SignificanceLight emitting diodes (LEDs) are commonly utilized for tissue spectroscopy due to their small size, low cost, and simplicity. However, LEDs are often approximated as single-wavelength devices despite having relatively broad spectral bandwidths. When paired with photodiodes, the wavelength information of detected light cannot be resolved. This can result in errors during chromophore concentration calculations. These errors are particularly apparent when analyzing water and fat in the 900 to 1000 nm window where the spectral bandwidth of LEDs can encompass much of the analysis region, resulting in intense crosstalk.AimWe utilize and present a spectral correction (SC) algorithm to correct for the spectral bandwidth of LEDs. We show the efficacy using a narrowband technique of spectrally broad and overlapping LEDs.ApproachNarrowband diffuse reflectance spectroscopy (nb-DRS), a technique capable of quantifying the hydration ratio (RH2O) of turbid media, was utilized. nb-DRS typically requires a broadband light source and spectrometer. We reduce the hardware to just five LEDs and a photodiode detector, relying on SC to compensate for spectral crosstalk. The effectiveness of our SC approach was tested in simulations as well as in an emulsion phantom and limited selection of human tissue.ResultsIn simulations, we show that calculated RH2O errors increased with the spectral bandwidth of LEDs but could be corrected using SC. Likewise, in emulsions, we found an average error of 8.7% (maximum error 14%) if SC was not used. By contrast, applying SC reduced the average error to 2.2% (maximum error of 6.4%). We show that despite utilizing multiple, spectrally broad, and overlapping LEDs, SC was still able to restore the performance of our narrowband method, making it comparable to a much larger full broadband system.
Refractive errors commonly cause vision impairments; current treatments are temporary and/or involve side-effects. We performed electromechanical reshaping (EMR), a potential laser eye surgery alternative, to determine its effect on reshaping corneal curvature in ex vivo rabbit corneas. Optical coherence tomography (OCT) was performed to ensure corneal curvature change. Second harmonic generation (SHG) was used to determine if collagen damage occurred. After EMR, shape change was visualized with OCT while SHG indicated weaker collagen signals in certain regions. EMR is a potential treatment for refractive errors. However, more experiments are required to determine efficacy and potential for clinical application.
Significance: Diffuse optical spectroscopic imaging (DOSI) is a versatile technology sensitive to changes in tissue composition and hemodynamics and has been used for a wide variety of clinical applications. Specific applications have prompted the development of versions of the DOSI technology to fit specific clinical needs. This work describes the development and characterization of a multi-modal DOSI (MM-DOSI) system that can acquire metabolic, compositional, and pulsatile information at multiple penetration depths in a single hardware platform. Additionally, a 3D tracking system is integrated with MM-DOSI, which enables registration of the acquired data to the physical imaging area.
Aim: We demonstrate imaging, layered compositional analysis, and metabolism tracking capabilities using a single MM-DOSI system on optical phantoms as well as in vivo human tissue.
Approach: We characterize system performance with a silicone phantom containing an embedded object. To demonstrate multi-layer sensitivity, we imaged human calf tissue with a 4.8-mm skin-adipose thickness. Human thenar tissue was also measured using a combined broadband DOSI and continuous-wave near-infrared spectroscopy method (∼15 Hz acquisition rate).
Results: High-resolution optical property maps of absorption (μa) and reduced scattering (μs ′ ) were recovered on the phantom by capturing over 1000 measurement points in under 5 minutes. On human calf tissue, we show two probing depth layers have significantly different (p < 0.001) total-hemo/myoglobin and μs ′ composition. On thenar tissue, we calculate tissue arterial oxygen saturation, venous oxygen saturation, and tissue metabolic rate of oxygen consumption during baseline and after release of an arterial occlusion.
Conclusions: The MM-DOSI can switch between collection of broadband spectra, high-resolution images, or multi-depth hemodynamics without any hardware reconfiguration. We conclude that MM-DOSI enables acquisition of high resolution, multi-modal data consolidated in a single platform, which can provide a more comprehensive understanding of tissue hemodynamics and composition for a wide range of clinical applications.
