The Process of Setting up a PET scan

The ability of a PET scanner to target specific functions or objects e.g. tumour makes it a very effective tool in non-invasive medical imaging and diagnostics. The process involves using radionuclides, so PET scanners aren’t available at every medical facility.

Related: Radionuclide Imaging Techniques

The process of setting a PET scan involves the following steps:

1. A nuclear medicine technician prepares the radionuclides or radiopharmaceutical drug. PET scans uses the following radionuclides: Carbon-11 (20.5-minute half-life), Nitrogen-13 (9.97-minute half-life), Oxygen-15 (2.03-minute half-life), and Fluorine-18 (110-minute half-life). The half-lives of these radionuclides are very short so they need to be prepared shortly before use.
2. A technician puts the radionuclides/radiopharmaceutical drug into the patient’s body. The radionuclides/radiopharmaceuticals travel within the body and collect at the target.
3. A positive beta particle is emitted when the radionuclide/radiopharmaceutical drug radioactively decays. A positive beta particle is a positron emitted from the nucleus. Positron is an anti-electron.
4. The beta particle can’t travel far in the body and usually stops within a distance less than 0.02 inches (0.5 millimetres) from where it was emitted. The majority of the positrons used in a PET scan have a mean energy of 250 kiloelectron volts (4 x 10^-14   joules), and they usually stop moving quickly. This length scale sets a lower limit on the resolution of a PET scan to about 0.04 inches (1 millimeter).  
5. The positrons usually stop moving before annihilating with an electron. Positron is an anti-electron and it will annihilate with a local electron.
6. The annihilation of the electron-positron pair creates two gamma particles that fly off in opposite direction. The two gamma photons both have energy of 511 kiloelectron volts (8.186 x 10^-14 joules), which is the rest mass energy of the electron and the positron as well.
7. The gamma detectors surround the patient in a ring and record a signal whenever a pair of gamma photons simultaneously hit the detectors. A line of response connects two detectors that record signals from the two gamma photons. After the measurements are completed, all the lines of response are put together, showing where there is a high concentration of radionuclides within the body.

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