X-ray phase-contrast tomography with a compact laser-driven synchrotron source

Abstract

Between X-ray tubes and large-scale synchrotron sources, a large gap in performance exists with respect to the monochromaticity and brilliance of the X-ray beam. However, due to their size and cost, large-scale synchrotrons are not available for more routine applications in small and medium-sized academic or industrial laboratories. This gap could be closed by laser-driven compact synchrotron light sources (CLS), which use an infrared (IR) laser cavity in combination with a small electron storage ring. Hard X-rays are produced through the process of inverse Compton scattering upon the intersection of the electron bunch with the focused laser beam. The produced X-ray beam is intrinsically monochromatic and highly collimated. This makes a CLS well-suited for applications of more advanced--and more challenging--X-ray imaging approaches, such as X-ray multimodal tomography. Here we present, to our knowledge, the first results of a first successful demonstration experiment in which a monochromatic X-ray beam from a CLS was used for multimodal, i.e., phase-, dark-field, and attenuation-contrast, X-ray tomography. We show results from a fluid phantom with different liquids and a biomedical application example in the form of a multimodal CT scan of a small animal (mouse, ex vivo). The results highlight particularly that quantitative multimodal CT has become feasible with laser-driven CLS, and that the results outperform more conventional approaches.

Keywords: X-ray imaging; dark-field tomography; grating interferometer; inverse Compton X-rays; phase-contrast tomography.

Fig. 1.

(A) Photograph of the fluid phantom. It consists of seven polyethylene rods containing seven different, chemically well-defined fluids (Table S1). (B and C) Average of 10 reconstructed slices of the linear attenuation coefficient μ (B) and the refractive index decrement δ (C). Fluids with similar attenuation coefficient show strong contrast in the phase image and vice versa. (Scale bar, 3 mm.) The white numbers in C correspond to the fluid sample number used in Table 1 and Table S1.

Fig. 2.

Scatter plot displays the attenuation coefficient and refractive index decrement for all pixels in the $10\times 10-{\text{pixel}}^2$ ROIs in the fluid phantom reconstructions (compare Fig. 1 B and C). Black triangles are the calculated values. Most substances show an overlap in either attenuation or phase signal alone, but all substances can clearly be distinguished using the combined information from both attenuation and phase. The different data clusters are labeled by numbers as used in Table 1 and Table S1.

Fig. 3.

Reconstructed slices of a grating-based, multimodal CT scan of a biological sample (a formalin fixated infant mouse). Shown are sagittal (Top Row) and axial (Bottom Row) slices. The reconstruction yields quantitative values of linear attenuation coefficient μ (A), refractive index decrement δ (B and C), and linear diffusion coefficient ε (D). For the phase image (C), an iterative reconstruction scheme (20) was used instead of conventional FBP reconstruction to reduce stripe artifacts and noise. (Scale bar, 2 mm.)

Fig. 4.

Reconstructed slices of a grating-based, multimodal CT scan of a biological sample (a formalin fixated infant mouse), in analogy to Fig. 3. Shown are sagittal (Top Row) and axial (Bottom Row) slices. The images show that brown adipose tissue is visible and can be discriminated from white adipose tissue in phase contrast (B and C) and dark-field contrast (D), but not in absorption contrast (A). (Scale bar, 2 mm.) Histological slices presented in E and F support this claim. E shows a sagittal section of the cervical/thoracic area stained with H&E of a mouse embryo (adapted from ref. 21). F shows an axial section of the interscapular area stained with H&E of a mouse embryo (adapted from ref. 22). Red arrows indicate brown adipose tissue; blue arrows indicate white adipose tissue.

Fig. 5.

Schematic drawing of the CLS as manufactured by Lyncean Technologies, Inc. An electron bunch is injected into and then stored in the electron storage ring. A laser pulse is stored in the optical cavity and collides with the electron bunch at the interaction point, producing a quasi-monochromatic X-ray beam.