Arguing for the moment that the 4th dimension is time, isn’t it simply a time-lapse video on a two-dimensional screen, and thus 3-D, Length * Width * Time?
Unless it’s also R2D2’s “Help me, Obi-Wan...” holographic projection dealie.
(I read the article)
The ultrasounds are that. Projections of them are not.
This very interesting article explains the differences between 2, 3, and 4-D sonograms. (I guess the 4 dimensions would be height, width, depth, and time). Basically, it's that the 4D sonogram is continuously updated. It becomes a moving image, like watching a movie.
Speaking of movie, here's the one-minute ad G.E. put out when it rolled out its 3D 4D sonogram in 2011.
I still choke up a little when I see it.