Optimization of pixel size and propagation distance in X-ray phase-contrast virtual histology

Abstract

X-ray phase-contrast coupled to high-spatial resolution imaging systems provides a high sensitivity for distinguishing soft tissue structures in small samples, thus being suited for X-ray virtual histology. Propagation-based phase-contrast tomography can deliver a considerable gain in signal-to-noise ratio (SNR) at small pixel sizes when it is combined to a suitable phase retrieval filter. We optimized acquisition parameters, namely the propagation distance and the pixel size, with the aim of providing adequate spatial resolution and sensitivity for virtual histology of breast surgery specimens, scanned with a phase-contrast microtomography (μCT) system employing a commercial sCMOS detector at the SYRMEP beamline of the Italian synchrotron facility Elettra (Trieste, Italy). A pathological breast tissue sample was embedded in paraffin and imaged using a polychromatic synchrotron beam at an average energy of 24 keV. The high numerical optical aperture of the imaging system enabled to adjust the pixel size to 1, 2.5 and 4 μm. The scans were acquired at five sample-to-detector distances: 4.5, 150, 250, 500 and 1000 mm. SNR was measured in an homogeneous region portion of the μCT image for each combination of pixel size and propagation distance. Experimental results were compared to a theoretical model taking into account the actual point spread function of the employed imaging system. The measured gain of SNR associated with the application of the phase-retrieval matched the predictions for large Fresnel numbers (N F > 2). For each pixel size, an optimal range of propagation distances was found. Optimal μCT reconstructions were then compared with their respective histopatological images, showing an excellent visibility of relevant structures. The optimization performed in this study will allow to select the most appropriate geometrical configurations for future acquisitions of virtual histology images of different specimens via phase-contrast microtomography.

Microvascular imaging of the unstained human superior colliculus using synchrotron-radiation phase-contrast microtomography

“…Each image was acquired with 3600 projections around 360° using half-acquisition mode 29 by a water-cooled 16-bits CMOS camera (Hamamatsu C11440-22C-Flash4.0 v2). Following calculations from 30 , the samples were measured at two different detector-to-sample-distances (DSDs); 200 mm for 0.94 µm isotropic images and 900 mm for 4.94 µm isotropic images. The exposure time was 200 ms for each projection.…”

Anatomical study of the red flour beetle using synchrotron radiation X‐ray phase‐contrast micro‐tomography

“…The projection images were obtained in the propagation‐based phase‐contrast regime (Brombal, 2020; Rigon, 2014) by setting a propagation distance equal to 100 mm between the sample and the detector. The propagation distance was set in order to optimize, in the near‐field regime, the signal‐to‐noise ratio once the pixel size has been set (Donato et al, 2022). Phase‐contrast effects resulting from propagation in free‐space lead to an enhanced contrast arising at the boundaries between details of different composition (the so‐called edge‐enhancement).…”

“…Tomographic data acquisition was performed at the SYRMEP (SYnchrotron Radiation for MEdical Physics) beamline of the Elettra Synchrotron facility in Trieste (Italy) illuminating the sample with a polychromatic radiation (Donato et al, 2022). The X-ray beam available at the beamline is generated by a storage ring-bending magnet and the energy of photons ranges from 8.5 to 40 keV.…”

Exploring Compound Eyes in Adults of Four Coleopteran Species Using Synchrotron X-ray Phase-Contrast Microtomography (SR-PhC Micro-CT)

“…Projection images were obtained in the propagation-based phase-contrast regime [ 18 , 58 ], setting a propagation distance between the sample and the detector. The propagation distance was set to optimise the signal-to-noise ratio in the near-field regime, once the pixel size had been set [ 59 ]. Phase-contrast effects emerging from the free-space propagation result in an enhanced contrast arising at the boundaries between details with different compositions (the so-called edge-enhancement).…”