In vivo volumetric blood flow imaging using optical microangiography at capillary level resolution

Optical micro-angiography (OMAG) [1,2,3] is a recently developed imaging method, capable of resolving 3D distribution of dynamic blood perfusion at the capillary level within microcirculatory beds in vivo. The imaging contrast of blood perfusion is based on the endogenous light scattering from the moving blood cells within biological tissue; thus no exogenous contrasting agents are necessary. This is achieved by efficient separation of the moving scattering elements from the static scattering ones within tissue through the OMAG hardware associated with mathematical analysis of the optical scattering signals from an illuminated sample. Its development has its origin in the Fourier domain optical coherence tomography (FDOCT) [4]. The original development of OMAG was performed by introducing a constant frequency modulation ƒM into the time-varying spectral interferograms at the time when the probing beam is scanned over the sample. The introduction of ƒM in the interferograms was achieved by linear translation of the reference mirror in the interferometer, synchronized with the OCT cross-sectional (B scan) imaging. This makes it possible to separate the light scattering signals backscattered from the moving particles, such as moving blood cells, from those backscattered from the static particles, such as bulk tissue, leading to high resolution mapping of dynamic blood perfusion down to capillary levels within thick tissue sample in vivo. In essence, the OMAG method maps the scattering signals from the moving particles into one image, i.e. flow image, and from the static particles into a second image, i.e. microstructural image.