Spectral CT of carotid atherosclerotic plaque: Comparison with histology

Objective: To distinguish components of vulnerable atherosclerotic plaque by imaging their energy response using spectral CT and comparing images with histology. Methods: After spectroscopic calibration using phantoms of plaque surrogates, excised human carotid atherosclerotic plaques were imaged using MARS CT using a photonprocessing detector with a silicon sensor layer and microfocus X-ray tube (50 kVp, 0.5 mA) at 38-μm voxel size. The plaques were imaged, sectioned and re-imaged using four threshold energies: 10, 16, 22 and 28 keV; then sequentially stained with modified Von Kossa, Perl's Prussian blue and Oil-Red O, and photographed. Relative Hounsfield units across the energies were entered into a linear algebraic material decomposition model to identify the unknown plaque components. Results: Lipid, calcium, iron and water-like components of plaque have distinguishable energy responses to Xray, visible on spectral CT images. CT images of the plaque surface correlated very well with histological photographs. Calcium deposits (>1,000 μm) in plaque are larger than iron deposits (<100 μm), but could not be distinguished from each other within the same voxel using the energy range available. Conclusions: Spectral CT displays energy information in image form at high spatial resolution, enhancing the intrinsic contrast of lipid, calcium and iron within atheroma. Key Points: • Spectral computed tomography offers new insights into tissue characterisation. • Components of vulnerable atherosclerotic plaque are spectrally distinct with intrinsic contrast. • Spectral CT of excised atherosclerotic plaques can display iron, calcium and lipid. • Calcium deposits are larger than iron deposits in atheroma. • Spectral CT may help in the non-invasive detection of vulnerable plaques.