A mathematical approach towards THz tomography for non-destructive imaging

Hubmer, Simon; Ploier, Alexander; Ramlau, Ronny; Fosodeder, Peter; Frank, Sandrine van

doi:10.3934/ipi.2021041

Cited by 5 publications

(4 citation statements)

References 31 publications

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“…In order to describe the CT measurement procedure (see section 2.3), we introduce the discrete sample positions 𝑠 𝑖 and projection angles 𝜃 𝑗 for each point measurement, and the density function 𝑓 (𝑥), representing the sample geometry. Analogously to our previous work [17], we now introduce the Radon transform 𝑅 [7] which is defined as the line integral along the line 𝐿 𝑖, 𝑗…”

Section: The Thz-imaging Modelmentioning

confidence: 99%

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Phase-contrast THz-CT for non-destructive testing

Fosodeder,

Hubmer,

Ploier

et al. 2021

Preprint

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Computed tomography (CT) is a well-established method for non-destructive testing (NDT), typically performed with X-radiation. Here, an alternative approach for CT based on THz radiation is presented. Optimized for the potential use-case of NDT on extruded plastic profiles, an imaging model and different resultant reconstruction approaches are derived. For experimental validation, 3D printed plastic profiles were tested with a THz time-domain spectrometer in transmission geometry. On the basis of differently complex samples, it is shown that the derived reconstruction approaches are highly robust. Quantitative analysis has further shown that the results are highly accurate for samples without curved structures.

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Section: The Thz-imaging Modelmentioning

confidence: 99%

“…In practice, these signals typically appear due to the finite cross-section of the THz beam (FWHM: 1 mm) travelling through differently thick parts of the sample simultaneously. We have recently discussed this effect in [17] by means of a more complex, non-linear imaging model.…”

Section: Pulse Phase Sinogram Mappingmentioning

confidence: 99%

Phase-contrast THz-CT for non-destructive testing

Fosodeder,

Hubmer,

Ploier

et al. 2021

Preprint

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“…THz imaging is a method established for NDT, utilizing information derived from the interaction between materials and THz radiation to produce reconstruction images. 14 THz time-domain spectrometer (TDS) systems are commonly utilized for this purpose, capitalizing on the advantages of THz waves. [15][16][17] Recently, THz computed tomography (CT) imaging systems utilizing TDS sources have seen growing prevalence within the realm of THz TDS systems.…”

Section: Introductionmentioning

confidence: 99%

“…THz imaging is a method established for NDT, utilizing information derived from the interaction between materials and THz radiation to produce reconstruction images 14 . THz time‐domain spectrometer (TDS) systems are commonly utilized for this purpose, capitalizing on the advantages of THz waves 15–17 .…”

Section: Introductionmentioning

confidence: 99%

Large‐wavelength Gaussian deconvolution phase‐contrast computed tomography for THz continuous wave (0.11 THz)

Cha,

An,

et al. 2024

Micro & Optical Tech Letters

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This letter was to present an attempt of large‐wavelength Gaussian deconvolution phase‐contrast computed tomography (LW‐GD‐PCCT) for promotion of image quality reconstructed in low‐frequency band of terahertz (THz) spectrum at 0.11 THz. The interaction between the imaging samples and the THz Gaussian beam were formulated firstly in this paper, where the unwrapped phase was extracted specifically to portray the spatial structure distribution of the samples. Additionally, a Gaussian deconvolution was employed for the further reduction of spatial distortions. Moreover, an image reconstruction was carried out with the obtained phase sinograms based on phase‐used inverse Radon transform from the different positions on the sample. For an experimental assessment of the concept of LW‐GD‐PCCT, a single ellipsoid reflector‐based THz Gaussian beam generating system was established and samples such as polystyrene (PS) foam cuboid (Sample 1), and cylinder (Sample 2) with hollow defects (air holes and triangles) were prepared carefully in this work. To experimentally evaluate the performance of the contributing to the structural imaging over soft samples. Two‐dimensional topographies of each sample were reconstructed successfully, and the obtained cross root‐mean‐square error (cross‐RMSE), cross peak signal‐to‐noise ratio (cross‐PSNR), and cross structural similarity (cross‐SSIM) were 151.6451, 26.3225, and 0.9616 for Sample 1 with a high dose of 180 projections respectively, as well as 30.3242, 33.3129, and 0.9711 for Sample 2 with a low dose of 36 projections, respectively. The obtained imaging indicators of this work showed a superiority of imaging quality over those of recent works. Furthermore, the investigation of the bearing capacity has shown promise in enhancing image quality even in low‐dose conditions. The presented results suggest that the unwrapped phase combining with Gaussian deconvolution in low‐frequency band of THz imaging would be useful to improve the reconstructed image quality, potential to highly feasible non‐destructive testing of polymer foam via large wavelength.

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Learned Anomaly Detection with Terahertz Radiation in Inline Process Monitoring

2022

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Terahertz tomographic imaging as well as machine learning tasks represent two emerging fields in the area of nondestructive testing. Detecting outliers in measurements that are caused by defects is the main challenge in inline process monitoring. An efficient inline control enables to intervene directly during the manufacturing process and, consequently, to reduce product discard. We focus on plastics and ceramics, for which terahertz radiation is perfectly suited because of its characteristics, and propose a density based technique to automatically detect anomalies in the measured radiation data. The algorithm relies on a classification method based on machine learning. For a verification, supervised data are generated by a measuring system that approximates an inline process. The experimental results show that the use of terahertz radiation, combined with the classification algorithm, has great potential for a real inline manufacturing process. In a further investigation additional data are simulated to enlarge the data set, especially the variety of defects. We model the propagation of terahertz radiation by means of the Eikonal equation.

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A mathematical approach towards THz tomography for non-destructive imaging

Cited by 5 publications

References 31 publications

Phase-contrast THz-CT for non-destructive testing

Phase-contrast THz-CT for non-destructive testing

Large‐wavelength Gaussian deconvolution phase‐contrast computed tomography for THz continuous wave (0.11 THz)

Learned Anomaly Detection with Terahertz Radiation in Inline Process Monitoring

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