Functional magnetic resonance imaging 226722 225805386 2008-07-15T14:13:44Z 117.201.64.87 /* Commercial use */ '''Functional MRI or functional [[Magnetic Resonance Imaging]] (fMRI)''' is a type of specialized [[MRI]] scan. It measures the [[haemodynamic response]] related to [[neuron|neural]] activity in the [[brain]] or [[spinal cord]] of [[human]]s or other animals. It is one of the most recently developed forms of [[neuroimaging]]. Since the early 1990s, fMRI has come to dominate the brain mapping field due to its low invasiveness, lack of radiation exposure, and relatively wide availability.<ref>http://en.wikipedia.org/wiki/History_of_brain_imaging#Magnetic_resonance_imaging</ref> Recent breakthroughs in non-invasive brain imaging have been somewhat limited because most of them have not been completely novel; rather, they are simply refining existing brain imaging techniques. fMRI is a perfect example of this from the early 1990s, and it still remains the most popular brain imaging technique available today.<ref>http://en.wikipedia.org/wiki/History_of_brain_imaging#Recent_Breakthroughs</ref> [[Image:FMRI.jpg|thumb|250px|right|fMRI statistics (yellow) overlaid on an average of the brain anatomies of several humans (gray)]] Dr. [[Raymond Vahan Damadian]] practically invented the [[MRI]]<ref>http://www.howstuffworks.com/mri.htm/printable</ref> (which gradually gave way to today's [[fMRI]]), along with his colleagues Dr. Larry Minkoff and Dr. Michael Goldsmith. He labored tirelessly for seven long years to reach this point. The first MRI exam ever performed on a human being took place on [[July 3]], [[1977]] under his supervision. This machine, which is now in the [[Smithsonian Institution]], took almost five hours to produce one image. Consequently, the 2003 Nobel Prize in Medicine award was vigorously protested by him.<ref>http://en.wikipedia.org/wiki/MRI#2003_Nobel_Prize</ref> Recently, there have been efforts in the field of recording EEG during fMRI<ref>http://depts.washington.edu/idl/eeg_mri.htm</ref> for the detection of seizures. == Background == Since the 1890s (Roy and [[Charles Scott Sherrington|Sherrington]], 1890)<ref>Roy CS, Sherrington CS. On the Regulation of the Blood-supply of the Brain. J Physiol. 1890 Jan;11(1-2):85-158.17.</ref> it has been known that changes in [[blood flow]] and blood oxygenation in the [[brain]] (collectively known as [[hemodynamics]]) are closely linked to neural activity. When nerve cells are active they consume [[oxygen]] carried by [[hemoglobin]] in [[red blood cells]] from local [[capillary|capillaries]]. The local response to this oxygen utilization is an increase in blood flow to regions of increased neural activity, occurring after a delay of approximately 1-5 seconds. This hemodynamic response rises to a peak over 4-5 seconds, before falling back to baseline (and typically undershooting slightly). This leads to local changes in the relative concentration of oxyhemoglobin and deoxyhemoglobin and changes in local cerebral [[blood volume]] in addition to this change in local [[cerebral blood flow]]. '''Blood-oxygen-level dependent''' or BOLD fMRI is a method of observing which areas of the [[brain]] are active at any given time. It was first found by Dr. [[Seiji Ogawa]]<ref>Ogawa, S., Lee, T.M., Nayak, A.S., and Glynn, P. (1990). Oxygenation-sensitive contrast in magnetic resonance image of rodent brain at high magnetic fields. Magn Reson Med 14, 68-78 </ref> in 1990 and following by Dr. [[Kenneth Kwong]] in 1992<ref>KK Kwong, JW Belliveau, DA Chesler, IE Goldberg, RM Weisskoff, BP Poncelet, DN Kennedy, BE Hoppel, MS Cohen, R Turner, H Cheng, TJ Brady, and BR Rosen, Dynamic Magnetic Resonance Imaging of Human Brain Activity During Primary Sensory Stimulation. PNAS, 89:5675-79, 1992</ref>. [[Neurons]] do not have internal reserves of energy in the form of [[glucose]] and [[oxygen]], so their firing causes a need for more energy to be brought in quickly. Through a process called the [[hemodynamic response]], blood releases oxygen to them at a greater rate than to inactive neurons, and the difference in [[magnetic susceptibility]] between oxyhemoglobin and [[Hemoglobin|deoxyhemoglobin]], and thus oxygenated or deoxygenated [[blood]], leads to magnetic signal variation which can be detected using an MRI scanner. Given many repetitions of a thought, action or experience, statistical methods can be used to determine