Parallel Imaging 1Psy 8960, Fall ‘06

Parallel Imaging

• SMASH and SENSE• High field advantage• Pros and cons

…

• But first, review of last few homework assignments

Parallel Imaging 2Psy 8960, Fall ‘06

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 3Psy 8960, Fall ‘06

Parallel Imaging – simplistic overview

Coil sensitivity maps

Partial k-space data from 2 coils

Reconstructed image

+ =

Parallel Imaging 4Psy 8960, Fall ‘06

Undersampled k-space = aliased image

Full k-space Undersampled k-space Reconstructed image

Parallel Imaging 5Psy 8960, Fall ‘06

Multiple coils = information to fix aliasing

Full k-space Undersampled k-space Coils with complementary sensitivities

Parallel Imaging 6Psy 8960, Fall ‘06

Parallel Imaging – SENSE

Coil sensitivity, partial k-space

RECONSTRUCTACQUIRE COMBINE

Images from each coil

Images from all coils, using coil sensitivity maps

Parallel Imaging 7Psy 8960, Fall ‘06

Parallel Imaging – SMASH

Coil sensitivity, partial k-space

RECONSTRUCTACQUIRE COMBINE

Missing lines of k-space, using coil sensitivity maps

Images from all coils

Parallel Imaging 8Psy 8960, Fall ‘06

SENSE recon: idealized example

Ln(x,y) = Cn(x,y)*(x,y) + Cn(x,y+NPE/2)*(x,y+NPE/2)

L1(x,y)

Reconstructed

Parallel Imaging 9Psy 8960, Fall ‘06

Pineapple: fake 2-channel coil, noise

(with perfect knowledge of coil sensitivity)

Parallel Imaging 10Psy 8960, Fall ‘06

Pineapple: fake 2-channel coil, noise

(with imperfect knowledge of coil sensitivity)

Parallel Imaging 11Psy 8960, Fall ‘06

Pineapple: fake 2-channel coil, not ind.

Parallel Imaging 12Psy 8960, Fall ‘06

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 …