August 2013
Spotlight Summary by Robert J. Zawadzki
Compartment-resolved imaging of cortical functional hyperemia with OCT angiography
Over the last decade OCT has become the leading technology for measuring in-vivo volumetric morphology of many biological tissues at micrometer resolution, with special focus on investigating neural tissues of the eye and brain. Despite many efforts, the application of OCT for direct measurements of tissue function by use of spectral information (absorption or fluorescence) remains very limited due to difficulties caused by OCT relying only on detection of elastically scattered photons. Therefore, quantifying changes in tissue scattering and correlating them with known tissue function is of great importance for establishing OCT as viable imaging tool in medicine and biology.
In their latest paper, Radhakrishnan and Srinivasan make a big step towards advancing OCT technology in this direction by showcasing the application of OCT angiography, one of the variations of OCT-based data acquisition and analysis methods, to study functional hyperemia in the rat somatosensory cortex in response to neuronal activation. In this work, the hemodynamic response to functional activation is extracted from OCT angiography data sets by analyzing the dynamic backscattering signal as an indicator of dynamic red blood cell (dRBC) content. The authors were able to show that arterial dRBC content increases along with prominent dilation, whereas venous dRBC content increases with slight dilation. They also confirmed that “all or none” capillary recruitment plays a negligible role in the hemodynamic response of the capillary bed. All the presented methods enable a more detailed and comprehensive characterization of the neurovascular relationship across compartments than was previously possible.
In summary, the three-dimensional microscopic movies of hemodynamic response to neural activation, presented here for the first time, are of great importance as they demonstrate that optical scattering signals, rather than absorption changes, can be reliably used to investigate in-vivo cortical activation. I also agree with the authors in that this work represents a novel and complementary approach compared to conventional optical intrinsic signal imaging, with the added benefit of measuring pure hemodynamic response without possible confounds from oximetric changes.
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In their latest paper, Radhakrishnan and Srinivasan make a big step towards advancing OCT technology in this direction by showcasing the application of OCT angiography, one of the variations of OCT-based data acquisition and analysis methods, to study functional hyperemia in the rat somatosensory cortex in response to neuronal activation. In this work, the hemodynamic response to functional activation is extracted from OCT angiography data sets by analyzing the dynamic backscattering signal as an indicator of dynamic red blood cell (dRBC) content. The authors were able to show that arterial dRBC content increases along with prominent dilation, whereas venous dRBC content increases with slight dilation. They also confirmed that “all or none” capillary recruitment plays a negligible role in the hemodynamic response of the capillary bed. All the presented methods enable a more detailed and comprehensive characterization of the neurovascular relationship across compartments than was previously possible.
In summary, the three-dimensional microscopic movies of hemodynamic response to neural activation, presented here for the first time, are of great importance as they demonstrate that optical scattering signals, rather than absorption changes, can be reliably used to investigate in-vivo cortical activation. I also agree with the authors in that this work represents a novel and complementary approach compared to conventional optical intrinsic signal imaging, with the added benefit of measuring pure hemodynamic response without possible confounds from oximetric changes.
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Article Information
Compartment-resolved imaging of cortical functional hyperemia with OCT angiography
Harsha Radhakrishnan and Vivek J. Srinivasan
Biomed. Opt. Express 4(8) 1255-1268 (2013) View: Abstract | HTML | PDF