Handling arbitrary unknown line-shape without introducing extra parameters

Introduction Although the technique of shimming is steadily progressing [1], distorted signal-decay (line-shape) can still occur. Lack of information about the decay function complicates MRS metabolite quantitation. In the absence of line overlap, complications can be avoided by integrating the individual lines, this requiring no knowledge of the decay function. In the presence of overlap, availability of a suitable reference line brings solace [2] under the condition that all individual spectral components have the same shape. When lines overlap and no reference line is available, the line-shape can be estimated from the metabolite signals themselves: Under the same condition as mentioned above, division of the MRS signal by an estimated non-decaying version -i.e., no relaxation -of that signal yields a `raw' noisy estimate of the decay [3]. The raw decay can be improved by modelling it with splines, wavelets, or exponentials [4]. However, such modelling requires estimation of extra parameters on top of the regular MRS model parameters. The present work avoids modelling with splines, wavelets, or exponentials so that no extra parameters need be estimated. This simplifies metabolite quantitation and reduces its errors.