Zero filling does not inherently improve precision of real relative to complex-domain fitting in 1H-MR spectra with physiological baselines

There remains controversy surrounding the use of zero filling during spectral quantification of in vivo proton magnetic resonance spectra (1H-MRS) using linear combination model (LCM) fitting. We examine the potential mixing of real and imaginary information theorized with zero filling, and whether this is demonstrated by a comparable change in accuracy and precision provided by complex fitting. We show that application of zero filling does improve fitting precision when a baseline is not present; with an imperfectly modeled unknown in vivo baseline, however, zero filling does not necessarily reduce error in real relative to complex fits.