X‐ray Based Imaging in Neurovascular Intervention – Requirements and Challenges
Division Neuroimaging and Intervention & The New England Center for Stroke Research Departments of Radiology, Neurology and Neurosurgery University of Massachusetts
Disclosure
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BSC (Educational Grant, Clinical Research)
Ev3 (Consultant, Research Grant, Clinical Research)
Codman J&J (Consultant, Educational Grant, Clinical Research)
Micrus (Consultant, Educational Grant, Clinical Research)
Microvention (Educational Grant, Consultant)
Surpass Med Ltd (Stockholder, Clinical Research)
Medtronic (Consultant)
Penumbra (Consultant, Clinical Research)
Covidien (Consultant)
Soteira (Consultant)
Philips (Research Grant, Equipment support)
NIH (NIBIB 1R21EB007767‐01; NINDS 5R01NS045753‐04; NINDS 1R21NS061132‐
01A1) Ischemic and Hemorrhagic
Stroke in USA
• Stroke is the third cause of death and leading cause of disability in the United States
• 700,000 new or recurrent stroke per year • Approximately 87% ischemic
• 40% due to large vessel occlusions
• Every 45 seconds someone in the U.S. has a stroke
• 160,000 fatal per year
• Stroke cost estimated at $62.7 billion in 2007
• 5‐year recurrence rate for stroke 24‐42%
• ~ 50,000 aneurysms treated
(~30,000 ruptured)
Medical Devices for Recanalization
• MERCI Retriever
• Multi‐MERCI trial: 17‐center, non‐
controlled, technical efficacy study (n=177)
• Recanalization in 55% of pts
• Procedural complications in 9.8%
• mRS ≤ 2 at 90 days: 36%
• 49% in pts with recanalization
• 9.6% in pts without recanalization
Smith WS, Sung G, Saver J, et al., for the MERCI Trial Investigators. Stroke 2008, 39: 1205
Medical Devices for Recanalization
• Penumbra System
• Penumbra trial: 24‐center, non‐
controlled, technical efficacy study (n=125)
• Recanalization in 82% of pts
•
•
ICA occlusion 18%
VB occlusion 9%
• Procedural but not device related complications in 3.2%
• mRS ≤ 2 at 90 days: 25% • 29% in pts with recanalization
• 9% in pts without recanalization
Presented at the 2008 ASA International Stroke Conference
in New Orleans by Cameron McDougall, M.D. on behalf of the Penumbra Stroke Trial investigators.
Acute Ischemia: Left ICA Dissection and Thromboembolic MCA Occlusion
CT, CT Angiography and CT Perfusion 60 y o m w NIHSS 21 (global aphasic and R UE/LE hemiplegia
Left ICA dissection and MCA Occlusion
Digital Subtraction Angiography Acute Stenting in left ICA dissection and MCA Occlusion Enterprise VRD* *Stenting procedure approved on case by case base by local IRB and FDA
Acute Stenting in left ICA dissection and MCA Occlusion Enterprise VRD stent* *Approved on case by case base by local IRB and FDA
Acute Stenting in left ICA dissection and MCA Occlusion Enterprise VRD* Acute Stenting in left ICA dissection and MCA Occlusion CT Post Revasc
CT D 2
MR FLAIR D 4
NIHSS 5 on D5 post revascularization What are the Challenges
Extravascular/Medical Management →
(minimally invasive) Endovascular
Physiology/
Flow Dynamics
Vessel Wall
Biological
Response
Vessel Wall
Biomechanics
Coagulation Anatomy/Morphology
System
Biplane 3D Neuroendovascular Surgical Suite
Flat Panel Detector
“The Endovascular Microscope”
Major Challenges
Delayed care due to lack of integration of multimodality imaging within the proximity
Improvement of spatial and temporal resolution of present imaging angiography system needed including faster sampling by FD
Soft tissue characterization
Morphology/Anatomy
Normal 3 D vascular anatomy
Imaging ‐ Illustrative case: Dysplastic PICA Aneurysm CT‐Angiography
DSA Image and 3 D Angiogram
Intraoperative view
Anatomy/Morphology
Current Features
• High resolution angiography
• 3D angiography
• Roadmap
• 3D Roadmap
• Integration of arterial, capillary and venous structures within the same display
Requirements/Challenges
