Labguy's world has an entry on the VTC-7100 with pictures of the tapes and the matching VC-500 camera.
These machines seemed to be popular in medical and biological research. Most of the hits on google are passing mentions in various research articles. Indeed Labguy's first encounter with them was servicing them as part of a cardiac imaging machines.
My one doesn't appear to have some from a research lab though as it have none of the usual asset tags or markings. The name/address label suggests it was someone's personal machine. I can't help but wonder if the junk dealer I bought this from may have overlooked a pile a odd cassettes on the same garbage pile thinking it was an audio recorder. This week the same dealer actually has a Sanyo audio cassette deck that looks very similar to this unit in terms of control layout and finish right down to the fake leather carry case.