17 Vibrational Microspectroscopy for Analysis of Atherosclerotic Arteries
525
sclerotic plaque [23, 47, 123–125]. the first real-time in vivo studies with the use
of Raman spectroscopy of human atherosclerosis were carried out in 2006 [47]. In
that work, 74 sites during caroid endarterectomy and femoral artery bypass surgeries were examined with the sensitivity and specificity of 79 and 85 %, respectively.
however, it is important to mention that such preliminary studies require long collection time to obtain acceptable signal-to-noise ratios [47]. In most in vivo experiments on sheep and humans, aortas were saline-flushed while spectra were acquired
[110, 123]. Recently, C. matthäus et al., employed Raman-probe spectroscopy to
characterize in vivo the plaque compositions in arterial walls of a rabbit model and
were able to analyze the biochemical composition of atherosclerotic plaques without markers, in a non-destructive way [126].
With the use of quantitative in vivo Raman spectroscopy, it was possible to create the scoring criteria of vulnerable plaque in human atherosclerosis (with a high
probability of rupture) [47]. to these criteria, we can include mainly thrombosis, ulceration, fibrous cap, hemoglobin, calcification, collagen and the sum of the contribution of cholesterol and foam cells/necrotic core. multimodal spectroscopy (where
the combination of dRS, IFS and Raman was applied) is also used in in vivo studies
of the human vulnerable atherosclerotic plaque during femoral bypass and carotid
endarterectomy surgeries [73]. this method allows for the ability to detect vulnerable plaque with a sensitivity of 96 % and specificity of 72 % and the possibility to
detect the thrombus on the surface of plaque [73]. Non-linear techniques, such as
coherent anti-Stokes Raman scattering (CARS), have also been suggested to be effective in the study of atherosclerotic plaque [127].
17.3.2.2 IR Spectroscopy
IR Spectral Features of Atherosclerotic tissue
Ft-IR analysis of the atherosclerotic tissue is mostly concentrated on lipids and
proteins, since those chemical classes are easily distinguishable in infrared spectroscopy. Proteins have characteristic amide bands (I, II A and B—1655, 1550, 3300
and 3100 cm
−1
, respectively) [53, 54], which are quite specific and usually do not
overlap with other tissue constituents. unique profiles of amide I and II bands allow to estimate the content of secondary structures of proteins and this allowed to
distinguish between collagen of type I, III and elastin [60].
Lipids on the other hand have a specific carbonyl band at 1740 cm
−1
, which is
usually assigned to cholesteryl esters but also to triglycerides. however, a more
general analysis of lipid standards [67] revealed that it is not possible to distinguish between triglycerides and cholesteryl esters based only on the 1740 cm
−1
band shift—cholesteryl esters tend to have slightly lower wavenumbers around
1735 cm
−1
, while triglycerides in the 1740–1750 cm
−1
range. this is due to the fact
that the C = o band position in triglycerides depends strongly on the conformation
of the three chains and therefore also on the exact state in which they are present.
different polymorphs show large shifts of this band.
525
sclerotic plaque [23, 47, 123–125]. the first real-time in vivo studies with the use
of Raman spectroscopy of human atherosclerosis were carried out in 2006 [47]. In
that work, 74 sites during caroid endarterectomy and femoral artery bypass surgeries were examined with the sensitivity and specificity of 79 and 85 %, respectively.
however, it is important to mention that such preliminary studies require long collection time to obtain acceptable signal-to-noise ratios [47]. In most in vivo experiments on sheep and humans, aortas were saline-flushed while spectra were acquired
[110, 123]. Recently, C. matthäus et al., employed Raman-probe spectroscopy to
characterize in vivo the plaque compositions in arterial walls of a rabbit model and
were able to analyze the biochemical composition of atherosclerotic plaques without markers, in a non-destructive way [126].
With the use of quantitative in vivo Raman spectroscopy, it was possible to create the scoring criteria of vulnerable plaque in human atherosclerosis (with a high
probability of rupture) [47]. to these criteria, we can include mainly thrombosis, ulceration, fibrous cap, hemoglobin, calcification, collagen and the sum of the contribution of cholesterol and foam cells/necrotic core. multimodal spectroscopy (where
the combination of dRS, IFS and Raman was applied) is also used in in vivo studies
of the human vulnerable atherosclerotic plaque during femoral bypass and carotid
endarterectomy surgeries [73]. this method allows for the ability to detect vulnerable plaque with a sensitivity of 96 % and specificity of 72 % and the possibility to
detect the thrombus on the surface of plaque [73]. Non-linear techniques, such as
coherent anti-Stokes Raman scattering (CARS), have also been suggested to be effective in the study of atherosclerotic plaque [127].
17.3.2.2 IR Spectroscopy
IR Spectral Features of Atherosclerotic tissue
Ft-IR analysis of the atherosclerotic tissue is mostly concentrated on lipids and
proteins, since those chemical classes are easily distinguishable in infrared spectroscopy. Proteins have characteristic amide bands (I, II A and B—1655, 1550, 3300
and 3100 cm
−1
, respectively) [53, 54], which are quite specific and usually do not
overlap with other tissue constituents. unique profiles of amide I and II bands allow to estimate the content of secondary structures of proteins and this allowed to
distinguish between collagen of type I, III and elastin [60].
Lipids on the other hand have a specific carbonyl band at 1740 cm
−1
, which is
usually assigned to cholesteryl esters but also to triglycerides. however, a more
general analysis of lipid standards [67] revealed that it is not possible to distinguish between triglycerides and cholesteryl esters based only on the 1740 cm
−1
band shift—cholesteryl esters tend to have slightly lower wavenumbers around
1735 cm
−1
, while triglycerides in the 1740–1750 cm
−1
range. this is due to the fact
that the C = o band position in triglycerides depends strongly on the conformation
of the three chains and therefore also on the exact state in which they are present.
different polymorphs show large shifts of this band.