See spec_op function for a more complete set of spectral operations.
int_spec(mrs_data, xlim = NULL, freq_scale = "ppm", mode = "re")
MRS data.
spectral range to be integrated (defaults to full range).
units of xlim, can be : "ppm", "hz" or "points".
spectral mode, can be : "re", "im", "mod" or "cplx".
an array of integral values.