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{{Importartikel}}
[[Image:Parasagittal MRI of human head in patient with benign familial macrocephaly prior to brain injury (ANIMATED).gif|thumb|right|MRT-Sagittalschnitt des Kopfes eines an familiärer [[Makrozephalie]] erkrankten Patienten.]]

Als '''Zerebrale Bildgebung''' (auch: ''Neurobildgebung'') werden [[Bildgebendes Verfahren (Medizin)|bildgebende Verfahren]] zur direkten oder indirekten  Erfassung der [[Neuroanatomie|Anatomie]] oder der [[Gehirn |Funktion]] des Gehirns bezeichnet. 
Dabei handelt es sich um einen verhältnismäßig jungen Zweig der [[Medizin]] bzw. [[Neurowissenschaften]] und [[Psychologie]]. <ref name=Filler2009b>Filler, AG: The history, development, and impact of computed imaging in neurological diagnosis and neurosurgery: CT, MRI, DTI: [http://precedings.nature.com/documents/3267/version/5 Nature Precedings ] {{doi|10.1038/npre.2009.3267.5}}.Neurosurgical Focus (in press)</ref> Mediziner, die sich auf die klinische Durchführung und Interpretation zerebraler Bildgebung spezialisieren, bezeichnet man als [[Neuroradiologie|Neuroradiologen.]]  

== Überblick ==
die Zerebrale Bildgebung teilt sich in zwei Bereiche: 
* Strukturelle Bildgebung, welche sich mit der Beschaffenheit des Gehirns und der Diagnose maßstäblich großer [[Schädel|intrakranieller]] Krankheiten (z.B. [[Tumor|Tumoren]]) und Verletzungen  befasst, sowie
* [[Funktionelle Bildgebung]] die zur Diagnose von Stoffwechselerkrankungen (wie z.B. der [[Alzheimer-Krankheit]]) und (maßstäblich) kleinerer Verletzungen, sowie in der Forschung im Bereich der [[Neuropsychologie]], der [[Kognitionspsychologie]] und der Entwicklung von [[Gehirn-Computer-Schnittstelle|Gehirn-Computer-Schnittstellen]] eingesetzt wird. 

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 research into "[[Thought identification]]" or mind-reading.

==History==
{{main|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]] introduced [[cerebral angiography]], whereby both normal and abnormal blood vessels in and around the brain could be visualized with great precision.

In the early 1970s, [[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. Cormack and Hounsfield won the 1979 [[Nobel Prize for Physiology or Medicine]] for their work. Soon after the introduction of CAT in the early 1980s, the development of [[radioligand]]s allowed [[single photon emission computed tomography]] (SPECT) and [[positron emission tomography]] (PET) of the brain.

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. In the early 1980s MRI was introduced clinically, and 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 could also be imaged by the correct type of MRI. [[Functional magnetic resonance imaging]] (fMRI) was born, and
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. As noted above fMRI is also beginning to dominate the field of stroke treatment.

In early 2000s 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 [[Direct mind-computer interface|brain-computer interface]].

==Brain imaging techniques==
=== Computed axial tomography ===
{{main|CT head}}
[[Computed tomography]] (CT) or ''Computed Axial Tomography'' (CAT) scanning uses a series of [[x-rays]] of the head taken from many different directions. Typically used for quickly viewing [[Acquired brain injury|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.<ref>Malcom Jeeves (1994). ''Mind Fields: Reflections on the Science of Mind and Brain''. Grand Rapids, MI: Baker Books., p. 21</ref>

=== Diffuse optical imaging ===
[[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 seen setbacks due to limited resolution. Early results have been promising, a comparison and validation of diffuse optical imaging against the standard of functional magnetic resonance imaging (fMRI) has been lacking.  HD-DOT has adequate image quality to be useful as a surrogate for fMRI.  
<ref>http://www.ncbi.nlm.nih.gov/pubmed/22330315</ref>

=== Event-related optical signal ===
[[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. It was developed at the University of Illinois at Urbana-Champaign where it is now used in the Cognitive Neuroimaging Laboratory of Dr. Gabriele Gratton and Dr. Monica Fabiani.

