Development of x-Ray Computed Tomography Image Quality

Development of x-Ray Computed Tomography Image Quality Indicators, “IQI”s

NASA Goddard Space Flight CenterMaterials Engineering BranchOSMA NDE Program

P.I. Justin S. Jones, Ph.D.

Collaborators: Antonio Moreno, Olivia Landgrover, Grace Fischetti

LaRC Additive Manufacturing Mini-TIM

November 9, 2018

From left: Convergent line pair gauge, duplex line pair gauge, step block, plaque penetrameter [ndtsupply.com]

2D DR Image

X-Ray Image Quality IndicatorsMotivation

Development of x-Ray Computed Tomography Image Quality Indicators, “IQI”s (GSFC-Jones)

2OSMA NDE ProgramLaRC AM Technical Interchange Meeting – November 9, 2018

3D CT Image

• Develop methodology and tools to assess Computed Tomography (CT) system performance.

– Fabricate Image Quality Indicators (IQIs) using materials and internal features useful for assessing inspection capabilities.

– Analyze IQI volume data to assess CT detectability limits, contrast sensitivity, resolution, etc.

– IQIs conducive to CT should be of more uniform cross-sectional aspect ratio

Program Goals/Initiatives

Original Concept: Cylindrical IQI

OSMA NDE ProgramLaRC AM Technical Interchange Meeting – November 9, 2018

Cylindrical IQI

Various design features ranging in size to assess both manufacturability (per AM method) and CT inspectability.

Flat bottom holes(4 - 0.5 mm OD)

Row of cylinders (0.5 mm OD)

Cone(4 – 0.05 mm OD)

Rectangular prisms (1 - 0.05 mm width)

Cylinders (4 - 1 mm OD) Cylinders

(0.5 – 0.05 mm OD)

Cylindrical IQI

Cylindrical IQI: Intended Performance Verification Elements

Diameter = 25.4 mm

• Resolution • Contrast Sensitivity• CT Dimensional Measurement Accuracy (CT

metrology relative to conventional measurements)

Contrast to Noise Ratio as function of:• Geometric shape• Size• Location• Density (using filled powder)

Edge sharpness/resolution:• Modulated transfer function (MTF)• Convergent features

Cylindrical IQI: as Assessment Tool for AM Process Control

1 mm1 mm 1 mm1 mm

7 mm6.5 mm5.5 mm 6 mm

Print defects

Incomplete Features

Inconsistencies

Hybrid Insert IQI

• Redesign to incorporate some existing features, but leave room for other additions:

• Rod or powder inserts to assess contrast sensitivity to various materials

• Flexible, rolled up test patterns to assess resolution

• Flexible IQI inserts tested on 100 or 125 micron Kapton substrates using either sputtered or photolithographic deposited gold.

Existing IQI features

Interchangeable, flexible, patterned inserts

Roll up

Not to scale. Features sizes exaggerated.

Hybrid IQI with Flexible Lithographic Patterned Inserts

20x25 mm Kapton film, typical of that used for the deposition substrate

Pre-existing photolithography patterns. ~2 mm total pattern length.

• Patterns came out well on first attempt. Good adhesion of Au to Kapton, though need protective coating for durability (e.g. parylene, polyurethane)

• Some “bubbling” observed on Kaptonsurface. May be residual from etch process.

• Challenges in dealing with microfabrication facility, high costs, schedules, etc.

Gold pattern thickness measured via laser confocal microscope: 536 nm

Lithographic pattern inserted into plastic SLA printed IQI

Some other CT IQI concepts

Hybrid IQI with Flexible Wire Grid Inserts

• Other insert materials being explored to avoid costly lithography• Wire meshes of varying, defined density, formed into screen

tubes and placed in concentric pattern IQI

Roll up and insert

Proof-of-Concept Trial

Taper IQI

Proof-of-Concept Trial

• Matching shell and insert, with slightly different taper angles.

• Idea is to create very small features within CT where tapers converge using simple design features.

• The above is a first cut proof of concept for more complex varying taper designs.

Most Recent Efforts: Pyramid IQI

Pyramid IQI

- Original design…

Pyramid IQI

• Pyramid 3D converging line pair gauge consists of a different sized pair of channels on each side

• As you approach top of pyramid, all features scale smaller

• Upon cross-section at any height, 2D slice provides a set of different sized line pairs

- Original design…

Pyramid IQI with sputtered gold inlays

Gold sputter deposition (~2 microns nominal) to aid in contrast of line pair tracks for higher kV scan applications.

Credit: Stephen Lebair/GSFC/ATA for Au sputter

Pyramid IQI with sputtered gold inlays

Pyramid IQI: SLA plastic with electroless nickel coating

UV projection 3D printed version

3D printed version with electroless Ni deposition to

aid contrast

Mini version with the electroless Ni

deposition

Pyramid IQI: SLA plastic with electroless nickel coating

Pyramid IQI: Ni-coated and use of external fiducials for alignment, elevation gauge, and external verification.

Pyramid IQI: Penetrameter Insert Concept (laser micro-machined discs)

Inner hole sizes not to scale. Actual holes will

be much smaller.

Conventional “2D” radiographic hole penetrameters

CT of xCT “Pyramid IQI”

Pyramid IQI: Penetrameter Insert Concept (laser micro-machined discs)

Inner hole sizes not to scale. Actual holes will

be much smaller.

Initial concept

Pyramid IQI, Next Steps

• Pursuing full metal version (~2-3x smaller) printed using micro laser sintering (possibly working with Precipart or 3D MicroPrint GmbH)

• Currently incorporating other “internal features” such as disc penetrameters

• Print IQI set to cover range of sizes and run CT system assessments

A few other activities in the lab…

• Round Robin testing of the ASTM E07/F42 Inserts and Prisms

• 9 scans; various combinations of inserts and both the small stepped pyramid and small cone

• Interested in line defects and contrast sensitivity of defect with increasing wall thickness

• New start proposal (OSMA NDE program) on AM Flaws

• Assess the key NDE signal-related differences between flaws in AM parts versus conventional parts

• Looking at 2 key variables: Surface roughness and grain structure

• NESC support for micrometeorite impact assessment for COPVs

• Cryogenic CT scan Capability• Contrast enhancements for CT and for PT of

AM parts• Various ongoing GSFC Program-related work• Lunar sample research• Efforts to push awareness for CT for In-Space

1st cryoCT scan Lunar meteorite

Thanks for your time!

Development of x-Ray Computed Tomography Image Quality

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