This document discusses non-invasive imaging of vulnerable plaque using macrophage targeting contrast agents such as superparamagnetic iron oxide (SPIO) nanoparticles. SPIO nanoparticles are engulfed by macrophages and accumulate in inflamed plaques, shortening MRI relaxation times and allowing identification of active plaques. Studies in animal models demonstrate the feasibility of SPIO-enhanced MRI for detecting vulnerable plaque. However, limitations include the need to balance morphology and activity imaging, as well as poor resolution for coronary applications and the cost and complexity of SPIO injection and delayed imaging.

1. Non-Invasive
Macrophage Imaging for
Detection of Vulnerable Plaque
Applications and Limitations
Amersham Oct 2003
Morteza Naghavi, MD

4. A
B

5. Which one is
vulnerable, A or B?
The one with
inflammation
(macrophage infiltration)

6. Morphology vs. Activity Imaging
Inactive and
non-inflamed
plaque
Active and
inflamed
plaque
Similar in
IVUS OCT MRI
w/o CM
Morphology
Different
Activity
Thermography, Spectroscopy,
immunoscintigraphy, MRI with
targeted contrast media…

7. Plaque Morphology
vs.
Plaque Activity
We Need Both

8. Imaging Inflammation
- by MRI
- by CT
Both are available today!

9. Imaging Inflammation
- by MRI
Pioneered in 1980s
Rummeny E, Weissleder R, Stark DD, Elizondo G, Ferrucci JT.
Radiologe. 1988 Aug;28(8):380-6.

10. SuperparamagneticSuperparamagnetic
andand
Ultra-superparamagneticUltra-superparamagnetic
Iron OxideIron Oxide
lBlood pool Magnetic resonance (MR)
imaging contrast media with a central
core of iron oxide generally coated by a
polysaccharide layer
Shortening MR relaxation time
Engulfed by and accumulated in cells
with phagocytic activity

11. Particle Core Size Particle Size Blood
(nm) (nm) Half-life
Combidex 5-6 20-30 8h
Feridex 4-6 35-50 2.4±0.2h
DDM 43/34/102 6.4 20-30 6h
Clariscan
MION 4-6 17 varies
Feruglose
--- --- --- ---
Examples of commercially available SPIOs

12. USPIOs Enter the AtheroscleroticUSPIOs Enter the Atherosclerotic
Plaque ThroughPlaque Through
lMacrophages that engulfed
them
lFissured or thin cap
l Extensive angiogenesis
l vasa vasorum leakage
l Intra plaque hemorrhage

13. 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).

14. FL-labeled SPIO Incubated Macrophages 24hr

15. Double DAPI Staining with Fluorescence-labeled SPIO Macrophages
after 24hr Incubation

16. Hypothesis

17. 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

18. SPIO and T2 Effect
In-vitro study to show the effect of
macrophage SPIO uptake on their
T2 relaxation time

20. 0
10
20
30
40
50
60
70
80
90
50 250 control
20 min
60 min
6 hours
24 hours
Macrophage Uptake of Feridex with Time
and Concentration Shown by T2 Reduction
Concentration µmol/ml

21. Histopathologic Studies of ApoE KO Mice
Injected with SPIO (Abdominal Aorta)
H&E staining
Iron Staining CD 68 staining
Iron particles

22. Histopathologic Study of Wild Type Mice
Injected With SPIO (Thoracic Aorta)
H&E staining
CD68 stainingIron staining

23. 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

24. 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

25. Injection of Cytokine Increases SPIO-Loaded Macrophage
Density in Aortic Plaques (Apo E Deficient Mice)
Naghavi et al Circulation 2003

26. Naghavi et al Circulation 2003
Injection of Cytokine Increases SPIO-Loaded Macrophage
Density in a Coronary Plaque (Apo E Deficient Mice)

27. Histopathologic studies of Thoracic aorta in Watanabe
Hereditary Hypercholesterolemic rabbit after SPIO injection
H&E staining
Iron staining
Iron staining

28. Histopathologic studies of Thoracic aorta in Watanabe
Hereditary Hypercholesterolemic rabbit after SPIO injection
H&E staining
Iron staining Iron staining
Iron particles

29. 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.

30. MR Angiography 3D with Gadolinium-DTPA in
Watanabe Rabbit
Before SPIO injection After SPIO injection

31. MRI Identifies Plaque Inflammation by SPIO Nanoparticles
Watanabe rabbit
Post-SPIO
Watanabe rabbit
control
NZW rabbit
control
NZW rabbit
Post-SPIO
Watanabe Rabbit
Post-SPIO
Watanabe Rabbit
Control
NZW Rabbit
Post-SPIO
NZW Rabbit
Control

32. 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

33. Schmitz et al

34. Schmitz et al

35. Schmitz et al

36. Ruhem et al

37. Ruhem et al

38. Ruhem et al

39. Ruhem et al

40. Ruhem et al

41. Kooi et al

42. Kooi et al

43. Kooi et al

44. Kooi et al

45. Ho et al

46. Ho et al

47. MR signal changes after CsA treatment. A group with allotransplants was treated with CsA for either 7 days
(n=5) or 4 days (n=5) after initial MRI experiments showed decrease of MR signal intensity according to degree
of graft rejection. On POD 14, transplanted rats were reinjected with USPIO particles, and then MRI
experiments were performed. Animals treated 7 days showed minimal changes in MR signal intensity 24 hours
after reinjection (A and B), and animals treated 4 days showed MR signal intensity that was significantly
decreased after USPIO injection (C and D). MR images of short-axis view of graft are shown. MR images before
USPIO infusion are at A and C, and images taken 24 hours after infusion are at B and D.
Ho et al

48. Ho et al

49. • Imaging Macrophage
Activity in the Brain Using
Ultrasmall Particles of Iron
Oxide
Jeff W.M. Bultea and Joseph A. Franka Laboratory of Diagnostic
Radiology Research National Institutes of Health Bethesda, MD

51. • SPIO MR imagine of macrophage will
is feasible for clinical applications.
• It will be of great interest to
investigate the cost-effectiveness of
this technique in comparison with
alternative diagnostic approaches.
Conclusion

52. • Poor spatial and temporal
resolution for coronary
applications
• Cost
• Cumbersome (injection and
delayed imaging)
Limitations