An electrogram ( EGM ) is a recording of electrical activity of organs such as the brain and heart , measured by monitoring changes in electric potential .
117-441: Electroencephalography ( EEG ) is a 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 (commonly called "scalp EEG") using
234-579: A portable MRI scanner approved by the FDA in 2020. Recently, MRI has been demonstrated also at ultra-low fields, i.e., in the microtesla-to-millitesla range, where sufficient signal quality is made possible by prepolarization (on the order of 10–100 mT) and by measuring the Larmor precession fields at about 100 microtesla with highly sensitive superconducting quantum interference devices ( SQUIDs ). Each tissue returns to its equilibrium state after excitation by
351-470: A voltmeter . Recording these voltages over time gives us the EEG. The electric potential generated by an individual neuron is far too small to be picked up by EEG or MEG. EEG activity therefore always reflects the summation of the synchronous activity of thousands or millions of neurons that have similar spatial orientation. If the cells do not have similar spatial orientation, their ions do not line up and create waves to be detected. Pyramidal neurons of
468-540: A T 2 -weighted image, magnetization is allowed to decay before measuring the MR signal by changing the echo time (TE). This image weighting is useful for detecting edema and inflammation, revealing white matter lesions , and assessing zonal anatomy in the prostate and uterus . The information from MRI scans comes in the form of image contrasts based on differences in the rate of relaxation of nuclear spins following their perturbation by an oscillating magnetic field (in
585-425: A clinical diagnosis of ADHD. Cardiac MRI is complementary to other imaging techniques, such as echocardiography , cardiac CT , and nuclear medicine . It can be used to assess the structure and the function of the heart. Its applications include assessment of myocardial ischemia and viability , cardiomyopathies , myocarditis , iron overload , vascular diseases, and congenital heart disease . Applications in
702-466: A clinical event. Epilepsy monitoring is often considered when patients continue having events despite being on anti-seizure medications or if there is concern that the patient's events have an alternate diagnosis, e.g., psychogenic non-epileptic seizures , syncope (fainting) , sub-cortical movement disorders , migraine variants, stroke, etc. In cases of epileptic seizures, continuous EEG monitoring helps to characterize seizures and localize/lateralize
819-700: A combined EEG/MEG (EMEG) approach has been investigated for the purpose of source reconstruction in epilepsy diagnosis. EEG has also been combined with positron emission tomography . This provides the advantage of allowing researchers to see what EEG signals are associated with different drug actions in the brain. Recent studies using machine learning techniques such as neural networks with statistical temporal features extracted from frontal lobe EEG brainwave data has shown high levels of success in classifying mental states (Relaxed, Neutral, Concentrating), mental emotional states (Negative, Neutral, Positive) and thalamocortical dysrhythmia . The brain's electrical charge
936-446: A drug safety communication that new warnings were to be included on all gadolinium-based contrast agents (GBCAs). The FDA also called for increased patient education and requiring gadolinium contrast vendors to conduct additional animal and clinical studies to assess the safety of these agents. Although gadolinium agents have proved useful for patients with kidney impairment, in patients with severe kidney failure requiring dialysis there
1053-546: A net nuclear spin could potentially be imaged with MRI. Such nuclei include helium-3 , lithium-7 , carbon-13 , fluorine -19, oxygen-17 , sodium -23, phosphorus -31 and xenon-129 . Na and P are naturally abundant in the body, so they can be imaged directly. Gaseous isotopes such as He or Xe must be hyperpolarized and then inhaled as their nuclear density is too low to yield a useful signal under normal conditions. O and F can be administered in sufficient quantities in liquid form (e.g. O -water) that hyperpolarization
1170-542: A number of early suggestions for using arrays of detectors to accelerate imaging went largely unremarked in the MRI field, parallel imaging saw widespread development and application following the introduction of the SiMultaneous Acquisition of Spatial Harmonics (SMASH) technique in 1996–7. The SENSitivity Encoding (SENSE) and Generalized Autocalibrating Partially Parallel Acquisitions (GRAPPA) techniques are
1287-541: A person is. The range of frequencies one observes are between 1 and 30 Hz, and amplitudes will vary between 20 and 100 μV. The observed frequencies are subdivided into various groups: alpha (8–13 Hz), beta (13–30 Hz), delta (0.5–4 Hz), and theta (4–7 Hz). Alpha waves are observed when a person is in a state of relaxed wakefulness and are mostly prominent over the parietal and occipital sites. During intense mental activity , beta waves are more prominent in frontal areas as well as other regions. If
SECTION 10
#17327731972621404-467: A prolonged EEG is typically performed accompanied by a time-synchronized video and audio recording. This can be done either as an outpatient (at home) or during a hospital admission, preferably to an Epilepsy Monitoring Unit (EMU) with nurses and other personnel trained in the care of patients with seizures. Outpatient ambulatory video EEGs typically last one to three days. An admission to an Epilepsy Monitoring Unit typically lasts several days but may last for
1521-455: A relaxed person is told to open their eyes, one observes alpha activity decreasing and an increase in beta activity. Theta and delta waves are not generally seen in wakefulness - if they are, it is a sign of brain dysfunction. EEG can detect abnormal electrical discharges such as sharp waves , spikes, or spike-and-wave complexes, as observable in people with epilepsy ; thus, it is often used to inform medical diagnosis . EEG can detect
1638-504: A research method). In cases where significant brain injury is suspected, e.g., after cardiac arrest, EEG can provide some prognostic information. If a patient with epilepsy is being considered for resective surgery to treat epilepsy, it is often necessary to localize the focus (source) of the epileptic brain activity with a resolution greater than what is provided by scalp EEG. In these cases, neurosurgeons typically implant strips and grids of electrodes or penetrating depth electrodes under
1755-410: A role in the detection of large polyps in patients at increased risk of colorectal cancer. Magnetic resonance angiography (MRA) generates pictures of the arteries to evaluate them for stenosis (abnormal narrowing) or aneurysms (vessel wall dilatations, at risk of rupture). MRA is often used to evaluate the arteries of the neck and brain, the thoracic and abdominal aorta, the renal arteries, and
