Patent Publication Number: US-2023162361-A1

Title: Assessment of skin toxicity in an in vitro tissue samples using deep learning

Description:
PRIORITY 
     This application is a continuation of International Application No. PCT/US2021/043623, filed on Jul. 29, 2021, which claims the benefit, under 35 U.S.C. § 119(e), of U.S. Provisional Pat. Application No. 63/059486, filed 31 Jul. 2020, which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present disclosure relates to a system and methods using machine-learning algorithms, such as deep learning, to evaluate tissue sample(s) comprising multiple layers. 
     INTRODUCTION 
     The skin consists of two main layers: the epidermis, a thin stratified epithelium primarily composed of keratinocytes, and the dermis, a thick layer derived from mesenchymal cells. Any disruption of cell cycle or differentiation of the keratinocyte results in a disturbed skin barrier leading to changes in epidermal thickness and compromised function. The epidermal growth factor receptor (EGFR) regulates multiple functions in the keratinocyte including proliferation, adhesion and migration, survival, and differentiation. EGFR mutants are therefore frequently associated with several cancers including breast, lung, ovarian, cervical, bladder, esophageal, brain, head, and neck cancers. Therapies that target mutant EGFR display on-target effects in the skin with evidence of rash, making skin toxicity a leading cause of dose reduction, or treatment termination, and poor prognosis in patients undergoing cancer therapy, should the severity of rash be life-threatening. Similarly, maculopapular rash and/or acneiform eruptions of variable severity have been observed in patients treated with drugs targeting the mitogen-activated protein kinase (MAPK) and the phosphoinositide 3-kinase (PI3K) pathways, and closely mirror the cutaneous toxicity profile described for EGFR-targeting compounds in its onset, course and treatment. Skin toxicity is a common safety concern associated with drugs that inhibit epidermal growth factor receptors as well as other targets involved in epidermal growth and differentiation. Severe skin toxicity may lead to outcomes such as warning language added to a drug label, dose reduction or termination, or poor prognosis of EGFR-targeted cancer therapy. Recently, the use of a 3D reconstructed human epidermis model enabled large-scale drug screening and demonstrated potential for predicting skin toxicity. 
     To combat the shortcomings of manually collected data, machine learning models designed to recognize and classify data are now used across disciplines from cancer detection and monitoring to drug development and safety assessment and across tissue sample types. However, traditional machine learning algorithms cannot be trained on raw data but instead require time-intensive training on input datasets with well-defined data features. These features must be iteratively refined to improve the predictive capabilities of the model. Deep learning models based on neural networks have been developed to overcome limitations such as these. Deep learning takes advantage of large datasets and general-purpose, non-linear learning algorithms to train multiple hidden, processing layers that are responsible for identifying different data features. The model itself defines these features based on the input data. 
     Deep learning models can also be used in image analysis, segmentation, and classification provided sufficiently large training sets of images are available with corresponding annotated, pixel level data. Deep learning has been applied to many areas of medical imaging and drug toxicology. Other deep learning methods take advantage of toxicity-induced structural alterations in cells or tissues. This method has been used in vitro to assess toxicity based on changes in fluorescently stained cell nuclei and to identify drug-induced structural changes in cardiomyocytes and hepatocytes that are too subtle for standard image analysis. Deep learning-based image analysis has also been applied to in vivo rodent models for ovarian toxicity as well as drug-induced retinal atrophy and cardiomyopathy. Furthermore, a deep learning model was developed to predict radiation-induced toxicity in patients undergoing treatment for cancers of the hepatobiliary system. Finally, deep-learning methods have been suggested as a means for identifying neurotoxicity using the robust segmentation framework that has already been developed for brain imaging. 
     SUMMARY OF PARTICULAR EMBODIMENTS 
     Herein is provided a system and methods which relate to the evaluation of tissue samples comprising multiple layers, including, but not limited to the determination of skin toxicity of reconstituted human epidermis samples. 
     With respect to human epidermis samples, although a decrease in epidermal thickness has been observed when 3-D reconstructed tissues are exposed to drugs causing skin toxicity, the thickness evaluation of epidermal layers from a pathologist is subjective and not easily reproducible nor scalable. In addition, the subtle thickness differences among tissues as well as the large number of samples to test can make cross-study comparison difficult when a manual evaluation strategy is employed. The embodiments disclosed herein use deep learning and image processing algorithms to assess and measure the thickness of particular layers of tissue samples and determine particular conditions or effects indicated by the samples. For example, in particular embodiments, deep learning and image processing algorithms can be used to measure the viable epidermal thickness from multiple studies. Empirical studies demonstrated that the thickness measured using techniques described herein was not only significantly correlated with a pathologist’s semi-quantitative evaluation but in close agreement with the quantitative measurement performed by pathologists. Moreover, a sensitivity of 0.8 and specificity of 0.75 was achieved when predicting the toxicity of 18 compounds with clinical observations using the epidermal thickness measuring approaches of the embodiments disclosed herein. The approach in the embodiments disclosed herein may be fully-automated, reproducible, transferrable and highly scalable, which not only demonstrates reasonable accuracy in predicting skin toxicity but enables cross-study comparison, high-throughput compound screening, and expansion to additional types of tissue samples. 
     In particular embodiments, a digital pathology image processing system may receive a querying image associated with a tissue sample after a treatment by a drug compound. The digital pathology image processing system may then identify, based on a machine-learning model trained to identify layers of tissue samples, a target layer of the tissue sample. The digital pathology image processing system may further calculate a normalized thickness of the identified target layer. In particular embodiments, the digital pathology image processing system may determine a toxicity indication of the treatment by the drug compound based on the normalized thickness of the identified target layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    illustrates a network of interacting computer systems that can be used, as described herein according to some embodiments of the present disclosure. 
         FIG.  2    illustrates an example method for determining skin toxicity of reconstituted human epidermis samples. 
         FIG.  3 A  illustrates an example reconstructed human epidermis (RHE) model. 
         FIG.  3 B  illustrates an example image of a RHE sample. 
         FIG.  3 C  illustrates example measurement locations for measurement of a tissue sample segment. 
         FIG.  4 A  illustrates example RHE samples for training a machine-learning model. 
         FIG.  4 B  illustrates an example annotation of an RHE sample with an example tile. 
         FIG.  5 A  illustrates an example annotation of an RHE sample with tissue sections. 
         FIG.  5 B  illustrates an example extraction of thickness of a tissue sample. 
         FIG.  5 C  illustrates an example normalization of the tissue thickness. 
         FIG.  6    illustrates an example workflow of the design of a retrospective study. 
         FIG.  7    illustrates example representative images from a pathologist measuring the viable epidermal thickness using an image viewer. 
         FIG.  8    illustrates example segmentations of viable epidermal area by the machine-learning model. 
         FIGS.  9 A- 9 D  illustrate example boxplots between normalized epidermal thickness measured based on the machine-learning model and normalized scores from a pathologist. 
         FIGS.  10 A- 10 D  illustrate example comparisons between viable epidermal thickness measured using the machine-learning model and measured by a pathologist. 
         FIG.  11 A  illustrates example normalized viable epidermal thickness from various compounds under different concentrations. 
         FIG.  11 B  illustrates an example impact of the in vitro test concentration on the epidermal thickness for compounds showing skin toxicity and those that do not. 
         FIG.  12    illustrates an example segmentation of a tissue sample. 
         FIGS.  13 A- 13 C  illustrate example tissue segmentations. 
         FIGS.  14 A- 14 B  illustrates example measured tissue segment thickness. 
         FIG.  15    illustrates an example of a computing system. 
     
    
    
