3D prewitt operator

Hello,

I'm trying to find the gradient of an 3D CT image. I need the magnitudes and the angles.

I was thinking of the prewitt operator but I couldn't find its mask for 3D images.

Can I use a operator like this?

h = zeros (3,3,3);

h(:,:,1)=[0 0 0; -1 -1 -1;0 0 0 ];

h(:,:,3)=[0 0 0; 1 1 1;0 0 0 ];

Grad = imfilter(Image,h,'replicate');

It gives something relevant but I don't know if I'm doing it right.

Thanks for the help.