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'''Neuroimaging''' includes the use of various techniques to either directly or indirectly  [[imaging|image]] the [[neuroanatomy|structure]], function, or [[pharmacology]] of the [[brain]]. It is a relatively new discipline within [[medicine]] and [[neuroscience]]. 

It 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 interface]]s. 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.

[[Image:70medimg.jpg|thumbnail|Neuroimaging was honored in a [[US Postal Service]] Stamp]]

==Types of brain imaging==

===EEG===
[[Image:1st-eeg.gif|right|frame|The first EEG recording, obtained by [[Hans Berger]] in 1929.]]
[[Electroencephalography]] (EEG) is the first non-invasive neuroimaging technique discovered. First reported by [[Neurology|neurologist]] [[Hans Berger]] in 1929, EEG measures the [[Electricity|electrical]] [[volt]]age potentials from ensembles of [[neuron]]s in the [[cerebral cortex]]. This technique is widely used in neuroscience research, with many stereotyped electrical potentials well-known (e.g., [[P300]], [[N400]]). This technique is occasionally used clinically to determine [[brain death]].

EEG-recorded responses to sensory or other stimuli are called evoked potentials (EPs) or sometimes event-related potentials (ERPs). The stimuli can be auditory, visual, tactile, olfactory, gustatory, or electric. EPs can be elicited also by [[Transcranial magnetic stimulation]].
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===MEG===
[[Magnetoencephalography]] (MEG) is similar to [[Electroencephalography|EEG]], but magnetic fields are measured instead of electric fields.

===CAT===
[[Image:CTscan.PNG||right|frame|CT scan slice showing indicating damage cause by [[stroke]] (arrow).]]
[[Computed tomography]] (CT or CAT) scanning uses a series of [[x-rays]] of the head taken from many different directions.  Typically used for quickly viewing brain injuries, CT scanning has a computer program that uses a set of [[algebra|algebraic equations]] to estimate how much x-ray is absorbed in a small area within a cross section of the brain (Jeeves 21).  In the final analysis, the harder a material is, the whiter it will appear on the scan.  CT scans are primarily used for evaluating swelling from tissue damage in the brain and in assessment of ventricle size.  Modern CT scanning exposes the subject to about as much radiation as a single x-ray and can provide reasonably good images in a matter of minutes.
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===MRI===
[[Image:MRIscan.gif||right|frame|High-resolution sagittal MRI slice at the midline.]]
[[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 [[magnet]] creates a [[magnetic field]] 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 frequency]] 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 [[anatomy|anatomical]] 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.
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===fMRI===
[[Image:FMRIscan.jpg||right|frame|Axial MRI slice at the level of the [[basal ganglia]], showing fMRI [[Blood oxygenation level-dependent|BOLD]] signal changes overlayed in red (increase) and blue (decrease) tones.]]
[[Functional magnetic resonance imaging]] (fMRI) 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 structures are activated (and how) during performance of different tasks. Most fMRI scanners allows 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 two or three 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 associated with particular [[neurotransmitters]] through its ability to image radiolabelled receptor ligands.
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===PET===
[[Image:PETscan.png||right|frame|PET scan of normal 20 year old brain.]]
[[Positron Emission Tomography]] (PET) measures emissions from radioactively labeled metabolically active 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). The [[positron]] emitting [[radioisotope]]s used are produced by a [[cyclotron]] and chemicals are labelled with these radioactive atoms. 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 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]].
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===SPECT===
SPECT is similar to PET. [[SPECT|Single photon emission computed tomography]] (SPECT) uses [[gamma ray]] emitting [[radioisotope]]s and a [[gamma camera]] to record data that a computer uses to construct two- or three-dimensional images of active brain regions (Ball). SPECT relies on an injection of radioactive tracer, which is rapidly taken up by the brain but does not redistribute. Uptake of SPECT agent is nearly 100% complete within 30 – 60s, reflecting cerebral blood flow (CBF) at the time of injection. 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 aquired after seizure termination (so long as the radioactive tracer was injected at the time of the seizure). A significant limitation of SPECT is its poor resolution (about 1 cm) compared to that of MRI.
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==History==
''See main article [[History of neuroimaging]]''

In 1918 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 1927 [[Egas Moniz]], professor of neurology in [[Lisbon]], introduced cerebral [[angiography]], whereby both normal and abnormal blood vessels in and around the brain could be visualized with great accuracy.

