mr-based mc for (pet-) mr€¦ · (pet-) mr motion compensation christoph kolbitsch scott ad,...

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

[email protected]

(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


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


Christoph Kolbitsch

Overview

• Effect of motion on MR images

• Motion compensation

• (PET-) MR applications

• Outlook for hackathon


Christoph Kolbitsch

Motion during MR gradients

• leads to additional image phase

• can be used to encode velocity, acceleration,…

Motion in MRI


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


Respiration5

ECG Blood pool

2D Nav + Data acq

MR Motion Surrogates

Cardiac motion6


Christoph Kolbitsch




Motion in MRI

Blood flow


Christoph Kolbitsch




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


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


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


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


Christoph Kolbitsch




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


Christoph Kolbitsch

Time

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ky

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Translation


Christoph Kolbitsch

Time

kx

ky

...

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Time

Translation


Christoph Kolbitsch

kx

ky

...

Time

Sinusoidal Translational Motion


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


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


Nav + Data acq

MR Motion Surrogates


Christoph Kolbitsch

Overview






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


Christoph Kolbitsch

Motion Compensation - Gating

MR acquisition

Expiration

Inspiration

Expiration Inspiration Expiration


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


Christoph Kolbitsch

Motion Compensation - Correction

MR acquisition


Christoph Kolbitsch


MR acquisition

Determine displacement of each pixel


Christoph Kolbitsch


Transform all images to same motion state

MR acquisition


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)


Christoph Kolbitsch

Overview






Christoph Kolbitsch

MR-based motion correction for PET-MR

• Correction prior to PET image reconstruction

PET

MR MF

PET Recon

Corr

PET raw data


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.


Christoph Kolbitsch


• Correction after PET image reconstruction (reconstruct-transform-average, RTA)

PET

MR MF

GatedPET

Recon

Corr


Christoph Kolbitsch


• 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.


Christoph Kolbitsch


• Correction during PET reconstruction (motion corrected image reconstruction, MCIR)

PET

MR MF

MCIR PET Recon

Corr

MCIR MR

Recon

Corr Uncorr

Uncorr


Christoph Kolbitsch

Rank et al., Medical Physics, 2016.

Uncorr Corr

MR-based respiratory motion correction


Christoph Kolbitsch

PET-MR - Joint motion estimation

Fieseler et al., Biomed Eng Online, 2014.

Motion estimation

MR motion estimation

PET motion estimation


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


Christoph Kolbitsch

Overview






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

mr-based mc for (pet-) mr€¦ · (pet-) mr motion compensation christoph kolbitsch scott ad,...

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