What is brain imaging technology

what is brain imaging technology

Neuroimaging

May 17,  · Brain imaging techniques allow doctors and researchers to view activity or problems within the human brain, without invasive neurosurgery. There are a . Brain imaging techniques provide the ability to non-invasively map the structure and function of the brain.

Brain imaging techniques allow doctors and researchers to view activity or problems within the human brain, without invasive neurosurgery.

There are a number of accepted, safe imaging techniques in use today in research facilities and hospitals throughout the world. Functional magnetic resonance imaging, or fMRI, is a technique for measuring brain activity. It works by detecting the changes in blood oxygenation and flow that occur in response to neural activity — when a brain area is more active it consumes more oxygen and to meet this increased demand blood flow increases to the active area.

Computed tomography CT scanning builds up a picture of the brain based on the differential absorption of X-rays. During a CT scan the subject lies on a table that slides in and out of a hollow, cylindrical apparatus. An x-ray source rides on a ring around the inside of the tube, with its beam aimed at the subjects head. Images made using x-rays depend on the absorption of the beam by the tissue it passes through. Bone the tongue weight of a trailer should be what percentage hard tissue absorb x-rays well, air and water absorb very little and soft tissue is somewhere in between.

Thus, CT scans reveal the gross features of the brain but do not resolve its structure well. Positron Emission Tomography PET uses trace amounts of short-lived radioactive material to map functional processes in the brain.

When the material undergoes radioactive decay a positron is emitted, which can be picked up be the detector. Areas of high radioactivity are associated with brain activity. Electroencephalography EEG is the measurement of the electrical activity of the brain by recording from electrodes placed on the scalp.

The resulting traces are known as an electroencephalogram EEG and represent an electrical signal from a large number of neurons. EEGs are frequently used in experimentation because the process is non-invasive to the research subject. The EEG is capable of detecting changes in electrical activity in the brain on a millisecond-level.

It is one of the few techniques available that has such high temporal resolution. Magnetoencephalography MEG is an imaging technique used to measure the magnetic fields produced by electrical activity in the brain via extremely sensitive devices known as SQUIDs. These measurements what is brain imaging technology commonly used in both research and clinical settings.

There are many uses for the MEG, including assisting surgeons in localizing a pathology, assisting researchers in determining the function of various parts of the brain, neurofeedback, and others.

Near infrared spectroscopy is an optical technique for measuring blood oxygenation in the brain. It works by shining light in the near infrared part of the spectrum nm through the skull and detecting how much the remerging light is attenuated.

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Functional magnetic resonance imaging (fMRI) scans are a series of MRIs measuring brain function via a computer’s combination of multiple images taken less than a second apart. Computed tomography (CT) scans are oblique X-ray slices that show the density of brain structures. Magnetic resonance imaging (MRI) uses changes in electrically charged molecules in a magnetic field to form images of the brain. Both technologies are more precise than ordinary X-rays and can help find problems when people fall ill. Introduction to brain imaging technologies Brain imaging techniques is a term which covers a range of different methods used to produce images of the brain. Images can be either structural (showing the structure of the brain) or functional (showing the activity of different parts of the brain.

Neuroimaging or brain imaging is the use of various techniques to either directly or indirectly image the structure , function, or pharmacology of the nervous system. It is a relatively new discipline within medicine , neuroscience , and psychology. Neuroimaging falls into two broad categories:. Functional imaging enables, for example, the processing of information by centers in the brain to be visualized directly.

Such processing causes the involved area of the brain to increase metabolism and "light up" on the scan. One of the more controversial uses of neuroimaging has been researching " thought identification " or mind-reading. The first chapter of the history of neuroimaging traces back to the Italian neuroscientist Angelo Mosso who invented the 'human circulation balance', which could non-invasively measure the redistribution of blood during emotional and intellectual activity.

