Quantitative analysis failure modes

There are two quantitative analysis failure modes:

• the curve fitting process fails to fit a peak in one or more of the designated regions of the spectrum
• a peak exists in the region but either the SNR, or the goodness of the fit of the peak fails to meet the minimum standards set for PROBE/SVQ spectra

If the curve fitting procedure fails to find a peak in a designated region of the spectrum, or if the center frequency of a detected peak is outside of the region, the process reports that the fit has failed. Specifically, a "-void-"entry is displayed for the missing peak values. For example, if a phantom is scanned at room temperature, the frequencies of the metabolite peaks will be out of their designated (relative to the temperature dependent water resonant frequency) regions and “-void-“will be reported for all metabolite values.

If the quantitative analysis routine finds and fits a peak in a region, a failure is reported if the SNR of the peak is less than 5 to 1, and/or the goodness of fit of the peak is less than 4. SNR is the usual signal-to-noise ratio; the noise is estimated by taking the average RMS value over two regions of data (see below, Estimation of the Noise Level). The goodness of fit is a ratio of the power of the peak (over the fitting region) versus the power of the residue. The power of the peak is taken to be the lesser of the power of the data over the region, and the power of the curve fit data over the region. If neither criteria is met, a failure is reported and “-NotDet-“(for Not Detected) is displayed for the peak values.