Translation of atherosclerotic plaque phase-contrast CT imaging from synchrotron radiation to a conventional lab-based X-ray source.

OBJECTIVES: Phase-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 METHODS: Five 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. RESULTS: In 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 p0.53 per mm(2), 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 (p0.98 and >0.84 for synchrotron and for laboratory-based measurements; respectively). CONCLUSION: Experimental 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

Mechanism of Calsequestrin Regulation of Single Cardiac Ryanodine Receptor in normal and pathological conditions

Release of Ca(2+) from the sarcoplasmic reticulum (SR) drives contractile function of cardiac myocytes. Luminal Ca(2+) regulation of SR Ca(2+) release is fundamental not only in physiology but also in physiopathology because abnormal luminal Ca(2+) regulation is known to lead to arrhythmias, catecholaminergic polymorphic ventricular tachycardia (CPVT), and/or sudden cardiac arrest, as inferred from animal model studies. Luminal Ca(2+) regulates ryanodine receptor (RyR)2-mediated SR Ca(2+) release through mechanisms localized inside the SR; one of these involves luminal Ca(2+) interacting with calsequestrin (CASQ), triadin, and/or junctin to regulate RyR2 function. CASQ2-RyR2 regulation was examined at the single RyR2 channel level. Single RyR2s were incorporated into planar lipid bilayers by the fusion of native SR vesicles isolated from either wild-type (WT), CASQ2 knockout (KO), or R33Q-CASQ2 knock-in (KI) mice. KO and KI mice have CPVT-like phenotypes. We show that CASQ2(WT) action on RyR2 function (either activation or inhibition) was strongly influenced by the presence of cytosolic MgATP. Function of the reconstituted CASQ2(WT)–RyR2 complex was unaffected by changes in luminal free [Ca(2+)] (from 0.1 to 1 mM). The inhibition exerted by CASQ2(WT) association with the RyR2 determined a reduction in cytosolic Ca(2+) activation sensitivity. RyR2s from KO mice were significantly more sensitive to cytosolic Ca(2+) activation and had significantly longer mean open times than RyR2s from WT mice. Sensitivity of RyR2s from KI mice was in between that of RyR2 channels from KO and WT mice. Enhanced cytosolic RyR2 Ca(2+) sensitivity and longer RyR2 open times likely explain the CPVT-like phenotype of both KO and KI mice

Comparison of PC-CT images recorded at synchrotron and laboratory sources.

<div><p>(A) Axial reconstructed PCI slice from the conventional X-ray tube of the common carotid artery with a large atherosclerotic plaque. The chevron points to a large lipid-rich necrotic core covered by a fibrous cap;.</p> <p>(B) Axial reconstructed PCI slice from the synchrotron facility of the distal external carotid artery with moderate intimal thickening; the arrow points at a detachment of the intimal layer.</p> <p>(C) and (D) corresponding histology sections (PCI = Phase Contrast Imaging; Length of the scale bar = 2 mm).</p></div

Comparison of PC-CT images and absorption CT images obtained with a conventional X-ray tube; and corresponding histology sections.

<p>(A) Axial reconstructed PC-CT slice from the conventional X-ray tube, (B) axial reconstructed CT slice from the conventional X-ray tube, (C) and (D) corresponding histology sections. This atherosclerotic lesion shows a large lipid-rich necrotic core and a relatively thin fibrous cap. The arrows point to the fibrous cap (FC), the lipid-rich necrotic core (NC) and an area of calcification (CA). Several other calcifications are seen in this specimen (PC-CT = Phase Contrast Computed Tomography; CT = Computed Tomography, Length of the scale bar = 2 mm).</p

Three-dimensional renderings of the phase contrast tomographic data sets.

<p>(A) Near-normal carotid artery imaged at the synchrotron beamline ID19, ESRF, France. Due to the high resolution of the images and the excellent soft tissue contrast, several vasa vasorum can be identified without the use of contrast dye. (B) Atherosclerotic lesion imaged at the laboratory (Images were rendered using VGStudioMax 2.1, Volume Graphics, Heidelberg, Germany)..</p

Schematic overview of the experimental setup.

<div><p>(A+B) Schematic drawing and photograph of the talbot interferometer set-up at the synchrotron beamline ID19, ESRF, France. Monochromatic, coherent X-rays travel through the sample and phase distortions are evaluated by a phase grating and an analyzer grating located in between sample and detector.</p> <p>(C+D) Schematic drawing and photograph of the talbot-Lau interferometer set-up used in the laboratory. X-rays originating from a conventional X-ray tube are primed by passing through an additional source grating. The remaining se-tup is analogous to Figure 1A+1B. The red arrow indicates the beam direction.</p></div