<qa>  What is the primary component in the VFA package?The principal investigator has previously developed and tested the primary component in the VFA package, cine-phase contrast and fast-phase contrast fast-PC MRI, demonstrating both to be highly accurate and precise in the measurement of normal 3D knee joint kinematics and biceps femoris strain. Additional investigators have previously developed techniques for imaging musculoskeletal structures using ultrasonography, demonstrating these techniques to be, likewise, highly accurate and precise in the measurement of biomechanical properties of the soft tissues surrounding the knee and the tendons of the quadriceps femoris. Under this protocol we propose to develop additional numerical reconstruction, image analysis, and display methods and test the applicability of fast-PC MRI and ultrasound to the study of various normal and impaired joints e.g., ankle, wrist, and knee. This development process will require data from human subjects obtained from both static and dynamic MR and ultrasound images. 