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New Developments in High Resolution Imaging of the Arterial Wall
David Saloner, PhD
Department of Radiology and Biomedical Imaging, Surgery and Bioengineering
VA Medical Center/University of California San Francisco
I have no financial disclosures
Gd and Ferumoxytol are not approved as MRA imaging agents
Disclosures
Patients with vascular disease may present with similar geometric conditions.
Some progress rapidly with devastating sequellae –others remain stable over many years.
How do we determine what the drivers of vascular disease progression are?
Can we modify the paradigm for when to intervene and when to pursue “watchful waiting”?
Overview
Monitor progression of the lumen and wall over time –carotid atherosclerosis, intracranial aneurysms
Hemodynamics - visualization of MR measured velocity fields using experimental and computational methods
Wall inflammation
Correlation of morphologic change with hemodynamics
Overview
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Current Evaluation
Stenosis - reduction in diameter of lumen
a
b
stenosis = (b - a)/b x 100 %
� Why diameter stenosis? - because it is available
• Traditional assessment in terms of diameter narrowing
• Is geometry sufficient?
Disease conditions – Carotid Atherosclerosis
What is the risk factor associated with carotid disease?
a b c d
Disease conditions – Carotid Atherosclerosis
• Is geometry sufficient?
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High Resolution MRI ex vivo
Carotid disease advantage – specimen availability from endarterectomy surgery
Characterize compositional and geometric morphology – compare MR features with histo-pathologic gold standard
Longitudinal MRI
Transverse MRI
Carotid specimen
0
10
20
30
40
50
60
circular crescentic elliptic lobular
freq
uenc
y
Cross-section through maximal stenosis for 9 specimens
Stenosis shape
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What is the diameter of England?High Resolution MRI In Vivo
• Can we obtain similar data in vivo that will permit us to follow the progression of plaque bulk, geometry, and compositional features?
• 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?
Calcification clearly noted
2D “black blood” vessel wall imagingIntraplaque hematoma
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Disease conditions – Carotid AtherosclerosisT1-weightedNon-contrast
T2-weightedNon-contrast
Is geometry & composition sufficient? fibrous cap and lipidic core
3T + bilateral 8-channel coils – improved SNR: deep & low
1.5T + bilateral 4-channel coils
Reduction in measurement error – �field strength
T1 T2
3D-TOF
T1-weighted T2-weighted
TOF-MRA – bright lumen
transverse reformat
3D Black Blood Imaging of Hemorrhage
Heavily T1-weighted; sensitive to methemoglobin
coronal reformat
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T1-weightedNon-contrast
T2-weightedNon-contrast
Carotid Atherosclerosis
Thromboembolism from plaque rupture
Pre rupture
Carotid Atherosclerosis
Thromboembolism from plaque rupture
Pre rupture Post rupture
MRV Can measure velocity field in addition to structural and compositional morphology
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Disease conditions – Carotid Atherosclerosis Disease conditions – Carotid Atherosclerosis
Disease conditions – Carotid Atherosclerosis
• MR powerful non-invasive method to monitor progression
• Flow limitation rarely of importance
• Can identify major components of plaque wall: calcification; lipid rich necrotic core; intra-plaque hemorrhage; fibrous cap
• 3D methods increasingly used at 3T
Ruptured aneurysms can have devastating clinical sequellae
Untreated aneurysms can continue to remodel, layer thrombus, or rupture
Little information is available on natural progression of untreated aneurysms
Role of hemodynamics in progression is undefined
Untreated Intracranial Aneurysms
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• Most current analyses of growth and rupture risk based on geometric considerations
• Absolute diameter, neck/diameter ratio …
• Is geometry sufficient?
Disease conditions –Intra-cranial Aneurysmal Disease
Longitudinal studies: MRA co-registration
Surfaces obtained from baseline and follow-up MRA are co-registered
• Quantitative measurement of the changes obtained by calculating the aneurysmal volume at each study
Aneurysm growth observed with CE-MRA studies over time
Flow computed with CFD
High Resolution Black Blood Intracranial Vessel Wall Imaging
3D SPACE – black blood vessel wall imaging
Suppress blood signal and obtain contrast between outer wall and adjacent tissue
0.5mmx0.5mmx0.6mm
10 mins
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Patient with a giant fusiform basilar artery aneurysm with heavy thrombus burden
Single slice from3D – black blood wall imaging 0.5mmx0.5mmx0.6mm
Single slice from3D – CE-MRA 0.7mmx0.7mmx0.7mm
Excellent wall visualization
Patient with a giant fusiform basilar artery aneurysm with heavy thrombus burden
Single slice from3D – black blood wall imaging 0.5mmx0.5mmx0.6mm
Single slice from3D – CE-MRA 0.7mmx0.7mmx0.7mm
Excellent wall visualization
Subject with ica terminus aneurysmSingle slice from3D – black blood wall imaging 0.5mmx0.5mmx0.6mm
Single slice from3D – CE-MRA 0.7mmx0.7mmx0.7mm
Good wall visualization
USPIO in the wall as a marker of inflammation?
Scavenged by macrophage
Potentially differentiate stable from active (growing) aneurysms
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Aortic Dissection – stable over 10 years
First pass –single slice Steady-state MI Ptrue versus false lumen
Aortic Dissection – stable over 10 years
Pre-uspio injection 5 days post
Aortic Dissection – rapid growth in AAA
Single slice sagittal Single slice corona lRepaired TAA AAA - thrombus
Aortic Dissection – rapid growth
Pre-uspio injection 5 days post
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Aortic Dissection – rapid growth
5 days post
T2* weighted image of aneurysm wall at the tip of the basilar artery imaged before (left) and five days following Ferumoxytol administration (right).
Uptake by inflammatory macrophage in the vessel wall (large red circle).
Intracranial Aneurysm– basilar tip
• Important to establish link to biomolecular and cellular pathways that are activated by adverse hemodynamics
• Establish presence of inflammatory agents in surgical specimens co-localized with hemodynamics
• Improved VWI at higher field strength (7T) and greater resolution
Future DirectionsRadiology Neurointerventional RadiologyVitaliy Rayz, PhD Randall Higashida, MD Chengcheng Zhu, PhD Van Halbach, MDAlastair Martin, PhD Chris Dowd, MDHenrik Haraldsson, PhD Steve Hetts, MDFarshid Farzaneh, MS BiostatisticsDonne Nieuwoudt, MD Chuck McCulloch, PhD
NeurosurgeryMichael Lawton, MD
Neurology Vascular SurgeryNerissa Ko, MD Joseph Rapp, MDWade Smith, MDAndy Josephson, MD Anthony Kim, MD Heather Fullerton, MD
Acknowledgments
FundingNIH (NINDS, NHLBI), VA Merit
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