Hyperspectral optical tomography of intrinsic signals in the rat cortex

Abstract

Abstract. We introduce a tomographic approach for three-dimensional imaging of evoked hemodynamic activity, using broadband illumination and diffuse optical tomography (DOT) image reconstruction. Changes in diffuse reflectance in the rat somatosensory cortex due to stimulation of a single whisker were imaged at a frame rate of 5 Hz using a hyperspectral image mapping spectrometer. In each frame, images in 38 wavelength bands from 484 to 652 nm were acquired simultaneously. For data analysis, we developed a hyperspectral DOT algorithm that used the Rytov approximation to quantify changes in tissue concentration of oxyhemoglobin (ctHbO 2 ) and deoxyhemoglobin (ctHb) in three dimensions. Using this algorithm, the maximum changes in ctHbO 2 and ctHb were found to occur at 0.29 AE 0.02 and 0.66 AE 0.04 mm beneath the surface of the cortex, respectively. Rytov tomographic reconstructions revealed maximal spatially localized increases and decreases in ctHbO 2 and ctHb of 321 AE 53 and 555 AE 96 nM, respectively, with these maximum changes occurring at 4 AE 0.2 s poststimulus. The localized optical signals from the Rytov approximation were greater than those from modified Beer-Lambert, likely due in part to the inability of planar reflectance to account for partial volume effects.

Structured illumination diffuse optical tomography for noninvasive functional neuroimaging in mice

“…25,26 As a function of depth, the SI-DOT images show an increase in HbO 2 and decrease in HbR corresponding to somatosensory layers 2 to 4. This depth-dependent hemodynamic activity is reasonably consistent with observations from invasive thinned-skull preparations in rats using multispectral imaging, 27 laminar optical tomography, 28 and noninvasive functional MRI studies in mice. The penetration depth and resolution of SI-DOT can be estimated from the system's sensitivity matrix.…”

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

“…SFDI also has the unique ability to provide the additional depth section capability for tomographic localization of hemodynamic signals during functional activation imaging. 117,125 Lin et al [126][127][128] have also done work to characterize SFDI optical signatures in degenerative diseases like Alzheimer's and characterized baseline properties while measuring vascular impairment due to neuronal death and amyloid-beta plaques. Due to continuous noninvasive imaging capability, treatments and disease can be tracked much more efficiently in preclinical research.…”

Optical methods for quantitative and label-free sensing in living human tissues: principles, techniques, and applications

“…This extra variable is often wavelength [15], time [16], or spatial (or temporal) frequency [17] of the incident light. Acquiring surface images of the tissue at different wavelengths can provide depth-sectioning capabilities because the tissue absorption and scattering properties are heavily wavelength-dependent, so the mean penetration depth of the photons can vary significantly with wavelength [15]. Time-gating of the detected photons also serves as a means to separate the photons that travelled different total path lengths (and thus, sampled different depths) within the tissue before returning to the surface [16].…”