signal processing of an ecg signal

226 Pages·2007·5.86 MB·English

by  Aditya Gupta

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Electronic Theses and Dissertations, 2004-2019
2007
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Aditya Gupta
University of Central Florida
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SIGNAL PROCESSING OF AN ECG SIGNAL
IN THE PRESENCE OF A STRONG STATIC MAGNETIC FIELD

by

ADITYA GUPTA
M.S. University of Central Florida, 2006
B. S. M S Ramaiah Institute of Technology, 2002

A dissertation submitted in partial fulfillment of the requirements
for the degree of Doctor of Philosophy
in the Department of Electrical and Computer Engineering
in the College of Engineering and Computer Science
at the University of Central Florida
Orlando, Florida

Fall Term
2007

Major Professor: Arthur Weeks
© 2007 Aditya Gupta

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ABSTRACT

This dissertation addresses the problem of elevation of the T wave of an
electrocardiogram (ECG) signal in the magnetic resonance imaging (MRI). In the MRI,
due to the strong static magnetic field the interaction of the blood flow with this strong
magnetic field induces a voltage in the body. This voltage appears as a superimposition at
the locus of the T wave of the ECG signal. This looses important information required by
the doctors to interpret the ST segment of the ECG and detect diseases such as
myocardial infarction.

This dissertation aims at finding a solution to the problem of elevation of the T wave of
an ECG signal in the MRI. The first step is to simulate the entire situation and obtain the
magnetic field dependent T wave elevation. This is achieved by building a model of the
aorta and simulating the blood flow in it. This model is then subjected to a static
magnetic field and the surface potential on the thorax is measured to observe the T wave
elevation. The various parameters on which the T wave elevation is dependent are then
analyzed.

Different approaches are used to reduce this T wave elevation problem. The direct
approach aims at computing the magnitude of T wave elevation using magneto-hydro-
dynamic equations. The indirect approach uses digital signal processing tools like the
least mean square adaptive filter to remove the T wave elevation and obtain artifact free
ECG signal in the MRI.
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Excellent results are obtained from the simulation model. The model perfectly simulates
the ECG signal in the MRI at all the 12 leads of the ECG. These results are compared
with ECG signals measured in the MRI. A simulation package is developed in MATLAB
based on the simulation model. This package is a graphical user interface allowing the
user to change the strength of magnetic field, the radius of the aorta and the orientation of
the aorta with respect to the heart and observe the ECG signals with the elevation at the
12 leads of the ECG.

Also the artifacts introduced due to the magnetic field can be removed by the least mean
square adaptive filter. The filter adapts the ECG signal in the MRI to the ECG signal of
the patient outside the MRI. Before the adaptation, the heart rate of the ECG outside the
MRI is matched to the ECG in the MRI by interpolation or decimation. The adaptive
filter works excellently to remove the T wave artifacts. When the cardiac output of the
patient changes, the simulation model is used along with the adaptive filter to obtain the
artifact free ECG signal.
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I dedicate this book to Lord Sri Krishna through my beloved grand-spiritual master
His Divine Grace A.C. Bhaktivedanta Swami Prabhupada, the Founder-Acarya of the
International Society for Krishna Consciousness.

Srila Prabhupada is always absorbed in the perfect samadhi of Krishna consciousness.
His mind and heart, his thoughts, words, and deeds
Forever concentrated on one point — Serving the lotus feet of Radha-Govinda.
He taught the world to enter Samadhi and taste the eternal bliss of the soul
Surrendered to God in service by constantly chanting Hare Krishna.

Srila Prabhupada gave the most authoritative and exact translation of the divine book
– “Bhagavad Gita As It Is.” It is not a mere product of his scholarship but a deeply
realized penetration into the very essence of life, the problems that haunt all men, and
solutions with which to exorcise them. Its powerful message of hope and
enlightenment lifts the reader above the petty and temporal. The wisdom of the Gita
leads to dimensions beyond ordinary education and enables one to analyze and
understand life in a revolutionary way.

