KEYWORDS: Artificial neural networks, Data modeling, Skin, RGB color model, Education and training, Hyperspectral imaging, Tissues, Nervous system, Performance modeling, In vivo imaging
SignificanceMachine learning models for the direct extraction of tissue parameters from hyperspectral images have been extensively researched recently, as they represent a faster alternative to the well-known iterative methods such as inverse Monte Carlo and inverse adding-doubling (IAD).AimWe aim to develop a Bayesian neural network model for robust prediction of physiological parameters from hyperspectral images.ApproachWe propose a two-component system for extracting physiological parameters from hyperspectral images. First, our system models the relationship between the measured spectra and the tissue parameters as a distribution rather than a point estimate and is thus able to generate multiple possible solutions. Second, the proposed tissue parameters are then refined using the neural network that approximates the biological tissue model.ResultsThe proposed model was tested on simulated and in vivo data. It outperformed current models with an overall mean absolute error of 0.0141 and can be used as a faster alternative to the IAD algorithm.ConclusionsResults suggest that Bayesian neural networks coupled with the approximation of a biological tissue model can be used to reliably and accurately extract tissue properties from hyperspectral images on the fly.
SignificanceHyperspectral imaging (HSI) of murine tumor models grown in dorsal skinfold window chambers (DSWCs) offers invaluable insight into the tumor microenvironment. However, light loss in a glass coverslip is often overlooked, and particular tissue characteristics are improperly modeled, leading to errors in tissue properties extracted from hyperspectral images.AimWe highlight the significance of spectral renormalization in HSI of DSWC models and demonstrate the benefit of incorporating enhanced green fluorescent protein (EGFP) excitation and emission in the skin tissue model for tumors expressing genes to produce EGFP.ApproachWe employed an HSI system for intravital imaging of mice with 4T1 mammary carcinoma in a DSWC over 14 days. We performed spectral renormalization of hyperspectral images based on the measured reflectance spectra of glass coverslips and utilized an inverse adding–doubling (IAD) algorithm with a two-layer murine skin model, to extract tissue parameters, such as total hemoglobin concentration and tissue oxygenation (StO2). The model was upgraded to consider EGFP fluorescence excitation and emission. Moreover, we conducted additional experiments involving tissue phantoms, human forearm skin imaging, and numerical simulations.ResultsHyperspectral image renormalization and the addition of EGFP fluorescence in the murine skin model reduced the mean absolute percentage errors (MAPEs) of fitted and measured spectra by up to 10% in tissue phantoms, 0.55% to 1.5% in the human forearm experiment and numerical simulations, and up to 0.7% in 4T1 tumors. Similarly, the MAPEs for tissue parameters extracted by IAD were reduced by up to 3% in human forearms and numerical simulations. For some parameters, statistically significant differences (p<0.05) were observed in 4T1 tumors. Ultimately, we have shown that fluorescence emission could be helpful for 4T1 tumor segmentation.ConclusionsThe results contribute to improving intravital monitoring of DWSC models using HSI and pave the way for more accurate and precise quantitative imaging.
Hyperspectral imaging (HSI) is a powerful tool for noninvasive assessment of skin properties, as it can capture the spectral signatures of different skin layers and components. However, HSI also requires efficient and accurate methods for estimating skin parameters, such as the thickness, scattering, and absorption coefficients of each skin layer, from the measured spectra. In recent years, much research has been done regarding the use of machine learning (ML) methods for reducing the time and computational cost required for estimating parameters, compared to classical methods, such as the inverse Monte Carlo (IMC) or the inverse adding-doubling (IAD) algorithm. In this study, we investigated the impact of using random Fourier features (RFF) with a simple linear regression model, as well as with an artificial neural network (ANN), to estimate parameter values directly from the spectra. We compared the proposed models with the ANN and a 1D convolutional neural network (CNN), both trained using the raw spectra as input. All models were trained on simulated data and evaluated on both simulated and in vivo measured spectra using mean absolute error (MAE). We found that even simple linear regression with RFFs performs comparably to the neural networks trained on raw spectra while having much lower training and inference time. The best results were attained with the RFF-based ANN, having an overall MAE of 0.0226, which is an improvement compared to the 1D-CNN, having an MAE of 0.0284.