     DESCRIPTION 
       FIG.  1    illustrates a network  100  of interacting computer systems that can be used, as described herein according to some embodiments of the present disclosure. 
     A digital pathology image generation system  120  can generate one or more whole slide images or other related digital pathology images, corresponding to a particular sample. For example, an image generated by digital pathology image generation system  120  can include a stained section of a biopsy sample. As another example, an image generated by digital pathology image generation system  120  can include a slide image (e.g., a blood film) of a liquid sample. As another example, an image generated by digital pathology image generation system  120  can include fluorescence microscopy such as a slide image depicting fluorescence in situ hybridization (FISH) after a fluorescent probe has been bound to a target DNA or RNA sequence. 
     Some types of samples (e.g., biopsies, solid samples and/or samples including tissue) can be processed by a sample preparation system  121  to fix and/or embed the sample. Sample preparation system  121  can facilitate infiltrating the sample with a fixating agent (e.g., liquid fixing agent, such as a formaldehyde solution) and/or embedding substance (e.g., a histological wax). For example, a sample fixation sub-system can fix a sample by exposing the sample to a fixating agent for at least a threshold amount of time (e.g., at least 3 hours, at least 6 hours, or at least 13 hours). A dehydration sub-system can dehydrate the sample (e.g., by exposing the fixed sample and/or a portion of the fixed sample to one or more ethanol solutions) and potentially clear the dehydrated sample using a clearing intermediate agent (e.g., that includes ethanol and a histological wax). A sample embedding sub-system can infiltrate the sample (e.g., one or more times for corresponding predefined time periods) with a heated (e.g., and thus liquid) histological wax. The histological wax can include a paraffin wax and potentially one or more resins (e.g., styrene or polyethylene). The sample and wax can then be cooled, and the wax-infiltrated sample can then be blocked out. 
     A sample slicer  122  can receive the fixed and embedded sample and can produce a set of sections. Sample slicer  122  can expose the fixed and embedded sample to cool or cold temperatures. Sample slicer  122  can then cut the chilled sample (or a trimmed version thereof) to produce a set of sections. Each section can have a thickness that is (for example) less than 100 µm, less than 50 µm, less than 10 µm or less than 5 µm. Each section can have a thickness that is (for example) greater than 0.1 µm,greater than 1 µm,greater than 2 µm or greater than 4 µm. The cutting of the chilled sample can be performed in a warm water bath (e.g., at a temperature of at least 30° C., at least 35° C. or at least 40° C.). 
     An automated staining system  123  can facilitate staining one or more of the sample sections by exposing each section to one or more staining agents. Each section can be exposed to a predefined volume of staining agent for a predefined period of time. In some instances, a single section is concurrently or sequentially exposed to multiple staining agents. 
     Each of one or more stained sections can be presented to an image scanner  124 , which can capture a digital image of the section. Image scanner  124  can include a microscope camera. The image scanner  124  can capture the digital image at multiple levels of magnification (e.g., using a 10x objective, 20x objective, 40x objective, etc.). Manipulation of the image can be used to capture a selected portion of the sample at the desired range of magnifications. Image scanner  124  can further capture annotations and/or morphometrics identified by a human operator. In some instances, a section is returned to automated staining system  123  after one or more images are captured, such that the section can be washed, exposed to one or more other stains, and imaged again. When multiple stains are used, the stains can be selected to have different color profiles, such that a first region of an image corresponding to a first section portion that absorbed a large amount of a first stain can be distinguished from a second region of the image (or a different image) corresponding to a second section portion that absorbed a large amount of a second stain. 
     It will be appreciated that one or more components of digital pathology image generation system  120  can, in some instances, operate in connection with human operators. For example, human operators can move the sample across various sub-systems (e.g., of sample preparation system  121  or of digital pathology image generation system  120 ) and/or initiate or terminate operation of one or more sub-systems, systems, or components of digital pathology image generation system  120 . As another example, part or all of one or more components of digital pathology image generation system (e.g., one or more subsystems of the sample preparation system  121 ) can be partly or entirely replaced with actions of a human operator. 
     Further, it will be appreciated that, while various described and depicted functions and components of digital pathology image generation system  120  pertain to processing of a solid and/or biopsy sample, other embodiments can relate to a liquid sample (e.g., a blood sample). For example, digital pathology image generation system  120  can receive a liquid-sample (e.g., blood or urine) slide, that includes a base slide, smeared liquid sample and cover. Image scanner  124  can then capture an image of the sample slide. Further embodiments of the digital pathology image generation system  120  can relate to capturing images of samples using advancing imaging techniques, such as FISH, described herein. For example, once a florescent probe has been introduced to a sample and allowed to bind to a target sequence appropriate imaging can be used to capture images of the sample for further analysis. 
     A given sample can be associated with one or more users (e.g., one or more physicians, laboratory technicians and/or medical providers) during processing and imaging. An associated user can include, by way of example and not of limitation, a person who ordered a test or biopsy that produced a sample being imaged, a person with permission to receive results of a test or biopsy, or a person who conducted analysis of the test or biopsy sample, among others. For example, a user can correspond to a physician, a pathologist, a clinician, or a subject. A user can use one or one user devices  130  to submit one or more requests (e.g., that identify a subject) that a sample be processed by digital pathology image generation system  120  and that a resulting image be processed by a digital pathology image processing system  110 . 
     Digital pathology image generation system  120  can transmit an image produced by image scanner  124  back to user device  130 . User device  130  then communicates with the digital pathology image processing system  110  to initiate automated processing of the image. In some instances, digital pathology image generation system  120  provides an image produced by image scanner  124  to the digital pathology image processing system  110  directly, e.g. at the direction of the user of a user device  130 . Although not illustrated, other intermediary devices (e.g., data stores of a server connected to the digital pathology image generation system  120  or digital pathology image processing system  110 ) can also be used. Additionally, for the sake of simplicity only one digital pathology image processing system  110 , image generating system  120 , and user device  130  is illustrated in the network  100 . This disclosure anticipates the use of one or more of each type of system and component thereof without necessarily deviating from the teachings of this disclosure. 
     The network  100  and associated systems shown in  FIG.  1    can be used in a variety of contexts where scanning and evaluation of digital pathology images, such as whole slide images, are an essential component of the work. As an example, the network  100  can be associated with a clinical environment, where a user is evaluating the sample for possible diagnostic purposes. The user can review the image using the user device  130  prior to providing the image to the digital pathology image processing system  110 . The user can provide additional information to the digital pathology image processing system  110  that can be used to guide or direct the analysis of the image by the digital pathology image processing system  110 . For example, the user can provide a prospective diagnosis or preliminary assessment of features within the scan. The user can also provide additional context, such as the type of tissue being reviewed. As another example, the network  100  can be associated with a laboratory environment were tissues are being examined, for example, to determine the efficacy or potential side effects of a drug. In this context, it can be commonplace for multiple types of tissues to be submitted for review to determine the effects on the whole body of said drug. This can present a particular challenge to human scan reviewers, who may need to determine the various contexts of the images, which can be highly dependent on the type of tissue being imaged. These contexts can optionally be provided to the digital pathology image processing system  110 . 
     Digital pathology image processing system  110  can process digital pathology images, including whole slide images, to classify the digital pathology images and generate annotations for the digital pathology images and related output. As an example, the digital pathology image processing system  110  can process whole slide images of tissue samples or tiles of the whole slide images of tissue samples generated by the digital pathology image processing system  110 , to identify layers of each tissue sample, compute thickness of each layer, and provide a toxicity assessment based on the computed thickness. The digital pathology image processing system  110  may use sliding windows to generate a mask over the layers. Besides for identifying the tissue sections, the mask may be also used for measuring thickness, determining areas of the layer, determining lengths for different endpoints, and determining curviness for tortuosity, and measuring volume in a three-dimensional scenario. The digital pathology image processing system  110  may then crop the querying image into a plurality of image tiles. A tile generating module  111  can define a set of tiles for each digital pathology image. To define the set of tiles, the tile generating module  111  can segment the digital pathology image into the set of tiles. As embodied herein, the tiles can be non-overlapping (e.g., each tile includes pixels of the image not included in any other tile) or overlapping (e.g., each tile includes some portion of pixels of the image that are included in at least one other tile). Features such as whether or not tiles overlap, in addition to the size of each tile and the stride of the window (e.g., the image distance or pixels between a tile and a subsequent tile) can increase or decrease the data set for analysis, with more tiles (e.g., through overlapping or smaller tiles) increasing the potential resolution of eventual output and visualizations. In some instances, tile generating module  111  defines a set of tiles for an image where each tile is of a predefined size and/or an offset between tiles is predefined. Continuing with the example of tissue samples, for each tissue section, the identified tissue area may be cropped into image tiles with width and height of certain number of pixels. Furthermore, the tile generating module  111  can create multiple sets of tiles of varying size, overlap, step size, etc., for each image. As an example, the width and height of pixels may be dynamically determined (i.e., not fixed) based on factors such as the evaluation task, the querying image itself, or any suitable factor. In some embodiments, the digital pathology image itself can contain tile overlap, which may result from the imaging technique. Even segmentation without tile overlapping can be a preferable solution to balance tile processing requirements and avoid influencing the embedding generation and weighting value generation discussed herein. A tile size or tile offset can be determined, for example, by calculating one or more performance metrics (e.g., precision, recall, accuracy, and/or error) for each size/offset and by selecting a tile size and/or offset associated with one or more performance metrics above a predetermined threshold and/or associated with one or more performance metric(s) (e.g., high precision, high recall, high accuracy, and/or low error). 
     The tile generating module  111  may further define a tile size depending on the type of abnormality being detected. For example, the tile generating module  111  can be configured with awareness of the type(s) of tissue abnormalities that the digital pathology image processing system  110  will be searching for and can customize the tile size according to the tissue abnormalities to improve detection. For example, the image generating module  111  can determine that, when the tissue abnormalities include searching for inflammation or necrosis in lung tissue, the tile size should be reduced to increase the scanning rate, while when the tissue abnormalities include abnormalities with Kupffer cells in liver tissues, the tile size should be increased to increase the opportunities for the digital pathology image processing system  110  to analyze the Kupffer cells holistically. In some instances, tile generating module  111  defines a set of tiles where a number of tiles in the set, size of the tiles of the set, resolution of the tiles for the set, or other related properties, for each image is defined and held constant for each of one or more images. 
     As embodied herein, the tile generating module  111  can further define the set of tiles for each digital pathology image along one or more color channels or color combinations. As an example, digital pathology images received by digital pathology image processing system  110  can include large-format multi-color channel images having pixel color values for each pixel of the image specified for one of several color channels. Example color specifications or color spaces that can be used include the RGB, CMYK, HSL, HSV, or HSB color specifications. The set of tiles can be defined based on segmenting the color channels and/or generating a brightness map or greyscale equivalent of each tile. For example, for each segment of an image, the tile generating module  111  can provide a red tile, blue tile, green tile, and/or brightness tile, or the equivalent for the color specification used. As explained herein, segmenting the digital pathology images based on segments of the image and/or color values of the segments can improve the accuracy and recognition rates of the networks used to generating embeddings for the tiles and image and to produce classifications of the image. Additionally, the digital pathology image processing system  110 , e.g., using tile generating module  111 , can convert between color specifications and/or prepare copies of the tiles using multiple color specifications. Color specification conversions can be selected based on a desired type of image augmentation (e.g., accentuating or boosting particular color channels, saturation levels, brightness levels, etc.). Color specification conversions can also be selected to improve compatibility between digital pathology image generation systems  120  and the digital pathology image processing system  110 . For example, a particular image scanning component can provide output in the HSL color specification and the models used in the digital pathology image processing system  110 , as described herein, can be trained using RGB images. Converting the tiles to the compatible color specification can ensure the tiles can still be analyzed. Additionally, the digital pathology image processing system can up-sample or down-sample images that are provided in particular color depth (e.g., 8-bit, 1-bit, etc.) to be usable by the digital pathology image processing system. Furthermore, the digital pathology image processing system  110  can cause tiles to be converted according to the type of image that has been captured (e.g., fluorescent images may include greater detail on color intensity or a wider range of colors). 
