Characterization of Arterial Biomechanical Properties with Ultrasound for Coronary Heart Disease (CHD) Diagnostics Group 8 Laura Tanenbaum, Sam Tavakoli,

Characterization of Arterial Biomechanical Properties with Ultrasound for Coronary Heart Disease (CHD) Diagnostics

Group 8Laura Tanenbaum, Sam Tavakoli, Shea Thompson, Barbara Thorne-Thomsen, Michelle Thorson

Significance of CHDPrimary cause of death in America◦785,000 first-time heart attacks each year◦470,000 recurrent heart attacks each year

33% of heart attacks result in sudden deathThe direct and indirect cost of this disease in

this past year alone was $165.4 billion

Developing a diagnostic tool to detect CHD before heart attack manifests would save

lives and money

Project OverviewGoal:

To characterize biomechanical properties of human arteries after a stress test using ultrasound to diagnose CHD

Aim 1:Determine

Elastic Modulus

Aim 2: Generate

Blood Velocity Profile

Aim 3: Determine Diagnostic Potential

Atherosclerosis Causes CHD Plaque build-up leads to stenosis

◦ Narrowing of the arteries Acute coronary syndrome : sudden occlusion blocks

blood flow in the coronary artery◦ Unstable, vulnerable plaques◦ Varying degrees of stenosis

Stable Plaque Unstable Plaque

High degree of stenosis Low degree of stenosisImage: www.heartonline.org/images/heartattack.jpg

Selected Parameters

Elastic modulus reveals arterial wall stiffness

Blood velocity profile changes with presence of plaques

Carotid arteryDetermined after

exercise stress test

Image: http://graphics8.nytimes.com

Current Methods are Limited

Method EKG Catheter Coronary Angiography

CT MRI

DescriptionMonitors electrical activity

X-ray images track blood flow

X-ray scans create 3D

model

Generates image from rotation

frequencies of H+ atoms

Average cost of test $140 $3,000 $800 $2,000

Weakness

Limited to electrical activity

High false positive rate

Invasive

Can’t detect all vulnerable plaques

Invasive

Long image acquisition

time

Expensive

Long image acquisition time

Doppler Mode Ultrasound

Transducer

Skin

Image: http://commons.wikimedia.org/wiki/File:DopplerSonographyBloodFlowDiagram-de.svg

Provides images of blood flow through arteries◦Noninvasive◦ Real-time◦ Average cost of

echocardiogram = $300

Can be used to generate elastic modulus and blood

velocity profile

Experimental DesignAll subjects age 40-60Blind study design

Cardiac coronary angiography used for preliminary diagnoses

Exercise stress test procedure on treadmill◦10% incline at steadily increasing rates◦10 minutes or until target heart rate reached

CHD Control

Male 25 25

Female 25 25

OutlineAim 1: Determine the Elastic Modulus

Aim 2: Generate the Blood Velocity Profile

Aim 3: Determine the Diagnostic Potential

Project OutlinePreliminary diagnosis with cardiac coronary angiography

Elastic Modulus

Velocity Profile

Exercise stress test

ULTRASOUND

CHD DiagnosisCalculate sensitivity, specificity, accuracy

EKG

Check ultrasound

results

CHD DiagnosisLiterature values for

sensitivity, specificity, accuracy

Determine superior diagnostic technique

Aim 1: Determine Elastic ModulusDecreased elasticity has been identified

as a risk factor for cardiovascular diseaseIndicator of CHD and presence of plaquesExperimental set-up◦Non-invasive technique◦Doppler ultrasound used to determine mean

arterial radius and generate point force◦Laser vibrometer measures wall displacement

Aim 1: Vessel ModelViscoelastic Model◦Homogeneous, isotropic, 3D, linear, thick-shelled,

cylindrical tube with constant thickness and radiusLove's theory used to compute the ring

resonant frequency matrix equation

Elastic modulus calculated from resonant frequencies

Only requires vessel diameter

Aim 1: Data AnalysisFrequency response

curve generated from laser vibrometer

Maxima represent resonant frequencies

Normalized curve used to determine quality factor for complex modulus Zhang 2006

Aim 2: Generate Blood Velocity ProfileBlood velocity profile reflects presence

and quantity of atherosclerotic plaquePlaque buildup is primary cause of CHDExperimental setup:

Fast Fourier Transform Processor

Digital Signal

Processor

Dirgenali 2006

Aim 2: Doppler Ultrasound128 range gates along ultrasound beamApproaches real-time capabilitiesDigital signal processor collects backscattered

signalsRaw data: frequency as a function of depthFast Fourier Transform converts spectral data to 3-

D plot

Tortoli 1996

Aim 2: Data AnalysisFrequency of backscattered signal varies as a

function of depth along the arteryMaximum frequency per given depth correlates

to maximum velocity of arterial blood flow

where W, F, and θ are properties of transducer and Doppler ultrasound beam, λ is beam wavelength

Generate velocity vs. depth profile

Aim 2: SignificanceFrequency varies significantly in healthy (left) vs.

atherosclerotic (right) patients

Noticeable differences with 5% stenosisStress test magnifies effectsPossible to determine plaque position in arteryPotential for CHD diagnosis

Dirgenali 2006

Aim 3: Diagnostic PotentialCalculate parameter values using

ultrasoundCompare to literature values◦Generate diagnosis

Compare to "true" diagnosis ◦Calculate sensitivity and specificity

Compare to EKG sensitivity and specificity◦Determine if ultrasound is a better diagnostic

tool for CHD

Timeline0-6 months•Recruit subjects•Obtain equipment

6-9 months•Conduct testing• Stress test• Ultrasound• EKG

9-18 months•Determine parameter values•Compare to literature values•Generate diagnoses

18-24 months•Calculate ultrasound sensitivity, specificity, accuracy•Compare to EKG•Determine superior technology

Advantages of Proposed TechniqueBiomechanical Relevance ◦ Blood velocity profile◦ Elastic modulus◦ Both indicators of CHD

Strengths◦ Non-invasive◦ Real-time◦ Biomechanical information◦ Inexpensive

Novelty◦ Combined system to diagnose CHD ◦ Using ultrasound after stress test

ConclusionCharacterization of elastic modulus and

blood velocity profile of carotid arteryDiagnosis of CHD using biomechanical

parametersPotential for revolutionizing CHD

diagnostics◦Save lives and money