X-ray Imaging

The first X-ray image, of his wife Anna's hand,
taken by W.C. Röntgen in 1895

First X-ray image

X-ray Imaging

From an ancient mummified hand, this fingertip
was recently imaged using a MetalJet source

X-ray Imaging

An image of a velvet worm "hand" revealed
by tomography using a NanoTube source

X-ray Imaging

Imaging is the first historic application using X-rays, as demonstrated already by W. C. Röntgen, and remains the most common application especially due to its wide use for medical imaging. Since the first X-ray image in 1895, an enormous development of X-ray equipment has taken place. Even though most imaging done today uses the same method as Röntgen did, the image quality has become far better thanks to the improved sources and detectors. Nowadays, X-ray imaging is also widely used in various fields, from industrial inspection & metrology to academic research.   

The improved equipment has also opened up the possibility of new methods for X-ray imaging. They all differ in imaging performance and in their requirements on the equipment. Below we give a brief overview of popular imaging methods together with application examples using the MetalJet and NanoTube sources. 

All the methods can be used either in two-dimensional projection imaging or three-dimensional computed tomography (CT). Whichever shall be used depends on the specific needs in the application!

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.

 

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/​).

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