BM402: Engineering in Medicine (24th October 2024) PDF

BM402: ENGINEERING IN MEDICINE 24th October 2024 M 2170 – South Campus MRI Functional MRI Applications of MRI and fMRI EEG Applications of EEG Multimodal Imaging EEG basics Electro-encephalo-gram Brain...

BM402: ENGINEERING IN MEDICINE 24th October 2024 M 2170 – South Campus MRI Functional MRI Applications of MRI and fMRI EEG Applications of EEG Multimodal Imaging EEG basics Electro-encephalo-gram Brain Electrical Picture/Record sleeping EEG is the measurement of electrical patterns at the surface of the scalp which reflect cortical activity - commonly referred as “brainwaves”. EEG basics Electro-encephalo-gram Brain Electrical Picture/Record sleeping EEG is the measurement of electrical patterns at the surface of the scalp which reflect cortical activity - commonly referred as “brainwaves”. International 10-20 system 21 channel EEG Electrocorticography ECoG, iEEG Grid and stick electrodes Dr Kareem Zaghloul - Neural signatures of memory and information in the human brain EEG History Analysis – next week(s) EEG History EEG - brain rhythms EEG - brain rhythms & frequency bands EEG - brain rhythms & frequency bands EEG - brain rhythms & frequency bands Light sleep Deep sleep REM sleep – rapid eye movement Recording the electrical activity of the brain Definition: An action potential is a rapid, large change in membrane potential that travels along the axon of a neuron, allowing for long-distance communication. Typically lasts about 1 milliseconds, with high- amplitude (~100 mV) pulses. Postsynaptic potentials To be clear, EEG does not measure action potentials, but rather postsynaptic potentials. An action potential is a rapid sequence of changes in the voltage across a membrane, ,i.e., a temporary shift (from negative to positive) in the neuron's membrane potential caused by ions suddenly flowing in and out of the neuron. Postsynaptic potentials (PSP) A temporary change in the electric polarization of the membrane of a nerve cell (neuron). The result of chemical transmission of a nerve impulse at the synapse (neuronal junction), the postsynaptic potential can lead to the firing of a new impulse. A postsynaptic potential is a change in the membrane potential of a postsynaptic neuron that occurs in response to neurotransmitter binding at synapses. PSPs are longer in duration than action potentials, lasting up to tens or even hundreds of milliseconds. Postsynaptic potentials Postsynaptic potentials International 10-20 system 21 channel EEG Electrocorticography ECoG, iEEG Grid and stick electrodes Dr Kareem Zaghloul - Neural signatures of memory and information in the human brain EEG History Analysis EEG History Simultaneous EEG-fMRI Simultaneous EEG-fMRI: how to make it compatible Simultaneous EEG-fMRI: how to make it compatible Simultaneous EEG-fMRI: how to make it compatible Parallel vs. concurrent Simultaneous EEG-fMRI: how to make it compatible - the presence of static and time-varying magnetic fields and - their associated EEG artefacts; - the need to limit radiofrequency (RF) emissions to preserve image quality; - and finally the obvious requirement to avoid the introduction of ferrous materials into the scanner environment. (A) electrode cap, (B) connector box containing current-limiting resistors, (C) battery power pack and (D) 32 channel EEG amplifier/digitizer. Simultaneous EEG-fMRI: how to make it compatible - MR bore: a “hostile” environment for the recording of EEG. - There are several reasons for this, mostly related to the homogeneous and gradient- switching magnetic environment of the MR bore. - In addition to the strong homogeneous static magnetic field of the scanner and also, more importantly, to the rapidly changing variable magnetic fields generated by gradient switching, the cap, electrodes, and electrode leads are also exposed to the profound radio frequency (RF) energy emitted during the scan sequence. Simultaneous EEG-fMRI: how to make it compatible Back view of a commonly used MR-compatible EEG cap system (BrainCap MR, Brain Products GmbH, Gilching, Germany). Safety features on this cap are: (1) plastic electrode holders to avoid direct contact of Ag/AgCl element with the scalp, (2) RF shielding resistor on electrode (e.g., black “dot”), Simultaneous EEG-fMRI: how to make it compatible Magnetic Properties Relevant to MRI: Ferromagnetism: Importance: Ferromagnetic materials are strongly attracted to magnetic fields. In the context of MRI, any ferromagnetic material (like iron) can pose safety risks, as it may be pulled into the magnet, potentially causing injury or equipment damage. MRI Design: MRI systems are designed to minimize the presence of ferromagnetic materials to ensure patient safety and equipment integrity. Paramagnetism: Importance: Paramagnetic substances, such as gadolinium, are Diamagnetism: