1 Office of Science and Engineering Laboratories (V.M.H., A.D.L.), Center of Devices and Radiological Health, Food and Drug Administration, Silver Spring, MD; Winchester Engineering and Analytical Center (C.R.C.), Food and Drug Administration, Winchester, MA; and Office of Device Evaluation (M.E.T., J.B., M.B.E.), Center of Devices and Radiological Health, Food and Drug Administration, Silver Spring, MD.