     As described herein, a tile embedding module  112  can generate an embedding for each tile in a corresponding feature embedding space. The embedding can be represented by the digital pathology image processing system  110  as a feature vector for the tile. The tile embedding module  112  can use a neural network (e.g., a convolutional neural network) to generate a feature vector that represents each tile of the image. In particular embodiments, the tile embedding neural network can be based on the ResNet image network trained on a dataset based on natural (e.g., non-medical) images, such as the ImageNet dataset. By using a non-specialized tile embedding network, the tile embedding module  112  can leverage known advances in efficiently processing images to generating embeddings. Furthermore, using a natural image dataset allows the embedding neural network to learn to discern differences between tile segments on a holistic level. 
     In other embodiments, the tile embedding network used by the tile embedding module  112  can be an embedding network customized to handle large numbers of tiles of large format images, such as digital pathology whole slide images. Additionally, the tile embedding network used by the tile embedding module  112  can be trained using a custom dataset. For example, the tile embedding network can be trained using a variety of samples of whole slide images or even trained using samples relevant to the subject matter for which the embedding network will be generating embeddings (e.g., scans of particular tissue types). Training the tile embedding network using specialized or customized sets of images can allow the tile embedding network to identify finer differences between tiles which can result in more detailed and accurate distances between tiles in the feature embedding space at the cost of additional time to acquire the images and the computational and economic cost of training multiple tile generating networks for use by the tile embedding module  112 . The tile embedding module  112  can select from a library of tile embedding networks based on the type of images being processed by the digital pathology image processing system  110 . 
     As described herein, tile embeddings can be generated from a deep learning neural network using visual features of the tiles. Tile embeddings can be further generated from contextual information associated with the tiles or from the content shown in the tile. For example, a tile embedding can include one or more features that indicate and/or correspond to a size of depicted objects (e.g., sizes of depicted cells or aberrations) and/or density of depicted objects (e.g., a density of depicted cells or aberrations). Size and density can be measured absolutely (e.g., width expressed in pixels or converted from pixels to nanometers) or relative to other tiles from the same digital pathology image, from a class of digital pathology images (e.g., produced using similar techniques or by a single digital pathology image generation system or scanner), or from a related family of digital pathology images. Furthermore, tiles can be classified prior to the tile embedding module  112  generating embeddings for the tiles such that the tile embedding module  112  considers the classification when preparing the embeddings. 
     For consistency, the tile embedding module  112  produces embeddings of a predefined size (e.g., vectors of 512 elements, vectors of 2048 bytes, etc.). The tile embedding module  112  can produce embeddings of various and arbitrary sizes. The tile embedding module  112  can adjust the sizes of the embeddings based on user direction or can be selected, for example, based on computation efficiency, accuracy, or other parameters. In particular embodiments, the embedding size can be based on the limitations or specifications of the deep learning neural network that generated the embeddings. Larger embedding sizes can be used to increase the amount of information captured in the embedding and improve the quality and accuracy of results, while smaller embedding sizes can be used to improve computational efficiency. 
     The digital pathology image processing system  110  can perform different inferences by apply one or more machine-learning models to the embeddings, i.e., inputting the embeddings to a machine-learning model. As an example, the digital pathology image processing system  110  can identify, based on a machine-learning model trained to identify layers of skin tissue samples, an epidermal layer of a skin tissue sample. In addition, the keratin and epidermal area may be segmented. In some embodiments, it may be not necessary to crop the image into image tiles, generate embeddings for these tiles, and then perform inferences based on such embeddings. Instead, the digital pathology image processing system  110  can directly apply the machine-learning model to the embedding of a whole slide image to make inference with sufficient GPU memory. The output of the machine-learning model may be resized into the shape of the input image. 
     A whole slide image access module  113  can manage requests to access whole slide images from other modules of the digital pathology image processing system  110  and the user device  130 . For example, the whole slide image access module  113  receive requests to identify a whole slide image based on a particular tile, an identifier for the tile, or an identifier for the whole slide image. The whole slide image access module  113  can perform tasks of confirming that the whole slide image is available to the user requesting, identifying the appropriate databases from which to retrieve the requested whole slide image, and retrieving any additional metadata that may be of interest to the requesting user or module. Additionally, the whole slide image access module  113  can handle efficiently streaming the appropriate data to the requesting device. As described herein, whole slide images may be provided to user devices in chunks, based on the likelihood that a user will wish to see the portion of the whole slide image. The whole slide image access module  113  can determine which regions of the whole slide image to provide and determine how to provide them. Furthermore, the whole slide image access module  113  can be empowered within the digital pathology image processing system  110  to ensure that no individual component locks up or otherwise misuses a database or whole slide image to the detriment of other components or users. 
     An output generating module  114  of the digital pathology image processing system  110  can generate output corresponding to result tile and result whole slide image datasets based on user request. As described herein, the output can include a variety of visualizations, interactive graphics, and reports based upon the type of request and the type of data that is available. In many embodiments, the output will be provided to the user device  130  for display, but in certain embodiments the output can be accessed directly from the digital pathology image processing system  110 . The output will be based on existence of and access to the appropriate data, so the output generating module will be empowered to access necessarily metadata and anonymized patient information as needed. As with the other modules of the digital pathology image processing system  110 , the output generating module  114  can be updated and improved in a modular fashion, so that new output features can be provided to users without requiring significant downtime. 
     The general techniques described herein can be integrated into a variety of tools and use cases. For example, as described, a user (e.g., pathology or clinician) can access a user device  130  that is in communication with the digital pathology image processing system  110  and provide a query image for analysis. The digital pathology image processing system  110 , or the connection to the digital pathology image processing system can be provided as a standalone software tool or package that searches for corresponding matches, identifies similar features, and generates appropriate output for the user upon request. As a standalone tool or plug-in that can be purchased or licensed on a streamlined basis, the tool can be used to augment the capabilities of a research or clinical lab. Additionally, the tool can be integrated into the services made available to the customer of digital pathology image generation systems. For example, the tool can be provided as a unified workflow, where a user who conducts or requests a whole slide image to be created automatically receives an report of noteworthy features within the image and/or similar whole slide images that have been previously indexed. Therefore, in addition to improving whole slide image analysis, the techniques can be integrated into existing systems to provide additional features not previously considered or possible. 
     Moreover, the digital pathology image processing system  110  can be trained and customized for use in particular settings. For example, the digital pathology image processing system  110  can be specifically trained for use in providing insights relating to specific types of tissue (e.g., lung, heart, blood, liver, etc.). As another example, the digital pathology image processing system  110  can be trained to assist with safety assessment, for example in determining levels or degrees of toxicity associated with drugs or other potential therapeutic treatments. Once trained for use in a specific subject matter or use case, the digital pathology image processing system  110  is not necessarily limited to that use case. Training may be performed in a particular context, e.g., toxicity assessment, due to a relatively larger set of at least partially labeled or annotated images. 
       FIG.  2    illustrates an example method  200  for determining skin toxicity of tissue samples. The method may begin at step  210 , where a digital pathology image processing system  110  may receive a querying image associated with a tissue sample after a treatment by a drug compound. As an example, in the context of evaluating skin tissue, the tissue sample may comprise a reconstructed human epidermis (RHE) sample such as RHE sample  310  illustrated in  FIG.  3 B . At step  220 , the digital pathology image processing system  110  may identify, based on a machine-learning model trained to identify layers of tissue samples, a target layer of the tissue sample. As an example, for the reconstructed human epidermis (RHE) sample  310 , the identified target layer may comprise an epidermal layer  312 . The digital pathology image processing system  110  may first perform image processing. For every RHE sample, both the two RHE tissue sections (i.e., keratin layer and viable epidermal layer) may be identified. Bounding boxes may be used to identify the tissue sections. In addition, the digital pathology image processing system  110  may use sliding windows to generate a mask over the layers. The digital pathology image processing system  110  may then crop the querying image into a plurality of image tiles using the tile generation module  111 . The digital pathology image processing system  110  may then perform model inference by applying a machine-learning model to the cropped image tiles. The output of the machine-learning model may be resized into the shape of the input image, i.e., resizing an output of the machine-learning model into a shape of the querying image. As a result, RHE tissue areas may be inferred by the machine-learning model and the keratin and epidermal area may be segmented. 
     At step  230 , the digital pathology image processing system  110  may calculate a normalized thickness of the identified target layer. In particular embodiments, the digital pathology image processing system  110  may measure the thickness at several locations of the identified target layer, up to and including every location. The digital pathology image processing system  110  may quantify the thickness at several locations, up to and including everything location. The digital pathology image processing system  110  may then provide the thickness endpoints to pathologists. In particular embodiments, the digital pathology image processing system  110  may operate in different ways to complete the measurement. As an example and not by way of limitation, the measurement by the digital pathology image processing system  110  may be fully automated and end-to-end. As another example and not by way of limitation, the measurement by the digital pathology image processing system  110  may be human-guided (e.g., a human may using the digital pathology image processing system  110  to select the locations to measure or draw the approximate measurements). As an example and not by way of limitation, the measurement by the digital pathology image processing system  110  may be human-assisting (e.g., the digital pathology image processing system may suggest measurements to pathologists). 
     At step  240 , the digital pathology image processing system  110  may determine a toxicity indication of the treatment by the drug compound based on the normalized thickness of the identified target layer. In particular embodiments, the toxicity indication may indicate whether there is toxicity, i.e., adverse effect from the treatment by the drug compound. As an example and not by way of limitation, the toxicity indication may be a binary result, e.g., 0 indicating there is no toxicity and 1 indicating there is toxicity. As another example and not by way of limitation, the toxicity indication may be a score indicating the probability of toxicity, e.g., 0.75 indicating higher probability of toxicity than 0.2. As yet another example and not by way of limitation, the toxicity indication may be a degree of toxicity, e.g., 5 indicating a more severe toxicity than 1. In particular embodiments, determining the toxicity indication based on the normalized thickness of the identified target layer may be based on comparing the normalized thickness with a threshold value. For example, the normalized thickness being smaller than the threshold value may reveal a decrease in the thickness of the target layer, which may further indicate there is toxicity. As another example, the normalized thickness being the same as or larger than the threshold value may indicate there is no toxicity. Determining the toxicity indication based on the normalized thickness of the identified target layer may be also based on comparing the normalized thickness with the thickness of the target layer before the treatment by the drug compound. For example, the normalized thickness being smaller than the thickness of the target layer before the treatment by the drug compound may indicate there is toxicity. As another example, the normalized thickness being the same as or larger than the thickness of the target layer before the treatment by the drug compound may indicate there is no toxicity. Determining the toxicity indication based on the normalized thickness of the identified target layer may be also based on a percentage calculated by dividing the normalized thickness by the thickness of the target layer before the treatment by the drug compound. For example, the percentage being smaller than 10% may indicate very severe toxicity; the percentage being between 10% and 50% may indicate severe toxicity; the percentage being between 50% and 80% may indicate mild toxicity; and the percentage being larger than 90% may indicate rare or no toxicity. Determining the toxicity indication based on the normalized thickness of the identified target layer may be also based on another machine-learning model. For example, the normalized thickness may be input to this machine-learning model trained to output toxicity indication based on the input of normalized thickness. Particular embodiments may repeat one or more steps of the method of  FIG.  2   , where appropriate. Although this disclosure describes and illustrates particular steps of the method of  FIG.  2    as occurring in a particular order, this disclosure contemplates any suitable steps of the method of  FIG.  2    occurring in any suitable order. Moreover, although this disclosure describes and illustrates an example method for determining skin toxicity of tissue samples, including the particular steps of the method of  FIG.  2   , this disclosure contemplates any suitable method for determining skin toxicity of tissue samples, including any suitable steps, which may include all, some, or none of the steps of the method of  FIG.  2   , where appropriate. Furthermore, although this disclosure describes and illustrates particular components, devices, or systems carrying out particular steps of the method of  FIG.  2   , this disclosure contemplates any suitable combination of any suitable components, devices, or systems carrying out any suitable steps of the method of  FIG.  2   . 