1872-468: A routine EEG to detect interictal epileptiform discharges at epilepsy centers has been reported to be in the range of 29–55%. Given the low to moderate sensitivity, a routine EEG (typically with a duration of 20–30 minutes) can be normal in people that have epilepsy. When an EEG shows interictal epileptiform discharges (e.g. sharp waves, spikes, spike-and-wave , etc.) it is confirmatory of epilepsy in nearly all cases (high specificity ), however up to 3.5% of
1989-406: A smaller parcel of brain surface) allow for better spatial resolution to narrow down the areas critical for seizure onset and propagation. Some clinical sites record data from penetrating microelectrodes. Sometimes it is more convenient or clinically necessary to perform ambulatory EEG recordings in the home of the person being tested. These studies typically have a duration of 24–72 hours. EEG and
2106-423: A span of hours. Therefore, research has been directed to developing dry and semi-dry EEG bioelectronic interfaces. Dry electrode signals depend upon mechanical contact. Therefore, it can be difficult getting a usable signal because of impedance between the skin and the electrode. Some EEG systems attempt to circumvent this issue by applying a saline solution. Others have a semi dry nature and release small amounts of
2223-406: A total magnetization M z . This magnetization along z is defined as the equilibrium magnetization; magnetization is defined as the sum of all magnetic dipoles in a sample. Following the equilibrium magnetization, a 90° radiofrequency (RF) pulse flips the direction of the magnetization vector in the xy-plane, and is then switched off. The initial magnetic field B 0 , however, is still applied. Thus,
2340-852: A typical field strength for clinical MRI, the difference between high and low energy states is approximately 9 molecules per 2 million. Improvements to increase MR sensitivity include increasing magnetic field strength and hyperpolarization via optical pumping or dynamic nuclear polarization. There are also a variety of signal amplification schemes based on chemical exchange that increase sensitivity. To achieve molecular imaging of disease biomarkers using MRI, targeted MRI contrast agents with high specificity and high relaxivity (sensitivity) are required. To date, many studies have been devoted to developing targeted-MRI contrast agents to achieve molecular imaging by MRI. Commonly, peptides, antibodies, or small ligands, and small protein domains, such as HER-2 affibodies, have been applied to achieve targeting. To enhance
2457-433: A week or longer. While in the hospital, seizure medications are usually withdrawn to increase the odds that a seizure will occur during admission. For reasons of safety, medications are not withdrawn during an EEG outside of the hospital. Ambulatory video EEGs, therefore, have the advantage of convenience and are less expensive than a hospital admission, but they also have the disadvantage of a decreased probability of recording
SECTION 20
#17327731972622574-445: Is intraoperative MRI , in which an MRI is used in surgery. Some specialized MRI systems allow imaging concurrent with the surgical procedure. More typically, the surgical procedure is temporarily interrupted so that MRI can assess the success of the procedure or guide subsequent surgical work. In guided therapy, high-intensity focused ultrasound (HIFU) beams are focused on a tissue, that are controlled using MR thermal imaging. Due to
2691-441: Is a medical application of nuclear magnetic resonance (NMR) which can also be used for imaging in other NMR applications , such as NMR spectroscopy . MRI is widely used in hospitals and clinics for medical diagnosis , staging and follow-up of disease. Compared to CT , MRI provides better contrast in images of soft tissues, e.g. in the brain or abdomen. However, it may be perceived as less comfortable by patients, due to
2808-445: Is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes inside the body. MRI scanners use strong magnetic fields , magnetic field gradients, and radio waves to generate images of the organs in the body. MRI does not involve X-rays or the use of ionizing radiation , which distinguishes it from computed tomography (CT) and positron emission tomography (PET) scans. MRI
2925-410: Is a particular setting of radiofrequency pulses and gradients, resulting in a particular image appearance. The T1 and T2 weighting can also be described as MRI sequences. edit This table does not include uncommon and experimental sequences . Standard foundation and comparison for other sequences Standard foundation and comparison for other sequences Magnetic resonance spectroscopy (MRS)
3042-418: Is a process similar to masers . In clinical and research MRI, hydrogen atoms are most often used to generate a macroscopic polarized radiation that is detected by the antennas. Hydrogen atoms are naturally abundant in humans and other biological organisms, particularly in water and fat . For this reason, most MRI scans essentially map the location of water and fat in the body. Pulses of radio waves excite
3159-447: Is a reliable indication of the occurrence of neural output. Not only do EEGs capture dendritic currents almost exclusively as opposed to axonal currents, they also show a preference for activity on populations of parallel dendrites and transmitting current in the same direction at the same time. Pyramidal neurons of cortical layers II/III and V extend apical dendrites to layer I. Currents moving up or down these processes underlie most of
3276-543: Is a risk of a rare but serious illness, nephrogenic systemic fibrosis , which may be linked to the use of certain gadolinium-containing agents. The most frequently linked is gadodiamide , but other agents have been linked too. Although a causal link has not been definitively established, current guidelines in the United States are that dialysis patients should only receive gadolinium agents where essential and that dialysis should be performed as soon as possible after
3393-689: Is a similar procedure that is used to image veins. In this method, the tissue is now excited inferiorly, while the signal is gathered in the plane immediately superior to the excitation plane—thus imaging the venous blood that recently moved from the excited plane. MRI for imaging anatomical structures or blood flow do not require contrast agents since the varying properties of the tissues or blood provide natural contrasts. However, for more specific types of imaging, exogenous contrast agents may be given intravenously , orally , or intra-articularly . Most contrast agents are either paramagnetic (e.g.: gadolinium, manganese, europium), and are used to shorten T1 in
