An infusion system may include a strontium-rubidium radioisotope generator that generates a radioactive eluate via elution, a beta detector, a gamma detector, and a controller. The beta detector and the gamma detector may be positioned to measure beta emissions and gamma emissions, respectively, emitted from the radioactive eluate. In some examples, the controller is configured to determine an activity of rubidium in the radioactive eluate based on the beta emissions measured by the beta detector and determine an activity of strontium in the radioactive eluate based on the gamma emissions measured by the gamma detector.