the areas of the brain which reliably have more of this difference as a result, and therefore which areas of the brain are active during that thought, action or experience. Almost all fMRI research uses BOLD as the method for determining where activity occurs in the brain as the result of various experiences, but because the signals are relative and not individually quantitative, some question its rigor. Other methods which propose to measure neural activity directly have been attempted (for example, measurement of the Oxygen Extraction Fraction, or OEF, in regions of the brain, which measures how much of the oxyhemoglobin in the blood has been converted to deoxyhemoglobin<ref>[http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&list_uids=7869897&dopt=Citation Theory of NMR signal behavior in magnetically inho...[Magn Reson Med. 1994&#93; - PubMed Result<!-- Bot generated title -->]</ref>), but because the electromagnetic fields created by an active or firing neuron are so weak, the [[signal-to-noise ratio]] is extremely low and [[Statistics|statistical]] methods used to extract quantitative data have been largely unsuccessful as of yet. [[Hemoglobin]] is [[diamagnetic]] when oxygenated but [[paramagnetic]] when deoxygenated. The [[magnetic resonance]] (MR) signal of blood is therefore slightly different depending on the level of oxygenation. These differential signals can be detected using an appropriate MR pulse sequence as [[blood-oxygen-level dependent]] (BOLD) contrast. Higher BOLD signal intensities arise from increases in the concentration of oxygenated [[hemoglobin]] since the blood [[magnetic susceptibility]] now more closely matches the tissue magnetic susceptibility. By collecting data in an [[MRI]] scanner with parameters sensitive to changes in magnetic susceptibility one can assess changes in BOLD contrast. These changes can be either positive or negative depending upon the relative changes in both cerebral blood flow (CBF) and oxygen consumption. Increases in CBF that outstrip changes in oxygen consumption will lead to increased BOLD signal, conversely decreases in CBF that outstrip changes in oxygen consumption will cause decreased BOLD signal intensity. ==Neural correlates of BOLD== The precise relationship between neural signals and BOLD is under active research. In general, changes in BOLD signal are well correlated with changes in blood flow. Numerous studies during the past several decades have identified a coupling between blood flow and [[Metabolism|metabolic rate]]; that is, the blood supply is tightly regulated in space and time to provide the nutrients for brain metabolism. However, [[neuroscience|neuroscientists]] have been seeking a more direct relationship between the blood supply and the neural inputs/outputs that can be related to observable electrical activity and circuit models of brain function. While current data indicate that [[local field potential]]s, an index of integrated electrical activity, form a marginally better correlation with blood flow than the spiking [[action potential]]s that are most directly associated with neural communication, no simple measure of electrical activity to date has provided an adequate correlation with metabolism and the blood supply across a wide dynamic range. Presumably, this reflects the complex nature of metabolic processes, which form a superset with regards to electrical activity. Some recent results have suggested that the increase in cerebral blood flow (CBF) following neural activity is not causally related to the metabolic demands of the brain region, but rather is driven by the presence of [[neurotransmitter]]s, especially [[Glutamic acid|glutamate]]. Some other recent results suggest that an initial small, negative dip before the main positive BOLD signal is more highly localized and also correlates with measured local decreases in tissue oxygen concentration (perhaps reflecting increased local [[metabolism]] during neuron activation). Use of this more localized negative BOLD signal has enabled imaging of human [[ocular dominance columns]] in [[Visual cortex|primary visual cortex]], with resolution of about 0.5 mm. One problem with this technique is that the early negative BOLD signal is small and can only be seen using larger scanners with magnetic fields of at least 3 [[Tesla (unit)|Tesla]]. Further, the signal is much smaller than the normal BOLD signal, making extraction