• Integration of information on soft tissue and vascular structures (e.g., calcification)
• Higher tissue contrast resolution
• Image segmentation of various sources within sub‐mm accuracy (MR, CT, DSA)
• Motion artifacts (breathing, head motion, vasculature pulsatility, brain motion)
Development of Soft Tissue Imaging ‐
Cone Beam CT
Case: Small brain arteriovenous malformation in a 6 y o boy with parenchymal hemorrhage
DSA
Soft tissue Imaging – Cone Beam CT
Small bAVM subependymal anterior thalamus at the level of foramen of Monro
Real High resolution Roadmap
Dural arteriovenous fistula with subdural hematoma
Acrylate Infusion ‐ Roadmap
Implants/Devices
Brain Aneurysm Implants
Coils
Stents
Pre
Flow Diverter
Post
6 mo FU
Stent Wall Apposition and Kink
Stent covering an underlying plaque/clot
Scatter Radiation
Flow Diverter – Insufficient spatial resolution
Flow Diverter
Device and Vasculature – Loss of Details due to Similarity in X‐ray Attenuation
Device and Soft Tissue
Current Features
• Improved spatial resolution with integration of tissue imaging (cone beam CT)
• Improved device‐
vasculature information
• Some soft tissue information
Requirements/Challenges
• Higher spatial resolution
• Higher tissue contrast
• Scatter radiation with high amount of metal mass (coils)
• Motion artifacts (arterial pulsation, brain pulsation, breathing, head motion)
• Introduction of new non‐
metallic implants/materials
Physiology
Physiology
• Ischemic Stroke: CBF, CBV, MTT and integration of imaging and intervention using the same FD – unit
• Pre and Post – Revascularization: Assessment of Brain Perfusion in Vasospasm, Intracranial Disease (ICD) and Extracranial Disease (ECD)
• Flow quantification and Flow pattern characterization for brain aneurysm
• Characterization of Tumor vascularity
Acute Ischemia: Left ICA Dissection and Thromboembolic MCA Occlusion
CT, CT Angiography and CT Perfusion Tissue Perfusion
Current Features
• Some soft tissue information (hematoma, CSF, vasculature)
• Good spatial resolution and contrast sensitivity ‐ CBV
• Some information on flow
Requirements/Challenges
• Higher temporal resolution
• Higher FD sampling rate
• CBF, CBV, MTT • Characterization of flow patterns and quantification of flow (contrast attenuation)
• Motion artifacts (arterial pulsation, brain pulsation, breathing, head motion)
High Speed Rotation for Cone Beam CT
Ahmed, Zellerhoff, Strother , et al. AJNR 2009
Comparison CTP and C‐arm CT
Regions of white matter, gray matter and basal ganglia were studied – iv contrast injection
Ahmed, Zellerhoff, Strother , et al. AJNR 2009
Ahmed, Zellerhoff, Strother , et al. AJNR 2009
Flow Diversion in Brain Aneurysm
Key Questions –
Brain Aneurysms and Flow
• Is there an interaction between flow and aneurysm growth and rupture?
• Can the interaction between flow and vascular wall biology be modeled?
• Flow diveters: virtual implantation
• Limitations of mathematical modeling
Aneurysmal Disease: Multi-Factorial Problem
HEMODYNAMICS
low WSS
endothelial
dysfunction
remodeling
intimal
thickening
high WSS
excess NO
apoptosis
degenerative
remodeling
wall
weakness
CLINICAL
genetics
gender , age
smoking
history of SAH
hypertension
ANEURYSM
stabilization
initiation
growth
rupture
BIOMECHANCICS
wall
stress
growth &
remodeling
Courtesy of Dr. C Putman
PERI‐ANEURYSMAL ENVIRONMENT
sharp
contacts
increased
stress
smooth
contacts
extra structural
support
wall injury
stabilization
Large
Impingement
Diffuse Concentrated
Inflow Jet Concentration and
Impingement Size – Various
Aneurysm Types –CFD Studies
Small Impingement
Courtesy of Dr. C Putman
Virtual vs Conventional
Angiography
Conventional
Angiogram
CFD Analysis
Virtual
Angiogram
Cebral, J.R., R. Pergolizzi, and C.M. Putman, “Computational
fluid dynamcis modeling of intracranial aneurysms:
qualitatively comparison with cerebral angiography”.
