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Functional magnetic resonance imaging. Magnetic resonance imaging. My discussion: MRI procedure. generate tissue contrast generate spatial localization. larmor frequency and RF pulse. Larmor frequency. RF pulse(classical view). z. B 0. M. . y. x’. y’. x. . Tissue contrast. y.

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Presentation Transcript
my discussion mri procedure
My discussion: MRI procedure
  • generate tissue contrast
  • generate spatial localization
larmor frequency and rf pulse
larmor frequency and RF pulse
  • Larmor frequency
  • RF pulse(classical view)

z

B0

M

y

x’

y’

x

t 2 decay constant

y

y

x

x

z

z

intrinsic spin-spin interactions

T2 decay constant

B’

90o RF(B1)

pause removed

Classical viewpoint

Mxy

Mxy

spin echo
Spin-echo

180o

180o

90o

90o

RF

signal

T2*

T2

TE

TR

T2=spin-spin relaxation

T2*=T2+static field inhomogeneities

different contrast images
Different contrast images

T2 contrast :

TR/TE = 5500/105 ms, 2 Nex, 512x256 matrix

White

Grey

CSF

TE(14)

TR(450)

TR(5500)

TE(105)

T1 contrast :

TR/TE= 450/14 ms, 1 Nex, 256x192 matrix

*Nex: number of acquisitions

spatial localization
Spatial localization
  • Slice select gradient
  • Frequency encode gradient
  • Phase encode gradient
slice select gradient slice thickness
Slice select gradient: slice thickness

2 ’

RF bandwidth

B+

2 

0

B0

B-

D1

Z

D2

D3

slice select gradient slice location
Slice select gradient: slice location

B+

RF bandwidth

2 

0

B0

B-

Z2

Z1

Z3

Z

frequency encode gradient
Frequency encode gradient

+Bx

-Bx

digitization

+f max

-f max

0

Fourier transform

phase encode gradient
Phase encode gradient

#128

#188

#60

-

+

Time

#256

#1

-

+

-

+

-

+

imaging spin echo

y

x

f(x,y)

repeat

Imaging: spin echo

90o

180o

RF pause

Slice selection

gradient

Phase encode gradient

Frequency encode gradient

ky

MR signal

kx

Data acquisition

F(kx,ky)

MR image

k-space

imaging spin echo planar fmri technique

90o

180o

Imaging: spin echo planar-FMRI technique

repeat

RF pause

Slice selection

gradient

Phase encode gradient

Within T2*

Frequency encode gradient

MR signal

Data acquisition

ky

y

kx

x

F(kx,ky)

f(x,y)

MR image

k-space

functional magnetic resonance imaging1
Functional magnetic resonance imaging
  • BOLD(blood-oxygen-level-dependent) fMRI is currently the most common fMRI technique
  • Noninvasive-no injection of radioactive isotopes
  • Spin echo planar imaging-extremely fast-50 ms
  • T2-T2* weighted images
t2 t2 weighted image
T2-T2* weighted image:

T2* is dependent on the presence of blood deoxygenation and that deoxygenated hemoglobin is a"BOLD" effect that can be observed by FMRI at high magnetic fields

more paramagnetic

shorter T2* longer T2*

fmri images
FMRI images

a high resolution scan is taken as background

a series of low resolution scans are taken over time during the experiment

the analyzed low resolution images are shown as colored blobs on top of the original high resolution scan, and also in 3D after proper analysis

slide23

The posterior lateral prefrontal cortex is a key neural substrate underlying the central bottleneck of information processing.

slide24

Central bottleneck model:

Task 1 Task 2

Experimental result:

slide25

Advantage:

  • FMRI can precisely locate the brain active spot with 1.5 x 1.5 mm in-plane resolution or even less than 1 mm.
  • FMRI can catch the blood flow in seconds with total scan time on the order of 1.5 to 2.0 min per run.