17 Vibrational Microspectroscopy for Analysis of Atherosclerotic Arteries
523
this imaging technique a very powerful method for the detection of unstable plaque.
Previous Raman studies also revealed the possible presence and pathophysiological
importance of retinal palmitate, ascorbic acid in ceroid deposits and α-tocopherol
[87]. It is important to mention that foam cells and necrotic cores are difficult to
recognize with the use of Raman spectroscopy [2, 114].
the combination of Raman techniques with virtual histology intravascular ultrasounds, or morphology-based diagnosis, allows for not only the definition of the
structures of plaque, but also relative quantification of some components—mainly
lipids and calcium salts, but also elastin, collagen, actin, triolein, cholesterol linoleate, free cholesterol and β-carotene [86–88, 92, 95, 105, 110].
one of the most important parts of a lesion, which is able to provide the information about the plaque vulnerability, is the lipid fraction. Such fractions can be divided into two groups. the first, cholesteryl esters, exists mainly in the liquid state,
while the second is the group of free cholesterol, which exists in the crystalline
form [100, 101, 115]. It has been found that the presence of the cholesteryl esters
may soften the plaque, while the presence of cholesterol (crystalline form) makes it
more stable [87, 100, 101, 116]. on the other hand, there were studies, which show
that the presence of cholesterol crystals induces inflammation and is connected with
plaque rupture [117, 118], presence of macrophages [119], as well as acute coronary
deaths [118, 120]. It was also found that the calcified deposits are located within the
area of cholesterol accumulation [88].
Figure 17.7 shows an example of cholesterol crystals observed inside plaque
with the Raman integration map and the spectrum of the cholesterol crystal and
cholesteryl esters obtained from the atherosclerotic plaque. two main bands at
1667–1674 cm
−1
(C = C stretching) and 1440 cm
−1
(C-h bending) are shared for
both free cholesterol and cholesteryl esters, while the band at 1655 cm
−1
is connected with C = C stretching in unsaturated fatty acids [100]. In the Raman spectrum
of cholesteryl esters, bands observed at lower frequencies due to cholesterol moiety,
(connected mainly with the vibration modes of steroid rings) are not as distinct as
in the case of pure cholesterol. the spectra of cholesteryl esters are mainly characterized by bands originating from a hydrocarbon chain, the C = o stretching at
around 1740 cm
−1
and the presence of the strongest band in the C-h stretching
region at 2885 cm
−1
. Spectra characteristic for crystalline forms of cholesterol (andydrous and monohydrate cholesterol) originate mainly form cholesterol moiety
(steroid rings) and are observed at around 550, 605, 700, 742 and 850 cm
−1
. Raman spectroscopy allows for the not only the recognition of cholesteryl esters from
cholesterol, but also the detection of the specific type of crystalline cholesterol (anhydrous, monohydrate, hydroxycholesterol) [94, 100]. Near-infrared Raman spectroscopy has also been used in quantitative analysis of cholesterol and cholesteryl
esters in human atherosclerotic plaques [121]. It was found that for quantitative
analysis of cholesterol and cholesteryl esters in human atherosclerosis plaques, the
most powerful method was partial least squares regression (PLS) based on factorial
analysis [100, 122].
523
this imaging technique a very powerful method for the detection of unstable plaque.
Previous Raman studies also revealed the possible presence and pathophysiological
importance of retinal palmitate, ascorbic acid in ceroid deposits and α-tocopherol
[87]. It is important to mention that foam cells and necrotic cores are difficult to
recognize with the use of Raman spectroscopy [2, 114].
the combination of Raman techniques with virtual histology intravascular ultrasounds, or morphology-based diagnosis, allows for not only the definition of the
structures of plaque, but also relative quantification of some components—mainly
lipids and calcium salts, but also elastin, collagen, actin, triolein, cholesterol linoleate, free cholesterol and β-carotene [86–88, 92, 95, 105, 110].
one of the most important parts of a lesion, which is able to provide the information about the plaque vulnerability, is the lipid fraction. Such fractions can be divided into two groups. the first, cholesteryl esters, exists mainly in the liquid state,
while the second is the group of free cholesterol, which exists in the crystalline
form [100, 101, 115]. It has been found that the presence of the cholesteryl esters
may soften the plaque, while the presence of cholesterol (crystalline form) makes it
more stable [87, 100, 101, 116]. on the other hand, there were studies, which show
that the presence of cholesterol crystals induces inflammation and is connected with
plaque rupture [117, 118], presence of macrophages [119], as well as acute coronary
deaths [118, 120]. It was also found that the calcified deposits are located within the
area of cholesterol accumulation [88].
Figure 17.7 shows an example of cholesterol crystals observed inside plaque
with the Raman integration map and the spectrum of the cholesterol crystal and
cholesteryl esters obtained from the atherosclerotic plaque. two main bands at
1667–1674 cm
−1
(C = C stretching) and 1440 cm
−1
(C-h bending) are shared for
both free cholesterol and cholesteryl esters, while the band at 1655 cm
−1
is connected with C = C stretching in unsaturated fatty acids [100]. In the Raman spectrum
of cholesteryl esters, bands observed at lower frequencies due to cholesterol moiety,
(connected mainly with the vibration modes of steroid rings) are not as distinct as
in the case of pure cholesterol. the spectra of cholesteryl esters are mainly characterized by bands originating from a hydrocarbon chain, the C = o stretching at
around 1740 cm
−1
and the presence of the strongest band in the C-h stretching
region at 2885 cm
−1
. Spectra characteristic for crystalline forms of cholesterol (andydrous and monohydrate cholesterol) originate mainly form cholesterol moiety
(steroid rings) and are observed at around 550, 605, 700, 742 and 850 cm
−1
. Raman spectroscopy allows for the not only the recognition of cholesteryl esters from
cholesterol, but also the detection of the specific type of crystalline cholesterol (anhydrous, monohydrate, hydroxycholesterol) [94, 100]. Near-infrared Raman spectroscopy has also been used in quantitative analysis of cholesterol and cholesteryl
esters in human atherosclerotic plaques [121]. It was found that for quantitative
analysis of cholesterol and cholesteryl esters in human atherosclerosis plaques, the
most powerful method was partial least squares regression (PLS) based on factorial
analysis [100, 122].