Hi Bruce,
The units are not standardized because the standard deviation across the surface does not equal 1.
>From line 227 in mris_inflate.c it says that the sulc file is demeaned before it is written out:
MRISzeroMeanCurvature(mris) ; /* make sulc zero mean */
However I am still unclear on what the units are. They are too small to be millimeters. Given other published measurements of sulcal depth I think they might be in centimeters, but can you confirm?
Thanks again,
Simon
>Hi Simon
>
>I just took a look at the code and I believe that we make it 0 median
>(not mean) and unit standard deviation. The curvatures can get quite large
>in regions where the vertex spacing is small and the median is robust to
>this.
>
>cheers
>Bruce
>
>
>On Sat, 24 Oct 2015, Simon Vandekar wrote:
>
>> Hi Bruce,
>>
>> I think that unnormalized sulcal depth would be useful. However, I am also curious what the units are in the standard output, because they appear to not be z-score standardized in each hemisphere.
>>
>> Thanks again,
>> Simon
>>
>>
>>> H I Simon
>>> Do you need the unnormalized sulc? It would be pretty easy to put something in to generate it
>>> Bruce
>>>
>>>> On Oct 22, 2015, at 3:23 PM, Simon Vandekar <simonv(a)mail.med.upenn.edu> wrote:
>>>>
>>>> Hi Bruce,
>>>>
>>>> I chose a random subject from the ADNI dataset and computed the mean and variance for the left and right hemispheres separately. It looks like the mean is close to 0, however the variance is not 1. Do you think it is possible that the surfaces are demeaned, but the units are still something meaningful (i.e. not unitless)?
>>>>
>>>>
>>>> sulc = read.table('rh.sulc.asc', header=FALSE, col.names=c('v', 'x', 'y', 'z', 'sulc'))
>>>>> mean(sulc$sulc)
>>>> [1] -1.236923e-08
>>>>
>>>>> var(sulc$sulc)
>>>> [1] 0.3276958
>>>>
>>>>> quantile(sulc$sulc)
>>>> 0% 25% 50% 75% 100%
>>>> -1.72503 -0.42128 -0.03963 0.40072 1.80980
>>>>
>>>>
>>>> Thanks again,
>>>> Simon
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> Hi Simon
>>>>
>>>> they are originally mm, but I believe we z-score normalize them so that
>>>> the sulc file is 0 mean and unit variance.
>>>>
>>>> cheers
>>>> Bruce
>>>> On Wed, 21 Oct 2015, Simon
>>>> Vandekar wrote:
>>>>
>>>>> Dear Freesurfer experts,
>>>>>
>>>>>
>>>>> I am reading the manuscript "Cortical Surface-Based Analysis II: Inflation, Flattening, and a Surface-Based Coordinate System" by Fischl, Sereno, and Dale (1999) where the estimation of sulcal depth is described on page 199, however from the description I am still unsure of the exact units of sulcal depth.
>>>>> Are the units for sulcal depth in mm or are they in arbitrary units?
>>>>>
>>>>> Thanks in advance,
>>>>> Simon