using vol2surf with X Y Z F(X,Y,Z) data set

I have a data set which represent the value of a parameter at various spots in a volume. The data was not acquired in a common Cartesian pattern which means that all the X,Y,Z are not equidistant.
I can put the data in some sort of 3D format using various interpolate functions. At the end, I would like to produce a surface which would look like it is wrapped around a set of point corresponding to a range of values of F(X,Y,Z). I watched the "Slicer" tutorial video and they talk about the "imageTransform vol2surf" function but I don't understand what format the data has to be to conform to this function. my data is similar to a series of MRI type slices but obviously not in the proper format. I keep getting the following error: "This image operation supports only unsigned char (/B/U)". All the data points F(X,Y,Z) are of values between 0 and 65535. I am sure the problem is in the way the data is set in the wave which causes the problem.

Thanks

Denis