Continuous SWIFT - Center for Magnetic Resonance Research

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Djaudat Idiyatullin*, Steven Suddarth+, Curt Corum*,
Gregor Adriany*, Michael Garwood*
*Center for Magnetic Resonance
Research and Department of Radiology
University of Minnesota Medical
School, Minneapolis, Minnesota, USA
+Agilent Technologies Santa Clara,
California, USA
ISMRM, 2011
Declaration of Relevant Financial Interests
or Relationships
Speaker Name: Idiyatullin Djaudat
I have the following conflict of interest to disclose with regard to the
subject matter of this presentation:
Company name: Steady State Imaging
Type of relationship: sales royalty and consulting fee
SWeep Imaging with Fourier Transform (SWIFT)
Fast and quiet MRI using a swept radiofrequency,
D. Idiyatullin, C. Corum, J.-Y. Park, M. Garwood,
JMR (2006).
Applications:
• Molecular imaging,
• Dental imaging,
• Lung imaging,
• Breast cancer,
• MSK,
• Brain calcification.
1
f
G
Sensitive to fast relaxing spins
Projection method
No “echo time”
Time shared excitation and acquisition
acq
p
Time shared acquisition, limitations
d c = p bw
1  dc
- excitation duty cycle
- acquisition duty cycle
S/N 
1  dc
bw
RFenergy 
dc
S/N 
p
trd
1  dc  trdbw
trd 
Q
0
1/ bw
bw - acquisition bandwidth
trd - coil ring-down time
The goal of the project
To test SWIFT in continuous mode
with Varian/Agilent DirectDrive system &
digital receiver.
1
f
Expected advantages
• acquisition duty cycle =1 -> higher S/N;
G
acq
• excitation duty cycle =1 -> lower power & SAR,
absence of sidebands;
• absence of coil ringing -> SWIFT efficiency at higher bandwidth,
with low Larmor frequency (low field, X-nuclear).
Could we acquire a signal when transmitter is “on”?
100
9.0909
4T,
Breast coil,
water phantom
cSWIFT, R=256
0.9091
40 db
1
0.0909
Receiver threshold
0.1
0.0091
Volts
1/2 , Hz
10
cSWIFT, R=4096
1 mm
MRI signal level
0.01
0.0009
Peak power needed for excitation calculated for:
θ = Ernst angle, T1= 1 s with TR=Tacq, bw=50 kHz, R = bwTp
Transmitter-receiver isolation
Quad coil
Tune/Match
Hybrid
Preamplifier
0
90
90
0
Transmitter
Self-duplexing radar technique
using circular polarization, ~30- 40 db.
Continuous SWIFT spectroscopy
Ethanol-water mixture, 4T, bw= 6kHz, 4096 points
Chirp
cSWIFT signal
c  exp(i bt )  exp   j / 4 b 

2
2
S   h(t )  c  c  Ae


Transmitter leakage
i
Smooth function
Continuous SWIFT spectroscopy
Ethanol-water mixture, 4T, bw= 6kHz, 4096 points
MRI signal reconstruction
Frequency sweep & time
h
(
t
)

c
c

Ae




i
Re
Im
h
(
t
)

c
c



h(t )  c
H ( ) 


F  h(t )  c

F (c )


62.5kHz
Wow, it is working!
Continuous SWIFT
4 Tesla
bw= 62 kHz
FOV=40 cm
4 minutes
10 Watt amplifier
0.8Watt
Regular SWIFT
31Watt
Continuous SWIFT imaging
Continuous SWIFT
Regular SWIFT
bone
cartilage
0.02Watt
2Watt
Human total knee arthroplasty sample,
9.4 Tesla, bw=71 kHz, 128000 views, 7 minutes,
without a transmitter’s amplifier.
Conclusions
• Continuous SWIFT up to 70kHz bandwidth can run in modern
MRI scanners without hardware modification.
• Challenges: Sensitive to transmitter instability, coil deformations,
subject motion, vibrations.
Future development:
1. Probe and connection
Crossed coils, Hybrids, Circulators
2. Hardware
Modulation technique: ωacq =ω0 +ωmod
3. Software
Digital Receivers: signal reconstruction, filtering
Acknowledgement
This research was supported by NIH P41
RR008079, S10 RR023730, S10 RR027290
RR008079, R21 CA139688 grants and WM Keck
Foundation. We also thank Jutta Ellermann and
Elizabeth Arendt for opportunity to use TKA
sample at this study.
Thanks
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