Departments of Medical Physics (J.A.M., P.A.C., O.W.), Pediatrics (A.G.B., G.P.B., K.N.G., M.W.E.), Medicine (K.N.G.), Biomedical Engineering (M.W.E., O.W.), and Radiology (C.J.F., O.W.), University of Wisconsin, 1111 Highland Ave, Room 1005, Madison, WI 53705.