Abstract
ObjectivesPhase-contrast imaging is a novel X-ray based technique that provides enhanced soft tissue contrast. The aim of this study was to evaluate the feasibility of visualizing human carotid arteries by grating-based phase-contrast tomography (PC-CT) at two different experimental set-ups: (i) applying synchrotron radiation and (ii) using a conventional X-ray tube.Materials and MethodsFive ex-vivo carotid artery specimens were examined with PC-CT either at the European Synchrotron Radiation Facility using a monochromatic X-ray beam (2 specimens; 23 keV; pixel size 5.4 µm), or at a laboratory set-up on a conventional X-ray tube (3 specimens; 35-40 kVp; 70 mA; pixel size 100 µm). Tomographic images were reconstructed and compared to histopathology. Two independent readers determined vessel dimensions and one reader determined signal-to-noise ratios (SNR) between PC-CT and absorption images.ResultsIn total, 51 sections were included in the analysis. Images from both set-ups provided sufficient contrast to differentiate individual vessel layers. All PCI-based measurements strongly predicted but significantly overestimated lumen, intima and vessel wall area for both the synchrotron and the laboratory-based measurements as compared with histology (all p<0.001 with slope >0.53 per mm2, 95%-CI: 0.35 to 0.70). Although synchrotron-based images were characterized by higher SNRs than laboratory-based images; both PC-CT set-ups had superior SNRs compared to corresponding conventional absorption-based images (p<0.001). Inter-reader reproducibility was excellent (ICCs >0.98 and >0.84 for synchrotron and for laboratory-based measurements; respectively).ConclusionExperimental PC-CT of carotid specimens is feasible with both synchrotron and conventional X-ray sources, producing high-resolution images suitable for vessel characterization and atherosclerosis research.
Highlights
Advanced imaging techniques have greatly contributed to our understanding of disease processes and play a pivotal role in the diagnostic work-up of major disease states
Visual inspection revealed that images obtained at the synchrotron radiation facility provided high contrast and resolution, allowing for sufficient differentiation of the individual vessel layers and visualization of very small anatomic details such as the vasa vasorum without the use of any contrast dye (Figure 2a)
Representative cross-sectional images with corresponding histopathology sections for both imaging set-ups are provided in Figure 3, illustrating the ability to differentiate individual vessel wall layers by both PC-computed tomography (CT) acquisitions
Summary
Advanced imaging techniques have greatly contributed to our understanding of disease processes and play a pivotal role in the diagnostic work-up of major disease states. The performance of X-ray computed tomography (CT) and magnetic resonance imaging (MRI) for vascular imaging has developed rapidly during the past years resulting in robust acquisitions of the vascular tree with high diagnostic accuracy [1] Despite these advances, one of the inherent drawbacks of CT is its limited soft-tissue resolution, which is crucial for characterization of atherosclerotic plaque composition [2], while MRI has excellent soft tissue contrast but is limited to large and stationary vessels such as the carotid arteries [3,4]. It has been shown that these phase-contrast imaging techniques provide improved and complementary images as compared to standard X-ray absorption methods [6,7,8,9,10] At this early stage, most clinically-motivated PCI tomography studies are carried out with monochromatic and brilliant X-ray sources at large-scale synchrotron facilities, impeding preclinical evaluation. Grating-based phase-contrast tomography (PCCT) has already been used to image cartilage/ tendons [14], heart tissue [13], ex-vivo brain tissue [9,15] as well as breast cancer [16] with conventional X-ray tubes
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