3510-412: Is about 10 μV to 100 μV in amplitude when measured from the scalp. Since an EEG voltage signal represents a difference between the voltages at two electrodes, the display of the EEG for the reading encephalographer may be set up in one of several ways. The representation of the EEG channels is referred to as a montage. When analog (paper) EEGs are used, the technologist switches between montages during
3627-402: Is an electrical recording of the activity of the brain taken from the scalp . An EEG can be used to diagnose seizures , sleep disorders , and for monitoring of level of anesthesia during surgery. An electrocorticogram is an electrical recording of the brain measured intracranially, that is, from within the brain. An electrooculogram (EOG) is an electrical recording of the potential between
Electroencephalography - Misplaced Pages Continue
3744-525: Is an integrated system made of an array of capacitive sensors with local integrated circuitry housed in a package with batteries to power the circuitry. This level of integration was required to achieve the functional performance obtained by the electrode. The electrode was tested on an electrical test bench and on human subjects in four modalities of EEG activity, namely: (1) spontaneous EEG, (2) sensory event-related potentials, (3) brain stem potentials, and (4) cognitive event-related potentials. The performance of
3861-550: Is applied, and the remaining spatial information is filled in by combining signals from various coils, based on their known spatial sensitivity patterns. The resulting acceleration is limited by the number of coils and by the signal to noise ratio (which decreases with increasing acceleration), but two- to four-fold accelerations may commonly be achieved with suitable coil array configurations, and substantially higher accelerations have been demonstrated with specialized coil arrays. Parallel MRI may be used with most MRI sequences . After
3978-461: Is attached to an individual wire. Some systems use caps or nets into which electrodes are embedded; this is particularly common when high-density arrays of electrodes are needed. Electrode locations and names are specified by the International 10–20 system for most clinical and research applications (except when high-density arrays are used). This system ensures that the naming of electrodes
4095-505: Is consistent across laboratories. In most clinical applications, 19 recording electrodes (plus ground and system reference) are used. A smaller number of electrodes are typically used when recording EEG from neonates . Additional electrodes can be added to the standard set-up when a clinical or research application demands increased spatial resolution for a particular area of the brain. High-density arrays (typically via cap or net) can contain up to 256 electrodes more-or-less evenly spaced around
4212-434: Is disputed in certain cases. MRI is the investigation of choice in the preoperative staging of rectal and prostate cancer and has a role in the diagnosis, staging, and follow-up of other tumors, as well as for determining areas of tissue for sampling in biobanking. MRI is the investigative tool of choice for neurological cancers over CT, as it offers better visualization of the posterior cranial fossa , containing
4329-409: Is maintained by billions of neurons . Neurons are electrically charged (or "polarized") by membrane transport proteins that pump ions across their membranes. Neurons are constantly exchanging ions with the extracellular milieu, for example to maintain resting potential and to propagate action potentials . Ions of similar charge repel each other, and when many ions are pushed out of many neurons at
4446-408: Is not a necessity. Using helium or xenon has the advantage of reduced background noise, and therefore increased contrast for the image itself, because these elements are not normally present in biological tissues. Moreover, the nucleus of any atom that has a net nuclear spin and that is bonded to a hydrogen atom could potentially be imaged via heteronuclear magnetization transfer MRI that would image
4563-452: Is processed in the same manner as digital scalp EEG (above), with a couple of caveats. ECoG is typically recorded at higher sampling rates than scalp EEG because of the requirements of Nyquist theorem – the subdural signal is composed of a higher predominance of higher frequency components. Also, many of the artifacts that affect scalp EEG do not impact ECoG, and therefore display filtering is often not needed. A typical adult human EEG signal
4680-453: Is processed to form an image of the body in terms of the density of those nuclei in a specific region. Given that the protons are affected by fields from other atoms to which they are bonded, it is possible to separate responses from hydrogen in specific compounds. To perform a study, the person is positioned within an MRI scanner that forms a strong magnetic field around the area to be imaged. First, energy from an oscillating magnetic field
4797-423: Is stored electronically and can be filtered for display. Typical settings for the high-pass filter and a low-pass filter are 0.5–1 Hz and 35–70 Hz respectively. The high-pass filter typically filters out slow artifact, such as electrogalvanic signals and movement artifact, whereas the low-pass filter filters out high-frequency artifacts, such as electromyographic signals. An additional notch filter
Electroencephalography - Misplaced Pages Continue
4914-411: Is temporarily applied to the patient at the appropriate resonance frequency. Scanning with X and Y gradient coils causes a selected region of the patient to experience the exact magnetic field required for the energy to be absorbed. The atoms are excited by a RF pulse and the resultant signal is measured by a receiving coil . The RF signal may be processed to deduce position information by looking at
5031-417: Is the lower incidence of nephrotoxicity, compared with iodinated agents, when given at usual doses—this has made contrast-enhanced MRI scanning an option for patients with renal impairment, who would otherwise not be able to undergo contrast-enhanced CT . Gadolinium-based contrast reagents are typically octadentate complexes of gadolinium(III) . The complex is very stable (log K > 20) so that, in use,
5148-469: Is then filtered (next paragraph), and the EEG signal is output as the deflection of pens as paper passes underneath. Most EEG systems these days, however, are digital, and the amplified signal is digitized via an analog-to-digital converter , after being passed through an anti-aliasing filter . Analog-to-digital sampling typically occurs at 256–512 Hz in clinical scalp EEG; sampling rates of up to 20 kHz are used in some research applications. During
5265-599: Is typically used to remove artifact caused by electrical power lines (60 Hz in the United States and 50 Hz in many other countries). The EEG signals can be captured with opensource hardware such as OpenBCI and the signal can be processed by freely available EEG software such as EEGLAB or the Neurophysiological Biomarker Toolbox . As part of an evaluation for epilepsy surgery, it may be necessary to insert electrodes near
