[A unit of mass concentration defined as the concentration of one nanogram of a substance per one liter of the mixture, or one picogram of a substance in unit volume of the mixture equal to one milliliter, or one microgram of a substance per one cubic meter of the mixture. The concept also refers to the metric unit of mass density (volumic mass) defined as the density of substance which mass equal to one nanogram occupies the volume one liter. ( NCI )]
UMLS (NCI) C0439297