Three dimensional visualisation of barley corn seed and fish tissue using Talbot Lau grating interferometer.

Transcription

1 Three dimensional visualisation of barley corn seed and fish tissue using Talbot Lau grating interferometer. Guruprasad Rao, Christian Gusenbauer, Sascha Senck, Johann Kastner University of Applied Sciences Upper Austria, Stelzhamerstraße Wels, Austria. Aim In this contribution we present the initial results concerning plant and animal tissue samples using a newly developed desktop Talbot-Lau grating interferometer XCT (Talbot-Lau XCT, SkyScan 1294). Plant tissue sample is an untreated and malted barley corn seed. Animal tissue sample is a fish. Talbot-Lau XCT is advantageous in non-destructive analysis field as it provides complementary information to standard absorption-based methods (AC) in the form of differential phase contrast (DPC) and dark-field images (DFI). In particular dark field imaging reveals information undisclosed by both AC and DPC imaging since dark field contrast delivers morphological information in the sub pixel regime depending on the local scattering power [1, 2]. As dark field images yield a high contrast and a strong signal of interfaces, the epidermal tissue of barley corn seed and gill organs of fish are visible. Method X-ray radiography and computed tomography are non-destructive analysis methods which disclose hidden inner structures of various materials. It is of particular interest to observe the inner structures of material samples of biological origin. By looking at internal morphology we can understand function and properties of various biological structures in a better way. In the last decade, one of the most important innovations in X ray technology has emerged by the introduction of the Talbot Lau grating interferometry [3, 4]. In 2002, the Talbot-Lau effect was first utilized for X-ray imaging of a so-called "phase object" using monochromatic synchrotron radiation [5]. The additional use of a source grating [3] enabled the introduction of this technique to polychromatic X-ray sources. In this set-up, the effect is based on the selfimaging of a grating whose period is a significant multiple of the wavelength. Using the Skyscan 1294, which makes this technology accessible in a desktop system, we scanned our samples in order to visualize internal morphology. This method provides simultaneous multiple assessment of the specimen using complementary X-ray and matter interactions characteristics in a single scan as follows: 1) Attenuation contrast (AC) 2) Differential phase contrast (DPC) 3) Dark-field images (DFI) Information provided by the AC is based on the absorption coefficient of the material. DPC image is dependent on the refractive nature of the X-rays inside the material. DFI is the resultant of small angle scattered X-rays due to the presence of microscopic inhomogeneity which can be either be present as a part of micro-voids present, fibrous structures and cracks or any other inherent inhomogeneity of the biological sample under consideration. Depending on the micro-structure, the scattering has a preferred direction perpendicular to the local orientation, which is reflected by the measured dark-field signal. [6] This immanent physical property of grating-based dark-field imaging can be used to extract directional

2 information about the angular variation of e.g. differently oriented carbon fiber bundles or layers [7]. In order to generate three-dimensional data, the three complementary sets of AC, DPC, and DFI projections are simultaneously acquired stepwise at different angles of a full rotation of the specimen and subsequently reconstructed. Some of the hardware specifications of Skyscan 1294 are as follows [8]: X-ray source 20-60kV, 100 W, 30 μm spot size. Three-grating phase extraction interferometer with design energy 30keV. 11 megapixel cooled CCD X-ray detector. Isotropic voxel size of (5.7 μm) 3, 4000 x 2672 detector pixels. Five drives motorised grating alignment system. Scanning parameters are mentioned in Table 1 below. Table 1: Scanning parameters: voltage (kv), current (µa), integration time (ms), binning (bin), Voxel size (µm 3 ), number of projections (Proj.), filter, rotation step (degrees) total scan duration (in minutes). kv µa ms bin VS Proj. Rot filter ation Min st ep Barley Al corns x ( (Skyscan) mm) Barley corns (Nanotom) Al Fish x ( mm) Results Figure 1 shows (a) untreated and malted barley corns. The untreated barley corns are bright in colour and become dark after malting procedure. The microstructure of barley corn has an important influence on the brewing process, since the inner structure facilitates the reactivation and the development of enzymes required for converting the grain's starches into sugars. The untreated barley corn shows a compact region of endosperm with fewer cracks as compared to the malted one. [9] Figure 1 (b) shows AC, DFI and high resolution (8.25 µm 3 ) image of the barley corn samples. The top seed is untreated and the bottom seed is malted. More material features are observed in high resolution scans. The epidermal layer of the barley seed can be prominently seen in the dark field image. The cracks in the malted seed produce a noticeable grey values as circled in the picture.

