Real-time, wide-field, and quantitative oxygenation imaging using spatiotemporal modulation of light

Abstract

Quantitative diffuse optical imaging has the potential to provide valuable functional information about tissue status, such as oxygen saturation or blood content to healthcare practitioners in real time. However, significant technical challenges have so far prevented such tools from being deployed in the clinic. Toward achieving this goal, prior research introduced methods based on spatial frequency domain imaging (SFDI) that allow real-time (within milliseconds) wide-field imaging of optical properties but at a single wavelength. However, for this technology to be useful to clinicians, images must be displayed in terms of metrics related to the physiological state of the tissue, hence interpretable to guide decision-making. For this purpose, recent developments introduced multispectral SFDI methods for rapid imaging of oxygenation parameters up to 16 frames per seconds (fps). We introduce real-time, wide-field, and quantitative blood parameters imaging using spatiotemporal modulation of light. Using this method, we are able to quantitatively obtain optical properties at 100 fps at two wavelengths (665 and 860 nm), and therefore oxygenation, oxyhemoglobin, and deoxyhemoglobin, using a single camera with, at most, 4.2% error in comparison with standard SFDI acquisitions.

Spatial frequency domain imaging in 2019: principles, applications, and perspectives

“…44 For instance, for a 572 × 672 pixels dataset, processing time could be improved from 2.5 s down to 18 ms. 44 As processing time has been reduced through the optimization of both data acquisition and processing at a single wavelength, more recent developments have focused on multiplexing the acquisition of multiple wavelengths by modulating the illumination both in time and space. 87,88 In this method depicted in Fig. 9, time is used to encode wavelengths and space to extract optical properties, both in the frequency domain.…”

“…The resulting images are first demodulated in time using a discrete Fourier transform to separate the different wavelength contributions, and then processed in space to extract the optical properties. 88,89 Other approaches have focused on multiplexed data collection on the detector side by introducing advanced camera hardware to simultaneously capture spectral content. 90…”

“…The resulting images are first processed in the temporal domain to separate wavelengths contributions and then in space to extract optical properties at these wavelengths. 88 severity and showed that SFDI was one of the most sensitive and specific techniques for burn diagnosis. There has been some pilot clinical work reported in the literature but the potential for SFDI as an adjunct method to measure burn depth and guide patient management is promising due to rapid widefield assessment and SFDI specific signatures in an area where the error margin is still quite large.…”

“…Simply combining SFDI-derived optical properties with other modalities such fluorescence, laser speckle imaging, multiphoton imaging, multispectral imaging, and Cerenkov can enhance the quantitative nature of each modality. 75,84,88,132 Finally, SFDI applications extend to wherever turbidity is an issue-including nonmedical applications. As an example, multiple groups are using SFDI to characterize produce and identify subsurface bruising in apples and pears as a quality control tool.…”

Special Section Guest Editorial: Special Section on Spatial Frequency Domain Imaging

“…5 A second category of articles focus on modeling in the spatial frequency domain (SFD), including assessment of optical sampling depth in the SFD, 6 development of analytical models for separation of surface and volumetric scattering, 7 implantation of machine learning methodology to rapidly extract optical properties, 8 and derivation of a deterministic radiative transport solver. 9 A third category of articles focus on new instrumentation advances to enable concurrent temporal and spatial modulation of light for rapid oxygenation imaging, 10 improvement of image quality via a single snapshot of optical properties, 11 and the potential of a single pixel camera in combination with SFDI, 12 and a hyperspectral SFDI acquisition system. 13 Finally, there is a group of articles to enhance clinical applications, including characterization of resected cancerous breast tissue, 14 guidance of intra-operative tumor resection, 15 and correction of light attenuation for improved Cherenkov imaging, 16 and monitoring of burn wound and skin graft healing.…”