of the signal from noise that much more difficult. Also, this initial dip occurs within 1-2 seconds of stimulus initiation, which may not be captured when signals are recorded at long repetition (TR). If the TR is sufficiently low, increased speed of the cerebral blood flow response due to consumption of vasoactive drugs (such as caffeine<ref>{{cite journal | author=Behzadi, Y. ''et al'' | title=Caffeine reduces the initial dip in the visual bold response at 3 t. | journal=Neuroimage | year=2006 | volume=32 | pages=9–15 | doi=10.1016/j.neuroimage.2006.03.005 }} </ref>) or natural differences in vascular responsivnesses may further obscure observation of the initial dip. The BOLD signal is composed of CBF contributions from larger arteries and veins, smaller arterioles and venules, and capillaries. Experimental results indicate that the BOLD signal can be weighted to the smaller vessels, and hence closer to the active neurons, by using larger magnetic fields. For example, whereas about 70% of the BOLD signal arises from larger vessels in a 1.5 tesla scanner, about 70% arises from smaller vessels in a 4 tesla scanner. Furthermore, the size of the BOLD signal increases roughly as the square of the magnetic field strength. Hence there has been a push for larger field scanners to both improve localization and increase the signal. A few 7 tesla commercial scanners have become operational, and experimental 8 and 9 tesla scanners are under development. [[Image:brain chrischan.jpg|thumb|250px|right|A sagittal slice of a Structural [[MRI]] scan of a human head. The nose is to the left.[[:Image:brain chrischan 300.gif|Click here]] to view an animated sequence of slices.]] [[Image:User-FastFission-brain-frame44.png|thumb|250px|right|A slice of an [[MRI]] scan of the brain. The forehead is at the top and the back of the head is at the bottom. [[:Image:User-FastFission-brain.gif|Click here]] to view an animation of the scan from top to bottom.]] == Technique == BOLD effects are measured using rapid volumetric acquisition of images with contrast weighed by T2 or T2* (see [[MRI]]). Such images can be acquired with moderately good spatial and temporal resolution; images are usually taken every 1–4 seconds, and the [[voxel]]s in the resulting image typically represent cubes of tissue about 2–4 millimeters on each side in humans. Recent technical advancements, such as the use of high magnetic fields and advanced "multichannel" RF reception, have advanced spatial resolution to the millimeter scale. Although responses to stimuli presented as close together as one or two seconds can be distinguished from one another, using a method known as event-related fMRI, the full time course of a BOLD response to a briefly presented stimulus lasts about 15 seconds for the robust positive response. == fMRI studies draw from many disciplines == To use fMRI effectively, an investigator must have a firm grasp of the relevant principles from all of these fields: * [[Physics]]: Researchers should have a reasonable understanding of the physical principles underlying fMRI. * [[Psychology]]: Almost all fMRI studies are essentially [[cognitive psychology|cognitive psychological]], [[physiological psychology|cognitive psychophysiological]], and/or [[psychophysics|psychophysical]] experiments in which the MRI scanner is used to obtain an extra set of measurements in addition to behavioral and [[electroencephalographic]] measurements. This allows for more detailed theory testing and inference on perceptual and cognitive processes, and allows to relate these to specific brain structures. * [[Neuroanatomy]]: The fMRI signals can be put into the context of previous knowledge only with an understanding of the neuroanatomy. Ultimately, the goal of all functional imaging experiments is to explain [[human cognition]] and behavior in terms of physical (anatomical) mechanisms. * [[Statistics]]: Correct application of statistics is essential to "tease out" observations and avoid [[Type I and type II errors|false-positive]] results. * [[Electrophysiology]]: Familiarity with neuronal behavior at the electrophysiological level can help investigators design a useful fMRI study. [[Seiji Ogawa]] and [[Kenneth Kwong]]{{Fact|date=June 2008}} are generally credited as the discoverers of the BOLD effect that underlies conventional fMRI. ==Advantages and Disadvantages of fMRI== Like any technique, fMRI has advantages and disadvantages, and in order to be useful, the experiments that employ it must be carefully designed and conducted to maximize its strengths and minimize its weaknesses. ===General disadvantages of the method=== * The BOLD signal is only an indirect measure of neural activity, and is therefore susceptible to influence by non-neural changes in the body. * BOLD signals are most strongly associated with the input to a given area rather than with the output. It is therefore possible (although unlikely) that a BOLD signal could be present in a given area even if there is no single unit activity.