Implementation of PROPELLER MRI method for Diffusion Tensor Reconstruction

1. Implementation of PROPELLER MRI methodfor Diffusion Tensor Reconstruction A. Cheryauka1, J. Lee1, A. Samsonov2, M. Defrise3, and G. Gullberg4 1 – MIRL, University of Utah 2 – SCI, University of Utah, 3 – Free University, Brussels 4 – Lawrence Berkeley National Lab

2. Objectives Magnetic Resonance Imaging To obtain images of good quality at appropriate speeds of acquisition and reconstruction for efficient clinical evaluation PROPELLER method - High-resolution imaging with promising capabilities, - Motion reduction, - Optimized for diffusion tensor imaging Our work - Explore the potential of PROPELLER - Develop image reconstruction & processing tools - Implement Diffusion Tensor PROPELLER

3. MRI acquisition schemes K-spaces Rectangular 256x256 Radial 256x406 PROPELLER 256x32x12

4. PROPELLER*(Periodically Rotated Overlapping ParallEL Lines with Enhanced Reconstruction ) • Diffusion-weighted image r - proton density b - attenuation constant D - diffusion tensor w - direction of diffusion gradient • Low-resolution image from blade • ( MR signal pw(k) of region Bq support ) Blade Bq

5. Proton Density Reconstruction( GE scanner ) Agar phantom MIRL image GE image

6. Head Imaging( Picker scanner ) • Acquisition parameters: • 24 cm FOV • 5 mm slice • TE/TR= 135/800 msec • no attenuation (b=0) • 256x24x16 k-space

7. Diffusion Tensor Imaging Objective: estimate an effective diffusion tensor (DT) in each voxel from series of diffusion-weighted images Motivation: DWI sensitivity to alternation of local fluid mobility or space geometry (epilepsy, myocardial ischemia, spinal lesion). PROPELLER vs EPI: combines the advantages of FSE, navigator echoes, and projection reconstruction into a single technique.

8. 2 -D Tensor Measurements Encoding • Stationary gradients( Basser, 1994) • - directions of gradients are the same for all blades • in global coordinate system • Partially rotated gradients (Defrise, 2002) • - several gradient directions in global coordinate system • DTT MRI with rotated gradients ( Gullberg, 1999 ) • - directions of gradients are the same for each • blade in local coordinate system

9. DW Image Reconstruction • Conventional DT MRI with stationary gradients • uses “mapping + 2D FFT” scheme. • DT Tomography MRI with rotated gradients • goes with iterative optimization solver L – objective functional p’,p – measured & predicted data m – model parameters Lprior – stabilizing functional a - regularization parameter Wd, Wm - weighing matrices

10. DT imaging (1)( 2-D, stationary gradients ) Eigenvalues & eigenvectors Proton density ‘Two-bottles’ numerical phantom, 5 % random noise

11. DT imaging (2)( 2-D, partially rotated gradients ) Eigenvalues & eigenvectors Proton density ‘Two-bottles’ numerical phantom, 5 % random noise

12. DT imaging (3)( 3-D, stationary gradients ) DT components Proton density ‘Gel – celery – agar’ phantom

13. Conclusions • Identified ways and strategies • Built new acquisition sequences (Picker scanner) • Developed image reconstruction and • processing tools • Tested on a variety of synthetic and real data …