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Physikalisch-Technische Bundesanstalt
Braunschweig und Berlin
National Metrology Institute
MR-based MC for (PET-) MR
Christoph Kolbitsch Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
(PET-) MR motion compensation
Christoph Kolbitsch
Motivation
Andre et al., Toward Quantifying the Prevalence, Severity, and Cost Associated With Patient Motion During Clinical MR Examinations, J Am Coll Radiol, 2015, 12:689-95
Retrospective analysis of MR scans carried out in one random
calendar week on three MR scanners:
20% of scans had to be repeated due to motion artefacts
Motion can lead to:
Blurring & Ghosting Signal loss
(PET-) MR motion compensation
Christoph Kolbitsch
Physiological Motion
Irregular motion
• Head motion
• Swallowing, peristaltic/gastric motion
• Bulk-motion (i.e. shift of body)
”Periodic” motion
• Respiration
• Heart beat
• Blood flow, pulsation
(PET-) MR motion compensation
Christoph Kolbitsch
Overview
• Effect of motion on MR images
• Motion compensation
• (PET-) MR applications
• Outlook for hackathon
(PET-) MR motion compensation
Christoph Kolbitsch
Motion during MR gradients
• leads to additional image phase
• can be used to encode velocity, acceleration,…
Motion in MRI
(PET-) MR motion compensation
Christoph Kolbitsch
1Ehman et al, Radiology, 1989, 173:255-263. 2Uribe et al., MRM, 2007, 57:606-613. Buerger et al., IEEE TMI, 2012, 31:805-815. 3Piccini et al., JMRI,
2016, 426-433. 5Henningsson et al., MRM, 2013, 69:486-494. 6Kolbitsch et al., MRM, 2014, 71:942-954
• Pencil beam navigator1
(1D motion of diaphragm in mm)
• Self-navigator2-4
• Image based navigators
1D Nav Data acquisition
Nav + Data acq
2D Nav Data acquisition
Respiration5
ECG Blood pool
2D Nav + Data acq
MR Motion Surrogates
Cardiac motion6
(PET-) MR motion compensation
Christoph Kolbitsch
Motion during MR gradients
• leads to additional image phase
• can be used to encode velocity, acceleration,…
Motion in MRI
Blood flow
(PET-) MR motion compensation
Christoph Kolbitsch
Motion during MR gradients
• leads to additional image phase
• can be used to encode velocity, acceleration,…
Motion along slice encoding direction
• through-plane motion
• leads to spins moving in and out of volume affected by MR
sequence
• can lead to signal drop-out or signal enhancement
Motion in MRI
(PET-) MR motion compensation
Christoph Kolbitsch
Zaitsev M, Maclaren J, Herbst M. Motion artifacts in MRI: A complex problem with many partial solutions. J. Magn. Reson. Imaging 2015
Through-plane Motion
(PET-) MR motion compensation
Christoph Kolbitsch
• Surrogate signal is obtained
(e.g. diaphragm)
• Shift for are of interest (e.g.
heart) is estimated
• For each acquisition, slice
position is updated
Slice Tracking
(PET-) MR motion compensation
Christoph Kolbitsch
Scott AD, Keegan J, Firmin DN. Motion in cardiovascular MR imaging. Radiology 2009;250:331–351.
Dark-blood TSE sequence of the heart
No slice tracking Tracking of LV Tracking of RV
Slice Tracking
(PET-) MR motion compensation
Christoph Kolbitsch
Motion during MR gradients
• leads to additional image phase
• can be used to encode velocity, acceleration,…
Motion along slice encoding direction
• through-plane motion
• leads to spins moving in and out of volume affected by MR
sequence
• can lead to signal drop-out or signal enhancement
Motion in between phase-encoding steps
• leads to blurring and ghosting
• effect depends on frequency and amplitude of motion
Motion in MRI
(PET-) MR motion compensation
Christoph Kolbitsch
Time
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Translation
(PET-) MR motion compensation
Christoph Kolbitsch
Time
kx
ky
...
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Time
Translation
(PET-) MR motion compensation
Christoph Kolbitsch
kx
ky
...
Time
Sinusoidal Translational Motion
(PET-) MR motion compensation
Christoph Kolbitsch
Translation (Fourier Shift Theorem):
ℱ 𝑓 𝑥 + ∆𝑥 = 𝑒−2𝜋𝑖𝑘∆𝑥𝐹(𝑘)
ℱ 𝑓 𝑥 = 𝐹(𝑘)
Scaling (Similarity Theorem):
ℱ 𝑓 𝑎𝑥 = 1
𝑎𝐹(
𝑘
𝑎)
2D Rotation by angle 𝜃:
ℱ 𝑓 𝑥𝑐 + 𝑦𝑠,−𝑥𝑠 + 𝑦𝑐 = 𝐹(𝑘𝑥𝑐 + 𝑘𝑦𝑠, −𝑘𝑥𝑠 + 𝑘𝑦𝑐)
with 𝑐 = cos 𝜃 𝑠 = sin 𝜃 and
Affine Motion
(PET-) MR motion compensation
Christoph Kolbitsch
1Ehman et al, Radiology, 1989, 173:255-263. 2Uribe et al., MRM, 2007, 57:606-613. Buerger et al., IEEE TMI, 2012, 31:805-815. 3Piccini et al., JMRI,
2016, 426-433. 5Henningsson et al., MRM, 2013, 69:486-494. 6Kolbitsch et al., MRM, 2014, 71:942-954
• Pencil beam navigator1
(1D motion of diaphragm in mm)
• Self-navigator2-4
1D Nav Data acquisition
Nav + Data acq
MR Motion Surrogates
(PET-) MR motion compensation
Christoph Kolbitsch
Overview
• Effect of motion on MR images
• Motion compensation
• (PET-) MR applications
• Outlook for hackathon
(PET-) MR motion compensation
Christoph Kolbitsch
Motion Compensation
• Patient coaching
• Breath-holds
• Sedation
• Averaging over multiple motion states
• Optimise MR data acquisition
• Real-time imaging
• Gating and triggering
Not always applicable
Does not fully remove motion artefacts
Limits FOV and resolution
(PET-) MR motion compensation
Christoph Kolbitsch
Motion Compensation - Gating
MR acquisition
Expiration
Inspiration
Expiration Inspiration Expiration
(PET-) MR motion compensation
Christoph Kolbitsch
Motion Compensation - Gating
MR acquisition
Define gating window in e.g. end-expiration
and only use data acquired within this window
Expiration Inspiration Expiration
(PET-) MR motion compensation
Christoph Kolbitsch
Motion Compensation - Correction
MR acquisition
(PET-) MR motion compensation
Christoph Kolbitsch
Motion Compensation - Correction
MR acquisition
Determine displacement of each pixel
(PET-) MR motion compensation
Christoph Kolbitsch
Motion Compensation - Correction
Transform all images to same motion state
MR acquisition
(PET-) MR motion compensation
Christoph Kolbitsch
Motion compensated image reconstruction
Influence of physiological
motion included by motion
operator 𝑈𝑑 which describes
the transformation from each
motion state d to a reference
motion free state.
