Calculate MEAN, SD

it is possible to calculate mean and SD and HU to draw ROI BY using 3d slicer.
if it is possible any one can guide me , how i can count

If you create a segmentation for your ROI, this example script shows how to extract voxel information for that specific region as a vector. then you can simply use standard mean or sd function to calculate.

Script repository — 3D Slicer documentation

You can also use the Segment Statistics to calculate the mean intensity inside the segment, but I am not sure if it does SD.