5382-595: Is used to measure the levels of different metabolites in body tissues, which can be achieved through a variety of single voxel or imaging-based techniques. The MR signal produces a spectrum of resonances that corresponds to different molecular arrangements of the isotope being "excited". This signature is used to diagnose certain metabolic disorders, especially those affecting the brain, and to provide information on tumor metabolism . Magnetic resonance spectroscopic imaging (MRSI) combines both spectroscopic and imaging methods to produce spatially localized spectra from within
5499-426: The International 10–20 system , or variations of it. Electrocorticography , involving surgical placement of electrodes, is sometimes called "intracranial EEG" . Clinical interpretation of EEG recordings is most often performed by visual inspection of the tracing or quantitative EEG analysis . Voltage fluctuations measured by the EEG bioamplifier and electrodes allow the evaluation of normal brain activity . As
5616-448: The brainstem and the cerebellum . The contrast provided between grey and white matter makes MRI the best choice for many conditions of the central nervous system , including demyelinating diseases , dementia , cerebrovascular disease , infectious diseases , Alzheimer's disease and epilepsy . Since many images are taken milliseconds apart, it shows how the brain responds to different stimuli, enabling researchers to study both
5733-443: The cornea and the retina , and does not change with visual stimuli . An EOG can measure movements of the eyes and can help in diagnosis of nystagmus . An electroretinogram (ERG) is an electrical recording of the electrical activity of the retina. An electrocardiogram (ECG or EKG) is an electrical recording of the activity of the heart. The typical meaning of an "ECG" is the 12-lead ECG that uses 10 wires or electrodes to record
5850-548: The dura mater , through either a craniotomy or a burr hole . The recording of these signals is referred to as electrocorticography (ECoG), subdural EEG (sdEEG), intracranial EEG (icEEG), or stereotactic EEG (sEEG). The signal recorded from ECoG is on a different scale of activity than the brain activity recorded from scalp EEG. Low-voltage, high-frequency components that cannot be seen easily (or at all) in scalp EEG can be seen clearly in ECoG. Further, smaller electrodes (which cover
5967-464: The equilibrium state . Exogenous contrast agents may be given to the person to make the image clearer. The major components of an MRI scanner are the main magnet , which polarizes the sample, the shim coils for correcting shifts in the homogeneity of the main magnetic field, the gradient system which is used to localize the region to be scanned and the RF system, which excites the sample and detects
SECTION 50
#17327731972626084-499: The joints and the heart . In many cases MRI examinations become easier and more comfortable for patients, especially for the patients who cannot calm their breathing or who have arrhythmia . The lack of harmful effects on the patient and the operator make MRI well-suited for interventional radiology , where the images produced by an MRI scanner guide minimally invasive procedures. Such procedures use no ferromagnetic instruments. A specialized growing subset of interventional MRI
6201-580: The nuclear spin energy transition, and magnetic field gradients localize the polarization in space. By varying the parameters of the pulse sequence , different contrasts may be generated between tissues based on the relaxation properties of the hydrogen atoms therein. Since its development in the 1970s and 1980s, MRI has proven to be a versatile imaging technique. While MRI is most prominently used in diagnostic medicine and biomedical research, it also may be used to form images of non-living objects, such as mummies . Diffusion MRI and functional MRI extend
6318-442: The EEG activity time-locked to the presentation of a stimulus of some sort (visual, somatosensory , or auditory). Event-related potentials ( ERPs ) refer to averaged EEG responses that are time-locked to more complex processing of stimuli; this technique is used in cognitive science , cognitive psychology , and psychophysiological research. EEG is the gold standard diagnostic procedure to confirm epilepsy . The sensitivity of
6435-401: 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 . A healthy human EEG will show certain patterns of activity that correlate with how awake
6552-456: The advantages of having very high spatial resolution and is very adept at morphological imaging and functional imaging. MRI does have several disadvantages though. First, MRI has a sensitivity of around 10 mol/L to 10 mol/L, which, compared to other types of imaging, can be very limiting. This problem stems from the fact that the population difference between the nuclear spin states is very small at room temperature. For example, at 1.5 teslas ,
6669-475: The advent of high-resolution anatomical imaging techniques such as magnetic resonance imaging (MRI) and computed tomography (CT). Despite its limited spatial resolution, EEG continues to be a valuable tool for research and diagnosis. It is one of the few mobile techniques available and offers millisecond-range temporal resolution, which is not possible with CT, PET, or MRI. Derivatives of the EEG technique include evoked potentials (EP), which involves averaging
6786-743: The application of a denoising system. The record for the highest spatial resolution of a whole intact brain (postmortem) is 100 microns, from Massachusetts General Hospital. The data was published in NATURE on 30 October 2019. Though MRI is used widely in research on mental disabilities, based on a 2024 systematic literature review and meta analysis commissioned by the Patient-Centered Outcomes Research Institute (PCORI), available research using MRI scans to diagnose ADHD showed great variability. The authors conclude that MRI cannot be reliably used to assist in making
6903-579: The brain after concussion, however, at this time there are no advanced imaging techniques that can be used clinically to diagnose or monitor recovery from concussion. Several other methods to study brain function exist, including functional magnetic resonance imaging (fMRI), positron emission tomography (PET), magnetoencephalography (MEG), nuclear magnetic resonance spectroscopy (NMR or MRS), electrocorticography (ECoG), single-photon emission computed tomography (SPECT), near-infrared spectroscopy (NIRS), and event-related optical signal (EROS). Despite
7020-420: The changes in RF level and phase caused by varying the local magnetic field using gradient coils . As these coils are rapidly switched during the excitation and response to perform a moving line scan, they create the characteristic repetitive noise of an MRI scan as the windings move slightly due to magnetostriction . The contrast between different tissues is determined by the rate at which excited atoms return to
