False colour scintigram (posterior view) of both human kidneys, showing normal left kidney and ischaemic right kidney (with a greatly reduced blood flow). Nuclear medicine allows organ functions to be assessed (as opposed to conventional x-rays and computed tomography, which afford structural views of organs). A pharmaceutical excreted by the kidneys is labelled with a radionuclide and injected into the circulation. As the radionuclide concentrates in the kidneys it emits radiations that are detected by the gamma camera. In the ischaemic kidney, with its poor blood supply, the radioactivity is less concentrated and the image less bright.