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Chapter 7
MRiLab Applications

This chapter shows a few examples for demonstrating the applications of MRiLab simulation

7.1 bSSFP with Non-uniform B0

This example (Figure 7.1) simulates the dark banding artifact in bSSFP images arisen from non-uniform B0 field. To perform this simulation, the following steps are needed:

  1. Load Brain (Standard Resolution 108 × 90 × 90)
  2. Load PSD_FIESTA3D
  3. Load Mag_GaussianHead

The user can adjust the ‘FlipAng’, ‘TR’ and ‘TE’ to modify the pattern of the banding artifact.

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Figure 7.1: Simulated 3D bSSFP brain image of matrix size of 100 × 80 × 20. The circular banding artifact is due to added Gaussian field simulating the main magnet field inhomogeneity. Left: TR/TE=16/8ms, FA=40∘; Middle: TR/TE=16/8ms, FA=40∘, Gaussian B0 applied; Right: TR/TE=32/16ms, FA=40∘, Gaussian B0 applied

7.2 Fat Chemical Shift

This example (Figure 7.2) simulates chemical shift artifact at the interface of water and fat in a GRE sequence. To perform this simulation, the following steps are needed:

  1. Load Water Fat Phantom (256 × 256 × 32 × 2)
  2. Load PSD_GRE3D

The user can adjust the ‘BandWidth’ and ‘FreqDir’ to modify the appearance of the chemical shift.

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Figure 7.2: Simulated 3D gradient echo image at 3.0T using cartilage-fat phantom showing water fat chemical shift at different readout bandwidth. The simulated in-plane matrix size is 100 × 100, TR/TE = 10s/50ms, Axial plane, A/P readout. Left: BW=400Hz/pixel; Right: BW=100Hz/pixel.

7.3 Multi RF Transmitting

This example (Figure 7.3) simulates multiple RF transmitting using a bSSFP sequence. To perform this simulation, the following steps are needed:

  1. Load Brain (Standard Resolution 108 × 90 × 90)
  2. Load PSD_FIESTA3D
  3. Load Coil_8ChHead to Tx
  4. Set ‘MultiTransmit’ to ‘on’

The user can adjust the ‘B1Level’ to modify the actual flip angle, modify the RF pulse using MR sequence Design Toolbox for individual RF source, or modify the coil configuration for generating desired B1+ field.

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Figure 7.3: Simulated 3D bSSFP brain image of matrix size of 100 × 80 × 4 with different Tx coil configuration. The simulated image uses FA=40∘, TR/TE = 16/8ms. Left: uniform unit B1+ field, RF transmitting from ‘MasterTxCoil’; Middle: multi RF transmitting from Coil1 and Coil3; Right: multi RF transmitting from all coil channels

7.4 Multi Receiving Coil

This example (Figure 7.4) simulates multiple receiving using a SE sequence. To perform this simulation, the following steps are needed:

  1. Load Brain (Standard Resolution 108 × 90 × 90)
  2. Load PSD_SE3D
  3. Load Coil_8ChHead to Rx

The user can adjust the coil configuration for generating desired B1- field. All eight channels will be receiving MR signal from the virtual object individually.

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Figure 7.4: Simulated brain spin echo image of matrix size of 100 × 80 with multi receiving Rx coil. The simulated image uses FA=90∘, TR/TE = 10s/10ms. Left: the combined image using ‘SumofMagn’; Right: individual image for each coil channel, notice that Coil2 and Coil4 receive no signal due to zero B1- field.

7.5 Image Gradient

This example (Figure 7.5) simulates applying non-unit gradient with a 3D SPGR sequence. To perform this simulation, the following steps are needed:

  1. Load Brain (Standard Resolution 108 × 90 × 90)
  2. Load PSD_SPGR3D
  3. Load Grad_LinearHead

The user can adjust the gradient structure for generating desired gradient field. Notice that this applied gradient in GyPE GradLine has a factor of 0.5 in the Y direction. This will cause image contraction in the Y direction.

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Figure 7.5: Simulated brain 3D SPGR image of matrix size of 100×80×2 with non-unit gradient. The simulated image uses FA=20∘, TR/TE = 60/8ms. Left: unit gradient applied; Right: non-unit gradient applied in Y direction.

7.6 Motion Artifact

This example (Figure 7.6) simulates motion artifact with a 3D GRE sequence. To perform this simulation, the following steps are needed:

  1. Load Brain (Standard Resolution 108 × 90 × 90)
  2. Load PSD_GRE3D
  3. Load Mot_ShiftHead

The user can adjust the motion structure to generate different motion track patterns, and/or modify motion triggering in the Ext sequence line to sample object movement.

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Figure 7.6: Simulated brain GRE image of matrix size of 100 × 80 with translation motion. The simulated image uses FA=90∘, TR/TE = 10s/50ms, Axial plane, A/P readout. Motion triggering happens one time per TR, and motion lasts for 400s. Left: no motion; Right: translation motion applied.

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