A method for determining the fast-ion population density in magnetically-confined plasmas as a function of radius-pitch values, (R, Lambda), using ssNPA-signal and NBI power-output data has been developed. Oscillations in the NBI power output are replicated only in the active part of the ssNPA signal, allowing this to be separated from the passive and background signals which usually complicate data from this diagnostic. Results obtained using this method are compared with those from standard techniques using data from the MAST-U spherical tokamak.