Final answer:
A PET scan is the best imaging technique to study the uptake of nutrients by rapidly multiplying cancer cells.
Step-by-step explanation:
The best imaging technique to study the uptake of nutrients by rapidly multiplying cancer cells would be a PET scan. PET scans use radiopharmaceuticals to create images of active blood flow and physiological activity of the targeted organ or organs. This imaging technique is effective for studying cancer cells because it can detect their increased metabolic activity and nutrient uptake.