Circulating blood is an extra-ordinary complex mixture when blood is collected with an anticoagulant , the whole blood divides into a plasma component and a cellular component . The cellular part is composed of three major portions ; erythrocytes, leukocytes and platelets . The use of radionuclides in clinical hematology began in 1938 when John Lawrence first utilized 32P , to treat a young man with chronic myelogenous leukemia . In 1939 , Hevesy introduced 32P-labeled red blood cells to measure blood volume . Since this beginnings, nuclear hematology has continued to figure importantly in the development of nuclear medicine.The isotopic labels of the cellular elements of the blood are of two general types : Cohort or pulse labels and random labels . The former is only available to the marrow precursors of a given cell type for a specific and limited length of time , while the random labels are radiopharmaceuticals that are applied to the circulating cells of the peripheral blood . Methods of labeling RBCs include ; In vivo , in vitro and combind in vivo and in vitro , while methods of labeling leukocytes and platelets include ; in vitro and in vivo . In 1962 , Cr51 labeled erythrocytes are used in measurement of red cell volume (and from this estimation of total blood volume), calculation of red cell survival, splenic sequestration ,quantification of occult blood loss and in vivo cross matching.In 1976 , Tc99m labeled erythrocytes are used for cardiovascular imaging detection and localization of gastrointestinal bleeding , measurement of erythrocyte volume and spleen imaging .Labeling efficiency can be decreased in presence of certain drugs e.g.antimicrobial agents , antidepressants , antihypertensive and anti-inflammatory drugs .Polito et al in 2005 used Tc-99m labelled red blood cells in the pre operative diagnosis of vascular orbital tumours such as cavernous hemangioma , adult-type lymphangioma and hemangiopericytoma when ultrasound , CT and MRI are not diagnostic .Schillaci and his associates in 2004 used Tc-99m red blood cells in detection of hepatic hemangiomas . Also Uslu and his associates used Tc-99m HMPAO labelled leukocyte in the diagnosis of pelvic inflammatory disease which is one of serious health problems of women of child –bearing age . Where early diagnosis and effective management of this condition can preserve fertility and prevent serious complications such as peritonitis and sepsis . Indium 111 oxine labeled white blood cells are used in clinical assessment of infection and inflammation. Also Tc99m HMPAO labeled leukocytes are used in cerebral perfusion imaging.Indium 111 oxine labeled platelets are used for clinical evaluation of deep venous thrombosis and atrial thrombosis.There is great interest in imaging infection and inflammation using PET . F18 -FDG increased with time , temperature and cell concentration , and did not result in activation or loss of viability of cells , although activation of cell further increased F18 - FDG accumulation .