used as contrast agents in MRI. These agents enhance the contrast of images by altering the relaxation times of nearby protons. Importance: Diamagnetic materials are slightly repelled by magnetic - Aluminum, Platinum fields and do not pose a safety risk in MRI. Most biological tissues are Deoxyhemoglobin (the form of hemoglobin without bound oxygen) weakly diamagnetic. has unpaired electrons and exhibits paramagnetic properties. This - Copper, Carbon, Silicon makes it attracted to magnetic fields. Behavior in MRI: While they do not enhance images, understanding their When hemoglobin binds oxygen, it undergoes a conformational properties is essential for interpreting the effects of magnetic fields on change that reduces its paramagnetic characteristics (it becomes body tissues. diamagnetic when fully oxygenated). Simultaneous EEG-fMRI: how to make it compatible Magnetic Properties Relevant to MRI: Ferromagnetism: Importance: Ferromagnetic materials are strongly attracted to magnetic fields. In the context of MRI, any ferromagnetic material (like iron) can pose safety risks, as it may be pulled into the magnet, potentially causing injury or equipment damage. MRI Design: MRI systems are designed to minimize the presence of ferromagnetic materials to ensure patient safety and equipment integrity. Paramagnetism: Importance: Paramagnetic substances, such as gadolinium, are Diamagnetism: used as contrast agents in MRI. These agents enhance the contrast of images by altering the relaxation times of nearby protons. Importance: Diamagnetic materials are slightly repelled by magnetic - Aluminum, Platinum fields and do not pose a safety risk in MRI. Most biological tissues are Deoxyhemoglobin (the form of hemoglobin without bound oxygen) weakly diamagnetic. has unpaired electrons and exhibits paramagnetic properties. This - Copper, Carbon, Silicon makes it attracted to magnetic fields. Behavior in MRI: While they do not enhance images, understanding their When hemoglobin binds oxygen, it undergoes a conformational properties is essential for interpreting the effects of magnetic fields on change that reduces its paramagnetic characteristics (it becomes body tissues. diamagnetic when fully oxygenated). Simultaneous EEG-fMRI: how to make it compatible Magnetic Properties Relevant to MRI: Ferromagnetism: Importance: Ferromagnetic materials are strongly attracted to magnetic fields. In the context of MRI, any ferromagnetic material (like iron) can pose safety risks, as it may be pulled into the magnet, potentially causing injury or equipment damage. MRI Design: MRI systems are designed to minimize the presence of ferromagnetic materials to ensure patient safety and equipment integrity. Paramagnetism: Importance: Paramagnetic substances, such as gadolinium, are Diamagnetism: used as contrast agents in MRI. These agents enhance the contrast of images by altering the relaxation times of nearby protons. Importance: Diamagnetic materials are slightly repelled by magnetic - Aluminum, Platinum fields and do not pose a safety risk in MRI. Most biological tissues are Deoxyhemoglobin (the form of hemoglobin without bound oxygen) weakly diamagnetic. has unpaired electrons and exhibits paramagnetic properties. This - Copper, Carbon, Silicon makes it attracted to magnetic fields. Behavior in MRI: While they do not enhance images, understanding their When hemoglobin binds oxygen, it undergoes a conformational properties is essential for interpreting the effects of magnetic fields on change that reduces its paramagnetic characteristics (it becomes body tissues. diamagnetic when fully oxygenated). Simultaneous EEG-fMRI: how to make it compatible Back view of a commonly used MR-compatible EEG cap system (BrainCap MR, Brain Products GmbH, Gilching, Germany). Safety features on this cap are: (1) plastic electrode holders to avoid direct contact of Ag/AgCl element with the scalp, (2) RF shielding resistor on electrode (e.g., black “dot”), (3) fixation of electrode cables with nylon, and (4) routing of electrode cables together in bundles of increasing numbers of electrodes. Simultaneous EEG-fMRI: how to make it compatible Back view of a commonly used MR-compatible EEG cap system (BrainCap MR, Brain Products GmbH, Gilching, Germany). Safety features on this cap are: (1) plastic electrode holders to avoid direct contact of Ag/AgCl element with the scalp, (2) RF shielding resistor on electrode (e.g., black “dot”), (3) fixation of electrode cables with nylon, and (4) routing of electrode cables together in bundles of increasing numbers of electrodes. Simultaneous EEG-fMRI: how to make it compatible The arrangement shown consists of two EEG amplifiers at the top and bottom with a rechargeable power pack positioned in the middle. Cap connections are made with standard flat ribbon cables at the front of the amplifiers. *Sandbags