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Brain imaging is a fairly recent discipline within medicine and neuroscience. Brain imaging falls into two broad categories -- structural imaging and functional imaging. The former deals with the overall structure of the brain and the precise diagnosis of intracranial disease and injury. The latter is used for neurological and cognitive science research and building brain-computer interfaces. It enables, for example, the processing of sensory information coming to the brain and of commands going from the brain to the organism to be "lit up" or visualized directly instead of by simple clinical inference.Brain imaging was honored in a US Postal Service Stamp
1 Types of brain imaging
1.1 PET
Positron Emission Tomography (PET) measures emissions from radioactively labeled chemicals that have been injected into the bloodstream and uses the data to produce two or three-dimensional images of the distribution of the chemicals throughout the brain (Nilsson 57). PET scans involve the use of a machine called a cyclotron to label chemicals with small amounts of radioactivity. The labeled compound, called 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 different regions of the brain. A computer uses the data gathered by the sensors to create multicolored two or three-dimensional images that show where the compound acts in the brain.
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 us to learn more about how the brain works. PET scans were superior in terms of resolution and speed of completion (as little as 30 seconds) when they first came online. The improved resolution permitted better judgments 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 (Nilsson 60). Before fMRI technology came online, PET scanning was the preferred method of brain imaging, and it still continues to make large contributions to neuroscience.
1.2 SPECT
Similar to PET, single photon emission computed tomography (SPECT) uses radioactive tracers and a scanner to record data that a computer uses to construct two- or three-dimensional images of active brain regions (Ball). SPECT tracers are considered to be more limited than PET scanners in the kinds of brain activity they have the ability to monitor. The tracers of SPECT are longer lasting than those of PET, which allows for different, longer lasting brain functions to be examined, but this also requires more time for the SPECT to be completed. The resolution of a SPECT is poor (about 1 cm) compared to that of PET. SPECT is often chosen over PET simply as a cost issue, for less equipment is involved and fewer staff is required to perform the tests.
1.3 EEG
Electroencephalography (EEG) is the oldest of the modern brain imaging techniques and uses electrodes placed on the scalp to detect and measure patterns of electrical activity coming from the brain. There have been many recent developments regarding EEG's ability to read brain activity data from the entire head simultaneously (Thompson, Bioinformatics). Using scale electrodes, EEG can determine the relative strengths and positions of electrical activity in different brain regions by measuring electrical activity on the outside of the brain. EEG records timing of activity very precisely but resolution is poor and does not directly record interior brain activity. As a result, researchers often use EEG images of brain electrical activity in combination with MRI scans to better pinpoint the location of the activity in the brain.
1.4 MRI
Magnetic Resonance Imaging (MRI) uses magnetic fields and radio waves to produce high quality two- or three-dimensional images of brain structures without injecting radioactive tracers. During an MRI, a large cylindrical magnetThis article is about magnetized material. Magnet is also the name of a commune in the Allier departement, in France A magnet is an object that has a magnetic field. A so-called permanent magnet is made of a ferromagnetic material. Such materials consist creates a magnetic fieldIn physics, a magnetic field is an entity produced by moving electric charges ( electric currents) that exerts a force on other moving charges. The quantum-mechanical spin of a particle produces magnetic fields and is acted on by them as though it were a around the head of the patient through which radio waves are sent. When the magnetic field is imposed, each point in space has a unique radio frequencyRF can also denote rheumatoid factor Radio frequency or RF refers to that portion of the electromagnetic spectrum in which electromagnetic waves can be generated by alternating current fed to an antenna. Such frequencies account for the following parts of at which the signal is received and transmitted (Preuss). Sensors read the frequencies and a computer uses the information to construct an image. The detection mechanisms are so precise that changes in structures over time can be detected. Using MRI, scientists can create images of both surface and subsurface structures with a high degree of anatomicalAnatomy (from the Greek anatome from ana-temnein to cut up), is the branch of biology that deals with the structure and organization of living things; thus there is animal anatomy ( zootomy) and plant anatomy ( phytonomy). The major branches of anatomy in detail. MRI scans can produce cross sectional images in any direction from top to bottom, side to side, or front to back. The problem with original MRI technology was that while it provides a detailed assessment of the physical appearance of the brain, it fails to provide information about how well the brain is working at the time of imaging. The distinction is now made between MRI imaging and functional imaging since the brain's function rather than the brain's structure is of interest.
