The ARDMS/ APCA Sonography Principles and Instrumentation (SPI) examination tests basic physical principles and instrumentation knowledge. Passing this exam is a requirement for the RDMS, RDCS, RVT, and MSKS credentials. Sonography professionals who seek a credential from ARDMS (or its physician-centric companion organization APCA) are required to pass both the SPI examination and a corresponding specialty examination within five years. The SPI exam is two hours long and contains 110 multiple-choice and Semi-interactive Console (SIC) questions.