jamienear
commented
3 years ago Hello,
What you are looking at is the z-magnetization produced an adiabatic full passage pulse as a function of its peak w1 amplitude (gamma * peak B1), assuming a starting magnetization of [0, 0, 1] (Mz=+1).
As w1 is increased, the Mz is decreased (corresponding to increasing flip angles, eventually reaching a value of ~-1 (corresponding to a flip angle of 180 degrees) at a certain w1 threshold. For all w1 values above that threshold, Mz stays at ~-1. i.e. As long as the peak w1 is above the “adiabatic threshold”, there is essentially perfect inversion, regardless of w1 field.
This step is to choose the w1 threshold that gives full inversion. Since, as you noted, the curve is asymptotic and may never actually reach Mz=-1, I typically pick the w1 value that corresponds to Mz=-0.99. Based on the Figure you sent me, a w1 value close to 1.0 kHz would probably suffice. If you were satisfied with this value, then you would enter ‘1.0’ when prompted.
Note, FID-A only asks this question when loading an adiabatic pulse. For conventional pulses, the w1max is calculated automatically.
Hope this helps.
Jamie
From: IgorIzyurov @.> Date: Saturday, March 13, 2021 at 2:06 AM To: CIC-methods/FID-A @.> Cc: Subscribed @.***> Subject: [CIC-methods/FID-A] Choosing w1max for RF waveform when simulating sLASER (#47)
Hello!
I'm trying to run example script run_simSLaserShaped_fast.m. When trying to load RF waveform for flip angle fa=180° refocusing pulse with io_loadRFwaveform('sampleAFPpulse_HS2_R15.RF','inv'); the plot of mag. field w1 frequency and magnetization at z-axis Mz is shown and I'm being asked to choose the frequency w1max, which corresponds to magnetization Mz at fa=180°. At fist, I thought that Mz at fa=180° should be -1. But w1max in that case goes along asymptote to infinite. I'm wondering, what would be the correct w1max and how this plot should be used? [Screenshot from 2021-03-13 07-48-22]https://user-images.githubusercontent.com/56837204/111022135-40976800-83d1-11eb-9ddd-b412f1d03a81.png
— You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHubhttps://github.com/CIC-methods/FID-A/issues/47, or unsubscribehttps://github.com/notifications/unsubscribe-auth/ACHTOQJEI6HHWJUSBNP5YPLTDMFIVANCNFSM4ZDQWJ4Q.
IgorIzyurov
Hello!
I'm trying to run example script _run_simSLaserShapedfast.m. When trying to load RF waveform for flip angle fa=180° refocusing pulse with _io_loadRFwaveform('sampleAFPpulse_HS2R15.RF','inv'); the plot of mag. field w1 frequency and magnetization at z-axis Mz is shown (in the attachment; I've made the figure a bit prettier :) ) and I'm being asked to choose the frequency w1max, which corresponds to magnetization Mz at fa=180°. At fist, I thought that Mz at fa=180° should be -1. But w1max in that case goes along asymptote to infinite. I'm wondering, what would be the correct w1max and how this plot should be used?