An electrogram ( EGM ) is a recording of electrical activity of organs such as the brain and heart , measured by monitoring changes in electric potential .
104-438: 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
208-470: 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
312-562: A 0.2 mm resolution. With modern dual-energy CT scanners, new areas of use have been established, such as aiding in the diagnosis of gout . CT is used in biomechanics to quickly reveal the geometry, anatomy, density and elastic moduli of biological tissues. Industrial CT scanning (industrial computed tomography) is a process which uses X-ray equipment to produce 3D representations of components both externally and internally. Industrial CT scanning has been used in many areas of industry for internal inspection of components. Some of
416-466: 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
520-700: 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
624-588: A computer using tomographic reconstruction algorithms to produce tomographic (cross-sectional) images (virtual "slices") of a body. CT scans can be used in patients with metallic implants or pacemakers, for whom magnetic resonance imaging (MRI) is contraindicated . Since its development in the 1970s, CT scanning has proven to be a versatile imaging technique. While CT is most prominently used in medical diagnosis , it can also be used to form images of non-living objects. The 1979 Nobel Prize in Physiology or Medicine
728-514: A full roll-out on 1 December 2022 and the TSA spent $ 781.2 million on an order for over 1,000 scanners, ready to go live in the summer. X-ray CT is used in geological studies to quickly reveal materials inside a drill core. Dense minerals such as pyrite and barite appear brighter and less dense components such as clay appear dull in CT images. Traditional methods of studying fossils are often destructive, such as
832-444: A key role in the fast-evolving field of transcatheter structural heart interventions , more specifically in the transcatheter repair and replacement of heart valves. The main forms of cardiac CT scanning are: To better visualize the anatomy, post-processing of the images is common. Most common are multiplanar reconstructions (MPR) and volume rendering . For more complex anatomies and procedures, such as heart valve interventions,
936-427: A mix of for example coloring and shading in order to create realistic and observable representations. Two-dimensional CT images are conventionally rendered so that the view is as though looking up at it from the patient's feet. Hence, the left side of the image is to the patient's right and vice versa, while anterior in the image also is the patient's anterior and vice versa. This left-right interchange corresponds to
1040-465: A particular location and then stops which is followed by the X-ray tube rotation and acquisition of a slice. The table then increments again, and another slice is taken. The table movement stops while taking slices. This results in an increased time of scanning. Spinning tube, commonly called spiral CT , or helical CT, is an imaging technique in which an entire X-ray tube is spun around the central axis of
1144-541: 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
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#17328490065881248-467: 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
1352-455: 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
1456-504: 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
1560-468: 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
1664-406: 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
1768-423: 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
1872-479: A technique to improve temporal resolution. Electron beam tomography (EBT) is a specific form of CT in which a large enough X-ray tube is constructed so that only the path of the electrons , travelling between the cathode and anode of the X-ray tube, are spun using deflection coils . This type had a major advantage since sweep speeds can be much faster, allowing for less blurry imaging of moving structures, such as
1976-416: A true 3D reconstruction or a 3D print is created based on these CT images to gain a deeper understanding. CT is an accurate technique for diagnosis of abdominal diseases like Crohn's disease , GIT bleeding, and diagnosis and staging of cancer, as well as follow-up after cancer treatment to assess response. It is commonly used to investigate acute abdominal pain . Non-enhanced computed tomography
2080-413: A very high dynamic range which must be reduced for display or printing. This is typically done via a process of "windowing", which maps a range (the "window") of pixel values to a grayscale ramp. For example, CT images of the brain are commonly viewed with a window extending from 0 HU to 80 HU. Pixel values of 0 and lower, are displayed as black; values of 80 and higher are displayed as white; values within
2184-433: 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
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#17328490065882288-419: Is a medical imaging technique used to obtain detailed internal images of the body. The personnel that perform CT scans are called radiographers or radiology technologists. CT scanners use a rotating X-ray tube and a row of detectors placed in a gantry to measure X-ray attenuations by different tissues inside the body. The multiple X-ray measurements taken from different angles are then processed on
2392-447: 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
2496-406: Is a specific form of CT to assess flow through blood vessels whilst injecting a contrast agent . Blood flow, blood transit time, and organ blood volume, can all be calculated with reasonable sensitivity and specificity . This type of CT may be used on the heart , although sensitivity and specificity for detecting abnormalities are still lower than for other forms of CT. This may also be used on
2600-408: Is a two dimensional unit based on the matrix size and the field of view. When the CT slice thickness is also factored in, the unit is known as a voxel , which is a three-dimensional unit. Water has an attenuation of 0 Hounsfield units (HU), while air is −1,000 HU, cancellous bone is typically +400 HU, and cranial bone can reach 2,000 HU. The attenuation of metallic implants depends on
