pub const GAMMA_BAR_HZ_PER_T: f64 = 42.576e6;Expand description
Proton reduced gyromagnetic ratio γ̄ = γ/2π, in Hz/T.
42.576 MHz/T, the value QSM.rs has always used and the one the QSM-CI contract states for Hz ↔ ppm.
CODATA 2018 reference values:
- shielded proton in water (25 °C, spherical sample), γ’ₚ/2π = 42.576 384 74 MHz/T, which is the relevant one for water-proton MRI;
- free proton, γₚ/2π = 42.577 478 518 MHz/T.
42.576 is within 1e-5 (relative) of the shielded value, closer to both than the 42.58 some toolboxes use. It is not set to the CODATA figure exactly because that would change every output; that is a separate decision.