John Port1, Balwinder Singh2, and Mark A Frye2
1Mayo Clinic, Rochester, MN, United States, 2Department of Psychiatry, Mayo Clinic, Rochester, MN, United States
1Mayo Clinic, Rochester, MN, United States, 2Department of Psychiatry, Mayo Clinic, Rochester, MN, United States
We developed a peak symmetry method to optimally
frequency/phase adjusting individual FIDS of an MRS acquisition, eliminating
patient/scanner artifacts. This allows
for long dynamic MRS studies that can measure neurotransmitter changes over
time.
Figure
1. Diagram and equation indicating the
method for calculating the Symmetry Index (SI) of a peak. The signal S at the center c of a perfectly
symmetric peak is maximal, with zero “penalty” from the adjacent pairs of n
points. K is simply a weighting factor
to keep the symmetry index more or less positive. If the points to the right or left of center
do not have equal signal, the SI is decreased by the amount of the difference.
Figure 2.
Diagram showing the frequency and phase corrections that give the maximal SI
for a given FID. The corrections and SI
are shown over the entire 53 minute (795 ON-OFF pairs) acquisition. Note how the frequency and phase corrections
change over time, while the symmetry is maintained.