     A decrease in epidermal thickness of the skin may be a toxicity indication for skin toxicities as well as for cutaneous disease. For example, one can calculate a percentage by dividing the epidermal thickness of the skin after the treatment by a drug compound by the epidermal thickness before the treatment. If the percentage is smaller than 10%, it may indicate very severe toxicity; if the percentage is between 10% and 50%, it may indicate severe toxicity; if the percentage is between 50% and 80%, it may indicate mild toxicity; and if the percentage is larger than 90%, it may indicate rare or no toxicity. There are few preclinical methods for evaluating in vivo skin toxicity prior to clinical trial. The last two decades have seen the advent of in vitro human skin models, which have a proven record of accurately predicting clinical skin toxicity.  FIG.  3 A  illustrates an example reconstructed human epidermis (RHE) model  300 . These reconstituted human epidermal (RHE) models  300  may be metabolically and mitotically active 3D models of the normal human epidermis derived from cultured human epidermal keratinocytes. The RHE models  300  may have in vivo-like morphology and growth characteristics. In particular embodiments, using RHE models  300  may have reasonable predictive value for skin toxicity. The RHE models  300  may have keratinocytes only but no dermis, vasculature or immune/inflammatory cells. As illustrated in  FIG.  3 A , the RHE model  300  may comprise three parts, culture insert  302 , tissue  304 , and medium  306 . 
       FIG.  3 B  illustrates an example image of a RHE sample  310 . As illustrated in  FIG.  3 B , the RHE sample  310  may comprise a viable epidermal layer  312 . As thickness of the epidermal layer  312  may reflect potential toxicity, one may measure the epidermal thickness in the RHE sample  310  to support skin toxicity assessment of EGFR molecules. After culture with a drug of interest, pathologists may evaluate the RHE samples  310  for signs of skin toxicity and use a semi-quantitative method to identify changes in epidermal thickness. However, this method may be time-consuming and subjective, leading to longer drug development timelines and a hindered ability for cross-study comparisons of skin toxicity. 
     Besides evaluating skin toxicity based on RHE samples  310 , the embodiments disclosed herein may have a variety of applications. As an example and not by way of limitation, the retina is composed of multiple layers and the embodiments disclosed herein may be used to evaluate changes in retinal thickness. As another example and not by way of limitation, the embodiments disclosed herein may be used in a diagnostic setting (e.g., using a biopsy sample) or to evaluate potential treatments and/or adverse reactions of patients to drugs that may be prescribed. In addition, the embodiments disclosed herein may be used outside of the lab and/or safety assessment environment. As an example and not by way of limitation, the assessment of layers of tissues samples may be used as part of a suite of available analytical techniques to apply to digital pathology images. In the embodiments as disclosed herein, particular examples will be described relating to the evaluation of skin tissues, and particularly the evaluation of epidermal thickness as it relates to indication of toxicity, but that similarly techniques may be applied to evaluation of any other suitable indications in skin tissues, evaluation of any other suitable layers of skin tissues, and/or evaluation of any other suitable types of tissues given the availability of sufficient training samples. 
     To address the issues of manual evaluation of RHE samples  310  for skin toxicity, the embodiments disclosed herein use deep learning to identify the viable epidermis of the RHE samples  310  and assist pathologists with quantitative endpoints. Using the embodiments disclosed herein, five skin toxicity studies evaluating drug compounds in clinical development were performed. The RHE samples  310  were first analyzed and then quantitative epidermal thickness endpoints were extracted. Four studies with manual pathologist evaluations were used to assess algorithm extracted epidermal thickness. The extracted measurement based on the machine-learning model also was compared to two studies with manual pathologist measurements. Finally, RHE samples  310 , each treated with compounds, with either known or suspected skin toxicity were used to evaluate the utility of the embodiments disclosed herein in identifying compounds at high risk for skin toxicity. Based on the success of the model in comparison to pathologist evaluation, an accurate, transferrable model for evaluating tissue sample segment thickness in relation to particular clinical outcomes and indications has been developed. 
       FIG.  3 C  illustrates example locations for measurement of a tissue sample segment. As an example, in the context of evaluating skin tissue, the tissue sample may comprise a reconstructed human epidermis (RHE) sample  310  and the identified target layer may comprise an epidermal layer  312 . In particular embodiments, the digital pathology image processing system  110  may measure the thickness at several locations, e.g., location  320   a , location  320   b , location  320   c , location  320   d , location  320   e , location  320   f , location  320   g , and location  320   h . As an example, the digital pathology image processing system  110  may measure the thickness at every predetermined or viable location. The aforementioned measurements may be part of step  230  illustrated in  FIG.  2   . 
     In particular embodiments, the machine-learning model may be trained based on a plurality of training images. Each training image may be associated with a RHE sample. In particular embodiments, each training image may comprise a plurality of image tiles. Each of the plurality of image tiles may comprise a plurality of pixels. Each of the plurality of pixels may be associated with an annotation indicting whether the corresponding pixel belongs to a first layer or a second layer (e.g., the target layer). As an example, in the context of evaluating skin tissue, the first layer may be a keratin layer and the second layer may be an epidermal layer. In other words, to train the machine-learning model, pixel-level annotations of the various layers from a plurality of samples may be needed, such as multiple annotations of the keratin layer and the viable epidermal layer  312  from a plurality of RHE samples  310 . In particular embodiments, during training, a variety of data augmentations may be applied to the training images. As an example and not by way of limitation, such data augmentations may comprise one or more of adding noise, changing hue, changing contrast, or elastic transformation. 
     The annotations may be created by a pathologist. As an example and not by way of limitation, nine RHE samples  310  may be used and image tiles with a width and height of 1024 pixels and the corresponding pixel-level annotations of these RHE samples  310  may be extracted at 40X resolution for training the machine-learning model. As another example and not by way of limitation, four RHE samples  310  may be used and image tiles with a width and height of 128, 256, or 512 pixels and the corresponding pixel-level annotations of these RHE samples  310  may be extracted at 2X, 5X, 10X, 20X, or 60X resolution for training the machine-learning model. Although this disclosure describes particular numbers of RHE samples used with image tiles with particular width and height and the corresponding pixel-level annotations being extracted at particular resolution in a particular manner, this disclosure contemplates any suitable number of RHE samples used with image tiles with any suitable width and height and the corresponding pixel-level annotations being extracted at any suitable resolution in any suitable manner.  FIG.  4 A  illustrates example RHE samples  310  for training the machine-learning model.  FIG.  4 B  illustrates example annotations of the RHE samples  310  with an example tile. As illustrated in  FIG.  4 B  illustrates the annotated epidermal layer  312  in each of the two RHE samples  310 . In addition, the image tile  410  may be a tile extracted with a width and height of 1024 pixels. 
     In particular embodiments, the machine-learning model may be based on one or more different deep-learning architectures. Specifically, the machine-learning model may be based on a deep learning algorithm. The architecture of the deep learning algorithm may be based on one or more of a U-net, a Resnet U-net, or a deep residual neural network. As an example and not by way of limitation, a variation of the U-Net, Resnet U-net, may be used for training the machine-learning model. Resnet U-net may be trained using Keras or Tensorflow. The encoder of the U-Net may be replaced with deep residual neural network (e.g., 50-layer version) and the rest of the U-Net architecture may remain the same. In particular embodiments, model training may be performed with a step size of 512 for 90 epochs with a batch size of 8 using GPUs. Data augmentation techniques including random rotation, cropping, scaling, shifting, adding noises and varying color contrast may be also applied during the training process. In particular embodiments, focal loss and Adam optimizer (e.g., with learning rate of 1x10 -3 ) may be used for optimization. Due to the time-consuming nature of the annotation process, instead of splitting out annotated data into validation and test sets, up to all of the annotated data may be used for training. 
       FIGS.  5 A- 5 C  illustrate example steps for quantifying epidermal layer thickness. In particular embodiments, once the machine-learning model is trained, the digital pathology image processing system  110  may use it to identify the target layer (e.g., the epidermal layer  312  of the RHE sample  310 ), which may be step  220  illustrated in  FIG.  2   . In the context of evaluation skin tissue, the digital pathology image processing system  110  may receive a querying image associated with a reconstructed human epidermis (RHE) sample  310  after a treatment by a drug compound, which may be step  210  illustrated in  FIG.  2   . The digital pathology image processing system  110  may first perform image processing, which may be part of step  220  in  FIG.  2   . In particular embodiments, for every RHE sample  310 , both the two RHE tissue sections (i.e., keratin layer and viable epidermal layer  312 ) may be identified. In particular embodiments, bounding boxes may be used to identify the tissue sections. In addition, the digital pathology image processing system  110  may use sliding windows to generate a mask over the layers. Besides for identifying the tissue sections, the mask may be also used for measuring thickness, determining areas of the layer, determining lengths for different endpoints, and determining curviness for tortuosity, and measuring volume in a three-dimensional scenario. In particular embodiments, the digital pathology image processing system  110  may crop the querying image into a plurality of image tiles, which may be part of step  220  in  FIG.  2   . As an example and not by way of limitation, for each RHE tissue section, the identified tissue area may be cropped into image tiles with width and height of 1024 pixels. In particular embodiments, the width and height of pixels may be dynamically determined (i.e., not fixed) based on factors such as the evaluation task, the querying image itself, or any suitable factor. Although this disclosure describes generating image tiles with width and height of particular pixels in a particular manner, this disclosure contemplates generating any suitable image tile with width and height of any suitable pixel in any suitable manner. The digital pathology image processing system  110  may then perform model inference by applying the trained machine-learning model to the cropped image tiles, i.e., inputting the plurality of image tiles to the machine-learning model, which may be part of step  220  in  FIG.  2   . In other words, the digital pathology image processing system  110  may identify, based on a machine-learning model trained to identify layers of RHE samples, an epidermal layer  312  of the RHE sample  310 . The inference may be performed using GPUs. In particular embodiments, it may be not necessary to crop the image into image tiles. Instead, the digital pathology image processing system  110  may directly apply the machine-learning model to the querying image to make inference with sufficient GPU memory. The output of the machine-learning model may be resized into the shape of the input image, i.e., resizing an output of the machine-learning model into a shape of the querying image. RHE tissue areas may be inferred by the machine-learning model and the keratin and epidermal area  312  may be segmented. In particular embodiments, any suitable image processing techniques may be used. As an example and not by way of limitation, such techniques may comprise adjusting the colors of the samples according to the stain used. In particular embodiments, the segmentations may be examined by pathologists to ensure both keratin and epidermal area were captured. 
       FIG.  5 A  illustrates an example annotation of an RHE sample  310  with tissue sections. As indicated in  FIG.  5 A , the tissue sections may comprise the keratin layer  510  and the epidermal layer  312 . After the epidermal area is identified, the thickness of the viable epidermal area may be computed, e.g., based on distance transformation. In particular embodiments, the median thickness value may be used to represent the thickness of the viable epidermal area for each tissue section and the average thickness of the two tissue sections of a RHE sample  310  may be used to represent a single RHE sample  310 .  FIG.  5 B  illustrates an example extraction of thickness of a tissue sample. As indicated in  FIG.  5 B , the digital pathology image processing system  110  may first determine a centerline  520  for the identified target layer (e.g., epidermal layer  312 ) and then calculate its thickness based on the centerline  520 . The digital pathology image processing system  110  may identify a plurality of locations associated with the identified target layer (e.g., epidermal layer  312 ). The digital pathology image processing system  110  may then quantify, based on the centerline, a thickness value for each of the plurality of locations. The digital pathology image processing system  110  may further determine, an average thickness value for the identified target layer (e.g., epidermal layer  312 ) based on the plurality of thickness values for the plurality of locations. In particular embodiments, the digital pathology image processing system  110  may divide the average thickness value of the identified target layer (e.g., epidermal layer  312 ) by an average thickness value of tissue samples (e.g., RHE samples  310 ) from a control group. This way, the thickness of each tissue sample (e.g., RHE sample  310 ) may be normalized.  FIG.  5 C  illustrates an example normalization of the tissue thickness. As illustrated in  FIG.  5 C , there may be on control group comprising four samples, a group A comprising four samples, and a group B comprising four samples. The left subfigure of  FIG.  5 C  may show the originally measured thickness whereas the right subfigure of  FIG.  5 C  may show the normalized thickness. Although this disclosure describes calculating normalized thickness in a particular manner, this disclosure contemplates calculating normalized thickness in any suitable manner. As an example and not by way of limitation, the digital pathology image processing system may determine a plurality of stepwise thickness measurements along an axis determined based on the epidermal layer, calculate a length and area of the epidermal layer with the thickness being derived from them, and then calculate the normalized thickness accordingly. 
     The embodiments disclosed herein further conduct a retrospective study based on RHE samples  310  from five studies that evaluated the skin toxicity of various compounds. Table 1 summarizes the five studies and the endpoints available for each study. The 3D in vitro human skin model was used for all studies. A total of 31 compounds with known or suspected clinical skin toxicity were evaluated for skin toxicity, some of which were evaluated in more than one study. Upon receipt of the RHE samples  310 , each tissue culture insert was transferred to a well of 6-well plate containing 1 mL/well of pre-warmed maintenance media and kept dry on top to maintain an air-liquid interface. The RHE samples  310  were equilibrated at 37° C., 5% CO 2  overnight, and fed with fresh media the next day. One day later, the RHE samples  310  were subjected to 4-day daily basolateral treatment with test articles at various concentrations, or vehicle control DMSO at 0.5%. Table 2 lists each compound, the study, and the different concentrations at which it was evaluated. Upon completion of treatment, the RHE samples  310  were harvested, fixed, processed to slides, and routinely stained with hematoxylin and eosin. Internal test compounds with suspected skin toxicity were anonymized.  
     