2704-405: Is a type of contrast CT to visualize the arteries and veins throughout the body. This ranges from arteries serving the brain to those bringing blood to the lungs , kidneys , arms and legs . An example of this type of exam is CT pulmonary angiogram (CTPA) used to diagnose pulmonary embolism (PE). It employs computed tomography and an iodine-based contrast agent to obtain an image of
2808-412: 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
2912-468: Is also under consideration for automated baggage/parcel security scanning using computer vision based object recognition algorithms that target the detection of specific threat items based on 3D appearance (e.g. guns, knives, liquid containers). Its usage in airport security pioneered at Shannon Airport in March 2022 has ended the ban on liquids over 100 ml there, a move that Heathrow Airport plans for
3016-402: 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
3120-525: 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
3224-454: 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
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3328-560: Is called high resolution CT that produces a sampling of the lung, and not continuous images. Bronchial wall thickening can be seen on lung CTs and generally (but not always) implies inflammation of the bronchi . An incidentally found nodule in the absence of symptoms (sometimes referred to as an incidentaloma ) may raise concerns that it might represent a tumor, either benign or malignant . Perhaps persuaded by fear, patients and doctors sometimes agree to an intensive schedule of CT scans, sometimes up to every three months and beyond
3432-505: 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
3536-458: Is how to reduce the radiation dose during CT examinations without compromising the image quality. In general, higher radiation doses result in higher-resolution images, while lower doses lead to increased image noise and unsharp images. However, increased dosage raises the adverse side effects, including the risk of radiation-induced cancer – a four-phase abdominal CT gives the same radiation dose as 300 chest X-rays. Several methods that can reduce
3640-695: Is imaging the contents of sarcophagi or ceramics. Recently, CWI in Amsterdam has collaborated with Rijksmuseum to investigate art object inside details in the framework called IntACT. Varied types of fungus can degrade wood to different degrees, one Belgium research group has been used X-ray CT 3 dimension with sub-micron resolution unveiled fungi can penetrate micropores of 0.6 μm under certain conditions. Sawmills use industrial CT scanners to detect round defects, for instance knots, to improve total value of timber productions. Most sawmills are planning to incorporate this robust detection tool to improve productivity in
3744-461: Is limited technique as it displays only the surfaces that meet a particular threshold density, and which are towards the viewer. However, In volume rendering, transparency, colours and shading are used which makes it easy to present a volume in a single image. For example, Pelvic bones could be displayed as semi-transparent, so that, even viewing at an oblique angle one part of the image does not hide another. An important issue within radiology today
3848-409: 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
3952-607: Is often the preferred investigation modality for thyroid abnormalities. A CT scan can be used for detecting both acute and chronic changes in the lung parenchyma , the tissue of the lungs . It is particularly relevant here because normal two-dimensional X-rays do not show such defects. A variety of techniques are used, depending on the suspected abnormality. For evaluation of chronic interstitial processes such as emphysema , and fibrosis , thin sections with high spatial frequency reconstructions are used; often scans are performed both on inspiration and expiration. This special technique
4056-441: Is possible as present CT scanners provide almost isotropic resolution. MPR is used almost in every scan. The spine is frequently examined with it. An image of the spine in axial plane can only show one vertebral bone at a time and cannot show its relation with other vertebral bones. By reformatting the data in other planes, visualization of the relative position can be achieved in sagittal and coronal plane. New software allows
4160-452: 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
4264-476: Is set by the operator (e.g., a level that corresponds to bone). With the help of edge detection image processing algorithms a 3D model can be constructed from the initial data and displayed on screen. Various thresholds can be used to get multiple models, each anatomical component such as muscle, bone and cartilage can be differentiated on the basis of different colours given to them. However, this mode of operation cannot show interior structures. Surface rendering
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4368-423: 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
4472-469: 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
4576-521: Is today the gold standard for diagnosing urinary stones . The size, volume and density of stones can be estimated to help clinicians guide further treatment; size is especially important in predicting spontaneous passage of a stone. For the axial skeleton and extremities , CT is often used to image complex fractures , especially ones around joints, because of its ability to reconstruct the area of interest in multiple planes. Fractures, ligamentous injuries, and dislocations can easily be recognized with
4680-578: 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
4784-426: 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
