Details

The Phase II Pulse Design Challenges:

The goal of Phase II is to judge how well contestants' pulses work in general. As in Phase I, pulses will be scored based on their durations. The winning team for each sub-challenge will be the one that can design the shortest pulses while meeting all constraints.

Please note that you will only be allowed to submit Phase II SMS solutions if you submitted a Phase I SMS solution with duration less than 15 ms, and you may only submit Phase II pTx solutions if you submitted a Phase I pTx solution with duration less than 10 ms.

  1. Simultaneous Multislice Refocusing
  2. Contestants will submit multiple pulse solutions for two scenarios: A refocusing (180 degree) pulse suitable for a TSE sequence, and a refocusing pulse for twice-refocused or double-pulse field gradient (dPFG) diffusion sequences. The pulses must meet the specifications below, as well as constraints on peak RF amplitude, SAR (which is a new constraint in Phase II!), gradient amplitude and slew rate, profile accuracy, and other pulse characteristics which are specified in the example MATLAB code. Submissions will be scored as the total duration of all 31 pulses.

    180-Degree Pulses for TSE:
    • Multiband factors (8, 10, 12, 14)
    • Slices spaced evenly over 24 cm coronal brain volume
    • Slice thickness (0.5, 1.0, 1.5, 2) mm
    • Slice profile time-bandwidth product 3
    • Constant through-slice phase
    180-Degree Pulses for Twice-Refocused/dPFG Diffusion:
    • Multiband factor (3, 4, 5)
    • Slices spaced evenly over 12 cm axial brain volume
    • Slice thickness (1, 1.25, 1.5, 1.75, 2) mm
    • Slice profile time-bandwidth product 4
    • No through-slice phase constraint (When the same pulse is used for both 180’s, the phase cancels)

    To get started, download the MATLAB example code: multibandExamples_PhaseII.zip
    Please Note: There should be a total of 9 files in that archive. We have found that on some Windows machines, not all the files are accessible. If that's the case for you, you can download the files individually here: multibandExamples_PhaseII (folder)

  3. Parallel Transmit Excitation Pulse Design
  4. Contestants will submit five sets of slice-selective small-tip-angle parallel transmit excitation pulses to excite three representative axial slices of a multislice GRE acquisition using 8 transmit channels in the abdomen at 7T1, as well as two multiband slice profiles for an SMS GRE acquisition using 16 transmit channels in the brain at 10.5T4. Contestants are provided with B1+ maps for pulse design with virtual observation points3 for SAR constraints (available below).

    Slice-Selective Excitation Pulses for 2D Abdominal Imaging at 7T: The abdominal pulses must meet the following specifications, which are derived from a T1-weighted spoiled gradient echo imaging sequence2:
    • 70 degree flip angle
    • Slice thickness 2 mm
    • Slice profile time-bandwidth product 4
    • Constant through-slice phase
    • No in-plane phase constraint
    • 20 W/kg max local SAR/4 W/kg max global SAR with 130 ms TR

    NEW: Multiband Slice-Selective Excitation Pulses for SMS Imaging at 10.5T: The brain pulses must meet the following specifications, which are representative for an SMS gradient echo imaging sequence for BOLD fMRI:
    • 60 degree flip angle
    • Slice thickness 1.5 mm
    • Slice profile time-bandwidth product 4
    • Constant through-slice phase
    • No in-plane phase constraint
    • 10 W/kg max local SAR/3.2 W/kg max global SAR with 60 ms TR
    • 5 slices in an axial orientation/6 slices in a coronal orientation

    To get started, download the MATLAB example code: pTxExamples_PhaseII.zip
    Please Note: There should be a total of 10 files in that archive. We have found that on some Windows machines, not all the files are accessible. If that's the case for you, you can download the files individually here: pTxExamples_PhaseII (folder)
    You will also need the B1+ maps and evaluation parameters (~1.2 GB total):


    To execute the evaluation and scoring code on your own computer it will help a lot to have the Gmri object from Jeff Fessler's Image Reconstruction Toolbox, which is available here: Image Reconstruction Toolbox

    Constraints on peak RF amplitude, gradient amplitude and slew rate, and profile accuracy are specified in the example MATLAB code.