7137-463: The concentration of the un-complexed Gd ions should be below the toxicity limit. The 9th place in the metal ion's coordination sphere is occupied by a water molecule which exchanges rapidly with water molecules in the reagent molecule's immediate environment, affecting the magnetic resonance relaxation time . In December 2017, the Food and Drug Administration (FDA) in the United States announced in
SECTION 60
#17327731972627254-413: The continuous monitoring of moving objects in real time. Traditionally, real-time MRI was possible only with low image quality or low temporal resolution. An iterative reconstruction algorithm removed limitations. Radial FLASH MRI (real-time) yields a temporal resolution of 20 to 30 milliseconds for images with an in-plane resolution of 1.5 to 2.0 mm. Real-time MRI adds information about diseases of
7371-500: The cortex are thought to produce the most EEG signal because they are well-aligned and fire together. Because voltage field gradients fall off with the square of distance, activity from deep sources is more difficult to detect than currents near the skull. Scalp EEG activity shows oscillations at a variety of frequencies. Several of these oscillations have characteristic frequency ranges , spatial distributions and are associated with different states of brain functioning (e.g., waking and
7488-416: The cortex, inside sulci , in midline or deep structures (such as the cingulate gyrus or hippocampus ), or producing currents that are tangential to the skull, make far less contribution to the EEG signal. EEG recordings do not directly capture axonal action potentials . An action potential can be accurately represented as a current quadrupole , meaning that the resulting field decreases more rapidly than
7605-409: The diagnostic yield of the EEG. At times, a routine EEG is not sufficient to establish the diagnosis or determine the best course of action in terms of treatment. In this case, attempts may be made to record an EEG while a seizure is occurring. This is known as an ictal recording, as opposed to an interictal recording, which refers to the EEG recording between seizures. To obtain an ictal recording,
7722-524: The distribution of air spaces within the lungs. Injectable solutions containing C or stabilized bubbles of hyperpolarized Xe have been studied as contrast agents for angiography and perfusion imaging. P can potentially provide information on bone density and structure, as well as functional imaging of the brain. Multinuclear imaging holds the potential to chart the distribution of lithium in the human brain, this element finding use as an important drug for those with conditions such as bipolar disorder. MRI has
7839-525: The dry electrode compared favorably with that of the standard wet electrodes in terms of skin preparation, no gel requirements (dry), and higher signal-to-noise ratio. In 1999 researchers at Case Western Reserve University , in Cleveland , Ohio , led by Hunter Peckham, used 64-electrode EEG skullcap to return limited hand movements to quadriplegic Jim Jatich. As Jatich concentrated on simple but opposite concepts like up and down, his beta-rhythm EEG output
7956-528: 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 bones, which act in a manner akin to resistors and capacitors in an electrical circuit . This means that not all neurons will contribute equally to an EEG signal, with an EEG predominately reflecting
8073-607: The first single and also multichannel dry active electrode arrays using micro-machining. The single channel dry EEG electrode construction and results were published in 1994. The arrayed electrode was also demonstrated to perform well compared to silver / silver chloride electrodes. The device consisted of four sites of sensors with integrated electronics to reduce noise by impedance matching . The advantages of such electrodes are: (1) no electrolyte used, (2) no skin preparation, (3) significantly reduced sensor size, and (4) compatibility with EEG monitoring systems. The active electrode array
8190-453: The following disorders: It can also: EEG can also be used in intensive care units for brain function monitoring to monitor for non-convulsive seizures/non-convulsive status epilepticus, to monitor the effect of sedative/anesthesia in patients in medically induced coma (for treatment of refractory seizures or increased intracranial pressure ), and to monitor for secondary brain damage in conditions such as subarachnoid hemorrhage (currently
8307-400: The form of radiofrequency pulses through the sample). The relaxation rates are a measure of the time it takes for a signal to decay back to an equilibrium state from either the longitudinal or transverse plane. Magnetization builds up along the z-axis in the presence of a magnetic field, B 0 , such that the magnetic dipoles in the sample will, on average, align with the z-axis summing to
8424-516: The functional and structural brain abnormalities in psychological disorders. MRI also is used in guided stereotactic surgery and radiosurgery for treatment of intracranial tumors, arteriovenous malformations, and other surgically treatable conditions using a device known as the N-localizer . New tools that implement artificial intelligence in healthcare have demonstrated higher image quality and morphometric analysis in neuroimaging with
8541-411: The gel upon contact with the scalp. Another solution uses spring loaded pin setups. These may be uncomfortable. They may also be dangerous if they were used in a situation where a patient could bump their head since they could become lodged after an impact trauma incident. Currently, headsets are available incorporating dry electrodes with up to 30 channels. Such designs are able to compensate for some of
8658-539: The general population may have epileptiform abnormalities in an EEG without ever having had a seizure (low false positive rate ) or with a very low risk of developing epilepsy in the future. When a routine EEG is normal and there is a high suspicion or need to confirm epilepsy, it may be repeated or performed with a longer duration in the epilepsy monitoring unit (EMU) or at home with an ambulatory EEG. In addition, there are activating maneuvers such as photic stimulation, hyperventilation and sleep deprivation that can increase
8775-567: The heart can be reduced by timing the MRI pulse according to heart cycles. Blood vessels flow artifacts can be reduced by applying saturation pulses above and below the region of interest. Hepatobiliary MR is used to detect and characterize lesions of the liver , pancreas , and bile ducts . Focal or diffuse disorders of the liver may be evaluated using diffusion-weighted , opposed-phase imaging and dynamic contrast enhancement sequences. Extracellular contrast agents are used widely in liver MRI, and newer hepatobiliary contrast agents also provide