4888-458: The brain , where CT perfusion imaging can often detect poor brain perfusion well before it is detected using a conventional spiral CT scan. This is better for stroke diagnosis than other CT types. Positron emission tomography–computed tomography is a hybrid CT modality which combines, in a single gantry, a positron emission tomography (PET) scanner and an X-ray computed tomography (CT) scanner, to acquire sequential images from both devices in
4992-443: 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
5096-544: 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
5200-411: The pulmonary arteries . CT scans can reduce the risk of angiography by providing clinicians with more information about the positioning and number of clots prior to the procedure. A CT scan of the heart is performed to gain knowledge about cardiac or coronary anatomy. Traditionally, cardiac CT scans are used to detect, diagnose, or follow up coronary artery disease . More recently CT has played
5304-423: The 1970s, CT has become an important tool in medical imaging to supplement conventional X-ray imaging and medical ultrasonography . It has more recently been used for preventive medicine or screening for disease, for example, CT colonography for people with a high risk of colon cancer , or full-motion heart scans for people with a high risk of heart disease. Several institutions offer full-body scans for
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#17328490065885408-442: 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
5512-401: 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
5616-475: 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
5720-461: The area being scanned. These are the dominant type of scanners on the market because they have been manufactured longer and offer a lower cost of production and purchase. The main limitation of this type of CT is the bulk and inertia of the equipment (X-ray tube assembly and detector array on the opposite side of the circle) which limits the speed at which the equipment can spin. Some designs use two X-ray sources and detector arrays offset by an angle, as
5824-408: The atomic number of the element used: Titanium usually has an amount of +1000 HU, iron steel can completely block the X-ray and is, therefore, responsible for well-known line-artifacts in computed tomograms. Artifacts are caused by abrupt transitions between low- and high-density materials, which results in data values that exceed the dynamic range of the processing electronics. CT data sets have
5928-505: The bends in a vessel, thereby helping to visualize a whole vessel in a single image or in multiple images. After a vessel has been "straightened", measurements such as cross-sectional area and length can be made. This is helpful in preoperative assessment of a surgical procedure. For 2D projections used in radiation therapy for quality assurance and planning of external beam radiotherapy , including digitally reconstructed radiographs, see Beam's eye view . A threshold value of radiodensity
6032-579: 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
6136-446: The conservation and preservation of objects of cultural heritage. For many fragile objects, direct research and observation can be damaging and can degrade the object over time. Using CT scans, conservators and researchers are able to determine the material composition of the objects they are exploring, such as the position of ink along the layers of a scroll, without any additional harm. These scans have been optimal for research focused on
6240-500: 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
6344-416: 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
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#17328490065886448-409: 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,
6552-520: 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
6656-528: 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
6760-607: 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
6864-453: 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
6968-411: 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
7072-409: The general population although this practice goes against the advice and official position of many professional organizations in the field primarily due to the radiation dose applied. The use of CT scans has increased dramatically over the last two decades in many countries. An estimated 72 million scans were performed in the United States in 2007 and more than 80 million in 2015. CT scanning of
7176-539: 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
7280-570: The head is also used in CT- 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 . Contrast CT is generally the initial study of choice for neck masses in adults. CT of the thyroid plays an important role in the evaluation of thyroid cancer . CT scan often incidentally finds thyroid abnormalities, and so
7384-453: The head is typically used to detect infarction ( stroke ), tumors , calcifications , haemorrhage , and bone trauma . Of the above, hypodense (dark) structures can indicate edema and infarction, hyperdense (bright) structures indicate calcifications and haemorrhage and bone trauma can be seen as disjunction in bone windows. Tumors can be detected by the swelling and anatomical distortion they cause, or by surrounding edema. CT scanning of
7488-578: The heart and arteries. Fewer scanners of this design have been produced when compared with spinning tube types, mainly due to the higher cost associated with building a much larger X-ray tube and detector array and limited anatomical coverage. Dual Energy CT, also known as Spectral CT, is an advancement of Computed Tomography in which two energies are used to create two sets of data. A Dual Energy CT may employ Dual source, Single source with dual detector layer, Single source with energy switching methods to get two different sets of data. CT perfusion imaging
7592-516: The insides of these objects, as was the case with the virtual unwrapping of the En-Gedi scroll and the Herculaneum papyri . Micro-CT has also proved useful for analyzing more recent artifacts such as still-sealed historic correspondence that employed the technique of letterlocking (complex folding and cuts) that provided a "tamper-evident locking mechanism". Further examples of use cases in archaeology
