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.
https://www.sciencedirect.com/science/article/pii/S0001299896800213
Cassen developed the first true radioisotope imaging system,
the scintiscanner. Cassen combined the Geiger counter, the only
detector of radioactivity at the time, with crystal components of the
newly developed photomultiplier tube, which facilitated amplification
and detection of gamma ray emissions
REFERENCES:
https://pubmed.ncbi.nlm.nih.gov/11155815/
https://www.sciencedirect.com/science/article/abs/pii/S0001299896800213