Multispectral Imaging for Hemoglobin Estimation by PCA (original) (raw)
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Molecules, 2019
Background: Hyperspectral Imaging (HSI) has a strong potential to be established as a new contact-free measuring method in medicine. Hyperspectral cameras and data processing have to fulfill requirements concerning practicability and validity to be integrated in clinical routine processes. Methods: Calculating physiological parameters which are of significant clinical value from recorded remission spectra is a complex challenge. We present a data processing method for HSI remission spectra based on a five-layer model of perfused tissue that generates perfusion parameters for every layer and presents them as depth profiles. The modeling of the radiation transport and the solution of the inverse problem are based on familiar approximations, but use partially heuristic methods for efficiency and to fulfill practical clinical requirements. Results: The parameter determination process is consistent, as the measured spectrum is practically completely reproducible by the modeling sequence;...
Imaging, Manipulation, and Analysis of Biomolecules, Cells, and Tissues XV
Hyperspectral imaging (HSI) can estimate the spatial distribution of skin blood oxygenation, using visible to near-infrared light. HSI oximeters often use a liquid-crystal tunable filter, an acousto-optic tunable filter or mechanically adjustable filter wheels, which has too long response/switching times to monitor tissue hemodynamics. This work aims to evaluate a multispectral snapshot imaging system to estimate skin blood volume and oxygen saturation with high temporal and spatial resolution. We use a snapshot imager, the xiSpec camera (MQ022HG-IM-SM4X4-VIS, XIMEA®), having 16 wavelength-specific Fabry-Perot filters overlaid on the custom CMOS-chip. The spectral distribution of the bands is however substantially overlapping, which needs to be taken into account for an accurate analysis. An inverse Monte Carlo analysis is performed using a two-layered skin tissue model, defined by epidermal thickness, haemoglobin concentration and oxygen saturation, melanin concentration and spectrally dependent reduced-scattering coefficient, all parameters relevant for human skin. The analysis takes into account the spectral detector response of the xiSpec camera. At each spatial location in the field-of-view, we compare the simulated output to the detected diffusively backscattered spectra to find the best fit. The imager is evaluated for spatial and temporal variations during arterial and venous occlusion protocols applied to the forearm. Estimated blood volume changes and oxygenation maps at 512x272 pixels show values that are comparable to reference measurements performed in contact with the skin tissue. We conclude that the snapshot xiSpec camera, paired with an inverse Monte Carlo algorithm, permits us to use this sensor for spatial and temporal measurement of varying physiological parameters, such as skin tissue blood volume and oxygenation.
A compact hyperspectral camera for measurement of perfusion parameters in medicine
Biomedical Engineering / Biomedizinische Technik, 2018
Worldwide, chronic wounds are still a major and increasing problem area in medicine with protracted suffering of patients and enormous costs. Beside conventional wound treatment, for instance kinds of oxygen therapy and cold plasma technology have been tested, providing an improvement in the perfusion of wounds and their healing potential, but these methods are unfortunately not sufficiently validated and accepted for clinical practice to date. Using hyperspectral imaging technology in the visible (VIS) and near infrared (NIR) region with high spectral and spatial resolution, perfusion parameters of tissue and wounds can be determined. We present a new compact hyperspectral camera which can be used in clinical practice. From hyperspectral data the hemoglobin oxygenation (StO2), the relative concentration of hemoglobin [tissue hemoglobin index (THI)] and the so-called NIR-perfusion index can be determined. The first two parameters are calculated from the VIS-part of the spectrum and ...
Journal of Biomedical Optics, 2021
Significance: Hemoglobin oxygen saturation and red blood cell (RBC) tissue fraction are important parameters when assessing microvascular status. Functional information can be attained using temporally resolved measurements performed during stimulus-response protocols. Pointwise assessments can currently be conducted with probe-based systems. However, snapshot multispectral imaging (MSI) can be used for spatial-temporal measurements. Aim: To validate if hemoglobin oxygen saturation and RBC tissue fraction can be quantified using a snapshot MSI system and an inverse Monte Carlo algorithm. Approach: Skin tissue measurements from the MSI system were compared to those from a validated probe-based system during arterial and venous occlusion provocation on 24 subjects in the wavelength interval 450 to 650 nm, to evaluate a wide range of hemoglobin oxygen saturation and RBC tissue fraction levels. Results: Arterial occlusion results show a mean linear regression R 2 ¼ 0.958 for hemoglobin oxygen saturation. Comparing relative RBC tissue fraction during venous occlusion results in R 2 ¼ 0.925. The MSI system shows larger dynamic changes than the reference system, which might be explained by a deeper sampling including more capacitance vessels. Conclusions: The snapshot MSI system estimates hemoglobin oxygen saturation and RBC tissue fraction in skin microcirculation showing a high correlation (R 2 > 0.9 in most subjects) with those measured by the reference method.