<ref>{{cite journal | author=Logothetis, N.K. | year=2001 | title=Neurophysiological investigation of the basis of the fMRI signal. | journal=Nature | volume=412 | url=http://www.ssc.uwo.ca/psychology/culhamlab/fmri/pdfs/Logothetis.pdf | pages=150 | doi=10.1038/35084005 }}</ref> * Different brain areas have different hemodynamic responses, which would not be accurately reflected by the [[general linear model]] often used to filter fMRI time signals. * For a non-invasive scan, fMRI has moderately good spatial resolution. However, the temporal response of the blood supply, which is the basis of fMRI, is poor relative to the electrical signals that define neuronal communication. Therefore, some research groups are working around this issue by combining fMRI with data collection techniques such as [[electroencephalography]] (EEG) or [[magnetoencephalography]] (MEG). EEG has much higher temporal resolution but rather poor spatial resolution, whereas MEG has much higher temporal resolution and similar spatial resolution. This has led some to suggest MEG is a more valuable tool than fMRI. * fMRI has often been used to show activation localized to specific regions, thus minimizing the distributed nature of processing in [[Biological neural network|neural networks]]. Several recent [[multivariate]] statistical techniques work around this issue by characterizing interactions between "active" regions found via traditional [[univariate]] techniques. Such techniques might prove useful in the future. * fMRI is usually used to try to determine "where" task-related activity occurs in the brain. This has led to the charge that it is simply a modern-day phrenology.{{Fact|date=May 2008}} Some scientists prefer models which explain "how" psychological mechanisms function. The counter-argument to this criticism is that knowing "where" a cognitive function is located is vitally important. [[Neuropsychology]], [[neurophysiology]], and [[functional imaging]] each give us different windows of understanding into what each brain region does and how. The analogy to phrenology is somewhat misleading: [[phrenology]] has little or no basis in the [[scientific method]], whereas fMRI permits hypotheses to be tested and strong inferences to be made. * Many theoretical models used to explain fMRI signals are so poorly specified that they are not [[Falsifiability|falsifiable]] (a central tenet from the [[scientific method]]). Hence, some argue, fMRI is not really a "science."{{Fact|date=May 2008}} The counter-argument is that an fMRI study can provide evidence to falsify a prior theory if it is well-designed. Also, well-specified mathematical and computational models of the neural processes underlying fMRI can make theories more concrete, allowing them to make predictions that can be verified or falsified by fMRI. ===Advantages of fMRI=== * It can noninvasively record brain signals (of humans and other animals) without risks of radiation inherent in other scanning methods, such as [[Computed tomography|CT]] scans. * It can record on a spatial resolution in the region of 3-6 millimeters, but with relatively poor temporal resolution (on the order of seconds) compared with techniques such as EEG. However, this is mainly because of the phenomena being measured, not because of the technique. EEG measures electrical/neural activity while fMRI measures blood activity, which has a longer response. The MRI equipment used for fMRI can be used for high temporal resolution, if one measures different phenomena. ===General counterargument=== Like any other technique, fMRI is as worthwhile as the design of the experiment using it. Many investigators have used fMRI ineffectively because they were not familiar with all aspects of the technique, or because they received their academic training in disciplines characterized by less