digital detector arrays - how to surpass film quality? · pdf filedigital detector arrays -...

Technology with Passion

Digital Detector Arrays - how to surpass film quality?

P. Kramm, K. Bavendiek, M. Kurfiss


Technology with Passion 14.4.20012 | 2

Outline

� Why use Digital Detector Arrays?� Important Parameters

� From Density to SNR� Can a High SNR compensate a Lower SRB?� Comparison - a real-life test

� Summary



Why use Digital Detector Arrays – DDA?

� Reduce Time of Inspection� Example: 6“ diameter Inconel, 10 welds

� Film: 2-3 hours� DDA: 12 minutes 10 seconds

� No Chemical Processing incl. associated facilities + waste waterhandling

� Easy Archiving and Fast Access every where � Ability to use Digital Image Processing like Filter, Zoom,

Measurement� Inspection of larger Range of Material Thicknesses within one Image

� Higher recognition rate of defects in production ...



Why use Digital Detector Arrays – DDA?

done by Bill Meade, Clay Kidwell, Greg Warren (Boeing Commercial Aircraft)



Outline



� Summary



Important Image Quality Paramter for DDAs

Quantum

Noise

Detector

Contrast

Subject

Contrast

Detector

Unsharpness

Geometrical

Unsharpness

Detector

Noise

SRB

CNR

SNR

1. SRB Basic Spatial Resolution (effective pixel size)

2. CNR Contrast to noise ratio (= 1 / Contrast Sensitivity)

3. SNR Signal to Noise Ratio

4. DR Dynamic Range

5. LAG Behaviour in time



Basic spatial resolution SR B

� Spatial detector resolution of the detector image in x- and y-direction � Also known as effective pixel size � Measured with the Duplex Wire (EN 462-5 or ASTM E2002)

D13 = 50 µm visible using

D2 film



SRB of film is much better than with DDAs

DDA with a pitch of 200 µm

� measured SRB is ~200 µm� Magnification is 1

D7 = 200 µm visible



Important for detail visibility: Spatial Resolution - SR

Same DDA used with magnification and a modern X-ray t ube

� measured Spatial Resolution is 50 µm too!� Magnification is 3.6

D13 = 50 µm visible!

Magnification compensates

lower SRB



Image Quality Parameter: Signal to Noise Ratio (SNR)

D-D

0

Signal

2*Noise== 2 SRMS

SNR = S

SRMS

Det

ecto

rU

nits

1024

2048

Noise is in nearly every image. Reasons for noise are :

� Quantum Noise (X-Ray)� Grain distribution (film) � Fog contribution (film)

� Electronic noise (DDA)� Structure noise (DDA)



Image Quality Parameter: Signal to Noise Ratio (SNR)

Example of different SNR at film

σDLoss of information



Image Quality Parameter: Contrast Sensitivity

Contrast Sensitivity (CS) indicates the smallest material difference, which can be resolved in the image

Contrast= ∆S

CS = = SRMS

∆S1

CNR



Outline



� Summary



From Film Density to SNR



From Film Density to SNR

Film: Base and fog Quantum noise too dark for readoutDDA: Electronic noise Quantum noise Structure noise

Does a DDA have the same characteristic?



Enhacing the SNR

How to get rid of the

Structure Noise?

raw image without calibration



Multiple gain optimizes the detector performance

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

0 10 20 30 40

Dose [arb. units]

Detector output signal [arb. units]

Detector signal with offset correction

Multigain compensation

Corrected signal (multi-gain and offset)

Ideal linearity

Correction points



A High SNR is optained with optimized calibration

(SNR is limited to ~1000 because of the Structure of the Material)

With 16s same quality like

with 500s andnormal

correction

With 16s same quality like

with 500s andnormal

correction



Outline



� Summary



Can a High SNR Compensate a Lower SR B?

800µm

200µm

127µm

400µm

1200µm

Aluminum wedge with 5 long holes inside;

Image from 400µm pixel pitch DDA

40mm Al

5mm Al

5mm

40mm

With a high SNR details can be seen more easily and even objects smaller than the pixel size can be detected



Can a High SNR Compensate a Lower SRB?

800µm

200µm

127µm

400µm

1200µm

Image from 400µm pixel pitch DDA

With a high SNR details can be seen more easily and even objects smaller than the pixel size can be detected

with high-pass filter

This is just a third of the pixel size.

How is this feasible?



Yes, a High SNR can Compensate a Lower SR B

Due to the high signal-to-noise ratio the hole can be detected, although it covers only a part of a pixel.

Although only a part of the pixel is covered by the IQI, the output signal is high enough for detection.