       
         
          TABLE 1
           
               
               
               
               
               
               
               
             
               
                 Summary of the study sample size and annotation. 
               
               
                 Study 
                 Number of compound 
                 Number of samples 
                 Number of control samples 
                 Number of slide with pixel level annotation 
                 Pathologist score? 
                 Manually measured thickness? 
               
             
            
               
                 1 2 3 4 5 
                 16 7 7 6 3 
                 96 49 56 64 16 
                 6 4 4 4 4 
                 1 0 4 3 1 
                 Yes (A) Yes (B) No Yes (C) Yes (C) 
                 No No No Yes (C) Yes (C) 
               
            
           
         
       
     
     
       
         
          TABLE 2
           
               
               
               
             
               
                 Summary of compounds, dose and sample size. 
               
               
                 Study 
                 Compounds 
                 Dose (number of samples) 
               
             
            
               
                 1 
                 G-0001 
                 0.5 µM, 5 µM (3, 3) 
               
               
                 G-0002 
                 0.5 µM, 5 µM (3, 3) 
               
               
                 Cetuximab 
                 50 µg/ml (3) 
               
               
                 G-0003 
                 0.5 µM, 5 µM (3, 3) 
               
               
                 G-0004 
                 0.5 µM, 5 µM (3, 3) 
               
               
                 Erlotinib 
                 2 µM (3) 
               
               
                 XL281 
                 0.5 µM, 5 µM (3, 3) 
               
               
                   
                 G-0005 
                 2 µM, 10 µM (3, 3) 
               
               
                 Imatinib 
                 2 µM, 10 µM (3, 3) 
               
               
                 Jnj-38877605 
                 2 µM, 10 µM (3, 3) 
               
               
                 Pf-04217903 
                 2 µM, 10 µM (3, 3) 
               
               
                 G-0006 
                 0.5 µM, 5 µM (3, 3) 
               
               
                 G-0007 
                 0.5 µM, 5 µM (3, 3) 
               
               
                 Ruxolitinib 
                 2 µM, 10 µM (3, 3) 
               
               
                 Sorafenib 
                 0.5 µM, 5 µM (3, 3) 
               
               
                 Tofacitinib 
                 2 µM, 10 µM (3, 3) 
               
               
                 DMSO (control) 
                 NA (6) 
               
               
                 2 
                 Alpelisib 
                 320 nM, 3200 nM (4, 4) 
               
               
                 Erlotinib 
                 10 µM (3) 
               
               
                 G-0008 
                 39 nM, 390 nM (4, 4) 
               
               
                 Idelalisib 
                 80 nM, 800 nM (4, 4) 
               
               
                 Imatinib 
                 10 nM (3) 
               
               
                 Palbociclib 
                 23 nM, 230 nM (4, 3) 
               
               
                 Pictilisib 
                 1 µM (3) 
               
               
                 DMSO (control) 
                 NA (4) 
               
               
                 3 
                 G-0009 
                 1 µM, 10 µM (4, 4) 
               
               
                 G-0010 
                 1 µM, 10 µM (4, 4) 
               
               
                 G-0011 
                 1 µM, 10 µM (4, 4) 
               
               
                 G-0012 
                 1 µM, 10 µM (4, 4) 
               
               
                 Cobimetinib 
                 0.02 µM, 1 µM (4, 4) 
               
               
                 Erlotinib 
                 10 µM (4) 
               
               
                 Pictilisib 
                 0.02 µM, 1 µM (4, 4) 
               
               
                 DMSO (control) 
                 NA (4) 
               
               
                 4 
                 Afatinib 
                 1 µM, 10 µM (4, 4) 
               
               
                 G-0013 
                 1 µM, 10 µM (4, 4) 
               
               
                 Erlotinib 
                 1 µM, 10 µM (8, 8) 
               
               
                 Lapatinib 
                 1 µM, 10 µM (4, 4) 
               
               
                 Osimertinib 
                 1 µM, 10 µM (4, 4) 
               
               
                 Poziotinib 
                 1 µM, 10 µM (4, 4) 
               
               
                 DMSO (control) 
                 NA (8) 
               
               
                 5 
                 Osimertinib 
                 300 nM, 3000 nM (4, 4) 
               
               
                 Poziotinib 
                 300 nM (4) 
               
               
                 DMSO (control) 
                 NA (4) 
               
            
           
         
       
     
       FIG.  6    illustrates an example workflow  600  of the design of a retrospective study. As illustrated in  FIG.  6   , the retrospective study may be based on three arms, i.e., arm A  605 , arm B  610 , and arm C  615 . The workflow  600  may begin with pixel-level annotations of keratin and viable epidermal layers  312  of RHE samples  310 . As an example and not by way of limitation, there may be nine RHE samples  310  from four of the skin toxicity studies  620  (i.e., study 1, study 3, study 4, and study 5) being annotated at the step of creating pixel-level annotation  625 . The machine-learning model based on deep learning (e.g., the algorithm  630  as indicated in  FIG.  6   ) may be trained from these samples to segment both the keratin and viable epidermal layers  312 . Then the trained machine-learning model may be used to segment the viable epidermal area. Next, the segmented viable epidermal area by the machine-learning model may be processed to compute the thickness. In arm A  605 , the segmented viable epidermal layers  312  from the studies  635  (i.e., studies 1-5) may be quantified with an image processing algorithm  640 . In addition, the computed viable epidermal thickness  645  of the samples for each compound from the studies was compared to enable rapid toxicity screening with respect to arm A at step  650 . Arm B  610  and arm C  615  were used to understand the relationship between the manual endpoints and the measured thickness based on the machine-learning model. In arm B  610 , the viable epidermal thicknesses of the RHE samples  310  in four studies  655  (i.e., studies 1, 2, 4, and 5) were scored by pathologists A, B, C and C, respectively. Study 3 was not scored by pathologists. The thickness scores  660  were compared with the corresponding algorithm measurement of the thickness (i.e., based on the machine-learning model) at step  665 . In arm C  615 , pathologist C was provided an image viewing software to measure the viable epidermal thickness for two studies  670  (i.e. studies 4-5). The pathologist measured epidermal thickness  675  was compared with the algorithm measured (i.e., based on the machine-learning model) thickness at step  680 . 
     RHE samples  310  in studies 1, 2, 4 and 5 were evaluated with optical microscopes by pathologists. The thickness of the viable epidermal area of the RHE samples  310  in studies 1, 2, 4 and 5 were scored by pathologists A, B, C and C, respectively. Each pathologist used a different scoring system to evaluate the thickness of the viable epidermal area. Pathologist A used the following system: marked epidermal thinning, moderate epidermal thinning, slight epidermal thinning, possible minimal decrease, no significant finding (same as control group), and possible increase in epidermal thickness. Pathologist B used a scoring scale of 2 to 8 with the following ranges: 2 to 3 (thinnest), 3 to 4, 4 to 5, 6 to 7 and 7 to 8 (same as the control group). Pathologist C used a scale of 0 - 4 where 0 was the same as the control group increasing to 4 which is the thinnest sample. To enable cross-study comparison, the scores from pathologists were normalized. The scores for the control group were set to 1 and then re-adjusted so the higher the score, the thinner the viable epidermal thickness. Table 3 summarizes the mapping from pathologist scores to the normalized scores.  
     
