Near-perfect efficiency in X-ray phase microtomography

TL;DR

The paper addresses the dose limitation in X-ray microtomography by integrating an X-ray waveguide, a structured phase modulator (Talbot array illuminator), and a photon-counting detector to achieve near-theoretical imaging performance. The authors demonstrate high visibility ($V \approx 95\%$) and high quantum efficiency ($QE \approx 98\%$) at energies around 8–10 keV, enabling dose-efficient multimodal tomography with single-micrometer resolution. They validate the approach with measurements of visibilities, angular sensitivity, and a tomographic reconstruction of mouse skin embedded in paraffin, showing bidirectional phase sensitivity and physiologically meaningful electron-density contrasts. The work highlights practical implications for imaging native-state biological specimens, offering routes to larger fields of view, higher flux, and potential dark-field integration, thereby advancing biomedical research and tissue characterization under physiological conditions.

Abstract

X-ray microtomography at synchrotron sources is fundamentally limited by the high radiation dose applied to the samples, which restricts investigations to non-native tissue states and thereby compromises the biological relevance of the resulting data. The limitation stems from inefficient indirect detection schemes that require prolonged exposures. Efforts to extract additional contrast through multimodal techniques, like modulation-based imaging, worsen the problem by requiring multiple tomographic scans. In addition, the techniques suffer from low modulator pattern visibility, which reduces measurement efficiency and sensitivity. We address both the detection efficiency and modulation visibility challenges using a novel setup that combines an X-ray waveguide, a structured phase modulator, and a photon-counting detector. Our approach simultaneously achieves near-theoretical limits in both visibility (95%) and quantum efficiency (98%), thereby enabling dose-efficient multimodal microtomography at single-micrometer resolution. This advance will enable new classes of experiments on native-state biological specimens with the potential to advance biomedical research, disease diagnostics, and our understanding of tissue structure in physiological environments.

Figures (4)

• Figure 1: The radiation produced by an undulator source and filtered by a monochromator (not shown) is focused onto a waveguide via a Kirkpatrick-Baez mirror. A phase modulator is placed a distance $s$ downstream of the waveguide, and the sample is located a distance $l$ downstream of the Talbot array. The detector is placed a distance $\Delta$ downstream of the sample. Due to the presence of the sample, phase effects lead to a refraction of the reference pattern by an angle $\alpha$.
• Figure 2: Visibility vs. effective propagation distance for different phase modulators. The top panels show the visibility as a function of the effective propagation distance for both detector types. The photon-counting detector camera (a) achieves a maximum visibility of 93.4%, and the CMOS detector (b) reaches 94.8%. The blue dashed line indicates how the effective pixel size increases with propagation distance. The bottom panels display the modulation patterns captured by each detector system at their respective maximum visibilities. Both use the 10µm period TAI. The intensity pattern of the photon counter (c) was captured at a beam energy of 8keV, and the pattern of the CMOS detector (d) was imaged at a beam energy of 10keV. The strong and regular intensity changes are clearly visible; however, the CMOS detector resolves the pattern better due to its smaller pixel size. The blur at approximately $y = 40$ in the photon-counting detector panel is due to interpolation of the detector gap.
• Figure 3: Combinations of visibility and modulator period from previous literature (blue) gustschin2021highmorgan2013sensitivereich2018scalabledos2018shackkagias2019diffractivezakharova2019inverted and the current work (orange and red). The highest available value for each combination was used, regardless of the detector type. Due to the strong intensity gradients created, a combination of small period size and high visibility is preferable for modulation-based retrieval of phase shifts. Compared to previous literature, our approach enables visibility values close to the theoretical upper limit of 100% at small period sizes.
• Figure 4: Tomographic phase scan of mouse skin embedded in a cylindrical piece of paraffin. (a) and (b) show projections of the differential phase signal projections in the $x$- and $y$-directions, respectively. These signals track the displacement of the reference pattern by the sample, in pixels, at the detector face. (c) shows a slice through the middle of the three-dimensional electron density map, obtained by 2D Fourier integration of the differential signals and tomographic reconstruction. (d) is a 3D rendering of the electron density volume.