In , the American neurosurgeon Walter Dandy introduced the technique of ventriculography. X-ray images of the ventricular system within the brain were obtained by injection of filtered air directly into one or both lateral ventricles of the brain. Dandy also observed that air introduced into the subarachnoid space via lumbar spinal puncture could enter the cerebral ventricles and also demonstrate the cerebrospinal fluid compartments around the base of the brain and over its surface.

This technique was called pneumoencephalography. In , Egas Moniz introduced cerebral angiography , whereby both normal and abnormal blood vessels in and around the brain could be visualized with great precision.

In the early s, Allan McLeod Cormack and Godfrey Newbold Hounsfield introduced computerized axial tomography CAT or CT scanning , and ever more detailed anatomic images of the brain became available for diagnostic and research purposes. In the early s MRI was introduced clinically, and during the s a veritable explosion of technical refinements and diagnostic MR applications took place.

Scientists soon learned that the large blood flow changes measured by PET could also be imaged by the correct type of MRI. Functional magnetic resonance imaging fMRI was born, and since the s, fMRI has come to dominate the brain mapping field due to its low invasiveness, lack of radiation exposure, and relatively wide availability.

In the early s, the field of neuroimaging reached the stage where limited practical applications of functional brain imaging have become feasible. The main application area is crude forms of brain-computer interface. Neuroimaging follows a neurological examination in which a physician has found cause to more deeply investigate a patient who has or may have a neurological disorder.

One of the more common neurological problems which a person may experience is simple syncope. Neuroimaging is not indicated for patients with stable headaches which are diagnosed as migraine. Another indication for neuroimaging is CT-, MRI- and PET- guided stereotactic surgery or radiosurgery for treatment of intracranial tumors, arteriovenous malformations and other surgically treatable conditions. Typically used for quickly viewing brain injuries , CT scanning uses a computer program that performs a numerical integral calculation the inverse Radon transform on the measured x-ray series to estimate how much of an x-ray beam is absorbed in a small volume of the brain.

Typically the information is presented as cross-sections of the brain. Diffuse optical imaging DOI or diffuse optical tomography DOT is a medical imaging modality which uses near infrared light to generate images of the body.

The technique measures the optical absorption of haemoglobin , and relies on the absorption spectrum of haemoglobin varying with its oxygenation status. High-density diffuse optical tomography HD-DOT has been compared directly to fMRI using response to visual stimulation in subjects studied with both techniques, with reassuringly similar results. Event-related optical signal EROS is a brain-scanning technique which uses infrared light through optical fibers to measure changes in optical properties of active areas of the cerebral cortex.

Whereas techniques such as diffuse optical imaging DOT and near-infrared spectroscopy NIRS measure optical absorption of haemoglobin, and thus are based on blood flow, EROS takes advantage of the scattering properties of the neurons themselves and thus provides a much more direct measure of cellular activity. EROS can pinpoint activity in the brain within millimeters spatially and within milliseconds temporally.

Its biggest downside is the inability to detect activity more than a few centimeters deep. EROS is a new, relatively inexpensive technique that is non-invasive to the test subject. Gabriele Gratton and Dr. Monica Fabiani. Magnetic resonance imaging MRI uses magnetic fields and radio waves to produce high quality two- or three-dimensional images of brain structures without the use of ionizing radiation X-rays or radioactive tracers.

Functional magnetic resonance imaging fMRI and arterial spin labeling ASL relies on the paramagnetic properties of oxygenated and deoxygenated hemoglobin to see images of changing blood flow in the brain associated with neural activity. This allows images to be generated that reflect which brain structures are activated and how during the performance of different tasks or at resting state.

According to the oxygenation hypothesis, changes in oxygen usage in regional cerebral blood flow during cognitive or behavioral activity can be associated with the regional neurons as being directly related to the cognitive or behavioral tasks being attended.

Most fMRI scanners allow subjects to be presented with different visual images, sounds and touch stimuli, and to make different actions such as pressing a button or moving a joystick.

