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X-rays see allX-ray computed microtomography (µCT) – a novel technique available at CERN for material and metrological inspection
Mariusz Jedrychowski EN/MME-MM
Introduction of new technique at CERN
16/05/2018
Article on CERN Bulletin
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12/12/2017
Shipment of Zeiss Metrotom CT 1500 to Bdg. 100.The lead-shielded closed-cabinet system came assembled in a 8100
kg truck pallet.
Open Day – 6th June 2018
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What we can see with X-rays?
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An x-ray radiograph of A Misereuse Accroupie
Photography by Craig Boyko/Art Gallery of Ontario
Wilhelm Roentgen
What we can see with X-rays?
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Molibden-Graphite prototype collimation
material for HL-LHC
(WP5-Collimation – ARIES)
Brazing inspectionHigh X-ray
absorption
inclusions
Voids / filling
imperfections
Electric circuit
µCT – outstanding possibility to see and analyse in 3D
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Inclusion analysis for Mo-Gr samples
µCT – outstanding possibility to see in 3D
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Superconducting cable for ITER project
Voltage: 225 kV,
Distance: 160 mm
Voxel size: 50 µm,
Projections: 2000,
Integration time: 2 s,
Measurement time:
2.5 h
Top
ViewFront View
µCT – outstanding possibility to see in 3D
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Superconducting cable for ITER project
µCT – outstanding possibility to see in 3D
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Superconducting cable for ITER project
µCT – outstanding possibility to see in 3D
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CLIC Spiral Load – 3D
printed titanium object
Voltage: 220 kV,
Distance: 750 mm,
Voxel size: 111 µm,
Projections: 2050,
Integration time:
1000 ms,
Measurement time:
1.5 h
Overview
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1. X-ray computed tomography
• Short introduction
• Possibilities: NDT, metrology
2. Zeiss Metrotom CT – specification
3. Software
4. Applications gallery
5. “X-rays see all”. How far we can see with µCT in practice ?
6. Image processing techniques developed at CERN
X-ray computed (micro)tomography - µCT
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Rotary table
Flat image detector
high-resolution: 2048 x 2048 pixels
X-ray tube determines
the range of applications:
• a smaller focal spot is used
for high resolution,
• a higher voltage is used for
more absorbent
(denser/thicker) pieces
Tube/detector distance
determines the available measuring range:
Piece
Regions with different
X-ray absorption
Projections
2D radiography
Precision axes
The workpiece can be moved on four axes with
extreme precision provided by coordinate measuring
technology which, in result, allows metrology
measurements.
X-ray computed (micro)tomography - µCT
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30 cm
X-ray computed (micro)tomography - µCT
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3D reconstruction3D set of grey level voxels
Projections
2D radiography
22.5º
Zeiss Metrotom CT
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Detector
Sample holder
– Rotary table
X-ray generator
Zeiss Metrotom CT
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Specification
• Microfocus X-ray tube:
Max. voltage 225 kV
Max. current 3000 µA
Max power 500 W
Min. focal spot size 7 µm
• High resolution flat panel imager:
40 x 40 cm
2048 x 2048 pixels, 16 bit
• Tube-detector distance: 1375 mm
• Max. spatial resolution: 4 μm
Inoptimum conditions: small piece
and contrasting materials.
Typically voxel size is 10 to 100 μm
• Length measurement error [µm]:
9 μm + L/50
Max through thickness
Material Max. through
thickness [mm]
Polymer > 300
Aluminium 300
Titanium 200
Steel 50
Copper 20 - 30
Sample size vs voxel size – extended field of view
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Carbon piece for ALICE detector
Horizontal and vertical
extensions used,
5 scans merged, Voltage: 190 kV,
Distance: 437 mm,
Voxel size: 65 µm,
time: 6.5 h
CT data size: 112 GB
Projection: 80° Surface mesh
70 cm
Analysis possibilities provided by CT data
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Obtained CT data are stored in form of 3D lattice of voxels that allows a wide
range of analyses to be performed:
1. 2D Cross-sections
2. 3D Qualitative visualization
3. Separation of different parts in a sample - grey level value segmentation
4. Particle analysis (size, position and shape descriptors)
5. Weld assessment
6. Surface mesh extraction
7. Wall thickness
8. Advanced applications: classification, quality control, corrections for
additive manufacturing settings, metrology measurements, FEM
simulations based on CT data
Software
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NDT Applications – qualitative observations
