We designed the upper part of the symbol to represent carbon, the "organic" element that is central to biochemistry and which constitutes about 18% of the human body by weight and almost 10% of all the atoms in the body. Carbon has two K electrons and four L electrons, as depicted here in Bohr's orbital atomic model. Carbon was chosen also for simplicity, since it has the lowest atomic number of any of our biochemical/ physiological elements which can be "represented" by a ±y-nuclide. Carbon-11

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... can be detected in the intact patient by means of the two 511-keV ±7-rays, which are emitted at 180° to each other, and which almost always accompany the "annihilation" of positron-electron pairs. Thus, it lends itself to the "insideout" methodology originated by Herrman L. Blumgart and his co-workers a half-century ago. Carbon-11 now is coming to be used frequently as