In 1953 William H. Sweet and Gordon L. Brownell at Massachusetts General Hospital, Boston, described the first positron imaging device, and and the first attempt to record three dimensional data in positron detection in their paper entitled "Localization of brain tumors with positron emitters',' Nucleonics XI (1953) 40-45. This was the beginning of positron emission tomography (PET).
"Despite the relatively crude nature of this imaging instrument, the brain images were markedly better than those obtained by other imaging devices. It also contained several features that were incorporated into future positron imaging devices. Data were obtained by translation of two opposed detectors using coincidence detection with mechanical motion in two dimensions and a printing mechanism to form a two-dimensional image of the positron source. This was our first attempt to record three-dimensional data in positron detection" (Brownell, A History of Positron Imaging , accessed 12-25-2008)