Function fansi_ppm_to_rad 

pub fn fansi_ppm_to_rad(b0: f64, te: f64) -> f64

ppm -> radians factor 2*pi*gamma*b0*te (gamma = GAMMA_BAR_MHZ_PER_T), for the FANSI solvers, which work on the phase in radians while the crate’s inversions take ppm. FANSI’s scripts use gyro = 2*pi*42.58; QSM.rs uses the shared constant, which is closer to the CODATA shielded-proton value (see crate::constants).