A Multi-Spectral Image Database for In-Vivo Hand Perfusion Evaluation
IEEE Access
The increasing prevalence of vascular diseases encourages the development of minimally invasive approaches to assess tissue perfusion. A significant challenge facing current state-of-the-art methods is their validation against clinical data. In this study, we introduce an open-source database designed to evaluate tissue perfusion during the application of an occlusion protocol. The database comprises sequences of multi-spectral images (visible and near-infrared region) from the subjects' predominant hand and their photoplethysmography data for validation. Our study recruited 45 healthy participants, including 21 females, with an age range between 18-24 years old (standard deviation equal to 1.73). The database was evaluated using two methods for estimating skin perfusion parameters based on multi-spectral images: a Kubelka-Munk model, and a linear regression. Meanwhile, for validation purposes, the changes in oxygenated and deoxygenated hemoglobin were evaluated by photoplethysmography data as baseline perfusion parameters. The Pearson correlation between plethysmography-based perfusion parameters and those extracted from multi-spectral images was evaluated in all cases as a validation metric. Our findings demonstrated a strong Pearson correlation (ρ > 0.7) between changes in oxygenated and deoxygenated hemoglobin and multispectral based perfusion parameters, suggesting that the database is useful for further research related to in-vivo perfusion assessment. The primary objective of this database is to provide open-source data from a controlled occlusion protocol to evaluate new approaches based on multi-spectral images in the visible and near-infrared regions. In addition, the validation by photoplethysmography data facilitates the development and assessment of innovative tissue perfusion estimation techniques. INDEX TERMS Tissue perfusion monitoring, multi-spectral image processing, functional monitoring and imaging, tissue oxygenation, microcirculation.
2016
This paper briefly reviews the feasibility of using multispectral imaging approach to noninvasively determine one's mean blood oxygen saturation, S m O 2 . We described the use of Extended Modified Lambert Beer (EMLB) model and a nonlinear fitting algorithm to quantitatively analyse the measured spectroscopic data over a wavelength range of 520 − 600 nm to give the best estimation of S m O 2 . The experimental work required spectroscopic images to be collected from the right index finger of four recruited volunteers at resting condition and after a pressure of 140 mmHg is applied on their upper right arm. The obtained results revealed a percent S m O 2 of 77.5 ± 1.06% at resting condition and 54.3 ± 0.42% during blood flow occlusion. These results are also compared to that reported in previous works. The results show that these ranges and the drop in the mean percent S m O 2 obtained for at rest compared to blood flow occlusion condition agreed considerably well with that report...
Reflectance Photoplethysmography as Noninvasive Monitoring of Tissue Blood Perfusion
—In the last decades, photoplethysmography (PPG) has been used as a noninvasive technique for monitoring arterial oxygen saturation by pulse oximetry (PO), whereas near-infrared spec-troscopy (NIRS) has been employed for monitoring tissue blood perfusion. While NIRS offers more parameters to evaluate oxygen delivery and consumption in deep tissues, PO only assesses the state of oxygen delivery. For a broader assessment of blood perfusion, this paper explores the utilization of dual-wavelength PPG by using the pulsatile (ac) and continuous (dc) PPG for the estimation of arterial oxygen saturation (SpO 2) by conventional PO. Additionally, the Beer–Lambert law is applied to the dc components only for the estimation of changes in deoxyhemoglobin (HHb), oxyhemoglobin (HbO 2), and total hemoglobin (tHb) as in NIRS. The system was evaluated on the forearm of 21 healthy volunteers during induction of venous occlusion (VO) and total occlusion (TO). A reflectance PPG probe and NIRS sensor were applied above the brachioradialis, PO sensors were applied on the fingers, and all the signals were acquired simultaneously. While NIRS and forearm SpO 2 indicated VO, SpO 2 from the finger did not exhibit any significant drop from baseline. During TO, all the indexes indicated the change in blood perfusion. HHb, HbO 2 , and tHb changes estimated by PPG presented high correlation with the same parameters obtained by NIRS during VO (r 2 = 0.960, r 2 = 0.821, and r 2 = 0.974, respectively) and during TO (r 2 = 0.988, r 2 = 0.940, and r 2 = 0.938, respectively). The system demonstrated the ability to extract valuable information from PPG signals for a broader assessment of tissue blood perfusion. Index Terms—Beer–Lambert law, near-infrared spec-troscopy (NIRS), optical sensors, photoplethysmography (PPG), physiological monitoring, pulse oximetry (PO).
