Tarquin Absolute Quantification

Analysis / Modeling Quantification / Calibration
1

Dear Experts,

I am wanting to confirm how the absolute quantification is calculated when using the Tarquin Gui. I have read the discussion from Absolute quantification.

When I supply a unsuppressed water file, the resulting amplitudes of metabolites are expressed in mM. I have read the Tarquin user guide, and noted the assumptions made. However, I am still unsure what assumptions (if any) are made regarding the fractions of WM/GM/CSF within the voxel.

I do not provide any T1 weighted file in Tarquin, so I am unsure if the amplitudes expressed in mM are calculated using average values for WM/GM/CSF fractions (from previous studies) or whether Tarquin is able to get this information from the SPAR/SDAT files I provided?

Any insights would be greatly appreciated.

Kind Regards,
Nathan

2

Hi @nathandelang ,

See chapter 10 of the Tarquin User Guide; the internal water scaling is fairly rudimentary, basically relying on a supplied (or default) attenuation factor and concentration for water. This is similar to the approach used in LCModel.

To account for different composition, one approach may be to calculate a combined scaling factor (eg, per Gasparovic et al 2006, Near et al 2020) and supply that as suggested in the absolute quantification thread you mentioned. However, this won’t allow for metabolite-specific relaxation parameters to be considered. Another possibility is to quantify initially with the default scaling, then numerically reverse this before applying per-subject, metabolite-specific scaling.