title: Dual-tracer PET using generalized factor analysis of dynamic sequences.
abstract: OBJECTIVE
  With single-photon emission computed tomography, simultaneous imaging of two physiological processes relies on discrimination of the energy of the emitted gamma rays, whereas the application of dual-tracer imaging to positron emission tomography (PET) imaging has been limited by the characteristic 511-keV emissions.
  
  
  METHODS
  To address this limitation, we developed a novel approach based on generalized factor analysis of dynamic sequences (GFADS) that exploits spatio-temporal differences between radiotracers and applied it to near-simultaneous imaging of 2-deoxy-2-[(18)F]fluoro-D-glucose (FDG) (brain metabolism) and (11)C-raclopride (D2) with simulated human data and experimental rhesus monkey data. We show theoretically and verify by simulation and measurement that GFADS can separate FDG and raclopride measurements that are made nearly simultaneously.
  
  
  RESULTS
  The theoretical development shows that GFADS can decompose the studies at several levels: (1) It decomposes the FDG and raclopride study so that they can be analyzed as though they were obtained separately. (2) If additional physiologic/anatomic constraints can be imposed, further decomposition is possible. (3) For the example of raclopride, specific and nonspecific binding can be determined on a pixel-by-pixel basis. We found good agreement between the estimated GFADS factors and the simulated ground truth time activity curves (TACs), and between the GFADS factor images and the corresponding ground truth activity distributions with errors less than 7.3 ± 1.3 %. Biases in estimation of specific D2 binding and relative metabolism activity were within 5.9 ± 3.6 % compared to the ground truth values. We also evaluated our approach in simultaneous dual-isotope brain PET studies in a rhesus monkey and obtained accuracy of better than 6 % in a mid-striatal volume, for striatal activity estimation.
  
  
  CONCLUSIONS
  Dynamic image sequences acquired following near-simultaneous injection of two PET radiopharmaceuticals can be separated into components based on the differences in the kinetics, provided their kinetic behaviors are distinct.
authors: Center for Advanced Medical Imaging Sciences NMMI, Radiology Department, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA, elfakhri@pet.mgh.harvard.edu.
authors: Georges
authors: G
authors: El Fakhri
authors: Cathryn M
authors: CM
authors: Trott
authors: Arkadiusz
authors: A
authors: Sitek
authors: Ali
authors: A
authors: Bonab
authors: Nathaniel M
authors: NM
authors: Alpert
mesh_terms: D000465:Algorithms; D000818:Animals; D001921:Brain / Q000378:metabolism; D001923:Brain Chemistry; D003198:Computer Simulation; D005163:Factor Analysis, Statistical; D005260:Female; D019788:Fluorodeoxyglucose F18 / Q000737:chemistry / Q000493:pharmacokinetics; D006801:Humans; D008253:Macaca mulatta; D008954:Models, Biological; D059906:Neuroimaging / Q000379:methods*; D049268:Positron-Emission Tomography / Q000379:methods*; D019275:Radiopharmaceuticals / Q000737:chemistry / Q000493:pharmacokinetics*
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18
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