Abstract
Atherosclerotic plaques are characterized as being vulnerable to rupture based on a series of histologically defined features, including a lipid-rich necrotic core, spotty calcification and ulceration. Existing imaging modalities have limitations in their ability to distinguish between different materials and structural features. We examined whether X-ray spectral photon-counting computer tomography (SPCCT) images were able to distinguish key plaque features in a surgically excised specimen from the carotid artery with comparison to histological images.
An excised carotid plaque was imaged in the diagnostic X-ray energy range of 30–120 keV using a small-bore SPCCT scanner equipped with a Medipix3RX photon-counting spectral X-ray detector with a cadmium telluride (CdTe) sensor. Material identification and quantification (MIQ) images of the carotid plaque were generated using proprietary MIQ software at 0.09 mm volumetric pixels (voxels). The plaque was sectioned, stained and photographed at high resolution for comparison.
A lipid-rich core with spotty calcification was identified in the MIQ images and confirmed by histology. MIQ showed a core region containing lipid, with a mean concentration of 260 mg lipid/ml corresponding to a mean value of −22HU. MIQ showed calcified regions with mean concentration of 41 mg Ca/ml corresponded to a mean value of 123HU. An ulceration of the carotid wall at the bifurcation was identified to be lipid-lined, with a small calcification identified near the breach of the artery wall.
SPCCT derived material identification and quantification images showed hallmarks of vulnerable plaque including a lipid-rich necrotic core, spotty calcifications and ulcerations.
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•An excised human carotid plaque was successfully imaged using a preclinical Spectral Photon Counting Computerized Tomography X-ray machine at the clinical X-ray energy range (30–120 KeV).•The spectral photon-counting CT data from a scan of excised human carotid atherosclerotic plaque was used for in silico material identification and quantification that identified lipid-rich and calcium-rich regions within the plaque at 0.1 mm resolution.•Histology confirmed the software-generated material identification spatial assignments within the images corresponded to hallmarks of vulnerable plaque, including lipid-rich necrotic core, spotty calcification and an ulceration associated with lipid and a small calcification.•Use of a filter-hardened X-ray spectrum (30–120 keV) indicates that material identification of lipid-rich regions such as a necrotic lipid core may be achievable with spectral photon-counting CT in a clinical setting.•Comparison of the software-generated material concentration maps to histology of closely associated lipid and calcification indicated that spectral photon-counting CT data will enable lipid measurement even in highly calcified regions of plaque.