Nuclear Medicine and PET
Nuclear medicine SPECT and PET scans may be may be used to evaluate the function of organs and/or tissues or for the presence of disease. It may also be used to follow the progress of treatment of some diagnosis.
At OHSU Diagnostic Imaging Services your care and experience is our number one priority. We are an ACR accredited facility and all our machines are certified. Our technologists are OBMI certified through the State of Oregon, as well as nationally registered with NMTCB and ARRT. Our radiologists have all completed an ACGME nuclear medicine residency. Your appointment is unique to you and each exam is protocoled by one of our Nuclear Medicine Radiologists. Please feel free to call with questions regarding your appointment:
What is Nuclear Medicine?
Nuclear Medicine is a specialized and rapidly evolving field of radiology that encompasses a wide variety of diagnostic tests and medical therapies. Common to all types of Nuclear Medicine tests and therapies is the use of radioactive substances called radiopharmaceuticals. These are also referred to radiotracers or just "tracers", for short. Diagnostic tests using radiotracers often have an advantage over other types of diagnostic imaging in that the radiotracers are able to show how a certain tissue or organ is functioning. Most other types of diagnostic imaging tests (e.g. CT scans, MRI scans, X-rays) simply show what an organ or tissue looks like, and not how it is functioning. Nuclear Medicine is most often used by oncologists, neurologists and neurosurgeons and cardiologists. A Nuclear Medicine scan consists of three parts: radiotracer administration, image acquisition, and image interpretation.
Tracer Administration and Image Acquisition
A wide variety of radiotracers are employed in the practice of Nuclear Medicine. They can be injected, inhaled or swallowed, depending on the type of exam being performed. Many radiotracer molecules have specially designed components that target them to specific tissues. For example, in PET scans performed to evaluate tumors, a radioactive form of the glucose molecule (F-18 fluorodeoxyglucose) is injected into the body and is rapidly taken-up by tumor cells that use the glucose for energy. Most radiotracers used in medicine have a very short half-life, meaning they exist for only a short period of time before transforming into non-radioactive substances or before being excreted from the body. Most radiotracers used for diagnostic imaging emit a small quantity of radiation that poses minimal risk to your health. Radiotracers used for medical therapy (e.g. treating tumors) emit a larger amount of radiation.
After the radioisotope has been administered and it has collected in the body tissue under study, it emits radiation that is detected by specialized cameras. The amount of time between when a radiotracer is administered and when the images are acquired can range from a few moments to a few days, depending on the specific type of test. The time required to obtain the images may also vary from minutes to hours to several days. Some studies require planar imaging that acquires 2D images. The two most common types of Nuclear Medicine tests are Single Photon Emission Computed Tomography (SPECT) and Positron Emission Tomography (PET) and these can be used to create 3D images.
What's the difference between Nuclear Medicine and PET?
SPECT (single photon emission computed tomography) scans result in creation of 2D or 3D images by measuring gamma ray emissions. Gamma rays are a form of short-wavelength electromagnetic radiation that are produced during the decay of radioisotopes. Gamma cameras are mounted on a rotating gantry that allows the detectors to be moved in a tight circle around a patient who is lying still on a table. A large number of projection images of the body are recorded at different angles and 3D images are then computer generated.
PET (positron emission tomography) works very similarly to SPECT but instead detects pairs of gamma rays emitted indirectly by the radioisotope. As the radioisotope breaks down, positrons are emitted. A positron is a particle with roughly the same mass as an electron but oppositely charged. Positrons and electrons are attracted to each other. When they meet, they annihilate each other and emit two photons (gamma rays) that shoot off in opposite directions. The detectors in the PET scanner measure these gamma rays and use the information to create images.