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Copper micro Nozzle
Voltage: 220 kV,
Distance: 165 mm,
Voxel size: 26 µm,
Projections: 1750
Image avg.: 3 images
Measurement time: 3 h
3D volume with clipping plane
3 cm
Beam hardening
NDT Applications – qualitative observations
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Voltage: 225 kV,
Distance: 470 mm,
Voxel size: 70 µm,
Projections: 3000,
Measurement time: 2 h 3D volume – side view
11 T magnet coil
80 cm
NDT Applications – qualitative observations
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Connector in cryogenic instrumentation for LHC
Voltage: 220 kV, Distance: 90 mm, Voxel size: 15 µm, Projections: 2050, Measurement time: 2.5h
1.5 cm
NDT Applications – electronics
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Electronic component for ATLAS Forward Proton Detector
Shorts ground-high voltage cable due to air bubbles found inside ATLAS ChipAim: to understand issues related with IC
packaging problem
Voltage: 215 kV, Distance: 55 mm , Voxel size: 9.64 µm,
Projections: 2050, Integration time: 2 s, Measurement
time: 2.5 h
3D volume and Top View cross-section
Voltage: 220 kV, Scan time: 1 h 10 min, Voxel size: 23 µm
1 cm
2.5 cm
NDT Applications – Porosity/Inclusion analysis
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Inclusion analysis for Mo-Gr samples
Porosity in brazed layers
of NA62 connector
1.5 cm
NDT Applications – Porosity analysis
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Copper brazed with steel
Test piece
identification
Filling
%
Conformity with
EN ISO 18279
quality level C
Unrolled brazing surface
1 >90% YES
2 >95% YES
3 >90% YES
4 >90% YES
5 >85% YES
6 90% YES
brazed connections for R2E-LHC2.5 cm
NDT Applications – Wall thickness analysis
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90 cm
Analysis of wall
thickness of ALICE
aluminium tubular
segments
NDT Applications – quantitative observations
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Voltage: 220 kV, Distance: 150 mm, Voxel size: 23 µm,
Projections: 2050, Integration time: 2000 ms, Measurement time: 2.5 h
PCB with socket
Aim: to understand issues
related with loosen connection
between socket and plug
Comparison: bad vs good socket
NDT Applications – quantitative observations
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CLIC Spiral Load
Surface rendering
Voltage: 220 kV,
Distance: 750 mm,
Voxel size: 111 µm,
Projections: 2050,
Integration time:
1000 ms,
Measurement time:
1.5 h
Metrology Applications
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1 – Importation of tomographic data on
Calypso
2 – Preparation measurement program
3 – Use of specific Calypso algorithms such as
Curve, Freeform for surface measurements of
Freeform shapes (impossible on VG Studio)
4 – Same program than CMM: possibility to
pass from CT to CMM for the same part
Metrology Applications
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CLIC Spiral Load Nominal-Actual Comparison
Applications - metrology
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Voltage: 215 kV, Distance: 55 mm, Voxel size: 9.64 µm, Projections: 1600
Image avg.: off, Integration time: 2000 ms, Measurement time: 1 h
Projection: 90° 3D volume with
clipping plane
2D cross-section
Titanium printed spring with Zirconia sphereAim: Metrology measurements in order to quantify sphericity and roundness of the interface between
sphere and spring
0.5 cm
Applications - metrology
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Aim: Metrology measurements for machining purpose – estimation of thickness to be removed
Titanium printed serpentine
3 scans merged
Voltage: 215 kV,
Distance: 186 mm,
Voxel size: 28.64 µm,
Measurement time: 4 h
3D volume with clipping plane
12 cm
Voxel size (Resolution)
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What is the voxel size for my sample ?
It depends on:
1. magnification (x position) / sample size
2. beam intensity / Image Contrast / Image Quality
focal spot size (micro focus – nano focus X-ray tube)
beam filtration
3. sample orientation
acquisition time and data size
resolution vs detectability
1. Magnification / voxel size
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Tube/piece/detector distances
magnification M = D/x
X - ray
tubeDetector
Object
D = 1375 mm
x
voxel_size [µm] = 410/1375 * x [µm] /2048 = 0.145 * x [mm]
410
Top View
W
A cube defined by W x W x W is considered
W = 2048 * voxel_size
W / x = 410 mm / D (from Thales relation)
(assuming that detector area is fully filled in by object projection)
1. Magnification – voxel size vs sample size
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Distance [mm]
50 70 140 280 550 700
Voxel size [µm] 7 10 20 40 80 100
W [mm]
(“Sample size”)14 20 40 80 160 200
Magnification 28 20 10 5 2.5 2
But this is the best case. In practice sample is not perfectly aligned with detector center/plane. Also, because of
maximum thickness to be passed through by X-rays (tilted orientation).