𝒔 = 𝐸𝑑𝒎 𝑑
𝐸𝑑 = 𝐿𝑑𝐹𝐶𝑈𝑑 with
𝒇(𝑛+1) = 𝒇 𝑑(𝑛)
𝑈𝑑𝑑 𝐻
𝑇 𝑈𝑑
𝑑
𝐻 𝑇
𝒑𝑑
𝐻 𝑈𝑑𝒇 (𝑛)
(PET-) MR motion compensation
Christoph Kolbitsch
Overview
• Effect of motion on MR images
• Motion compensation
• (PET-) MR applications
• Outlook for hackathon
(PET-) MR motion compensation
Christoph Kolbitsch
MR-based motion correction for PET-MR
• Correction prior to PET image reconstruction
PET
MR MF
PET Recon
Corr
PET raw data
(PET-) MR motion compensation
Christoph Kolbitsch
PET-MR - Head motion correction
Motion measurement over time
Uncorr Corr MR
PET 3D 3D 3D 3D 3D 3D
Image courtesy of Ciprian Catana, MGH
Catana et al., J Nucl Med, 2011.
(PET-) MR motion compensation
Christoph Kolbitsch
MR-based motion correction for PET-MR
• Correction after PET image reconstruction (reconstruct-transform-average, RTA)
PET
MR MF
GatedPET
Recon
Corr
(PET-) MR motion compensation
Christoph Kolbitsch
MR-based motion correction for PET-MR
• Correction during PET reconstruction (motion corrected image reconstruction, MCIR)
PET
MR MF
MCIR PET Recon
Corr Uncorr
Polycarpou et al., Medial Physics, 2012, 39:6474-6483.
(PET-) MR motion compensation
Christoph Kolbitsch
MR-based motion correction for PET-MR
• Correction during PET reconstruction (motion corrected image reconstruction, MCIR)
PET
MR MF
MCIR PET Recon
Corr
MCIR MR
Recon
Corr Uncorr
Uncorr
(PET-) MR motion compensation
Christoph Kolbitsch
MR-based motion correction for PET-MR
• Correction during PET reconstruction (motion corrected image reconstruction, MCIR)
PET
MR MF
MCIR PET Recon
Corr
MCIR MR
Recon
Corr Uncorr
Uncorr
(PET-) MR motion compensation
Christoph Kolbitsch
Rank et al., Medical Physics, 2016.
Uncorr Corr
MR-based respiratory motion correction
(PET-) MR motion compensation
Christoph Kolbitsch
PET-MR - Joint motion estimation
Fieseler et al., Biomed Eng Online, 2014.
Motion estimation
MR motion estimation
PET motion estimation
(PET-) MR motion compensation
Christoph Kolbitsch
PET-MR - Joint synergistic motion estimation
Kolbitsch et al., Joint PET-MR image registration for cardiac and respiratory motion correction of simultaneous cardiac PET-MR, PMB 2018
(PET-) MR motion compensation
Christoph Kolbitsch
PET-MR - Joint synergistic motion estimation
Kolbitsch et al., Joint PET-MR image registration for cardiac and respiratory motion correction of simultaneous cardiac PET-MR, PMB 2018
(PET-) MR motion compensation
Christoph Kolbitsch
PET-MR - Joint synergistic motion estimation
Kolbitsch et al., Joint PET-MR image registration for cardiac and respiratory motion correction of simultaneous cardiac PET-MR, PMB 2018
(PET-) MR motion compensation
Christoph Kolbitsch
PET-MR - Joint synergistic motion estimation
Kolbitsch et al., Joint PET-MR image registration for cardiac and respiratory motion correction of simultaneous cardiac PET-MR, PMB 2018
(PET-) MR motion compensation
Christoph Kolbitsch
Overview
• Effect of motion on MR images
• Motion compensation
• (PET-) MR applications
• Outlook for hackathon
(PET-) MR motion compensation
Christoph Kolbitsch
Outlook - Hackathon
• Enable MCIR for both PET and MR using given motion fields
• Enable MR and PET image registration in SIRF
• Implement joint MCIR PET-MR reconstruction with
optimisation of motion fields