Functional Magnetic Resonance Imaging
TL;DR: FMRI reveals short-term physiological changes associated with active brain functioning, and in this way, fMRI can identify different parts of the brain where particular men-tal processes occur and can characterize the patterns of acti-vation associated with those processes.
About: This article is published in Seminars in Roentgenology.The article was published on 2010-04-01. It has received 1430 citations till now. The article focuses on the topics: Resting state fMRI & Brain mapping.
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TL;DR: The inception of this journal has been foreshadowed by an ever-increasing number of publications on functional connectivity, causal modeling, connectomics, and multivariate analyses of distributed patterns of brain responses.
Abstract: Over the past 20 years, neuroimaging has become a predominant technique in systems neuroscience. One might envisage that over the next 20 years the neuroimaging of distributed processing and connectivity will play a major role in disclosing the brain's functional architecture and operational principles. The inception of this journal has been foreshadowed by an ever-increasing number of publications on functional connectivity, causal modeling, connectomics, and multivariate analyses of distributed patterns of brain responses. I accepted the invitation to write this review with great pleasure and hope to celebrate and critique the achievements to date, while addressing the challenges ahead.
2,822 citations
TL;DR: The newly developed toolbox, DPABI, which was evolved from REST and DPARSF is introduced, designed to make data analysis require fewer manual operations, be less time-consuming, have a lower skill requirement, a smaller risk of inadvertent mistakes, and be more comparable across studies.
Abstract: Brain imaging efforts are being increasingly devoted to decode the functioning of the human brain. Among neuroimaging techniques, resting-state fMRI (R-fMRI) is currently expanding exponentially. Beyond the general neuroimaging analysis packages (e.g., SPM, AFNI and FSL), REST and DPARSF were developed to meet the increasing need of user-friendly toolboxes for R-fMRI data processing. To address recently identified methodological challenges of R-fMRI, we introduce the newly developed toolbox, DPABI, which was evolved from REST and DPARSF. DPABI incorporates recent research advances on head motion control and measurement standardization, thus allowing users to evaluate results using stringent control strategies. DPABI also emphasizes test-retest reliability and quality control of data processing. Furthermore, DPABI provides a user-friendly pipeline analysis toolkit for rat/monkey R-fMRI data analysis to reflect the rapid advances in animal imaging. In addition, DPABI includes preprocessing modules for task-based fMRI, voxel-based morphometry analysis, statistical analysis and results viewing. DPABI is designed to make data analysis require fewer manual operations, be less time-consuming, have a lower skill requirement, a smaller risk of inadvertent mistakes, and be more comparable across studies. We anticipate this open-source toolbox will assist novices and expert users alike and continue to support advancing R-fMRI methodology and its application to clinical translational studies.
2,179 citations
Cites background from "Functional Magnetic Resonance Imagi..."
...By detecting local concentrations of deoxygenated and oxygenated hemoglobin, fMRI blood-oxygen level dependent (BOLD) signals allow inferring blood flow changes associated with differential neural activity during distinct tasks (Huettel et al., 2004)....
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TL;DR: A review of the challenges that have been overcome in this field, the practicalities of performing fNIRS in infants, and the technological and methodological advances made in the study design, optical probe development, and interpretation and analyses of the haemodynamic response.
717 citations
Cites background from "Functional Magnetic Resonance Imagi..."
...…measure the same haemodynamic response, generally fMRI techniques have an intrinsically limited acquisition rate usually at a minimum of one hertz (Huettel et al., 2003; but see Weishaupt et al., 2008), whereas fNIRS can acquire data rapidly, up to hundreds of hertz, thus providing a more…...
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...Though fMRI and fNIRS measure the same haemodynamic response, generally fMRI techniques have an intrinsically limited acquisition rate usually at a minimum of one hertz (Huettel et al., 2003; but see Weishaupt et al., 2008), whereas fNIRS can acquire data rapidly, up to hundreds of hertz, thus providing a more complete temporal picture (Huppert et al....
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TL;DR: In this article, the authors argue that the human mind/brain is composed of a set of highly specialized components, each carrying out a specific aspect of human cognition, or is it more of a general-purpose device, in which each component participates in a wide variety of cognitive processes.
Abstract: Is the human mind/brain composed of a set of highly specialized components, each carrying out a specific aspect of human cognition, or is it more of a general-purpose device, in which each component participates in a wide variety of cognitive processes? For nearly two centuries, proponents of specialized organs or modules of the mind and brain—from the phrenologists to Broca to Chomsky and Fodor—have jousted with the proponents of distributed cognitive and neural processing—from Flourens to Lashley to McClelland and Rumelhart. I argue here that research using functional MRI is beginning to answer this long-standing question with new clarity and precision by indicating that at least a few specific aspects of cognition are implemented in brain regions that are highly specialized for that process alone. Cortical regions have been identified that are specialized not only for basic sensory and motor processes but also for the high-level perceptual analysis of faces, places, bodies, visually presented words, and even for the very abstract cognitive function of thinking about another person’s thoughts. I further consider the as-yet unanswered questions of how much of the mind and brain are made up of these functionally specialized components and how they arise developmentally.
