Magnetic Resonance Imaging of Fast Relaxing Spins: Acquisition during Adiabatic Excitation November...
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![Page 1: Magnetic Resonance Imaging of Fast Relaxing Spins: Acquisition during Adiabatic Excitation November 14, 2005, CMRR : Djaudat Idiyatullin.](https://reader036.fdocuments.us/reader036/viewer/2022062519/5697c0001a28abf838cc2043/html5/thumbnails/1.jpg)
Magnetic Resonance Imaging of Fast Relaxing Spins:
Acquisition during Adiabatic Excitation
November 14, 2005, CMRR : Djaudat Idiyatullin
![Page 2: Magnetic Resonance Imaging of Fast Relaxing Spins: Acquisition during Adiabatic Excitation November 14, 2005, CMRR : Djaudat Idiyatullin.](https://reader036.fdocuments.us/reader036/viewer/2022062519/5697c0001a28abf838cc2043/html5/thumbnails/2.jpg)
Mike’s crazy idea is working
![Page 3: Magnetic Resonance Imaging of Fast Relaxing Spins: Acquisition during Adiabatic Excitation November 14, 2005, CMRR : Djaudat Idiyatullin.](https://reader036.fdocuments.us/reader036/viewer/2022062519/5697c0001a28abf838cc2043/html5/thumbnails/3.jpg)
Interleaved excitation and sampling during a frequency-swept pulse
1. Steady state 2. Sensitive to spins with a very
short T23. It is not FID but the signal
predictable by Bloch simulation.
d
p
. . .
BIR4
……
![Page 4: Magnetic Resonance Imaging of Fast Relaxing Spins: Acquisition during Adiabatic Excitation November 14, 2005, CMRR : Djaudat Idiyatullin.](https://reader036.fdocuments.us/reader036/viewer/2022062519/5697c0001a28abf838cc2043/html5/thumbnails/4.jpg)
How to extract information from this weird sampling during swept excitation?
Least square method Monte Carlo simulation Wavelet transform
22 1aT
21/ 1a
![Page 5: Magnetic Resonance Imaging of Fast Relaxing Spins: Acquisition during Adiabatic Excitation November 14, 2005, CMRR : Djaudat Idiyatullin.](https://reader036.fdocuments.us/reader036/viewer/2022062519/5697c0001a28abf838cc2043/html5/thumbnails/5.jpg)
How to extract information from this weird sampling during swept excitation?
Solution:
1. Away from adiabatic condition
22 1aT
21/ 1a
2 21 1a a
2. Linear system- Correlation method
0 0180 90
![Page 6: Magnetic Resonance Imaging of Fast Relaxing Spins: Acquisition during Adiabatic Excitation November 14, 2005, CMRR : Djaudat Idiyatullin.](https://reader036.fdocuments.us/reader036/viewer/2022062519/5697c0001a28abf838cc2043/html5/thumbnails/6.jpg)
Linear system
Output r(t)
Input x(t)
System h(t)
A system is linear if:1. Linearity : Output = C * Input2. Shift invariant : delaying of Input → same delaying of Output
0 τ t
x(τ) → x(τ)h(t- τ)( ) ( ) ( )r t x h t d
( ) ( ) ( )R X H
Convolution
Fourier theorem:
![Page 7: Magnetic Resonance Imaging of Fast Relaxing Spins: Acquisition during Adiabatic Excitation November 14, 2005, CMRR : Djaudat Idiyatullin.](https://reader036.fdocuments.us/reader036/viewer/2022062519/5697c0001a28abf838cc2043/html5/thumbnails/7.jpg)
Evolution of the isochromats during HS8 pulse (dw=10mks, (~ 30 degree), R2=500Hz)
30kHz
time
20kHz
10kHz
0kHz
-10kHz
-20kHz
-40-20
02040
30kHz
frequency
20kHz
10kHz
0kHz
-10kHz
