Real-Time Motion Correction for High-Resolution Imaging of the Larynx: Implementation and Initial

Results

Presentation: Thursday @ 2pm#

5036

Electrical EngineeringStanford University

Joëlle K. Barral Juan M. Santos Dwight G. Nishimura

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In a Nutshell

We propose a real-time algorithm to combat the main types of motion that corrupt high-resolution larynx imaging.

Our algorithm combines navigator-based motion correction with a reacquisition strategy.

MOTIVATION

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The Larynx

Thyroid cartilage

Sagittalhttp://www.antiquescientifica.com -- Drawing courtesy of Julie C. DiCarlo

Axial

Thyroid cartilage

Anterior commissure

Cricoid cartilage

Vocal cords

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Laryngeal Motion

Healthy volunteer

Real-time acquisition: 13 frames per secondNotice swallowing at time t = 18 s!

QuickTime™ and aYUV420 codec decompressor

are needed to see this picture.

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Laryngeal Motion

Cancer patient

: Outliers (Sporadic motion)

: Bulk motion (Drift)

High-frequencies: Respiration, 14 cycles per min

Motion detected by Cartesian navigators

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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

METHODS

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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

1.5 TRTHawk

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

Ma, MRM 35:903-910, 1996 -- Song, MRM 41:947-953, 1999

QuickTime™ and aYUV420 codec decompressor

are needed to see this picture.

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Encodes Ordering

Sequential

Square spiral

Pseudo-random

kz

ky

Examples with 32 phase encodes and 16 slice encodes

Elliptical (concentric)

Wilman, MRM 38: 793-802, 1997 -- Bernstein, MRM 50: 802-812, 2003

QuickTime™ and aYUV420 codec decompressor

are needed to see this picture.

QuickTime™ and aYUV420 codec decompressor

are needed to see this picture.

QuickTime™ and aYUV420 codec decompressor

are needed to see this picture.

QuickTime™ and aYUV420 codec decompressor

are needed to see this picture.

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Reconstruction Pipeline

Barral, ISMRM Motion Workshop 2010, p. 18

The user stops the scan when satisfactory image quality is obtained.

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GUI

X Y Z

S

S

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Experimental ParametersFOV 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

PHANTOM EXPERIMENTS

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No Motion

An orange was scanned.

Phantom Experiment 1:

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No MotionOne pass = Full acquisition

As expected, image and corrected image are identical

Phantom Experiment 1:

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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.

Phantom Experiment 2:

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DVAPass # 1 = Full acquisition: 4096 encodes acquired As expected, motion correction fails

Motion detection successful Shift information meaningless

Phantom Experiment 2:

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DVAPass # 1

Pass # 6

When corrupted encodes are reacquired, a motion-free image is obtained.

Phantom Experiment 2:

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Motion Correction

Towards the middle of the scan, the table was manually translated. It was brought back to its original position several seconds later.

Phantom Experiment 3:

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Motion CorrectionPass # 1 = Full acquisition: 4096 encodes acquired

As expected, motion correction works

Phantom Experiment 3:

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Motion Correction

Blurry: the final position of the table did not perfectly match the original position.

Phantom Experiment 3:

Pass # 1

Pass # 4

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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.

Phantom Experiment 4:

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Combined Algorithm

Pass # 1 = Full acquisition: 4096 encodes acquired

Motion correction successfully accounts for the translation

Phantom Experiment 4:

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Combined Algorithm

Pass # 1

Pass # 6

Reacquisition needed to correct for non-rigid motion

Phantom Experiment 4:

IN VIVO EXPERIMENTS

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Without Instructions

A healthy volunteer was scanned.

In Vivo Experiment 1:

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Without Instructions One pass = Full acquisition

Slice 20/32

X

Y

In Vivo Experiment 1:

Slice 26/32

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Without Instructions

Sagittal reformat

In Vivo Experiment 1:

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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.

In Vivo Experiment 2:

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With Instructions Pass # 1 = Full acquisition: 4096 encodes acquired

X

Y

In Vivo Experiment 2:

Swallowing properly detected

Only bulk motion corrected by motion-correction

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With Instructions

When corrupted encodes are reacquired, motion correction is needed to account for bulk shift (drift) that happened between passes.

In Vivo Experiment 2:

Pass # 1

Pass # 3

WRAP-UP

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Conclusion & Future Work

Our real-time algorithm corrects for rigid-body 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!