704 citations
TL;DR: The analysis of fMRI data is discussed, from the initial acquisition of the raw data to its use in locating brain activity, making inference about brain connectivity and predictions about psychological or disease states.
Abstract: In recent years there has been explosive growth in the number of neuroimaging studies performed using functional Magnetic Resonance Imaging (fMRI). The field that has grown around the acquisition and analysis of fMRI data is intrinsically interdisciplinary in nature and involves contributions from researchers in neuroscience, psychology, physics and statistics, among others. A standard fMRI study gives rise to massive amounts of noisy data with a complicated spatio-temporal correlation structure. Statistics plays a crucial role in understanding the nature of the data and obtaining relevant results that can be used and interpreted by neuroscientists. In this paper we discuss the analysis of fMRI data, from the initial acquisition of the raw data to its use in locating brain activity, making inference about brain connectivity and predictions about psychological or disease states. Along the way, we illustrate interesting and important issues where statistics already plays a crucial role. We also seek to illustrate areas where statistics has perhaps been underutilized and will have an increased role in the future.
607 citations
References
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TL;DR: In this paper, the authors demonstrate in vivo images of brain microvasculature with image contrast reflecting the blood oxygen level, which can be used to provide in vivo real-time maps of blood oxygenation in the brain under normal physiological conditions.
Abstract: Paramagnetic deoxyhemoglobin in venous blood is a naturally occurring contrast agent for magnetic resonance imaging (MRI). By accentuating the effects of this agent through the use of gradient-echo techniques in high fields, we demonstrate in vivo images of brain microvasculature with image contrast reflecting the blood oxygen level. This blood oxygenation level-dependent (BOLD) contrast follows blood oxygen changes induced by anesthetics, by insulin-induced hypoglycemia, and by inhaled gas mixtures that alter metabolic demand or blood flow. The results suggest that BOLD contrast can be used to provide in vivo real-time maps of blood oxygenation in the brain under normal physiological conditions. BOLD contrast adds an additional feature to magnetic resonance imaging and complements other techniques that are attempting to provide positron emission tomography-like measurements related to regional neural activity.
5,812 citations
01 Jan 1990
TL;DR: It is demonstrated that in vivo images of brain microvasculature with image contrast reflecting the blood oxygen level can be used to provide in vivo real-time maps of blood oxygenation in the brain under normal physiological conditions.
Abstract: Paramagnetic deoxyhemoglobin invenous bloodisanaturally occurring contrast agent formagnetic resonance imaging (MRI). Byaccentuating theeffects ofthis agentthrough theuseofgradient-echo techniques inhigh fields, wedemonstrate invivo images ofbrain microvasculature withimagecontrast reflecting theblood oxygen level. This bloodoxygenation level-dependent (BOLD)contrast follows bloodoxygen changes induced byanesthetics, byinsulin- induced hypoglycemia, andbyinhaled gasmixtures that alter metabolic demandorbloodflow. Theresults suggest that BOLDcontrast canbeusedtoprovide invivo real-time maps ofblood oxygenation inthebrain undernormal physiological conditions. BOLDcontrast addsanadditional feature tomag- netic resonance imaging andcomplements other techniques that areattempting toprovide positron emission tomography- like measurements related toregional neural activity. Magnetic resonance imaging (MRI)isawidely accepted modality forproviding anatomical information. Current re- search (1)involves extending MRImethods toprovide in- formation about biological function, inaddition tothecon- comitant anatomical information. Inaddition tolocalized spectroscopy (2)andchemical shift imaging (3)thatare applicable tomanychemical species, MRIofwaterprotons hasbeenfunctionally extended toNMR angiography (4), perfusion imaging (5,6),andperfusion imaging enhanced by exogenous contrast agents (7). Since waterisbyfarthe predominant molecule intissue, andsince itssignal domi- nates theinformation content inproton images, onewould ideally like toexploit changes inthewatersignal that arise fromphysiological events. Except forcasesofwatermove- ment,suchasblood flow, these changes arenormally very small. Ithaspreviously beendemonstrated (8,9)that thepres- enceofdeoxyhemoglobin inblood changes theproton signal fromwatermolecules surrounding ablood vessel ingradient- echoMRI,producing bloodoxygenation level-dependent (BOLD)contrast. BOLD contrast hasitsorigin inthefact that whennormally diamagnetic oxyhemoglobin gives upits oxygen, theresulting deoxyhemoglobin isparamagnetic. The presence ofparamagnetic molecules inblood produces a difference inmagnetic susceptibility between theblood ves- selandthesurrounding tissue. Thissusceptibility difference is"felt" bothbythewatermolecules intheblood andby those inthesurrounding