When the contrast of an MR image is predominantly dependent on the spin density the term of this image is R-weighted. Also called (PD) proton density weighted image.

An image produced by controlling the selection of scan parameters to minimize the effects of T1 and T2, resulting in an image dependent primarily on the density of protons in the imaging volume. Proton density contrast is a quantitative summary of the number of protons per unit tissue. The higher the number of protons in a given unit of tissue, the greater the transverse component of magnetization, and the brighter the signal on the proton density contrast image. Conversely the lower the number of protons in a given unit of tissue, the less the transverse magnetization and the darker the signal on the proton density image. Also called (Rho) ρ-weighted.

See also Density Weighted Imaging and Image Contrast Characteristics.