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MR Imaging for the Evaluation of Carotid Atherosclerosis
David Saloner, PhDProfessor of Radiology
VA Medical CenterUniversity of California San Francisco
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What is the risk factor associated with carotid disease?
a b c dIdentical diameter stenosis but different
geometries and/or composition
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Standard of truth - excised specimen
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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)
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Longitudinal MRI
Transverse MRI
Carotid specimen
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circular crescentic elliptic lobular
freq
uenc
yCross-section through maximal stenosis for 9 specimens
Stenosis shape
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Fibrous cap over necrotic core
Histology MRIMRI shows good contrast between fibrous cap and necrotic core as confirmed on histology
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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?
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High resolution TOF-MRA using high sensitivity phase-array carotid coil
0.7mm x 0.7mm x1.0mm
Tacq = 6min
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time
carotid jugular
Inject 30cc
Ttr
TdAcquisition time
Intravenous injection of GdDTPA - contrast enhanced MRA (CE-MRA) -can be used to address some shortcomings of conventional MRA.
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CE-MRA 3D TOF
CE-MRA (25 s) has little motion blurring compared to 3D TOF (10 min)
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CE-MRA 3D TOF
CE-MRA (TE=1.5 ms)has reduced sensitivity to complex flow cf 3D TOF (TE=6.5ms)
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CE-MRA
3D TOF
Caveat: CE-MRA not always better.Tight stenosis seen as flow void on CE-MRA
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Dedicated equipment provides improvements - phased-array carotid coil gives increased SNR hence better resolution
Conventional coil Phased-array coil
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High-resolution 3D imaging of lumenal contours
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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
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Native imagewith coil
Adjusted image
Phased-array coils with postprocessing
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Calcification
Calcification also noted on MRI
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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
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Dr. David Saloner, VASF, and Dr. F. Scott Pereles, Northwestern
High ResolutionCarotid Imaging
3D CE-MRA 3D TrueFISP 2D T2-TSENew rapid methods - new hardware
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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