Empty and Zero Values in BrainVisa Output

[mhnshf]

Hi everyone,

I am using BrainVISA for sulcal measurements, and I have noticed that the output file contains some empty and zero values for certain subjects and sulcal measure.

I was wondering:

What do these values represent?
Are empty cells indicative of missing data, processing errors, or something else?
Do zero values have a specific meaning (e.g., anatomical absence, failed measurement)?

How should I handle them?
Should I treat them as missing values (NA) for statistical analysis?
Are there recommended ways to preprocess or filter these cases?

I’d appreciate any insights or recommendations on how to manage these values properly.

Thanks in advance!

[denisri]

Hi,
There may be missing data, yes, if a particular sulcus is not found in a brain, either because it is absent (some minor sulci are not always formed), or because the identification process hasn't succeeded in identifying it (sometimes two sluci are more or less merged into a single one).
There are 2 morphometry processes for sulcal measurements, one is named "Sulci graph morphometry by subject", and the other (older) is named "morphometry statistics".
The former is included in the main Morphologist pipeline, and outputs "Nan" for all features when a sulcus is not found. The latter outputs 0 for all features for a missing sulcus. So it depends which process you are using.
Anyway a missing sulcus doesn't mean that there has been a processing error, it's rather "anatomical absence" or "not able to identify it" (which is related but not the same, I agree ;) ).
In addition there are a few features which can be 0 when the sulcus actually exists: typically, the length measurements. The sulcus length is measured as the junction line between the fold and the brain hull. However a few burried sulci do not actually touch the external hull, like the insula, or some deep branches of the sylvian fissure (F.C.L.r.sc.post and F.C.L.r..sc.ant for instance). In such case the length is not measured at all, and the value is 0. It can be seen either as a missing value, or the continuity of the length when a sulcus does not connect the outside hull, but I guess treating it as a missing value is sane. It will generally be always the same sulci which will miss these values.
Denis