Feature Of The Week 4/24/11: In vivo 3D imaging of intra-cochlear microstructures and microvascular perfusion in mice with ultra-high sensitive optical micro-angiography (UHS-OMAG)
Researchers from the Biophotonics and Imaging Laboratory (BAIL) at Oregon Health & Science University (OHSU) have recently pioneered a novel ultra-high sensitive volumetric perfusion imaging modality based on optical micro-angiography (OMAG), which is a spectral-domain functional optical coherence tomographic imaging modality capable of imaging blood perfusion with very high flow sensitivity of 4microns/sec down to capillary level resolution. The imaging contrast of blood perfusion in OMAG is based on endogenous light scattering from moving blood cells; thus, no exogenous contrast agents are necessary for imaging. In traditional OMAG imaging, in order to separate the moving scatters from static one, a constant modulation frequency was introduced into the spectral interferogram along the B-scan direction. This modulation frequency can be introduced either by using a moving reference arm mirror mounted onto a linear piezo-translational stage or by offsetting the scanning probe beam on the x-scanning mirror in the sample, and by using sophisticated spatial filtering based on Hilbert transform along the B-frame direction OMAG can provide high resolution perfusion map. However, in traditional OMAG, the minimal blood flow imaging of the system was limited to 300 μm/s, which is empirically determined by this modulation frequency of the reference arm and as well as the optical heterogeneous properties of the cochlea tissue.
In order to improve the flow sensitivity of OMAG, the researchers at OHSU introduced a novel scanning protocol and image processing algorithm into their OMAG imaging method. The new method acquires low density B-scan frame (i.e. x-direction scan) with 128 A-lines with a spacing of ~11.5μm (which is of the order of the least sampling distance of 10 μm for the system lateral resolution of 16 μm) between adjacent A-lines, which covers a total x-scan range of ~1.5mm. For obtaining slow the microcirculation within capillary vessels, the new algorithm uses the high pass filtering along the C-scan direction, rather than in the B-scan direction in the traditional OMAG, in order to remove the DC signal and the static signals due to the microstructures of the sample. In collaboration with Oregon Hearing Research Centre at OHSU, the researchers demonstrated the feasibility of their new imaging modality for in-vivo imaging of both microvascular structures and microvascular perfusion in mice model.
For more information see references below. Courtesy Hrebesh Subhash.
Hrebesh M. Subhash, Viviana Davila, Hai Sun, Anh T. Nguyen-Huynh, Alfred L. Nuttall, Ruikang K. Wang, "Volumetric in vivo imaging of microvascular perfusion within the intact cochlea in mice using ultra-high sensitive optical microangiography", IEEE Trans Med Imaging.,30(2), 224 - 230 (2011).
Hrebesh M. Subhash, Viviana Davila, Hai Sun, Anh T. Nguyen-Huynh, Alfred L. Nuttall, Ruikang K. Wang, "Volumetric in vivo imaging of intracochlear microstructures in mice by high-speed spectral domain optical coherence tomography", J. Biomed. Opt., Vol. 15, 036024 (2010).