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089 intravascular magnetic resonance imaging

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089 intravascular magnetic resonance imaging

  1. 1. Intravascular Magnetic Resonance Imaging Albert C. Lardo, Ph.D. Assistant Professor of Radiology, Biomedical Engineering and Surgery - Johns Hopkins University School of Medicine and Chief Scientific Officer - Surgi-Vision, Inc.
  2. 2. Intravascular Coils – Two Modes • Active visualization of catheters, guidewires and devices • Enables MR-guided intervention Tracking • Very high local signal for imaging structures directly adjacent to the coil • Enables diagnostic vascular imaging Imaging
  3. 3. External surface coils • Cardiac mechanical function • Perfusion • Metabolic Imaging • Angiography • Plaque characterization and therapy assessment?? Problem Spatial resolution limitation (~1 mm) Cardiovascular MRI - From the Outside In
  4. 4. Why do we need more spatial resolution? External Aorta ~10 Renal ~7 Iliac ~5 Coronary ~7 Artery Distance from Coil (cm) Chest depth (180lb male) ~300mm Quantitative assessment of deep thoracic arteries commonly prone to atherosclerotic disease (e.g. aorta, renal, iliac, coronary) Goal: Detection of small but potentially unstable plaques Fibrous cap detection (70-400µm)
  5. 5. Intravascular MRI - From the Inside Out MR Coil Miniaturization Endovascular MRI – Placement of small radiofrequency receiver antennas (coils) directly into blood vessels for active tracking and high resolution imaging (Atalar et al 1996). 8 cm 100-185 cm Coaxial transmission line DTC Decoupling and tuning circuit Scanner Inner conductorOuter conductor
  6. 6. MR Signal Strength Depends on Coil Distance from the Energy Source Signal→ Distance → Energy Source CoilTissue
  7. 7. Distance from coil (cm) SNR Internal vs. External Coil External Aorta ~10 0.4, 2 Renal ~7 ~0.4 Iliac ~4.5 ~0.6 Coronary ~7.5 ~0.2 InternalArtery Distance from Coil (cm) Chest depth (180lb male) ~300mm Distance from Coil and Structure of Interest Internal Coil 2 106 External Coil 10 26
  8. 8. Endovascular Coils - Two Designs • High local signal and moderate resolution • Signal falls off with distance (1/R) • Can be made very small and flexible (>1F) • Very high local signal and thus resolution • Signal falls off very rapidly with distance (1/R2 ) • Larger in size and less flexible Loopless Loop Resolution ~ 200 µm Resolution ~ 60 µm
  9. 9. MRI Intravascular Guidewire • Loopless antenna design • Gold plated Nitinol core • Nitinol tubing • Intravascular placement • OD = 0.032” and 0.014” • Fully tuned and decoupled Antenna whip Nitinol tube
  10. 10. Interactive Interface Gutman, McVeigh, NHLBI
  11. 11. MR-guided Applications • Intravascular MR imaging • MR-guided Catheterization • Real-Time Angiography • MR-guided Balloon Angioplasty • MR-guided Stent Placement • MR-guided Invasive Electrophysiology •MR-Guided Gene Therapy Require Imaging and Tracking
  12. 12. IVUS versus IVMRI Intravascular UltrasoundIntravascular Ultrasound Intravascular MRIIntravascular MRI Explanted Human Aortic Specimen Atalar et al.
  13. 13. Intravascular Rabbit Aortic Imaging DIR-FSE TE=20ms, ETL= 20, FOV=6cm DIR-FSE TE=26.4ms, ETL= 20, FOV=4cm Resolution – 150µmResolution – 234µm Yucel et al. Serfaty et al.
  14. 14. Intravascular MRI of Watanabe Rabbits mm B FSE, 1200/13-msec TR/TE, Double IR blood suppression, 16 ETL, 4-cm FOV, 32 NEX, 256x256 matrix ACM • Resolution: 150 µm Watanabe rabbit with a 0.032” MRI-Guidewire Serfaty et al.
  15. 15. Intravenous Guidewire - Swine 0.16x0.16x4 mm, TR 531, TE 11, BSP, 6 NEX, 2:25 stent iliac a. iliac v. Bluemke et al.
  16. 16. Cardiac Coil Ch2 Cardiac Coil Ch3Cardiac Coil Ch1 All Channels External vs. Endovascular Coil Iliac Imaging - Pig Lederman et al. DIR-FSE TR=1558ms, TE=26ms, ETL= 24, FOV=4cm Endovascular coil 156 µm resolution
  17. 17. MR ScoutX-ray Fluoroscopy High resolution MR Iliac wall vein R Iliac DIR-FSE TR=2000ms, TE=6.1ms, ETL= 24, FOV=10cm, st=4 mm Human IVMRI Iliac Imaging Yucel et al.
  18. 18. Design Plaque Plaque Vessel 0.014” MRIG Balloon - 3% Gd Gd/blue-dye medium or Gd/GFP-lentivirus medium Xiaoming Yang, et al. Johns Hopkins Hospital
  19. 19. Control Gd/GFP-lentivirus Immunohistochemistry G H Xiaoming Yang, et al. Johns Hopkins Hospital MR imaging of Gd/GFP-lentivirus transfer a fed cb
  20. 20. Summary • Intravascular MR coils and guidewires provide active device localization and high resolution imaging • MRI guided cardiovascular intervention is feasible on currently available scanners • Further improvements in spatial and temporal resolution, device localization and MR scanner design are required for general clinical use
  21. 21. Challenges • Further loop coil miniaturization for coronary imaging • Effects of cardiac motion during coronary imaging • Real-time quantitative device localization • Reduction of image acquisition time