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Aha 2001 presentation maziar

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Aha 2001 presentation maziar

  1. 1. Non-Invasive High Resolution Detection of Active Atherosclerotic Plaque in ApoE Deficient Mice by Magnetic Resonance Imaging after Injection of Super Paramagnetic Iron Oxide (SPIO) Center for Vulnerable Plaque Research University of Texas at Houston Texas Heart Institute
  2. 2. Vulnerable Plaque? Atherosclerotic plaques which are characterized by active inflammation (macrophage infiltration), extensive angiogenesis, thin permeable cap and large lipid core that are prone to rupture and cause sudden luminal clot formation and lead to heart attack and stroke.
  3. 3. Plaque Morphology vs. Plaque Activity Why do we need both? The short answer is: because not all plaques with similar morphology would result in similar outcome.
  4. 4. Morphology vs. Activity Imaging Inactive and non-inflamed plaque Active and inflamed plaque Appear Similar in IVUS OCT MRI w/o CM Morphology Show Different Activity Thermography, Spectroscopy, immunoscintigraphy, MRI with targeted contrast media…
  5. 5. Human Carotid Plaque Courtesy of Dr. Chun Yuan University of Washington
  6. 6. ?
  7. 7. 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- …?
  8. 8. Super ParamagneticSuper Paramagnetic andand Ultra SmallUltra Small Super ParamagneticSuper Paramagnetic Iron OxideIron Oxide lBlood pool magnetic resonance (MR) imaging contrast media with a central core of iron oxide generally coated by a polysaccharide layer lShortening MR relaxation time lEngulfed by and accumulated in cells with phagocytic activity
  9. 9. 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
  10. 10. Emerging Applications of SPIO in MR Imaging of Inflammation -Monitoring rejection of transplanted heart in the animal model of allograft transplantation. -Kidney allograft transplant rejection model in animal Models. -Experimental detection of encephalitis in laboratory animals.
  11. 11. HypothesisHypothesis 1- SPIO nanoparticles are accumulated in atherosclerotic plaque and their accumulation correlates with histologic evidence of macrophage infiltration. 2- Accumulated SPIO in plaque can be detected by MRI comparing the signal intensity of plaque before and after SPIO injection.
  12. 12. 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
  13. 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. SPIO particles were labeled by a fluorescent dye (DCFA).
  14. 14. FL-labeled SPIO Incubated Macrophages 24hr
  15. 15. Double DAPI Staining with Fluorescence-labeled SPIO Macrophages after 24hr Incubation
  16. 16. SPIO and T2 Effect In-vitro study to show the effect of macrophage SPIO uptake on their T2 relaxation time
  17. 17. 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
  18. 18. •Intra-macrophage SPIO reduces T2 relaxation time similar to extra- cellular free SPIO.
  19. 19. In-vivo distribution of SPIO in ApoE deficient and wild type mice: •For the initial study, we use the mouse model of atherosclerosis. • •ApoE deficient mouse has similar atherosclerotic lesions to human and the lesions are more common in the aortic arch and thoracic aorta. • We used ApoE deficient mice and normal variant (C57BL mice) as control. •Animals were sacrificed on day 3 and 5 after injection.
  20. 20. Pre and Post-SPIO Enhanced Magnetic Resonance Imaging of ApoE K/O and Wild Type Mice:              We  used  4.7  tesla  MRI  unit  (University  of  Texas,  Galveston MRI Unit, Galveston, TX) in our study.       After baseline MR imaging with respiratory gating, we  injected  1mMolFe/kg  super  paramagnetic  iron  oxide  to  six ApoE deficient and two C57bl mice through the tail  vein.       Post-contrast MR imaging were performed in day 5 with  the  same  parameters  (TR=2.5  sec,  TE=0.012  sec,  FOV=6.6  cm,  slice  thickness=2.0mm,  flip  angle  (orient)=trans, and matrices=256x256).       We selected the aorta at the level of kidney for              comparison of the baseline and post-contrast images.
