title: Index matching to improve optical coherence tomography imaging through blood.
abstract: BACKGROUND
  Most myocardial infarctions are caused by the rupture of small rather than large plaques in the arteries of the heart that are beyond the detection limit of current technologies.
  
  
  RESULTS
  Recently, optical coherence tomography (OCT) has demonstrated considerable potential as a method for high-resolution assessment of vulnerable plaque. However, intravascular OCT imaging is complicated by the need to remove blood from the imaging field because blood results in substantial signal attenuation. This work examines index matching as a method for increasing penetration. Index matching is based on the hypothesis that the predominant source of scattering in blood is the difference in refractive index between the cytoplasm of erythrocytes and serum. By increasing the refractive index of serum to a value near that of the cytoplasm, or index matching, scattering can be substantially reduced. The concept was tested with a system that pumped blood in vitro through transparent tubing. The test compounds, dextran and intravenous contrast agent, both led to significant improvements in penetration (69+/-12% and 45+/-4%). No significant effect was seen with the saline control. For dextran, the effect could not be attributed to reductions of red cell number or volume because changes in these parameters were not different from the control. In the case of intravenous contrast, a small but significant relative reduction in red cell volume was seen.
  
  
  CONCLUSIONS
  This study demonstrates the feasibility of index matching for improving OCT imaging through blood. Future studies are required to identify compounds for effective index matching in vivo.
authors: Department of Orthopedics, Harvard Medical School, Brigham and Women's Hospital, Boston, Massachusetts, USA. mebrezin@mit.edu
authors: M
authors: M
authors: Brezinski
authors: K
authors: K
authors: Saunders
authors: C
authors: C
authors: Jesser
authors: X
authors: X
authors: Li
authors: J
authors: J
authors: Fujimoto
mesh_terms: D001769:Blood / Q000187:drug effects; D001783:Blood Flow Velocity; D001790:Blood Physiological Phenomena; D003287:Contrast Media; D003327:Coronary Disease / Q000175:diagnosis; D003911:Dextrans; D004906:Erythrocyte Count; D004911:Erythrocyte Volume / Q000187:drug effects; D005240:Feasibility Studies; D006461:Hemolysis; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007485:Ioxaglic Acid; D008955:Models, Cardiovascular; D055095:Optics and Photonics; D019047:Phantoms, Imaging; D010953:Plasma Volume; D012031:Refractometry; D012542:Scattering, Radiation; D014054:Tomography / Q000379:methods*
chemical_list: D003287:Contrast Media; D003911:Dextrans; D007485:Ioxaglic Acid