title: Comparison of 250 MHz electron spin echo and continuous wave oxygen EPR imaging methods for in vivo applications.
abstract: OBJECTIVE
  The authors compare two electron paramagnetic resonance imaging modalities at 250 MHz to determine advantages and disadvantages of those modalities for in vivo oxygen imaging.
  
  
  METHODS
  Electron spin echo (ESE) and continuous wave (CW) methodologies were used to obtain three-dimensional images of a narrow linewidth, water soluble, nontoxic oxygen-sensitive trityl molecule OX063 in vitro and in vivo. The authors also examined sequential images obtained from the same animal injected intravenously with trityl spin probe to determine temporal stability of methodologies.
  
  
  RESULTS
  A study of phantoms with different oxygen concentrations revealed a threefold advantage of the ESE methodology in terms of reduced imaging time and more precise oxygen resolution for samples with less than 70 torr oxygen partial pressure. Above  100 torr, CW performed better. The images produced by both methodologies showed pO2 distributions with similar mean values. However, ESE images demonstrated superior performance in low pO2 regions while missing voxels in high pO2 regions.
  
  
  CONCLUSIONS
  ESE and CW have different areas of applicability. ESE is superior for hypoxia studies in tumors.
authors.affiliation: Department of Radiation and Cellular Oncology, Center for EPR Imaging In Vivo Physiology, University of Chicago, MC1105, 5841 South Maryland Avenue, Chicago, Illinois 60637, USA. bepel@uchicago.edu
authors.forename: Boris
authors.initials: B
authors.lastname: Epel
authors.forename: Subramanian V
authors.initials: SV
authors.lastname: Sundramoorthy
authors.forename: Eugene D
authors.initials: ED
authors.lastname: Barth
authors.forename: Colin
authors.initials: C
authors.lastname: Mailer
authors.forename: Howard J
authors.initials: HJ
authors.lastname: Halpern
mesh_terms: D000818:Animals; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D004583:Electrons; D005260:Female; D005354:Fibrosarcoma / Q000378:metabolism / Q000473:pathology; D051379:Mice; D057054:Molecular Imaging / Q000379:methods*; D010100:Oxygen / Q000378:metabolism*
chemical_list: D010100:Oxygen