Image Registration Narendhran Vijayakumar (Naren) 12/17/2007 Department of Electrical and Computer Engineering 1

Image Registration(1/2) Process of estimating the Geometric transformation function between two images. – Rigid Transformation Rotational and Translational misalignment – Affine Transformation Rotational, Translational, Shearing and Scaling 2

T2 FLAIR & diffusion weighted MRI (a) A T2 FLAIR diffusion weighted MR image of a patient with ROI marked. (b) Corresponding Diffusion weighted MR image of the patient. (a)(b) 3

Commercial Software Philips Syntegra – Cross Correlation – Local Correlation – Mutual Information (MI) BrainScan – Mutual Information

Registration Algorithms Anatomical point landmark based methods – Labor intensive, Accuracy depends on user – Each slice has different structure Surface-based registration – Limited by surface segmentation error Voxel based registration – Cross correlation, Local correlation – Mutual information Fourier Based Registration 5

Mutual information Quantity that measures mutual dependence of two random variables Maximum MI implies good registration – Search for (t x,t y,β z ) where MI is maximum Definitions 6

Entropy Measures dispersion of probability density function. H(A,B) for misaligned images. Source: Pluim et al., “Mutual-information-based registration of medical images: a survey”, IEEE transactions on medical imaging, Vol 22, no 8, Aug

MI on Distributed system Algorithm – Step1: Master sends the Reference image I1 and floating image I2 to the workers. – Step2: Master then sends the range of search space to the workers. – Step 3: Workers receives the images I1 and I2, and find the global maxima (MI) for their given search space. – Step 4: Workers send the global maxima MI and the corresponding X and Y locations to the Master. – Step 5: Master Receives the MI and the corresponding X, Y values from all the workers. – Step 6: The maximum MI among the received values is the global maxima. 8

Results 9

Conclusion Up to 6 times speed up was achieved. Speed up limitation – Saturates at when Np=5 – Amdahl’s Law Fourier based registration – May be more fast 10