Low-radiation dose scanning Compton X-ray microscopy


Recently, the Saša Bajt team from the Free Electron Laser Center in Germany designed and manufactured a new scanning Compton X-ray microscope, which can significantly reduce the radiation dose required for imaging, reduce the damage to biological samples, and provide strong support for the further development of soft matter and biological material imaging technology.

Research background

Shortwave radiation, such as X-rays or electrons, can be used for spatial resolution imaging close to the atomic scale, however, the radiant energy of Ångström wavelengths is sufficient to ionize the material under study, causing structural changes in the material that limits the quality of the sample image. This problem is particularly critical in bioimaging, where the biomaterial can only withstand a certain maximum dose to avoid structural damage caused by radiation affecting the imaging effect.

For cryogenic cooled hydrated biological samples, the length scale of structural degradation is approximately linear with the dose. THEREFORE, THE ACCEPTABLE DOSE IS PROPORTIONAL TO THE RESOLUTION, AND IT WAS FOUND THAT THE DOSE PER 1 NM OF STRUCTURAL DEGRADATION WAS APPROXIMATELY 100 MGy. In order to minimize the dose required for imaging while maintaining the quality of imaging, scholars have proposed a number of methods, among which it has been demonstrated that phase-contrast X-ray imaging can be effectively imaged at photon energies of about 10 keV, because this radiation can penetrate the sample more and its shorter wavelength can provide greater depth of focus. Therefore, if the radiation dose required for effective imaging can be further reduced on the basis of existing research, it is of great significance for the development of biomedical imaging and other fields.

Innovative research

In this study, the research team’s theoretical and experimental studies showed that scanning Compton X-ray microscopy can provide high-resolution images at a lower dose than phase contrast imaging. The research team tested the scanning Compton X-ray microscopy method with a 60 keV detection beam focused at about 70 nm using a new thick wedge-shaped multilayer Laue lens designed for focusing high-energy X-rays (Figures 1, 2, 3). The findings demonstrate applicability to imaging biological materials and show imaging of dry objects (spirulina bacteria, diatoms, and pollen grains) (Figure IV), which were obtained at doses well below the tolerable limits of cooled hydrated samples.

This research result opens up broader research prospects for the further development of biological imaging technology, and the scanning Compton X-ray microscopy technology, combined with the large stereo angle effective detector and the high brightness of the next-generation synchrotron radiation source, is expected to further develop high-resolution scanning Compton X-ray microscope, which provides a promising path for subsequent research.

Figure I: (a) Schematic diagram of the microscope. (b) Scanning electron micrograph of one of the multilayer Laue lenses, beam propagation direction (z-direction) 35 μm thick and 51 μm high (y direction). The multilayer structure appears gray above the Si substrate and looks darker. (c) Carbon sections in cm2/g/solid angles at 60 keV photon energies, and (d) sections of C (blue), N (yellow), O (green), and Si (orange) sections in the same units as (c). The dotted line indicates the receiving angle of the probe.

Figure 2: (a) Measurement signals from the upper (blue) and lower (green) off-axis detectors of the silicon wedge sample with an exposure time of 2000 ms per data point and an incident flux of 1.54×106 ph/ms. (b) Background-de-removed detector cross-section of Si, displayed in grayscale from 0 (black) to 8×10-8 cm2/g (white). The outline of the scattering angle β is annotated. (c) The response along the orange dashed line in (b) and the corresponding calculated cross-section (dashed line).

Figure 3: (a,b) Darkfield image of a 750 nm thick star structure measured in steps of 50 nm and 15 nm, with dwell times of 10 ms and 20 ms per pixel. (c) The Fourier ring correlation function formed by the same scan as (b) indicates a resolution of 72 nm. One-bit criterion is shown in an olive green curve. (d) The point spread function of the lens, obtained by wavefront measurements. (e) Focal spots of a 100 μm * 100 μm source with a calculated distance of 42 m and a relative bandwidth of 0.05%.

Figure IV: Darkfield images of (a) pine pollen grains, (b) spirulina blue-green algae, and (c) silicate diatom shells.

The article was published in Light: Science & Applications in the top international academic journal “Dose-efficient Scanning Compton X-ray Microscopy”, with Tang Li as the first author and Henry N. Chapman and Saša Bajt as co-corresponding authors. (Source: LightScienceApplications)

Related paper information:‍-023-0‍1176-5

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