In the early 1970s, [[Allan McLeod Cormack]] and [[Godfrey Newbold Hounsfield]] brought about the use [[computerized axial tomography]] (CAT or CT scanning), and ever more detailed anatomic images of the brain became available for diagnostic and research purposes. Cormack and Hounsfield won the 1979 [[Nobel Prize for Physiology or Medicine]] for their work. Soon after the introduction of CAT, the development of [[radioligand]]s allowed [[single photon emission computed tomography]] (SPECT) and [[positron emission tomography]] (PET).

More or less concurrently, [[magnetic resonance imaging]] (MRI or MR scanning) was developed by researchers including [[Peter Mansfield]] and [[Paul Lauterbur]], who were awarded the [[Nobel Prize for Physiology or Medicine]] in 2003.  During the 1980s a veritable explosion of technical refinements and diagnostic MR applications took place. Scientists soon learned that the large blood flow changes measured by PET were also imaged by MRI. [[Functional magnetic resonance imaging]] (fMRI) was born. Since the 1990s, fMRI has come to dominate the brain mapping field due to its low invasiveness, lack of radiation exposure, and relatively wide availability.

In early 2000s the field of neuroimaging reached the stage where limited practical applications of functional brain imaging became feasible. The main application area is crude forms of [[Direct mind-computer interface|brain-computer interface]].

==See also==
*[[Functional neuroimaging]]
*[[History of brain imaging]]
*[[Human Cognome Project]]
*[[Medical imaging]]
*[[Statistical parametric mapping]]

==Works cited==
* Ball, Philip.  "Brain Imaging Explained."  Online at http://www.nature.com/nsu/010712/010712-13.html
* Beaumont, J. Graham.  Introduction to Neuropsychology.  New York:  The Guilford Press, 1983.  314 pages.
* Changeux, Jean-Pierre.  Neuronal Man:  The Biology of Mind.  New York:  Oxford University Press, 1985.  348 pages.
** Jeeves, Malcom.  Mind Fields:  Reflections on the Science of Mind and Brain.  Grand Rapids, MI:  Baker Books, 1994.  141 pages.
* Johnson, Keith A.  "Neuroimaging Primer." [http://www.med.harvard.edu/AANLIB/hms1.html]
* Leventon, Michael.  "Transcranial Magnetic Stimulation."  In assosiation with MIT AI Lab.  [http://www.ai.mit.edu/projects/medical-vision/surgery/tms.html]
* Lister, Richard G. and Herbert J. Weingartner.  Perspectives on Cognitive Neuroscience.  New York:  Oxford University Press, 1991.  508 pages.
* Mattson, James and Merrill Simon.   The Pioneers of NMR and Magnetic Resonance in Medicine.  United States:  Dean Books Company, 1996.  838 pages.
* Nilsson, Lars-Goran and Hans J. Markowitsch.  Cognitive Neuroscience of Memory.  Seattle:  Hogrefe & Huber Publishers, 1999.  307 pages.
* Norman, Donald A.  Perspectives on Cognitive Science.  New Jersey:  Ablex Publishing Corporation, 1981.  303 pages.
* Pande, G.C.  "Neurosciences and Philosophy."  [http://www.iias-library.org/Dissemination%20of%20knowledge%20series/Neuroscience%20and%20Philosphy.htm]
* Rapp, Brenda.  The Handbook of Cognitive Neuropsychology.  Ann Arbor, MI:  Psychology Press, 2001.  652 pages.
* Shorey, Jamie.  "Foundations of fMRI." [http://www.ee.duke.edu/~jshorey/MRIHomepage/MRImain.html]

[[Category:Radiology]]
[[Category:Neuroimaging| ]]

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