Significance: Spatial frequency domain imaging (SFDI) is a diffuse optical measurement technique that can quantify tissue optical absorption (μa) and reduced scattering () on a pixel-by-pixel basis. Measurements of μa at different wavelengths enable the extraction of molar concentrations of tissue chromophores over a wide field, providing a noncontact and label-free means to assess tissue viability, oxygenation, microarchitecture, and molecular content. We present here openSFDI: an open-source guide for building a low-cost, small-footprint, three-wavelength SFDI system capable of quantifying μa and as well as oxyhemoglobin and deoxyhemoglobin concentrations in biological tissue. The companion website provides a complete parts list along with detailed instructions for assembling the openSFDI system.
Aim: We describe the design of openSFDI and report on the accuracy and precision of optical property extractions for three different systems fabricated according to the instructions on the openSFDI website.
Approach: Accuracy was assessed by measuring nine tissue-simulating optical phantoms with a physiologically relevant range of μa and with the openSFDI systems and a commercial SFDI device. Precision was assessed by repeatedly measuring the same phantom over 1 h.
Results: The openSFDI systems had an error of 0 ± 6 % in μa and −2 ± 3 % in , compared to a commercial SFDI system. Bland–Altman analysis revealed the limits of agreement between the two systems to be ± 0.004 mm − 1 for μa and −0.06 to 0.1 mm − 1 for . The openSFDI system had low drift with an average standard deviation of 0.0007 mm − 1 and 0.05 mm − 1 in μa and , respectively.
Conclusion: The openSFDI provides a customizable hardware platform for research groups seeking to utilize SFDI for quantitative diffuse optical imaging.
Novel imaging methods permitting real-time, wide-field and quantitative optical mapping of biological tissue properties offer an unprecedented range of potential new applications for clinical use such as guided surgery or patient monitoring. However, significant technical challenges have so far prevented such tools from performing in real-time (for both acquisition and processing) and therefore from being deployed in clinical practice. To overcome these limitations, recent research introduced methods based on Spatial Frequency Domain Imaging (SFDI) that allow real-time (within milliseconds) wide-field imaging of optical properties. In this study we present a novel implementation of general purpose graphic processing unit (GPGPU) direct programming in C CUDA (Compute Unified Device Architecture) for real-time, wide-field and quantitative multispectral imaging using our recently-developed spatio-temporal modulation of light imaging method. Using this new method, we are able to quantitatively obtain optical properties images (1 megapixel) at 2 wavelengths (665 nm and 860 nm) in only 1.52 ms with at most 1% error in comparison with standard Matlab processing.
We have developed a low-cost, wearable, CMOS-based device for the long-term measurement of skin physiological parameters in contact with tissue from spatially resolved diffuse reflectance measurements. The device has been tested for the assessment of the tissue oxygenation in vivo.
We present the effects of using a single-pixel camera approach to extract optical properties with the single-snapshot spatial frequency-domain imaging method. We acquired images of a human hand for spatial frequencies ranging from 0.1 to 0.4 mm − 1 with increasing compression ratios using adaptive basis scan wavelet prediction strategy. In summary, our findings indicate that the extracted optical properties remained usable up to 99% of compression rate at a spatial frequency of 0.2 mm − 1 with errors of 5% in reduced scattering and 10% in absorption.
Imaging methods permitting real-time, wide-field, and quantitative optical mapping of biological tissue properties offer an unprecedented range of applications for clinical use. Following the development of spatial frequency domain imaging, we introduce a real-time demodulation method called single snapshot of optical properties (SSOPs). However, since this method uses only a single image to generate absorption and reduced scattering maps, it was limited by a degraded image quality resulting in artifacts that diminished its potential for clinical use. We present filtering strategies for improving the image quality of optical properties maps obtained using SSOPs. We investigate the effect of anisotropic two-dimensional filtering strategies for spatial frequencies ranging from 0.1 to 0.4 mm − 1 directly onto N = 10 hands. Both accuracy and image quality of the optical properties are quantified in comparison with standard, multiple image acquisitions in the spatial frequency domain. Overall, using optimized filters, mean errors in predicting optical properties using SSOP remain under 8.8% in absorption and 7.5% in reduced scattering, while significantly improving image quality. Overall this work contributes to advance real-time, wide-field, and quantitative diffuse optical imaging toward clinical evaluation.
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.