=== Magnetic resonance imaging ===
{{main|MRI of brain and brain stem}} 
[[Image:Sagittal brain MRI.JPG||right|thumbnail|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 use of ionizing radiation (X-rays) or radioactive tracers.

=== Functional magnetic resonance imaging ===
[[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 brain structures are activated (and how) during performance of different tasks. 

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 2-3 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 [[Receptor (biochemistry)|receptors]] (or [[Monoamine transporter|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 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 afterwards. Brain changes seen on fMRI may help to make the decision to treat with these agents.  
With between 72% and 90% accuracy where chance would achieve 0.8%,<ref>{{cite news|author=Smith, Kerri|title=Mind-reading with a brain scan|url=http://www.nature.com/news/2008/080305/full/news.2008.650.html|work=Nature News|publisher=Nature Publishing Group|date=March 5, 2008|accessdate=2008-03-05}}</ref> fMRI techniques can decide which of a set of known images the subject is viewing.<ref>{{cite news|author=Keim, Brandon|title=Brain Scanner Can Tell What You're Looking At|url=http://www.wired.com/science/discoveries/news/2008/03/mri_vision|work=Wired News|publisher=CondéNet|date=March 5, 2008|accessdate=2008-03-05}}</ref>

=== Magnetoencephalography ===
[[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 [[SQUID|superconducting quantum interference devices]] (SQUIDs). 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 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). While skull anisotropy has negligible effect on MEG (unlike EEG), white matter anisotropy strongly affects MEG measurements for radial and deep sources.<ref>Wolters et al, "Influence of tissue conductivity anisotropy on EEG/MEG field and return current computation in a realistic head model: A simulation and visualization study using high-resolution finite element modeling, NeuroImage, 30(3):813-26 (2006)"</ref> Note, however, that the skull was assumed to be uniformly anisotropic in this study, which is not true for a real head: the absolute and relative thicknesses of [[diploë]] and tables layers vary among and within the skull bones. This makes it likely that MEG is also affected by the skull anisotropy,<ref>Ramon et al., "Influence of head models on neuromagnetic fields and inverse source localizations", BioMedical Engineering OnLine 2006, 5:55</ref> 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 ===
<!-- Deleted image removed: [[Image:PETscan.png||right|frame|PET scan of a normal 20-year-old brain.]] -->
[[Positron emission tomography]] (PET) measures 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.<ref>Lars-Goran Nilsson and Hans J. Markowitsch (1999). ''Cognitive Neuroscience of Memory''. Seattle: Hogrefe & Huber Publishers., page 57</ref> The [[positron]] emitting [[radioisotope]]s used are produced by a [[cyclotron]], and chemicals are labeled 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 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.<ref>Lars-Goran Nilsson and Hans J. Markowitsch (1999). ''Cognitive Neuroscience of Memory''. Seattle: Hogrefe & Huber Publishers., pg. 60</ref>  Before fMRI technology came online, PET scanning was the preferred method of functional (as opposed to structural) brain imaging, and it still continues to make large contributions to [[neuroscience]].

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 ===
[[Single-photon emission computed tomography]] (SPECT) is similar to PET and 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.<ref>Philip Ball ''Brain Imaging Explained''</ref> SPECT relies on an injection of radioactive tracer, or "SPECT agent," which is rapidly taken up by the brain but does not redistribute. Uptake of SPECT agent is nearly 100% complete within 30 to 60 seconds, 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 acquired 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&nbsp;cm) compared to that of MRI.

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. Neuro-PET has a disadvantage of requiring use of tracers with [[biological half-life|half-lives]] of at most 110 minutes, such as [[fludeoxyglucose (18F)|FDG]]. 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 technetium-99m, and as a result, is far more widely available.

