Scatter Correction for Industrial Cone-Beam Computed Tomography

3D industrial cone-beam computed tomography (CBCT) using flat panel imagers has become a powerful tool for applications like dimensional metrology, non-destructive testing, defect identification, and general quality control. One of CBCT’s unique advantages is that it allows for the entire volume to be scanned in a single rotation thus greatly increasing throughput. However, the wide-area cone-beam beam generates a large amount of scattered radiation that, if not corrected for, produces images that suffer from artifacts such as cupping, shading, streaks, false inhomogeneities, and quantification inaccuracies. To solve these issues the team at Varex is developing 3D VSHARP, a next generation CBCT scatter correction algorithm that quickly calculates the photon transport through a first-pass CBCT volume model and separately estimates the primary photons and scattered photons arriving in the panel detector. 3D VSHARP uses this information to remove the estimated scattered signal from the original projections. By coupling a fast finite-element deterministic photon transport solver with an NVidia GPU, the aim is to greatly improve the quality of industrial CBCT while maintaining reconstruction speeds that are fast enough to open up the possibility of using CBCT for parts inspection on an assembly line.

Amy Shiroma, Imaging Scientist at Varex Imaging Corporation, presented the results of the first demonstrations of 3D VSHARP on aluminium and Inconel parts in a paper titled ‘Scatter Correction for Industrial Cone-Beam Computed Tomography (CBCT) Using 3D VSHARP, a fast GPU-Based Linear Boltzmann Transport Equation Solver.” at the recent 9th International Conference on Industrial Computed Tomography held in Padova, Italy.

The development of 3D VSHARP originated with medical CBCT work at Varian Medical Systems, Varex’s former parent company, and has been extended to industrial applications by collaboration between Varian and Varex teams.

To experimentally verify the new 3D VSHARP scatter-correction tool, Varex engineers looked at industrial CBCT scans of an aluminum motorcycle cylinder head performed at 450kV.  The scans were taken on a Varex Scanning Services 450 kV system using a 1620-AN3 panel with an active area of 41cm x41cm and a 200µm pixel pitch.

The image below shows a central axial slice of both a 3D VSHARP-corrected and a non-scatter-corrected volume. As can be seen, the 3D VSHARP reconstruction is crisper and has improved material homogeneity. The red box outlines a zoomed-in region where a thin aluminum wall is only visible following scatter correction. When the CBCT volumes are rendered in Volume Graphics VG Studio we see improved surface definition following 3D VSHARP scatter correction reflecting the improvement in the material uniformity. Artifactual holes appear in the side walls of the uncorrected volume when none are, in fact, present.

Aluminum motorcycle cylinder head central axial-slice from the 3D VSHARP scatter-correction (left) and with no scatter-correction (right). Zoomed-in region on the top right showing restoration of a thin aluminum wall following scatter correction.
Surface renderings (VG Studio Max 3.1) of the aluminum motorcycle cylinder head with 3D VSHARP correction (left) and without correction (right). The red arrows point to missing aluminum walls in the non-scatter-corrected volume.

The algorithm is currently being incorporated into Varex’s Cone Beam Software Toolset (CST) where it will undergo extensive testing in preparation for a beta release targeted towards the end of FY ’19.

For more results and a deeper explanation of the algorithm, and results of inconel turbine blade reconstruction download the complete white paper.

For more information: www.vareximaging.com

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