gcfp - global coherent free precession
http://circ.ahajournals.org/cgi/content/full/111/8/1033
http://cds.ismrm.org/ismrm-2004/Files/000004.pdf
http://circ.ahajournals.org/cgi/content/full/111/8/1033
http://cds.ismrm.org/ismrm-2004/Files/000004.pdf