportional to the wall thickness.

b) Digitized film.The grey level is proportional tothe light intensity behind the film.

Comparison:a) Imaging plates (IP) andb) Film

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Subject Contrast

Image Quality Parameters

Radiographic Image Quality is the basis for all comparisonsDigital Detector

Detector Contrast Noise Detector Unsharpness Projected Unsharpness

SNR Detector Contrast: Signalfor linear detectors

Detectors can be qualified and classified by its SNR and BSR values!

CNRCNR - Contrast/Noise Ratio SNR - Signal/Noise Ratio

BSR – Basic Spatial Resolution(effektive pixel size)

CNR = SNR(ITot) ⋅ Δw⋅µ/(1 + k)

k = IScatter / I Primary

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Signal/Noise Ratio

Definition of Signal/Noise Ratio andContrast/Noise Ratio

Signal

2*Noise

Contrast

D-D

0

0

Signal proportionalto radiation dose!

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Digital Industrial Radiology

Film Replacement

Standards, Regulations

• Welding

• Casting

All film based standards require:

• Minimum optical Density (e.g. > 2.0)• Maximum film system class (e.g. ≤ ASTM special) • Maximum unsharpness (> 0.1 mm, FFD/FOD)

Comparison of SystemsComparison of Systems

Standards EN 14784 for CR were developed to be comparable with EN 444, EN 584-1, EN 462-5 !

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Film replacement: What is the Optical Density ?

Film

Luxmeter

6000

Luxmeter

60

Light sourceLight intensity measurement

Io

I1

Optical Density = log (Io / I1)

• The opt. density is a measure of light absorption by film

• No digital X-ray detector yields an optical density

• There exist software on the market which provides wrong equivalent values for the optical density of CR or DR systems!

Film reading from light box, D=2:

Sensor

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NDT film as linear radiation detector (D-D0) ∝ K:NDT film as linear radiation detector (D-D0) ∝ K:

steel, 160 kV

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Film system classes havedifferent SNR values atopt. density = 2 fordifferent dose values(EN 584-1, ASTM E 1815)

Film system classes havedifferent SNR values atopt. density = 2 fordifferent dose values(EN 584-1, ASTM E 1815)

AGFA films 2002 -2004In mixed systems

all NDT film systemsof all vendorsalong one line!

SNRfilm ∝√(D-D0)SNRfilm ∝√(D-D0)

SNRMax(class Cx, D<4.5)SNRMax(class Cx, D<4.5)

square root (dose / mGy)

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Film System Classes are the Basis for CR Classificationand all Digital Detectors

Film System Classes are the Basis for CR Classificationand all Digital Detectors

Tab. 1: Overview about the film system classes in different standards and

the corresponding SNR values and G2/σD values.

Minimum gradient-noise ratio at Signal to Noise Ratio

D=2 above D0 D=2 above D0

G2/σD SNRC1 Special 300 130C2 270 117C3 180 78C4 150 65

T3 C5 II T3 120 52

T4 C6 III T4 100 43

W-A W-A 135W-B W-B 110W-C W-C 80

T1

T2

System class

T1

T2

World ISO 11699-1

Europe CEN 584-1

USA ASTM

E1815-01

Japan K7627-97

I

SNR = log(e) ⋅ (G2/σD)for linear detectors only

230! 100!

EN 14784 Part 1: Classification of Systems

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Table 1: IP-scanner system classes in dependence on the minimum SNR

IP System classes System class CEN

System class ISO

System class ASTM

Minimum Signal-noise ratio

IP 1 IP-AS Special 130 IP 2 IP-T 1 117 IP 3 78 IP 4 IP-T2 IP-AS 1 65 IP 5 IP-T3 IP-AS 2 52 IP 6 IP-T4 IP-AS 3 43 NOTE:The SNR-values of table 1 are equivalent to EN 584-1, ISO 11699-1, ASTM E 1815-96 They are calculated by: SNR = log (e) · (Gradient/Granularity) of table 1 of the corresponding standards and up-rounded. The calculation of measured SNR values shall be performed from dose proportional data.

CR System classesCR System classes

New table 1 with 6 classes!