       
         
          TABLE 3
           
               
               
               
             
               
                 Mapping of pathologist score to normalized score. 
               
               
                 Pathologist 
                 Pathologist score 
                 Normalized score 
               
             
            
               
                 A 
                 Possible increase in epidermal thickness 
                 0 
               
               
                 No significant finding 
                 1* 
               
               
                 Possible minimal decrease in epidermal thickness 
                 2 
               
               
                   
                 Slight epidermal thinning 
                 3 
               
               
                 Moderate epidermal thinning 
                 4 
               
               
                 Marked epidermal thinning 
                 5 
               
               
                 B 
                 7 to 8 
                 1* 
               
               
                 6 to 7 
                 2 
               
               
                 5 to 6 
                 3 
               
               
                 4 to 5 
                 4 
               
               
                 3 to 4 
                 5 
               
               
                 2 to 3 
                 6 
               
               
                 C 
                 0 
                 1* 
               
               
                 0.5 
                 1.5 
               
               
                 1 
                 2 
               
               
                 1.5 
                 2.5 
               
               
                 2 
                 3 
               
               
                 3 
                 4 
               
               
                 4 
                 5 
               
               
                 *: Score for samples with no significant finding. 
               
            
           
         
       
     
     In addition to the manual scoring, the viable epidermal thickness of each sample in studies 4 and 5 was measured by pathologist C using an image viewing software.  FIG.  7    illustrates example representative images from a pathologist measuring the viable epidermal thickness using an image viewer. As illustrated in  FIG.  7   , pathologist C chose three representative regions, i.e., region  710 , region  720 , and region  730 , from each sample and measured the thickness of the RHE tissue, which resulted in three measured epidermal thickness endpoints per sample. As an example and not by way of limitation, the measured thickness for these three regions may be 34.26 um, 37.97 um, and 26.51 um, respectively. These three measurements were compared with the measurements determined based on the machine-learning model. These manual measurements were also served to validate the thickness measurement based on the machine-learning model, providing pathologist insights of how close the measured thickness based on the machine-learning model and the manual measured thickness are. To aid in the interpretation of any meaningful change in epidermal thickness, the presence of specific microscopic characteristics was assessed. The evaluation was performed by the three pathologists and included a qualitative assessment of the stratum corneum and stratum granulosum, presence of parakeratosis, single or widespread keratinocyte necrosis, and evidence of keratinocyte swelling, usually due to vacuolation. 
     The embodiments disclosed herein additionally performed statistical analyses for the retrospective study. Image analyses and statistical analyses may be performed with different software tools such as Python. To evaluate the relationship between the pathologist scores and the measured thickness based on the machine-learning model, Kendall’s Tau-b correlation coefficients were computed. The correlations were computed between the normalized pathologist scores and the normalized averaged thickness measured based on the machine-learning model for studies 1, 2, 4, and 5. 
     The quantitative thickness measurements in studies 4-5 from the machine-learning model and pathologist C were also compared. The difference between the two measurements was expected to decrease as more manual measurements were made since the machine-learning model measured the thickness from the entire RHE sample  310 , whereas the manual measurements were only made at three regions of interest (ROI). Therefore, a single thickness measurement was first randomly selected from the three measurements made from the pathologists. The randomly selected measurement for each sample was compared to the average measurement by the machine-learning model for that sample. Next, for each sample, the average of the three measurements from pathologist C were compared with the average measurement by the machine-learning model. The agreement between the model-measured epidermal thickness and the manually measured thickness by pathologist C in studies 4-5 was assessed, e.g., by using the Bland-Altman method. 
     To compare the rank orders across studies, the rank orders of the control samples were set to 1. In addition, the rank order increased to a maximum of 5 with a decrease in viable epidermal thickness. Zero or negative rank orders may suggest an increase in viable epidermal thickness. The embodiments disclosed herein refer to the converted rank order as the normalized pathologist score for simplicity. 
     The mean thickness of the normalized viable epidermal thickness from each study was grouped together and compared with the normalized viable epidermal thickness for each test compound. The same test compound and the same experimental protocol from different studies were combined. Additionally, a conventional method for multiple comparison was used. 
     Based on the retrospective study, the embodiments disclosed herein found that viable epidermal thickness measured based on the machine-learning model significantly correlates with pathologist scores. The correlation may be discovered as follows. To begin with, the machine-learning model may segment the viable epidermal area for the samples from each study.  FIG.  8    illustrates example segmentations of viable epidermal area by the machine-learning model. As illustrated in  FIG.  8   , the trained machine-learning model can segment the viable epidermal area. The viable epidermal area and the keratin layer were accurately identified when the normalized epidermal thickness is greater than 1.0 or less than 0.75. 
       FIGS.  9 A- 9 D  illustrate example boxplots between normalized epidermal thickness measured based on the machine-learning model and normalized scores from a pathologist.  FIG.  9 A  illustrates example boxplots between normalized epidermal thickness measured based on the machine-learning model and normalized scores from pathologist A for study 1.  FIG.  9 B  illustrates example boxplots between normalized epidermal thickness measured based on the machine-learning model and normalized scores from pathologist B for study 2.  FIG.  9 C  illustrates example boxplots between normalized epidermal thickness measured based on the machine-learning model and normalized scores from pathologist C for study 4.  FIG.  9 D  illustrates example boxplots between normalized epidermal thickness measured based on the machine-learning model and normalized scores from pathologist C for study 5. The pathologist scores of the control group were set to 1 and the scores were adjusted so the higher the scores, the thinner the viable epidermal thickness. The algorithm measured epidermal thickness was normalized to the average thickness of the control group in each study. Kendall’s Tau-b correlation coefficients were computed. Significant correlations (R = -0.62 for Study 1, -0.76 for 2, -0.67 for 4, and -0.84 for 5, p &lt; 0.01 for all) were observed between viable epidermal thickness measured based on the machine-learning model and the scores from pathologists. Notably, three samples in Study 1 dosed at 10 times the clinically relevant concentration were diagnosed with full thickness epidermal necrosis. The measured thickness for these three samples was zero ( FIG.  9 A ). Additionally, in study 4, due to microscopic finding of keratinocyte vacuolar degeneration with associated cell swelling in seven samples, the manual decrease in thickness score was lower than expected, which was reflected in the score calculated based on the machine-learning model. 
     The retrospective study also indicates differences in epidermal thickness may decrease with increasing manual measurements. To provide more accurate comparisons between the pathologist thickness evaluation and measurements of the epidermal area based on the machine-learning model, pathologist C used software to manually measure the epidermal thickness of three ROIs (locations) from a RHE tissue. One manual measurement was randomly selected from the three ROIs and compared to the thickness measured based on the machine-learning model. The comparison is based on Bland-Altman plots and absolute error and standard deviation were computed.  FIGS.  10 A- 10 D  illustrate example comparisons between viable epidermal thickness measured using the machine-learning model and measured by a pathologist.  FIG.  10 A  illustrates an example comparison between viable epidermal thickness measured by a pathologist and that measured based on the machine-learning model at one random location from a single tissue section for every sample in study 4. The absolute errors between the epidermal thickness measured based on the machine-learning model and the epidermal thickness measured by the pathologist were 1.55 ± 0.959 µm for study 4.  FIG.  10 B  illustrates an example comparison between viable epidermal thickness measured by a pathologist and that measured based on the machine-learning model at one random location from a single tissue section for every sample in study 5. The absolute errors between the epidermal thickness measured based on the machine-learning model and the epidermal thickness measured by the pathologist were 1.25 ± 1.200 µm for study 5.  FIG.  10 C  illustrates an example comparison between viable epidermal thickness measured by a pathologist and that measured based on the machine-learning model at three random locations from a single tissue section for every sample in Study 4. The measured thicknesses from multiple locations were averaged.  FIG.  10 D  illustrates an example comparison between viable epidermal thickness measured by a pathologist and that measured based on the machine-learning model at three random locations from a single tissue section for every sample in study 5. For  FIGS.  10 C- 10 D , the measured thicknesses from multiple locations were averaged. When all three ROIs were used to compute the average measured thickness from the pathologist, the absolute errors between the algorithm measured and the pathologist measured epidermal thickness were reduced to 1.33 ± 0.918 µm and 1.02 ± 0.943 µm for study 4 and study 5, respectively. These results may suggest that as the number of manual pathologist measurements and ROIs increase, the measured thickness may become more similar to the results measured based on the machine-learning model. 
     In particular embodiments, normalized epidermal thickness may enable cross-study comparison and reveal potential clinical toxicity. Normalized epidermal thickness of compounds with clinical observations were extracted from studies 1, 2, 3, 4, and 5, and the correlation of epidermal thickness and clinical skin toxicity was analyzed retrospectively. Clinical skin toxicity may be defined as rash, pruritus, acne, dermatitis, alopecia, and/or dry skin described in the labels for marketed compounds, or publications reporting safety of compounds under clinical development.  FIG.  11 A  illustrates example normalized viable epidermal thickness from various compounds under different concentrations. The normalized thickness is obtained based on the machine-learning model. The results were ordered by the median epidermal thickness from each experiment across the studies. A conventional method for multiple comparison was used. In  FIG.  11 A , numbers in the parentheses show the sample sizes (*: p&lt;0.05, **: p&lt;0.01). Three samples in study 1 that were dosed at 10 times the clinically relevant concentration were removed from this analysis. A total of eight compounds (afatinib, alpelisib, erlotinib, cobimetinib, osimertibib, poziotinib, lapatinib and pictilisib) with a significant decrease in epidermal thickness demonstrated clinical toxicity. Conversely, three compounds (tofacitinib, ruxolitnib, Pf-04217903) with significant decrease in epidermal thickness did not exhibit clinical toxicity. Except Pf-04217903 (10 µM), all compounds with a normalized epidermal thickness decrease of greater than 20% demonstrated clinical toxicity. Accordingly, determining the toxicity indication of the treatment by the drug compound based on the normalized thickness of the identified target layer (e.g., epidermal layer  312 ) may comprise comparing the normalized thickness with a threshold thickness value. In particular embodiments, the threshold may be determined based on machine-learning approaches. As an example and not by way of limitation, such approaches may be based on unsupervised learning. In alternative embodiments, determining the toxicity indication of the treatment by the drug compound based on the normalized thickness of the identified target layer (e.g., epidermal layer  312 ) may be based on another machine-learning model trained to determine the toxicity indication based on the normalized thickness.  FIG.  11 B  illustrates an example impact of the in vitro test concentration on the epidermal thickness for compounds showing skin toxicity and those that do not. Horizontal dashed line indicates 20% decrease in normalized thickness. Vertical dashed line indicates 5-fold increase in concentration compared to the clinical exposure. In particular embodiments, the digital pathology image processing system  110  may receive a confirmation of the toxicity of the treatment by the drug compound. As an example and not by way of limitation, such confirmation may comprise one or more of a patient outcome based on the drug compound, a result of further testing (such as more focused testing of the drug compound initiated based on the toxicity indication), or a cross-study comparison. The digital pathology image processing system  110  may further retrain the machine-learning model based on the confirmation. 
     Table 4 illustrates the comparison of test concentration and clinical plasma exposure to test compounds. Mean value of normalized thickness for different compounds in the context of test concentrations and clinical exposure is displayed. Most of the skin toxic compounds decreased epidermal thickness by more than 20% at concentrations greater than 5-fold of clinical exposure (maximal free concentrations measured in plasma, C max _free). In contrast, most of the non-toxic compounds decreased epidermal thickness by less than 20% even at relatively high concentrations (5-fold higher than C max _free). Interestingly, a B-Raf inhibitor (XL-281) demonstrated an increase in epidermal thickness both by pathologist score and by the machine-learning model (albeit not statistically significant), indicating that compounds that induced hyperplastic toxicity may also be picked up with our machine-learning model. A cut of 0.80 (median normalized thickness from the Osimertinib 300 nM group) was used to compute the sensitivity and specificity for classifying skin toxicity with our machine-learning model.  
     
