Speaker
Description
Abstract
X-ray Virtual Histology (XVH) has been proposed as a tool for improving the workflow of histopathological evaluation. Compared to conventional histology, which is inherently a bi-dimensional technique, XVH is based on micro-computed tomography (µCT), thus providing a 3D depiction of the imaged sample. This feature proved to be beneficial in the identification of structures that exhibit a high variability across the sample thickness, such as in micro-infiltrating tumors [1]. XVH is a non-destructive technique and does not require dedicated sample preparation. For this reason, it can also be considered as an additional tool to guide the pathologist in the sample sectioning, potentially increasing the sensitivity of histological examination and reducing the burden associated with multiple sectioning.
The main challenge of XVH is related to the low X-ray contrast of soft tissue structures, which has been tackled in many cases by implementing phase-sensitive techniques. This is de-facto the imaging standard at high-coherence synchrotron radiation facilities and is becoming widely adopted also in compact tabletop systems [2].
In parallel to, but independently from, the development of XVH, the availability of small-pixel chromatic detectors has paved the way for spectral µCT applications. Specifically, adopting devices equipped with high-Z sensors, pixel-pitch below 100 µm, and charge-sharing compensation mechanisms allows material separation at spatial resolution in the order of tens of microns.
This work aims to combine XVH and spectral µCT to visualize and quantify the iodine content within pathological samples of human thyroid. The study has been conducted at the novel multi-modal X-ray laboratory PEPI [3] (INFN, Trieste), employing a CdTe spectral detector [4] (Pixirad-PixieIII) featuring a pixel pitch of 62 µm, a 512×402 pixel matrix, two thresholds per pixel and the charge sharing compensation, and a tungsten anode microfocal X-ray tube, with an adjustable source size in the range 5 to 30 µm. To implement propagation-based phase contrast, the detector was positioned ~40 cm downstream from the sample, and the magnification was adjusted to have an effective pixel size between 15 and 20 µm (depending on the sample size). Two consecutive scans with different lateral displacements of the detector were performed to extend the field of view, yielding axial slices with lateral dimensions in the order of 1400 pixels. Accurate material decomposition was ensured by a thorough modeling of the detector’s spectral response which was obtained from a dedicated Geant4 simulation incorporating the experimental characterization of the device [5].
The imaging results were benchmarked against scans of the same samples performed at the European Synchrotron Radiation Facility (ESRF, beamline BM05) in the propagation-based mode, at a pixel size of 6.5 µm, and monochromatic radiation at two energies below and above the iodine K-edge (33.2 keV).
Results demonstrate a good correspondence in the iodine distribution within the sample between synchrotron and laboratory-based images (see attached figure a), which exhibit sensitivity to concentrations down to ~1 mg/ml. Concerning soft tissue visibility, the laboratory spectral µCT can capture the main features (parenchyma, lesion, capsule), despite the overall image quality being inferior to the synchrotron scan.
When comparing different samples, each with a different pathology, a major variability in the iodine maps is observed, corresponding to different distributions and health status of the thyroid's follicular component, the primary iodine reservoir. Additionally, large differences in the total (0.02 – 0.20 mg) and mean (0.1 – 1.1 mg/ml) iodine contents, readily computed from iodine maps, were observed. Although these findings need to be confirmed on a larger number of samples, the presented results suggest that spectral XVH can be used for providing quantitative insight into thyroid specimens, potentially aiding pathological evaluation and therapeutic management.
References
[1] S Donato et al., EPJ Plus (2024), in press
[2] K Tajbakhsh et al., IEEE TMI (2024). 10.1109/TMI.2024.3372602
[3] L Brombal et al., Scientific Reports 13.1 (2023), 4206
[4] R Bellazzini et al., JINST 10.01 (2015), C01032.
[5] V Di Trapani et al., Optics Express 30.24 (2022), 42995-43011.
Acknowledgments
We acknowledge financial support under the National Recovery and Resilience Plan (NRRP), Mission 4, Component 2, Investment 1.1, Call for tender No. 1409 published on 14.9.2022 by the Italian Ministry of University and Research (MUR), funded by the European Union – NextGenerationEU– Project Title A compact multimodal X-ray system for 3D micro-imaging of soft tissue based on the integration of spectral and phase-contrast techniques – CUP J53D23014070001 - Grant Assignment Decree No. 1383 adopted on 01/09/2023 by the Italian Ministry of Ministry of University and Research (MUR) and from INFN-CSN5, call 22260/2020, project PEPI
