How do you determine whether a device is just being used in a study (like an approved MRI device, a device that makes a dental mold, a CT scanner) vs. a study device? Is there a rule of thumb for this?

Under 21 CFR 812.2(c), a legally marketed device (i.e. a cleared or approved device) may be used in a clinical investigation (as defined in 21 CFR 56.102(c)) if used in accordance with its labeling. If the IRB is uncertain regarding the regulatory status of a device, the IRB should request additional information/documentation. However, studies of a cleared device for a new use must comply with the human subject protection, IRB, and IDE regulations.