8892-407: The high energy at the focus, the temperature rises to above 65 °C (150 °F) which completely destroys the tissue. This technology can achieve precise ablation of diseased tissue. MR imaging provides a three-dimensional view of the target tissue, allowing for the precise focusing of ultrasound energy. The MR imaging provides quantitative, real-time, thermal images of the treated area. This allows
9009-540: The high-gyromagnetic-ratio hydrogen nucleus instead of the low-gyromagnetic-ratio nucleus that is bonded to the hydrogen atom. In principle, heteronuclear magnetization transfer MRI could be used to detect the presence or absence of specific chemical bonds. Multinuclear imaging is primarily a research technique at present. However, potential applications include functional imaging and imaging of organs poorly seen on H MRI (e.g., lungs and bones) or as alternative contrast agents. Inhaled hyperpolarized He can be used to image
9126-417: The image contrast in a typical scan. The standard display of MR images is to represent fluid characteristics in black-and-white images, where different tissues turn out as follows: MRI has a wide range of applications in medical diagnosis and around 50,000 scanners are estimated to be in use worldwide. MRI affects diagnosis and treatment in many specialties although the effect on improved health outcomes
9243-578: The independent relaxation processes of T 1 ( spin-lattice ; that is, magnetization in the same direction as the static magnetic field) and T 2 ( spin-spin ; transverse to the static magnetic field). To create a T 1 -weighted image, magnetization is allowed to recover before measuring the MR signal by changing the repetition time (TR). This image weighting is useful for assessing the cerebral cortex, identifying fatty tissue, characterizing focal liver lesions, and in general, obtaining morphological information, as well as for post-contrast imaging. To create
9360-409: The interpretation of EEGs for clinical purposes. This is done by visual inspection of the waveforms, called graphoelements. The use of computer signal processing of the EEG – so-called quantitative electroencephalography – is somewhat controversial when used for clinical purposes (although there are many research uses). In the early 1990s Babak Taheri, at University of California, Davis demonstrated
9477-567: The legs (called a "run-off"). A variety of techniques can be used to generate the pictures, such as administration of a paramagnetic contrast agent ( gadolinium ) or using a technique known as "flow-related enhancement" (e.g., 2D and 3D time-of-flight sequences), where most of the signal on an image is due to blood that recently moved into that plane (see also FLASH MRI ). Techniques involving phase accumulation (known as phase contrast angiography) can also be used to generate flow velocity maps easily and accurately. Magnetic resonance venography (MRV)
9594-405: The most streamlined of MRI sequences , there are physical and physiologic limits to the rate of gradient switching. Parallel MRI circumvents these limits by gathering some portion of the data simultaneously, rather than in a traditional sequential fashion. This is accomplished using arrays of radiofrequency (RF) detector coils, each with a different 'view' of the body. A reduced set of gradient steps
9711-486: The musculoskeletal system include spinal imaging , assessment of joint disease, and soft tissue tumors . Also, MRI techniques can be used for diagnostic imaging of systemic muscle diseases including genetic muscle diseases. Swallowing movement of throat and oesophagus can cause motion artifact over the imaged spine. Therefore, a saturation pulse applied over this region the throat and oesophagus can help to avoid this artifact. Motion artifact arising due to pumping of
9828-472: The ones produced by the current dipole of post-synaptic potentials. In addition, since EEGs represent averages of thousands of neurons, a large population of cells in synchronous activity is necessary to cause a significant deflection on the recordings. Action potentials are very fast and, as a consequence, the chances of field summation are slim. However, neural backpropagation , as a typically longer dendritic current dipole, can be picked up by EEG electrodes and
9945-417: The onset and spatio-temporal (location and time) evolution of seizures and the presence of status epilepticus . It is also used to help diagnose sleep disorders , depth of anesthesia , coma , encephalopathies , cerebral hypoxia after cardiac arrest , and brain death . EEG used to be a first-line method of diagnosis for tumors , stroke , and other focal brain disorders, but this use has decreased with
10062-414: The opportunity to perform functional biliary imaging. Anatomical imaging of the bile ducts is achieved by using a heavily T2-weighted sequence in magnetic resonance cholangiopancreatography (MRCP). Functional imaging of the pancreas is performed following administration of secretin . MR enterography provides non-invasive assessment of inflammatory bowel disease and small bowel tumors. MR-colonography may play
10179-717: The parallel imaging methods in most common use today. The advent of parallel MRI resulted in extensive research and development in image reconstruction and RF coil design, as well as in a rapid expansion of the number of receiver channels available on commercial MR systems. Parallel MRI is now used routinely for MRI examinations in a wide range of body areas and clinical or research applications. Most MRI focuses on qualitative interpretation of MR data by acquiring spatial maps of relative variations in signal strength which are "weighted" by certain parameters. Quantitative methods instead attempt to determine spatial maps of accurate tissue relaxometry parameter values or magnetic field, or to measure
10296-441: The physician to ensure that the temperature generated during each cycle of ultrasound energy is sufficient to cause thermal ablation within the desired tissue and if not, to adapt the parameters to ensure effective treatment. Hydrogen has the most frequently imaged nucleus in MRI because it is present in biological tissues in great abundance, and because its high gyromagnetic ratio gives a strong signal. However, any nucleus with
10413-542: The recording in order to highlight or better characterize certain features of the EEG. With digital EEG, all signals are typically digitized and stored in a particular (usually referential) montage; since any montage can be constructed mathematically from any other, the EEG can be viewed by the electroencephalographer in any display montage that is desired. The EEG is read by a clinical neurophysiologist or neurologist (depending on local custom and law regarding medical specialities ), optimally one who has specific training in
10530-422: The recording, a series of activation procedures may be used. These procedures may induce normal or abnormal EEG activity that might not otherwise be seen. These procedures include hyperventilation, photic stimulation (with a strobe light), eye closure, mental activity, sleep and sleep deprivation. During (inpatient) epilepsy monitoring, a patient's typical seizure medications may be withdrawn. The digital EEG signal
