9/6/2014 Disclosures New Developments in High Resolution Imaging - - PowerPoint PPT Presentation

9/6/2014 1

New Developments in High Resolution Imaging

• f 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 –

• thers 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

9/6/2014 2 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?

9/6/2014 3 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

10 20 30 40 50 60 circular crescentic elliptic lobular

frequency Cross-section through maximal stenosis for 9 specimens

Stenosis shape

9/6/2014 4 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 imaging Intraplaque hematoma

9/6/2014 5 Disease conditions – Carotid Atherosclerosis

T1-weighted Non-contrast T2-weighted Non-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

9/6/2014 6

T1-weighted Non-contrast T2-weighted Non-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

9/6/2014 7 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

9/6/2014 8

• 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
• f 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

9/6/2014 9 Patient with a giant fusiform basilar artery aneurysm with heavy thrombus burden

Single slice from 3D – black blood wall imaging 0.5mmx0.5mmx0.6mm Single slice from 3D – CE-MRA 0.7mmx0.7mmx0.7mm

Excellent wall visualization

Patient with a giant fusiform basilar artery aneurysm with heavy thrombus burden

Single slice from 3D – black blood wall imaging 0.5mmx0.5mmx0.6mm Single slice from 3D – CE-MRA 0.7mmx0.7mmx0.7mm

Excellent wall visualization

Subject with ica terminus aneurysm

Single slice from 3D – black blood wall imaging 0.5mmx0.5mmx0.6mm Single slice from 3D – 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

9/6/2014 10

Aortic Dissection – stable over 10 years First pass –single slice Steady-state MIP true 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 coronal Repaired TAA AAA - thrombus Aortic Dissection – rapid growth Pre-uspio injection 5 days post

9/6/2014 11

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 Directions

Radiology Neurointerventional Radiology Vitaliy Rayz, PhD Randall Higashida, MD Chengcheng Zhu, PhD Van Halbach, MD Alastair Martin, PhD Chris Dowd, MD Henrik Haraldsson, PhD Steve Hetts, MD Farshid Farzaneh, MS Biostatistics Donne Nieuwoudt, MD Chuck McCulloch, PhD Neurosurgery Michael Lawton, MD Neurology Vascular Surgery Nerissa Ko, MD Joseph Rapp, MD Wade Smith, MD Andy Josephson, MD Anthony Kim, MD Heather Fullerton, MD

Acknowledgments

Funding NIH (NINDS, NHLBI), VA Merit