DEVELOPMENT OF AN EMBEDDED SYSTEM FOR
ASSESSING EXTREMITY BLOOD VOLUMES BASED ON
ELECTROCARDIOGRAPHY
Faculty Mentor: Zion Tsz Ho Tse
Graduate Mentor: T. Stan Gregory
Driftmier Annex, Room 120
Spring 2015 Senior Design
College of Engineering
The University of Georgia
ELECTROCARDIOGRAM (ECG)
•
Main ECG Components
• PQRST
•
QRS Complex
• Ventricular Contraction
• Synchronize Heart with external
devices (Registration)
•
S-T Segment
• Useful in Ischemia Detection
• Correlates to Peak Systolic Arterial
Blood Pressure
ECG Signal Features Are Shown to Correlate Directly With Arterial Blood Pressure
12-LEAD ECG
•
Diagnostic Information
• Spatial & Temporal
• Detect Disease
• During Imaging
• CT, MRI, etc…
Precordial electrodes V1-V6, illustrating spatial information
obtained through 12-lead ECG recording
MAGNETIC RESONANCE IMAGING (MRI)
•
High Quality Images
•
Magnetic Field (B 0)
• Strong (1.5T, 3T, 7T,15T)
• Uniform
•
Magnetic Gradients
• RF excites Protons
• RF energy released
Subject Undergoing
Exercise Stress Testing
to Study Stress-Induced
Variations in Aortic
Blood Flow
INTRA-MRI ECG
•
Cardiac MRI Synchronization
•
Aids in CINE Studies
• Flow, CV Dynamics
•
High-Risk Patient Monitoring
•
Major Hurdles
• Gradient Noise
• Magnetohydrodynamics
• MRI-compatibility
Cardiac MRI Scan
Sagittal Aortic View
“Candy Cane”
MAGNETOHYDRODYNAMIC (MHD) EFFECT
• MHD Voltages (VMHD)
• Induced in ECG due to
interaction between B0 &
ionic blood flow
• Dominant during early systole
• Blood rapidly ejected from
left ventricle to aorta
• MHD eclipses ECG in high field
MRI, causing
• Distorted S-T Segment
• VMHD >> QRS complex
• Improper gating
• Image motion artifacts
ECG OVERLAY
Healthy Subject Outside MRI
Healthy Subject at 3 Tesla (T)
Sensitivity in QRS Complex Detection is Reduced in Intra-MRI 12-lead ECG Recordings
MHD DIRECTIONALITY
B0
Induced VMHD is Dependent on Direction of Magnetic Field and Blood Flow
RELATIONSHIP TO BLOOD FLOW
Hypothesis: Extracted MHD voltages directly
correlate with aortic blood flow, and can be used
to derive aortic blood flow in real time flow.
Aortic PC MRI, magnitude (top) & velocityencoded (bottom) images
High resolution, averaged over 30 cycles
Real-Time Phase Contrast MRI (RTPC) rather
than conventional PC MRI must be used to
achieve beat-to-beat validation.s
BLOOD FLOW CURVE FITTING
•
Subject-Specific Fits
•
Derived Based on Relationship to Blood
Flow
Subject-Specific Equations of Fit Can Be Derived to Fit Extracted VMHD to Aortic Blood Flow
ESTIMATE MHD VOLTAGE DISTRIBUTIONS
Objective: Study
contributions of regional
vasculature and blood flow
to the net MHD signal
recorded in intra-MRI
ECGs.
Incremental Introduction
into the MRI bore
Raw ECGs (V4) obtained inside the MRI (3T) at each displacement level
(d). Increases in VMHD contribution to signal are observed as the
displacement from the bore isocenter is decreased.
LINEAR DECOMPOSITION OF LOCAL MHD CONTRIBUTION
Local Segmental Perfusion (SP) calculated for a total displacement of N cm, and for M body regions
𝑊1,𝑥=0
𝑊1,𝑥=10
𝑊1,𝑥=20
⋮
𝑊1,𝑥=𝑁
𝑊2,𝑥=0
𝑊2,𝑥=10
𝑊2,𝑥=20
⋮
𝑊2,𝑥=𝑁
𝑊3,𝑥=0
𝑊3,𝑥=10
𝑊3,𝑥=20
⋮
𝑊3,𝑥=𝑁
…
…
…
⋱
…
𝑊𝑀,𝑥=0 𝑆𝑃1
𝐺𝑃𝑥=0
𝑊𝑀,𝑥=10 𝑆𝑃2
𝐺𝑃𝑥=10
𝑊𝑀,𝑥=20 𝑆𝑃3 = 𝐺𝑃𝑥=20
⋮
⋮
⋮
𝐺𝑃𝑥=𝑁
𝑊𝑀,𝑥=𝑁 𝑆𝑃𝑀
𝐵𝑥
𝑊𝑥 =
,
𝐵0
B0 = 3T
Local field strength Bx as a function of distance Relationship of Global Perfusion (GP) to SP, where GP
from the isocenter
is attributed to weighted SP sums.
SP describing local vasculature perfusion can be estimated from the equation
MHD-DERIVED PERFUSION DISTRIBUTION
MRI images of aorto-femoral vasculature
taken
(coronal (left) & sagittal (right) views)
MHD-derived Perfusion overlaid with MRI angiogram. Aortic
arch locations indicated by vertical line occur at max VMHD
in subjects 1-5.
(Measured 2.80)
Extracted VMHD & MRA based perfusion traces
overlaid
Correlation of 0.96 and 0.97 in perfusion levels for
abdominal and thoracic cavities was found between
the MRA and MHD-derived perfusion traces
SENIOR DESIGN PROJECT
Objective: Convert this
technology into a portable
hand-held device that can be
used bed-side by clinicians.
1st Steps!!! Get that ECG!!!!!
INA 128 – INSTRUMENTATION AMPLIFIER IC
EASY ECG ACQUISITION
1. Breadboard the INA 128 circuit
2. Use leads + electrodes & vary the chip gain (external resistor) until you have a nice ECG
1. Record and document the circuit diagram into your notebooks
2. Record gain + resistor values + electrode positions used (tabulate)
3. Take an ECG using leads on (1) right/left hands, and (2) one arm
4. Use the o-scope, and take photos of nice ECGs obtained
3. Experiment with replacing electrodes with small squares of metal (< a few sq in)
4. How is the ECG signal? Does it require additional filtering? Diagnose it!
5. Acquire ECG signal using an Arduino (use the serial port monitor)
1. Remember the Arduino analog inputs only accept 0V to 5V
2. Plot a nice ECG using this data
NEXT WEEK
•
Biomedical instrumentation design
•
Typical ECG recorder flow chart (circuit block diagram)
• How would I modify it to record other physiological signals (EOG, EEG, etc…)?
•
FDA Approval + 510k Premarket Notifications
•
How to access your grades online?
• Everyone email me a secret # to use as login into grades system.
QUESTION TIME
•
Who likes CAD the best????
• Names: --
•
Who likes to program a lot????
• Names: --