| locate.peaks {FTICRMS} | R Documentation |
Locates peaks in FT-ICR MS spectra assuming that the peaks are roughly parabolic on the log scale.
locate.peaks(peak.base, num.pts = 5, R2.thresh = 0.98,
oneside.min = 1, peak.method = "parabola",
thresh = -Inf)
peak.base |
numeric matrix with two columns containing the masses and the pre-transformed spectrum intensities |
num.pts |
minimum number of points needed to have a peak |
R2.thresh |
minimum R^2 needed to have a peak |
oneside.min |
minimum number of points needed on each side of the local maximum |
peak.method |
how to locate peaks; currently the only options are "parabola" and "locmax" |
thresh |
only local maxes that are larger than this will be checked to see if they are peaks |
If peak.method = "parabola", the algorithm works by locating local maxima in the spectrum,
then seeing if any num.pts consecutive points with at least oneside.min point(s) on each side
of the local maximum have a coefficient of determination (R^2) of at least R2.thresh when fitted with a
quadratic. If, in addition, the coefficient of the squared term is negative, then this is declared a peak
and the vertex of the corresponding parabola is located. The coordinates of the vertex give the components
Center_hat and Max_hat in the return value. The Width_hat component is the negative
reciprocal of the coefficient of the squared term.
If peak.method = "locmax", then the algorithm merely returns the set of local maxima, and the
Width_hat component of the return value is NA.
A data frame with columns
Center_hat |
estimated mass of peak |
Max_hat |
estimated intensity of peak |
Width_hat |
estimated width of peak |
An extremely large value for Width_hat most likely indicates a bad fit.
Using peak.method = "locmax" will vastly speed up the runtime, but may affect the
quality of the analysis.
Don Barkauskas (barkda@wald.ucdavis.edu)
Barkauskas, D.A. et al. (2008) “Detecting glycan cancer biomarkers in serum samples using MALDI FT-ICR mass spectrometry data”. Submitted to Bioinformatics