Patient motion was most prevalent in the blood phase and MBF and MFR errors increased most substantially with motion in the inferior direction. Motion correction focused on these motions is needed to reduce MBF and MFR errors.
Background.-Patient motion can lead to misalignment of left ventricular (LV) volumes-ofinterest (VOIs) and subsequently inaccurate quantification of myocardial blood flow (MBF) and flow reserve (MFR) from dynamic PET myocardial perfusion images. We aimed to develop an image-based 3D-automated motion-correction algorithm that corrects the full dynamic sequence for translational motion, especially in the early blood phase frames (~ first minute) where the injected tracer activity is transitioning from the blood pool to the myocardium and where conventional image registration algorithms have had limited success. Methods.-We studied 225 consecutive patients who underwent dynamic rest/stress rubidium-82 chloride (82 Rb) PET imaging. Dynamic image series consisting of 30 frames were reconstructed with frame durations ranging from 5 to 80 seconds. An automated algorithm localized the RV and LV blood pools in space and time and then registered each frame to a tissue reference image volume using normalized gradient fields with a modification of a signed distance function. The computed shifts and their global and regional flow estimates were compared to those of reference shifts that were assessed by three physician readers.
An accurate model of the nonlinear detector response of organic scintillators to neutrons is required to correctly simulate fast neutron detection, as well as interpret measured pulse height data. Several empirical and semi-empirical models are available to fit measured scintillator light output data. In this work, EJ-309 light output data from neutrons depositing 1.15 MeV to 5.15 MeV on hydrogen wereanalyzed using empirical models as well as semi-empirical models based on the work of Birks and Voltz. Although all tested models fit the experimental light output data well in the measured range, the models were observed to diverge in low-energy extrapolation. The modelswerethen tested by comparing a measurement and MCNPX-PoliMi simulation of an EJ-309 detector response to fast neutrons from a 252 Cf spontaneous fission source. The agreement between the measured and simulated pulse height distributionsvaried significantly depending on the light output model used. The best agreement between simulated and measured neutron pulse height distributionswas achieved by using the Birks model. The bin-by-bin agreement was better than 5% over the range 0.08 to 2.18 MeVee, and better than 10% from 2.18 to 3.13 MeVee. The integral count rate over the range 0.08 to 3.14 MeVee differed by less than 1% in absolute units. 1.0 Introduction The IAEA is interested in high-fidelity Monte Carlo modeling of detector technologies for international safeguards applications[1]. Several ongoingsafeguards projects employ organic scintillators as fast neutron detectors, such as theLiquid-Scintillator Neutron Coincidence Collar (LS-NCC) [1],the Fast Neutron Multiplicity Counter (UM-FNMC) [2,3],radiation portal monitors (RPMs)[4,5], and the Dual Particle Imager (DPI) [6-8]. Organic scintillators are also frequently employed in a wide variety of applications including, but not limited to, nuclear physics [9], material characterization [6,3,10,2], imaging [6-8], and nuclear medicine[11,12].
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.