More recently, Cherenkov light has been used to image substances in the body. These discoveries have led to intense interest around the idea of using this light signal to quantify and/or detect radiation in the body, either from internal sources such as injected radiopharmaceuticals or from external beam radiotherapy in oncology. Radioisotopes such as the positron emitters F and N or beta emitters P or Y have measurable Cherenkov emission and isotopes F and I have been imaged in humans for diagnostic value demonstration.