Feature Of The Week 10/18/09: Three-dimensional combined photoacoustic and optical coherence microscopy for in vivo microcirculation studies
Feature Of The Week 10/18/09: Researchers from the Optical Imaging Laboratory at Washington University in St. Louis, led by Dr. Lihong Wang, have been very active developing techniques that combine photoacoustic microscopy and optical coherence tomography. Combining sound and light imaging can provide several benefits including images at greater depths with complementary contrasts. Recently researcher Li Li et al published work on "Three-dimensional combined photoacoustic and optical coherence microscopy for in vivo microcirculation studies".
Microcirculation is vital to sustain human health, and disturbed microcirculation is involved in most if not all diseases, such as hypertension, diabetes, cancer, sepsis, etc. Existing microscopic imaging techniques suffer from several limitations in terms of microcirculation studies. Intravital microscopy and orthogonal polarization spectral imaging lack depth resolution, and thus are unable to provide three-dimensional morphology of microvasculature and exact estimation of blood flow. Confocal and multiphoton microscopy, although they can image tissue in three dimensions, generally require invasive introduction of exogenous fluorescence contrast agents, which not only raises concerns of toxicity, but also limits the frequency of longitudinal studies. This paper proposed that a novel multimodal microscopy combining photoacoustic microscopy (PAM) and optical coherence tomography (OCT) can overcome these problems and can potentially facilitate microcirculation research.
PAM and OCT are naturally complementary to each other. PAM is predominantly sensitive to optical absorption, while OCT exploits optical backscattering. Integrating their different contrasts can provide comprehensive information about biological tissue. The first dual-modality microscope following this strategy for studying microcirculation was developed. Three-dimensional imaging of microvasculature and its local environment has been demonstrated at micrometer-order resolution using only endogenous contrast in vivo. Currently efforts are being made to integrate the demonstrated functional imaging capabilities of both PAM and OCT into the system to provide quantitative estimation of local hematocrit, oxygenation and blood flow. More importantly, with all these efforts, it is expected that a combined photoacoustic and optical coherence microscope can provide previously unavailable functional indicators, such as the local oxygen metabolic rate, which may serve as a potential biomarker for diseases.
By modifying how the system accesses the target tissue, optimizing choice of parameters of PAM and OCT systems, and improving imaging speed, it is anticipated that such a tool can impact both laboratorial investigations in small animal models (e.g. tumor microcirculation, brain function) and clinical practice (e.g. diagnosis of dermatological and ophthalmological diseases, intraoperative monitoring of microcirculatory functions).