Background:
Reliable non-invasive imaging modalities to characterize atherosclerotic plaque components are clinically desirable for detecting unstable coronary plaques, which cause acute coronary syndrome or sudden death. Although recent clinical developments in computed tomography (CT) have enabled the visualization of luminal narrowing and calcified plaques in coronary arteries, the evaluation of non-calcified plaque components remains difficult. Phase-contrast X-ray CT imaging has great potential to reveal the structures inside soft tissues because its sensitivity to light elements is almost 1000 times greater than that of absorption-contrast clinical X-ray imaging. We for the first time examined mouse atherosclerotic plaques using phase-contrast X-ray CT and found promising results.
Methods and Results:
Ex vivo
phase-contrast X-ray CT was performed using a synchrotron radiation source (SPring-8, Japan) to investigate atherosclerotic plaque components in mice. Samples were also histologically analyzed. Phase-contrast X-ray CT at a spatial resolution of 10 –20 μm revealed atherosclerotic plaque components, and thin fibrous caps could be easily detected. The specific mass densities of these components were estimated using dδ (differences in the refractive indexes relative to water). While lipid-rich areas showed low dδ (0.79 ± 0.13 × 10
−8
) and mass density (1.011 ± 0.001 g/ml), the smooth muscle- and collagen-rich areas showed high dδ (4.18 ± 0.10 × 10
−8
and 5.93 ± 0.13 × 10
−8
, respectively) and mass density (1.057 ± 0.001 g/ml and 1.08 ± 0.002 g/ml, respectively). It was rather easy to evaluate or differentiate the atherosclerotic plaque components using this novel phase-contrast X-ray CT imaging. Moreover, the three-dimensional assessment of plaques was possible, and it enabled the imaging of their anatomical information.
Conclusions:
Phase-contrast X-ray CT can estimate the tissue-mass density of atherosclerotic plaques and distinguish the lipid-rich areas from the collagen-rich areas. This is a promising non-invasive technique for the investigation of plaque components and detection of unstable coronary plaques.
Translation of Atherosclerotic Plaque Phase-Contrast CT Imaging from Synchrotron Radiation to a Conventional Lab-Based X-Ray Source
