profile_rf sequence description
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!!! NOT FOR USE IN HUMAN SUBJECTS !!!

Purpose:

Measurement of RF pusle profiles and their calibration.


History:

9/1/1999, Jan Hrabe 
- original version with 2 arbitrarily rotated slice-selective 
pulses followed by spin echo measurement.


Notes:

To measure an inversion pulse, implement it as rsat03 pulse with
ALPHA. Use 90 degrees pulse as rsat02. 

To measure a 90 degree pulse (or small alpha pulse), implement 
it as rsat02 with ALPHA (rsat03 is not needed). Check/adjust 
the slice selection and slice compensation gradients, symmetry 
around SE 180, and minimum TE.

In the user interface, "slice" is the SE 180 slice. Tested
pulses are implemented as saturation slice-selective pulses. 
Saturation pulse #1 for 90, saturation pulse #2 for 180.

Negative 8 mT/m spoilers for 4.5 ms preceed rsat03 (phase and read), 
positive 8 mT/m spoilers for 4.5 ms preceed rsat02. Minimum FOV
60 mm gives max readout gradient ~20mT/m (256x256). That yields
about 0.25 mm resolution (at best) for the slice profile 
measurement on a standard Siemens phantom.

Delay time TD #1 can be added to the minimum inversion time 
11 ms (this minimum can change if the pulse lengths change).
Inversion time is running between rsat03 and rsat02 pulses.

TE is fixed to its minimum value 22 ms, BW per pixel is 130Hz.
Use number of acquisitions at least 2 (and even) if N/2 artefact
appears.

Native Siemens sinc pulses have to be specified as srfNN with "I", 
not as rsatNN. Otherwise the default profile for 1mT/m logical slice 
gradient is used no matter what is specified. Also, the empirical
factor has to be specified (use, e.g., #1.01). Even though
the srfNN is in the rsat section in this case, slice thickness
is still taken from the imaging slice, not from the saturation slab.


Recomended measurement setups:

1. Profile of a pulse ~90 degrees and smaller. Put it in as 
rsat02 (saturation slab 1). Use sagittal acquisition, 
transverse saturation #1, head-feet readout.

2. Profile of inversion pulse (saturation slice 1 for 90 
degrees pulse and 2 for the tested inversion pulse). Sagittal 
acquisition, identical sagittal saturation slice 1, transverse 
saturation pulse 2, head-feet readout.

3. 90-180 pulse interaction (sat 1 for 90, sat 2 for 180). Sagittal
acquisition, both saturation slices transverse (but different THs),
head-feet readout.

4. Calibration of 90 degrees (sat 1 for 90 only). Leave Inline
Adj ON to get comparable amplitudes (otherwise rsat amplitudes
don't get adjusted with ALPHA), find ALPHA that maximizes the
profile signal. Set amplitude integral that makes this ALPHA 90.

5. Inversion pulse power calibration. Setup as for inversion profile
measurement (item 2) but acquisition slice coronal, sat 1 identical
coronal, sat 2 sagital, left-right readout. Observe inversion quality
along the head-feet direction. Use long cylindrical phantom.