Dual-energy CT imaging of atherosclerotic plaque using novel ultrasmall superparamagnetic iron oxide in hyperlipidemic rabbits

Abstract

Background A study using magnetic resonance imaging (MRI) revealed that ultra-small superparamagnetic iron oxide is phagocytosed by macrophages. However, MRI has limitations in obtaining clear images due to its poor spatial and temporal resolutions. Purpose To examine whether the use of dual-energy computed tomography (DECT) facilitated the visualization of carboxymethyl-diethylaminoethyl dextran magnetite ultra-small superparamagnetic iron oxide (CMEADM-U) accumulation in arteriosclerotic lesions using hyperlipidemic rabbits. Material and Methods CMEADM-U at 0.5 mmol Fe/kg was administered to Watanabe hereditary atherosclerotic (WHHL) rabbits (n = 6, 24 sections) and New Zealand white (NZW) rabbits (n = 2, 6 sections). After 72 h, DECT was performed to prepare virtual monochromatic images (35 keV, 70 keV) and an iron-based map. Subsequently, the aorta was collected along with hematoxylin and eosin staining, Berlin blue (BB) staining, and RAM11 immunostaining. Results In the WHHL rabbits, CMEADM-U accumulation was not observed at 70 keV. However, CMEADM-U accumulation consistent with an arteriosclerotic lesion was observed at 35 keV and the iron-based map. On the other hand, in the NZW rabbits, there was no accumulation of CMEADM-U in any images. Further, there were significant differences in the iron-based map value at the site of accumulation among the grades of expression on BB staining and RAM11 immunostaining. In addition, there was a good correlation at 35 kev and iron-based map value (r = 0.42; P < 0.05). Conclusion DECT imaging for CMEADM-U facilitated the assessment of macrophage accumulation in atherosclerotic lesions in an in vivo study using a rabbit model of induced aortic atherosclerosis.