The long hole, just a third of a pixel width

Pixel Grid of the

Detector

Compensation principle II



Outline



� Summary



Test object: Welding seam

BAM 5 welding seam: 8 mm steel plate with additional 2 mm at weldingseam

EN 462-5Duplex wire gauge

ASTM E1025Inconel „5“HolePenetrameter

EN 462-1 / ASTM E747FE 13 Wire Penetrameter

EN 462-2 step/holepenetrameter „H1“



High class film (D2)

150 kV, 5 mA, Pb Filter, 1000 mm FFD, Exposure time 330 s Scanned with Primescan 7100 (10 µm pixel distance, aperture 21 µm, averaged to 50 µm acc. to ISO 14096; 16 Bit gray values



Digital Detector Array Y.XRD 1620

160 kV, 2.8 mA0.5 mm focal spotno filtergeometr. magn.: 3 FDD 1180 mmExp. time: 300 sec

[210 mGy]

Y.XRD 162016 Bit gray value200 µm pixel size



Spatial Resolution of the film

Duplex wire No. 13 can be resolved.Spatial resolution better than 50 µm.

Wire Distance Wire DistanceD4 400 µm D9 130 µmD5 320 µm D10 100 µmD6 250 µm D11 80 µmD7 200 µm D12 63 µmD8 160 µm D13 50 µm



Spatial Resolution of the DDA Y.XRD 1620

Duplex wire No. 12 can be resolved.Spatial resolution 63 µm

Wire Distance Wire DistanceD4 400 µm D9 130 µmD5 320 µm D10 100 µmD6 250 µm D11 80 µmD7 200 µm D12 63 µmD8 160 µm D13 50 µm



Contrast sensitivity of the film

200 µm holesare visible

Hole diameteris equal tostep thickness

H1 125 µm 0.005“H2 160 µm 0.006“H3 200 µm 0.008“H4 250 µm 0.01“H5 320 µm 0.013“H6 400 µm 0.016“



Contrast sensitivity of the film

200 µm holesare visible

Hole diameteris equal tostep thickness


Highpass filter



Contrast sensitivity of the DDA Y.XRD 1620

hole diameter = step thickness


H1 holes are visible

contrast sensitivity better than 125 µm



Contrast sensitivity of the DDA Y.XRD 1620

hole diameter = step thickness


H1 holes are visible

contrast sensitivity better than 125 µm

Highpass filter



Welding seam with Y.XRD 1620 and 3 x geom. Mag.

SNRnorm ≈ 1040

Highpass filter



Welding seam - comparison

Film: SNRnorm≈ 246 DDA: SNRnorm≈ 1040




Another example with 8mm steel weld (test weld BAM5)

D2 film, class C1 EN 584-1330 s exposure time

Y.XRD1620 detector (200 µm SRB), magnification of 3.0 100 s exposure time only




D2 film (mini-focus, 6.5 min) Y.XRD 1620 (mini-focus, 6.0 min)



Why are more details visible with DDAs?

� The film has a better geometrical resolution

� But why are the images taken with the DDA better?

� The DDA has a better resolution in beam direction (contrast sensitivity).

Contrast= DSCS = =

SRMS

DS1

CNR



100 mm Fe

10

100

1000

10000

80 90 100 110

w Fe (mm)

B (m

A x

min

)

450 kV

520 kV

600 kV

Film C5/D7

� d: 1 mm / 1500 W, FFA 1000 mm

� D = 2.5 / SNRN ≈ 60� 450 kV � 4.7 h

� 600 kV � 1.1 h

DDA

� d: 1 mm / 1500 W, FDA 1330 mm� Mag: 2,2

� SNRN min 60 ≈ D7 D = 2.5� 450 kV � 240 x 1 sec, SNRN = 62

� 600 kV � 240 x 1 sec, SNRN = 82



Outline



� Summary



Summary

� A high contrast sensitivity leads to the detection of smallest defects

� SNR of DDA systems depends on� radiation quality� integration time� calibration procedure

� Digital Detector Arrays surpass film quality

State of the art digital X-ray

systems



DDA a key for CT

600 kV Digital Laminography



Questions?

� K. Bavendiek, MR21/A Radiography 346, Wednesday 16:20New Measurement Methods of Focal-Spot Size and Shape of X-Ray Tubes in Digital Radiological Applications in Comparison to Current Standards

� F. Herold, MR21/B Computed Tomography 150, Thursday 10:30Fast and Analytical Exact Reconstruction of Large CT Volumes

� M. Kurfiss, MR21/B Computed Tomography 160, Thursday 9:303-dimensional X-ray inspection of very large objects 600 kV - Digital Laminography offers a solution

Please visit our YXLON booth (121-123) for further disc ussions!


Thank you for your attention.© 2012 YXLON International GmbH

YXLON International GmbHa company of the COMET GroupEssener Bogen 15, D-22419 HamburgTel. +49 40 52729 0, Fax +49 40 52729 [email protected], www.yxlon.com


YXLON International GmbHa company of the COMET GroupAm Walzwerk 41, D-45527 HattingenTel. +49 2324 5629-0, Fax +49 2324 [email protected], www.yxlon.de

digital detector arrays - how to surpass film quality? · pdf filedigital detector arrays -...

Documents