“How is nuclear medicine contained to not contaminate the air?”

Most nuclear medicine pharmaceuticals are not volatile. They are in liquid form and injected into the body. There is a finite limit as to how much radiation is emitted from a patient and generally does not travel far. The one volatile/gaseous radiopharmaceutical is Xenon 133. This is used for ventilation studies of the lung. Studies are done in a negative pressure room and exhaled xenon is captured and released above the roof of the building. Again decay half life prevents long term exposure to the environment.