Registration of functional PET and structural MR images

PVEOut satellite meeting

Budapest, June 11th 2004

Peter Willendrup & Claus Svarer

Neurobiology Research Unit

Copenhagen

NRU, 2004

Registration needed PVEOut

• Structural MR and functional PET image has to be registered/aligned as the structural information is applied to each voxel in the functional image

• As image are coming from same subject only a rigid 6 parameter transformation has to be estimated:

– 3 translations (along X, Y and Z axis)– 3 rotations (around X, Y and Z axis)

NRU, 2004

What automatic methods are available?

• West J, Fitzpatrick JM, Dawant BM, et al.

• Headmounted fiducials serves as ``Gold standard'' coregistration between the modalities (MR/CT/PET).• Coregistration parameters are kept for reference, and fiducials are removed from the datasets and

replaced by artificial noise.• Methods are tested ``blindly'' - no knowledge of the Gold standard answer.

Method Mean(mm) Med.(mm) Max.(mm) Method Mean(mm) Med.(mm) Max.(mm)Pluim 3.04 2.34 10.10 Rohlfing 3 3.72 3.40 10.00 Woods 1 2.67 2.35 5.81 Maintz 3.86 3.48 10.63 Rohlfing 5 3.15 2.60 8.09 Tanacs 1 5.31 3.56 16.80 Rohlfing 4 6.32 2.61 50.90 Luo 2 3.85 3.59 7.45 Rohlfing corrected 1 4.09 2.62 23.45 Collignon 4.63 3.64 12.73 Rohlfing corrected 2 12.29 2.74 115.57 Noz 4.57 3.64 11.37 Harkness 3.74 2.78 12.09 Ding 3.76 3.74 9.44 Pelizzari 3.36 2.89 9.99 Thevenaz 2 9.85 3.97 27.57 Thevenaz 3 4.52 2.98 14.34 Robb 3 4.21 4.01 9.44 Arata 2 3.00 3.01 5.43 Ashburner 2 4.14 4.20 7.46 Hsu 3.70 3.06 12.79 Malandain 4.24 4.21 8.54 Rohlfing 6 4.46 3.11 17.69 Nikou 1 4.24 4.29 8.62 Woods 2 3.00 3.14 5.97 Barillot 4.57 4.58 11.48 Ren 3.54 3.20 9.51 Thevenaz 1 4.86 5.03 10.13 Hill 3.50 3.25 9.32 Nikou 2 6.28 5.06 12.28 Tanacs 2 5.82 3.29 19.74 Ashburner 1 5.57 5.11 11.62 Robb 4 3.48 3.35 5.90 Capek 9.08 9.02 9.84

AIR

SPM

NRU, 2004

Why are the automatic approaches not always a good idea?

• These methods are very well suited for registration of images where:

– There in the PET image is an equal uptake in all brain regions– There is no inhomogenity variation in the MR images

• This is not the case for all receptor PET images, e.g. 5-HT2A

altanserin PET images where there are very limited uptake in Cerebellum

Limited

uptake

NRU, 2004

What manual methods have been proposed?

Many different approches exist in the litterature• Landmark based: "Graphics applied to medical image registration", G. Q. Maguire, Jr., M. E. Noz, H.

Rusinek, et al., Comput Graph Appl, 1991, vol. 11, pp. 20-29. • Surface based: "Accurate three-dimensional registration of CT, PET, and/or MR images of the brain", C.

A. Pelizzari, G. T. Y. Chen, D.R. Spelbring, R. R. Wechselbaum, and C-T. Chen, J Comput AssistTomogr, 1989, vol. 13, pp. 20-26.

• Image overlay: "Quantitative Comparison of Automatic and Interactive Methods for MRI-SPECT Image Registration of the Brain Based on 3-Dimensional Calculation of Error ”, Pfluger T, Vollmar C et al.: J Nucl Med 2000; 41:1823-1829

• Voxel based: "MRI-PET registration with automated algorithm", R. P. Woods, J. C. Mazziotta, and S. R. Cherry, J Comput Assist Tomogr, 1993, vol. 17, pp. 536-546.

NRU, 2004

MARSMultiple Algorithms for Registration of Scans

• Modular design– The problem of coregistration can be divided into subtasks

• Data selection• Registration• Visualisation / Inspection• Parameter I/O• Reslicing / Re-Interpolation

– All subtasks realised by ‘plugins’ - easy inclusion of alternative method

– Different registration approaches benefit from shared code

NRU, 2004

MARS

• Main program

• This is now included in pvelab

NRU, 2004

MARS

• Subtask modules– Registration

• Interface to Air 5.0 - Roger P. Woods• Interface to SPM 2 - J. Ashburner et. al.• IIO (Interactive Image Overlay) - NRU *• IPS (Interactive Point Selection) - NRU *

– Visualisation• Inspect (NRU visualisation program) *

• Asterisk-marked will be further explained

NRU, 2004

Registration 1: Interactive Image Overlay

NRU, 2004

Registration 1: Interactive Image Overlay

Translation and rotation

of overlay image and surface

by keyboard commands

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Registration 1: Interactive Image Overlay

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Registration 2: Interactive Point Selection

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Registration 2: Interactive Point Selection

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Inspection of registration

OverlaySide by side

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Evaluation study: Setup

• Images (5 subjects)– T1 weighted MR images (MPRAGE)

– 18F-Altanserin 5HT-2A receptor images

– Simulated PET images

• Evaluation by 7 volunteers– 3 rounds of MR / Altanserin registration

– 1 round of MR / Simulated PET registration

– Registration order randomised

– Max. one ‘round’ of registrations pr. day

• Images also registered using SPM99 and Air 3.0

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Evaluation study: Simulated PET

• Simulated PET datasets – Good: known registration parameters

– Bad: “easy” for cost fct. Based methods

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Evaluation study: Altanserin PET

• Altanserin PET images– Bad: Lack of gold standard registration method

– Good: Real world ‘limited uptake’ images

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Evaluation study

• Error measure - Euclidean distance between transformation endpoints

• Evaluated for 1% evenly distributed brain voxels. • Mean and std. dev. calculated

• Mean transformation realized by 6-parameter estimation to mean of transformed voxels

MR PET

vvv BxAxE

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Evaluation study: Simulated PET

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Evaluation study: Altanserin PET

NRU, 2004

Evaluation study: Result

SPM Air Mean manual

No Altanserin binding

should be seen in

Cerebellum,

Rotation problem? Too little binding in

Altanserin image,

Translation problem?

NRU, 2004

• Two manual co-registration methods and the interface to two automatic methods have been implemented and incorporated in the PVEOut SW package (pvelab).

• Four registration methods are included:– Interface to SPM 2 (J. Ashburner et. al.)– Interface to Air (R. Woods)– IIO (NRU)– IPS (NRU)

• For FDG/flow type images, SPM and Air are preferred, with reported errors in the range 2-3 mm.

• For neuroreceptor type images, with limited binding in areas of the brain, the manual methods can be used and possibly preferred.

• Measured errors:

Registration: Conclusion

Simulated images F18-Altanserin images