Advanced 3D Guidance for EVAR Procedures

Gilles Soulez, MD, MSc

University of Montreal

Disclosure & Acknowledgments

• Research Grants• Canadian Health Research Institute

• Canadian Fundation of Innovation

• Natural Sciences and Engineering Research Council

• Fonds Recherche Québec-Santé

• Siemens Medical

• Cook Medical

• CAE

• Patent licensing (Cook Medical)

Current limitation of CT planning and 2D DSA guidance for EVAR

• Procedure planning performed on CTA

• DSA guidance• Radiation exposure and CIN

• Need to recreate ideal projection for each procedural step

• No visualization of thrombus to delineate landing zones

• Increasing incidence of complex EVAR

• Hostile neck

• Branched/Fenestrated

• Chimney

Renal function & EVAR

• GFR ml/min• Stage 1 >90

• Stage 2 60-89

• Stage 3 30-59

• Stage 4 15-29

• Stage 5 < 15

Brown LC. An Surg 2010;251-966-975

Irradiation

• EVAR & irradiation1

• Planning CT

• EVAR + CT FU at 1, 3, 6 and 12 months and annually

• 145-205 mSv on 5 years• 70-year-old = attributable cancer risk = 0.60% (1 in 170).

• 50-year-old = 1.03% (1 in 100)

• 30% of CT scan unnecessary 2

• Stochastic injuries due to staff exposition3

1.White HA. J Cardiovasc Surg 2010 51:95-104 2. Zhou W. J Vasc Surg 2010 3. Stecker MS-JVIR-2009

• Alignment 3D and 2D projection

• Real time fluoroscopy with2D/3D overlay

• Synchronization of 3D rendering with C-arm angulation

Improve guidance 3Droadmap

Per-operative 2D/3D Workflow

Limitation of overlaying CT volume rendering and fluoro

• Thrombus outline is not seen

• Superposition of VR will mask guidewires, delivery device and stent markers

• Only a rigid registration can be performed since you do not have a mathematical geometric model (Mesh)

How to improve volume overlay

• Fading in and out

• Stent boost

• Use vessel transparent dysplay

• Complete segmentation of AAA lumen and thrombus outlines

• Create a lumen and thrombus mesh

• Dysplay only the mesh

Dijkstra-ML-J-Vasc-Surg-2011Tacher-V-JVIR-2013

AAA segmentation and modeling• Longitudinal view of the

AAA

• Outerwall segmentation from the celiac trunk to one selected iliac artery

• Segmentation plans defined on transverse section of the AAA

• 3D rendering of the AAA lumen and thrombus

• Automated D-Max and volume measurements

Kauffmann C et al. EJR 2011;77:502-8

Automatic CT segmentation for lumen and thrombus

Planning

• Define centerlines• Aorta, iliac, renal arteries• CT, SMA• Internal iliac arteries

• Propose and define the best working view for each procedural steps

• Orthogonal projection to target vessel centerline

• Adjust if needed for C-arm mechanical range

3D/3D Registration

• Perform a CBCT• Before draping

• Automatic bone registration• Spine/spine

• Fine tuning of registration based on vascular

• Calcification alignement• Vessel ostia

• Projection of 3D CT mesh in the fluoroscopic spac

• Synchronization of C-arm, table, magnification with the new 3D/3D space

Registration with Biplanar Fluoroscopy

• Separate VR of spine and aortic lumen from CT

• Spine fusion /biplanar fluoroscopy

• Replacement of spine by aortic lumen

• Advantage• Dose• Easy

• Drawback• Absence of precise vascular

alignement

Rigid registration

Live DSA correction

Live DSA correction

Registration accuracy

Registration renal arteries Error X axis

Error z axis

Before correction mm 10.6±11 7.4±5.3

Bone based correction mm 3.5±2.5 4.6±3.7

DSA correction mm 0.6±0.7 0.3±0.4

•3D/3D registration is generated at the onset of the procedure (before patient draping)

•Need to minimize patient motion

•Influenced by anesthesia

•Arm position

Kaufmann et al. JVIR 2015

Optimization of overlay for bone correction

• Substraction of bone marrow to outline bone contours

• Manual bone based correction of the 3D/3D alignement during fluoroscopy

• Manual alignement optimization based on DSA

• Mean error on renal• 1.95 ±2.46 mm (0-7 mm)

Fukuda-T et al. Europ-J Vascular-Endovasc-Surg-2013

Iliac artery

• Iliac centerline deviation• 38.3±15.6mm

• Ostia internal iliac artery• Ipsi lateral

• 5.6±2mm (x axis)

• 4.3±3mm (z axis)

• Contralateral• 6.1±3mm (x axis)

• 5.5±4.2 (z axis)

