Atherosclerosis
The progression of atherosclerosis depends on the amount of lipid accumulation in the intima of the arteries. The increased amount of lipid accumulation creates a risk of sudden rupture or rupture of plaques characterized by high extracellular lipid content, abundant macrophages, small amounts of smooth muscle cells, and relatively low concentrations of collagen and glycosaminoglycans.[7,232,233] This ultimately results in the crystallization of mineral crystals. Raman spectroscopy can accurately quantify the relative amounts of calcium salts, cholesterol, triglycerides, and phospholipids in arterial tissue (Figure 9a ). There are large differences in the construction of conventional atherosclerotic mouse models, while the sclerotic plaques are not easily localized. And the differences in Raman spectroscopy results in that cause atherosclerotic lesion sites suggest that the causes of atherosclerosis are diverse.[234–236] Apolipoprotein E/low-density lipoproteins (ApoE/LDLR) knockout was used as an indicator for the construction of atherosclerosis model mice.[62,7]The Raman spectroscopy imaging method was adjusted to distinguish the main biomolecules present in this atherosclerotic tissue to reveal the relationship between apatite, cholesterol, and triglycerides (Figure 9b ).[135,237,238] Besides, Raman spectroscopy was used to analyze the pharmacological effects of drugs in the atherosclerotic plaque in situ, providing a strong basis for the development of drugs for atherosclerosis treatment.[234,239]
In addition to the analysis of the causes of atherosclerosis, Raman spectroscopy can be also utilized as a diagnostic tool for atherosclerosis due to the specific chemical composition of atherosclerotic plaques. Stimulated Raman scattering microscopy combined with second harmonic generation microscopy effectively distinguishes between cholesterol monocrystals, aliphatic lipids, structural proteins of the tissue matrix, and other condensed structures.[240,241] Some researchers reported a fiber-optic Raman spectroscopy method to achieve in vivoatherosclerosis detection with a specificity and sensitivity of 79% and 85%.[235,242] To increase the detection time and accuracy of atherosclerosis, techniques such as fluorescence lifetime imaging and fluorescence imaging are used in combination with Raman spectroscopy for lesion site identification.[238,243–245]
Atherosclerosis is highly individualized, which greatly limits the study of its triggering mechanisms. Moreover, the presence of hemoglobin leads to strong tissue autofluorescence and interference with Raman spectroscopy results. All these problems need to be addressed in subsequent studies.