title: A novel MRI marker for prostate brachytherapy.
abstract: OBJECTIVE
  Magnetic resonance imaging (MRI) is the optimal imaging modality for the prostate and surrounding critical organ structures. However, on MRI, the titanium radioactive seeds used for brachytherapy appear as black holes (negative contrast) and cannot be accurately localized. We sought to develop an encapsulated contrast agent marker (ECAM) with high-signal intensity on MRI to permit accurate localization of radioactive seeds with MRI during and after prostate brachytherapy.
  
  
  METHODS
  We investigated several agents with paramagnetic and superparamagnetic properties. The agents were injected into titanium, acrylic, and glass seeds, which were linked together in various combinations and imaged with MRI. The agent with the greatest T1-weighted signal was tested further in a canine prostate and agarose phantom. Studies were performed on a 1.5-T clinical MRI scanner.
  
  
  RESULTS
  The cobalt-chloride complex contrast (C4) agent with stoichiometry (CoCl(2))(0.8)(C(2)H(5)NO(2))(0.2) had the greatest T1-weighted signal (positive contrast) with a relaxivity ratio >1 (r(2)/r(1) = 1.21 +/- 0.29). Acrylic-titanium and glass-titanium seed strands were clearly visualized with the encapsulated contrast agent marker.
  
  
  CONCLUSIONS
  We have developed a novel ECAM that permits positive identification of the radioactive seeds used for prostate brachytherapy on MRI. Preclinical in vitro phantom studies and in vivo canine studies are needed to further optimize MRI sequencing techniques to facilitate MRI-based dosimetry.
authors.affiliation: Department of Radiation Oncology, University of Texas M.D. Anderson Cancer Center, Houston, TX 77030, USA. sjfrank@mdanderson.org
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Frank
authors.forename: R Jason
authors.initials: RJ
authors.lastname: Stafford
authors.forename: James A
authors.initials: JA
authors.lastname: Bankson
authors.forename: Chun
authors.initials: C
authors.lastname: Li
authors.forename: David A
authors.initials: DA
authors.lastname: Swanson
authors.forename: Rajat J
authors.initials: RJ
authors.lastname: Kudchadker
authors.forename: Karen S
authors.initials: KS
authors.lastname: Martirosyan
mesh_terms: D000179:Acrylates / Q000737:chemistry; D000818:Animals; D001918:Brachytherapy / Q000295:instrumentation*; D003035:Cobalt / Q000737:chemistry; D003287:Contrast Media / Q000737:chemistry*; D004285:Dogs; D005898:Glass / Q000737:chemistry; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008280:Magnetics; D008297:Male; D009566:Nitrates / Q000737:chemistry; D019047:Phantoms, Imaging; D011471:Prostatic Neoplasms / Q000532:radiotherapy*
chemical_list: D000179:Acrylates; D003287:Contrast Media; D009566:Nitrates; D003035:Cobalt; C465446:ethyl nitrate; C018021:cobaltous chloride