A new way to reveal previously invisible features of objects non-destructively and in 3D is realized in the world’s first commercially available phase-contrast desk-top microtomography scanner, the SkyScan-1294. On top of traditionally observed local object absorption, the system allows you to reveal local X-ray refraction and scattering in object features, far beyond reconstructed pixel sizes. The new SkyScan1294 is based on the unique technology of phase-contrast imaging with polychromatic X-rays patented by the Paul Scherrer Institute at the Swiss Light Source (Zurich, Switzerland) and licensed to Bruker microCT for commercialization.
Simultaneous extraction of absorption, differential phase and dark-field (scattering) images
Three-grating X-ray interferometer with 30 keV design energy
Microfocus 100 W X-ray source, 20-60 keV peak energy
Five position filter changer for energy window selection
11 megapixel cooled CCD X-ray detector
Compact, fully shielded desk-top instrument
World’s fastest hierarchical InstaRecon® 3D reconstruction
Touchscreen control for main functions
Surface and volume rendering, export results to phones and tablets
How Does the Phase-Contrast Scanner Work?
While passing through the object, the X-ray beam changes. It loses some intensity by object absorption and changes also the wave phase because of differences in propagation speed. The wavefront behind the object becomes modulated by object absorption and changes the direction of propagation due to the phase shift. Conventional X-ray cameras are not sensitive to the direction of incoming X-rays and can detect only absorption in the object. At the same time, the directional part may contain information about object details without significant absorption and at sizes much smaller than can be distinguished by a particular camera.
To recover phase-shift information, it should be converted to an intensity signal detectable by the X-ray camera. Such a conversion is performed by a special set-up named the Talbot-Lau X-ray interferometer, which contains several absorption and phase-shift gratings with a micron-size pitch. The phase grating G1 creates an interference pattern with local maxima and minima of intensity. If the object changes the direction of the primary beam, the pattern becomes locally shifted. The absorption grating G2 strips this pattern and converts it to intensity modulation, which can be detected by relatively large pixels in the detector. To create the necessary conditions for interference, an additional absorption grating G0 in front of the X-ray source divides the primary beam into a large number of spatially correlated thin beams. All gratings are precisely aligned with each other.
The X-ray interferometer allows the converting of local phase shifts in the object to intensity modulation, which can be detected by the camera together with absorption information. To separate information from the phase-shift from the absorption information, one of the three gratings is moved through several positions inside a single grating pitch. Such movement creates sinusoidal modulation for every pixel of the camera. By comparing sine curves with and without the object in every pixel, the phase shift and scattering information can be separated from the absorption information. All types of information are extracted in a single calculation process and can be displayed on-screen simultaneously. The camera image is shown in the top left corner, the absorption image - in the top right part, the differential phase-contrast image at the bottom left and the dark-field (scattering) at the bottom right.