10647-676: The region of the brain from which a seizure originates. This can help identify appropriate non-medication treatment options. In clinical use, EEG traces are visually analyzed by neurologists to look at various features. Increasingly, quantitative analysis of EEG is being used in conjunction with visual analysis. Quantitative analysis displays like power spectrum analysis, alpha-delta ratio, amplitude integrated EEG, and spike detection can help quickly identify segments of EEG that need close visual analysis or, in some cases, be used as surrogates for quick identification of seizures in long-term recordings. An EEG might also be helpful for diagnosing or treating
10764-430: The related study of ERPs are used extensively in neuroscience , cognitive science , cognitive psychology , neurolinguistics , and psychophysiological research, as well as to study human functions such as swallowing. Any EEG techniques used in research are not sufficiently standardised for clinical use, and many ERP studies fail to report all of the necessary processing steps for data collection and reduction, limiting
10881-494: The relatively poor spatial sensitivity of EEG, the "one-dimensional signals from localised peripheral regions on the head make it attractive for its simplistic fidelity and has allowed high clinical and basic research throughput". Thus, EEG possesses some advantages over some of those other techniques: EEG also has some characteristics that compare favorably with behavioral testing: Simultaneous EEG recordings and fMRI scans have been obtained successfully, though recording both at
10998-605: The reproducibility and replicability of many studies. Based on a 2024 systematic literature review and meta analysis commissioned by the Patient-Centered Outcomes Research Institute (PCORI), EEG scans cannot be used reliably to assist in making a clinical diagnosis of ADHD. However, EEG continues to be used in research on mental disabilities, such as auditory processing disorder (APD), ADD , and ADHD . EEGs have also been studied for their utility in detecting neurophysiological changes in
11115-421: The resultant evolving spin polarization can induce an RF signal in a radio frequency coil and thereby be detected. In other words, the nuclear magnetic spin of protons in the hydrogen nuclei resonates with the RF incident waves and emit coherent radiation with compact direction, energy (frequency) and phase. This coherent amplified radiation is easily detected by RF antennas close to the subject being examined. It
11232-1012: The resulting NMR signal. The whole system is controlled by one or more computers. MRI requires a magnetic field that is both strong and uniform to a few parts per million across the scan volume. The field strength of the magnet is measured in teslas – and while the majority of systems operate at 1.5 T, commercial systems are available between 0.2 and 7 T. 3T MRI systems, also called 3 Tesla MRIs, have stronger magnets than 1.5 systems and are considered better for images of organs and soft tissue. Whole-body MRI systems for research applications operate in e.g. 9.4T, 10.5T, 11.7T. Even higher field whole-body MRI systems e.g. 14 T and beyond are in conceptual proposal or in engineering design. Most clinical magnets are superconducting magnets, which require liquid helium to keep them at low temperatures. Lower field strengths can be achieved with permanent magnets, which are often used in "open" MRI scanners for claustrophobic patients. Lower field strengths are also used in
11349-860: The same time effectively requires that several technical difficulties be overcome, such as the presence of ballistocardiographic artifact, MRI pulse artifact and the induction of electrical currents in EEG wires that move within the strong magnetic fields of the MRI. While challenging, these have been successfully overcome in a number of studies. MRI's produce detailed images created by generating strong magnetic fields that may induce potentially harmful displacement force and torque. These fields produce potentially harmful radio frequency heating and create image artifacts rendering images useless. Due to these potential risks, only certain medical devices can be used in an MR environment. Similarly, simultaneous recordings with MEG and EEG have also been conducted, which has several advantages over using either technique alone: Recently,
11466-408: The same time, they can push their neighbours, who push their neighbours, and so on, in a wave. This process is known as volume conduction. When the wave of ions reaches the electrodes on the scalp, they can push or pull electrons on the metal in the electrodes. Since metal conducts the push and pull of electrons easily, the difference in push or pull voltages between any two electrodes can be measured by
11583-680: The sample or patient. The spatial resolution is much lower (limited by the available SNR ), but the spectra in each voxel contains information about many metabolites. Because the available signal is used to encode spatial and spectral information, MRSI requires high SNR achievable only at higher field strengths (3 T and above). The high procurement and maintenance costs of MRI with extremely high field strengths inhibit their popularity. However, recent compressed sensing -based software algorithms ( e.g. , SAMV ) have been proposed to achieve super-resolution without requiring such high field strengths. Real-time magnetic resonance imaging (RT-MRI) refers to
11700-401: The scalp. Each electrode is connected to one input of a differential amplifier (one amplifier per pair of electrodes); a common system reference electrode is connected to the other input of each differential amplifier. These amplifiers amplify the voltage between the active electrode and the reference (typically 1,000–100,000 times, or 60–100 dB of power gain). In analog EEG, the signal
11817-403: The scan to remove the agent from the body promptly. In Europe, where more gadolinium-containing agents are available, a classification of agents according to potential risks has been released. In 2008, a new contrast agent named gadoxetate , brand name Eovist (US) or Primovist (EU), was approved for diagnostic use: This has the theoretical benefit of a dual excretion path. An MRI sequence
11934-668: The sensitivity of the contrast agents, these targeting moieties are usually linked to high payload MRI contrast agents or MRI contrast agents with high relaxivities. A new class of gene targeting MR contrast agents has been introduced to show gene action of unique mRNA and gene transcription factor proteins. These new contrast agents can trace cells with unique mRNA, microRNA and virus; tissue response to inflammation in living brains. The MR reports change in gene expression with positive correlation to TaqMan analysis, optical and electron microscopy. It takes time to gather MRI data using sequential applications of magnetic field gradients. Even for
