1. Registration of functional PET and structural MR images PVEOut satellite meeting Budapest, June 11 th 2004 Peter Willendrup & Claus Svarer Neurobiology Research Unit Copenhagen

2. 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)

3. 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. AIR SPM

4. 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-HT 2A altanserin PET images where there are very limited uptake in Cerebellum Limited uptake

5. 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.

6. NRU, 2004 MARS Multiple 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

7. NRU, 2004 MARS Main program This is now included in pvelab

8. 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

9. NRU, 2004 Registration 1: Interactive Image Overlay

10. NRU, 2004 Registration 1: Interactive Image Overlay Translation and rotation of overlay image and surface by keyboard commands

11. NRU, 2004 Registration 1: Interactive Image Overlay

12. NRU, 2004 Registration 2: Interactive Point Selection

13. NRU, 2004 Registration 2: Interactive Point Selection

14. NRU, 2004 Inspection of registration Overlay Side by side

15. NRU, 2004 Evaluation study: Setup Images (5 subjects) –T1 weighted MR images (MPRAGE) – 18 F-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

16. NRU, 2004 Evaluation study: Simulated PET Simulated PET datasets –Good: known registration parameters –Bad: “easy” for cost fct. Based methods

17. NRU, 2004 Evaluation study: Altanserin PET Altanserin PET images –Bad:Lack of gold standard registration method –Good:Real world ‘limited uptake’ images

18. NRU, 2004 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 MRPET

19. NRU, 2004 Evaluation study: Simulated PET

20. NRU, 2004 Evaluation study: Altanserin PET

21. NRU, 2004 Evaluation study: Result SPMAirMean manual No Altanserin binding should be seen in Cerebellum, Rotation problem? Too little binding in Altanserin image, Translation problem?

22. 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 imagesF18-Altanserin images