-20kHz
sum of all
![Page 8: Magnetic Resonance Imaging of Fast Relaxing Spins: Acquisition during Adiabatic Excitation November 14, 2005, CMRR : Djaudat Idiyatullin.](https://reader036.fdocuments.us/reader036/viewer/2022062519/5697c0001a28abf838cc2043/html5/thumbnails/8.jpg)
Evolution of the isochromats during HS8 pulse (dw=10mks, (~ 30 degree), R2=500Hz)
30kHz
time
20kHz
10kHz
0kHz
-10kHz
-20kHz
-40-20
02040
30kHz
frequency
20kHz
10kHz
0kHz
-10kHz
-20kHz
sum of all
Linear system
![Page 9: Magnetic Resonance Imaging of Fast Relaxing Spins: Acquisition during Adiabatic Excitation November 14, 2005, CMRR : Djaudat Idiyatullin.](https://reader036.fdocuments.us/reader036/viewer/2022062519/5697c0001a28abf838cc2043/html5/thumbnails/9.jpg)
Correlation method for linear system
( ) ( ) ( )r t x h t d
Response r(t)
Excitation x(t)
Spin system h(t) FT
FT
( ) ( ) ( )R X H *
2
( ) ( ) ( )( )
( )( )
R X RH
XX
( )H
)(X
( )R
System spectrum
*
![Page 10: Magnetic Resonance Imaging of Fast Relaxing Spins: Acquisition during Adiabatic Excitation November 14, 2005, CMRR : Djaudat Idiyatullin.](https://reader036.fdocuments.us/reader036/viewer/2022062519/5697c0001a28abf838cc2043/html5/thumbnails/10.jpg)
Simulated data HS4 pulse
100 isochromats from -12.5kHz step 250Hz
dw=10mks R1=500Hz
-40 -20 0 20 40
Hy()
f
/2 , kHz
eH
x()
dX
x()
cR
x()
bR
xy()
a
spin density
![Page 11: Magnetic Resonance Imaging of Fast Relaxing Spins: Acquisition during Adiabatic Excitation November 14, 2005, CMRR : Djaudat Idiyatullin.](https://reader036.fdocuments.us/reader036/viewer/2022062519/5697c0001a28abf838cc2043/html5/thumbnails/11.jpg)
SWeep Imaging
with Fourier Transform (SWIFT)
(a)
Gz
Gy
Gx
acq
RF
1
RF
1
acq
(b)
. . .
Tp
Tr
HSn pulsesFlip angle < 90 degreeTr ~ TpBw=sw=2πN/TpBack-projection reconstruction
![Page 12: Magnetic Resonance Imaging of Fast Relaxing Spins: Acquisition during Adiabatic Excitation November 14, 2005, CMRR : Djaudat Idiyatullin.](https://reader036.fdocuments.us/reader036/viewer/2022062519/5697c0001a28abf838cc2043/html5/thumbnails/12.jpg)
SWIFT, characteristics
Signal intensity depends only on T1 and spin density (M0) :
Maximum signal intensity Ernst angle:
Maximum T1 contrast:
Spin density contrast:
Sensitive to short T2 :
10
1
1 exp( / )sin( )
1 exp( / )cos( )tr
tr
T TS M
T T
1cos( ) exp( / )opt trT T
1.7 opt
opt
2 1/ ~ 10T s s
![Page 13: Magnetic Resonance Imaging of Fast Relaxing Spins: Acquisition during Adiabatic Excitation November 14, 2005, CMRR : Djaudat Idiyatullin.](https://reader036.fdocuments.us/reader036/viewer/2022062519/5697c0001a28abf838cc2043/html5/thumbnails/13.jpg)
SWIFT, hardware problems
“Dead time” after pulse
4.7T , 7T : ~ 3μs : sw < 130kHz
4T : ~ 20μs : sw < 40kHz
FIFO underflow happens if:
Tr < 5ms for 128 samplingTr < 10ms for 256 samplingsw ~ 25-35 kHz
![Page 14: Magnetic Resonance Imaging of Fast Relaxing Spins: Acquisition during Adiabatic Excitation November 14, 2005, CMRR : Djaudat Idiyatullin.](https://reader036.fdocuments.us/reader036/viewer/2022062519/5697c0001a28abf838cc2043/html5/thumbnails/14.jpg)
MIP of 3D image sw=32kHz
128x128 x 644T
