Hard pulses at 3t
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Hard Pulses at 3T. Jason Su Oct. 10, 2011. Issues. Been having problems getting correct flip angles from modified width Fermi hard pulses Used rfstat to generate/calibrate 200us, 300us, and 400us pulses This is a critical problem for DESPOT-related experiments

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Hard Pulses at 3T

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Hard pulses at 3t

Hard Pulses at 3T

Jason Su

Oct. 10, 2011


Issues

Issues

  • Been having problems getting correct flip angles from modified width Fermi hard pulses

    • Used rfstat to generate/calibrate 200us, 300us, and 400us pulses

  • This is a critical problem for DESPOT-related experiments

  • Initial thoughts on solutions:

    • nom_pw was incorrectly set to 100us (“fix”)

    • nom_bw did not scale with the pulses when ns3d_flag was on (“fix2”, includes nom_pw correction)


Experiment

Experiment

  • 3T2, agar phantom

  • Measure signal curve vs. flip angle with mean of central ROI

    • Slab profile shouldn’t be big issue

  • Using 801 soft pulse as our target curve (800us min phase, low BW pulse)

    • This is what was being used at 1.5T

    • Shown in blue


Normalized spgr signal vs prescribed

Normalized SPGR Signal vs. Prescribed


Normalized spgr signal vs actual

Normalized SPGR Signal vs. “Actual”


Comments

Comments

  • 200us and 300us hard pulses are underflipping by a factor of 2x and 3x compared to 100us

  • The “actual” flip angle axis is scaled by lining up the max of the curves

    • Predicts that hp200 is underflipping by 0.6 compared to 801

  • Neither of the proposed fixes had much effect


Plotter spgr fa18 100us

Plotter – spgr_fa18_100us


Plotter spgr fa18 200us

Plotter – spgr_fa18_200us


Plotter spgr fa18 300us

Plotter – spgr_fa18_300us


Comments1

Comments

  • Pulsewidth seems to be as we expect

  • The prewind gradient appears to overlap with the RF pulse or is this an artifact of plotter?


100us fermi pulse

100us Fermi Pulse

  • R1/R2/TG = 12/29/148

  • 18/10^(-xmtaddScan/200) = 18 deg.


2 00us fermi pulse

200us Fermi Pulse

  • R1/R2/TG = 11/29/132

  • 18/10^(-xmtaddScan/200) = 59.241 deg.


300us fermi pulse

300us Fermi Pulse

  • R1/R2/TG = 11/29/132

  • 18/10^(-xmtaddScan/200) = 135.0696 deg.


Thoughts

Thoughts?


Ismrm abstracts

ISMRM Abstracts

  • kT points with DESPOT1 mapping @ 7T

    • Observed modest improvements with 1ch kT pts.

    • Correction with a B1 map is better than kT points alone

    • Need get back and quantify improvement

    • Try to apply kT+B1 correction with our AFI data

  • Accelerated DESPOT1

    • View sharing with proper scaling accelerates collection of SPGR DESPOT angles

    • LCAMP may go even faster but still some work to be done

  • MSmcDESPOT – baseline and 1yr MS study

    • Not much new since last time even with full 1yr set for normals

    • Progressive patients have greater increase in DV than CIS or RR

    • TBSS?

  • DEV/CISmcDESPOT – longitudinal MS studies with 1-3 month sampling interval

    • Christine and Nora are now editing lesion segmentation

    • Potential questions:

      • How does MWF/DV in a lesion change over time?

      • Greater shifts in EDSS than MSmcDESPOT, potential for more interesting longitudinal correlations


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