Towards Traceability of CT Dimensional Measurements

Ferrucci, Massimiliano

doi:10.1007/978-3-319-59573-3_7

Cited by 9 publications

(8 citation statements)

References 29 publications

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“…Minimization methods consist of finding the set of modelled geometrical parameters that minimize the least-squares error between modelled and observed center projection coordinates, known as the reprojection error [2,5]. A ray-tracing model is used to generate the center projection coordinates for a reference object with known sphere positions given an initial set of geometrical parameter values.…”

Section: Measurement By Minimization Of Reprojection Errorsmentioning

confidence: 99%

“…The set of modelled center projection coordinates ( mod , mod ) , are compared to the set of observed center projection coordinates ( obs , obs ) , from analysis of acquired radiographs. The sum of squared residuals (SSR) between modelled and observed center projection coordinates, shown in equation (2), is used as the objective function to be minimized. It should be noted that the objective function can take other algebraic forms, for example keeping the and components of the center projection residuals separate prior to summing instead of summing in quadrature.…”

Section: Measurement By Minimization Of Reprojection Errorsmentioning

confidence: 99%

“…If the geometry used in the back projection step is not accurately known, the attenuation values for each voxel will be erroneously calculated and subsequent measurements performed on the reconstructed volume will also include errors. It is therefore critical that the geometry of the CT instrument be known accurately to ensure correct tomographic reconstruction of scanned parts [2].…”

Section: Introductionmentioning

confidence: 99%

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Measurement of the X-ray computed tomography instrument geometry by minimization of reprojection errors—Implementation on simulated data

Ferrucci

Hermanek

Ametova

et al. 2018

Precision Engineering

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The X-ray computed tomography (CT) measurement process suffers from a variety of error sources including geometrical misalignments of the CT imaging components: X-ray source focal spot, rotation stage, and X-ray detector. Effective correction of these misalignments demands accurate measurement of the instrument geometry. A common method to measure geometrical parameters involves radiographically imaging a reference object consisting of several high X-ray absorption spheres. The resulting projection images are used to solve the CT geometry of the instrument. Geometrical parameters can be solved either analytically or by minimization of reprojection errors. In this study, the minimization technique is chosen over analytical methods due to the relative versatility in its practical implementation. Various precautions must be taken when using minimization techniques and these are discussed. Errors in the data acquisition and subsequent minimization procedure introduce errors in the measured geometry and are investigated here. The geometrical measurement procedure is performed on simulated data using the Computed Tomography Calibration Tube (CT 2), a reference object that was designed to reduce sphere overlaps in the projected images while at the same time broadening the distribution of projected spheres across the detector area. It should be noted, however, that the proposed procedure can be implemented with any reference object consisting of high X-ray absorption spheres, provided the coordinate positions of the sphere centers in a local frame are known. Residual errors between the true (simulated) and measured geometrical parameters are shown to be negligible from tomographic reconstruction of datasets acquired in the presence of these residual errors.

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Section: Measurement By Minimization Of Reprojection Errorsmentioning

confidence: 99%

Section: Measurement By Minimization Of Reprojection Errorsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Measurement of the X-ray computed tomography instrument geometry by minimization of reprojection errors—Implementation on simulated data

Ferrucci

Hermanek

Ametova

et al. 2018

Precision Engineering

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“…The geometry of a cone-beam CT instrument is defined by the relative position and orientation of X-ray source focal spot, axis of object rotation (AOR), and detector [1]. The following description of the coordinate convention is supplemented by the diagram in figure 1, which also includes the parameterization of the reference object position and orientation.…”

Section: Cone-beam Ct Geometrymentioning

confidence: 99%

“…The geometry of an X-ray computed tomography (CT) instrument is defined by the relative positions and orientations of the three major components: X-ray source focal spot, sample rotation axis, and detector. Discrepancies between the geometry of the CT instrument with which radiographic projection images are acquired and the backprojection geometry in tomographic reconstruction from the images will contribute to inconsistencies between dimensional measurements performed on the reconstructed volume and the actual dimensions on the measured part(s) [1]. Consequently, these inconsistencies will result in errors of measurements performed on the volumetric data.…”

Section: Introductionmentioning

confidence: 99%

Measurement of the X-ray computed tomography instrument geometry by minimization of reprojection errors—Implementation on experimental data

Ferrucci

Hermanek

Ametova

et al. 2018

Precision Engineering

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A procedure for measuring the geometry of X-ray computed tomography (CT) instruments is applied to an experimental CT instrument. In this study, the geometrical measurement procedure is implemented with the CT 2 reference object, comprising steel spheres with known center positions in a local coordinate frame affixed to a cylindrical carbon fiber framework. The procedure can be implemented with other sphere-based reference objects, provided the sphere center coordinates are known. The effects of number of acquired projections and rotation mode (stepped or continuous) on the quality of measured geometrical parameters are studied. Finally, the output of the geometrical measurement procedure is used to inform the physical adjustment of the experimental CT instrument to its ideal alignment. The effectiveness of the measurement procedure to correctly determine the instrument geometry is demonstrated from dimensional measurements performed on a tomographically reconstructed validation object from radiographs acquired under initial (misaligned) and adjusted (aligned) instrument geometry.

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New multi-function building plate for improving metal laser powder bed fusion by enhancing the alignment accuracy of in-process monitoring data, computed tomography measurements, and building volume geometry

Zanini,

Bonato,

Carmignato

2024

Int J Adv Manuf Technol

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Laser-based powder bed fusion of metals (PBF-LB/M) is an additive manufacturing process enabling the fabrication of parts with highly complex and customizable geometries, enhanced strength-to-weight properties, and minimized material waste. Despite its unique capabilities, PBF-LB/M needs research and innovation efforts to enhance process dynamics and product quality, as well as to broaden its adoption in high-value industrial sectors, such as aerospace and biomedical. In this context, in-process monitoring solutions and post-process part quality evaluations are fundamental to improving the process towards sustainable, first-time-right, and zero-defect production. This paper describes a novel building plate concept for metal laser powder fusion, whose characteristics were specifically designed to enable and improve the performances of in-process monitoring and high-resolution X-ray computed tomography (CT) measurements. In particular, the plate features markers for perspective correction in off-axis optical monitoring and dismountable inserts with machined geometrical elements to be used for the precise alignment between high-resolution CT reconstructions, in-process gathered data, and building volume geometry. The plate capabilities were demonstrated through examples related to in-process monitoring and post-process X-ray CT measurements.

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Towards Traceability of CT Dimensional Measurements

Cited by 9 publications

References 29 publications

Measurement of the X-ray computed tomography instrument geometry by minimization of reprojection errors—Implementation on simulated data

Measurement of the X-ray computed tomography instrument geometry by minimization of reprojection errors—Implementation on simulated data

Measurement of the X-ray computed tomography instrument geometry by minimization of reprojection errors—Implementation on experimental data

New multi-function building plate for improving metal laser powder bed fusion by enhancing the alignment accuracy of in-process monitoring data, computed tomography measurements, and building volume geometry

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