Consequently, fMRI can be used to reveal brain structures and processes associated with perception, thought and action. The resolution of fMRI is about millimeters at present, limited by the spatial spread of the hemodynamic response to neural activity. It has largely superseded PET for the study of brain activation patterns. PET, however, retains the significant advantage of being able to identify specific brain receptors or transporters associated with particular neurotransmitters through its ability to image radiolabelled receptor "ligands" receptor ligands are any chemicals that stick to receptors.

As well as research on healthy subjects, fMRI is increasingly used for the medical diagnosis of disease. Because fMRI is exquisitely sensitive to oxygen usage in blood flow, it is extremely sensitive to early changes in the brain resulting from ischemia abnormally low blood flow , such as the changes which follow stroke.

Early diagnosis of certain types of stroke is increasingly important in neurology, since substances which dissolve blood clots may be used in the first few hours after certain types of stroke occur, but are dangerous to use afterward. Brain changes seen on fMRI may help to make the decision to treat with these agents.

Magnetoencephalography MEG is an imaging technique used to measure the magnetic fields produced by electrical activity in the brain via extremely sensitive devices such as superconducting quantum interference devices SQUIDs or spin exchange relaxation-free [17] SERF magnetometers.

MEG offers a very direct measurement of neural electrical activity compared to fMRI for example with very high temporal resolution but relatively low spatial resolution. The advantage of measuring the magnetic fields produced by neural activity is that they are likely to be less distorted by surrounding tissue particularly the skull and scalp compared to the electric fields measured by electroencephalography EEG.

Specifically, it can be shown that magnetic fields produced by electrical activity are not affected by the surrounding head tissue, when the head is modeled as a set of concentric spherical shells, each being an isotropic homogeneous conductor. Real heads are non-spherical and have largely anisotropic conductivities particularly white matter and skull.

This makes it likely that MEG is also affected by the skull anisotropy, [19] although probably not to the same degree as EEG.

There are many uses for MEG, including assisting surgeons in localizing a pathology, assisting researchers in determining the function of various parts of the brain, neurofeedback, and others. Positron emission tomography PET and brain positron emission tomography , measure emissions from radioactively labeled metabolically active chemicals that have been injected into the bloodstream. The emission data are computer-processed to produce 2- or 3-dimensional images of the distribution of the chemicals throughout the brain.

The labeled compound, called a radiotracer , is injected into the bloodstream and eventually makes its way to the brain. Sensors in the PET scanner detect the radioactivity as the compound accumulates in various regions of the brain. A computer uses the data gathered by the sensors to create multicolored 2- or 3-dimensional images that show where the compound acts in the brain.

Especially useful are a wide array of ligands used to map different aspects of neurotransmitter activity, with by far the most commonly used PET tracer being a labeled form of glucose see Fludeoxyglucose 18F FDG.

The greatest benefit of PET scanning is that different compounds can show blood flow and oxygen and glucose metabolism in the tissues of the working brain. These measurements reflect the amount of brain activity in the various regions of the brain and allow to learn more about how the brain works.

PET scans were superior to all other metabolic imaging methods in terms of resolution and speed of completion as little as 30 seconds when they first became available. The improved resolution permitted better study to be made as to the area of the brain activated by a particular task. The biggest drawback of PET scanning is that because the radioactivity decays rapidly, it is limited to monitoring short tasks. PET scanning is also used for diagnosis of brain disease, most notably because brain tumors, strokes, and neuron-damaging diseases which cause dementia such as Alzheimer's disease all cause great changes in brain metabolism, which in turn causes easily detectable changes in PET scans.

PET is probably most useful in early cases of certain dementias with classic examples being Alzheimer's disease and Pick's disease where the early damage is too diffuse and makes too little difference in brain volume and gross structure to change CT and standard MRI images enough to be able to reliably differentiate it from the "normal" range of cortical atrophy which occurs with aging in many but not all persons, and which does not cause clinical dementia.

