Forty years after the publication of a landmark paper by the Ad Hoc Committee of 
the Harvard Medical School, the general concept of brain death has achieved 
widespread acceptance. In the United States, irreversible dysfunction of the 
brain and brainstem are required for the diagnosis of brain death. Although 
primarily based on clinical evaluation, confirmatory examinations, including 
radionuclide blood flow studies, play an important role in augmenting the 
physical examination in special situations when some of its specific components 
cannot be performed or reliably evaluated. The 2 main radionuclidic techniques 
used in evaluation of brain death are radionuclide angiography with 
nonlipophilic radiopharmaceuticals and parenchymal imaging with lipophilic 
agents. Specific technical guidelines for determination of brain death have been 
promulgated by professional medical societies. In the vast majority of cases, 
blood flow examinations are useful in confirming brain death. Nonetheless, on 
occasion patients clinically diagnosed with brain death will exhibit persistent 
intracranial blood flow or electrical activity. Existence of these contradictory 
cases reveals underlying inconsistencies in the definitions of brain death. We 
hypothesize that the existence of these apparent contradictions is related to 
differences in sensitivity of the physical examination and the confirmatory 
examinations, differences in localization of the physical examination and 
confirmatory tests, and differences between blood flow and cerebral function as 
markers of brain death.