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120 mr imaging for the evaluation of carotid atherosclerosis


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120 mr imaging for the evaluation of carotid atherosclerosis

  1. 1. MR Imaging for the Evaluation of Carotid Atherosclerosis David Saloner, PhD Professor of Radiology VA Medical Center University of California San Francisco
  2. 2. What is the risk factor associated with carotid disease? a b c d Identical diameter stenosis but different geometries and/or composition
  3. 3. Standard of truth - excised specimen
  4. 4. High Resolution MRI of Resected Plaque • Provides perspective on wealth of information available from MR imaging of geometry and composition • (200µm)3 resolution (not currently obtainable in vivo)
  5. 5. Longitudinal MRI Transverse MRI Carotid specimen
  6. 6. 0 10 20 30 40 50 60 circular crescentic elliptic lobular frequency Cross-section through maximal stenosis for 9 specimens Stenosis shape
  7. 7. Fibrous cap over necrotic core Histology MRI MRI shows good contrast between fibrous cap and necrotic core as confirmed on histology
  8. 8. High Resolution MRI In Vivo • Can we obtain comparable data in vivo that will provide measures of 3d descriptors? Will these permit us to follow the progression of geometry (X-sectional area, plaque bulk), and compositional features (lipidic core, fibrous cap)? • Can we identify the features of the plaque that correlate with rapid progression in a prospective fashion? • Can we identify the features of the plaque that confer neurological risk?
  9. 9. High resolution TOF-MRA using high sensitivity phase-array carotid coil 0.7mm x 0.7mm x1.0mm Tacq = 6min
  10. 10. time carotid jugular Inject 30cc Ttr Td Acquisition time Intravenous injection of GdDTPA - contrast enhanced MRA (CE-MRA) -can be used to address some shortcomings of conventional MRA.
  11. 11. CE-MRA 3D TOF CE-MRA (25 s) has little motion blurring compared to 3D TOF (10 min)
  12. 12. CE-MRA 3D TOF CE-MRA (TE=1.5 ms) has reduced sensitivity to complex flow cf 3D TOF (TE=6.5ms)
  13. 13. CE-MRA 3D TOF Caveat: CE-MRA not always better. Tight stenosis seen as flow void on CE-MRA
  14. 14. Dedicated equipment provides improvements - phased-array carotid coil gives increased SNR hence better resolution Conventional coil Phased-array coil
  15. 15. High-resolution 3D imaging of lumenal contours
  16. 16. High resoln. MRA of lumenal contours in vivo • Provides good delineation of vascular contours with reasonable resolution - about 0.5 mm3 voxel • 3D depiction of contours • Little or no invasiveness • Provides potential to evaluate cross-sectional area, and surface irregularities
  17. 17. Native image with coil Adjusted image Phased-array coils with postprocessing
  18. 18. Calcification Calcification also noted on MRI
  19. 19. High resoln. MRI of vessel wall in vivo • Provides good delineation of plaque components with reasonable resolution - about 0.5 mm3 voxel • Sequential 2D slices providing 3D overview • Non invasive • Provides potential to evaluate plaque inhomogeneity - perhaps lipid core, fibrous cap, calcification, intraplaque hemorrhage
  20. 20. Dr. David Saloner, VASF, and Dr. F. Scott Pereles, Northwestern High Resolution Carotid Imaging 3D CE-MRA 3D TrueFISP 2D T2-TSE New rapid methods - new hardware
  21. 21. Future of MRA/I • Improved hardware and software • Use of 3D black blood studies, plaque enhancement following contrast injection • Implementation in longitudinal studies of disease progression/regression • Establish true determinants of neurological risk