Physics, Techniques and Procedures

Spin density

number of resonating spins (protons) per unit volume in an NMR experiment and one of the major signal determinants (see Bloch equations, T1 relaxation, T2 relaxation,spin echo pulse sequence, gradient echo pulse sequence). There are about 0.11 moles of hydrogen/cm³ corresponding to 6 10²² spins/cm³ in water. Spin density varies very little between different human soft tissues and is not therefore an important contrast parameter in MR imaging.

GvS