Abstract
BackgroundMacrophage burden is a major factor in the risk of atherosclerotic plaque rupture, and its evaluation remains challenging with molecular noninvasive imaging approaches. Photon-counting CT (PCCT) with k-edge imaging aims to allow for the specific detection of macrophages using gold nanoparticles.PurposeTo perform k-edge imaging in combination with gold nanoparticles to detect and quantify the macrophage burden within the atherosclerotic aortas of rabbits.Materials and MethodsAtherosclerotic and control New Zealand white rabbits were imaged before and at several time points up to 2 days after intravenous injection of gold nanoparticles (3.5 mL/kg, 65 mg gold per milliliter). Aortic CT angiography was performed at the end of the follow-up using an intravenous injection of an iodinated contrast material. Gold k-edge and conventional CT images were reconstructed for qualitative and quantitative assessment of the macrophage burden. PCCT imaging results were compared with findings at histologic examination, quantitative histomorphometry, transmission electron microscopy, and quantitative inductively coupled plasma optical emission spectrometry. Pearson correlations between the macrophage area measured in immunostained sections and the concentration of gold and attenuation measured in the corresponding PCCT sections were calculated.ResultsSeven rabbits with atherosclerosis and four control rabbits without atherosclerosis were analyzed. In atherosclerotic rabbits, calcifications were observed along the aortic wall before injection. At 2 days after injection of gold nanoparticles, only gold k-edge images allowed for the distinction of plaque enhancement within calcifications and for lumen enhancement during angiography. A good correlation was observed between the gold concentration measured within the wall and the macrophage area in 35 plaques (five per rabbit) (r = 0.82; 95% CI: 0.67, 0.91; P < .001), which was higher than that observed on conventional CT images (r = 0.41; 95% CI: 0.09, 0.65; P = .01). Transmission electron microscopy and inductively coupled plasma optical emission spectrometry analyses confirmed the gold k-edge imaging findings.ConclusionPhoton-counting CT with gold nanoparticles allowed for the noninvasive evaluation of both molecular and anatomic information in vivo in rabbits with atherosclerotic plaques.Published under a CC BY 4.0 license.Online supplemental material is available for this article.See also the editorial by Leiner in this issue.
Highlights
Ong the candidates for k-edge imaging, promising results have been reported using gold nanoparticles [9,10]
Noninvasive imaging of the macrophage burden, an important determinant of atherosclerotic plaque vulnerability, can assist in diagnosing patients who are at a high risk of rupture [2,3]
CT imaging is a method of choice for coronary artery disease, and it produces thin-section images of coronary arteries in less than 1 second [4]
Summary
Ong the candidates for k-edge imaging, promising results have been reported using gold nanoparticles [9,10]. Gold nanoparticles are highly biocompatible, are extremely dense, and have low viscosity, which is important for in vivo applications [11]. PCCT has shown encouraging results for cardiovascular imaging in phantoms, animals, and human studies [7,12,13,14], including proof of concept of k-edge imaging for assessing atherosclerotic change [9,15,16,17,18,19]
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