Tracking the infiltration of gold-labelled monocytes into live human atherosclerotic plaques: Spectral photon counting CT imaging analysis

Background Atherosclerotic plaques are complex tissues comprised of various cell types. Monocytes contribute to the growth of atherosclerotic plaques through infiltration, differentiation and accumulation. Previous studies exhibiting this behaviour have been derived from experimental animals. Here, we tracked the movement of human monocytes into live atherosclerotic plaque samples via gold labelling, using spectral photon counting computed tomography (SPCCT). Methods Monocytes isolated from human peripheral blood were incubated with gold nanoparticles for 24 hours and uptake measured using microwave plasma atomic emission spectroscopy (MP-AES) and SPCCT imaging. Excised carotid plaques were sliced into 3-5 mm thick sections and incubated with the gold-labelled monocytes in tissue culture media for up to 24 hours at 37°C. At selected times the plaque sections were imaged using the MARS SPCCT X-ray scanner with an energy range from 20-120 keV. Material identification and quantification images of the carotid plaque were generated using proprietary software at 0.09 mm 3 volumetric pixels (voxels). Results Analysis of gold uptake in monocytes from MP-AES and SPCCT imaging provided comparable results, indicating uptake of 135 pg Au/cell. SPCCT imaging showed rapid movement of gold-labelled monocytes deep into the soft tissue rich regions of plaque, while excluding calcified regions. Quantitative analysis indicated an average uptake rate of 2.5 x 10 4 monocytes per hour. Conclusion SPCCT imaging of live atherosclerotic plaques demonstrated the dynamic environment of the tissue and the ease in which monocytes can penetrate deep into the tissue.