Nuclear Medicine: PET-CT & Gamma Camera

Nuclear medicine encompasses both diagnostic imaging and treatment of disease, and may also be referred to as molecular medicine or molecular imaging & therapeutics. Nuclear medicine uses certain properties of isotopes and the energetic particles emitted from radioactive material to diagnose or treat various pathology. Different from the typical concept of anatomic radiology, nuclear medicine enables assessment of physiology. This function-based approach to medical evaluation has useful applications in most subspecialties, notably oncology, neurology, and cardiology.

Gamma cameras are used in e.g. Scintigraphy, SPECT and PET to detect regions of biologic activity that may be associated with disease. Relatively short lived isotope is administered to the patient. Isotopes are often preferentially absorbed by biologically active tissue in the body, and can be used to identify tumours or fracture points in bone. Scintigraphy ("scint") is a form of diagnostic test wherein radioisotopes are taken internally, for example intravenously or orally. Then, gamma cameras capture and form two-dimensional images from the radiation emitted by the radiopharmaceuticals.

At least one mammography screening every two years is recommended in women between the ages of 40 and 74.

Research indicates that repeated mammography starting at age 50 saves about 1.8 lives over 15 years for every 1,000 women screened. However, higher frequency use of mammography may result in overtreatment, and radiation exposure.

  • SPECT is a 3D tomographic technique that uses gamma camera data from many projections and can be reconstructed in different planes. A dual detector head gamma camera combined with a CT scanner, which provides localization of functional SPECT data, is termed a SPECT-CT camera, and has shown utility in advancing the field of molecular imaging. In most other medical imaging modalities, energy is passed through the body and the reaction or result is read by detectors. In SPECT imaging, the patient is injected with a radioisotope (most commonly Thallium 201TI, Technetium 99mTC, Iodine 123I, and Gallium 67Ga). The radioactive gamma rays are emitted through the body as the natural decaying process of these isotopes takes place. The emissions of the gamma rays are captured by detectors that surround the body.

  • Positron emission tomography (PET) uses coincidence detection to image functional processes. Short-lived positron emitting isotope, such as 18F, is incorporated with an organic substance such as glucose, creating F18-fluorodeoxyglucose, which can be used as a marker of metabolic utilization. Images of activity distribution throughout the body can show rapidly growing tissue, like tumour, metastasis, or infection. PET images can be viewed in comparison to computed tomography scans to determine an anatomic correlate.