fMRI and its application

Group 5 高名彥 許恬寧 段昭誼

Outline

• What is MRI?

• What is fMRI?

What is MRI

•MRI (Magnetic Resonance Imaging)核磁共振

•MRI is a medical imaging technique used in radiology to investigate the anatomy and physiology of the body in both health and disease. MRI scanners use magnetic fields and radio waves to form images of the body.

What is MRI?

Source: http://www.mnc.umd.edu/sites/default/files/images/facilities/mri-2.png

What is MRI?

• Magnetic system:• main coil

• 0.2-7(T) for human

• 4.7-9.4(T) for animal

• gradient coils• Generate gradient on X- Y- Z- direction to realize NMR signal space encoding

• RF system:• RF emitter

• RF receiver

Physics of MRI

S: spin of the nucleus(原子核的自旋)ϒ: gyromagnetic ratio(磁旋比)μ: magnetic moment of nucleus(核磁矩)

h bar: h/2pi m: half-integer or integer, e.g. -1 0 1 or -1/2 +1/2 Iz: spin projection along applied magnetic field

Physics of MRI

Source: http://www.mynewager.com/articles/images/q2a.gif

B

μz: magnetic moment along applied magnetic field

E: energy

Applied magnetic fieldDifferent value for different atom

Source: http://www.mynewager.com/articles/images/q2a.gif

E=hν

Exceptions: O16, C12 have no nucleus spin

Conclusion of MRI

• Magnetic field

• =>split of energy(different for different kinds of atom)

• =>when the energy of EM wave equal to the split difference

• =>be absorbed

• Use the spectrum to analyze.

What is fMRI?

• functional MRI (fMRI)

• Fact: Cerebral blood flow and neuronal activation are coupled.• Brain activity=> blood flow↑

• fMRI uses MRI technology that measures brain activity by detecting changes associated with blood flow.

• More specifically, deoxygenated hemoglobin (dHb) is more magnetic (paramagnetic) than oxygenated hemoglobin (Hb).

What is fMRI?

fMRI imagePositive: 相對興奮Negative: 相對抑制

MRI vs fMRI

Source: http://www.faculty.Jacobs-university.de/llinsen/teaching/320562/Teodora_Chitiboi_1.pdf

MRI vs fMRI

Source: http://www.faculty.Jacobs-university.de/llinsen/teaching/320562/Teodora_Chitiboi_1.pdf

Outline

• fMRI data explanation

• Three types of fMRI in experiment design

• Several viewpoints on fMRI

Hemodynamic response (HDR)

convolution

Voxel by voxel analysis, GLM(general linear model)27 mm3 , Each one represents a tidy cube of brain tissue~106 cells

** The power of using fMRI on small rodents to study brain pharmacology and disease

Paper studying

Several nouns to clarify

• CBV: cerebral blood volume 腦血容積

• CBF: cerebral blood flow 腦微灌流

• ASL: arterial spin labelling 動脈標記法

• FC: function connectivity

1. Stimulus-evoked fMRI (st-fMRI)

Specific stimulus, sensory or cognitive stimuli

- Block design, two or more different conditions are altered (preclinical studies) ,pros: powerful

- Event-related design, time in between vary and much shorter stimuli are used ,pros: latency, shape

- Timing depends on predefined paradigm

2. Pharmacological modulation on neuronal activity (phMRI)

Acute injection of a compound during fMRI evokes changes in the BOLD response

- Express specific receptors for the injected compound and also in their projection areas

- Experiment design dependent profile of the drug

- Timing and amplitude of the stimuli (more challenging than st-fMRI)

3. Monitoring BOLD signal at rest (rsfMRI)

rest, signal show spontaneous BOLD fluctuations over time

- spontaneous low frequency fluctuations of the BOLD signal are used as indirect marker to depict the functional architecture of the brain.

** Functional connectivity (FC) is defined as the temporal correlation of low frequency(0.01–0.1Hz)fluctuations of the BOLD signal between spatially distinct brain regions

Overview of application of fMRI methods

rs-fMRI basic analysis

Independent Component Analysis-voxels of one component represent regions that are functionally connected

Voxel-based Analysis-the time course is compared to all other voxels in the brain, resulting in FC map

ROI-based Analysis-the time course is compared to all other regions in the brain, resulting in FC matrix

Cabeza: Compensatory Hypothesis

• fMRI could help discover more info than outward behavior

** PFC activity during source memory was right lateralized in Young and Old-Low participants but bilateral in Old-High participants.

Aging Gracefully: Compensatory Brain Activity in High-Performing Older Adults Roberto Cabeza,*,1 Nicole D. Anderson,†, ‡ Jill K. Locantore,† and Anthony R. McIntosh†, §

Future fMRI application

• self control of brain activation region, pain controlling

• mind reading, brain reading

Several viewpoints on fMRI

1. Not precisely : too slow to capture all of the changes in the brain. Each scan 1~2s, a neuron to fire >100 times.

2. Hard to normalize between individuals :BOLD signal is not direct outcome from neuron activity.

3. Low Sensitivity: Strongest BOLD signal on Visual cortex only ~4% difference (2%~4%), SNR < 50 (1.5T)

fMRIVisual

Perception

Visual Perception is really hard to understand…

Thanks to fMRI!

Visual Pathway

Dissociation

What Where/How

Visually guided grasping produces fMRI activation in dorsal but not ventral stream brain areas

Object-directed action

Object Recognition

Isolating Specific Brain Activity

fMRI Result

Dissociation

Object recognition

Object-directed action

With fMRI…

• Gaining knowledge about human perception

• Pinpoint the problem

• Help find the cure for some diseases

REF

• Culham, J. C., et al. (2003). "Visually guided grasping produces fMRIactivation in dorsal but not ventral stream brain areas."

• Kanwisher, et al. (1997). “The Fusiform Face Area: A module in Human Extrastriate Cortex Specialized for Face Perception.”

• Goldstein, E.B. (2014). Sensation and Perception . 9th edition.

Thanks for your time and listening!

Appendix

FFA(Fusiform Face Gyrus)

PPA

EBA

Experience-dependent Plasticity

• Gauthier (1991)

• Greebles

Expertise Hypothesis

reference

• https://zh.wikipedia.org/wiki/%E6%A0%B8%E7%A3%81%E5%85%B1%E6%8C%AF%E6%88%90%E5%83%8F

• https://zh.wikipedia.org/wiki/%E6%8A%97%E7%A3%81%E6%80%A7

• https://en.wikipedia.org/wiki/Functional_magnetic_resonance_imaging

• http://www.faculty.jacobs-university.de/llinsen/teaching/320562/Teodora_Chitiboi_1.pdf