18F-Fludeoxyglucose (FDG) is the most widely-used contrast radiotracer in PET. Fludeoxyglucose is a compound in which the F18 radioisotope attaches to a glucose or sugar molecule. Once in the body, FDG is taken up by different tissues and is detected by the PET scanner. The images obtained reveal how the FDG radiotracer is distributed in the body, rendering it possible to assess how the body is functioning and diagnose different medical conditions.
Molecular imaging involves the use of imaging technologies to evaluate the body’s biological activity with a view to obtaining medical information which would otherwise require exploratory surgery or more expensive diagnostic tests.
Nuclear molecular diagnosis
Nuclear molecular diagnosis uses a broad range of imaging devices and radiopharmaceuticals, including PET (positron emission tomography) and SPECT (single photon emission computed tomography). These imaging technologies are extremely sensitive and allow physicians to diagnose different types of cancer, cardiovascular diseases, neurological disorders and other illnesses in their early stages.
Nuclear molecular therapy
Nuclear molecular therapy uses radiopharmaceuticals that emit ionizing radiation for therapeutic purposes. The different radiotherapeutic modalities in nuclear molecular therapy are named according to the characteristics of the radiation involved and the equipment used to generate it.
Positron emission tomography (PET)
Positron emission tomography is a nuclear medicine imaging technique used for diagnosis and biomedical research. It involves the administration of a molecule labelled with a short half-life positron-emitting radionuclide. The radiopharmaceutical’s activity is quantified in all the target organs. The data are analysed and reconstructed by computer to generate functional images of the scanned organs.
A radiopharmaceutical is a radioactively-labelled molecule administered in trace doses for diagnostic or therapeutic purposes.
Single photon emission computed tomography (SPECT)
The SPECT imaging technique is used in nuclear medicine for diagnosis and biomedical research and involves the injection of a radiolabeled molecule into the bloodstream. The molecule emits gamma radiation which in turn is detected by the SPECT chamber. The technique differs from PET in that the tracer remains in the bloodstream instead of being taken up by the surrounding tissues – thereby limiting the images to zones in which blood flows.
Theragnosis is a patient management strategy involving the integration of diagnosis and therapy. In the context of molecular nuclear medicine, theragnosis refers to the use of molecules labelled with radionuclides for diagnostic purposes or molecules labelled with therapeutic radionuclides for the diagnosis and treatment of a given disease.