Single-photon emission computed tomography SPECT is similar to PET and uses gamma ray -emitting radioisotopes and a gamma camera to record data that a computer uses to construct two- or three-dimensional images of active brain regions. These properties of SPECT make it particularly well-suited for epilepsy imaging, which is usually made difficult by problems with patient movement and variable seizure types. SPECT provides a "snapshot" of cerebral blood flow since scans can be acquired after seizure termination so long as the radioactive tracer was injected at the time of the seizure.

Tomographic reconstruction , mainly used for functional "snapshots" of the brain requires multiple projections from Detector Heads which rotate around the human skull, so some researchers have developed 6 and 11 Detector Head SPECT machines to cut imaging time and give higher resolution.

Like PET, SPECT also can be used to differentiate different kinds of disease processes which produce dementia, and it is increasingly used for this purpose. These must be made in a cyclotron, and are expensive or even unavailable if necessary transport times are prolonged more than a few half-lives. SPECT, however, is able to make use of tracers with much longer half-lives, such as technetiumm, and as a result, is far more widely available. Cranial ultrasound is usually only used in babies, whose open fontanelles provide acoustic windows allowing ultrasound imaging of the brain.

Advantages include the absence of ionising radiation and the possibility of bedside scanning, but the lack of soft-tissue detail means MRI is preferred for some conditions. Functional ultrasound imaging fUS is a medical ultrasound imaging technique of detecting or measuring changes in neural activities or metabolism, for example, the loci of brain activity, typically through measuring blood flow or hemodynamic changes.

Functional ultrasound relies on Ultrasensitive Doppler and ultrafast ultrasound imaging which allows high sensitivity blood flow imaging. BOLD-contrast is a naturally occurring process in the body so fMRI is often preferred over imaging methods that require radioactive markers to produce similar imaging.

The magnetic resonance MR emitted from the equipment can cause failure of medical devices and attract metallic objects in the body if not properly screened for. The CT scan was introduced in the s and quickly became one of the most widely used methods of imaging.

A CT scan can be performed in under a second and produce rapid results for clinicians, with its ease of use leading to an increase in CT scans performed in the United States from 3 million in to 62 million in In PET scans, imaging does not rely on intrinsic biological processes, but relies on a foreign substance injected into the bloodstream traveling to the brain. Patients are injected with radioisotopes that are metabolized in the brain and emit positrons to produce a visualization of brain activity.

EEG electrodes detect electrical signals produced by neurons to measure brain activity and MEG uses oscillations in the magnetic field produced by these electrical currents to measure activity. Some scientists have criticized the brain image-based claims made in scientific journals and the popular press, like the discovery of "the part of the brain responsible" for functions like talents, specific memories, or generating emotions such as love.

Many mapping techniques have a relatively low resolution, including hundreds of thousands of neurons in a single voxel. Many functions also involve multiple parts of the brain, meaning that this type of claim is probably both unverifiable with the equipment used, and generally based on an incorrect assumption about how brain functions are divided.

It may be that most brain functions will only be described correctly after being measured with much more fine-grained measurements that look not at large regions but instead at a very large number of tiny individual brain circuits.

Many of these studies also have technical problems like small sample size or poor equipment calibration which means they cannot be reproduced - considerations which are sometimes ignored to produce a sensational journal article or news headline.

In some cases the brain mapping techniques are used for commercial purposes, lie detection, or medical diagnosis in ways which have not been scientifically validated. From Wikipedia, the free encyclopedia. This article is about imaging. For imagery and creating maps, see Brain mapping and Outline of brain mapping. Set of techniques to measure and visualize aspects of the nervous system. Para-sagittal MRI of the head in a patient with benign familial macrocephaly. Main article: History of neuroimaging.

Main article: CT head. Main article: Magnetic resonance imaging of the brain.

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