  21. 21. •Tissues from different organs including liver,  kidneys, lung, heart, spleen and aorta  (including valve region ascending, descending  and abdominal) was obtained and stained. • We used Hematoxyline and Eosin (H&E), Iron,  CD68 and Movat staining.  • After Iron staining, aortic wall of the ApoE  deficient mice and normal variant were  compared based on the number of Iron  particle. • Also different doses of Feridex and The  timing between injection and tissue obtaining  was considered.
  22. 22. Histopathologic Study of the Mice Injected  with SPIO (Aortic Root) ApoE KO mouse, Movat staining, proximal aorta Coronary Cross section Atherosclerosis plaque
  23. 23. Histopathologic study of ApoE KO Mice injected  With SPIO (Aortic Root) CD68 staining (coronary plaque) Iron Staining (aortic plaque) Iron Staining (coronary section) Iron particles Iron particles
  24. 24. Histopathologic Study of ApoE KO Mice  Injected With SPIO (Abdominal Aorta) H&E staining Iron Staining CD 68 staining Iron particles
  25. 25. Histopathologic Study of Wild Type Mice  Injected with SPIO (Thoracic Aorta) H&E staining CD68 stainingIron staining
  26. 26. 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
  27. 27. MR Image of Abdominal Aorta After SPIO Injection in ApoE and Control Mice ApoE deficient 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
  28. 28. 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).
  29. 29. 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
  30. 30. Histopathologic Studies of Thoracic Aorta in Watanabe Hereditary Hypercholesterolemic Rabbit after SPIO Injection H&E staining Iron staining Macrophage staining
  31. 31. Histopathologic studies of Thoracic aorta in Watanabe Hereditary Hypercholesterolemic rabbit after SPIO injection H&E staining Macrophage staining Iron staining Iron particles
  32. 32. 0 10 20 30 40 50 60 0 10 20 30 40 50 60 70 macrophage (foam cell) density SPIOpositivecell-Iron staining Series1 R=0.956 Correlation between Iron positive cells in Iron staining and foam cell density in H&E staining in rabbit atherosclerotic aorta.
  33. 33. MR Angiography 3D with Gadolinium-DTPA in Watanabe Rabbit Before SPIO injection After SPIO injection 3D-TOF TR=59ms TE=7.0ms Flip=30 3D-TOF TR=59ms TE=7.0ms Flip=30 Baseline Day 5
  34. 34. Ex-vivo MR Study of Thoracic Aorta in SPIO-injected Atherosclerotic and Normal Rabbits after Compared to Non-injected Controls from both. (3D MR Angiography with Gadolinium-DTPA) Watanabe rabbit post-SPIO Watanabe rabbit without SPIO NZW rabbit without SPIO NZW rabbit post-SPIO
  35. 35. Ex-vivo MR Study of Thoracic Aorta in SPIO-Injected Atherosclerotic and Normal Rabbits compared to Non- Injected Controls from both. (Gradient Echo MRI) Watanabe rabbit Post-SPIO Watanabe rabbit Without SPIO NZW rabbit Post-SPIO NZW rabbit Without SPIO
  36. 36. MR Angiography 3D with Gadolinium-DTPA in Watanabe Rabbit Before SPIO injection After SPIO injection
  37. 37. Conclusion: 1) SPIO nanoparticles are actively accumulating n some (not all) areas of atherosclerotic lesions in rabbits and mice. 2) There is a strong correlation between the areas of foamy cells infiltration and SPIO uptake in the mice and rabbit plaques. 3) MR imaging of these atherosclerotic plaques show Significant changes after SPIO injection compared to the baseline, suggesting a possible role for iron particles o detect the areas of active atherosclerotic plaque with nflammation; although other possibilities could not be ruled out at this time and warrants further studies.
  38. 38. Human Clinical Trial Detection of Vulnerable Carotid Plaque using SPIO Enhanced MRI Carotid Coil MRI of first carotid patient Patients undergoing Carotid surgery Baseline MR imaging SPIO Injection Post-contrast MR imaging Histologic study of the plaque after surgery Currently underway… MRI Pathway Inc.

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