Rationale and Objectives
Atherothrombosis usually occurs on macrophage- and lipid-rich unstable plaque, but rarely on smooth muscle cell (SMC)-rich stable plaque. Magnetic resonance imaging (MRI) has been extensively applied for noninvasive vascular imaging. We therefore investigated whether MRI provides valuable information about the characteristics of atherosclerotic vessels using rabbit models of macrophage-rich or SMC-rich atherosclerotic arteries.
Materials and Methods
Rabbits were fed with a conventional (CD group, n = 3) or 0.5% cholesterol (ChD group, n = 3) diet for 1 week before and 3 weeks after balloon injury of the left iliac arteries. Three weeks later, these arteries were investigates by 1.5 T MRI and by conventional angiographic imaging, followed by histological and immunohistochemical analyses.
Results
Three weeks after balloon injury, injured iliac arteries of both groups formed neointima with luminal stenosis. Conventional and MRI angiographic findings of the luminal diameter significantly and positively correlated. T1 relaxation time was significantly shorter and the lipid content was much higher in injured arteries from the ChD than from the CD group. The injured arteries from the ChD also contained more macrophages and less SMCs that those from the CD group. The T1 relaxation time and lipid content in injured arteries negatively and positively correlated with the degree of macrophage accumulation, respectively.
Conclusion
These results showed that MRI could provide valuable information about luminal stenosis and the characteristics of atherosclerotic vessels in rabbits.
Thrombus formation after atherosclerotic plaque disruption is a major cause of acute coronary syndrome and stroke. Atherothrombosis usually occurs on macrophage- and lipid-rich unstable plaque, but rarely on smooth muscle cell (SMC)-rich stable plaque . Beside luminal stenosis, plaque composition and morphology are key determinants of whether a plaque will cause cardiovascular events. Despite major advances in treatment, a high ratio of apparently healthy and asymptomatic patients dies of atherosclerosis . Therefore the development of screening and diagnostic methods to identify and characterize plaque composition is very important to determine the patient-specific risk of cardiovascular events and improve treatment strategies.
Magnetic resonance imaging (MRI) is used extensively for noninvasive vascular imaging, because it can identify components of atherosclerotic plaques such as a lipid-rich/necrotic core, calcification, and hemorrhage . It can also visualize and quantify lipid-rich human carotid plaque and the rabbit aorta . However, whether or not MRI can distinguish between stable and unstable atherosclerotic vessels in vivo is unknown. The aim of the study is to investigate whether MRI can distinguish between rabbit iliac arteries with macrophage-rich and SMC-rich atherosclerotic lesions.
Materials and methods
Experimental Design
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MRI
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Ex vivo Study
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Image and Data Analysis
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T1=TRln(sinα⋅cosβ⋅Iβ−sinβ⋅cosα⋅Iαsinα⋅Iβ−sinβ⋅Iα) T
1
=
T
R
ln
(
sin
α
⋅
cos
β
⋅
I
β
−
sin
β
⋅
cos
α
⋅
I
α
sin
α
⋅
I
β
−
sin
β
⋅
I
α
)
T2=TE2−TE1ln(I1I2) T
2
=
T
E
2
−
T
E
1
ln
(
I
1
I
2
)
Lipid content by percentage (%) was derived from the following respective equations :
Lipid content(%)=I(T1WIwithoutfatsaturation)−I(T1WIwithfatsaturation)I(T1WIwithoutfatsaturation)×100 Lipid content
(
%
)
=
I
(
T
1
W
I
without
fat
saturation
)
−
I
(
T
1
W
I
with
fat
saturation
)
I
(
T
1
W
I
without
fat
saturation
)
×
100
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Serum Lipid Marker Sampling and Analysis
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Light Microscopy and Immunohistochemistry
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Statistical Analysis
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Results
Serum Concentrations of TC and TG 4 Weeks after Diets
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Magnetic Resonance Angiography 3 Weeks after Balloon Injury
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MRI in vivo 3 Weeks after Balloon Injury
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Histopathological Correlation
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Ex vivo MRI and Histopathological Correlation
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Discussion
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