rigor than some other branches of psychology and neuroscience. Ineffective use of the technique is a problem for the field, but it is not a consequence of the technique itself. While the mechanistic information provided by fMRI is limited relative to classical techniques of electrophysiology and molecular biology, this is a general criticism of systems-level biology based upon changes in metabolism, blood supply, or ensemble indices of electrical activity. Most researchers believe that both "bottom-up" and "top-down" measurements are needed to inform our understanding of the complex mechanisms that transpose neural activity into behavior. === Commercial use === ''Omneuron'' [http://www.omneuron.com/] is a US-based company founded by [[Christopher deCharms]] that is researching potential practical and clinical applications of real time fMRI. ''Applied fMRI Institute'' [http://www.appliedfmri.org] is a [[San Diego, CA]] based company offering commercial use of their [[Siemens]] 3T TIM Trio. ''Neurognostics'' [http://www.neurognostics.com/] is a US-based company that offers a standardized fMRI system ''Imagilys'' [http://www.imagilys.com/] is a European company specialized in clinical and research fMRI. At least two companies have been set up to use fMRI in [[lie detection]]. They are ''No Lie MRI, Inc'' [http://www.noliemri.com/] and ''Cephos Corporation'' [http://www.cephoscorp.com/]. In episode 109 of the popular science show [[Mythbusters]], the three members of the build team attempted to fool an FMRI test. Although two of them were unsuccessful, the third was able to successfully fool the machine. The signals are extrapolated from the fMRI machine onto a screen, displaying the active regions of the brain. Depending on what regions are the most active, the technician can determine whether a subject is telling the truth or not. This technology is in its early stages of development, and many of its proponents hope to replace older lie detection techniques. Recently, there have also been efforts for the development of cheap & portable fMRI scanners.<ref>http://neurophilosophy.wordpress.com/2006/09/06/hi-res-cheap-portable-mri/</ref> == Scanning in practice == [[Image:Varian4T.jpg|thumb|250px|right|[[University of California, Berkeley|Berkeley's]] 4T fMRI scanner.]] Subjects participating in a fMRI experiment are asked to lie still and are usually restrained with soft pads to prevent small motions from disturbing measurements. Some labs also employ bite bars to reduce motion, although these are unpopular as they can cause some discomfort to subjects. It is possible to correct for some amount of head movement with post-processing of the data, but large transient motion can render these attempts futile. Generally motion in excess of 3 millimeters will result in unusable data. The issue of motion is present for all populations, but most notably within populations that are not physically or emotionally equipped for even short MRI sessions (e.g., those with [[Alzheimer's Disease]] or [[schizophrenia]], or young children). In these populations, various and negative [[reinforcement]] strategies can be employed in an attempt to attenuate motion artifacts, but in general the solution lies in designing a compatible paradigm with these populations. An fMRI experiment usually lasts between 15 minutes and 2 hours. Depending on the purpose of study, subjects may view movies, hear sounds, smell odors, perform cognitive tasks such as memorization or imagination, press a few buttons, or perform other tasks. Researchers are required to give detailed instructions and descriptions of the experiment plan to each subject, who must sign a consent form before the experiment. Safety is a very important issue in all experiments involving MRI. Potential subjects must ensure that they are able to enter the MRI environment. Due to the nature of the MRI scanner, there is an extremely strong magnetic field surrounding the MRI scanner (at least 1.5 [[tesla (unit)|teslas]], possibly stronger). Potential subjects must be thoroughly examined for any ferromagnetic objects (e.g. watches, glasses, hair pins, pacemakers, bone plates and screws, etc.) before entering the scanning environment. == Related techniques == Aside from fMRI, there are other related ways to probe brain activity using magnetic resonance properties: ===Contrast MR=== An injected [[Radiocontrast|contrast agent]] such as an [[iron oxide]] that has been coated by a [[sugar]] or [[starch]] (to hide from the body's defense system), causes a local disturbance in the [[magnetic field]] that is measurable by the MRI scanner. The signals associated with these kinds of contrast agents are proportional to the cerebral blood volume. While this semi-invasive method presents a considerable disadvantage in terms of studying brain function in normal subjects, it enables far greater detection sensitivity than BOLD signal, which may increase the viability of fMRI in clinical populations. Other methods of investigating blood volume that do not require an injection are a subject of current research, although no alternative technique in theory can match the high sensitivity provided by injection of contrast agent. ===Arterial spin labeling=== By magnetic labeling the proximal blood supply using "arterial spin labeling" ASL, the associated signal is proportional to the cerebral blood flow, or [[perfusion]]. This method provides more quantitative physiological information than BOLD signal, and has the same sensitivity for detecting task-induced changes in local brain function ===Magnetic resonance spectroscopic imaging=== Magnetic resonance spectroscopic imaging (MRS) is another, [[Nuclear magnetic resonance|NMR]]-based process for assessing function within the living brain. MRS takes advantage of the fact that [[proton]]s ([[hydrogen]] atoms) residing in differing chemical environments depending upon the molecule they inhabit (H<sub>2</sub>O vs. [[protein]], for example) possess slightly different resonant properties. For a given volume of brain (typically > 1 cubic cm), the distribution of these H resonances can be displayed as a [[spectroscopy|spectrum]]. The area under the peak for each resonance provides a quantitative measure of the relative abundance of that compound. The largest peak is composed of H<sub>2</sub>O. However, there are also discernible peaks for [[choline]], [[creatine]], [[N-Acetylaspartate|''N''-acetylaspartate]] (NAA) and [[lactic acid|lactate]]. Fortuitously, NAA is mostly inactive within the neuron, serving as a precursor to glutamate and as storage for acetyl groups (to be used in [[fatty acid]] synthesis) &mdash; but its relative levels are a reasonable approximation of neuronal integrity and functional status. Brain diseases ([[schizophrenia]], [[stroke]], certain [[tumor]]s, [[multiple sclerosis]]) can be characterized by the regional alteration in NAA levels when compared to healthy subjects. Creatine is used as a relative control value since its levels remain fairly constant, while choline and lactate levels have been used to evaluate [[brain tumor]]s. ===Diffusion tensor imaging=== [[Diffusion tensor imaging]] (DTI) is a related use of MR to measure anatomical connectivity between areas. Although it is not strictly a functional imaging technique because it does not measure dynamic changes in brain function, the measures of inter-area connectivity it provides are complementary to images of [[cerebral cortex|cortical]] function provided by BOLD fMRI. [[White matter]] bundles carry functional information between brain regions. The diffusion of water molecules is hindered across the axes of these bundles, such that measurements of water diffusion can reveal information about the location of large white matter pathways. Illnesses that disrupt the normal organization or integrity of cerebral white matter (such as multiple sclerosis) have a quantitative impact on DTI measures. == Approaches to fMRI data analysis == The ultimate goal of fMRI data analysis is to detect correlations between brain activation and the task the subject performs during the scan. The BOLD signature of activation is relatively weak, however, so other sources of noise in the acquired data must be carefully controlled. This means that a series of processing steps must be performed on the acquired images before the actual statistical search for task-related activation can begin. For a typical fMRI scan, the 3D volume of the subject's head is imaged every one or two seconds, producing a few hundred to a few thousand complete images per scanning session. The nature of MRI is such that these images are acquired in [[Fourier transform]] space, so they must be transformed back to image space to be useful. Because of practical limitations of the scanner the Fourier samples are not acquired on a grid, and scanner