title: Photoacoustic imaging of vascular hemodynamics: validation with blood oxygenation level-dependent MR imaging.
abstract: OBJECTIVE
  To noninvasively assess vascular hemodynamics with photoacoustic imaging (PAI) and blood oxygenation level-dependent (BOLD) magnetic resonance (MR) imaging in phantoms and in an animal model.
  
  
  METHODS
  In vivo studies were performed with institutional animal care and use committee approval. In vitro experiments were performed by using a tissue-mimicking phantom in multiple oxygenation conditions (n = 6) to compare PAI measurements and BOLD MR imaging measurements. PAI and T2-weighted spin-echo-based BOLD MR imaging were performed to assess tumor response to carbogen (95% O2, 5% CO2) in mice with head and neck tumors before (n = 11) and after (n = 9) treatment with a vascular disrupting agent (VDA). Two-tailed Pearson correlation analysis was performed to determine the correlation between the parameters measured with PAI and BOLD MR imaging in vitro. Two-tailed paired t tests were used to compare change in tumor hemoglobin oxygen saturation (sO2) levels and BOLD signal in response to carbogen. Changes in PAI and BOLD signal intensity before and after VDA treatment were analyzed for significance by using analysis of variance with repeated measures.
  
  
  RESULTS
  Phantom measurements yielded good correlation between photoacoustically derived sO2 levels and BOLD signal intensity (r = 0.937, P = .005) and partial pressure of oxygen (r = 0.981, P = .005). In vivo hemodynamic response to carbogen was characterized by a significant increase in tumor sO2 levels (P = .003) and BOLD signal (P = .001). When compared with pretreatment estimates, treatment with VDA resulted in a significant reduction in the tumor hemodynamic response to carbogen at PAI (P = .030).
  
  
  CONCLUSIONS
  Carbogen-based functional imaging with PAI and BOLD MR imaging enables monitoring of early changes in tumor hemodynamics after vascular targeted therapy.
authors.affiliation: From the Departments of Molecular and Cellular Biophysics (L.J.R., M.S.), Pharmacology and Therapeutics (M.S.) and Head and Neck Surgery (M.S.), Roswell Park Cancer Institute, CGP L4-314, Elm and Carlton Streets, Buffalo, NY 14263.
authors.forename: Laurie J
authors.initials: LJ
authors.lastname: Rich
authors.forename: Mukund
authors.initials: M
authors.lastname: Seshadri
mesh_terms: D000818:Animals; D001578:Benzopyrans; D002245:Carbon Dioxide; D002294:Carcinoma, Squamous Cell / Q000098:blood supply*; D003287:Contrast Media; D004195:Disease Models, Animal; D054459:Elasticity Imaging Techniques / Q000379:methods*; D006439:Hemodynamics / Q000502:physiology*; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods*; D051379:Mice; D016513:Mice, SCID; D010100:Oxygen; D019047:Phantoms, Imaging
chemical_list: D001578:Benzopyrans; D003287:Contrast Media; D002245:Carbon Dioxide; C011700:carbogen; C000598757:crolibulin; D010100:Oxygen