Nanorose and lipid detection in atherosclerotic plaque using dual-wavelength photothermal wave imaging

Atherosclerosis and specifically rupture of vulnerable plaques account for 23% of all deaths worldwide, far surpassing both infectious diseases and cancer. In atherosclerosis, macrophages can infiltrate plaques which are often associated with lipid deposits. Photothermal wave imaging is based on the periodic thermal modulation of a sample using intensity modulated light. Intensity modulated light enters the sample and is absorbed by targeted chromophores and generates a periodic thermal modulation. We report use of photothermal wave imaging to visualize nanoroses (taken up by macrophages via endocytosis) and lipids in atherosclerotic plaques. Two excitation wavelengths were selected to image nanoroses (800 nm) and lipids (1210 nm). Atherosclerotic plaque in a rabbit abdominal artery was irradiated (800 nm and 1210 nm separately) at a frequency of 4 Hz to generate photothermal waves. The radiometric temperature at the tissue surface was recorded by an infrared (IR) camera over a 10 second time period at the frame rate of 25.6 Hz. Extraction of images (256 × 256 pixels) at various frequencies was performed by Fourier transform at each pixel. Frequency amplitude images were obtained corresponding to 800 nm and 1210 nm laser irradiation. Computed images suggest that the distributions of both nanorose and lipid can be identified in amplitude images at a frequency of 4 Hz. Nanoroses taken up by macrophages are distributed at the edges of lipid deposits. Observation of high concentration of nanoroses in atherosclerotic plaque confirms that nanoroses are present at locations associated with lipid deposits.