Uncertainty quantification in positron emission particle tracking

Abstract

Positron Emission Particle Tracking (PEPT) is an imaging method for the visualization of fluid motion, capable of reconstructing three-dimensional trajectories of small tracer particles suspended in nearly any medium, including fluids that are opaque or contained within opaque vessels. The particles are labeled radioactively, and their positions are reconstructed from the detection of pairs of back-to-back photons emitted by positron annihilation. Current reconstruction algorithms are heuristic and typically based on minimizing the distance between the particles and the so-called lines of response (LoRs) joining the detection points, while accounting for spurious LoRs generated by scattering. Here we develop a probabilistic framework for the Bayesian inference and uncertainty quantification of particle positions from PEPT data. We formulate a likelihood by describing the emission of photons and their noisy detection as a Poisson process in the space of LoRs. We derive formulas for the corresponding Poisson rate in the case of cylindrical detectors, accounting for both undetected and scattered photons. We illustrate the formulation by quantifying the uncertainty in the reconstruction of the position of a single particle on a circular path from data generated by stateof-the-art Monte Carlo simulations. The results show how the observation time ∆t can be chosen optimally to balance the need for a large number of LoRs with the requirement of small particle displacement imposed by the assumption that the particle is static over ∆t. We further show how this assumption can be relaxed by inferring jointly the position and velocity of the particle, with clear benefits for the accuracy of the reconstruction.

On the Ability of Positron Emission Particle Tracking (PEPT) to Track Turbulent Flow Paths with Monte Carlo Simulations in GATE

“…Recent examples of location uncertainty quantification for PEPT measurements suggest values for different PEPT systems on the order of magnitudes 0.1 mm and 1 mm [19,[23][24][25][26][27].…”

“…GATE is built upon the Geant4 (GEometry ANd Tracking 4) toolkit developed at CERN [36]. GATE simulations are improving the treatment of PEPT data, specifically for the quantification of uncertainty in a PEPT measurement [26], dynamic optimization of tracking parameters where the flow behaviour of the system is predictable [37], validation with other simulation techniques such as Discrete Element Method (DEM) models [28], and comparison with the performance of different PEPT location algorithms relative to the scanners commonly used for PEPT [24].…”