Nuclear Medicine & PET-CT
Nuclear medicine a branch of medicine where patients swallow or are injected with a radioactive drug. Most nuclear medicine procedures are for imaging. The radioactive drug goes to certain parts of the body and emits radiation. Specialized nuclear cameras detect that radiation and make a map of where the drug goes to. Nuclear medicine images are not nearly as clear and sharp as CT images, but they show different things: CT images show all the cells of the patient’s body, while Nuclear Medicine images highlight those cells which take up the injected drug. There are many types of nuclear medicine scans with a wide variety of radioactive drugs, but two of the most commonly used for the diagnosis of breast cancer are MIBI and FDG PET-CT.
MIBI (also known as 99mTc sestamibi or Cardiolite) is a radioactive drug that tends to concentrate in the mitochondria of cells. Mitochondria are small parts of a cell which help the cell get energy from food. Since cancer cells need extra energy to divide quickly, they tend to have more mitochondria than normal cells and so MIBI tends to concentrate in cancer cells. Frequently, like in CT, the nuclear camera will rotate around the breast of the patient taking several images, and these images are combined in a computer to generate a 3-D image. This process is known as SPECT (where the CT at the end of SPECT stands for computed tomography).
PET is a special kind of nuclear medicine scan in which the radioactive decay actually makes a bit of antimatter known as a positron (the P in PET). Positrons have a special property that they turn into two gamma rays moving in opposite directions. When both of these gamma rays are detected, we know that the positron must have been somewhere between the two detectors. This property can make PET images clearer than SPECT images using less radiation, but PET requires special detectors which are more expensive. Today, PET scans are usually combined with CT scans to make a PET-CT image. Typically the patient is injected with a radioactive sugar called FDG. Since cancer cells need more energy than regular cells to divide quickly, they take in more of this radioactive sugar than regular cells and can appear as hot spots on PET-CT images.
Nuclear medicine images involve more radiation than regular X-ray mammography. The risk from this radiation is small, but still these scans should not be used unless the patient has a particular risk of breast cancer.