PET: Iterativna rekonstrukcija slike

slovenian

2025

volume 12, issue 2

image reconstruction   medical imaging   medical physics   positron emission tomography

Univerza v Ljubljani, Fakulteta za matematiko in fiziko
(Obvezni izvod spletne publikacije)

Positron emission tomography (PET) is an important medical imaging technique, based on the detection of radiation from radioactive ?$\beta^+$? emitters. These are introduced into the patient’s body in small amounts as part of molecules called radiopharmaceuticals. In ?$\beta^+$? decay, a positron is produced, which quickly stops in the tissue and annihilates with a nearby electron, releasing energy in the form of two anti-collinear photons. These are intercepted by a detector ring, composed of scintillators that absorb ionizing radiation and convert it into visible light, which can then be detected by photodetectors. From the measurements of coincident photons, reconstruction of a 3D distribution of the radiopharmaceutical in the body is possible. Currently, prevalent reconstruction method is iterative reconstruction, which uses a likelihood function to account for the statistical nature of radioactive decay and measurement procedure. An assumption about a linear relationship between the image vector and the measurement vector is made, described by a system matrix. The reconstruction algorithm iteratively updates the image values, moving towards the most likely image (given the specific measurement). The resolution is limited by several factors (e.g., positron range in tissue, non-collinearity of annihilation), but it is improving with the development of more precise detectors. Fast detectors are also being developed for TOF PET, which takes into account the time difference between the detection of two photons. As an alternative to iterative reconstruction, convolutional neural network-based methods are emerging, but they lack validation for common clinical use.

23.09.2026