On the possibility to detect lipid in atherosclerotic plaques using intravascular photoacoustic imaging.

Large lipid core is common in rupture-prone atherosclerotic plaques. Detection of the location and distribution of lipid in the atherosclerotic plaques can greatly benefit the diagnosis and treatment of vulnerable plaques. Recently introduced intravascular photoacoustic (IVPA) imaging - a technique to image the optical absorption property of tissue - can be used to detect and differentiate atherosclerotic plaques. In this work, we further investigated the ability of using spectroscopic IVPA imaging to visualize the lipid in atherosclerotic plaques. IVPA imaging was performed on an ex-vivo rabbit aorta in the 1200 - 1230 nm wavelength range. In the lipid-rich plaques, the photoacoustic signal strength within this spectral range behaved similar to the optical absorption spectrum of fatty tissue. To distinguish lipid from other types of tissue, correlation analysis was used. Specifically, intraclass correlation between the IVPA signals and the absorption spectrum of lipid reconstructed from multi-wavelength IVPA images was conducted on a pixel-by-pixel basis. The resulted correlation map showed the distribution of lipid in the atherosclerotic plaques. The distribution of lipid is further confirmed by histopathological analysis of tissue. The results of our study suggest that spectroscopic IVPA imaging, together with correlation analysis, may be used to detect lipid in atherosclerotic plaques.