The development of the rectilinear scanner by Benedict Cassen was preceded by his successful fabrication of a directional scintillation detector probe. In 1950, Cassen assembled the first automated scanning system that was comprised of a motor driven scintillation detector coupled to a relay printer. The scanner was used to image thyroid glands after the administration of radioiodine. Initial studies that were performed at the West Los Angeles Veterans Administration Medical Center led to the extensive use of the scanning system for thyroid imaging during the early 1950s. Cassen's development of the rectilinear scanner was a defining event in the evolution of clinical nuclear medicine. In 1956, Kuhl and his colleagues developed a photographic attachment for the Cassen scanner that improved its sensitivity and resolution. With the development of organ-specific radiopharmaceuticals, a commercial model of this system was widely used during the late 1950s until the early 1970s to scan the major body organs. The decline of the rectilinear photoscanner began in 1973 with the advent of computed axial tomography.