High-speed spatial frequency domain imaging of rat cortex detects dynamic optical and physiological properties following cardiac arrest and resuscitation

Abstract

Quantifying rapidly varying perturbations in cerebral tissue absorption and scattering can potentially help to characterize changes in brain function caused by ischemic trauma. We have developed a platform for rapid intrinsic signal brain optical imaging using macroscopically structured light. The device performs fast, multispectral, spatial frequency domain imaging (SFDI), detecting backscattered light from three-phase binary square-wave projected patterns, which have a much higher refresh rate than sinusoidal patterns used in conventional SFDI. Although not as fast as "single-snapshot" spatial frequency methods that do not require three-phase projection, square-wave patterns allow accurate image demodulation in applications such as small animal imaging where the limited field of view does not allow single-phase demodulation. By using 655, 730, and 850 nm light-emitting diodes, two spatial frequencies ([Formula: see text] and [Formula: see text]), three spatial phases (120 deg, 240 deg, and 360 deg), and an overall camera acquisition rate of 167 Hz, we map changes in tissue absorption and reduced scattering parameters ([Formula: see text] and [Formula: see text]) and oxy- and deoxyhemoglobin concentration at [Formula: see text]. We apply this method to a rat model of cardiac arrest (CA) and cardiopulmonary resuscitation (CPR) to quantify hemodynamics and scattering on temporal scales ([Formula: see text]) ranging from tens of milliseconds to minutes. We observe rapid concurrent spatiotemporal changes in tissue oxygenation and scattering during CA and following CPR, even when the cerebral electrical signal is absent. We conclude that square-wave SFDI provides an effective technical strategy for assessing cortical optical and physiological properties by balancing competing performance demands for fast signal acquisition, small fields of view, and quantitative information content.

Characterisation of impaired wound healing in a preclinical model of induced diabetes using wide‐field imaging and conventional immunohistochemistry assays

“…SFDI provides quantitative two‐dimensional mapping of subsurface tissue chromophore concentrations, including HbO 2 and Hb. Based on these values, it calculates the StO 2 values . More details on SFDI instrumentation can be found in the literature .…”

“…Based on these values, it calculates the StO 2 values. 28,30,[38][39][40] More details on SFDI instrumentation can be found in the literature. 31,41,42 Briefly, a 250 W quartztungsten lamp (Newport Oriel, Stratford, Connecticut) coupled to a digital micromirror device (DMD) (Texas Instruments, Dallas, Texas) projects a series of sinusoidal intensity patterns onto a 90 × 66 mm field of view.…”

High-speed quantitative optical imaging of absolute metabolism in the rat cortex

“…Ten male Wistar rats (weight ~300-400 g) were imaged for this study, and the animal preparation procedures are described in our previous publications [7,8,13,14]. Before the experiment, all rats were endotracheally intubated under isoflurane anesthesia.…”

“…For SFDI, light-emitting diodes (LEDs) of three different wavelengths (655 nm, 730 nm, 850 nm) were used as light sources. The light from the LEDs was directed to a spatial light modulator that projected square-wave patterns onto the brain [8]. Backscattered light was captured using a scientific complementary metal-oxide semiconductor (sCMOS) camera (Hamamatsu Photonics).…”

“…Recently, we demonstrated that the combination of Spatial Frequency Domain Imaging (SFDI) and Laser Speckle Imaging (LSI)) can quantify tissue metabolic changes with high spatial and temporal resolution [6]. We also recently applied high-speed LSI [7] and SFDI [8] to measure perfusion, oxygenation, and tissue scattering in the brain in a cardiac arrest (CA) model of global cerebral ischemia. The capability of our rapid multimodal SFDI+LSI system to image blood flow and hemoglobin concentration simultaneously enables high-speed measurement of CMRO 2 [9].…”