Technetium is essential for medical imaging, yet supplies of this short-lived radioactive manmade element are far from guaranteed. Justin Rowlatt heads to University College London Hospital to see a technetium scan in progress, to view the clean rooms where technetium cows are milked, and to speak to nuclear medicine researcher Dr Kerstin Sander about a possible solution to cancer.

Professor Andrea Sella explains why this element sparked a 70-year wild goose chase by chemists in the 19th Century. And, we dispatch Matt Wells to Winnipeg in Canada to meet the team hoping to come up with an alternative source of technetium, when the biggest current source - the Chalk River reactor in Ontario - shuts down in 2016.