Purpose: Synchrotron radiation-based tomography yields microanatomical features in human and animal tissues without physical slicing. Recent advances in instrumentation have made laboratory-based phase tomography feasible. We compared the performance of three cutting-edge laboratory systems benchmarked by synchrotron radiation-based tomography for three specimens. As an additional criterion, the user-friendliness of the three microtomography systems was considered.
Approach: The three tomography systems—SkyScan 2214 (Bruker-microCT, Kontich, Belgium), Exciscope prototype (Stockholm, Sweden), and Xradia 620 Versa (Zeiss, Oberkochen, Germany)—were given 36 h to measure three medically relevant specimens, namely, zebrafish larva, archaeological human tooth, and porcine nerve. The obtained datasets were registered to the benchmark synchrotron radiation-based tomography from the same specimens and selected ones to the SkyScan 1275 and phoenix nanotom m® laboratory systems to characterize development over the last decade.
Results: Next-generation laboratory-based microtomography almost reached the quality achieved by synchrotron-radiation facilities with respect to spatial and density resolution, as indicated by the visualization of the medically relevant microanatomical features. The SkyScan 2214 system and the Exciscope prototype demonstrated the complementarity of phase information by imaging the eyes of the zebrafish larva. The 3-μm thin annual layers in the tooth cementum were identified using Xradia 620 Versa.
Conclusions: SkyScan 2214 was the simplest system and was well-suited to visualizing the wealth of anatomical features in the zebrafish larva. Data from the Exciscope prototype with the high photon flux from the liquid metal source showed the spiral nature of the myelin sheaths in the porcine nerve. Xradia 620 Versa, with detector optics as typically installed for synchrotron tomography beamlines, enabled the three-dimensional visualization of the zebrafish larva with comparable quality to the synchrotron data and the annual layers in the tooth cementum.
Inline phase tomography using synchrotron radiation with sub-micrometer voxel sizes is nowadays the gold standard for investigation of soft and hard tissues with micron resolution. Recent developments on detectors and X-ray sources allow the transfer of the technique into laboratory environment. For the comparison of three manufacturers, we performed microtomography with advanced laboratory microtomography devices with micron resolution on a porcine nerve, a zebrafish embryo and a historic human tooth. These data sets were also compared with data acquired at the ANATOMIX beamline at Synchrotron Soleil and the TOMCAT beamline at SLS. For the lab-based experiments following scanners were chosen: Skyscan 2214 (Bruker-microCT, Kontich, Belgium), Xradia 620 Versa (Zeiss, Oberkochen, Germany) and a prototype with a MetalJet X-ray source from Exillum from the company Exciscope (Stockholm, Sweden). All devices contained detectors including X-ray optics.
Hard X-ray micro computed tomography can be used for three-dimensional histological phenotyping of zebrafish embryos down to 1 µm or below without the need for staining or physical slicing. Current advances in ze- brafish embryo imaging, however, mostly rely on synchrotron radiation sources or highly advanced laboratory sources, which despite their evident strengths with regard to their beam properties and the implementation of phase contrast imaging techniques, lack accessibility. Therefore, we evaluated the performance of a conventional SkyScan 1275 laboratory µCT scanner in absorption contrast mode for the visualization of anatomical features in ethanol- and paraffin-embedded zebrafish embryos. We compare our results to readily available synchrotron data where 35 anatomical structures were identified. Despite having a more than ten times larger voxel length, approximately two thirds of the features could also be determined with laboratory microtomography. This could allow to monitor morphological changes during development or disease progression on large sample numbers, enabling the performance of preclinical studies in a local laboratory.
Successful tomographic imaging of soft tissues with micrometer resolution includes preparation, acquisition, re- construction, and data evaluation. Tissue preparation is essential for hard X-ray microtomography, because staining- and embedding materials can substantially alter the biological tissue post mortem. We performed to- mographic imaging of zebrafish embryos in alcohol and after paraffin embedding with a conventional X-ray source and at a synchrotron radiation facility. The resulting multi-modal, three-dimensional data were registered for direct comparison. Single-cell precision was reached for the synchrotron radiation-based approach, which allows for segmentation of full organs such as the embryonic kidneys. While this approach offers an order of magnitude higher spatial resolution, many of the anatomical features can be readily recognized with the more accessible laboratory system. Propagation-based data acquisition enabled us to demonstrate the complementary nature of the edge-enhanced absorption contrast- and the phase contrast-based modality for visualizing multiple microanatomical features. While ethanol and paraffin embeddings allowed for identification of the same anatomical structures, paraffin-embedding, however, led to more artefacts and shrinkage. The presented multi-modal imaging approaches can be further extended to visualize three to four orders of magnitude larger volumes such as adult zebrafish or complete organs of larger animals such as mouse brains. Going towards even larger volumes, such as the human brain, presents further challenges related to paraffin embedding, data acquisition and handling of the peta-byte scale data volumes. This study provided a multi-modal imaging strategy by the combination of X-ray sources and sample embeddings which can play a role in addressing these challenges.
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