PET Energy-Based Scatter Estimation in the Presence of Randoms, and Image Reconstruction With Energy-Dependent Scatter and Randoms Corrections

Abstract

In this paper, we address the problem of energy-based scatter estimation in PET in the presence of randoms. We refine a previous proposed model for comprehensive use of the energy information in PET [Phys. Med. Biol., vol. 51, pp. 2919-2937, 2006] by introducing a model for the random coincidences. This model is used to estimate the scatter components in randoms from delayed coincidence data, and then of the nonrandom coincidence scatters from the prompt coincidence data. By performing these estimations on a spatial grid covering the data space, we obtain scatter and randoms correction terms that depend both on position and energy. These terms are incorporated into the list-mode image reconstruction algorithm, thus allowing for an individual treatment of each event according to its position and energy information. We test this approach by using a recently developed image quality evaluation procedure that measures the detectability of signals at unknown locations. The procedure combines a three-dimensional image scanning technique with a novel nonparametric freeresponse data analysis method that provides a signal detectability metric by using an exponential transformation of the free-response operating characteristic (EFROC). The method allows for scaling of the detectability index to any given image size, a property that makes it advantageous for application to phantom experiments with multiple signals, or large background volumes that can be scanned for false signals. Such experiments can provide substantial signal detectability information with only a few images, as we show here. Image reconstructions using traditional, no energy-dependent, and energy-dependent corrections are compared for different time-of-flight (TOF) resolutions, and number of counts. A comparison of PET time-of-flight (TOF) performance versus no-TOF is also presented.

Algorithms for joint activity–attenuation estimation from positron emission tomography scatter

“…In reality, the use of scattered photons is complicated by the fact that the detected signal of a nonscattered 511 keV photon, when it deposits only part of its energy in the detector, resembles that of a lower-energy, object-scattered photon [34]. One solution may be the use of an object-scatter energy window above the Compton edge (at 341 keV) and below the photopeak, which is virtually free of detector-scattered photons ([40], Fig. 1).…”

Evaluation of the Feasibility and Quantitative Accuracy of a Generalized Scatter 2D PET Reconstruction Method

“…With list-mode acquisitions in modern PET and improved detector technology, the use of the energy of individual photons becomes feasible and some authors have proposed new approaches that include the energy information in the estimation of the scatter distribution and image reconstruction process [6,[26][27][28]. These approaches attempt to improve the accuracy of the rejection of scattered coincidences from measured data but are limited by the energy resolution of the detectors [29].…”