Tuesday, 3 March 2015

Setting up a MEGA-PRESS scan from PRESS

These instructions are intended to help anyone with our patch get things set up for GABA editing. They are Philips- and patch-specific.

  1. Start with a short-TE PRESS scan
  2. In Initial, increase the TE to 68 ms.
  3. In Geometry, change the voxel size to ~3x3x3 cm^3.
  4. In Contrast:
    • Change Gradient mode to Maximum and PNS mode to high.
    • Select MEGA basic in BASING pulse options.
    • Pulse duration 14ms, freq1 7.46 ppm, freq2 1.9 ppm. [OFF first, edit 8/19/12]
  5. In Motion, set phase cycles to 16, averages to 2, startup acquisitions 0.
    • -------------------------------------------------------------
    • EDIT 5/5/2015 Even the window-averaged frequency correction is not consistent. Current best advice is to turn it off.
    • Turn on frequency correction, and set freq stab window to 8. 
    • Set+freq stab odd dyn: yes (in the dyn/ang tab). This makes sure the frequency only updates on the first TR of an odd dynamic scan, helping minimize subtraction artefacts.
    • ----------------------------------------------------------------------
  6. In Dyn/ang, Dynamic study individual, 160 dynamic scans.
  7. In Postproc, turn on spectral correction. Set Apply Spectral Correction to no. Acquire 16 averages. 
Make sure you read this post as well: http://gabamrs.blogspot.com/2014/10/frequency-stabilization.html.


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