title: Alginate moulding: an empirical method for magnetic resonance imaging/positron emission tomography co-registration in a tumor rat model.
abstract: OBJECTIVE
  In the experimental field of animal models, co-registration between positron emission tomography (PET) and magnetic resonance imaging (MRI) data still relies on non-automated post-processing using sophisticated algorithms and software developments. We assessed the value of an empirical method using alginate moulding for PET-MR co-registration in a tumor rat model.
  
  
  METHODS
  Male WAG/RijHsd rats bearing grafted syngenic rhabdomyosarcoma were examined under general anesthesia by MRI using a clinical whole-body 3-T system equipped with a sensitivity-encoding four-channel wrist coil and by a small animal PET system using labelled [(18)F]-fluorocholine as tracer. An alginate mould including a system of external fiducials was manufactured for each animal, allowing strict immobilization and similar positioning for both modalities. Fourteen rats (27 tumors) had only one MR/PET imaging session. Five rats (9 tumors) had a similar MR/PET session before and 3 days after external radiation therapy (13 Gy in one fraction) using the same mould. Co-registration was performed using the Pmod release 2.75 software (PMOD Technologies, Ltd., Adliswil, Switzerland) with mutual information algorithm.
  
  
  RESULTS
  The manufacture of the alginate moulds was easy and innocuous. Imaging sessions were well tolerated. PET-MR co-registration based on mutual information was perfect at visual examination, which was confirmed by the superimposition of external fiducials on fused images. Reuse of the same mould for the post-therapeutic session was feasible 3 days after the pre-therapeutic one in spite of tumor growth.
  
  
  CONCLUSIONS
  The empirical method using alginate moulding with external fiducials for PET-MR co-registration in a rodent tumor model was feasible and accurate.
authors.affiliation: Department of Radiology and Medical Imaging, Universite Catholique de Louvain, Brussels, Belgium. denis.rommel@uclouvain.be
authors.forename: Denis
authors.initials: D
authors.lastname: Rommel
authors.forename: Jorge
authors.initials: J
authors.lastname: Abarca-Quinones
authors.forename: Nicolas
authors.initials: N
authors.lastname: Christian
authors.forename: Frank
authors.initials: F
authors.lastname: Peeters
authors.forename: Max
authors.initials: M
authors.lastname: Lonneux
authors.forename: Daniel
authors.initials: D
authors.lastname: Labar
authors.forename: Anne
authors.initials: A
authors.lastname: Bol
authors.forename: Vincent
authors.initials: V
authors.lastname: Gregoire
authors.forename: Thierry
authors.initials: T
authors.lastname: Duprez
mesh_terms: D000464:Alginates; D000758:Anesthesia; D000818:Animals; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D009374:Neoplasms, Experimental / Q000000981:diagnostic imaging* / Q000473:pathology*; D049268:Positron-Emission Tomography / Q000379:methods*; D051381:Rats; D012149:Restraint, Physical / Q000295:instrumentation*
chemical_list: D000464:Alginates