This document discusses vulnerable plaque detection using superparamagnetic iron oxide (SPIO) nanoparticles and MRI. It describes how SPIOs are taken up by macrophages in atherosclerotic plaques, decreasing the MRI signal and allowing plaque visualization. Studies in mice and rabbits show SPIO uptake correlates with plaque inflammation and macrophage content on histology. MRI of rabbits post-SPIO injection detected more signal decrease in hypercholesterolemic rabbits compared to controls, indicating potential to identify vulnerable plaque.
15. Compensatory Enlargement
of Human Atherosclerotic Coronary
Arteries
N Engl J Med 1987 May
28;316(22):1371-5
<50%
stenosis
Luminal area is not endangered until more than 40% of
internal elastic lamina is destructed and occupied by plaque
Coronary artery disease is a disease of arterial wall
disease not lumen.
PositiveRemodeling
<80%
stenosis
19. We need MRI with vulnerable plaque
targeted contrast media that identifies:
1- Inflammation (macrophage infiltration),
2- Fissured/Permeable Cap,
3- Leaking Angiogenesis and
4- Intra-Plaque Hemorrhage
5- …?
22. Current applications of SPIO in MR imaging:
-Detection of Hepatic Lesions
(primary and metastatic cancers)
-Experimental Nephritic syndrome in Laboratory animals
-Monitoring rejection of transplanted heart or kidney in
the animal model of allograft transplantation.
-Experimental detection of CNS lesions in laboratory
animals.
23. USPIOs Enter the AtheroscleroticUSPIOs Enter the Atherosclerotic
Plaque ThroughPlaque Through
l-Macrophages that engulfed
them
l-Fissured or thin cap
l-Extensive angiogenesis
l-vasa vasorum leakage
l-Intra plaque hemorrhage
24. In-vitro Study of Macrophage
SPIO Uptake
In a series of in-vitro studies we have tested
the rate of SPIO uptake by human activated
monocytes in different conditions regarding
incubation time and concentration of SPIO.
All SPIO were labeled by a fluorescent dye
(DCFA).
26. Double DAPI Staining with Fluorescence-labeled SPIO Macrophages
after 24hr Incubation
27. HypothesisHypothesis
Active macrophages residing inside
the inflamed vulnerable plaques can
be visualized following injection of
SPIO or USPIOs into the systemic
circulation by virtue of a decrease in
the magnetic resonance signal
intensity of the plaque,and correlate
with histopathologic characteristics of
vulnerability to rupture.
28. vasa vasorum
Over magnification is a major advantage of SPIO
Darkening property of SPIO in the white background of fat
and water of plaque is another advantage
29. SPIO and T2 Effect
In-vitro study to show the effect of
macrophage SPIO uptake on their
T2 relaxation time
32. Histopathologic study of the Mouse injected
With SPIO (Thoracic Aorta)
ApoE KO mouse, Movat staining,
proximal aorta
Coronary
Cross section
Atherosclerosis
plaque
33. Histopathologic study of ApoE KO Mouse injected
With SPIO (Thoracic Aorta)
CD68 staining
(aortic plaque)
Iron Staining (aortic plaque) Iron Staining (coronary section)
Iron particles Iron particles
34. Histopathologic study of ApoE KO Mouse
injected With SPIO (Abdominal Aorta)
H&E staining
Iron Staining CD 68 staining
Iron particles
35. Histopathologic study of wild type Mouse
injected With SPIO (Thoracic Aorta)
H&E staining
CD68 stainingIron staining
36. Comparison of the Number of the Iron Particles (per
HPF) in ApoE KO Mice Plaque vs. Normal Wall
0
5
10
15
Atherosclerotic
Aorta
Average
number of iron
particles per
sample
P <0.001
37. Iron Staining H&E Staining
Apo E-deficient mouse injected with SPIO
Cytokines added
38. MR Image of Abdominal Aorta After SPIO
Injection in ApoE and Control Mice
ApoE
deficien
t mouse
C57B1
(control)
mouse
Before Injection After Injection (5 Days )
Dark (negatively enhanced) aortic wall, full of iron particles
Bright aortic lumen and wall without negative
enhancement and no significant number of iron particles
39. Typical in vivo MR images of a live mouse at the heart (left)
and renal level (right). Various vessels and aortic arch can
easily e seen in these images. The slice thickness is 0.5 mm
and the in-plane resolution is 50 µm (7.1 T MR system).
40. We chose Watanabe Hereditary Hypercholesterolemic rabbits (WHHR) and
New Zealand White rabbits (NZW) for this study.
We injected them with SPIO (Feridex) 1 mMol Fe/kg and obtained baseline
as well as 5-day post-SPIO injection MR images of the aorta (1.5 Tesla
MRI system at the University of Texas, MD Anderson,Houston,Texas).
Then we compared the images in hypercholesterolemic rabbits with
the normal,wild type NZW rabbits.
Rabbit ex-vivo MRI studies:
After the in-vivo MR images, we sacrificed the animals and excised the aorta.
Then we put the isolated aorta in a gel medium, clamped both ends and any
side branches and injected gadolinium inside the lumen.
We did the same procedure for all rabbits.
We also used 2 more rabbits, one WHHR and one NZW that were not injected
with SPIO, as control, in the ex-vivo MR study.
SPIO-Enhanced MRI study in rabbits
41. Histopathologic studies of Thoracic aorta in Watanabe
Hereditary Hypercholesterolemic rabbit after SPIO injection
H&E staining
Iron staining
Iron staining
42. Histopathologic studies of Thoracic aorta in Watanabe
Hereditary Hypercholesterolemic rabbit after SPIO injection
H&E staining
Iron staining Iron staining
Iron particles
43. Plaque Cell Density vs SPIO
0
10
20
30
40
50
60
0 10 20 30 40 50 60 70
Cell Denity in H&E staining
SPIOpositivecell-Iron
staining
Series1
R=0.956
Correlation between Iron positive cells in Iron
staining and cell density in H&E staining in rabbit
atherosclerotic aorta.
44. MR Angiography 3D with Gadolinium-DTPA in
Watanabe Rabbit
Before SPIO injection After SPIO injection
45. Ex-vivo MR study of the thoracic aorta in Watanabe and
Wild type rabbit after SPIO injection compared to control.
3D MR Angiography with Gadolinium-DTPA
Watanabe rabbit
Post-SPIO
Watanabe rabbit
control
NZW rabbit
control
NZW rabbit
Post-SPIO
46. Ex-vivo MR study of the thoracic aorta in Watanabe and
Wild type rabbit after SPIO injection compared to control.
(Gradient echo)
Watanabe rabbit
Post-SPIO
Watanabe rabbit
control
NZW rabbit
Post-SPIO
NZW rabbit
control