Empty “16”-element TEM head coil
![Page 15: Magnetic Resonance Imaging of Fast Relaxing Spins: Acquisition during Adiabatic Excitation November 14, 2005, CMRR : Djaudat Idiyatullin.](https://reader036.fdocuments.us/reader036/viewer/2022062519/5697c0001a28abf838cc2043/html5/thumbnails/15.jpg)
3D image of thermoplastic
T2~0.3ms sw=100kHz
128x128 x 1284.7T
Sensitivity to short T2
![Page 16: Magnetic Resonance Imaging of Fast Relaxing Spins: Acquisition during Adiabatic Excitation November 14, 2005, CMRR : Djaudat Idiyatullin.](https://reader036.fdocuments.us/reader036/viewer/2022062519/5697c0001a28abf838cc2043/html5/thumbnails/16.jpg)
MIP of 3D image plastic toy in breast coil sw=39kHz
128x128 x 128D=25cm
4T
Sensitivity to short T2
![Page 17: Magnetic Resonance Imaging of Fast Relaxing Spins: Acquisition during Adiabatic Excitation November 14, 2005, CMRR : Djaudat Idiyatullin.](https://reader036.fdocuments.us/reader036/viewer/2022062519/5697c0001a28abf838cc2043/html5/thumbnails/17.jpg)
Slices of 3D image of feet
sw=20kHz4T
First in vivo SWIFT 3D images
![Page 18: Magnetic Resonance Imaging of Fast Relaxing Spins: Acquisition during Adiabatic Excitation November 14, 2005, CMRR : Djaudat Idiyatullin.](https://reader036.fdocuments.us/reader036/viewer/2022062519/5697c0001a28abf838cc2043/html5/thumbnails/18.jpg)
Slices of 3D image
raspberryin vivo
sw=100kHz128x128x128
D=3cm4.7T
Sensitivity to raspberry
![Page 19: Magnetic Resonance Imaging of Fast Relaxing Spins: Acquisition during Adiabatic Excitation November 14, 2005, CMRR : Djaudat Idiyatullin.](https://reader036.fdocuments.us/reader036/viewer/2022062519/5697c0001a28abf838cc2043/html5/thumbnails/19.jpg)
Advantages Disadvantages
fast Too fast for VARIAN
FIFO underflow
Sensitive to short T2 Sensitive to coil material
Reduced motion artifacts(zero echo time, back projection reconstruction)
Problems with slice selection
Reduced signal dynamic range ?
quiet Too quiet
![Page 20: Magnetic Resonance Imaging of Fast Relaxing Spins: Acquisition during Adiabatic Excitation November 14, 2005, CMRR : Djaudat Idiyatullin.](https://reader036.fdocuments.us/reader036/viewer/2022062519/5697c0001a28abf838cc2043/html5/thumbnails/20.jpg)
AnotherMike’s
crazy idea
![Page 21: Magnetic Resonance Imaging of Fast Relaxing Spins: Acquisition during Adiabatic Excitation November 14, 2005, CMRR : Djaudat Idiyatullin.](https://reader036.fdocuments.us/reader036/viewer/2022062519/5697c0001a28abf838cc2043/html5/thumbnails/21.jpg)
Breast MR scanner
![Page 22: Magnetic Resonance Imaging of Fast Relaxing Spins: Acquisition during Adiabatic Excitation November 14, 2005, CMRR : Djaudat Idiyatullin.](https://reader036.fdocuments.us/reader036/viewer/2022062519/5697c0001a28abf838cc2043/html5/thumbnails/22.jpg)
Thanks to:Ivan Tkac Gregor Adriany Peter Andersen Tommy Vaughan Xiaoliang ZhangCarl SnyderBrian Hanna John StruppJanis Zeltins Patrick BolanLance DelaBarreUte Goerke
all CMMR
Fast & Quiet MRI by Sweeping Radiofrequency
Djaudat Idiyatullin, Curt Corum, Jang-Yeon Park, Michael Garwood
Macros, C programming
Hardware
Software
Yellow pages of CMRR Discussion