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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. - PowerPoint PPT Presentation
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Magnetic resonance imaging
My discussion: MRI procedure
• generate tissue contrast
• generate spatial localization
larmor frequency and RF pulse
RF pulse(classical view)
0B
• Larmor frequency
y’
z
x’
x
y
B0 M
Tissue contrast
T2 decay constant
20
T
t
xy eMM
intrinsic spin-spin interactions
y
xz Mxy
y
xz
Mxy 90o RF(B1)
pause removed
Classical viewpoint
B’
T1 relaxation constant
)1( 10
T
t
z eMM
Spin-lattice relaxation
90o RF(B1) pause added
energy
Spin-echo
T2 T2*
TR
TE
90o 180o
90o 180o
RF
signal
T2=spin-spin relaxationT2*=T2+static field inhomogeneities
Different contrast images
T2 contrast : TR/TE = 5500/105 ms, 2 Nex, 512x256 matrix
T1 contrast : TR/TE= 450/14 ms, 1 Nex, 256x192 matrix
*Nex: number of acquisitions
TE(14)
TR(450) TR(5500)
TE(105)
WhiteGrey CSF
Spatial localization
• Slice select gradient• Frequency encode gradient• Phase encode gradient
Magnetic field gradient
Slice select gradient: slice thickness
B0
RF bandwidth
ZD1
D2
D3
B-
B+’
Slice select gradient: slice location
B0
RF bandwidth
Z Z1Z2Z3
B-
B+
Frequency encode gradient
digitization
-Bx
+Bx
-f max +f max0
Fourier transform
Phase encode gradient
-
+
#1
#60
#256
#188
#128
-
-
-
+
+
+
Time
Imaging: spin echo
x
y
f(x,y)
kx
ky
k-space
F(kx,ky)
MR image
RF pause
Slice selection gradient
Frequency encode gradient
Phase encode gradient
MR signal
Data acquisition
90o 180o repeat
x
y
f(x,y)
kx
ky
k-space
F(kx,ky)
MR image
RF pause
Slice selection gradient
Frequency encode gradient
Phase encode gradient
MR signal
Data acquisition
90o 180o repeat
Imaging: spin echo planar-FMRI technique
Within T2*
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* 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
shorter T2* longer T2*
more paramagnetic
FMRI actual measurement
FMRI images
1. a high resolution scan is taken as background
2. a series of low resolution scans are taken over time during the experiment
3. 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
FMRI head coil
The posterior lateral prefrontal cortex is a key neural substrate underlying the central bottleneck of information processing.
Central bottleneck model:
Experimental result:
Task 1 Task 2
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.
Advantage:
Thanks!