title: Retro-orbital injection is an effective route for radiopharmaceutical administration in mice during small-animal PET studies.
abstract: OBJECTIVE
  Small-animal PET is acquiring importance for pre-clinical studies. In rodents, radiotracers are usually administrated via the tail vein. This procedure can be very difficult and time-consuming as soft tissue extravasations are very frequent and tail scars can prevent repeated injections after initial failure. The aim of our study was to compare the retro-orbital (RO) versus tail vein intravenous (i.v.) administration of (18)F-FDG and (11)C-choline in mice for small-animal PET studies.
  
  
  METHODS
  We evaluated four healthy female ICR CD1 mice according to the following protocol. Day 1: each animal underwent an i.v. injection of 28 MBq of (11)C-choline. PET scan was performed after 10 min and 40 min. Day 2: each animal received an RO injection of 28 MBq of (11)C-choline. A PET scan was performed after 10 min and 40 min. Day 3: each animal received an i.v. injection of 28 MBq of (18)F-FDG. A PET scan was performed after 60 min and 120 min. Day 4: each animal received an RO injection of 28 MBq of (18)F-FDG. A PET scan was performed after 60 min and 120 min. Administration and image acquisition were performed under gas anaesthesia. For FDG studies the animals fasted for 2 h and were kept asleep for 20-30 min after injection, to avoid muscular uptake. Images were reconstructed with 2-D OSEM. For each scan ROIs were drawn on liver, kidneys, lung, brain, heart brown fat and muscles, and the SUV was calculated. We finally compared choline i.v. standard acquisition to choline RO standard acquisition; choline i.v. delayed acquisition to choline RO delayed acquisition; FDG i.v. standard acquisition to FDG RO standard acquisition; FDG i.v. delayed acquisition to FDG RO delayed acquisition.
  
  
  RESULTS
  The RO injections for both (18)F-FDG and (11)C-choline were comparable to the intravenous injection of F-FDG for the standard and delayed acquisitions.
  
  
  CONCLUSIONS
  The RO administration in mice represents a technical advantage over intravenous administration in being an easier and faster procedure. However, its use requires high specific activity while its value in peptides and other receptor-specific radiopharmaceuticals needs further assessment.
authors.affiliation: Nuclear Medicine Department, Azienda Ospedaliero-Universitaria di Bologna Policlinico S. Orsola-Malpighi, Italy.
authors.forename: Cristina
authors.initials: C
authors.lastname: Nanni
authors.forename: Cinzia
authors.initials: C
authors.lastname: Pettinato
authors.forename: Valentina
authors.initials: V
authors.lastname: Ambrosini
authors.forename: Antonello
authors.initials: A
authors.lastname: Spinelli
authors.forename: Silvia
authors.initials: S
authors.lastname: Trespidi
authors.forename: Domenico
authors.initials: D
authors.lastname: Rubello
authors.forename: Adil
authors.initials: A
authors.lastname: Al-Nahhas
authors.forename: Roberto
authors.initials: R
authors.lastname: Franchi
authors.forename: Abass
authors.initials: A
authors.lastname: Alavi
authors.forename: Stefano
authors.initials: S
authors.lastname: Fanti
mesh_terms: D000818:Animals; D002250:Carbon Radioisotopes / Q000008:administration & dosage / Q000493:pharmacokinetics; D002794:Choline / Q000008:administration & dosage* / Q000493:pharmacokinetics*; D005260:Female; D019788:Fluorodeoxyglucose F18 / Q000008:administration & dosage* / Q000493:pharmacokinetics*; D007089:Image Enhancement / Q000379:methods; D007275:Injections, Intravenous; D008657:Metabolic Clearance Rate; D051379:Mice; D008813:Mice, Inbred ICR; D009928:Organ Specificity; D049268:Positron-Emission Tomography / Q000379:methods* / Q000662:veterinary*; D019275:Radiopharmaceuticals / Q000008:administration & dosage / Q000493:pharmacokinetics; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014018:Tissue Distribution; D051598:Whole Body Imaging / Q000379:methods / Q000662:veterinary
chemical_list: D002250:Carbon Radioisotopes; D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18; D002794:Choline