Hyperspectral imaging is a method that uses UV-NIR light to capture the physiological and morphological properties of biological tissues. A promising use case of HSI is the study and diagnosis of various types of tumors by extracting tissue parameters. This study examines various tissue indices as an alternative to tissue parameters extracted using the inverse adding-doubling (IAD) algorithm. Tissue indices were compared to tissue parameters extracted using IAD from simulated spectra, mice models, and healthy human forearms. Preliminary results indicate a positive linear correlation between melanin concentration and melanin indices, as well as total hemoglobin and hemoglobin indices. Tissue indices are promising for real-time tissue property extraction from hyperspectral images. They can potentially be used as a fast and accurate tool to aid in the diagnosis of tumors.
Tumor vasculature plays an essential role in tumor growth and is a potential target for cancer treatment. Monitoring the vasculature during tumor growth, disease progression, and after treatment (e.g., radiotherapy and gene electrotransfer (GET)) could provide valuable diagnostic information and improve knowledge of tumors and their microenvironment. Moreover, it could provide predictive information for tumor treatment and improve therapeutic outcomes. This study combined hyperspectral imaging (HSI) with laser speckle contrast imaging (LSCI) to monitor 4T1 murine mammary carcinomas grown subcutaneously in dorsal skinfold window chambers (DSWCs) over 14 days. Specifically, we utilized a custom-built HSI system with a spectral range of 400–1000 nm and an LSCI system with a 650 nm laser. Using LSCI, we monitored the blood flow in blood vessels and tissue perfusion, while HSI enabled us to detect tumor margins and track oxygenation changes during tumor growth and after electroporation-based therapy. Our findings indicate an immediate >70% reduction in blood flow within tumor vessels after the GET procedure, which could be attributed to vasoconstriction induced by the electrical pulses. Additionally, the overall tumor perfusion decreased by at least 30% post-treatment and gradually increased in the following days. In contrast, a control tumor that received no treatment exhibited a substantial increase in blood flow, possibly linked to an elevated need for oxygen and nutrients due to tumor progression. Our study demonstrates that the combined HSI and LSCI optical imaging techniques effectively monitor blood flow, tumor perfusion, and oxygenation alterations within tumor vessels following electroporation-based therapy.
Non-invasively monitoring tumors during their growth and disease progression could provide invaluable diagnostic information and improve our understanding of tumors and their microenvironment, especially blood vessels. Hyperspectral imaging (HSI) with integrated three-dimensional optical profilometry (3D OP) provides the necessary tools for non-invasive and contactless disease diagnosis by utilizing intrinsic tissue contrast of incoming visible and near-infrared light. Therefore, information about tissue, morphology, and pathology could be extracted from the images. In this study, we monitored six female BALB/c mice with a subcutaneously grown CT26 murine colon carcinoma over a period of 14 days, starting on the day of tumor cells injection. Blood vessels in the tumor and its surrounding healthy tissue were segmented from hyperspectral images, and physiological properties such as blood volume fraction and tissue oxygenation were extracted using the inverse adding-doubling (IAD) algorithm. The results indicate that oxygenation in blood vessels within the CT26 tumors and surrounding tissue peaks eight days after tumor cell injection at 35 %, a two-fold increase from the beginning of the study, and then gradually decreases to around 25 % 14 days after injection.
A two-layer GPU-accelerated inverse adding-doubling algorithm was applied to hyperspectral images of a forearm to extract skin optical properties before, during, and after a cuff-test. Calculated and measured skin reflectance show great agreement.
Significance: Hyperspectral imaging (HSI) has emerged as a promising optical technique. Besides optical properties of a sample, other sample physical properties also affect the recorded images. They are significantly affected by the sample curvature and sample surface to camera distance. A correction method to reduce the artifacts is necessary to reliably extract sample properties.
Aim: Our aim is to correct hyperspectral images using the three-dimensional (3D) surface data and assess how the correction affects the extracted sample properties.
Approach: We propose the combination of HSI and 3D profilometry to correct the images using the Lambert cosine law. The feasibility of the correction method is presented first on hemispherical tissue phantoms and next on human hands before, during, and after the vascular occlusion test (VOT).
Results: Seven different phantoms with known optical properties were created and imaged with a hyperspectral system. The correction method worked up to 60 deg inclination angle, whereas for uncorrected images the maximum angles were 20 deg. Imaging hands before, during, and after VOT shows good agreement between the expected and extracted skin physiological parameters.
Conclusions: The correction method was successfully applied on the images of tissue phantoms of known optical properties and geometry and VOT. The proposed method could be applied to any reflectance optical imaging technique and should be used whenever the sample parameters need to be extracted from a curved surface sample.
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