Measurement of a lesion in the liver, the large, dark-red organ located in the cranial portion of the abdomen of vertebrates, just behind or below the diaphragm, that secretes bile and is active in the formation of certain blood proteins, in the metabolism of carbohydrates, fats, and proteins and in the detoxification of noxious substances. A lesion is a localized pathological change in structure of an organ or tissue due to injury or disease; especially one that is circumscribed and well defined.