Chapter 8: PET

20 flashcards · Biology · by Kristóf Nagy

1. Random Coincidences

   Coincidence events caused by two unrelated photons arriving at the detectors within the coincidence time window, contributing to background noise in PET images1920.

2. Coincidence Detection

   The detection of two gamma rays arriving at opposite detectors within a very short time window (coincidence time window), indicating that they likely originated from the same annihilation event16.

3. Image Reconstruction Filters

   Mathematical filters used to process the acquired data and improve image quality, influencing image resolution and noise levels16.

4. SiPM (Silicon Photomultiplier)

   A solid-state photosensor consisting of an array of Geiger-mode APDs, offering high gain, excellent time resolution, and compactness, increasingly used in modern PET systems2324.

5. Block Detector

   A type of PET detector consisting of multiple scintillator crystals coupled to a smaller number of PMTs, reducing cost while increasing pixel density22.

6. Absolute Quantification

   The ability to measure the absolute amount of radioactivity (e.g., in Bq/ml) within a region of interest in a PET image, enabling accurate assessment of biological processes21.

7. Noise Equivalent Count Rate (NECR)

   The “pure” count rate (without scatter and random events) that would give the same statistical noise level as the observed count rate (including scatter and randoms)20.

8. Partial Volume Effect

   An effect where the measured radioactivity in a voxel is underestimated if the source of radioactivity is smaller than the image resolution, leading to blurring and inaccurate quantification21.

9. Momentum Conservation

   The principle that the total momentum of a system remains constant in the absence of external forces, applied to the electron-positron annihilation process, requiring the two gamma rays to travel in opposite directions to conserve momentum15.

10. Energy Conservation

    The principle that energy cannot be created or destroyed, only converted from one form to another, applied to the electron-positron annihilation process where the total energy of the gamma rays equals the rest mass energy of the electron and positron15.

11. Electron-Positron Annihilation

    The process in which a positron and an electron interact and annihilate each other, producing two gamma rays with energies of 511 keV each that travel in opposite directions15.

12. PET (Positron Emission Tomography)

    A nuclear medicine imaging technique that detects pairs of gamma rays emitted indirectly by a positron-emitting radionuclide in the body, allowing for 3D image reconstruction and quantification of biological processes15.

13. Scatter Coincidences

    Coincidence events caused by one or both annihilation photons scattering before reaching the detectors, leading to mispositioning of the event19.

14. Depth-of-Interaction (DOI)

    The depth at which the annihilation photons interact within the detector, affecting the accuracy of position determination16.

15. Attenuation Correction

    A correction applied to account for the attenuation of annihilation photons as they pass through the patient’s body, crucial for quantitative accuracy in PET imaging19.

16. True Coincidence Count Rate

    The rate of detected coincidence events that truly originate from the same annihilation event18.

17. Non-Colinearity

    The slight deviation from 180° of the emitted annihilation photons, contributing to the blurring of PET images16.

18. Positron Range

    The distance a positron travels from its point of emission to its point of annihilation, influencing the spatial resolution of PET images16.

19. Sampling

    The process of acquiring data at discrete points in space, affecting image resolution16.

20. Time-of-Flight (TOF) PET

    A PET technique that measures the difference in arrival times of the two annihilation photons, improving image resolution by localizing the annihilation event along the line of response1617.