Topic summary
SPECT
Extracted from the Wikipedia article Single-photon emission computed tomography.
Principles
SPECT is similar to PET in its use of radioactive tracer material and detection of gamma rays. In contrast with PET, the tracers used in SPECT emit gamma radiation that is measured directly, whereas PET measures two gamma rays created from the annihilation of positrons that travel in opposing directions. A PET scanner detects these emissions "coincident" in time, which allows for more precise collimation which results in higher spatial resolution and higher quality images than SPECT. PET resolution typically lies within 0.5–6 mm for the more modern PET systems and around 1 cm for SPECT systems. Partly from this, SPECT scanners are cheaper than PET scans because of the more durable and plentiful radioisotopes that are used, such as technetium-99m.