Biomedical Imaging and Instrumentation (Lecture) - University of Santo Tomas - ECE 21132

ECE 21132 (IC-ELE3-BII): Biomedical Imaging and Instrumentation (Lecture) MODULE 2: Biomedical Transducers and Sensors Lecture 3: Electrophysiological Sensors...

ECE 21132 (IC-ELE3-BII): Biomedical Imaging and Instrumentation (Lecture) MODULE 2: Biomedical Transducers and Sensors Lecture 3: Electrophysiological Sensors and Recording Technologies Dr. Seigfred V. Prado, SMIEEE Electronics Engineering Department 1 Electronics Engineering Department 2 Electronics Engineering Department 3 Electrophysiology ▪ Electrophysiology studies the electrical properties of biological cells and tissues. ▪ It involves the measurement of voltage changes or electric current on a wide variety of scales, from single ion channels to whole organs like the heart or brain. ▪ Electrophysiological techniques are essential in biomedical research, diagnostics, and therapeutic devices. Electronics Engineering Department 4 Electrophysiological Signals ▪ Electrophysiological signals arise from the electrical activity of cells, especially neurons, muscle cells, and cardiac cells. Electronics Engineering Department 5 Electrophysiological Signals ▪ Examples of Electrophysiological Signals 1. Electroencephalogram (EEG): ▪ Measures brain wave activity 2. Electrocardiogram (ECG): ▪ Records electrical activity of the heart 3. Electromyogram (EMG): ▪ Detects electrical signals from muscle activity 4. Electroretinogram (ERG): ▪ Measures electrical responses of the retina 5. Electrogastrogram (EGG): ▪ Captures stomach muscle activity Electronics Engineering Department 6 Electronics Engineering Department 7 Principles of Electrophysiology ▪ Cellular Membrane Potential ▪ The membrane potential is the voltage difference across a cell's plasma membrane, primarily driven by ion gradients and membrane permeability. ▪ Resting membrane potential typically ranges from -60 mV to -90 mV in neurons and muscle cells. ▪ Action Potentials ▪ A rapid rise and fall in voltage across the membrane due to ion channel activity. ▪ Key phases: ▪ Depolarization (Na+ influx) ▪ Repolarization (K+ efflux) ▪ Hyperpolarization ▪ Propagation of action potentials is crucial for communication in excitable tissues like nerves and muscles. Electronics Engineering Department 8 Principles of Electrophysiology ▪ Synaptic Transmission ▪ Synaptic transmission is the process by which a neuron communicates with another cell, typically at a synapse. ▪ It begins when an action potential (an electrical signal) reaches the axon terminal of the presynaptic neuron. ▪ This triggers the release of neurotransmitters into the synaptic cleft. ▪ These neurotransmitters bind to receptors on the postsynaptic cell, causing ion channels to open and leading to changes in the membrane potential. ▪ If the depolarization is strong enough, it can trigger an action potential in the postsynaptic cell, continuing the transmission of the signal. ▪ In this way, synaptic transmission is directly related to the initiation and propagation of action potentials in neural communication. Electronics Engineering Department 9 Principles of Electrophysiology ▪ Synaptic Tranmission Electronics Engineering Department 10 Electrophysiological Sensors ▪ Electrophysiological recording technologies involve sensors (electrodes) that capture the electrical activity of tissues. 1. Surface Electrodes ▪ Non-invasive electrodes placed on the skin to record bioelectric signals ▪ Examples: ▪ EEG Electrodes: Typically small metal discs placed on the scalp to measure brain activity. ▪ ECG Electrodes: Often adhesive patches placed on the chest to capture heart rhythms. ▪ EMG Electrodes: Placed on muscles to detect muscle electrical activity. Electronics Engineering Department 11 Electrophysiological Sensors ▪ Electrophysiological recording technologies involve sensors (electrodes) that capture the electrical activity of tissues. 1. Surface Electrodes ▪ Electrode Configuration ▪ Monopolar Recording: Measures voltage between an active electrode and a reference electrode. ▪ Bipolar Recording: Measures the difference in voltage between two active electrodes. ▪ Material and Design ▪ Common materials: Ag/AgCl, gold, platinum. ▪ Electrode gel or conductive paste is often used to enhance skin contact and reduce impedance. Electronics Engineering Department 12 Electrophysiological Sensors 2. Intracellular Recording ▪ Microelectrodes: Fine-tipped electrodes inserted into individual cells to measure intracellular potentials. ▪ Patch-Clamp Technique: A powerful method to study ion channels in single cells by isolating tiny patches of membrane. ▪ Applications: Widely used in neuroscience to study the electrophysiology of neurons and ion channels. Electronics Engineering Department 13 Electrophysiological Sensors Electronics Engineering Department 14 Electrophysiological Sensors 3. Needle Electrodes ▪ Invasive electrodes inserted into tissues