An Introduction to Functional MRI Brain Imaging and Analysis Center FMRI Graduate Course Summary 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 weeks Outline 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 fMRI What 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 Growth of fMRI Published Studies 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 0 100 200 300 400 500 600 700 800 900 Why 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 personnel New 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 1000ms Cheng Waggoner Tanaka 2001 Neuron Sakai Rowe Passingham 2002 Nature Neuroscience Image provided by Dr James Voyvodic Duke BIAC Key Concepts Contrast Spatial Resolution Temporal Resolution Functional Resolution Anatomical Contrast Definition The ability to distinguish between two or more different properties of tissue Blood Oxygenation Level Dependent BOLD Contrast From Mosley Glover 1995 Design Effects on Functional Contrast Contrast 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 Voxels Voxel 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 1 5mm2 2mm2 1mm2 Temporal 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 design From Jezzard et al 2001 Functional Resolution The 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 Imaging Timeline of MR Imaging 1924 Pauli suggests that nuclear particles may have angular momentum spin 1972 Damadian patents idea for large NMR scanner to detect malignant tissue 1937 Rabi measures magnetic moment of nucleus Coins magnetic resonance 1944 Rabi wins Nobel prize in Physics 1952 Purcell and Bloch share Nobel prize in Physics 1920 1930 1940 1950 1946 Purcell shows that matter absorbs energy at a resonant frequency 1960 1959 Singer measures blood flow using NMR in mice 1946 Bloch demonstrates that nuclear precession can be measured in detector coils 1985 Insurance reimbursements for MRI exams begin 1973 Lauterbur publishes method for generating images using NMR gradients MRI scanners become clinically prevalent NMR becomes MRI 1970 1980 1973 Mansfield independently publishes gradient approach to MR 1975 Ernst develops 2D Fourier transform for MR 1990 2000 1990 Ogawa and colleagues create functional images using endogenous bloodoxygenation contrast 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 Felix Bloch They shared the 1952 Nobel Prize in Physics Edward Purcell Timeline of MR Imaging 1924 Pauli suggests that nuclear particles may have angular momentum spin 1972 Damadian patents idea for large NMR scanner to detect malignant tissue 1937 Rabi measures magnetic moment of nucleus Coins magnetic resonance 1944 Rabi wins Nobel prize in Physics 1952 Purcell and Bloch share Nobel prize in Physics 1920 1930 1940 1950 1946 Purcell shows that matter absorbs energy at a resonant frequency 1960 1959 Singer measures blood flow using NMR in mice 1946 Bloch demonstrates that nuclear precession can be measured in detector coils 1985 Insurance reimbursements for MRI exams begin 1973 Lauterbur publishes method for generating images using NMR gradients MRI scanners become clinically prevalent NMR becomes MRI 1970 1980 1973 Mansfield independently publishes gradient approach to MR 1975 Ernst develops 2D Fourier transform for MR 1990 2000 1990 Ogawa and colleagues create functional images using endogenous bloodoxygenation contrast Early Uses of NMR Most early NMR was used for chemical analysis No medical applications 1971 Damadian publishes and patents idea for using NMR to distinguish healthy and malignant tissues Tumor detection by nuclear magnetic resonance Science Proposes using differences in relaxation times No image formation method proposed 1973 Lauterbur describes projection method for creating NMR images