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SUMMARY:Multi‑Start Likelihood Reconstruction with Bayesian Penalisation
  for Low‑Statistic Positronium Lifetime Imaging
DTSTART;VALUE=DATE-TIME:20260911T095000Z
DTEND;VALUE=DATE-TIME:20260911T102000Z
DTSTAMP;VALUE=DATE-TIME:20260922T182702Z
UID:indico-contribution-2039@events.ncbj.gov.pl
DESCRIPTION:Speakers: Roman Shopa (National Centre for Nuclear Research)\n
 We explore the adaptive algorithm in Positronium Lifetime Imaging (PLI)\, 
 a new technique that analyses the local behaviour of positronium (Ps) – 
 a quasi-stable electron-positron ($e^−e^+$) compound [1]. Voxel-dependen
 t Ps lifetime spectra can be acquired using Positron Emission Tomography (
 PET) with specific $\\beta^+\\gamma$ sources that emit an additional promp
 t gamma photon. But mostly due to a need for 3-photon coincidence data\, t
 he sensitivity is much lower than in standard PET [2].\n\nBased on the pre
 vious development of PLI algorithms based on non-linear fitting of noisy v
 oxel-dependent Ps lifetime spectra [3]\, we further address the challenge 
 of low-count data. A multi-variable Bayesian penalisation factor is added 
 to the negative log‑likelihood minimisation\, using prior information fr
 om the approximate low-resolution image. There is a major issue that the m
 ulti-channel Ps decay model tends to overfit and converge to local minima.
  A proposed solution is a multi-start optimisation with random initial gue
 sses\, split into two stages – each with different variables fixed or pe
 nalised from priors.\n\nWe also conduct an inferential analysis of the ini
 tial guess distributions and their adjustment to the regions that converge
  best. That allows for a decrease in their minimal number for successful m
 inimisation and for a performance boost of the PLI algorithm.\n\n[1] Deuts
 ch M. Phys.Rev. 82 455 (1951)\n[2] Huang B et al. Comm.Phys. 8 1 (2025)\n[
 3] Shopa RY\, Dulski K. BAMS 19 54 (2023)\n\nhttps://events.ncbj.gov.pl/ev
 ent/468/contributions/2039/
LOCATION:
URL:https://events.ncbj.gov.pl/event/468/contributions/2039/
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