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Parallel Imaging

Parallel Imaging. SMASH and SENSE High field advantage Pros and cons … But first, review of last few homework assignments. Bibliography: parallel imaging. Original SMASH and SENSE papers

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Parallel Imaging

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  1. Parallel Imaging • SMASH and SENSE • High field advantage • Pros and cons… • But first, review of last few homework assignments Parallel Imaging

  2. Bibliography: parallel imaging • Original SMASH and SENSE papers • Griswold MA, Jakob PM, Chen Q, Goldfarb JW, Manning WJ, Edelman RR, Sodickson DK (1999). Resolution enhancement in single-shot imaging using simultaneous acquisition of spatial harmonics (SMASH). Magn Reson Med. 41(6):1236-45. • Pruessmann KP, Weiger M, Scheidegger MB, Boesiger P (1999). SENSE: sensitivity encoding for fast MRI. Magn Reson Med. 42(5):952-62. • Additional references • Sodickson, DK (2000). Tailored SMASH image reconstructions for robust in vivo parallel MR imaging. Magn Reson Med 44:243-251. • Weiger, M, Boesiger, P, Hilfiker, PR, Weishaupt, D, Pruessmann, KP (2005). Sensitivity encoding as a means of enhancing the SNR efficiency in steady-state MRI. Magn Reson Med 53:177-185. • Griswold MA, Jakob PM, Heidemann RM, Nittka M, Jellus V, Wang J, Kiefer B, Haase A. (2002). Generalized autocalibrating partially parallel acquisitions (GRAPPA). Magn Reson Med. 47(6):1202-1210. • Sodickson, DK, McKenzie, CA (2001). A generalized approach to parallel magnetic resonance imaging. Med Phys 28(8):1629. Parallel Imaging

  3. Parallel Imaging – simplistic overview Coil sensitivity maps Partial k-space data from 2 coils Reconstructed image + = Parallel Imaging

  4. Undersampled k-space = aliased image Full k-space Undersampled k-space Reconstructed image Parallel Imaging

  5. Multiple coils = information to fix aliasing Coils with complementary sensitivities Full k-space Undersampled k-space Parallel Imaging

  6. Parallel Imaging – SENSE ACQUIRE RECONSTRUCT COMBINE Coil sensitivity, partial k-space Images from each coil Images from all coils, using coil sensitivity maps Parallel Imaging

  7. Parallel Imaging – SMASH ACQUIRE RECONSTRUCT COMBINE Coil sensitivity, partial k-space Missing lines of k-space, using coil sensitivity maps Images from all coils Parallel Imaging

  8. SENSE recon: idealized example L1(x,y) Reconstructed  Ln(x,y) = Cn(x,y)*(x,y) + Cn(x,y+NPE/2)*(x,y+NPE/2) Parallel Imaging

  9. Pineapple: fake 2-channel coil, noise (with perfect knowledge of coil sensitivity) Parallel Imaging

  10. Pineapple: fake 2-channel coil, noise (with imperfect knowledge of coil sensitivity) Parallel Imaging

  11. Pineapple: fake 2-channel coil, not ind. Parallel Imaging

  12. Parallel imaging terminology • Methods • iPAT – Siemens name for all of its parallel imaging implementations • SENSE • SMASH • GRAPPA – auto-calibrating SMASH-like technique • Parameters • Reduction factor: integer describing k-space undersampling • g: describes degradation of reconstructed image due to lack of independence between coil sensitivities (limits useful reduction factor) • High field advantage • … of course … Parallel Imaging

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