Yesterday Today and Tomorrow â€ẫ€THESTRENGTH OFPOSI tron emission tomography [PET],―says Michel M. Ter Pbgossian, one of the technique's de velopers, â€oeis not so much due to the reconstruction process itself, but due to the handful ofshort-lived radionuclides that are important in the body and that decay through the emission of posi trons?' Although extensive research starting in the early 1940s had estab lished the biological significance of severalofthese positron-emitting, short lived,

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... otron-pmduced radionucides, at the time, there was no adequate method to generate images from them. So, ironically, the properties that make PET radionuclides so desirable today â€" their short half-lives and positron-emis sions â€"are what limited their use early on. It wasn't until detection and image reconstruction techniques evolved that PET really got off the ground. The realization that short half-lives meant excellent studies with small doses of radiation to patients was an impetus to push PET technology forward. Re searchers were beginning to uncover the value of radionuclides with short half lives. In an article in the October 1966 issue of Nucleonics, Dr. Ter-Pbgossian and Henry N. Wagner, Jr. , MD, pro fessor ofmedicine, radiology, and envi ronmental health sciences at The Johns Hopkins Medical Institutions, Balti more, Maryland, wrote, â€oeBecause of their short effective half-lives, more in formation (in the form of higher count rates) is available with short-half-life nucides fbr a given dose ofradiation de ivered to the system than with a longer ived nucide of the same element― (1). They also noted, â€oeShort-lived nuclides also have the advantage of letting one make repeated measurements in the same system because the rapidly dis Fjgw@1; â€oeC.aufrntwiil, â€oeC-iliprenor@e and 1aF7v@ images in a jxz dentwitha kft tampons! lobe seizure jbcus. In creasedopiatereceptor binthngis@s!'senw!inthe l$tenqwmlneoaRtexin areasof reducedglucose utilization(leftcolumn). (Cowfesy I. F@vst,The Johns Hopkins Medical Institutions.) encephalography]. PEThasclinicaleffi cacy in areas of localization of seizure foci in patients with refractory seizure disorders who are candidates for epi lepsy surgery, in the differential diag nosis of dementia and movement dis orders, in the grading of brain tumors, in the localization oftumor biopsy sites, and in the differentiation of recurrent high grade gliomas from radiation-in duced brain necrosis. The application of PETprovidespreviouslyunavailablein formation about these disease categories that should lead to a reduction in patient morbidity, mortality, and cost―(3). â€oeIn these areas, conventional imaging techniques really provide no help to the practicing neurologist or neurosurgeon,― says John Mazziotta, MD, PhD, pro fessor of neurology and radiological sciences, vice chairman of neurology, University of California, Los Angeles (UCLA) School of Medicine. He says that at UCLA all patients with primary or recurrent tumors and all those that are being evaluated for surgery for epilepsy are imaged with a PET scan prior to surgery. Dr. Mazziotta points to several areas where there are â€oepotential future Fâ€"OEOXYGLUCOSE appearing activity does not interfere with subsequent measurements― (1). Also, the development of coincidence detection, turnedpositronemission in to an advantage. Reviewing the history ofPET in the 1985book PositronEmis sion Tomography,Dr. Ter-Pbgossian, wrote â€oeOne of the considerable advan tages ofutilizing positron-emittinglabels for in vivo imaging studies is the very high efficiency that can be achieved throughthe coincidence collimation of the annihilation radiation― (2). Applications of PET Since the beginnings of PET, the techniquehas been appied to many areas ofmedicine. It is especially useful to im age neurological and psychiatric dis orders, heart disease, and cancer. The American Academy of Neurology pub lished an assessment of PET in the February 1991issue of Neurology. The executive summary of the report states, â€oePET with FDG or oxygen-iS is a safe and efficacious diagnostic clinical tech nique. It is atleast complimentary to, and often unique ratherthan redundant with, structural imaging and EEG [electro Newsline 15N