Cerebral microhemorrhages (CMHs) are associated with cognitive impairment and several conditions, diseases, and normal aging processes. Current histological methods manually identify and quantify Prussian blue-stained CMHs, which can take months to complete. To speed up this labor-intensive process, we developed a spectroscopic, semi-automated approach. We used the ratio of the red and green intensities relative to the blue intensity squared to discriminate CMH-pixels from background pixels. We calculated a sensitivity and specificity of 83.75% and 99.74%, respectively. The intraclass correlation coefficient was 0.992 (95% confidence interval: 0.989-0.995). Future studies are needed to test if this approach works in other CMH models.
Subglottic stenosis (SGS) is a challenging disease to diagnose in neonates. Long-range optical coherence tomography (OCT) is an optical imaging modality that has been described to image the subglottis in intubated neonates. A major challenge associated with OCT imaging is the lack of an automated method for image analysis and micrometry of large volumes of data that are acquired with each airway scan (1 to 2 Gb). We developed a tissue segmentation algorithm that identifies, measures, and conducts image analysis on tissue layers within the mucosa and submucosa and compared these automated tissue measurements with manual tracings. We noted small but statistically significant differences in thickness measurements of the mucosa and submucosa layers in the larynx (p < 0.001), subglottis (p = 0.015), and trachea (p = 0.012). The automated algorithm was also shown to be over 8 times faster than the manual approach. Moderate Pearson correlations were found between different tissue texture parameters and the patient’s gestational age at birth, age in days, duration of intubation, and differences with age (mean age 17 days). Automated OCT data analysis is necessary in the diagnosis and monitoring of SGS, as it can provide vital information about the airway in real time and aid clinicians in making management decisions for intubated neonates.
This paper describes RTBioT, one of the first Internet of Things (IoT) healthcare platforms based on spatially resolved near infrared (NIR) spectroscopy to support non-invasively quantify chromophores in biological tissue. Bluetooth Low Energy (BLE) is used as the primary communication protocol, an IR-enhanced Si PIN photodiode is for a light-receiving element, and a compact fiber-stub type beam combiner is employed as a multiple wavelengths light-emitting source. Most of all, a lock-in amplifier is to retrieve the low noise signal from photodiode which enables accurate measurement of small modulated signals in the presence of noise interference orders of magnitude greater than the signal amplitude by using phase-sensitive detection technique (PSD). The sampling rate of the RTBioT is up to 33Hz, so that it can directly measure mayer wave oscillation, respiration, and cardiac cycle from the raw data. However, it is necessary to approach to the statistical analysis to quantify the concentration of tissue chromophores. First, we determine the optical absorption and scattering properties in the tissue from the locked-in received signal by using the algorithm composed of least square method and diffusion equation. Then, inverse-matrix equation with absorption, reduced scattering and extinction coefficients is solved by the algorithm with respect to chromophores. We conducted an experiment through phantoms simulating human tissue and human subjects to demonstrate its feasibility for the IoT healthcare platform. The experimental results show that it is possible to monitor the biological signals and the concentrations of chromophores in a human subject in near real time fashion.
Many biomedical applications require an efficient combination and localization of multiple discrete light sources. In this paper, we present a compact six-channel combiner of optical sub-assembly type that couples the output of independent solid-state light sources into a single 400 μm diameter optical fiber. It is equipped with six discrete laser diodes, 658, 690, 705, 785, 830, and 850 nm for the measurement of the tissue optical properties from optical spectroscopy and imaging. We demonstrate coupling efficiencies ≥ 77% and output optical power ≥ 20 mW for each of the 6 laser diodes installed into the prototype. The design supports the use of continuous wave and intensity modulated laser diodes (with bandwidth ≥ 3 GHz). The developed light source could be used to construct custom multi-wavelength sources for tissue oximeters, diffuse optical imaging, and molecular imaging technologies.
This paper presents a safe, affordable, and noninvasive approach to estimate subcutaneous fat thickness by using a multi-distance
near infrared (MD-NIR) interactance-based wireless sensing platform. In order to perform the simultaneous
measurements at several distances, two light sources with different wavelengths are located at one end of a line followed
by seven photo diodes. Bluetooth Low Energy are adopted as their primary communication protocol as a wireless
communication. The measured data from the MD-NIR interactance sensors are wirelessly transmitted to a smartphone or
a tablet for analysis. The feasibility of the approach and wireless platform is demonstrated using the ex vivo pig fat layer
phantoms.
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