Improved random coincidence estimation including triple coincidences for high quantitation accuracy in PET imaging

Abstract

Coincidence detection in PET is inherently prone to misidentification due to the presence of randomly occurring singles from different decays within the coincidence time window. Random triple coincidences, arising when three singles from at least two decays are detected within this window, can lead to bias by acceptance without further consideration in the double coincidence identification, or result in sensitivity loss if rejected. True triple coincidences, which occur with β +-γ-emitters used in dual-tracer PET and positronium lifetime imaging, are also affected by random coincidences, leading to errors that necessitate appropriate correction. The aim of this work was to develop an accurate method for estimating random double and triple coincidences in PET imaging. To process double and triple coincidences separately, coincidence identification schemes were defined with intervals free of other singles as vetoes for accepted coincidences. Random coincidences were estimated using extended delayed window techniques, which match the interval sizes for coincidence windows and vetoes. Coincidences comprising singles from two and three decays were separated in simulation studies, and two delayed windows were applied to guarantee the singles' independence for the latter case. Correction factors from additional coincidence identification schemes were used to compensate for differences in the total veto interval size between the prompt and delayed methods. The methods were evaluated using simulations for different isotopes, coincidence windows, phantom shapes and activities. The simulation results were then validated against measurements obtained with a brain PET scanner. The total random coincidence rate for the entire scanner was estimated with a relative deviation of < 3 % for double coincidences and < 5 % for triple coincidences of two decays of β +-emitters and β +-γ-emitters for the investigated coincidence identification schemes and simulated cases. The accurate estimation of random triple coincidences is crucial for quantitative PET imaging of β +-and β +-γ-emitters. This study evaluates the number of random triple coincidences for both emitter types and proposes random estimation methods based on the delayed window method, which explicitly consider random triple coincidences.

Authors 6

1. Debora Niekämper Aachen Department of Physics

   RWTH Aachen University

   Affiliation as printed

   Department of Physics, RWTH Aachen University

   Institute of Neuroscience and Medicine

2. Jürgen J Scheins
   Affiliation as printed

   Institute of Neuroscience and Medicine

3. Elisabeth A. G. Pfaehler
   Affiliation as printed

   Institute of Neuroscience and Medicine

4. Joaquín L. Herraiz

   Universidad Complutense de Madrid

   Affiliation as printed

   Nuclear Physics Group, EMFTEL and IPARCOS, Complutense University of Madrid

5. Nadim Jon Shah Aachen Department of Neurology

   Forschungszentrum Jülich · Jülich Aachen Research Alliance · RWTH Aachen University

   Affiliation as printed

   Department of Neurology, RWTH Aachen University

   Forschungszentrum Jülich GmbH

   Institute of Neuroscience and Medicine

   Institute of Neuroscience and Medicine, Forschungszentrum Jülich GmbH

   JARA -BRAIN -Translational Medicine

6. Christoph W. Lerche
   Affiliation as printed

   Institute of Neuroscience and Medicine