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Structural and Functional Imaging

• Cortical Flattening– Software such as

BrainVoyager can “inflate” the cortex like a balloon so that sulci and gyri are “flattened”

– functional data can be transformed with the same complex function

– functional and structural data can be overlaid so that distribution on cortical sheet can be visualized

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Principles of MRI

Principles of MRI

• Some terms:– Nuclear Magnetic Resonance (NMR)

• quantum property of protons

• energy absorbed when precession frequency matches radio frequency

– Magnetic Resonance Imaging (MRI)• uses spatial differences in resonance frequencies to form an

image

• basis of anatomical MRI

– functional Magnetic Resonance Imaging (fMRI)• exploits magnetic properties of hemaglobin to create images

changes in cortical blood flow

Principles of MRI

• Some terms:– Nuclear Magnetic Resonance (NMR)

• quantum property of protons

• energy absorbed when precession frequency matches radio frequency

– Magnetic Resonance Imaging (MRI)• uses spatial differences in resonance frequencies to form an

image

• basis of anatomical MRI

– functional Magnetic Resonance Imaging (fMRI)• exploits magnetic properties of hemaglobin to create images

changes in cortical blood flow

Principles of MRI

• Some terms:– Nuclear Magnetic Resonance (NMR)

• quantum property of protons

• energy absorbed when precession frequency matches radio frequency

– Magnetic Resonance Imaging (MRI)• uses spatial differences in resonance frequencies to form an

image

• basis of anatomical MRI

– functional Magnetic Resonance Imaging (fMRI)• exploits magnetic properties of hemaglobin to create images

changes in cortical blood flow

Principles of MRI

• Some terms:– Nuclear Magnetic Resonance (NMR)

• quantum property of protons

• energy absorbed when precession frequency matches radio frequency

– Magnetic Resonance Imaging (MRI)• uses spatial differences in resonance frequencies to form an

image

• basis of anatomical MRI

– functional Magnetic Resonance Imaging (fMRI)• exploits magnetic properties of hemaglobin to create images

changes in cortical blood flow

Principles of NMR

• Protons are like little magnets– they orient in magnetic fields like

compass needles

– what way do they normally point?

QuickTime™ and a decompressor

are needed to see this picture.

Principles of NMR

• Protons are like little magnets– they orient in magnetic fields like

compass needles

– what way do they normally point?

– normally aligned with Earth’s magnetic field

Principles of NMR

• Protons are like little magnets– they orient in magnetic fields like

compass needles

– what way do they normally point?

– normally aligned with Earth’s magnetic field

– NMR uses a big magnet to align all the protons in a sample (e.g. brain tissue)

Principles of NMR

• Protons are like little magnets– Radio Frequency pulse will knock

protons at an angle relative to the magnetic field

Principles of NMR

• Protons are like little magnets– Radio Frequency pulse will knock

protons at an angle relative to the magnetic field

– once out of alignment, the protons begin to precess

Principles of NMR

• Protons are like little magnets– Radio Frequency pulse will knock

protons at an angle relative to the magnetic field

– once out of alignment, the protons begin to precess

– protons gradually realign with field (relaxation)

Principles of NMR

• Protons are like little magnets– Radio Frequency pulse will knock

protons at an angle relative to the magnetic field

– once out of alignment, the protons begin to precess

– protons gradually realign with field (relaxation)

– protons “echo” back the radio frequency that originally tipped them over

– That radio “echo” forms the basis of the MRI image

Principles of NMR

• Protons are like little magnets– The following simple equation

explains MRI image formation

MRI Image Formation

• First you need a scanner:

– The first MRI scanner

MRI Image Formation

• Modern Scanners

MRI Image Formation

• Our Scanner

MRI Image Formation

• Our Scanner

MRI Image Formation

• Our Scanner

MRI Image Formation

• Our Scanner

MRI Image Formation

• MRI Image formation– resonance frequency

depends on field strength

– gradient coils alter resonance frequency over distance

– slight differences in the “echo” frequency indicate the location of each proton

– second-dimension of a slice is coded by the phase of the protons

field gradient = frequency gradient

Functional Imaging

• Functional Imaging must provide a spatial depiction of some process that is at least indirectly related to neural activity

• in most imaging (i.e. PET, fMRI) that process is change in blood oxygenation related to changes in regional cerebral blood flow

• Why should we measure blood oxygenation?

Functional Imaging

• Why should we measure blood oxygenation?

• Onset of a stimulus (or cognitive task) changes local blood oxygenation– first with a decrease

– then with an “overshoot”

Functional Imaging

• Why should we measure blood oxygenation?

• Onset of a stimulus (or cognitive task) changes local blood oxygenation– first with a decrease

– then with an “overshoot”

• How do we measure changes in blood oxygenation?