CLINICAL EVALUATION OF AN ULTRASOUND BASED IMAGING SYSTEM F - PowerPoint Presentation

Slide1

CLINICAL EVALUATION OF AN ULTRASOUND BASED IMAGING SYSTEM FOR GUIDING CARDIAC ABLATION

Patrick D. Wolf, Stephanie A.

Eyerly

, Douglas M. Dumont, Gregg E.

Trahey

, and

Tristram D. Bahnson

Duke University

Department of Biomedical

Engineering

Duke University Medical CenterSlide2

Introduction

Normal Sinus Rhythm (NSR)

Atrial Fibrillation (AF)

Thousands of cardiac ablation procedures performed daily to treat

tachy

-arrhythmias

Increase in the number of procedures that are anatomically guided rather than electrically guided

Atrial

Fibrillation

3 M now

7 M by 2050 Slide3

Introduction

Single lesions directly ablate

arrhythmogenic

tissue

AVNRT, WPW, MAT

Lines

of

lesion isolate regions (pulmonary veins) - AF

Treating Arrhythmias: Transcatheter Cardiac Ablation

(

TCA)

http://www.heart.org/HEARTORG/Conditions/Arrhythmia/PreventionandTreatmentofArrhythmia/Ablation_UCM_301991_Article.jspSlide4

Introduction

Radiofrequency Ablation (RFA) in TCA

procedures

Lines of RFA lesions must be transmural and continuous to block conduction

Electrical reconnection occurs at unablated gaps

Blood flow around catheter tip and tip-tissue contact affect lesion formation

L

esion size not predictable from delivery parameters

Real-time image based evaluation would confirm transmurality and line contiguity

Non-transmural lesion

Transmural

lesion

Unablated

Gap

RFA

Catheter

Transmural

lesion

Endocardium

Epicardium

Blood flowSlide5

Introduction

Radiofrequency Ablation (RFA)

Young’s Modulus of RFA treated tissue

Pernot et al. Mapping Myocardial Elasticity Changes After RF-Ablation Using Supersonic Shear Imaging. Computers in Cardiology. 2009; 36:793-796

In vitro

In vitro

In vivo diastole

Un-treated

~ 27

kPa

~ 10

kPa

RF-treated

~

54

kPa

~ 20-30

kPa

RF current heats the tissue

creating a discrete and stiff lesion volume Slide6

Introduction

Acoustic Radiation Force Impulse (ARFI) Imaging

An ultrasound pulse applies radiation force F [kg/cm

2

·s

2

] over a small region at the focus

[1]

absorbed power = W

absorbed

,

[W/

cm

3

]

absorption coefficient =

α

~ 0.00072 [Np/cm]

[2]

speed of

sound = c ~ 1540 or 1615±15 [m/s]

[3]Temporal average intensity = I [W/cm2

] Radiation force creates μm scale tissue displacements

mechanical properties Ultrasound scan lines spatially and temporally monitor tissue response

RF Lines

Displacement [

μ

m]

t

4

Time

ARFI!

t

0

t

1

t

2

t

3

Axial Response

Time (t)

[1] Trahey

, G.E., et al.,

Acoustic radiation force impulse imaging of the mechanical properties of arteries: in vivo and ex vivo results.

Ultrasound in Medicine & Biology, 2004.

[2]

Sagar

, K.B., et al.,

Quantitative ultrasonic assessment of normal and

ischaemic

myocardium with an acoustic microscope: relationship to integrated backscatter.

Cardiovascular research, 1990.

[3]

Masugata

, H., et al.,

Relationship between myocardial tissue density measured by

microgravimetry

and sound speed measured by acoustic

microscopy

.

Ultrasound in Medicine and Biology,

1999.Slide7

In vitro proof of concept

ARFI for RFA Lesion Assessment

(

in vitro

proof of concept)

AccuNav

ICE catheter and Siemens

Anteres

scanner

RFA lesion

differentiable

from the surrounding myocardium

in vitro

by

measured ARFI-induced

displacements

2D ARFI able to provide lesion assessment

Lateral [cm]

Pathology

B-Mode

ARFI

4

2

0

μ

m

Axial [cm]

Eyerly et. al. In vitro assessment of ARFI imaging for cardiac visualizing RFA lesions

.

J Cardiovasc Electrophysiol.

Vol 21, 5: 557-563

.Slide8

In vivo obstacles

Three (3) major obstacles to performing this imaging

in vivo:

Heart stiffens and softens during each beat

Small ARFI induced displacements must be measured in the presence of substantial gross motion

A blind search of the myocardium to find lesions is extremely difficult

Eyerly et. al. In vitro assessment of ARFI imaging for cardiac visualizing RFA lesions

.

J Cardiovasc Electrophysiol.

Vol 21, 5: 557-563

.Slide9

Problem 1 Stiffness Contrast

ARFI images must acquired in diastole when there is minimal cardiac motion and there is maximum elasticity contrast between the RFA lesion and the surrounding myocardium.

Eyerly SA, Hsu SJ, Trahey GE, Wolf PD. In vivo differentiation of myocardial ablation lesions via a stiffness ratio with acoustic radiation force impulse imaging.

Eighth International Conference on the Ultrasonic Measurements and Imaging of Tissue Elasticity

. Vlissingen, Netherlands: September 2009.

