PET vs SPECT | The basics (Updated video)

foreign are the two major molecular Imaging modalities used in nuclear medicine my name is Pauline I'm a Belgian nuclear medicine residence and in this short video I will explain the key differences between the two techniques before we start you have to know that pet inspect are different from other Imaging modalities such as x-ray CT or MRI in the sense that pet inspect visualize organ function whereas the others assess the anatomy this is one of the main reasons why diagnosing staging cancer is such a big part of a nuclear medicine Physician's job that inspect scans May

detect biochemical changes in an organ that can identify cancer lesions before anatomical changes can be seen with CT or MRI pet scans can detect cancer on average six months earlier than a CT scan but what our pattern spec scans exactly but stands for positron emission tomography and uses positron emitting radialisotopes the most commonly used radioisotope is fluorine 18. spect on the other hand stands for single Photon emission tomography and uses gamma emitting radial isotopes the most commonly used radioisotope is technetium these Isotopes are then Incorporated either into compounds normally used by the body such as

glucose water or ammonia or into molecules that bind to receptors for example when fluorine 18 is prepared it is attached to a specific form of glucose this forms fluorodioxy glucose fluorodioxic glucose is a radio labeled pharmaceutical or in short a radiopharmaceutical when given to a patient the body assumes that it is glucose the fdg is sent to metabolically active areas in our body such as the heart the brain but also cancer cells in fact the degree of aggressiveness for most cancers is roughly parallel by the rate of glucose uptake a quick summary of what we've

discussed so far a radio pharmaceutical consists of a radioactive isotope which creates the image and a tracer which determines where the signal accumulates to form the image so radio Pharmaceuticals function like a GPS tag allowing doctors to track not only where in the body the atom goes but also how it behaves both spect and Pathway to Pharmaceuticals Decay by emitting gamma rays which are picked up by a special camera but they both do it in a different way fluorine 18 produces small particles called positrons when a positron encounters an election which happens very quickly in

the body both particles vanish in a burst of energy this energy comes in the form of two gamma rays that travel in opposite directions and can be detected by the pet scanner only gamma rays that interact at the same time with a pair of detectors are recorded the trajectories trace back to the point of annihilation allowing a computer to form an image technician on the other hand produces only a single Photon of radiation this photo moves out of the body and is detected by the camera combining thousands of these photons ultimately result in image creation

here's another picture to illustrate this fluorine 18 produces positrons positrons encounter electrons and vanish they released two gamma rays that are detected by the camera technician produces a single version of radiation that is also detected by the camera to form an image a typical path scanner incorporates hundreds of detectors in the form of rings around the patient spec scans on the other hand typically have two large rectangular detectors that rotate around the patient specs and pet scans are most often combined with CT scans to provide both anatomical and metabolic information thank you so much for

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