Attenuation-contrast imaging

Attenuation-contrast imaging is the conventional way of obtaining X-ray images. Materials with higher density or higher atomic number attenuate more X-rays, and therefore give less transmission.

Direct imaging of the transmitted intensity resembles a shadow of the object and is therefore referred to as shadow projection imaging. This method is widely used for medical imaging, but also for many other imaging tasks.

The technology development towards fast high-resolution imaging has been driven by the needs in scientific research, industrial R&D, and production quality control. To visualize fine details of the microstructure in the object, the imaging can be done either by using X-ray radiation coming from a small emission spot, or by using X-ray optics to build a microscope setup.

An X-ray tube with extremely small emission spot size can give high resolution imaging without optics. The advantages of this approach without optics, is the efficiency across the full energy spectrum as well as the ease in getting a large field of view. Thanks to the geometric magnification produced by the point source, the object can be imaged at much higher resolution than the detector can handle.

With a minimal emission spot size below 400 nm, the Excillum NanoTube enables lensless sub-micron X-ray microscopy and NanoCT in the laboratory. For the applications where a 5-20 µm spot is enough, the MetalJet offers up to 10 times more brightness than any other microfocus tube.

High resolution imaging can sometimes require very long acquisition times. During the acquisition, environmental stability is necessary in all parts of the imaging system. The source emission spot stability is critical, as it will otherwise cause blurring in the images.

NanoTube for attenuation-contrast imaging

The Excillum NanoTube is based on advanced electron optics refined from the MetalJet e-beam platform and the latest tungsten-diamond transmission target technology. In the NanoTube, the bulk anode is replaced by a cutting-edge thin tungsten layer on top of a diamond substrate, which is transparent to X-ray and has good thermal conductivity. This makes it possible to achieve a smaller focal spot size compared to the conventional transmission type tube where the electron diffusion in the bulk anode material makes this difficult. As a consequence, it enables an unprecedented true resolution of e.g. repetitive patterns of 150 nm lines and spaces such as JIMA or Siemens star.  Automatic e-beam focusing and astigmatism correction ensures that the smallest possible truly round spot is achieved at any voltage and current setting. The NanoTube has the unique feature that it internally measures and reports the current spot size. In addition, advanced cooling and thermal design lead to its extreme stability over long-time exposure.

Features and benefits

  • True small X-ray round spot for 2D/ 3D imaging with isotropic high resolution
  • Ultimate spot stability, guaranteed by long-time measurement
  • Automatic E-beam focusing and astigmatism correction at each user defined tube setting.
  • Cone-shaped front surface of the tube for excellent geometric access to the focal spot
  • Absolute internal spot size measurement
  • User-friendly graphic user interface and API support
  • Capability of shifting E-beam within target area

MetalJet for attenuation-contrast imaging

The MetalJet is Excillum’s patented, high-brilliance micro-focus X-ray source.  It uses a fast-flowing liquid jet of metal instead of a solid anode metal target, thereby allowing a greater power loading to be placed on the metal target. The high-speed jet efficiently transports heat away from the interaction point and quickly regenerates the alloy. In this way, the MetalJet can generate a much higher-brilliance than conventional solid anode X-ray tubes.

Features and benefits

  • Extreme microfocus source power, with ~10x higher brilliance than conventional microfocus X-ray tubes
  • Small, adjustable and well-defined X-ray spot
  • Stable X-ray emission and spot position, which is essential for long-time measurements
  • User-friendly Graphical User Interface with remote control through TCP/IP protocol for full control of source settings
  • User selectable e-beam size and position on the metal-jet enables variable take-off angle, to adjust X-ray spot size, flux and spectrum hardness
  • Advanced e-beam technology and algorithm for internal absolute spot size calibration in micrometers
  • Unique target material enables the use of characteristic lines
  • Optional dual-port mode, enables two setups from the same source

Application examples

A NanoCT device comprising of a NanoTube and a photon counting detector provides the ability of tomography with very high resolution. At the Technical University of Munich (Germany) the device has achieved a state-of-art ~100 nm spatial resolution and capability of investigating phase-contrast imaging.

Nano-CT images of the limb of Onychophora (0.4 mm long). The surface morphology (left) can be visualized with an image quality similar to scanning electron microscopy, and simultaneously the visualization of internal musculature (right) at a resolution higher than confocal laser scanning microscopy.  

M. Müller, et al., “Myoanatomy of the velvet worm leg revealed by laboratory-based nanofocus X-ray source tomography“, PNAS (2017).

As another example from the same NanoCT system, the anatomical structures in the cortex of a mouse kidney sample was studied with a new staining method. The minimum intensity projection slice (left) of its Nano-CT image gains a good comparison to histological data (right).

M. Busse et al., “Three-dimensional virtual histology enabled through cytoplasm-specific X-ray stain for microscopic and nanoscopic computed tomography”, PNAS (2018).

Similar Nano-CT system with NanoTube has been commissioned at Fraunhofer IIS, Würzburg, Germany, together with an EIGER2 Detector (replaced by EIGER2 CdTe in 2018). 

Volumetric rendering of a 200 µm diameter Diatom (unpublished). Image in courtesy by Dr. Christian Fella from Fraunhofer IIS.

Unless otherwise stated, pictures and content is published under license for CC-BY (https://creativecommons.org/licenses/by/4.0/​).

Recommended products for attenuation-contrast imaging

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