== See also ==
*[[Brain mapping]]
*[[Functional neuroimaging]]
*[[functional near-infrared imaging]]
*[[History of brain imaging]]
*[[Human Cognome Project]]
*[[Magnetic resonance imaging]]
*[[Magnetoencephalography]]
*[[Medical imaging]]
*[[List of neuroscience databases]]
*[[Neuroimaging software]]
*[[Statistical parametric mapping]]
*[[Transcranial magnetic stimulation]]
*[[Voxel-based morphometry]]

== Einzelnachweise ==
<references />

==Weblinks==
{{Commonscat|Neuroimaging}}
* [http://www.med.harvard.edu/AANLIB/home.html The Whole Brain Atlas @ Harvard]
* [http://www2.bic.mni.mcgill.ca/ The McConnell Brain Imaging Center, McGill University]
* [http://www.asnweb.org/ The American Society of Neuroimaging (ASN)].
* [http://www.brainmapping.org/NITP UCLA Neuroimaging Training Program].
* [http://www.loni.ucla.edu/ Laboratory of Neuro Imaging] at [[UCLA]]
* [http://www.mri-tutorial.com/ A Neuroimaging portal]
* [http://www.brainmapping.org/ BrainMapping.org, ''a free BrainMapping community information portal'']
* [http://www.fil.ion.ucl.ac.uk/~wpenny/mbi/ Lecture notes on mathematical aspects of neuroimaging] by Will Penny, [[University College London]]
* [http://www.ai.mit.edu/projects/medical-vision/surgery/tms.html "Transcranial Magnetic Stimulation"]. by Michael Leventon in association with [[MIT AI Lab]].
* [http://www.ee.duke.edu/~jshorey/MRIHomepage/MRImain.html ''Foundations of fMRI''] by Jamie Shorey.
* [http://www.isnip.org/ International Society for Neuroimaging in Psychiatry (ISNIP)]
* [http://www.wiley.com/bw/journal.asp?ref=1051-2284 Journal of Neuroimaging]

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[[zh:神经成像]]-->Brain imaging is a fairly recent discipline within medicine and neuroscience.  Brain imaging falls into two broad categories -- structural and functional imaging.  Structural imaging began with early radiographic techniques to image the human brain.  Unfortunately, largely composed of soft tissue, the brain and brain abnormalities remained largely invisible.  Crude images of the ventricular system within the brain were obtained by air injection -- a painful procedure.  With the advent of computerized axial tomography (CAT scanning), detailed anatomic images of the brain became available for diagnostic and research purposes.  Soon after, the development of radioligands that either remained within the blood stream or entered the brain to bind to certain receptors within brain started the functional imaging revolution.  Radioligands are either single photon or positron emitters.  Thus, single photon emission computerized tomography (SPECT) and positron emission tomography (PET) became available as long as facilities were present to synthesize the ligands needed.  Early techniques such as xenon inhalation provided the first blood flow maps of the brain.  Functional imaging took a large step forward with the development of H20-15 imaging.  H20-15 emits positrons and creates images based on regional blood flow within the brain.  Since active neurons recruit a robust blood supply, H20-15 PET allowed investigators to make regional maps of brain activity during various cognitive tasks.  Concurrently, magnetic resonance imaging (MRI) was developed. Rather than radiation, MRI uses variation in signal produced largely by the body's protons when the head is placed in a strong magnetic field.  At first, structural imaging benefited most from the introduction of MRI.  However, scientists soon learned that the large blood flow changes measured by H20-15 PET were also imaged by MRI. Functional magnetic resonance imaging (fMRI) was born.  Within the last 10 years, fMRI has come to dominate the brain mapping field due to its low invasiveness, lack of radiation exposure, and relatively wide availability.  Physicists have also developed other MRI based techniques such as magnetic resonance spectroscopy (for measuring some key metabolites such as n-acetylaspartate and lactate within living brain) and diffusion tensor imaging (for mapping white matter tracts within living brain).  Structural MRI and CAT scanning have a large place in medicine, however fMRI and its brethren are still largely devoted to neuroscience research.