One of the seven hundred transcendental verses of the Bhagavad Gita:

v
yat karoñi yad açnäsi
yaj juhoñi dadäsi yat
yat tapasyasi kaunteya
tat kuruñva mad-arpaëam
TRANSLATION
Whatever you do, whatever you eat, whatever you offer or give away, and whatever
austerities you perform—do that, O son of Kunté, as an offering to Me.
PURPORT
Thus, it is the duty of everyone to mold his life in such a way that he will not forget
Kåñëa in any circumstance. Everyone has to work for maintenance of his body and
soul together, and Kåñëa recommends herein that one should work for Him. Everyone
has to eat something to live; therefore he should accept the remnants of foodstuffs
offered to Kåñëa. Any civilized man has to perform some religious ritualistic
ceremonies; therefore Kåñëa recommends, "Do it for Me," and this is called arcana.
Everyone has a tendency to give something in charity; Kåñëa says, "Give it to Me," and
this means that all surplus money accumulated should be utilized in furthering the
Kåñëa consciousness movement. Nowadays people are very much inclined to the
meditational process, which is not practical in this age, but if anyone practices
meditating on Kåñëa twenty-four hours a day by chanting the Hare Kåñëa mantra
round his beads, he is surely the greatest meditator and the greatest yogé.
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ACKNOWLEDGMENTS

I thank my advisor, Arthur R Weeks, for his guidance and support throughout my
research. He gave me the opportunity to work on very interesting research projects and
challenged me to expand my problem solving abilities.

I thank my committee members Samuel M Richie, Harold I Klee, Christian S Bauer and
David Nicholson for their time and valuable comments.

I thank Oosterom, A. van from the Department of Cardiology, University of Lausanne,
Netherlands for his help and valuable suggestions for improving my research work.

I thank Invivo Corp., now Royal Philips Electronics for their financial support throughout
my work.

I heartily thank my parents, Ravindra K Gupta and Radhika Gupta, who deserve a vast
amount of credit for supporting me throughout my education and life and most of all for
believing in my intellectual capacity.

I thank all my friends and relatives, who have encouraged and supported my endeavor
and my work.

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Most of all I thank Lord Sri Krishna, the Supreme Personality of Godhead who gives the
intelligence and guides every activity of the living entity as the most beloved friend. I
thank my instructing spiritual master His Holiness Trivikrama Swami Maharaj who
mercifully encouraged me and kept my spiritual life alive during my stay in Orlando. I
thank my eternal spiritual master His Holiness Bhakti Charu Swami Maharaj and my
grand spiritual master His Divine Grace Abhay Charan Bhaktivedanta Swami Srila
Prabhupada, who opens the eyes of the ignorant with a torch of knowledge and gives the
intelligence of the higher dimension.
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TABLE OF CONTENTS

LIST OF FIGURES.........................................................................................................xiii
LIST OF TABLES...........................................................................................................xvi
LIST OF SYMBOLS......................................................................................................xvii
LIST OF ABBREVIATIONS..........................................................................................xix
CHAPTER 1 INTRODUCTION.....................................................................................1
1.1 Problem Statement..............................................................................................1
1.2 The Electrocardiogram (ECG) signal.................................................................4
1.2.1 Basic structure of the heart and its physiology...........................................4
1.2.2 Cardiac Electrophysiology..........................................................................6
1.2.3 Segments of the ECG wave........................................................................9
1.2.4 Orientation of the 12 Lead ECG...............................................................10
1.3 Magnetic Resonance Imaging (MRI)................................................................12
1.3.1 Basics of MRI...........................................................................................12
1.3.2 The MRI system........................................................................................13
1.3.3 Gradient Echo and Spin Echo...................................................................15
1.3.4 Frequency Encoding - Imaging.................................................................15
1.3.5 Advantages over other imaging systems...................................................16
1.4 Flow of Electric Charges in Magnetic Field.....................................................16
1.4.1 Lorentz Force and Hall Effect...................................................................16
1.5 ECG Signal Distortions.....................................................................................18
1.6 Approach to remove the T wave elevation.......................................................19
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