Psy 8960, Fall ‘06 Fieldmaps1 Fieldmaps and distortion Using fieldmaps to correct distortion Using fieldmaps to predict through-slice dephasing

Psy 8960, Fall ‘06 Fieldmaps2 Scaled phase data: phase evolution during dTE TE = 5.19ms TE = 7.65ms Transverse plane

Psy 8960, Fall ‘06 Fieldmaps3 Functional imaging experiment EPI data Anatomical reference Field map

Psy 8960, Fall ‘06 Fieldmaps4 Alignment b/w EPI and T 1 anatomy Option 1: Assume they’re in the right place Option 2: Use intensity-based or mutual information algorithm to find rigid-body transformation of EPI to anat.

Psy 8960, Fall ‘06 Fieldmaps5 Perfectly aligned EPI still doesn’t match

Psy 8960, Fall ‘06 Fieldmaps6 Distortion prediction EPI slice Field map

Psy 8960, Fall ‘06 Fieldmaps7 Distortion prediction EPI slice Field map

Psy 8960, Fall ‘06 Fieldmaps8 Distortion prediction EPI slice Voxel displacement map (Hz map divided by pixel BW)

Psy 8960, Fall ‘06 Fieldmaps9 Distortion prediction EPI slice Voxel displacement map (Hz map divided by pixel BW)

Psy 8960, Fall ‘06 Fieldmaps10 Distortion correction +=

Psy 8960, Fall ‘06 Fieldmaps11 Unwarping Ground truthWarped overlayUnwarped overlay

Psy 8960, Fall ‘06 Fieldmaps12 BeforeAfter

Psy 8960, Fall ‘06 Fieldmaps13 BeforeAfter

Psy 8960, Fall ‘06 Fieldmaps14 Predicting through-slice dephasing

Psy 8960, Fall ‘06 Fieldmaps15 Field map and gradients, inferior slice

Psy 8960, Fall ‘06 Fieldmaps16 Field map and gradients, middle slice

Psy 8960, Fall ‘06 Fieldmaps17 Field map and gradients: artifacts

Psy 8960, Fall ‘06 Fieldmaps18 Field map and gradients: artifacts

Psy 8960, Fall ‘06 Fieldmaps19 Predicting drop-out Need to know: –(Linear) field gradient in through-slice direction –Echo time

Psy 8960, Fall ‘06 Fieldmaps20