This work was partly supported by the French ANR within the Investissements d'Avenir program (Labex CAMI)

under reference ANR-11-LABX-0004.

Tracking of structures for the endovascular

treatment of aortic pathologies

08/12/2015 1

Long Hung Nguyen-Duc

INSERM, U1099, Laboratoire de Traitement du Signal et de l’Image (LTSI)

Université de Rennes 1, Rennes

Thesis supervisor: Prof. Pascal Haigron

Clinical partners: vascular surgery (Rennes, Grenoble), interventional cardiology (Rennes)

08/12/2015 2

I. Context and objectives

Anatomy of the aorta

I. Context and objectives

08/12/2015 3

Aortic valve stenosis (AVS)

• Narrowing of the aortic valve opening

• Calcified aortic valve leaflets

Pathologies

stenosis/aneurysm

Abdominal aortic aneurysm (AAA)

• Localized rupture of the parallelism

of the aortic walls

For example:

I. Context and objectives

08/12/2015 4

Endovascular repair

Transcatheter aortic valve

implantation (TAVI)

Endovascular aneurysm repair

(EVAR)

- Catheterization under 2D X-ray guidance.- Vasculatures are visible only instantly with contrast product injection.- Intra-operative positioning and deployment have to be performed at the site planned from the pre-operative CT.

X-ray angiographic and

fluoroscopic guidance

Aortic valve stenosis

(AVS)

TranscatheterHeart Valve

(THV)

Aortic abdominal aneurysm

(AAA)

Catheterization

Device positioning and deployment

I. Context and objectives

08/12/2015 5

Electromagnetic tracking of endovascular devices (motionless structures)

- Navigation by using electromagnetic tracking system (EMTS)

- Track endovascular devices with respect to the vasculature

3D-3D registration between the EMT 3D space and the patient anatomy 3D

space.

Image-based tracking of vasculatures (moving structures)

- Navigation by using fluoroscopic X-rays imaging

- Track the vasculature with respect to endovascular devices

Real-time 2D object tracking in low-contrasted fluoroscopic sequences

Motivation: to limit the use of X-rays and contrast agent in the course of endovascular

interventions.

• Augmented perception: to reconsider/improve the tracking of endovascular devices and /

or vasculatures

II. Electromagnetic tracking of endovascular devices

08/12/2015 6

08/12/2015 7

Electromagnetic tracking (EMT)

Could be used to locate devices through tissues.

The first issue: matching of the 3D EMT coordinate system and the 3D patient coordinate system.

Field generator Magnetic field Vascular structure Catheter tip

position and direction

II. Electromagnetic tracking of endovascular devices

matching

II. Electromagnetic tracking of endovascular devices

08/12/2015 8

Registration between the EMT 3D space and the patient 3D space

Current limitations:

- Low accuracy (distortion, velocity errors, registration errors) : 3-5mm

- Compatibility with the clinical workflow : fiducial-free approach?

Main objective: to propose a robust and precise 3D-3D registration approach that does not

require fiducial landmarks placed into the patient.

General idea: using of the tracked trajectories of the magnetic sensor inside the vasculature.

3D-3D Transformation

Rotation, Translation ?

Intra-operative

3D electromagnetic trajectory

Pre-operative CT

3D description of the patient vasculature

[de Lambert A et al., EJVES 2012]

[Manstad-Hulaas F et al., 2007]

08/12/2015 9

Proposed registration approach

Entire lumen Centerlines Minimum Bending

Energy Path (minBEP)Reduced lumen

Potential location of the EM trajectory within the lumen

The EM outliers compared to the 3D vasculature description are managed by a robust framework.

due to dissimilarity between the 3D EM trajectory and the 3D vasculature description

distortion of the magnetic field, velocity errors [Alfred M. Franz et al., TMI 2014]

II. Electromagnetic tracking of endovascular devices

Intra-operative

3D electromagnetic

Trajectory (ET)

Pre-operative CT

3D description

of the patient vasculature (VL)

Analysis of different distance criteria between the electromagnetic trajectory and the 3D description of the

patient vasculature.

non constrained constrained

outliers

outliers

Pre-operative CT

3D description

of the vasculature

electromagnetic points

08/12/2015 10

Proposed registration approach

Based on a RANSAC strategy, with two hypotheses :

“Inliers” inside the 3D vasculature description.