tissue, theeffect extending signifi- cantly beyond thevessel wall. Thisincrease inthenumber of spins affected bydeoxyhemoglobin isaformofamplification. Whenthesusceptibility-i nduced local field differences exist within animaging voxel, there isaresultant distribution of shifts inwaterresonance frequencies. Inthegradient-echo method, aphase dispersion ofwaterproton signals ispro- ducedattheechotime. Thisdispersion reduces thesignal intensity andthevoxelappears darkintheimage. These intensity losses, which athighmagnetic fields (-4T)extend significantly beyond theboundary oftheblood vessel, arethe source ofBOLD contrast. Thisformofcontrast isnot observed inspin-echo images. Through simulations (9), we haveshownthat vessels assmall as50,umindiameter canbe detected inimages with apixel size of100pum. We havealso demonstrated that thesize ofthesusceptibility-i nduced local field depends on(i) theconcentration ofparamagnetic deox- yhemoglobin and(ii) theorientation ofthevessel relative to themainmagnetic field (8,9). SinceBOLD contrast depends onthestate ofblood oxygenation, physiological events thatchangetheoxy/ deoxyhemoglobin ratio should lendthemselves tononinva- sive detection through theaccentuation ofBOLDcontrast in gradient-echo proton images athighmagnetic fields. We report herethatthis isindeed thecaseanddemonstrate changes inBOLD-contrast microimages ofbrain produced by changes ininhaled gasmixture under urethane anesthesia, by insulin-induced hypoglycemia under diazepam sedation, and bychanges inthelevel ofhalothane anesthesia. Theobserved changes inBOLD contrast correlate withtheanticipated changes inblood oxygen level produced byaltered metabolic loadorblood flow(10).
5,513 citations
TL;DR: It is reported that visual stimulation produces an easily detectable (5-20%) transient increase in the intensity of water proton magnetic resonance signals in human primary visual cortex in gradient echo images at 4-T magnetic-field strength.
Abstract: We report that visual stimulation produces an easily detectable (5-20%) transient increase in the intensity of water proton magnetic resonance signals in human primary visual cortex in gradient echo images at 4-T magnetic-field strength. The observed changes predominantly occur in areas containing gray matter and can be used to produce high-spatial-resolution functional brain maps in humans. Reducing the image-acquisition echo time from 40 msec to 8 msec reduces the amplitude of the fractional signal change, suggesting that it is produced by a change in apparent transverse relaxation time T*2. The amplitude, sign, and echo-time dependence of these intrinsic signal changes are consistent with the idea that neural activation increases regional cerebral blood flow and concomitantly increases venous-blood oxygenation.
3,568 citations
TL;DR: Cortical magnification factor curves for striate and extrastriate cortical areas were determined, which showed that human visual areas have a greater emphasis on the center-of-gaze than their counterparts in monkeys.
Abstract: The borders of human visual areas V1, V2, VP, V3, and V4 were precisely and noninvasively determined. Functional magnetic resonance images were recorded during phase-encoded retinal stimulation. This volume data set was then sampled with a cortical surface reconstruction, making it possible to calculate the local visual field sign (mirror image versus non-mirror image representation). This method automatically and objectively outlines area borders because adjacent areas often have the opposite field sign. Cortical magnification factor curves for striate and extrastriate cortical areas were determined, which showed that human visual areas have a greater emphasis on the center-of-gaze than their counterparts in monkeys. Retinotopically organized visual areas in humans extend anteriorly to overlap several areas previously shown to be activated by written words.
2,590 citations
TL;DR: At high magnetic fields (7 and 8.4 T), water proton magnetic resonance images of brains of live mice and rats under pentobarbital anesthetization have been measured by a gradient echo pulse sequence with a spatial resolution of 65 × 65‐ μm pixel size and 700‐μm slice thickness.
Abstract: At high magnetic fields (7 and 8.4 T), water proton magnetic resonance images of brains of live mice and rats under pentobarbital anesthetization have been measured by a gradient echo pulse sequence with a spatial resolution of 65 x 65-microns pixel size and 700-microns slice thickness. The contrast in these images depicts anatomical details of the brain by numerous dark lines of various sizes. These lines are absent in the image taken by the usual spin echo sequence. They represent the blood vessels in the image slice and appear when the deoxyhemoglobin content in the red cells increases. This contrast is most pronounced in an anoxy brain but not present in a brain with diamagnetic oxy or carbon monoxide hemoglobin. The local field induced by the magnetic susceptibility change in the blood due to the paramagnetic deoxyhemoglobin causes the intra voxel dephasing of the water signals of the blood and the surrounding tissue. This oxygenation-dependent contrast is appreciable in high field images with high spatial resolution.
2,246 citations