12051-444: The signal across the chest. Interpretation of an ECG is the basis of a number of cardiac diseases including myocardial infarction (heart attack) and arrhythmias such as atrial fibrillation . When electrical recordings are made from the skin , it is considered to be an ECG as described above. However, electrical recordings made from within the heart such as with an artificial cardiac pacemaker or during an electrophysiology study ,
12168-435: The signal quality degradation related to high impedances by optimizing pre-amplification, shielding and supporting mechanics. EEG has several limitations. Most important is its poor spatial resolution. EEG is most sensitive to a particular set of post-synaptic potentials: those generated in superficial layers of the cortex, on the crests of gyri directly abutting the skull and radial to the skull. Dendrites which are deeper in
12285-402: The signals produced by electroencephalography. EEG thus provides information with a large bias in favor of particular neuron types, locations and orientations. So it generally should not be used to make claims about global brain activity. The meninges , cerebrospinal fluid and skull "smear" the EEG signal, obscuring its intracranial source. Electrogram An electroencephalogram (EEG)
12402-478: The signals recorded are considered an "electrogram" instead of an ECG. These signals are not interpreted in the same manner as an ECG. An electromyogram (EMG) is an electrical recording of the activity of a muscle or muscle group. An EMG study can be combined with a nerve conduction study to diagnose neuromuscular diseases such as peripheral neuropathy and amyotrophic lateral sclerosis . Magnetic resonance imaging Magnetic resonance imaging ( MRI )
12519-604: The size of certain spatial features. Examples of quantitative MRI methods are: Quantitative MRI aims to increase the reproducibility of MR images and interpretations, but has historically require longer scan times. Quantitative MRI (or qMRI) sometimes more specifically refers to multi-parametric quantitative MRI, the mapping of multiple tissue relaxometry parameters in a single imaging session. Efforts to make multi-parametric quantitative MRI faster have produced sequences which map multiple parameters simultaneously, either by building separate encoding methods for each parameter into
12636-455: The spin magnetization vector will slowly return from the xy-plane back to the equilibrium state. The time it takes for the magnetization vector to return to its equilibrium value, M z , is referred to as the longitudinal relaxation time, T 1 . Subsequently, the rate at which this happens is simply the reciprocal of the relaxation time: 1 T 1 = R 1 {\displaystyle {\frac {1}{T1}}=R1} . Similarly,
12753-458: The surface of the brain, under the surface of the dura mater . This is accomplished via burr hole or craniotomy . This is referred to variously as "electrocorticography (ECoG)" , "intracranial EEG (I-EEG)" or "subdural EEG (SD-EEG)". Depth electrodes may also be placed into brain structures, such as the amygdala or hippocampus , structures, which are common epileptic foci and may not be "seen" clearly by scalp EEG. The electrocorticographic signal
12870-484: The time in which it takes for M xy to return to zero is T 2 , with the rate 1 T 2 = R 2 {\displaystyle {\frac {1}{T2}}=R2} . Magnetization as a function of time is defined by the Bloch equations . T 1 and T 2 values are dependent on the chemical environment of the sample; hence their utility in MRI. Soft tissue and muscle tissue relax at different rates, yielding
12987-551: The tissue they accumulate in, or super-paramagnetic (SPIONs), and are used to shorten T2 and T2* in healthy tissue reducing its signal intensity (negative contrast agents). The most commonly used intravenous contrast agents are based on chelates of gadolinium , which is highly paramagnetic. In general, these agents have proved safer than the iodinated contrast agents used in X-ray radiography or CT. Anaphylactoid reactions are rare, occurring in approx. 0.03–0.1%. Of particular interest
13104-432: The two is complex, with a combination of EEG power in the gamma band and phase in the delta band relating most strongly to neuron spike activity. In conventional scalp EEG, the recording is obtained by placing electrodes on the scalp with a conductive gel or paste, usually after preparing the scalp area by light abrasion to reduce impedance due to dead skin cells. Many systems typically use electrodes, each of which
13221-541: The usually longer and louder measurements with the subject in a long, confining tube, although "open" MRI designs mostly relieve this. Additionally, implants and other non-removable metal in the body can pose a risk and may exclude some patients from undergoing an MRI examination safely. MRI was originally called NMRI (nuclear magnetic resonance imaging), but "nuclear" was dropped to avoid negative associations . Certain atomic nuclei are able to absorb radio frequency (RF) energy when placed in an external magnetic field ;
13338-400: The utility of MRI to capture neuronal tracts and blood flow respectively in the nervous system, in addition to detailed spatial images. The sustained increase in demand for MRI within health systems has led to concerns about cost effectiveness and overdiagnosis . In most medical applications, hydrogen nuclei, which consist solely of a proton , that are in tissues create a signal that
13455-420: The various sleep stages ). These oscillations represent synchronized activity over a network of neurons. The neuronal networks underlying some of these oscillations are understood (e.g., the thalamocortical resonance underlying sleep spindles ), while many others are not (e.g., the system that generates the posterior basic rhythm). Research that measures both EEG and neuron spiking finds the relationship between
13572-469: Was analysed using software to identify patterns in the noise. A basic pattern was identified and used to control a switch: Above average activity was set to on, below average off. As well as enabling Jatich to control a computer cursor the signals were also used to drive the nerve controllers embedded in his hands, restoring some movement. In 2018, a functional dry electrode composed of a polydimethylsiloxane elastomer filled with conductive carbon nanofibers
13689-520: Was reported. This research was conducted at the U.S. Army Research Laboratory . EEG technology often involves applying a gel to the scalp which facilitates strong signal-to-noise ratio. This results in more reproducible and reliable experimental results. Since patients dislike having their hair filled with gel, and the lengthy setup requires trained staff on hand, utilizing EEG outside the laboratory setting can be difficult. Additionally, it has been observed that wet electrode sensors' performance reduces after
#261738