Hi,

Is there a way in Slicer to calculate the mean DTI distortion (e.g. as mean transform needed to align DTI to T2w, like the root mean square deviation).

I found this:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5118068/#R34 ->

## From the paper:

"We also calculated the root mean square (RMS) deviation for each subject, which combines the six rigid body parameters into a single estimator of mean displacement [Jenkinson, 1999; Reuter et al., 2015]:

RMS = sqrt{r∗r ∕ 5 + tr[(M−I)T(M − I)] + tTt},

## where t is the translation vector, M is (here) the 3×3 rotation matrix, I is the identity matrix, tr[] is the trace operator, and r is the approximate spherical radius of the brain (here, estimated from the data to be 65 mm). The rigid body parameters and RMS values of the navigator logs were also examined."

I have a slicer transform file (.h5) for each of my subjects and wonder if there is a way to calculate the RMS (or a similar measure) from them.

Thanks, Lorenz