The Phase I Pulse Design Challenges (Closed 15th March 2016):

There are two sub-challenges. You can compete in one or both! Pulses will be scored based on their durations. The winning team for each sub-challenge will be the one that can design the shortest pulses while meeting constraints on peak RF amplitude, gradient amplitude and slew rate, profile accuracy, and other pulse characteristics.
  1. Simultaneous Multislice Refocusing
  2. Contestants will submit two pulse solutions: A refocusing (180 degree) pulse suitable for a TSE sequence, and a refocusing pulse for twice-refocused or double-pulse field gradient (dPFG) diffusion sequences. The pulses must meet the specifications below. Submissions will be scored as the total duration of the two pulses.

    180-Degree Pulse for TSE:
    • Multiband factor 12
    • Slices spaced evenly over 24 cm coronal brain volume
    • Slice thickness 1 mm
    • Slice profile time-bandwidth product 3
    • Constant through-slice phase
    180-Degree Pulse for Twice-Refocused/dPFG Diffusion:
    • Multiband factor 5
    • Slices spaced evenly over 12 cm axial brain volume
    • Slice thickness 1.25 mm
    • Slice profile time-bandwidth product 4
    • No through-slice phase constraint (When the same pulse is used for both 180’s, the phase cancels)

    To get started, download the MATLAB example code: multibandExamples.zip
    Please Note: There should be a total of 11 files in that archive. We have found that on some Windows machines, not all the files are accessible. If that's the case for you, you can download the files individually here: multibandExamples (folder)
    You should also go through this walkthrough of the example code: MBChallengeCodeWalkthrough.pdf

    Constraints on peak RF amplitude, gradient amplitude and slew rate, and profile accuracy are specified in the example MATLAB code.


  3. Parallel Transmit Excitation
  4. Contestants will submit a set of slice-selective small-tip-angle parallel transmit excitation pulses to excite the central slice of a multislice GRE acquisition using 8 transmit channels in the abdomen at 7T1. The pulses must meet the specifications below, which are derived from a T1-weighted spoiled gradient echo imaging sequence2. Contestants will be provided with B1+ maps for pulse design with virtual observation points3 for SAR constraints (available below).

    Slice-Selective Excitation Pulses for 2D Abdominal Imaging at 7T:
    • 70 degree flip angle
    • Slice thickness 2 mm
    • Slice profile time-bandwidth product 4
    • Constant through-slice phase
    • No in-plane phase constraint
    • 20 W/kg max local SAR/4 W/kg max global SAR with 130 ms TR

    To get started, download the MATLAB example code: pTxExamples.zip
    Please Note: There should be a total of 8 files in that archive. We have found that on some Windows machines, not all the files are accessible. If that's the case for you, you can download the files individually here: pTxExamples (folder)
    You will also need the B1+ maps and evaluation parameters (~500 MB): torso_maps.mat
    To execute the evaluation and scoring code on your own computer it will help a lot to have the Gmri object from Jeff Fessler's Image Reconstruction Toolbox, which is available here: Image Reconstruction Toolbox
    You should also go through this walkthrough of the example code: pTxChallengeCodeWalkthrough.pdf

    Constraints on peak RF amplitude, gradient amplitude and slew rate, and profile accuracy are specified in the example MATLAB code.



  1. B1+ and SAR maps courtesy of Arcan Erturk, University of Minnesota
  2. L. Umutlu, A. K. Bitz, S. Maderwald, S. Orzada, S. Kinner, O. Kraff, I. Brote, S. C. Ladd, T. Schroeder, M. Forsting, G. Antoch, M. E. Ladd, H. H. Quick, and T. C. Lauenstein. Contrast-enhanced ultra-high- field liver MRI: A feasibility trial. Eur J Radiol, 82:760–767, 2013.
  3. G. Eichfelder and M. Gebhardt. Local specific absorption rate control for parallel transmission by virtual observation points. Magn Reson Med, 66:1468–76, 2011.
  4. B1+ and SAR maps courtesy of Nicolas Boulant (Neurospin) and Pierre-Francois Van de Moortele (University of Minnesota). From: N. Boulant, X. Wu, G. Adriany, S. Schmitter, K. Ugurbil, and P.-F. Van de Moortele. Direct Control of the Temperature Rise in Parallel Transmission by Means of Temperature Virtual Observation Points: Simulations at 10.5 Tesla. Magn Reson Med, 75:249–256, 2016.