European Instituteof Molecular Imaging

Generation of multiple respiratory phases in PET/CT

A phantom study

Mohammad Dawood, F Büther, O Schober, M Schäfers, KP Schäfers

European Institute for Molecular ImagingUniversity of Münster, Germany

European Institutefor Molecular Imaging

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European Instituteof Molecular Imaging Generating Multiple Respiratory CT Phases

PET, Minutes

CT, Seconds

Motivation

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European Instituteof Molecular Imaging Generating Multiple Respiratory CT Phases

CT based attenuation of PET data at inspiration

CT based attenuation of PET data at expiration

Problem

Myocardial Uptake: NCAT phantom data

Corresponding PET and CT Non-Corresponding PET and CT Difference

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European Instituteof Molecular Imaging Generating Multiple Respiratory CT Phases

1. Use PET data to estimate motion with optical flow methods

2. Apply motion vectors to the given CT to generate 4D-CT respiratory phases

Proposed solution

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European Instituteof Molecular Imaging Generating Multiple Respiratory CT Phases

Generating FDG PET data using NCAT

Emission map

Attenuation map

Emission sinogram

Attenuation sinogram

Attenuated emission sinogram

Simulation of 10 respiratory gates @ 30 mm diaphragm motion10 emission and 10 attenuation maps

Noisy emission sinogram

→ EM reconstruction(20 iterations):

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European Instituteof Molecular Imaging Generating Multiple Respiratory CT Phases

Optical flow

As a voxel at position 1 moves to position 2 its gray value remains the same:

I : Gray value (Activity)x,y,z,t : Position

Brightness consistency constraint

V : Flow (Motion)

Motion estimation

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European Instituteof Molecular Imaging Generating Multiple Respiratory CT Phases

Discontinuity Preserving Algorithm

Local Consistency + Global smoothness + Organ boundaries

Motion estimation

Dawood, Büther, Jiang, Schäfers: Motion correction in 3d PET/CT with advanced optical flow algorithms. IEEE Trans Med Imaging, 2008; 27(8):1164-75.

Global smoothnessLocal consistency

PET patient data without ACCoronal slice from 3D volume

FDG, 1 h p.i.

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European Instituteof Molecular Imaging Generating Multiple Respiratory CT Phases

Application to the given CT respiratory phase

Ground truth NCAT phantom data

Generated respiratory phases by the proposed method

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European Instituteof Molecular Imaging Generating Multiple Respiratory CT Phases

Ground truth Generated

Results: Position of the diaphragm

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European Instituteof Molecular Imaging Generating Multiple Respiratory CT Phases

Respiratory phase No Ground truth data Generated data

1 2.9 2.9

2 3.1 3.1

3 3.4 3.4

4 3.7 3.7

5 4.0 3.9

6 4.1 4.0

7 3.9 3.8

8 3.6 3.6

9 3.3 3.3

10 3.0 3.1

Average 3.50 3.48

Lung volume analysis

(volume in liters)

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European Instituteof Molecular Imaging Generating Multiple Respiratory CT Phases

Results: Myocardial uptake in LV on NCAT phantom data

PET : Insp. GeneratedCT : Insp.

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20

10

0

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PET : Insp. Ground TruthCT : Insp.

=

PET : Exp. Ground TruthCT : Exp.

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90

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Artifacts are removed if corresponding PET/CT phases are used for attenuation correction

Difference between generated and ground truth: Average 0.5%, Maximum = 4.3%

Difference

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European Instituteof Molecular Imaging Generating Multiple Respiratory CT Phases

Results: Myocardial uptake on patient data

PET : Insp.CT : Insp.

PET : Exp.CT : Insp.

PET : Exp.CT : Exp. (generated)

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European Instituteof Molecular Imaging Generating Multiple Respiratory CT Phases

Conclusions

- Respiratory motion leads to artifacts during attenuation correction

- up to 20% in this case

- Corresponding respiratory phases are required

- An optical flow based method is proposed to solve this problem

- Studies on NCAT phantom data showed encouraging results

- uptake error reduced to 0.5% on average, 4.3% max- correlation with ground truth 98.6%- lung volumes corresponded 99.4% with ground truth data- position of diaphragm same

- Further studies on patient data to be conducted soon

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European Instituteof Molecular Imaging Generating Multiple Respiratory CT Phases

Thank you !

EIMI - Technology team

Torsten BudumluFlorian BütherKatharina BüscherBjörn CzekallaMohammad DawoodMichael FieselerFabian GigengackThomas KöstersKlaus SchäfersSönke SchmidDaniel TenbrinckSusanne Zeglin