The optimal transformation must brings most of the points into the arterial lumen.

RANSAC Principle

(RANdom SAmple Consensus [Fischler, Bolles 1981])

II. Electromagnetic tracking of endovascular devices

In set of data points

Out

08/12/2015 11

Experimental results

Phantom study of RANSAC-based 3D-3D registration between EM trajectories and the vasculature

P1

P2 P3

P4

Positions/

3D description

P1 P2 P3 P4 Mean Stdev

Entire lumen 1.825 1.801 1.576 2.627 1.957 0.433

Reduced lumen 1.720 0.887 0.897 2.205 1.427 0.211

Centerlines 1.596 1.313 0.677 2.080 1.416 0.285

minBEP 2.646 1.849 2.212 3.816 2.631 0.854

Registration and navigation interfaces implemented in

C++ with CamiTK [C. Fouard et al., 2012]

- For each 3D vasculature description, the registration

procedure was repeated 9 times.

- Errors are reported from 4 different positions.

- Error measurement by exploiting the CBCT.

Target Registration Errors

Constrained EM trajectory

Positions/

3D description

P1 P2 P3 P4 Mean Stdev

Entire lumen 3.456 3.134 2.205 3.389 3.046 0.578

Reduced lumen 3.147 2.979 2.125 3.019 2.817 0.467

Centerlines 2.984 2.761 1.924 2.777 2.612 0.470

minBEP 2.653 2.796 1.695 2.527 2.417 0.494

Non constrained EM trajectory

II. Electromagnetic tracking of endovascular devices

III. Image-based tracking of vasculatures

08/12/2015 12

III. Image-based tracking of vasculatures

08/12/2015 13

Objective: to provide additional references for endovascular devices positioning and deployment.General idea: tracking of aortic valve calcifications in intra-operative fluoroscopic images in order totrack the aortic valve plane.

Several approaches for object tracking :

• Recursive tracking [Lucas, B.D., Kanade T, 1981]

• Tracking-by-detection [Ozuysal, M., 2007]

• Adaptive methods [Kalal, Z., 2011]

Difficulties: size and density of calcifications, low-contrasted fluoroscopic images.

III. Image-based tracking of vasculatures

08/12/2015 14

Based on an adaptive detection scheme, the tracking process consists in:• Finding new patches that correspond to the initial calcification patch.• Learning of appearance changes of the target calcification.

Proposed method : Tracking of calcifications using online learning

• Variance filter

• Pixel pair comparisons

III. Image-based tracking of vasculatures

08/12/2015 15

Experimental Results

Qualitative results

Tracking errors reported from 10 sequences

Tested on 10 patients• Average detection rate greater than 88%.• Tracking error less than 1.0mm for 93.3% ofthe tracked frames.• Average processing time less than 30ms foreach frame.

Change of image quality Presence of guidewireLow-contrasted fluoroscopic images

III. Image-based tracking of vasculatures

08/12/2015 16

Application to computer-assisted navigation in the context of TAVI

Example of augmented fluoroscopic sequence

!

Trackingofaorticvalvecalcifications

Pre-operative

3DModels+3D/2DStaticRegistration

Intra-operative

2DLandmarks

Dynamicoverlayof2DlandmarksLiveFluoroscopicImages Dynamicoverlayof3Dmodels

III. Conclusions and Perspectives

08/12/2015 17

Conclusions

Solutions to contribute to the endovascular navigation.

Electromagnetic tracking of endovascular devices (motionless structures)

RANSAC-based fiducially-free 3D-3D registration for electro-magnetic navigation.

Without Intra-operative X-ray Imaging, without fiducial landmark. [SURGETICA 2014]

Phantom study: precision of 1.4mm.

Perspectives: in vivo experiment to assist catheter navigation and reach specific targets (renal artery

catheterization).

Image-based tracking of vasculatures (moving structures)

Novel approach to track the aortic valve calcifications in fluoroscopy imaging (mean error less than 1.0mm).

[GRETSI 2015]

Minimal user-interaction is required to initialize the algorithm.

Could be used to track the aortic valve plane that represents the moving target for endoprosthesis deployment,

in order to limit the use of contrast agent. [IEEE EMBC 2013]

Could be applied also for the tracking of other structures of interest. [SURGETICA 2014]

Perspectives: combination with electromagnetic tracking of devices for navigation inside the moving structure.

Thank you!