Multi-CFD Timing Estimators for PET Block Detectors

Abstract

Abstract-In a conventional PET system with block detectors, a timing estimator is created by generating the analog sum of the signals from the four photomultiplier tubes (PMT) in a module and discriminating the sum with a single constant fraction discriminator (CFD). The differences in the propagation time between the PMTs in the module can potentially degrade the timing resolution of the module. While this degradation is probably too small to affect performance in conventional PET imaging, it may impact the timing inaccuracy for time-of-flight PET systems (which have higher timing resolution requirements). Using a separate CFD for each PMT would allow for propagation time differences to be removed through calibration and correction in software.In this paper we investigate and quantify the timing resolution achievable when the signal from each of the 4 PMTs is digitized by a separate CFD. Several methods are explored for both obtaining values for the propagation time differences between the PMTs and combining the four arrival times to form a single timing estimator. We find that the propagation time correction factors are best derived through an exhaustive search, and that the "weighted average" method provides the best timing estimator. Using these methods, the timing resolution achieved with 4 CFDs (1052 ± 82 ps) is equivalent to the timing resolution with the conventional single CFD setup (1067 ± 158 ps).

OpenPET: A Flexible Electronics System for Radiotracer Imaging

“…A TDC implemented within the detector FPGA generates a time stamp indicating the arrival time of the timing signal. If multiple detector channels are involved in creating a time estimator [14], the appropriate processing is done in the FPGA. The detector FPGA and its associated memory also analyzes the ADC data from this channel and combines it with information from other channels (if necessary) to compute the deposited energy, the interaction position, and the event time.…”

Estudio e implementación de algoritmos digitales para la mejora de la resolución temporal en sistemas de tomografía por emisión de positrones

“…Desde entonces, el CFD es y ha sido uno de los métodos de extracción de tiempos más comúnmente usado. En la literatura, pueden encontrarse una gran cantidad de implementaciones electrónicas diferentes (entre ellas, [118,119,120,121,122,123,124,125]). …”

Βελτιστοποίηση Της Λειτουργίας Συστημάτων Τομογραφίας Εκπομπής Ποζιτρονίων (PET)

“…Παρακάτω δίνεται συνοπτική περιγραφή των κριτηρίων τα οποία πρέπει να πληροί μία σύμπτωση για να θεωρηθεί αληθινή καθώς επίσης και η περιγραφή των μη επιθυμητών τύπων συμπτώσεων. Τέλος, επιχειρείται και η συνοπτική περιγραφή των αντίστοιχων μεθόδων διορθώσεων(98)(99)(100)(101)(102)(103).Για να θεωρηθεί μία σύμπτωση ως αληθινή πρέπει να πληροί το κριτήριο της χρονικής σύμπτωσης. Αυτό πρακτικά σημαίνει ότι σε κάθε προσπίπτουσα ακτίνα γ αποδίδεται μία χρονική στάμπα και υπολογίζεται η απόλυτη χρονική διαφορά μεταξύ των δύο χρονικών στιγμών όλων των προσπιπτουσών ακτίνων.…”