Docta Complutense
Open Access Institutional Repository of the Complutense University of Madrid, that compiles scientific production to promote the visibility and impact of Complutense research.
With the collaboration of the Ministerio de Ciencia e Innovación and the Spanish Foundation for Science and Technology (FECYT).
Recent Submissions
Improved random coincidence estimation including triple coincidence detection in PET
(Frontiers in Nuclear Medicine, 2026) Niekämper, Debora; Scheins, Jürgen J.; Pfaehler, Elisabeth; López Herraiz, Joaquín; Shah, N. Jon; Lerche, Christoph
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 (Formula presented.) -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 which is crucial for quantitative PET imaging of (Formula presented.) and (Formula presented.) -emitters. The number of random triple coincidences was evaluated for both emitter types. 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 in 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 (Formula presented.) -emitters and (Formula presented.) -emitters for the investigated coincidence identification schemes and for the simulated cases.
Experimental validation of designs for permeable diffractive lenses based on photon sieves for the sensing of running fluids
(Photonics, 2025) Pastor Villarrubia, Verónica; Soria García, Ángela; Andres Porras, Joaquin; Del Hoyo Muñoz, Jesús; Elshorbagy, Mahmoud H.; Sánchez Brea, Luis Miguel; Alda Serrano, Javier
This study reports the experimental validation of several designs of photon sieves with focusing capabilities. These permeable optical elements were implemented with a spatial light modulator working in pure-amplitude mode. The focal region was scanned using a traveling stage, holding a camera. Using this experimental setup, we characterized the focal region of the photon sieves and determined some parameters of interest, such as the depth of focus and the transverse extent of the focal region. These parameters and their evolution were measured and analyzed to compare the optical performance of different designs. Moreover, the permeability of the mask was also evaluated and is included in the discussion. When the photon sieve is intended to be used as an optical element for the monitoring of running fluids, one of the designs studied, labeled the Ring-by-Ring method, behaves in a quite balanced manner and thus has become the preferred choice. Through simulations for a refractometric sensor, we obtained the Figure of Merit of the Ring-by-Ring mask, which reached a maximum value of 7860 RIU−1, which is competitive with plasmonic sensing devices
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