used to fix the electrode cables in place to avoid cable movement induced by mechanical resonances caused by gradient switching and by the action of the Helium pump. Simultaneous EEG-fMRI: main artifacts Correction of gradient and cardioballistic artifacts is valuable for ensuring data quality A much less commonly seen cardiac artifact is cardioballistic artifact, in which the EEG electrode is placed just above an artery, and each pulsation of the artery is picked up as motion artifact on the EEG. Simultaneous EEG-fMRI: main artifacts Gradient artifact (GA) is the largest source of noise in EEG-fMRI, and is used for fMRI acquisition due to the magnetic field gradients, which induce current in EEG electrodes up to 400 times larger than neural activity, therefore obscuring the EEG information of interest. Ballistocardiogram (BCG) artifact occurs due to the subject's cardio-respiratory patterns, specifically scalp pulse and cardiac-related motion. Simultaneous EEG-fMRI: main artifacts Gradient artifact (GA) is the largest source of noise in EEG-fMRI, and is used for fMRI acquisition due to the magnetic field gradients, which induce current in EEG electrodes up to 400 times larger than neural activity, therefore obscuring the EEG information of interest. Ballistocardiogram (BCG) artifact occurs due to the subject's cardio-respiratory patterns, specifically scalp pulse and cardiac-related motion. Motion artifact occurs when movement of the subject's head within the scanner creates artifacts on the EEG due to induced current at electrodes. Environmental artifact occurring on the EEG recording is mostly due to interference from power line noise, ventilation, and lights in the MR room, as well as the vibration arising from the helium cooling pump. Simultaneous EEG-fMRI: main artifacts – how bad? Correction of gradient and cardioballistic artifacts is valuable for ensuring data quality Ikemoto et al. 2022 Simultaneous EEG-fMRI: main artifacts – how bad? Correction of gradient and cardioballistic artifacts is valuable for ensuring data quality Ikemoto et al. 2022 Main gradient artifact (GA) correction methods A. Template methods B. Blind source separation C. Filtering Main gradient artifact (GA) correction methods A. Template methods B. Blind source separation C. Filtering Template methods are techniques that create an estimate of the artifact, which is removed from the noisy data, to obtain clean EEG. GA is assumed to be repetitive and time-locked to each repetition time (TR). Template methods average the signal over many TRs, leveraging the fact that the neuronal EEG signal, which is not time locked to the TR, will average out toward zero. Main gradient artifact (GA) correction methods A. Template methods B. Blind source separation C. Filtering Bullock et al. 2021  (A) The raw EEG during periodic fMRI flat (B) The averaged imaging artifact. (C): (A) – (B) (D) The averaged pulse artifact. (E): (C) – (D) - > alpha power visible EEG recorded outside the scanner Illustrative example of 10 seconds of EEG data Marino et al. 2018 Break – 15 minutes Frequency based analysis EEG & SLEEP  Markers of deep sleep Markers of N2 –light- sleep EEG & SLEEP Frequency based analysis Frequency based analysis In Berger’s first EEG recordings from the human scalp in the late 1920s, he noticed a prominent sinusoidal wave of around 10 cycles/s that he later named the alpha rhythm (8-12Hz). The alpha rhythm is highest in amplitude when a subject is awake and relaxed with eyes closed, and is attenuated by opening the eyes and by mental effort, as well as by drowsiness or sleep. Frequency based analysis fMRI & EEG alpha Alpha rhythm as an index of cortical inactivity that may be generated in part by the thalamus. Reading time: 15 minutes Event related potentials (ERPs) What is an ERP? An event-related potential (ERP) is the neural response associated with a specific sensory, e.g., cognitive, or motor event. An ERP can be recorded using scalp EEG and looks at the average change in voltage over time starting at the onset of the stimulus over multiple trials. Event related potentials (ERPs) What is an ERP? An event-related potential (ERP) is the neural response associated with a specific sensory, e.g., cognitive, or motor event. An ERP can be recorded using scalp EEG and looks at the average change in voltage over time starting at the onset of the stimulus over multiple trials. How to record? ERPs are evoked by stimuli and measured at the scalp with EEG. They are recorded in response to an isolated, discrete event. Usually, this stimulus is presented multiple times, which allows the EEG to be averaged after discarding low-quality trials. Event related potentials (ERPs) ERPs are positive and negative voltage fluctuations (or components) in the ongoing EEG that are time-locked to the onset of a sensory, motor, or