Gyromagnetic ratio γ : An intrinsic property of a nucleus. It determines the Larmor frequency through the relation ω0 = −γ B0 .
k-space: The reciprocal of object space, k-space describes MRI data acquisition in the spatial Fourier transform coordinate system.
Larmor frequencyω0: The frequency of precession of the spins. It depends on the product of the applied flux density B0 and on the gyromagnetic ratio γ . The Larmor frequency is ω0 = −γ B0.
Magnetization M: The macroscopic ensemble of nuclear moments. The moments are induced by an applied magnetic field. At body temperatures, the amount of magnetization is linearly proportional (M0 = 4 × 10−9H0) to the applied magnetic field.
Precession: The term used to describe the motion of the magnetization about an applied magnetic field. The vector locus traverses a cone. The precession frequency is the frequency of the magnetization components perpendicular to the applied field. The precession frequency is also called the Larmor frequency ω0.
Spin echo: The transverse magnetization response to a π RF pulse. The effects of field inhomogeneity are refocused at the middle of the spin echo.
Spin–lattice relaxation T1: The exponential rate constant describing the decay of the z component of magnetization toward the equilibrium magnetization. Typical values in the body are between 300 and 3000 msec.
Spin–spin relaxation T2: The exponential rate constant describing the decay of the transverse components of magnetization (Mx and My ).
Spins M: Another name for magnetization.
2D FT: A rectilinear trajectory through k-space. This popular acquisition scheme requires several (usually 128 to 256) excitations separated by a time TR, which is determined by the desired contrast, RF flip angle, and the T1 of the desired components of the image.