Academic Radiology, 14(7):804‐813, 2007.
Virtual Angiograms: Flow
Effect and Residence Time
Pre‐coiling Post‐coiling
Courtesy of Dr. C Putman
Flow Blockage by Coils
Flow
Pattern
Iso‐Velocity
Courtesy of Dr. C Putman
Virtual Angiograms
Pre-Stenting
Post-Stenting
1
Optimization of Flow Diverter
2
3
4
Particle Image Velocimetry
1
Average hydrodynamic circulation ⋅ ∫
Γ ( t ) d t
=
w h e r e : Γ
∫
T
T
Γ
m
=
0
Lieber, Nikolaidis, Wakhloo Ann Biomed Eng 1998
A
∫
( ∇
×
V
r
)
r
⋅ n d A
Flow Diverter in Rabbit Elastase Aneurysm
Contrast washout and X‐ray attenuation
Pre FD
Post FD
3 wks FU
MATHEMATICAL MODEL – Use of Functional Angiography
Convection
f(t)=ρ1
t
1
∫ σπ
0
−
2
(η−μ) 2
2σ 2
e
∗
Diffusion
1
τ1
−
t−η
e
τ1
⎡t 1
dη +ρ2 ⎢∫
⎢⎣ 0 σ 2π
−
e
σ,μ = Contrast injection related parameters.
ρ1
τ1
ρ2
τ2
= Relative magnitude of contrast convected out of aneurysm.
= Convection time constant. = Relative magnitude of contrast diffused out of aneurysm.
= Diffusion time constant.
Lieber, Gounis, Chander, Wakhloo Crit. Rev Biomed Eng 2004
⎛
−τt
dη − ⎜1‐ e
⎜
⎝
(η−μ) 2
2σ 2
2
⎞⎤
⎟⎥
⎟⎥
⎠⎦
Rabbit Elastase Aneurysm – Flow diverters
High‐speed DSA immediately after Flowdivertor –
Flow stagnation and delayed contrast washout
Arterial Phase
Flowdivertor
Ophthalmic Artery
Arterial ‐ Capillary Phase
g p
y
Surpass Flowdivertor – Flow stagnation and delayed contrast wash‐out
Capillary Phase
Venous Phase
Retinal Blush
Late Venous Phase
Retinal Blush
Retinal Blush
MRI (Axial source images TOF with contrast)
Before Surpass Flowdivertor
24 hours after Surpass Flowdivertor
Virtual Stenting – Second Generation
Integration of Morphology and Flow Information
Vessel Wall Biomechanics
Wall Compliance Effects
Some Observations:
30+ patients imaged with dynamic DSA & 4DCTA
2/3 of aneurysm exhibit motion, 1/3 no motion
2/3 of blebs deformed with larger amplitude than sac
BA tip aneurysms had a bending motion of the BA
Wall motion characteristics varied from patient to patient
Wall Tracking
Zones
Sforza D, Putman C, Oubel E, DeCraene M, Frangi
A, Cebral JR, “Characterization of wall motion
in cerebral aneurysms from dynamic angiography”, Proc. ASNR, New Orleans, 2008.
Rigid Deforming Dempere‐Marco, L., E. Oubel, M.A. Castro, C.M. Putman, A.F. Frangi, and J.R. Cebral, “Estimation of wall motion in
intracranial aneurysms and its effects on hemodynamic patterns”. Lecture Notes in Computer Science, 4191: 438‐445
2006.
Thank you “We are what we repeatedly do. Excellence, then, is not an act, but a habit.”
Aristotle 384 BC‐322 BC