An Introduction to Functional MRISummary of the CourseOutline for TodayWhat is fMRI?Growth of fMRI : Published StudiesWhy the Growth of fMRI?Slide 7New Cognitive AnalysesPowerPoint PresentationSlide 10Key ConceptsAnatomical ContrastBlood Oxygenation Level Dependent (BOLD) ContrastDesign Effects on Functional ContrastSpatial Resolution: VoxelsSpatial Resolution: ExamplesTemporal ResolutionSlide 18Functional ResolutionHistory of Magnetic Resonance ImagingTimeline of MR ImagingDiscovery of Nuclear Magnetic Resonance Absorption (1946)Slide 23Early Uses of NMRThe First ZMR NMR ImageEarly Human MR Images (Damadian)Slide 27Slide 28Using MRI to Study Brain FunctionParts of a MR ScannerSlide 31MRI SafetySlide 33MR IncidentsIssues in MR SafetyPossible Effects of Magnetic FieldsRisks of MRIProjectile Effects: ExternalRadiofrequency EnergyProjectile/Torsion Effects: InternalAcoustic NoiseGradient Field ChangesClaustrophobiaQuenchingScanner VisitAn Introduction to Functional MRIBrain Imaging and Analysis Center FMRI Graduate CourseSummary of the Course•Combines lectures and laboratory sessions–Laboratories will illustrate concepts from lectures•Grading basis–Participation in course sessions (attendance, discussion)–Completion of laboratory exercises–One take-home test (mid-term)–Practicum research project at end of semester•Course web page (www.biac.duke.edu/education)–BIAC Logins•Readings –Buxton, Introduction to fMRI–Original papers (generally posted on the web page)–Full reading list to be posted over upcoming weeksOutline for Today•Why use fMRI to image brain function?•Key concepts of fMRI•History of fMRI•Parts of a MR scanner•MR safety•Laboratory: Scanner Visit (Dr. Jim Voyvodic)–Scanner hardware–Stimulus presentation and recording hardware–Demonstration of real-time fMRIWhat is fMRI?•A technique for measuring changes in brain activity over time using principles of magnetic resonance.•Scanning procedures and restrictions are generally similar to clinical MR.•Most fMRI studies use changes in BOLD contrast, although other measures exist.0 100 200 300 400 500 600 700 800 9002002200120001999199819971996199519941993199219911990…Growth of fMRI : Published StudiesWhy the Growth of fMRI?Why the Growth of fMRI?•Powerful–Improved ability to understand cognition–Better spatial resolution than PET–Allows new forms of analysis•High benefit/risk ratio–Non-invasive (no contrast agents)–Repeated studies (multisession, longitudinal)•Accessible–Uses clinically prevalent equipment–No isotopes required –Little special training for personnelNew Cognitive Analyses•Sampling rate affects experimental design–PET: >30s/data point ; fMRI: 1s/data point–Cognitive processes being measured must change more slowly than sampling rate•New forms of analyses–Event-related: sorting trials by accuracy, response time, type of condition–Rapid stimulus presentation•Allows creation of process models of activity–Difference in activation timing between regions is often on order of 100-1000msCheng, Waggoner, & Tanaka (2001) Neuron Sakai, Rowe, & Passingham (2002) Nature NeuroscienceImage provided by Dr. James Voyvodic (Duke BIAC)Key Concepts•Contrast•Spatial Resolution•Temporal Resolution•Functional ResolutionAnatomical ContrastDefinition: The ability to distinguish between two (or more) different properties of tissue.Blood Oxygenation Level Dependent (BOLD) ContrastFrom Mosley & Glover (1995)Design Effects on Functional ContrastContrast should really be considered as “contrast to noise”: how effectively can we decide whether a given brain region has property X or property Y?Spatial Resolution: VoxelsVoxel: A small rectangular prism that is the basic sampling unit of fMRI. Typical functional voxel: (4mm)3. Typical anatomical voxel: (1.5mm)3.Spatial Resolution: Examples~8mm2~4mm2~2mm2~1.5mm2~1mm2Temporal Resolution•Importance depends upon research question –Type I: Detection•Temporal resolution is only indirectly important if your study investigates whether or not a given brain region is active.–Type II: Estimation•Temporal resolution is extremely important when attempting to understand the properties of an active region.•Determining factors–Sampling rate, usually repetition time (TR)–Dependent variable, usually BOLD response•BOLD response is sluggish, taking 2-3 seconds to rise above baseline and 4-6 seconds to peak–Experimental designFrom Jezzard et al., 2001Functional ResolutionThe ability of a measurement technique to identify the relation between underlying neuronal activity and a cognitive or behavioral phenomenon.Functional resolution is limited both by the intrinsic properties of our brain measure and by our ability to manipulate the experimental design to allow variation in the phenomenon of interest.History of Magnetic Resonance ImagingTimeline of MR Imaging1920 1930 1940 1950 1960 1970 1980 1990 20001924 - Pauli suggests that nuclear particles may have angular momentum (spin).1937 – Rabi measures magnetic moment of nucleus. Coins “magnetic resonance”.1944 – Rabi wins Nobel prize in Physics.1946 – Purcell shows that matter absorbs energy at a resonant frequency.1946 – Bloch demonstrates that nuclear precession can be measured in detector coils.1952 – Purcell and Bloch share Nobel prize in Physics.1972 – Damadian patents idea for large NMR scanner to detect malignant tissue.1959 – Singer measures blood flow using NMR (in mice).1973 – Lauterbur publishes method for generating images using NMR gradients.1973 – Mansfield independently publishes gradient approach to MR.1975 – Ernst develops 2D-Fourier transform for MR.NMR becomes MRIMRI scanners become clinically prevalent.1990 – Ogawa and colleagues create functional images using endogenous, blood-oxygenation contrast.1985 – Insurance reimbursements for MRI exams begin.Discovery of Nuclear Magnetic Resonance Absorption (1946)•Bloch and Purcell independently discovered how to measure nuclear moment in bulk matter (1946)–Determined relaxation times.•They showed that energy applied at a resonant frequency was absorbed by matter, and the re-emission could be measured in detector coils•They shared the 1952 Nobel Prize in PhysicsFelix BlochEdward PurcellTimeline of MR Imaging1920 1930 1940 1950 1960 1970 1980 1990 20001924 - Pauli suggests that nuclear particles may have angular momentum (spin).1937 – Rabi measures