imperfections like thermal drift and spike noise introduce additional distortions. Small motions on the part of the subject and the subject's pulse and respiration will also affect the images. The most common situation is that the researcher uses a [[mri#resonance and relaxation|pulse sequence]] supplied by the scanner vendor, such as an [[mri|imaging|echo-planar imaging (EPI)]] sequence that allows for relatively rapid acquisition of many images. Software in the scanner platform itself then performs the reconstruction of images from Fourier transform space. During this stage some information is lost (specifically the complex phase of the reconstructed signal). Some types of artifacts, for example spike noise, become more difficult to remove after reconstruction, but if the scanner is working well these artifacts are thought to be relatively unimportant. For pulse sequences not provided by the vendor, for example spiral EPI, reconstruction must be done by software running on a separate platform. After reconstruction the output of the scanning session consists of a series of 3D images of the brain. The most common corrections performed on these images are motion correction and correction for physiological effects. Outlier correction and spatial and/or temporal filtering may also be performed. If the task performed by the subject is thought to produce bursts of activation which are short compared to the BOLD response time (on the order of 6 seconds), temporal filtering may be performed at this stage to attempt to [[deconvolution|deconvolve]] out the [[BOLD]] response and recover the temporal pattern of activation. At this point the data provides a time series of samples for each voxel in the scanned volume. A variety of methods are used to correlate these voxel time series with the task in order to produce maps of task-dependent activation. Some fMRI [[neuroimaging software]]: * [[Analysis of Functional NeuroImages|AFNI]] [http://afni.nimh.nih.gov] * [[BrainVoyager]] [http://www.brainvoyager.com] * [[Cambridge Brain Analysis|CamBA]] [http://sourceforge.net/projects/camba] * Fiasco/FIAT [http://www.stat.cmu.edu/~fiasco] * [[FreeSurfer]] [http://surfer.nmr.mgh.harvard.edu] * [[mrVista]][http://white.stanford.edu/newlm/index.php/Software] * [[FMRIB Software Library|FSL]] [http://www.fmrib.ox.ac.uk/fsl] * [[Statistical parametric mapping|SPM]] [http://www.fil.ion.ucl.ac.uk/spm] * [http://www.imagilys.com/autospm.html AutoSPM: Automated SPM for Surgical Planning] * [http://www.bioimagesuite.org BioImage Suite] * [http://www.nordicimaginglab.com/ nordicICE] ==Cost of fMRI== Cost of fMRI scanners are about the same as [[MRI]] scanners because fMRI is only a specialized type of MRI scan (''functional'' MRI). MRI equipment is expensive, though the cost is expected to exponentially decline soon in spurt of recent breakthroughs. New 1.5 tesla scanners often cost between $1,000,000 USD and $1,500,000 USD. New 3.0 tesla scanners often cost between $2,000,000 and $2,300,000 USD. Construction of MRI suites can cost $500,000 USD. Currently, in the US, there is increasing interest in reducing the costs associated with fMRI services and simultaneously improving the ability to effectively and efficiently provide fMRI examination services to larger numbers of researchers/other people with the same equipment. ==fMRI vs EEG== [[EEG]] has several strong sides as a tool of exploring brain activity; for example, its time resolution is very high (on the level of a single millisecond). Other methods of looking at brain activity, such as [[Pet scan|PET]] and [[fMRI]] have time resolution between seconds and minutes. EEG measures the brain's electrical activity directly, while other methods record changes in blood flow (e.g., [[Single photon emission computed tomography|SPECT]], [[functional magnetic resonance imaging|fMRI]]) or metabolic activity (e.g., [[Positron emission tomography|PET]]), which are indirect markers of brain electrical activity. EEG can be used simultaneously with [[functional magnetic resonance imaging|fMRI]] so that high-temporal-resolution data can be recorded at the same time as high-spatial-resolution data, however, since the data derived from each occurs over a different time course, the data sets do not necessarily represent the exact same brain activity. There are technical difficulties associated with combining these two modalities, including the need to remove