Hi Kasper

a) Yes, the sign of H is defined by the convention you choose for the surface normals. We choose outwards pointing normals, which implies that H is negative in convex regions (think of the sign of the coefficient on the quadratic term with the surface normal as the z axis)

b) more or less, although it is a differential quantity so reflects local properties more than regional ones (and I assume by higher, you mean in the absolute value sense)

cheers Bruce

On Fri, 9 Mar 2018, Kasper Jessen wrote:

Hej Bruce,

Based on the formular for mean curvature stated below and the article by R. Pienaar (https://surfer.nmr.mgh.harvard.edu/pub/articles/AMethodologyForAnalyzingCurv...)

H = 0.5(k1 + k2)

i understand the following:

k1 is by definition larger than k2. Thus values of H is primarily driven by k1 (which primarily describes the curvature in the gyral/sulcal "banks")e.

therefore: if k1 is negative: more variation in the outward curvatures (gyrus) than inward curvatures if k1 is positive: more variation in the inward curvature (sulcus) than outward curvatures

Question: a) So if a H values for a particular ROI (Desikan atlas) is positive, would mean that that the variation is 'primarily' in the inward curvature direction (sulcus)? b) The higher value of H, the more 'sharp' the curvature.

Is this correctly understood?

and again, thank you for the quick reply.

BW Kasper

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On March 8, 2018 4:13 PM, Bruce Fischl fischl@nmr.mgh.harvard.edu wrote:

...

Hi Kaspar

I don't think so.

cheers

Bruce

On Thu, 8 Mar 2018, Kasper Jessen wrote:

...

Hej FreeSurfer,

Question regarding the meancurv extracted from the Desikan atlas using aparcstats2table.

Is the meancurv the absolute mean curvature? Thus all the values are positive?

Best regards

Kasper

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