How can I create an isosurface from a matrix defined in cylindrical coordinates?

The problem im struggling with is to plot an isosurface from a 3D matrix wich is defined in cylindrical coordinate system, for example f(r,phi,z), where r is radius, phi is angle and z is height. Is it possible, in some way, to draw an isosurface from a 3D matrix like this? Any help or hints would be appreciated!