[Homer-users] units for concentration changes in Homer

[Andrei Medvedev]

This is a question to Ted Huppert.

Hi Ted,

I was wondering about the units for concentration changes calculated within the Homer.

If my dOD signal 'response' is 0.05-0.1 (a typical value for a good NIR response), the Homer calculates dConc as ~5E-5. For example, for the FakeData.mat file (supplied with the Homer), dOD is ~0.1 and dConc is ~4E-5. If this is in Moles, it looks like too high value for dConc (that is, ~40-50 mkM). Published values of dConc during finger tapping and other tasks are ~1 mkM. The same 1 mkM you can get as a dConc estimate for dOD ~5-10% from the Beer-Lambert law (I used the formula from Boas et al, NeuroImage 2001 and the approximate values for the extinction coefficients plotted there).

Could you please explain in what units the concentration change is calculated in Homer? 

Thank you,

Andrei.

Dr. Andrei Medvedev, Ph.D.
Assistant Professor,
Center for Functional and Molecular Imaging
Georgetown University Medical Center
3900 Reservoir Rd, NW
Preclinical Science Building LM-14
Washington, DC 20057-1488