to record electrical activity from specific muscle groups or deep neural structures ▪ Common Uses: ▪ Intramuscular EMG: Captures detailed muscle activity and is used for diagnosing neuromuscular disorders. ▪ Deep Brain Recording: Used in research and clinical settings (e.g., Parkinson’s disease studies). ▪ Design: ▪ Typically insulated except for the tip, ensuring that the recording is localized. Electronics Engineering Department 15 Electrophysiological Sensors 3. Needle Electrodes Electronics Engineering Department 16 Electrophysiological Sensors 4. Microelectrode Arrays ▪ Arrays of small electrodes used for high-density recording of neural activity Electronics Engineering Department 17 Electroencephalography (EEG) Electronics Engineering Department 18 Electroencephalography (EEG) ▪ Method to record an electrogram of the spontaneous electrical activity of the brain ▪ The biosignals detected by EEG have been shown to represent the postsynaptic potentials of pyramidal neurons in the neocortex and allocortex. ▪ It is typically non-invasive, with the EEG electrodes placed along the scalp using the International 10-20 System, or variations of it. Electronics Engineering Department 19 Electroencephalography (EEG) ▪ As the electrical activity monitored by EEG originates in neurons in the underlying brain tissue, the recordings made by the electrodes on the surface of the scalp vary in accordance with their orientation and distance to the source of the activity. ▪ Furthermore, the value recorded is distorted by intermediary tissues and bone which act in a manner akin to resistors and capacitors in an electrical circuit. ▪ This means not all neurons will contribute equally to an EEG signal with an EEG predominately reflecting the activity of cortical neurons near the electrodes on the scalp. ▪ Deep structures within the brain further away from the electrodes will not contribute directly to an EEG – these include the base of the cortical gyrus, mesial walls of the major lobes, hippocampus, thalamus and brain stem. Electronics Engineering Department 20 Electroencephalography (EEG) ▪ Electrocorticography (ECoG) ▪ Sometimes called intracranial EEG ▪ Involves surgical placement of electrodes Electronics Engineering Department 21 Brief History of EEG ▪ 1875: Richard Caton ▪ He presented his findings about the electrical phenomena of the exposed cerebral hemispheres of rabbits and monkeys in the British Medical Journal. ▪ 1890: Adolf Beck ▪ He published an investigation of spontaneous electrical activity of the brain of rabbits and dogs that included rhythmic oscillations altered by light. ▪ He placed electrodes directly on the surface of the brain to test for sensory stimulation. ▪ His observation of fluctuating brain activity led to the conclusion of brain waves. ▪ 1924: Hans Berger ▪ He recorded the first human EEG. ▪ Expanding on work previously conducted on animals by Richard Caton and others, Berger also invented the electroencephalogram (giving the device its name), an invention described "as one of the most surprising, remarkable, and momentous developments in the history of clinical neurology". Electronics Engineering Department 22 Brief History of EEG Electronics Engineering Department 23 Non-Invasive Measurements of EEG ▪ Prepare scalp area (light abrasion to reduce impedance due to dead skin cells) ▪ Place electrodes on scalp with a conductive gel or paste ▪ Place ground electrode and choose reference electrode(s) ▪ Connect each electrode to one input of the differential amplifier ▪ Connect reference electrode(s) to the other input of the differential amplifier Electronics Engineering Department 24 Non-Invasive Measurements of EEG Electronics Engineering Department 25 Non-Invasive Measurements of EEG Electronics Engineering Department 26 Non-Invasive Measurements of EEG Electronics Engineering Department 27 Non-Invasive Measurements of EEG ▪ Amplification: x 103-105 ▪ Note: EEG has a very small amplitude (~10-50 uV; since action potentials are ~60- 100 mV) ▪ Low-pass Filter: 0.5-1 Hz ▪ High-pass Filter: 35-70 Hz ▪ Sampling Rate: ~200 Hz (typically 256 Hz) Electronics Engineering Department 28 Non-Invasive Measurements of EEG ▪ Technical Artifacts ▪ Power line ▪ Broken cable, dirty connectors ▪ Different electrode materials ▪ Poor grounding ▪ Biological Artifacts ▪ Eye-induced artifacts (blink, movement) ▪ Cardiac-induced artifacts (heartbeat, pulse) ▪ Muscle-induced artifacts (movement, chewing) ▪ Sweating Electronics Engineering Department 29 Non-Invasive Measurements of EEG Electronics Engineering Department 30 EEG Bands Electronics Engineering Department 31 EEG Bands Electronics Engineering Department 32 EEG Bands Electronics Engineering Department 33 EEG for Diagnosis and Treatment of Disorders ▪ An EEG is helpful for diagnosing or treating the following disorders: ▪ Epilepsy (EEG: gold standard diagnostic procedure to confirm epilepsy) ▪ Brain tumor ▪ Brain damage from head injury ▪ Brain dysfunction that can have a variety of causes (encephalopathy) ▪ Inflammation of the brain (encephalitis) ▪ Stroke ▪ Sleep disorders Electronics Engineering Department 34 EEG during Epilepsy Electronics Engineering Department 35 EEG during Epilepsy Electronics Engineering Department 36 EEG for Research Electronics Engineering Department 37 Brain-Computer Interfaces Postgraduate Research (2014-2015) Development of a Generative Adaptive Subspace Self-Organising Map (GASSOM) Model for Classification of EEG Signals in Brain-Computer Interfaces Electronics Engineering Department 38 Electrocardiography (ECG) Electronics Engineering Department 39 Electrocardiography (ECG) ▪ Process of producing an electrocardiogram (ECG or EKG), a recording of the heart’s electrical activity ▪ It is an electrogram of the heart which is a graph of voltage versus time of the electrical activity of the heart using electrodes placed on the skin. ▪ These electrodes detect the small electrical changes that are a consequence of cardiac muscle depolarization followed by a repolarization during each cardiac cycle (”heartbeat”). ▪ Changes in the normal ECG pattern occur in numerous cardiac abnormalities, including cardiac rhythm disturbances (such as atrial fibrillation and ventricular tachycardia), inadequate coronary artery blood flow (such as myocardial ischemia and myocardial infarction), and electrolyte disturbances (such as hypokalemia and hyperkalemia). Electronics Engineering Department 40 Brief History of ECG ▪ 1872: Alexander Muirhead ▪ He attached wires to the wrist of a patient with fever to obtain an electronic record of his heartbeat ▪ 1887: Augustus Waller ▪ He invented an ECG machine consisting of a Lippmann capillary electrometer fixed to a projector. ▪ The trace from the heartbeat was projected onto a photographic plate that was itself fixed to a toy train. ▪ This allowed a heartbeat to be recorded in real time. ▪ 1901: Willem Einthoven ▪ He used a string galvanometer: the first practical ECG. ▪ This device was much more sensitive than the capillary electrometer Waller used. Electronics Engineering Department 41 Brief History of ECG Electronics Engineering Department 42 Brief History of ECG ▪ 1924: Willem Einthoven ▪ He was awarded the Nobel Prize in Medicine for his pioneering work in developing the ECG. ▪ 1937: Taro Takemi ▪ He invented a new portable ECG machine. ▪ 1942: Emanuel Goldberger ▪ He increases the voltage of unipolar leads by 50% and creates the augmented limb leads aVR, aVL and aVF. ▪ When added to Einthoven's three limb leads and the six chest leads, we arrive at the 12-lead electrocardiogram that is used today. Electronics Engineering Department 43 Heart Conduction System Electronics Engineering Department 44 The Cardiac Pacemaker a h a s atr a e e tr e tr ar s e e et ster r e r e ht e ers Electronics Engineering Department 45 The Cardiac Pacemaker The contraction of cardiac muscle (heart muscle) in all animals is initiated by electrical impulses known as action potentials that in the heart are known as cardiac action potentials. The rate at which these impulses fire controls the rate of cardiac contraction, that is, the heart rate. The cells that create these rhythmic impulses, setting the pace for blood pumping, are called pacemaker cells, and they directly control the heart rate. They make up the cardiac pacemaker, that is, the natural pacemaker of the heart. In most humans, the highest concentration of pacemaker cells is in the sinoatrial (SA) node, the natural and primary pacemaker, and the resultant rhythm is a sinus rhythm. Electronics Engineering Department 46 The ECG Pattern There are three main components to an ECG: the P wave, which represents depolarization of the atria; the QRS complex, which represents depolarization of the ventricles; and the T wave, which represents repolarization of the ventricles. Electronics Engineering Department 47  1 small square = 1 mm (0.1 mV) Vertical Axis 1 large square = 5 mm (0.5 mV) ‘y’ 2 large squares = 10 mm (1 mV) 1 small square = 0.04 seconds Horizontal Axis 1 large square = 0.2 seconds ‘x’ 5 large squares = 1 sec Electronics Engineering Department 48 The ECG Rhythm ▪ Is it fast or slow? ▪ Is it regular or irregular? ▪ Are there P waves present? ▪ Are all P waves the same? ▪ Does each QRS have a P wave? ▪ Is the PR interval constant? ▪ Are the P waves and QRS complexes associated with each other? ▪ Are the QRS complexes narrow or wide? ▪ Are the QRS complexes grouped or not? ▪ Are there dropped beats? Electronics Engineering Department 49 The ECG Rhythm Feature Description Pathology Duration The P wave is typically upright in most leads except for aVR; an unusual P wave axis The P wave represents depolarization of (inverted in other leads) can indicate the atria. Atrial depolarization spreads an ectopic atrial pacemaker. If the P wave is P wave from the SA node towards the AV node, of unusually long duration, it may represent