Analytical Chemistry, 2002
We characterize a visible reflectance hyperspectral imaging system for noninvasive, in vivo, quantitative analysis of human tissue in a clinical environment. The subject area is illuminated with a quartz-tungsten-halogen light source, and the reflected light is spectrally discriminated by a liquid crystal tunable filter (LCTF) and imaged onto a silicon charge-coupled device detector. The LCTF is continuously tunable within its useful visible spectral range (525-725 nm) with an average spectral full width at half-height bandwidth of 0.38 nm and an average transmittance of 10.0%. A standard resolution target placed 5.5 ft from the system results in a field of view with a 17-cm diameter and an optimal spatial resolution of 0.45 mm. The measured reflectance spectra are quantified in terms of apparent absorbance and formatted as a hyperspectral image cube. As a clinical example, we examine a model of vascular dysfunction involving both ischemia and reactive hyperemia during tissue reperfusion. In this model, spectral images, based upon oxyhemoglobin and deoxyhemoblobin signals in the 525-645-nm region, are deconvoluted using a multivariate least-squares regression analysis to visualize the spatial distribution of the percentages of oxyhemoglobin and deoxyhemoglobin in specific skin tissue areas.
Depth-Dependent Hemoglobin Analysis From Multispectral Transillumination Images
IEEE Transactions on Biomedical Engineering, 2010
Multispectral transillumination imaging is a promising modality for noninvasive imaging of living tissue. Multispectral Nevoscope imaging is directed toward the imaging of skin lesions for the detection and characterization of skin cancers through the volumetric analysis of selected chromophores, such as melanin, oxy-, and deoxyhemoglobin. In this letter, we present a novel method of recovering depth-dependent measurements from transillumination images obtained through the Nevoscope. A method for estimating the depth-dependent point spread function is presented and used in recovering multispectral transillumination images of a skin phantom or lesion through blind deconvolution. A method for ratiometric analysis for the quantification of oxyand deoxyhemoglobin is then presented and evaluated on a skin phantom. The presented methods would allow reliable quantitative analysis of multispectral Nevoscope images for early detection of angiogenesis leading to early diagnosis of skin cancers.
Journal of Biomedical Optics, 2022
Significance: Developing algorithms for estimating blood oxygenation from snapshot multispectral imaging (MSI) data is challenging due to the complexity of sensor characteristics and photon transport modeling in tissue. We circumvent this using a method where artificial neural networks (ANNs) are trained on in vivo MSI data with target values from a point-measuring reference method. Aim: To develop and evaluate a methodology where a snapshot filter mosaic camera is utilized for imaging skin hemoglobin oxygen saturation (S O 2), using ANNs. Approach: MSI data were acquired during occlusion provocations. ANNs were trained to estimate S O 2 with MSI data as input, targeting data from a validated probe-based reference system. Performance of ANNs with different properties and training data sets was compared. Results: The method enables spatially resolved estimation of skin tissue S O 2. Results are comparable to those acquired using a Monte-Carlo-based approach when relevant training data are used. Conclusions: Training an ANN on in vivo MSI data covering a wide range of target values acquired during an occlusion protocol enable real-time estimation of S O 2 maps. Data from the probe-based reference system can be used as target despite differences in sampling depth and measurement position.