The strength of nuclear medicine lies in using the tracer method to acquire information about how an organ is or is not functioning as it should. This modality, therefore, focuses on physiological organ function for diagnoses and not on anatomical information such as X ray computed tomography (CT) or magnetic resonance imaging. The three aspects involved in the process are: (i) choice of radioactive tracer, (ii) method of detection of the emissions from the tracer, and (iii) analysis of the results of the detection. The radioactive tracers on which nuclear medicine (or molecular imaging as it is increasingly being called) is based are designed to participate in or ‘trace’ a chosen function of the body. Their distribution is then found by detecting and locating the emissions, usually γ photons, of the radioactive tracer. The tracer may be involved in a metabolic process, such as iodine in the thyroid, or it may take part in a physiological process because of its physical make-up, such as macroaggregate of albumin (MAA) in the lungs.
Myers, M. J. 
- Institute of Clinical Sciences, Imperial College London, London (United Kingdom)