RF pulse artifact and ballistocardiographic artifact (a results from the movement of pulsed blood) from the EEG. Furthermore, currents can be induced in moving EEG electrode wires due to the magnetic field of the MRI. EEG can be recorded at the same time as [[Magnetoencephalography|MEG]] so that data from these complimentary high-time-resolution techniques can be combined. ==See also== * [[Brain Mapping]] * [[Brain function]] * [[Event related fMRI]] * [[Spinal fMRI]] * [[Signal enhancement by extravascular water protons| SEEP fMRI]] * [[EEG-fMRI]] * [[Real-time fMRI]] * [[Functional neuroimaging]] * [[The fMRI Data Centre]] * [[Linear transform model]] ==References== <references/> ===Textbooks=== Scott A. Huettel, Allen W. Song, Gregory McCarthy, ''Functional Magnetic Resonance Imaging'', Sinauer Associates, 2004, ISBN 0-87893-288-7 Richard B. Buxton, ''An Introduction to Functional Magnetic Resonance Imaging: Principles and Techniques'', Cambridge Univ Press, 2002, ISBN 0-52158-113-3 ===Journal articles=== {{cite journal | author=Weiller C ''et al'' | title=Role of functional imaging in neurological disorders | journal=Journal of Magnetic Resonance Imaging | year=2006 | volume=23 | issue=6 | pages= 840–850 | doi=10.1002/jmri.20591}} {{cite journal | author=Lin, Lyons, and Berkowitz | title=Somatotopic Identification of Language-SMA in Language Processing via fMRI | journal=Journal of Scientific and Practical Computing | year=2007 | volume=1 | issue=2 | pages= 3–8}} [http://www.spclab.com/publisher/journals/Vol1No2/L1.pdf] == External links == * [http://rcbi.rochester.edu Rochester Center for Brain Imaging] at the [[University of Rochester]] which has a 3T scanner open for research purposes * [http://www.biophysics.mcw.edu Department of Biophysics] at [[Medical College of Wisconsin]] * [[Laboratory of Neuro Imaging]] at [[UCLA]] * [[Athinoula A. Martinos Center for Biomedical Imaging]] [http://www.nmr.mgh.harvard.edu/martinos] at [[Massachusetts General Hospital]], which develops and supports [[FreeSurfer]] * [http://radiologyinfo.org/en/info.cfm?pg=fmribrain RadiologyInfo]- The radiology information resource for patients: Functional Magnetic Resonance Imaging of the Brain * [http://www.fmridc.org The fMRI Data Center (fMRIDC)] at [[Dartmouth College]] * [http://www.fil.ion.ucl.ac.uk The Functional Imaging Laboratory] at [[University College London]] * [http://www.fmrib.ox.ac.uk The Centre for Functional Magnetic Resonance Imaging of the Brain] at [[Oxford University]] * [http://www.magres.nottingham.ac.uk/projects/ Sir Peter Mansfield Magnetic Resonance Centre,] University of Nottingham * [http://www-bmu.psychiatry.cam.ac.uk The Brain Mapping Unit (BMU)], [[University of Cambridge]] * [http://www.fmri.org/fmri.htm About fMRI] from [http://www.fmri.org/ Functional MRI Research Center], [[Columbia University]] * [http://www.fmrib.ox.ac.uk/fmri_intro/ Introduction to FMRI] from the [http://www.fmrib.ox.ac.uk/ Oxford Centre for Functional Magnetic Resonance Imaging of the Brain], [[Oxford University]] * [http://sccn.ucsd.edu/fmrlab/index.html FMRLAB] Toolbox for fMRI data analysis * [http://www.brainmapping.org BrainMapping.ORG project] Community web site for information Brain Mapping and methods * [https://www.ynic.york.ac.uk York Neuroimaging Center] at [[University of York]] * [http://fmri.pl fMRI.pl Functional Imaging Lab] at [[Warsaw University of Technology]] * [http://www.neuroimago.usp.br Functional Neuroimaging Lab] at [[University of Sao Paulo - Ribeirao Preto - Brazil]] * [http://www.mri-tutorial.com/tutorial_fmri.html A list of the best introductions to fMRI on the web] * [http://www.fmrimethods.org/ fMRI Methods Wiki] - with advice on how to report on fMRI studies * [http://www.scholarpedia.org/article/Functional_magnetic_resonance_imaging fMRI entry at Scholarpedia] ==Notes== {{reflist}} [[Category:Magnetic resonance imaging]] [[Category:Medical tests]] [[Category:Neuroimaging]] [[Category:Cognitive science]] [[de:Funktionelle Magnetresonanztomographie]] [[el:Λειτουργική Απεικόνιση Μαγνητικού Συντονισμού]] [[fr:Imagerie par résonance magnétique fonctionnelle]] [[is:Starfræn segulómmyndun]] [[it:Risonanza magnetica funzionale]] [[hu:Funkcionális mágneses rezonancia-vizsgálat]] [[nl:Functionele MRI]] [[ja:FMRI]] [[no:Funksjonell Magnetresonanstomografi]] [[pl:Funkcjonalny magnetyczny rezonans jądrowy]] [[pt:Ressonância magnética]] [[zh:功能性磁共振成像]]