Lucas,
NI's IMAQ products do not provide TWAIN support in their drivers, as to be called using the TWAIN protocol. There is a company called Graftek, www.graftek.com that has some LabVIEW TWAIN drivers. They might be able to give you a closer suggestions for solutions. But our boards do not support or are supported under the TWAIN protocol.
Good luck!
Nestor.
Nestor