title: FDG-PET reproducibility in tumor-bearing mice: comparing a traditional SUV approach with a tumor-to-brain tissue ratio approach.
abstract: BACKGROUND
  Current [F-18]-fluorodeoxyglucose positron emission tomography (FDG-PET) procedures in tumor-bearing mice typically includes fasting, anesthesia, and standardized uptake value (SUV)-based quantification. Such procedures may be inappropriate for prolonged multiscan experiments. We hypothesize that normalization of tumor FDG retention relative to a suitable reference tissue may improve accuracy as this method may be less susceptible to uncontrollable day-to-day changes in blood glucose levels, physical activity, or unnoticed imperfect tail vein injections.
  
  
  METHODS
  Fed non-anesthetized tumor-bearing mice were administered FDG intravenously (i.v.) or intraperitoneally (i.p.) and PET scanned on consecutive days using a Mediso nanoScan PET/magnetic resonance imaging (MRI). Reproducibility of various PET-deduced measures of tumor FDG retention, including normalization to FDG signal in reference organs and a conventional SUV approach, was evaluated.
  
  
  RESULTS
  Day-to-day variability in i.v. injected mice was lower when tumor FDG retention was normalized to brain signal (T/B), compared to normalization to other tissues or when using SUV-based normalization. Assessment of tissue radioactivity in dissected tissues confirmed the validity of PET-derived T/B ratios. Mean T/B and SUV values were similar in i.v. and i.p. administered animals, but SUV normalization was more robust in the i.p. group than in the i.v. group.
  
  
  CONCLUSIONS
  Multimodality scanners allow tissue delineation and normalization of tumor FDG uptake relative to reference tissues. Normalization to brain, but not liver or kidney, improved scan reproducibility considerably and was superior to traditional SUV quantification in i.v. tracer-injected animals. Day-to-day variability in SUV's was lower in i.p. than in i.v. injected animals, and i.p. injections may therefore be a valuable alternative in prolonged rodent studies, where repeated vein injections are undesirable.
authors.affiliation: a Department of Experimental Clinical Oncology , Aarhus University Hospital , Aarhus , Denmark.
authors.forename: Morten
authors.initials: M
authors.lastname: Busk
authors.affiliation: b Department of Nuclear Medicine & PET Center, Aarhus University Hospital , Aarhus , Denmark.
authors.forename: Ole L
authors.initials: OL
authors.lastname: Munk
authors.affiliation: b Department of Nuclear Medicine & PET Center, Aarhus University Hospital , Aarhus , Denmark.
authors.forename: Steen
authors.initials: S
authors.lastname: Jakobsen
authors.affiliation: b Department of Nuclear Medicine & PET Center, Aarhus University Hospital , Aarhus , Denmark.
authors.forename: Jørgen
authors.initials: J
authors.lastname: Frøkiær
authors.affiliation: a Department of Experimental Clinical Oncology , Aarhus University Hospital , Aarhus , Denmark.
authors.forename: Jens
authors.initials: J
authors.lastname: Overgaard
authors.affiliation: a Department of Experimental Clinical Oncology , Aarhus University Hospital , Aarhus , Denmark.
authors.forename: Michael R
authors.initials: MR
authors.lastname: Horsman
mesh_terms: D000818:Animals; D001932:Brain Neoplasms / Q000000981:diagnostic imaging* / Q000378:metabolism / Q000556:secondary; D005260:Female; D019788:Fluorodeoxyglucose F18 / Q000378:metabolism*; D015674:Mammary Neoplasms, Animal / Q000000981:diagnostic imaging* / Q000378:metabolism / Q000473:pathology; D051379:Mice; D049268:Positron-Emission Tomography / Q000379:methods*; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000378:metabolism*
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18