title: EM reconstruction of dual isotope PET using staggered injections and prompt gamma positron emitters.
abstract: OBJECTIVE
  The aim of dual isotope positron emission tomography (DIPET) is to create two separate images of two coinjected PET radiotracers. DIPET shortens the duration of the study, reduces patient discomfort, and produces perfectly coregistered images compared to the case when two radiotracers would be imaged independently (sequential PET studies). Reconstruction of data from such simultaneous acquisition of two PET radiotracers is difficult because positron decay of any isotope creates only 511 keV photons; therefore, the isotopes cannot be differentiated based on the detected energy.
  
  
  METHODS
  Recently, the authors have proposed a DIPET technique that uses a combination of radiotracer A which is a pure positron emitter (such as(18)F or (11)C) and radiotracer B in which positron decay is accompanied by the emission of a high-energy (HE) prompt gamma (such as (38)K or (60)Cu). Events that are detected as triple coincidences of HE gammas with the corresponding two 511 keV photons allow the authors to identify the lines-of-response (LORs) of isotope B. These LORs are used to separate the two intertwined distributions, using a dedicated image reconstruction algorithm. In this work the authors propose a new version of the DIPET EM-based reconstruction algorithm that allows the authors to include an additional, independent estimate of radiotracer A distribution which may be obtained if radioisotopes are administered using a staggered injections method. In this work the method is tested on simple simulations of static PET acquisitions.
  
  
  RESULTS
  The authors' experiments performed using Monte-Carlo simulations with static acquisitions demonstrate that the combined method provides better results (crosstalk errors decrease by up to 50%) than the positron-gamma DIPET method or staggered injections alone.
  
  
  CONCLUSIONS
  The authors demonstrate that the authors' new EM algorithm which combines information from triple coincidences with prompt gammas and staggered injections improves the accuracy of DIPET reconstructions for static acquisitions so they reach almost the benchmark level calculated for perfectly separated tracers.
authors: Philips Healthcare, Highland Heights, Ohio 44143.
authors: Andriy
authors: A
authors: Andreyev
authors: Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114.
authors: Arkadiusz
authors: A
authors: Sitek
authors: Department of Radiology, University of British Columbia, Vancouver V5Z 1M9, Canada.
authors: Anna
authors: A
authors: Celler
mesh_terms: D000465:Algorithms; D005720:Gamma Rays; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D049268:Positron-Emission Tomography / Q000379:methods*; D011868:Radioisotopes
chemical_list: D011868:Radioisotopes