Classification by - SNR and- Spatial resolutione.g.: IP-3/200

Part 1: Classification of Systems

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FUJI XG-1 CR System Classification (BSR = 130 µm)

SNR 0.1mm Pb f&b versus SQRT(Dose/mGy)

y = -0,7114x4 + 11,315x3 - 63,635x2 + 159xR2 = 0,9974

0,00

20,00

40,00

60,00

80,00

100,00

120,00

140,00

160,00

180,00

0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8

01Pb f&b 130µm

Polynomisch (01Pb f&b 130µm)

Wurzel (Dosis)

SNR

CR problem:SNR limited by structure noiseof imaging plates!

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Exp. Time 1x Exp. Time 4.3x Exp. Time 43x

BAM 5 test weld, 8 mm Steel, 120 kV, different exposure time:

magnification CR-System: FujiFilm DynamiX (XG 1)

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• Film systems are characterized by sensitivity(speed) and the SNR at D=2. The spatialresolution is high, rarely used and typicallylimited by geometrical unsharpness of exposureset-up (shortest exposure time!).

• Digital detectors have a higher dynamic range, theSNR depends on exposure. The spatial resolutionis limited (digital file size!).

Basic differencesFilm – Imaging Plate:

Basic differencesFilm – Imaging Plate:

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Status and Situation for CR:

- 2005: Computed Radiology standards were completed and published in USA and Europe!

- The CR procedure is different from the film radiography procedure

- The optical impression of digital radiographic images is not different from film images in its structure (if not digitally processed, except brightness and contrast control)

- RT-trained personal can interpret digital images in analogy to film

- Digital images need a PC for presentation and may be altered by specialized image processing

- A basic training in image processing is essential to avoid miss interpretation

- Quantitative assessment of flaw sizes is improved by digital processing but the results may differ from those ones of film interpretation

- Electronic reference catalogues may support correct image assessment

CR ProcedureCEN EN 14784-2

ASTM E 2033

CR ProcedureCEN EN 14784-2

ASTM E 2033

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2005

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- The contrast sensitivity improves with the increasing exposure time (better SNR, weaker details becomes visible!)

- The structural noise of the IPs limits the max. achievable SNR

- Step hole, plate hole and wire image quality indicators measure the increase of CNR and improvement of contrast sensitivity

- Unsharp imaging plates achieve a higher max. SNR and need less exposuretime

- The normalized SNRN (with BSR) is independent on the unsharpness, but depends on the efficiency and plate homogeneity

- Only unsharp IPs for radiography with higher energy (about > 250 keV) yield a considerable reduction of exposure time in comparison to film.

Achievable Contrast Sensitivity and Exposure Time

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Wire IQI EN 462-1

Description of Wire -IQI

See also ASTM E747-97→ but different to EN 462

For contrast only !For contrast only !

Duplex wire IQI / EN 462-5 / ASTM E 2002

Lead marks Plastic

Both IQI’s are requiredfor CR!Both IQI’s are requiredfor CR!

For unsharpness only !For unsharpness only !

Step-Hole IQI EN 462-2

Required Image Quality Indicators for CR

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CRSystem Selection

European StandardEN 14784-2

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EN 14784-2

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8 9 10 11 12 13 double wire0.32 0.25 0.20 0.16 0.13 0.10 mm unsharpness

Agfa Prototype (blue)

FujiFilm NDT

Agfa NDT

X-ray tube: Seifert Isovolt 320100 kV, 1 mA, 1 min, small focusSDD = 1000 mm

X-ray tube: Seifert Isovolt 320100 kV, 1 mA, 1 min, small focusSDD = 1000 mm

digitised grey valuesscanning: Agfa DPS, pixel distance: 28.2 µm (900 dpi)

8 9 10 11 12 13

Correct IP-Type

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High Definition CR – Dürr Germany -High Definition CR – Dürr Germany -

Flexible IP (14“x17“) on mobile CR scanner (Dürr)50 k€

Important Advantages:- flexible imaging plates (IP) indirect contact with inner canister wall

- arbitrary formats possible (length notlimited, width max. 14“ (35cm)

- could even be tried with existing set-up (colimator, rotating canister)

- small Laser spot (8 µm) allowssmall BSR for high resolution plates

High resolution mode (BSR=40 µm with suitableImaging plate) available, with thicker IP high Sensitivity achievable (BSR 100 … 200 µm)