Right ventricular wall before and after ablation. Movie made with multi-beat synthesis using a

transthoracic

probe positioned on the RV

epicardium

. Slide10

Problem 1 & 2: Contrast and Motion

Trigger the scanner to start the ARFI sequence during the passive filling phase of diastole.

Maximum stiffness contrast with softened myocardium

Minimum motion related to contractionSlide11

Problem 2: Motion

Take multiple scan lines before and after the ARFI ‘push’

Track bulk motion

Fit to a quadratic function and interpolate

Subtract bulk motion

Find ‘Peak Displacement’

Confirm motion filter with ‘zero push’ sequences

Hsu, S.,

Acoustic Radiation Force Impulse Imaging of Myocardial Performance

, in

Biomedical Engnieering

2009, Duke University.Slide12

Problem 3: Find the Lesions

Imaging and Guidance Tools Used in TCA Procedures

Fluoroscopy

Visualize catheter

position/orientation

in the

body

Can not visualize soft tissue

Intracardiac Echo (B-Mode)

Identifies

anatomical

structures

Assess

catheter-tissue contact

Can not differentiate lesion from normal tissue

http://emedicine.medscape.com/article/151907-overview

http://www.touchcardiology.com/img/Image/acunav.gifSlide13

Find the Lesions

Electroanatomical

Mapping (EAM):

CARTO (

Biosense

/Webster)

Magnetic fields determine the 3D location of

catheters

NaviStar™

mapping/ablation catheter: contains a location coil that measures magnetic field strength

All points plotted relative to a reference patch on the patient’s back

Real-time guidance

for TCA

procedures

http://www.ipej.org/0801/bhakta.htm

http://www.pages.drexel.edu/~gn52/MEDICAL_ROBOTICS/Downloads_files/Carto%20XP%20EP%20Navigation%20System.pdfSlide14

Find the Lesions

Electroanatomical

Mapping (EAM):

CARTO (

Biosense

Webster)

Construct 3D cartoon of chamber geometry

M

apping catheter collects endocardial EG

s

, local activation times (LAT)

Visualization of electrical propagation, identifies arrhythmogenic regions

Real-time guidance

for TCA

proceduresSlide15

Find the Lesions

Tracking and 2D ICE based imaging

Magnetic tracking of imaging tip

Registered display of B-mode images on cartoon

Shows “where you are looking”

64 element

phased array

http://www.biosensewebster.com/products/navigation/cartosound.aspx

Hsu, S.J., et al.,

Challenges and implementation of radiation-force imaging with an intracardiac ultrasound transducer.

Ieee

Transactions on

Ultrasonics

Ferroelectrics and Frequency Control, 2007.

54

(5): p. 996-1009.Slide16

In vivo testing

Paced from coronary sinus catheter

Mapped electrical activation using CARTO

ARFI imaged normal tissue

Created a lesion line with ≈1 cm gap

ARFI imaged line and gap

Closed the gap

ARFI imaged line

Poster by

Eyerly

Right atrium mapped using

CARTO EAM system

No Lesion

Lesion with Gap

Gap ClosedSlide17

Normal and Gap Images

RFA

Lesion

Gap

RFA

Lesion

GapSlide18

Linear RFA

ARFI image lesion assessments correlate with electrical block in CARTO LAT maps

In vivo

Results

CARTO LAT Maps

TA

81ms

24ms

TA

RFA Lesion

Gap at TA

Continuous

RFA Lesion

RFA Lesion

8

6.4

4.8

1.6

3.2

0

μmSlide19

Moving to the Clinic -

ARFIi

Clinical Tool

Research Tool

Acquire ECG synchronous ARFI data on S2000 scanner

Download data to laptop

Calculate and display ARFI displacements on laptop screen

Clinical Tool

Acquire ECG synchronous ARFI data on S2000 scanner

Process and display ARFI data on S2000 screen

Done by Duke in collaboration with Siemens Medical

Slide20

Moving to the Clinic – FDA Considerations

Mechanical Index (MI)

FDA limit 1.9

Measured peak for our sequences <1.6

Face Heating

FDA limit < 6 °C in standing water

Siemens internal limit <2 °C

Measured change for our sequences <2 °C

Slide21

Moving to the Clinic

Clinically, we seek to understand

The elasticity contrast for lesions in senescent and diseased hearts

The ability to access all lesions in both the right and left atria with a limited field of view

The effect of

atrial

fibrillation on

ARFIi

contrast

The correlation of

ARFIi

evaluation with electrical outcome in

atrial

flutter and

atrial

fibrillation ablation procedures Slide22

Clinical Study Outline

Patients undergoing

AFl

ablation or AF ablation

Following each round of ablation in the normal therapeutic procedure image normal and

lesioned

tissue with ARFI

blinded results to the physician

Characterize “normal” and ablated tissue

In sinus rhythm

In AFSlide23

ARFI imaging of ablation lesions can be implemented clinically with significant but minor modifications to existing equipment commonly used in the EP lab (CARTO, ICE).

Lesion boundary correlates with ARFI imaged stiffness boundary

Electrical block correlates with

ARFIi

determined contiguous and

transmural

lesions

The tools for clinical evaluation have been created

SummarySlide24

Thank you to Dr.

Kapur

et al for organizing workshop

NIH Grant:

R21-EB-

007741

NIH Grant: R01-EB-012384

Biosense

Webster and Siemens Medical Solutions USA, Inc. for their hardware and system support

Acknowledgements