Contact

Dr. Martina Bieberle

m.bieberleAthzdr.de
Phone: +49 351 260 3283

Prof. Dr.-Ing. Dr. h. c. Uwe Hampel

Head
Experimental Thermal Fluid Dynamics
u.hampel@hzdr.de
Phone: +49 351 260 2772

Ultrafast limited angle X-ray computed tomography

Ultrafast limited angle X-ray computed tomography is a tomographic measurement technique that enables data acquisition with a frame rate of up to 10,000 s-1 and a spatial resolution of about 1 mm. Thus, transient processes like multi-phase flows, mechanical switching operations or chemical processes can be investigated. The gathering of projections from different directions, which is required for the reconstruction of non-superimposed cross-sectional images, is not realised by rotating the object or the measurement system. Instead, the electron beam, which generates x-ray emitting focal spot on the target, is electronically deflected.

Measurement principle

A moving X-ray source is realised by deflecting the electron beam along a linear path on the target. Thus, projections of the object of investigation from different directions can be acquired. The electron beam is guided in vacuum to generate a 0.3 mm wide X-ray emitting spot on the target. The radiation intensity at the detector is converted into a voltage signal that is sampled with 1 MHz for all detector elements in parallel. The digital voltage signal is then transferred to a measurement PC for further processing.

 LAT Aufbau englisch

Image reconstruction

From the X-ray projections non-superimposed cross-sectional images of the object of investigation can be calculated using image reconstruction algorithms. In this setup, X-ray spot path and detector are lying within one plane, which provides maximal axial resolution. However, the effective angular range for projections is limited. In order to be able to reconstruct cross-sectional images in spite of the missing projection angles, special iterative image reconstruction algorithms on the basis of the level-set-method were developed, which directly reconstruct phase or material boundaries.

 MN

Level-Set-Rekonstruktion

Level set reconstruction suppressing
disturbing limited-angle artefacts

Two-plane tomography

Volumetric tomography

To be able to determine phase velocities besides the phase distribution within the imaging plane, a two-plane tomography setup was realised by alternatively scanning two vertically displaced X-ray spot paths. From the two tomography planes generated this way, velocity information can be derived using cross-correlation techniques.

The extension of the measurement setup towards an ultra-fast volumetric tomography is realised by applying a stepped target. Similar to the two-plane tomography setup, a number of X-ray paths is scanned successively to generate multiple tomography planes. From the resulting projection data a three-dimensional image of the object of investigation can be reconstructed with a frame rate of 500 s-1.

Zweiebenentomographie

Volumentomographie englisch

FlyingBalls

Future activities

Present research aims at the further development of the volumetric tomography towards a full-angle tomography by using a target that is transparent for X-rays.

Publications

Co-operation partners

Universität Stuttgart, Institut für Kernenergetik und Energiesysteme

Acknowledgement

This work has been supported by Deutsche Forschungsgemeinschaft (DFG)
(Grant numbers HA 3088/3-1 and KO 2942/3-1).