Nuclear Medicine is the most super specialized field of modern medicine wherein a specific radioactive substance is administered into the patient in calculated quantity, either to diagnose or treat a disease. Accordingly, it is broadly classified into DIAGNOSTIC NUCLEAR MEDICINE and THERAPEUTIC NUCLEAR MEDICINE.
In this modality, a short lived suitable radionuclide in the desired chemical form is administered to the patient through a vein, in trace quantity. The tracer is uniformly and thoroughly mixed during the blood circulation. The flow of the tracer to different region of the body indicates the nature of blood supply to that region. Its accumulation into and subsequent elimination from an organ gives the direct index of the function of that organ.
The distribution of the injected tracer inside the human body can be followed and mapped sequentially using specially designed Nuclear Imaging equipments. When this equipment is coupled with a dedicated computer system having special software, it is possible to derive clinically very important information such as how fast and how much blood supply is to a particular organ and the percentage of its functional capacity. The clinical parameter may be in the form of numerical data, curves, graphs and images depending upon the nature of the scan. These parameters are viewed by NM specialist to diagnose the nature of the disease at very early stage. This branch of NM is further subdivided into PET and SPECT, based on the type of the tracer used. If the tracer used is a positron emitter (eg.18F-FDG: Fluoro De-oxy Glucose), it is called PET (Positron Emission Tomography) imaging. The machine used for this purpose is called PET machine .This gives only the functional information. In order to get better structural information it is fused to CT (Computed Tomography) machine. This is known as PET-CT machine. PET-CT images give minute details of the cell function and can tell about the nature of the disease at molecular level. That is why PET-CT imaging is generally referred to as ‘Molecular Imaging’ or ‘Molecular Probe’.
When we use radio nuclides that emit gamma radiation (eg.99mTc-Radiopharmaceuticals), it is called Gamma Imaging; but nowadays it is commonly known as SPECT imaging. This is carried out by using the equipment called Gamma Camera which is generally known as SPECT camera. As SPECT imaging gives functional details of an organ it is popularly known as ‘Functional Imaging’.
Here, relatively large doses of a long lived suitable radioactive substance are given to the patient in the same way as mentioned for nuclear diagnosis. This is again divided into two categories-Palliative Therapy and Curative Therapy based on the effect of the radionuclide. If the pain caused by the cancer is reduced by the nuclear therapy it is called Palliative Therapy (eg.89Sr,153Sm,32P) and if the disease is completely cured by the nuclear therapy then it is called Curative therapy(eg.131I).
Once radioactive material accumulates in the organ or area of your body being examined, it gives off a small amount of energy in the form of gamma rays. Special cameras detect this energy, as areas of greater intensity, called "hot spots,". This indicates high level of chemical or metabolic activity. Less intense areas, or "cold spots," indicate a smaller concentration of radiotracer and less chemical activity.