title: Optical imaging of cancer heterogeneity with multispectral optoacoustic tomography.
abstract: OBJECTIVE
  To investigate whether multispectral optoacoustic tomography (MSOT) can reveal the heterogeneous distributions of exogenous agents of interest and vascular characteristics through tumors of several millimeters in diameter in vivo.
  
  
  METHODS
  Procedures involving animals were approved by the government of Upper Bavaria. Imaging of subcutaneous tumors in mice was performed by using an experimental MSOT setup that produces transverse images at 10 frames per second with an in-plane resolution of approximately 150 μm. To study dynamic contrast enhancement, three mice with 4T1 tumors were imaged before and immediately, 20 minutes, 4 hours, and 24 hours after systemic injection of indocyanine green (ICG). Epifluorescence imaging was used for comparison. MSOT of a targeted fluorescent agent (6 hours after injection) and hemoglobin oxygenation was performed simultaneously (4T1 tumors: n = 3). Epifluorescence of cryosections served as validation. The accumulation owing to enhanced permeability and retention in tumors (4T1 tumors: n = 4, HT29 tumors: n = 3, A2780 tumors: n = 2) was evaluated with use of long-circulating gold nanorods (before and immediately, 1 hour, 5 hours, and 24 hours after injection). Dark-field microscopy was used for validation.
  
  
  RESULTS
  Dynamic contrast enhancement with ICG was possible. MSOT, in contrast to epifluorescence imaging, showed a heterogeneous intratumoral agent distribution. Simultaneous imaging of a targeted fluorescent agent and oxy- and deoxyhemoglobin gave functional information about tumor vasculature in addition to the related agent uptake. The accumulation of gold nanorods in tumors seen at MSOT over time also showed heterogeneous uptake.
  
  
  CONCLUSIONS
  MSOT enables live high-spatial-resolution observations through tumors, producing images of distributions of fluorochromes and nanoparticles as well as tumor vasculature.
authors.affiliation: Institute for Biological and Medical Imaging, Technische Universität München and Helmholtz Zentrum München, Neuherberg, Germany.
authors.forename: Eva
authors.initials: E
authors.lastname: Herzog
authors.forename: Adrian
authors.initials: A
authors.lastname: Taruttis
authors.forename: Nicolas
authors.initials: N
authors.lastname: Beziere
authors.forename: Andrey A
authors.initials: AA
authors.lastname: Lutich
authors.forename: Daniel
authors.initials: D
authors.lastname: Razansky
authors.forename: Vasilis
authors.initials: V
authors.lastname: Ntziachristos
mesh_terms: D000230:Adenocarcinoma / Q000175:diagnosis*; D000818:Animals; D003110:Colonic Neoplasms / Q000175:diagnosis*; D003287:Contrast Media / Q000493:pharmacokinetics; D004195:Disease Models, Animal; D005260:Female; D005456:Fluorescent Dyes / Q000493:pharmacokinetics; D006046:Gold / Q000493:pharmacokinetics; D007091:Image Processing, Computer-Assisted; D007208:Indocyanine Green / Q000493:pharmacokinetics; D008325:Mammary Neoplasms, Experimental / Q000175:diagnosis*; D051379:Mice; D053758:Nanoparticles; D013057:Spectrum Analysis / Q000379:methods; D041622:Tomography, Optical / Q000379:methods*
chemical_list: D003287:Contrast Media; D005456:Fluorescent Dyes; D006046:Gold; D007208:Indocyanine Green