Almost any protein can be labelled with Tc-99m, including monoclonal antibodies and their Fab fragments. Tc-99m-human serum albumin was originally developed as a blood pool agent and used for MUGA studies as described under Tc-99m-labelled erythrocytes. It can also be used for lymphoscintigraphy. Tc-99m-polyclonal IgG has also been used for lymphoscintigraphy and for imaging inflammation. Positive images result from the increased capillary permeability of inflammation rather than specific binding of IgG at the site of inflammation. Macro-aggregated protein is particulate and trapped in pulmonary arterioles following i.v. injection. It is therefore widely used in ventilation-perfusion lung scanning for diagnosing pulmonary embolism. It undergoes right-to-left shunting in some forms of pulmonary arteriovenous disease and is therefore used to diagnose conditions such as hepatopulmonary syndrome.