Final answer:
The procedure using radioactive sugar molecules to detect active neurons on photographic film is the PET scan, where a radioactive tracer like 18-FDG shows areas of high metabolic activity on detailed images.
Step-by-step explanation:
The procedure that involves the use of radioactive sugar molecules, which are absorbed by active neurons and then detected on photographic film, is known as positron emission tomography (PET). The PET scan utilizes a radioactive tracer, typically fluorine-18 labeled deoxyglucose (18-FDG), which mimics glucose. As active brain regions consume more glucose, they also take up more of the 18-FDG, which emits positrons. These positrons interact with electrons resulting in the emission of gamma rays that are detected by the scanner. The result is a detailed, three-dimensional, color image showing the metabolic activity of various brain regions. A radiologist can interpret these images, with bright "hot spots" indicating zones of high metabolic activity, like rapidly dividing cancer cells. Although PET scans expose patients to radiation, they are invaluable in diagnosing and monitoring conditions such as cancer, heart disease, and neurological disorders.