Table 6.

Recommendations for quantification referenced to water.

Method	Recommendations
Reference signal and quantification units	- Comparing metabolite signals to tissue water within the same region of interest, and calculating concentrations in either molarity or molality is the most robust and technically straightforward approach to ‘absolute’ quantification. - Whatever concentrations are used, it must be explicitly stated in any publication of the findings; preferably along with the specific quantification formulae that were used as well all assumed parameter values, so that the reader can fully reproduce the quantification method.
TE and TR	- While short TEs and long TRs are not an option for many pulse sequences, if absolute concentration estimates are a goal of the study, pulse sequences capable of very short TEs, such as STEAM120 or SPECIAL29, could be considered; - If short TE (<10 ms) and/or long TR (> 4 s) is not possible, measured or literature values of the metabolite and water relaxation constants (T1, T2) should be used in quantification. - All assumed values for relaxation constants, tissue water densities, etc. must be reported, so that others may compare results.
ERETIC	- The ERETIC method, while promising, is not yet widely available. We encourage scanner manufacturers to develop ERETIC referencing capabilities into their products, which we believe would be an important step towards reliable absolute quantification on clinical systems.