Hence, it has to be placed further away from the X-ray tube in order to decrease magnification (fit inside
projection frame)
2. Influence of focal spot size
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Point
Source
Small
Focal Spot
Large
Focal Spot
Object
Image
Detector
penumbra
Focal spot size has to be adjusted in respect to object size in order to avoid blurred projections
2. Effect of focal spot size – blurred projections
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2. Spot size – blurred projections
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Spot size = 90 µm
Current = 500 µA
Voltage = 180 kV
Magnification = 65
2. Spot size – blurred projections
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Spot size = 36 µm
Current = 200 µA
Voltage = 180 kV
Magnification = 65
2. Spot size – sharp projections
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Spot size = 7 µm
Current = 50 µA
Voltage = 180 kV
Magnification = 65
2. Spot size – reconstructed thin tungsten wire
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Spot size = 7 µm Spot size = 46 µm
voxel size
9.3 µm
3. Beam intensity – why beam has to be filtered?
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Beam hardening (BH) artefact Main reason of BH
Uncorrected BH
Corrected BH
3. Beam intensity – why beam has to be filtered?
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Theoretical energy spectra for 420-kV X-ray source with
tungsten target, calculated combining 5-keV intervals.
Spectra consist of continuous Bremsstrahlung and
characteristic K-series peaks at 57–59 and 67–69 keV.
R.A. Ketcham, W.D. Carlson / Computers & Geosciences
27 (2001) 381–400
3. Beam intensity – Filtering of Energy distribution
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No filter, 220 kV, 400 µA, spot size = 88 µm
Cu = 2 mm, 220 kV, 400 µA, spot size = 88 µm
No filter, 180 kV, 490 µA, spot size = 88 µm
Cu = 2 mm, 180 kV, 490 µA, spot size = 88 µm
3. Beam intensity – how it can be increased
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We take advantage of detector capabilities in order to increase signal registered
Solution Consequence
• Longer integration time => Longer acquisition
• Higher gain (signal amplification) => increased noise
• Binning 2 x 2 => reduced CT voxel size
(increased detector pixel size, 1024 x 1024 px instead of 2048 x 2048 px)
3. Beam intensity – [Gain = 16, Integration time = 2 s]
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Cu = 2.5 mm, 220 kV, 488 µA, spot size = 70 µA
Cu = 2.5 mm, 220 kV, 45 µA, spot size = 7 µA
Contrast = Max Intensity – Min Intensity
4. Sample orientation – Feldkamp reconstruction artefact
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electronic components in power amplifiers
for LIU-SPS project
Sample orientation – Feldkamp reconstruction artefact
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Sample orientation – Feldkamp reconstruction artefact
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4. Sample orientation – Feldkamp reconstruction artefact
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Developed Applications – Pore segmentation algorithms
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Several image
processing methods
were developed in
order to estimate
porosity of brazing
Developed
algorithm
Standard
approach
Final result
Developed Applications – CT vs Ultrasound inspection
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A method was developed in order to compare porosity estimation obtained
from µCT measurements and ultrasound inspection
Voltage: 215 kV,
Distance: 90 mm,
Voxel size: 15 µm,
Projections: 1600,
Measurement time: 2 h
Defects found by UT (red areas on the left) and CT (dark areas on the right)
Developed Applications – X-ray radioscopy
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Chip0FF - 1840
Chip1FF - 1840
Chip2FF - 1840
Chip3FF - 1840
Chip4FF - 1840
Chip5FF - 1840
Chip6FF - 1840
Chip7FF - 1840
Chip8FF - 1840
Chip9FF - 1840
Sphere diameter < 20 µm !
Developed Applications – X-ray radioscopy
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A Flat Field algorithm was developed at CERN in order to perform manual X-ray
radioscopy using Zeiss Metrotom CT
– standard scan mode imposes sample rotation which limits resolution in the case of a flat sample.
Corrected Image = (Raw_Projection – Dark_Frame)/(Bright_Frame – Dark_Frame)
RAW projection Bright Frame (Gain) Dark Frame (no beam) Corrected projection
Developed Applications – X-ray radioscopy
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Width = 15 cm
Summary
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1. NDT
New possibilities to analyse quantitatively and qualitatively internal structure of materials
2. METROLOGY
• Complementary to CMM and other measurement means
• Good accuracy for many parts
3. Custom Algorithms and image processing methods were developed. One of them will be presented at the iCT Conference 2019 in Padova
Thank you for your attention!
Developed Applications – Pore segmentation algorithms
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Several image processing methods were developed in order to estimate porosity of brazing
Binary
cleaningAuto local
threshold
Noise
reductionCLAHEStandard
threshold Final result
Applications - metrology
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Aim: 1. Comparison of 3D printed sample with CAD model used for printing.
2. Estimation of surface thickness removed during following polishing
Titanium sample 3D printed and polished (designed for crab cavity)
Voltage: 220 kV
Distance: 755 mm
Voxel size: 112 µm
Projections: 2200
Image avg.: 3 images
Integration time: 1 s
Measurement time: 2 h
Projection: 90°Nominal/actual comparison
with CAD model
3D volume with
clipping plane