Kaufmann et al. JVIR 2015

Vascular displacement is a concern

Deformation induced by endovascular devices

Elastic registration with automated detection of endovascular devices

Lessard S et al. Med Eng Phys 2015

Device segmentation

• Errors at the internal iliac ostia estimation after a mesh deformation, measured offline

• 28 patients (21 EVAR and 7 FEVAR)

• 43 measures

• Before correction mean error 11.3±7mm

• After correction 1.99±2.03 mm

• 19 no error

• Principal suspected causes of error

• External iliac high curvature

• High calcification score

Preliminary results

Lessard S et al. Manuscript in preparation

Deformation influenced by calcification and curvature

Ideal Workflow for minimizing misregistration

• AAA mesh creation > MIP or VR overlay

• CBCT > biplanar ?• Better alignment of vascular structure on CBCT (calcification)

• Continuous and automated process of bone correction to correct bone displacement

• Apply correction on CBCT/CT fusion model

• Update of vascular structure• Guidewire (geometric centerline alignement)• After each DSA

• Mechanical modeling (FEA)

Clinical utility for standard EVAR

• 72 pts database /matching based on BMI

• 16 vessel navigator

• 16 conventional DSA

Stangenberg-L-J-Vasc-Surg-2015

2D/3D interesting for complex EVAR

• Increasing proportion of EVAR in hostile neck anatomies

• Fenestrated/branched SG/chimney procedures

• Helpful to align fenestration and catheterize side vessels

Fenestrated/branched EVAR

Tacher-V et al JVIR 2013

Clinical utility

Clinical utility: fenestrated, branched SG

• 72 patients FEVAR• 41 no CT fusion

• 31 after CT fusion

• Less• Fluoro, procedure time

• Radiation, Contrast dose

• Less blood loss (p<0.0001)

• Trend for lower hospital stay (p=0.07)

Mc Nally et al. J Vasc Surg 2015

102 pts intra-operative fusionStandard (44)/Fenestrated (18)/Branched (26)/Thoracic (14)

Hartault-A-Eur-J-Vasc-Endovasc-Surg-2015

Comprehensive biomechanical modeling of EVAR

• Developing a comprehensive patient-specific biomechanical model of the aorto-iliac vascular structure and surrounding organs

• Intra-luminal thrombus

• Abdominal fat

• Spine

• Simulating EVAR to perform advanced procedural planning

• Assessing arterial deformations during EVAR

• Improving 2D/3D roadmap guidance (elastic registration using the simulation outputs

• Performing procedural rehearsal for physicians training

EVAR simulation

• Use the mesh to create a biomechanical model

• Aorta• Stent-graft

• Use Finite element analysis to estimate the interaction between SG and aorta

• Simulate SG deploiement to optimize SG planning

• Simulate vessel deformation to optimize image guidance

• Procedure reharsal for training

Roy D et al. IMA Journal of Applied Mathematics 2014;79:1011-1026

Displacement = 80mm

Lumen only

Finite element mesh

Points defining the spine curve

Done in 10 min. from segmentation files.

Simulation: aorta

Roy D et al. Numerical analysis 2014

Overall Workflow

StartPatients AAA, Thrombus, Spine, Pelvic

Bone and Fat Reconstruction

Deformation and configuration

Plug in for translating patient data to LSDYNA

Select stent-graft

Deployment Simulation

Zero Pressure GeometrySimu

lation

Translating simulation result to prioperative softwareR

oad

map

Tools identification

Proper simulation selection

Tools detection

3D roadmap

Patient geometry reconstruction

Thrombus

Patient from LCTI database

Spine

Lumen

ORS software

Numerical Model

Device Characterization (Cook Medical)

1

23

Equivalent mean properties for typical sections of body and leg catheters.

123

Eaxial = 402 MPaEcirc. = 165 MPa

Stent(Steel/nitinol)

Graft(Dacron)

Abdominal fat characterization

• The hyper-Viscoelastic material is considered for the surrounding organ

• The experimental data on human adipose

tissue is taken from Gerhard Sommer et al.

Stress strain data

Vessel Wall characterization

• AAA exhibits significant anisotropic behavior

Stress strain data

39

•Hyperelastic Matrix •Collagen fibers reinforcement•Layered structure of AAA

Matrix Fibers

I=IntimaM=MediaA=Adventitia

Results: Arterial deformation by guidewires

Dugas A et al. CVIR 2012;35:779-87

Results: Stent-Graft Deployment

(1) (2) (3)

(4) (5)

(6)

41

Results: Stent-Graft Deployment

Multimodal image fusion and simulation for EVAR

• 3D roadmap will minimize procedure time, contrast, irradiation and complication in complex EVAR procedures

• Improved visualization and correction if overlay done after AAA segmentation and mesh creation

• Automated device detection useful to perform geometric correction during the procedure

• Biomechanical simulation of AAA, SG and their mutual interaction will play a major role in the future