 Today, most of what is known of the selective permeability of the blood–brain barrier was either established by Oldendorf in his laboratory, or by others using his ingenious techniques.These results have been essential in developing PET and SPECT imaging; in studying glucose transport and brain metabolism; and in characterizing clinically important diseases such as cerebral ischemia, starvation, and epilepsy.Oldendorf's experiments were also was the first to prove that cerebrospinal fluid functions as a "sink" in relationship to brain metabolism, a concept that is being investigated in relation to the pathophysiology of presenile dementias such as Alzheimer's disease.