characterization of arterial biomechanical properties with ultrasound for coronary heart disease...
TRANSCRIPT
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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
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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
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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
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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
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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
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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
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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
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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
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OutlineAim 1: Determine the Elastic Modulus
Aim 2: Generate the Blood Velocity Profile
Aim 3: Determine the Diagnostic Potential
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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ConclusionCharacterization of elastic modulus and
blood velocity profile of carotid arteryDiagnosis of CHD using biomechanical
parametersPotential for revolutionizing CHD
diagnostics◦Save lives and money