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Presentation: Thursday @ 2pm
Real-Time Motion Correction
for High-Resolution Imaging of the Larynx:
Implementation and Initial Results
Joëlle K. Barral
Juan M. Santos
Electrical Engineering
Stanford University
Dwight G. Nishimura
In a Nutshell
We propose a real-time algorithm to combat the
main types of motion that corrupt highresolution larynx imaging.
Our algorithm combines navigator-based motion
correction with a reacquisition strategy.
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MOTIVATION
The Larynx
Anterior commissure
Vocal
cords
Thyroid
cartilage
Thyroid
cartilage
Cricoid
cartilage
Axial
Sagittal
http://www.antiquescientifica.com -- Drawing courtesy of Julie C. DiCarlo
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Laryngeal Motion
Real-time acquisition: 13 frames per second
Notice swallowing at time t = 18 s!
QuickTime™ and a
YUV420 codec decompressor
are needed to see this picture.
Healthy volunteer
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Laryngeal Motion
Motion detected by Cartesian navigators
: Outliers (Sporadic motion)
: Bulk motion (Drift)
High-frequencies:
Respiration, 14 cycles per min
Cancer patient
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Laryngeal Motion Types
 How to mitigate their effects
 Intermittent, sporadic motion:
– Swallowing, coughing, jolting
 Alternative ordering schemes
 Continuous motion:
–Flow (carotid arteries)  Phase encodes L/R
–Bulk motion (drift)
 Physical restraints; Coaching; Navigators
–Respiration  Diminishing Variance Algorithm (DVA)
If a continuous drift happens, DVA never converges.
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Diminishing Variance Algorithm (DVA)
Sachs, MRM 34: 412-422, 1995 -- Sachs, IEEE-TMI19: 73-79, 2000
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METHODS
Proposed Approach
We propose to first correct the data based on the
shift information. We then reacquire encodes
whose projections could not be properly
corrected.
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Implementation
RTHawk
1.5 T
Santos, IEEE-EMBS 2: 1048-1051, 2004
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Pulse Sequence
Fast Large Angle Spin Echo = FLASE
– Spin echo: immune against flow & off-resonances
– 3D: high-resolution
– T1-weighted contrast
QuickTime™ and a
YUV420 codec decompressor
are needed to see this picture.
Ma, MRM 35:903-910, 1996 -- Song, MRM 41:947-953, 1999
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Encodes Ordering
Examples with 32 phase encodes and 16 slice encodes
QuickTime™ and a
YUV420 codec decompressor
are needed to see this picture.
QuickTime™ and a
YUV420 codec decompressor
are needed to see this picture.
kz
ky
Sequential
Elliptical (concentric)
QuickTime™ and a
YUV420 codec decompressor
are needed to see this picture.
QuickTime™ and a
YUV420 codec decompressor
are needed to see this picture.
Square spiral
Pseudo-random
Wilman, MRM 38: 793-802, 1997 -- Bernstein, MRM 50: 802-812, 2003
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Reconstruction Pipeline
The user stops the scan when
satisfactory image quality is obtained.
Barral, ISMRM Motion Workshop 2010, p. 18
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GUI
X
Y
Z
S
S
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Experimental Parameters
FOV 12 cm - Matrix size 256x128x32 - TR/TE = 80/10 ms
Sequential encodes order
Three-coil larynx dedicated array
First pass (full acquisition: 4096 encodes): 5 min 28 s
Each additional pass (64 encodes reacquired): 5 s
Phantom (orange) scans: coronal acquisitions
In vivo (larynx) scans: axial acquisitions
Barral, ISMRM 2009, p. 1318 -- Coil picture courtesy of Marta G. Zanchi
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PHANTOM
EXPERIMENTS
Phantom Experiment 1:
No Motion
 An orange was scanned.
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Phantom Experiment 1:
No Motion
One pass = Full acquisition
 As expected, image
and corrected image
are identical
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Phantom Experiment 2:
DVA
 Non-rigid motion was simulated by
switching from the coronal acquisition to an
axial acquisition towards the middle of the
scan, for several seconds.
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Phantom Experiment 2:
DVA
Pass # 1 = Full acquisition: 4096 encodes acquired
 As expected, motion correction fails
 Motion detection successful
 Shift information meaningless
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Phantom Experiment 2:
DVA
Pass # 1
Pass # 6
 When corrupted encodes are reacquired,
a motion-free image is obtained.
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Phantom Experiment 3:
Motion Correction
 Towards the middle of the scan, the table
was manually translated. It was brought back
to its original position several seconds later.
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Phantom Experiment 3:
Motion Correction
Pass # 1 = Full acquisition: 4096 encodes acquired
 As expected, motion correction works
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Phantom Experiment 3:
Motion Correction
Pass # 1
Pass # 4
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 Blurry: the final position
of the table did not
perfectly
match
the
original position.
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Phantom Experiment 4:
Combined Algorithm
 Non-rigid motion was simulated by switching
to an axial acquisition towards the middle of the
scan, for several seconds. The table was then
manually translated.
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Phantom Experiment 4:
Combined Algorithm
Pass # 1 = Full acquisition: 4096 encodes acquired
 Motion correction successfully accounts
for the translation
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Phantom Experiment 4:
Combined Algorithm
Pass # 1
Pass # 6
 Reacquisition needed to
correct for non-rigid motion
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IN VIVO
EXPERIMENTS
In Vivo Experiment 1:
Without Instructions
 A healthy volunteer was scanned.
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In Vivo Experiment 1:
Without Instructions
One pass = Full acquisition
Slice 20/32
X
Y
Slice 26/32
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In Vivo Experiment 1:
Without Instructions
Sagittal reformat
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In Vivo Experiment 2:
With Instructions
 A healthy volunteer was scanned. He was
asked to swallow at will and to accentuate
motion when the center of k-space was being
acquired. For this experiment, 192 encodes
were reacquired each additional pass.
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In Vivo Experiment 2:
With Instructions
Pass # 1 = Full acquisition: 4096 encodes acquired
 Swallowing properly detected
 Only bulk motion corrected
by motion-correction
X
Y
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In Vivo Experiment 2:
With Instructions
Pass # 1
Pass # 3
 When corrupted encodes are reacquired,
motion correction is needed to account for
bulk shift (drift) that happened between passes.
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WRAP-UP
Conclusion & Future Work
 Our real-time algorithm corrects for rigidbody motion and reacquires encodes that
could not be corrected.
 Additional scans are needed to validate the
robustness of the method in vivo.
 Future work will improve the flexibility of
the algorithm and improve the user interface.
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Thank you!
Contact:
jbarral@stanford.edu
On larynx imaging, see also posters # 2410 and 2416!
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