3 Un-treated Malted (a) (b) (c) (d) Fig. 1 (a) Untreated barley corn and malted barley corn, (b) Absorption contrast, (c) Dark field (effect due to micro cracks), and (d) high resolution Absorption contrast (Nanotom 8.25 µm 3 )

4 Figure 2 shows image of fish inside a PMMA polymer, AC, DFI and DPC images. Fish bones and lungs are very clearly seen in the AC images. Tissue features near gills and lungs of the fish are seen in dark field images. Eye of the fish can only be seen separately in phase contrast image. Gill structures Lung Bones (a) (b) Eye Gill structures (c) (d) Fig. 2 (a) Fish inside PMMA polymer, (b) Absorption contrast image, (c) Dark-field image and (d) Phase contrast image

5 Conclusions In this study we presented different visualisations of the plant and animal tissue using a desktop Talbot Lau grating interferometry XCT system (Skyscan 1294). We observed that the dark field images shows features of the materials not visualised by absorption contrast and phase contrast. Detailed cracks in the malted barley corn were visible in high resolution absorption image. The epidermal layers of the barley corn and gill structures were seen in DFI images. The eye of the fish was visible only in DPC image. Different morphological information was acquired using AC, DFI and DPC images provided by Talbot-Lau XCT system. The obtained data can subsequently be used for the anatomical analysis of fish and cellular feature studies and effects of micro-cracks in barley corns on its brewing performances. Acknowledgements The work was financed by the K-Project ZPT+ supported by COMET programme of FFG and by the federal government of Upper Austria and Styria. The research leading to these results has also received funding from the European Union s Seventh Framework Programme (FP7/ ) under grant agreement No (INTERAQCT: International Network for the Training of Early stage Researchers on Advanced Quality control by Computed Tomography). References [1] M. Bech, O. Bunk, T. Donath, R. Feidenhansl, C. David, F. Pfeiffer, Quantitative x-ray dark-field computed tomography, Phys. Med. Biol. 55, , 2010 [2] V. Revol, B. Plank, C. Kottler, J. Kastner, R. Kaufmann, A. Dommann, A. Neels, Laminate fibre structure characterisation by orientation-selective X-ray grating interferometry, Proc. 5th Conf. Ind. Computed Tomography. Wels (Austria), 45 51, 2014 [3] F. Pfeiffer, T. Weitkamp, O. Bunk, C. David, Phase retrieval and differential phase-contrast imaging with low-brilliance X-ray sources, Nat. Phys. 2, , 2006 [4] F. Pfeiffer, C. Kottler, O. Bunk, C. David, Hard X-Ray Phase Tomography with Low- Brilliance Sources, Phys. Rev. Lett. 98, , 2007 [5] C. David, B. Noḧammer, H.H. Solak, E. Ziegler, Differential x-ray phase contrast imaging using a shearing interferometer, Appl. Phys. Lett. 81, , 2002 [6] Kastner, J., Plank, B., Gusenbauer, C., Senck, S., Revol, V., & Sasov, A. Talbot-Lau grating interferometer X-ray computed tomography for the characterization of fiber-reinforced polymers, Digital Industrial Radiology and Computed Tomography (DIR 2015) June 2015, Belgium, Ghent [7] V. Revol, B. Plank, R. Kaufmann, J. Kastner, C. Kottler, A. Neels, Laminate fibre structure characterisation of carbon fibre-reinforced polymers by X-ray scatter dark field imaging with a grating interferometer, NDT E Int. 58, 64 71, 2013 [8] Skyscan 1294: Phase contrast desktop X-ray micro-ct - a new way to reveal the invisible ( [9] Gusenbauer, C., Leiss-Holzinger, E., Senck, S., Mathmann, K., Kastner, J., Hunger, S., & Birkfellner, W. (2016). Characterization of medical and biological samples with a Talbot Lau grating interferometer μxct in comparison to reference methods, Case Studies in Nondestructive Testing and Evaluation February 2016.