cognitive event. ERPs reflect brain activity that is specifically related to some stimulus or other event. This activity cannot be directly observed in the EEG, as the "signal" (the brain response to some event) is swamped by the "noise" (the brain activity that is unrelated to that event). The solution to this problem is to present not just one instance of the event of interest, but many instances: Epochs Event related potentials (ERPs) The "random" activity washes out during averaging, whereas the brain activity of interest -- namely, what is constant over presentations of the event of interest -- stays in the signal. Through this signal-averaging procedure, it is possible to isolate the brain response that is specifically elicited in response to some event of interest. ERP components are usually named in terms of their polarity (N/P: negative/positive) and peak latency (in milliseconds). Event related potentials (ERPs) The majority of ERP studies investigated responses that occur in the first 100–500 ms following a stimulus. Early components (P100, N100, P200) relate to sensory properties of stimuli and to selective attention. Later ERP waves are used to index endogenous cognitive activity. Event related potentials (ERPs) Later ERP waves are used to index endogenous cognitive activity. The positive going ERP component at 300 ms (P300) is related to processes that involve classifying or updating memory representations of stimuli. The amplitude of the P300 increases as the demand for cognitive resources increases and as the significance of the event and its relevance to the subject increases. Latency and amplitude Shorter latencies indicate superior mental performance relative to longer latencies. P3 amplitude seems to reflect stimulus information such that greater attention produces larger P3 waves. Reduced P300 amplitude is an indicator of the broad neurobiological vulnerability that underlies disorders within the externalizing spectrum {alcohol dependence, drug dependence, nicotine dependence, conduct disorder and adult antisocial behavior} (Patrick et al., 2006). Event-related potential changes in psychiatric disorders – P300 One of the most robust neurophysiological findings in schizophrenia is decrease in P300 amplitude. P300 latency was found to be increased in schizophrenic patients but not in their first-degree relatives (Simlai & Nizamie, 1998). Salisbury et al. (1999) have recently noted P300 reduction in manic psychosis. Latency prolongation and amplitude reduction were seen both in schizophrenia and chronic bipolar patients (O’Donell et al., 2004). Event-related potential changes in psychiatric disorders – P300 Latency prolongation and amplitude reduction were seen both in schizophrenia and chronic bipolar patients (O’Donell et al., 2004). Event-related potential changes in psychiatric disorders – P300 Latency prolongation and amplitude reduction were seen both in schizophrenia and chronic bipolar patients (O’Donell et al., 2004). Event-related potential changes in psychiatric disorders – P300 Results suggest that while both bipolar patients and patients with schizophrenia have reduced P300 amplitude and prolonged latency, patients with schizophrenia additionally have disturbances of earlier stages of auditory processing. P300 latency prolongation is suggestive of deficits in attentional or working memory systems. Caffeine effect on P300 Caffeine effect on P300 Caffeine effect on P300 Caffeine yields quicker mental processing and less overall demand on attention resources required for task performance. Caffeine may modulate the mental processing for repeated stimulus by reducing the overall demand on attention and producing a net increase in allocating attention resources for task performance. Tiredness, getting bored with the task. Reading – 15 minutes Simultaneous EEG-fMRI: an overnight sleep study 3T EEG fMRI 12 successful subjects, ~ 10% of total participants 3T, GE-EPI, TR = 3s, TE = 36ms Physiology Respiratory bellow & pulse oximeter EEG 64 channel Manual sleep scoring (based on 30-s epochs) Moehlman et al., J. Neur. Methods 2019 Simultaneous EEG-fMRI: an overnight sleep study 0.5 - Sleep stages Wake NREM1 NREM2 - 20 NREM3 NREM2 NREM3 1000 LF-EEG 3T Frequency (µV2) (Hz) 100 - EEG PPG-AMP 0 (a.u.) 0.52 - % fMRIGM 0 signal change -2 Sleep stages hypnogram fMRI Wake NREM1 Rotation Degree 3T, GE-EPI, TR = 3s, TE = 36ms NREM2 1 NREM30 Physiology LF-EEG 1000 1 300 600 900 1200 1500 1800 2100 2400 2676 Respiratory bellow & pulse oximeter (µV2) time (sec) 0 EEG 64 channel PPG-AMP 0 (a.u.) Manual sleep scoring (based on 30-s epochs) 2 % fMRIGM 0 signal change -2 Özbay et al., Commun. Biol. 2019 Reminder for upcoming classes: Xray, CT, PET, PET-MRI Neurofeedback Midterm Biomechanichs Biomaterials Trends, e.g., Big data, open science, AI Ethics Presentations Lab visits