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 N2 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, high stability is necessary in all parts of the imaging system. The source emission spot stability is critical, in terms of spot size change and positional drift, since it may cause image blurring or require additional efforts in image processing. The new NanoTube N2 60 kV achieves an increase in flux by more than 3 times compared to its predecessor, the NanoTube N1, while maintaining the same sharp focus (the new NanoTube N2 110 kV enables higher penetrating power and even higher imaging speed). Thus, reducing the measurement time significantly. At the same time, the signal-to-noise ratio gives even higher image quality due to the reduced possibility of sample motion/environmental instability within the shorter CT measurement.

Application examples:

NanoCT for life sciences

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 video and image of the limb of a velvet worm (Onychophora), 0.4 mm long. The surface morphology can be visualized with an image quality similar to scanning electron microscopy, and simultaneously the visualization of internal musculature 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).

NanoCT for material science

A similar NanoCT system with the new Excillum NanoTube N2 has been designed, developed and commissioned at Fraunhofer IIS, Würzburg, Germany. Together with an EIGER2 CdTe detector, the system has been optimized for materials characterization and NDT applications.

NanoCT for geological and raw materials

3D rendering of the phase-contrast NanoCT of an alder wood sample, revealing the inner microstructure of the wood in high resolution. Voxel sampling 300 nm.

3D rendering of the phase-contrast Nano-CT of a basalt sample, revealing the different phases, elements and structures help geologists to further understand this sample. Voxel sampling 350 nm.

NanoCT for battery research

3D rendering of the NanoCT of a lithium ion battery cathode (NCA/LCO-E), showing particles of different sizes. Voxel sampling 140 nm.

NanoCT for NDT, metrology and inspection

With its small spot size, the NanoTube N2 is ideal to study the ever-shrinking structures of electronics. This example shows a tomographic slice from a NanoCT of an SD-card, performed with the NanoTube N1 60 kV (top image) and the NanoTube N2 60 kV (bottom image) – achieving a voxel sampling of 200nm.

The comparative NanoCT measurement was done by keeping a similar level of photon counts. The NanoTube N2 60 kV achieves an increase in flux by more than 3 times and, thus, the measurement time was reduced from 15 hours to 4 hours. At the same time, the signal-to-noise ratio gave even higher image quality, due to the reduced motion within the CT measurement.

A 3D rendering of the above mentioned SD card, showing the full reconstruction of the internal features and structures. Voxel sampling 200 nm.

Photo credit if not stated otherwise: Dr. Christian Fella, Fraunhofer Institute for Integrated Circuits IIS, Würzburg, Germany

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