[Homer-users] Using Short-Separation

[Scholkmann Felix]

Hi Mathieu,

"there doesn’t seem to be any effect on the short-separation itself"
-> This is what is expected since regressing out the information of the short separation channel (SSC) from he SSC itself causes a flat line (i.e. it's a proof that the regression works)

"there doesn’t seem to be any effect on all other channels in my case…
-> There are many reasons why there could be not effect of the SSC regression. I think there are two main ones:
1) The information in the SSC mainly contains noise, or information that is largely unrelated to the information in the long separation channels (LSC)
2) The location of the SSC does not match well with the LSC locations

The distance between the LSC and the SCC should not be too far. A good paper about how the hemodynamics of the scalp blood flow is correlated on the human head is this here: Zhang et al., 2015, Multiregional functional near-infrared spectroscopy reveals globally symmetrical and frequency-specific patterns of superficial interference. Biom. Opt. Exp. -> https://www.osapublishing.org/boe/abstract.cfm?uri=boe-6-8-2786
Look at Figure 4 to see how the regions of the head are linked regarding the scalp blood flow dynamics. This could be used to decide if it makes sense to use a specific SSC-LSC pair.

Best,
Felix



________________________________________
Von: homer-users-bounces at nmr.mgh.harvard.edu [homer-users-bounces at nmr.mgh.harvard.edu]" im Auftrag von "Mathieu Coursolle [mathieu at rogue-research.com]
Gesendet: Donnerstag, 30. Juli 2015 16:23
An: homer-users at nmr.mgh.harvard.edu
Betreff: [Homer-users] Using Short-Separation

Hi,

I am currently using Homer2 (v2.0) (Matlab R2013a) and am trying to use the short separation measurements.

I only have a single short-separation for this acquisition, but I am hoping to see if I can use that one short-separation to process all the other channels.

I viewed the Homer2 training from 13/03/04 (Youtube) and created a similar process stream (task is 30 sec tapping, 30 sec rest).
https://www.youtube.com/watch?v=tqzVcEj0FeA

I used:

- intensity_to_OD
- Bandpass_Filter
        hpf = 0
        lpf = 0.3
- OD_to_Conc
        ppf = [6.0, 6.0]
- GLM_HRF_ShortSep_Drift
        trange = [-2, 40]
        gstd = 1.0
        gms = 1.0
        rhoSD_ssThresh = 15.0

>From the training session, it seems that after processing, the short-separation becomes a flat line, and the other channels should be processed using the closest short-separation.

However, there doesn’t seem to be any effect on the short-separation itself (and all other channels) in my case…

Is my understanding/process stream ok?

Thank you,

Mathieu
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