Journal
MAGNETIC RESONANCE IN MEDICINE
Volume 75, Issue 1, Pages 15-18Publisher
WILEY-BLACKWELL
DOI: 10.1002/mrm.25568
Keywords
MR spectroscopy; quality control; errors; quality filtering; Cramer Rao minimum variance bounds
Funding
- Swiss National Science Foundation [320030_156952]
- EU [316679 TRANSACT]
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Cramer Rao Lower Bounds (CRLB) have become the standard for expression of uncertainties in quantitative MR spectroscopy. If properly interpreted as a lower threshold of the error associated with model fitting, and if the limits of its estimation are respected, CRLB are certainly a very valuable tool to give an idea of minimal uncertainties in magnetic resonance spectroscopy (MRS), although other sources of error may be larger. Unfortunately, it has also become standard practice to use relative CRLB expressed as a percentage of the presently estimated area or concentration value as unsupervised exclusion criterion for bad quality spectra. It is shown that such quality filtering with widely used threshold levels of 20% to 50% CRLB readily causes bias in the estimated mean concentrations of cohort data, leading to wrong or missed statistical findings- and if applied rigorously-to the failure of using MRS as a clinical instrument to diagnose disease characterized by low levels of metabolites. Instead, absolute CRLB in comparison to those of the normal group or CRLB in relation to normal metabolite levels may be more useful as quality criteria. (C) 2015 Wiley Periodicals, Inc.
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