       
         
          TABLE 4
           
               
               
               
               
               
               
               
             
               
                 Comparison of test concentration and clinical plasma exposure to test compounds. 
               
               
                 Compound 
                 Concentration (uM) 
                 C max _free (uM) 
                 PK Reference 
                 Fold to C max _free 
                 Skin tox. 
                 Normalized thickness 
               
             
            
               
                 Jnj-38877605 
                 10 
                 0.13* 
                 39, 40 
                 76.9 
                 No 
                 0.91 
               
               
                 Jnj-38877605 
                 2 
                 0.13* 
                 39, 40 
                 15.4 
                 No 
                 0.82 
               
               
                 Pf-04217903 
                 10 
                 0.015 
                 41 
                 666.7 
                 No 
                 0.72 
               
               
                 Pf-04217903 
                 2 
                 0.015 
                 41 
                 133.3 
                 No 
                 0.91 
               
               
                 Ruxolitinib 
                 10 
                 0.033 
                 42, 43 
                 303.0 
                 No 
                 0.81 
               
               
                 Ruxolitinib 
                 2 
                 0.033 
                 42, 43 
                 60.6 
                 No 
                 0.85 
               
               
                 Tofacitinib 
                 2 
                 0.08 
                 (tofacitinib label) 44 
 
                 25.0 
                 No 
                 0.84 
               
               
                 Tofacitinib 
                 10 
                 0.08 
                 (tofacitinib label) 44 
 
                 125.0 
                 No 
                 0.82 
               
               
                 XL281 
                 0.5 
                 4.5* 
                 45 
                 0.1 
                 No 
                 1.14 
               
               
                 XL281 
                 5 
                 4.5* 
                 45 
                 1.1 
                 No 
                 0.89 
               
               
                 Afatinib 
                 10 
                 0.0042 
                 46 
                 &gt;1000 
                 Yes 
                 0.77 
               
               
                 Afatinib 
                 1 
                 0.0042 
                 46 
                 238.1 
                 Yes 
                 0.70 
               
               
                 Alpelisib 
                 0.32 
                 0.61 
                 (alpelisib label) 
                 0.5 
                 Yes 
                 0.75 
               
               
                 Alpelisib 
                 3.2 
                 0.61 
                 (alpelisib label) 
                 5.2 
                 Yes 
                 0.45 
               
               
                 Cetuximab 
                 50 ug/ml 
                 235 ug/mL 
                 (cetuximab label) 
                 0.2 
                 Yes 
                 0.88 
               
               
                 Cobimetinib 
                 0.02 
                 0.03 
                 (cobimetinib label) 
                 0.7 
                 Yes 
                 0.91 
               
               
                 Cobimetinib 
                 1 
                 0.03 
                 (cobimetinib label) 
                 33.3 
                 Yes 
                 0.71 
               
               
                 Erlotinib 
                 2 
                 0.38 
                 47 
                 5.3 
                 Yes 
                 0.75 
               
               
                 Erlotinib 
                 1 
                 0.38 
                 47 
                 2.6 
                 Yes 
                 0.53 
               
               
                 Erlotinib 
                 10 
                 0.38 
                 47 
                 26.3 
                 Yes 
                 0.41 
               
               
                 Idelalisib 
                 0.8 
                 0.84 
                 (idelalisib label) 48 
 
                 1.0 
                 Yes 
                 1.00 
               
               
                 Idelalisib 
                 0.08 
                 0.84 
                 (idelalisib label) 48 
 
                 0.1 
                 Yes 
                 0.95 
               
               
                 Imatinib 
                 10 
                 0.35 
                 49 
                 28.6 
                 Yes 
                 0.95 
               
               
                 Imatinib 
                 2 
                 0.35 
                 49 
                 5.7 
                 Yes 
                 0.98 
               
               
                 Lapatinib 
                 1 
                 0.000039 
                 (lapatinib label) 
                 &gt;1000 
                 Yes 
                 0.66 
               
               
                 Lapatinib 
                 10 
                 0.000039 
                 (lapatinib label) 
                 &gt;1000 
                 Yes 
                 0.47 
               
               
                 Osimertinib 
                 0.3 
                 0.025 
                 50 
                 12.0 
                 Yes 
                 0.85 
               
               
                 Osimertinib 
                 10 
                 0.025 
                 50 
                 400.0 
                 Yes 
                 0.76 
               
               
                 Osimertinib 
                 1 
                 0.025 
                 50 
                 40.0 
                 Yes 
                 0.61 
               
               
                 Osimertinib 
                 3 
                 0.025 
                 50 
                 120.0 
                 Yes 
                 0.45 
               
               
                 Palbociclib 
                 0.023 
                 0.06 
                 (palbociclib label) 51 
 
                 0.4 
                 Yes 
                 1.02 
               
               
                 Palbociclib 
                 0.23 
                 0.06 
                 (palbociclib label) 51 
 
                 3.8 
                 Yes 
                 0.99 
               
               
                 Pictilisib 
                 0.02 
                 0.18 
                 52, 53 
                 0.1 
                 Yes 
                 0.94 
               
               
                 Pictilisib 
                 1 
                 0.18 
                 52, 53 
                 5.6 
                 Yes 
                 0.46 
               
               
                 Poziotinib 
                 10 
                 0.0021 
                 54 
                 &gt;1000 
                 Yes 
                 0.73 
               
               
                 Poziotinib 
                 0.3 
                 0.0021 
                 54 
                 142.9 
                 Yes 
                 0.72 
               
               
                 Poziotinib 
                 1 
                 0.0021 
                 54 
                 476.2 
                 Yes 
                 0.65 
               
               
                 Sorafenib 
                 0.5 
                 0.07 
                 55 
                 7.1 
                 Yes 
                 0.87 
               
               
                 Sorafenib 
                 5 
                 0.07 
                 55 
                 71.4 
                 Yes 
                 0.85 
               
               
                 *: Plasma protein binding unavailable. Total concentration used in fold calculation. 
               
            
           
         
       
     
     Table 5 summarizes the performance of using epidermal thickness alone and in combination with testing concentrations to identify skin toxic compounds retrospectively. Given the fact that only one compound causes hyperplastic toxicity in this retrospective analysis, it may be impossible to identify a threshold for an increase of epidermal thickness to capture skin toxicity. Thus, XL-281 was not included in performance analysis.  
     
       
         
          TABLE 5
           
               
               
               
               
               
               
               
               
             
               
                 Performance summary of epidermal thickness alone and in combination with testing concentration to identify skin toxic compounds retrospectively. 
               
               
                 Inclusion criteria 
                 Number of drugs 
                 True positive 
                 False positive 
                 True negative 
                 False negative 
                 Sensitivity 
                 Specificity 
               
             
            
               
                 All compounds (exclude XL-281) 
                 17 
                 8 
                 1 
                 3 
                 5 
                 0.62 
                 0.75 
               
               
                 Only include compounds that were tested at concentrations &gt;5-fold clinical exposure 
                 14 
                 8 
                 1 
                 3 
                 2 
                 0.80 
                 0.75 
               
            
           
         
       