7696-409: 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
7800-487: The key uses for CT scanning have been flaw detection, failure analysis, metrology, assembly analysis, image-based finite element methods and reverse engineering applications. CT scanning is also employed in the imaging and conservation of museum artifacts. CT scanning has also found an application in transport security (predominantly airport security ) where it is currently used in a materials analysis context for explosives detection CTX (explosive-detection device) and
7904-441: The long run, however initial investment cost is high. The result of a CT scan is a volume of voxels , which may be presented to a human observer by various methods, which broadly fit into the following categories: Technically, all volume renderings become projections when viewed on a 2-dimensional display , making the distinction between projections and volume renderings a bit vague. The epitomes of volume rendering models feature
8008-472: 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
8112-417: 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
8216-587: The recommended guidelines, in an attempt to do surveillance on the nodules. However, established guidelines advise that patients without a prior history of cancer and whose solid nodules have not grown over a two-year period are unlikely to have any malignant cancer. For this reason, and because no research provides supporting evidence that intensive surveillance gives better outcomes, and because of risks associated with having CT scans, patients should not receive CT screening in excess of those recommended by established guidelines. Computed tomography angiography (CTA)
8320-450: The reconstruction of data in non-orthogonal (oblique) planes, which help in the visualization of organs which are not in orthogonal planes. It is better suited for visualization of the anatomical structure of the bronchi as they do not lie orthogonal to the direction of the scan. Curved-plane reconstruction (or curved planar reformation = CPR) is performed mainly for the evaluation of vessels. This type of reconstruction helps to straighten
8424-542: 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
8528-422: 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
8632-676: 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
8736-430: 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
8840-494: 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
8944-588: 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
9048-479: The same session, which are combined into a single superposed ( co-registered ) image. Thus, functional imaging obtained by PET, which depicts the spatial distribution of metabolic or biochemical activity in the body can be more precisely aligned or correlated with anatomic imaging obtained by CT scanning. PET-CT gives both anatomical and functional details of an organ under examination and is helpful in detecting different type of cancers. Since its introduction in
9152-906: 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,
9256-408: 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
9360-401: 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
9464-444: 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 ,
9568-435: 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
9672-402: 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)
9776-544: 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 . Computed tomography A computed tomography scan ( CT scan ), formerly called computed axial tomography scan ( CAT scan ),
9880-458: 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
9984-432: 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
10088-422: The use of thin sections and physical preparation. X-ray CT is used in paleontology to non-destructively visualize fossils in 3D. This has many advantages. For example, we can look at fragile structures that might never otherwise be able to be studied. In addition, one can freely move around models of fossils in virtual 3D space to inspect it without damaging the fossil. X-ray CT and micro-CT can also be used for
10192-420: 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
10296-453: The view that physicians generally have in reality when positioned in front of patients. Pixels in an image obtained by CT scanning are displayed in terms of relative radiodensity . The pixel itself is displayed according to the mean attenuation of the tissue(s) that it corresponds to on a scale from +3,071 (most attenuating) to −1,024 (least attenuating) on the Hounsfield scale . A pixel
10400-529: The window are displayed as a gray intensity proportional to position within the window. The window used for display must be matched to the X-ray density of the object of interest, in order to optimize the visible detail. Window width and window level parameters are used to control the windowing of a scan. Multiplanar reconstruction (MPR) is the process of converting data from one anatomical plane (usually transverse ) to other planes. It can be used for thin slices as well as projections. Multiplanar reconstruction
10504-553: The workings of the Antikythera mechanism or the text hidden inside the charred outer layers of the En-Gedi Scroll . However, they are not optimal for every object subject to these kinds of research questions, as there are certain artifacts like the Herculaneum papyri in which the material composition has very little variation along the inside of the object. After scanning these objects, computational methods can be employed to examine
10608-469: 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
10712-436: Was awarded jointly to South African-American physicist Allan MacLeod Cormack and British electrical engineer Godfrey Hounsfield "for the development of computer-assisted tomography". On the basis of image acquisition and procedures, various type of scanners are available in the market. Sequential CT, also known as step-and-shoot CT, is a type of scanning method in which the CT table moves stepwise. The table increments to
10816-520: 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
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