Spectral fiber-photometry derives hemoglobin-absorption changes for accurate measurement of fluorescent sensors

Fiber-photometry is an emerging technique for recording fluorescent sensor activity in the brain. Here we demonstrate significant hemoglobin-absorption artifacts that may be misinterpreted as sensor activity changes. Because hemoglobin exists in nearly every location in the brain and its concentration varies over time, such artifacts could significantly impede the accuracy of photometry recording results. We present a novel use of spectral photometry technique and propose a computational method to quantify photon absorption effect from an activity-independent fluorescent protein, which can be used to derive oxy- and deoxy-hemoglobin concentration changes and correct target sensor activities across spectra. We further demonstrate the utility of this method for delineating brain regional differences in neurovascular transfer functions and shed light on the interpretation of hemodynamic-based neuroimaging data.

Visible-Near Infrared Spectroscopic Assessment of Urogenital Tissue in Premenopausal and Postmenopausal Women

Background: A clinical study was conducted to evaluate the feasibility of using visible and near-infrared (NIR) spectroscopy as a potential noninvasive measure of genital skin health in premenopausal and postmenopausal women. Methods: A total of 45 female subjects (aged 21-70 years), all of whom gave fully informed consent to participate, were enrolled in the study and assigned to 1 of 3 groups: 15 premenopausal (Pre-M), 15 postmenopausal receiving hormone replacement therapy (Post-M HRT), and 15 postmenopausal receiving no form of hormone replacement therapy (Post-M non-HRT). Spectral measurements were taken at the vaginal mucosa, and spectral data were evaluated for the erythema index (EI), hemoglobin index (HI), bilirubin/β-carotene, and melanin. The color index (CI; calculated as the ratio of absorbance at 480 nm/540 nm) was also determined. Results were compared with previously published results on biomarkers and physical characteristic of genital tissue measured on the same groups of women. Results: Spectral measurements from the Post-M Non-HRT subjects indicated a significant reduction in HI compared with the Pre-M group ( P = .0003) and to the Post-M HRT group ( P < .0001). Similarly, EI was reduced in the Post-M Non-HRT ( P < .0001 and P = .0041 for the Pre-M and Post-M HRT groups, respectively). In contrast, the Post-M Non-HRT subjects exhibited a significant increase in β-carotene compared with the Pre-M subjects ( P = .0098). Bilirubin and melanin were not significantly affected. The Post-M Non-HRT group exhibited a significant increase in CI, indicating a shift away from the hemoglobin absorption region (510-620 nm wavelength) and toward the bilirubin/β-carotene absorption region (450-490 nm wavelength). This change was significant when compared with both the Pre-M group ( P < .0001) and the Post-M HRT group ( P = .0048). The changes in spectral measurements were consistent with previously reported changes in physical parameters (vaginal atrophy, increased pH, decreased skin temperature) and with decreased concentrations of the biomarkers histamine and histidine. Conclusions: Hemodynamic spectral characteristics differ in postmenopausal vaginal tissue compared with tissue in premenopausal women, with decreased absorbance in the hemoglobin absorption region (510-620 nm wavelength) and an increased absorbance in the bilirubin/β-carotene absorption region (450-490 nm wavelength). A change in absorbance in the visible and NIR wavelengths is a promising, additional measure of genital skin health related to menopause and vulvovaginal atrophy.