Disadvantages:- No automated inspection- Manual handling for IP read-out- IP based on BaFBr have limitedabsorption efficiency

scan direction

For more information see www.duerr-ndt.de

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High Definition CR Systems

HD CR 35 NDT:of Dürr, Germany

HD-IP, light blue

Systems available down to• 12 µm pixel pitch and • 40 µm basic spatial resolution

• “weld quality”

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BAM Certification 2006

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Improvement of CNRUnder Discussion:- Intermediate filters- Pre filters- Max tube voltage

Lead screens may damage the IPs! EN 14784-2

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Improvement of CNRUnder Discussion:- Intermediate filters- Pre filters- Max tube voltage (lower than for film!) Designation: E 2033–xx

Draft

Lead screens may damage the IPs!

TABLE 1 Lead Screen and Filter Thickness

Lead Thickness A KV Range Front Screen Maximum, in. Back Screen Minimum, in. Filter at Tube port > 40kV None. None. <2mm Be Tube Port 40 to 55kV None. None. 0.04 Alum. (1mm) 55 to 90kV None – 0.001 (25µm) None - 0.001 (25µm) 0.04 Alum. (1mm) 90 to 120 kV 0.002 (50µm) 0.002 (50µm) 0.08 Alum. (2mm) 120 to 160kV 0.005 (125µm) 0.005 (125µm) 0.01 Copper (250µm) 160 to 200 kV 0.01 (0.25 mm) 0.01 (0.25 mm) 0.04 Copper (1mm) 200 to 320kV 0.02 (0.5mm) 0.02 (0.5mm) 0.118 Copper (3mm) 320kV-420kV 0.04 (1mm) 0.04 (1mm) 0.236 Copper (6mm) 1MeV to < ? 0.04 (1mm) ?0.04 (1mm) None Se135 0.01 (0.25mm) 0.01 (0.25mm) None Ir192 0.02 (0.5mm) 0.02 (0.5mm) None Co60 0.04 (1mm) 0.04 (1mm) None

≥ ≥

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EN 14784-1, ASTM E 2445

CR Phantom- long term stability tests -

Evaluation of Phantom:

• spatial resolution (by duplex-wire method, optional converging line pairs)• contrast (recognized contrast percentage of the material to examine)• slipping (yes/no)• jitter (yes/no) • MTF (European standard only)• shading (percentage at selected distance)• SNRN (Intensity) near BAM-snail 20x400 window recommended

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EN 14784-1Appendix B:

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Photograph:

35x43 cm²

Protoype

Available from:

- Fluke Biomedical,Part/No. 07-605-2435, 14”x17”www.flukebiomedical.com/rms

- CIT (8”x10”) in U.K.

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CR radiograph90 kV, 2m, 4mAminCR radiograph90 kV, 2m, 4mAmin

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Duplex wire IQIDuplex wire IQI

BAM-snail for test of source position 20% dip

Pair 9 = 260 µm

EN 462-5: unsharpness 0.26 mm

BSR = 0.13 mm

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Converging line pair IQI

3.6 lp/mmUnsharpness = 280 µm

Basic Spatial Resolution = 140 µm

Problems arise for high resolutionsystems; aliasing effects

Problems arise for high resolutionsystems; aliasing effects

BAM-snail for test of source position

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Linearity test - Check rulers- Slipping IP was detected by

a line structure in the image.

Scanner needs repair!

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Profile for MTF - MTF calculation from profile:

MTF20 = 1.6 lp/mmUnsharpness = 0.62 mm (too high!)

MTF

Zero Frequency drop indicates internal scatter

- Jitter Test: no problem

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SNRN (Intensity) near BAM-snail 20x400 window recommended

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Documentation of Long Term Stability Tests

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The practice for CR (EN 14784-2) is based on EN 444 and ISO 5579 for NDT film.

Film can be substituted by IPs

The exposure conditions have to be selected to achieve the required SNR and CNR

2 IQIs are required for CNR and BSR

Tab. 4 in EN 14784-2 regulates the device selection, especially the required basic spatial resolution (BSR)

The max tube voltage should be reduced in comparison to film application

Long term stability can be checked by CR Phantom

Summary:Summary:

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END

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CR UweZ BAM - Shield · PDF file- The CR procedure is different from the film radiography procedure - The optical impression of digital radiographic images is not different ... CR_UweZ_BAM.ppt