     
     The embodiments disclosed herein demonstrated a skin toxicity risk threshold that corresponded with a 20% decrease in epidermal thickness in the RHE model. Although histopathology represents an important source of descriptive data in biomedical research, the use of tissue scoring may have enhanced reproducibility of research studies. However, this traditional method of pathological scoring may be semi-quantitative, thus being subjective to bias, and very time-consuming. Additionally, pathologists may often use different scoring systems to evaluate microscopic changes including skin thickness (as indicated in Table 3), making it challenging to differentiate between subtle reductions in epidermal thickness and impossible to compare across studies that were scored by different pathologists. As demonstrated by the data collected, by utilizing thickness measured based on the machine-learning model, the scoring may be better understood and further normalized. The embodiments disclosed herein may empower a rapid, quantitative, and accurate measurement of epidermal thickness to capture subtle reductions, on the micron level, that may normally go unnoticed with traditional pathological evaluation. Besides improving scoring for epidermal thickness, the scoring derived from the embodiments disclosed herein may also help in the evaluation of thickness of other multi-layered tissues such as the retina. 
     The subtle changes in thickness as well as a lack of quantitative endpoints may make it difficult to evaluate thickness, particularly for studies with large sample sizes. In the retrospective study disclosed herein, significant correlations may be observed between the algorithm measured tissue thickness (e.g., epidermal thickness) and pathologist scores for studies 1, 2, 4 and 5. Additionally, the smaller the sample size, the stronger the correlation (R = -0.84, -0.76, -0.67 and -0.62 when N= 16, 44, 64 and 96, respectively in  FIGS.  9 A- 9 D ). This may suggest that manual evaluation of the tissue thickness (e.g., epidermal thickness) may be more challenging as sample size increases. Tissue thickness may vary from location to location within a tissue sample. As an example, in the context of evaluating skin tissue, epidermal thickness may vary from location to location within an RHE sample  310 . While more consistent thickness may be present in the central portion of the tissue, harvesting-related artifacts at the edge of the samples and detachment of the basal lamina may further challenge the scoring process. To capture any meaningful variation, the pathologists may typically select multiple regions of interest in adequately preserved areas, take measurements and report the median value from the selected regions.  FIGS.  10 A- 10 D  Error! Reference source not found. demonstrate that digital tools may minimize the discrepancy between manual measurements and measurements based on the machine-learning model to less than two microns. Furthermore, this discrepancy may be reduced as more manual measurements are made. 
     Several factors may potentially impact the manual measurements made by pathologists. As an example and not by way of limitation, different manual methods may result in varying thickness measurements. Thickness measured vertically from the basement membrane may easily vary from measurements made perpendicular to the basement membrane for the same sample. The number of measured regions may also affect the measured value due to thickness variation of the epidermal area. Lastly, ROI selection and the measurement starting and ending point may be difficult to reproduce. Therefore, it may be possible that the same sample may result in different thickness values during repetitive experiments. While our results showed that the discrepancy between manual measurements and measurements based on the machine-learning model were small, manual measurements may be subjective, not-reproducible, time-consuming, not scalable and thus not recommended, particularly when a large sample size is involved. 
     One caveat of the RHE model  300  may be that it does not contain melanocytes nor an immune component. Human skin is characterized by a variable number of epidermal and hair melanocytes, and it contains various immune cell populations, including Langerhans cells, macrophages, mast cells, and T cells in the dermis. The lack of the aforementioned components may render the RHE model  300  of limited immunologic significance and preclude the evaluation of melanocyte contribution to drug-induced cutaneous toxicity. Nevertheless, the sole presence of keratinocytes may provide the advantage of examining the drug effects on a single cell population without any confounding influences from other cell populations. Aside from measuring the epidermal thickness, the qualitative microscopic evaluation of the samples may provide further insights into pathologic findings that may influence the thickness itself. As an example and not by way of limitation, the presence of widespread epidermal necrosis with no remaining measurable layer translated in a score of zero. Conversely, the presence of vacuolar degeneration with enlarged, swollen keratinocytes translated into minor decrease in epidermal thickness, thus leading to a score that was lower than expected. As such, a qualitative microscopic evaluation may remain pivotal in uncovering underlying factor that may influence the interpretation of the automated scoring system for epidermal thickness. 
     In the oncology field, a papulopustular rash mostly affecting face and upper trunk has been reported in a high percentage of patients treated with EGFR inhibitors. This on-target effect may be not surprising and, given that this toxicity represents an indicator of clinical efficacy, patients may be often dosed to rash. The retrospective analysis disclosed herein may have confirmed that the RHE model  300  may be a useful tool for measuring skin toxicity following EGFR inhibition (afatinib, erlotinib, lapatinib, osimertinib, and poziotinib as examples). In addition, the RHE model  300  may be responsive to drugs that inhibit PI3Kα/δ (pictilisib), PI3Kα (alpelisib), and MEK (cobimetinib), recapitulating the clinical cutaneous toxicity phenotype 8, 14, 31. In comparison, the kinase inhibitors imatinib (up to 29-fold over clinical C max  _free) and sorafenib (up to 71-fold over clinical C max _free), failed to cause any meaningful change in epidermal thickness, as indicated in  FIG.  11 A . Since immune mechanisms seem to be involved in the imatinib-associated skin rash observed clinically, it may be not surprising that epidermal effects are not reproduced by the RHE model  300 . Similarly, for sorafenib, the higher drug concentration observed in the areas of rash appears to be related to the eccrine activity of the skin, which may not be recapitulated by the RHE model  300  given the absence of sweat glands. As such, the RHE model  300  may not be sensitive to certain signal pathway inhibitor-induced skin toxicity, including BCR-ABL and Raf, with few caveats. Adverse epidermal proliferative lesions have been reported in patients with BRAF-V600 mutated metastatic melanoma when treated with certain B-Raf inhibitors due to paradoxical MAPK pathway activation. In this instance, the epidermal hyperplasia induced by these B-Raf inhibitors at lower pharmacologically relevant concentrations appears to be reproduced by the RHE model  300 , while manifesting as epidermal thinning and toxicity at suprapharmacologic higher concentrations. Here, increased epidermal thickness has been confirmed in Raf inhibitor-treated RHE model and correlated with epidermal hyperplasia and the induction of epidermal tumors observed preclinically and clinically. Thus, the predictive value of the RHE model  300  may be dependent on the mechanism of action as well as the concentration of each compound teste. 
     The prediction value of the RHE model  300  may also need to be put into context of compound test concentrations. Non-toxic compounds cause less than 20% epidermal thinning regardless of the testing concentration (from 0.1-fold to 300-fold over clinical C max_ free). Thus, the specificity of the RHE model  300  may be similar across different inclusion criteria for the test concentrations. However, the retrospective analysis showed that skin-toxic compounds decreased epidermal thickness when tested at concentrations equivalent to 5-fold the therapeutic clinical exposure ( FIG.  11 B ). The sensitivity of the RHE model  300  increased from 0.62 to 0.8 and the specificity decreased from 0.8 to 0.75 when adding the test concentration in the inclusion criteria for predictively analysis (Table 5). 
     In the embodiments disclosed herein, the RHE model  300  was treated with test compounds for four days, which is shorter than the time course for skin toxicity manifestation in clinic. Due to these considerations, the compound concentrations required to cause changes in the epidermal thickening in the RHE model  300  may be higher than the maximal exposure seen in clinic. Thus, the RHE model  300  may only have good predictive value when compounds are tested at concentrations equivalent to 5-fold the therapeutic clinical exposure or higher. 
     As discussed above, deep learning and image processing algorithms may provide quantitative endpoints of epidermal thickness. The embodiments disclosed herein demonstrated that this computed epidermal thickness from the RHE model  300  may reflect potential clinical skin toxicity. The embodiments disclosed herein may be fully automated, scalable and reproducible. Therefore, the embodiments disclosed herein may potentially enhance the throughput for compound screening. With time, as more quantitative data are collected, confidence in predicting clinical skin toxicity may only grow. 
     In particular embodiments, the machine-learning model may be used to identify other features of the RHE samples  310 . As an example and not by way of limitation, such features may comprise colors, cell sizes, cell morphology, different cell types, etc. The machine-learning model may be also used for in vivo skins such as biopsy from either animals or humans as long as thickness measurement is of interest. As an example and not by way of limitation, the embodiments disclosed herein may provide more evaluation or provide a diagnosis to pathologist for in vivo biopsies. The embodiments disclosed herein may be also used to determine the density of cells within the viable epidermal layer given high-enough resolution and identify different cell types (e.g., looking for specific types of cell-death) during the segmentation process. As an example and not by way of limitation, rather than just counting up the layers, the embodiments disclosed herein may be used to perform a nuclei count. The machine-learning model may be further used in analysis of other organs. As an example and not by way of limitation, such organs may comprise an eye ball (i.e., different layers in the retina).  FIG.  12    illustrates an example segmentation of a tissue sample. The tissue sample is a cyno skin. The tissue sample may have been cut with an angle. The embodiments disclosed herein may use the information that there are hair follicles in the cyno skin to estimate the thickness of the skin. 
     In particular embodiments, the machine-learning model may be also used for determining treatment efficacy based on the thickness of on one or more identified layers, such as the epidermal layer  312 . The digital pathology image processing system  110  may receive a querying image associated with a reconstructed human epidermis (RHE) sample  310  after a treatment by a drug compound. The digital pathology image processing system  110  may then identify, based on a machine-learning model trained to identify layers of RHE samples  310 , an epidermal layer  312  of the RHE sample  310 . In particular embodiments, the digital pathology image processing system  110  may calculate a normalized thickness of the identified epidermal layer  312 . The digital pathology image processing system  110  may further determine an efficacy indication of the treatment by the drug compound based on the normalized thickness of the identified epidermal layer  312 . In particular embodiments, determining the efficacy indication of the treatment by the drug compound based on the normalized thickness of the identified epidermal layer may comprise comparing the normalized thickness with a threshold thickness value. In particular embodiments, the threshold may be determined based on machine-learning approaches such as unsupervised learning. In alternative embodiments, determining the efficacy indication of the treatment by the drug compound based on the normalized thickness of the epidermal layer  312  may be based on another machine-learning model trained to determine the efficacy indication based on the normalized thickness. In particular embodiments, the digital pathology image processing system  110  may receive a confirmation of the efficacy of the treatment by the drug compound. As an example and not by way of limitation, such confirmation may comprise one or more of a patient outcome based on the drug compound, a result of further testing (such as more focused testing of the drug compound initiated based on the efficacy indication), or a cross-study comparison. The digital pathology image processing system  110  may further retrain the machine-learning model based on the confirmation. 
     In particular embodiments, the machine-learning model may be additionally used for retina segmentation of retina and thickness measurement of the retina. In this case, the tissue sample may comprise a reconstructed eye sample and the identified target layer may comprise a retina layer. In particular embodiments, the digital pathology image processing system  110  may train the machine-learning model based on a plurality of training images. Each training image may be associated with a reconstructed eye sample. Each training image may comprises a plurality of image tiles. In particular embodiments, each of the plurality of image tiles may comprise a plurality of pixels. Each of the plurality of pixels may be associated with an annotation indicting whether the corresponding pixel belong to a retina layer. Based on such machine-learning model, one may segment retina within the images of eyes, e.g., eight retina layers. In particular embodiments, the digital pathology image processing system  110  may further measure the thickness of the segmented retina. The measured thickness may be also relative thickness not just the raw values.  FIGS.  13 A- 13 C  illustrate example tissue segmentations.  FIG.  13 A  illustrates example retina segmentations from a first study. In the first study, the retina segmentations may correspond to ideal eyeballs with distinct layers.  FIG.  13 B  illustrates example retina segmentations from a second study. In the second study, the retina segmentations may correspond to eyeballs with artifacts or eyeballs where the tissues were cut at the edge of the eyeballs. These eyeballs may be less ideal for the evaluation, i.e., thickness comparison.  FIG.  13 C  illustrates example retina segmentations from a third study. In the third study, the retina segmentations may correspond to eyeballs that are less ideal than those in the first study but more ideal than those in the second study. 
       FIGS.  14 A- 14 B  illustrate example measured tissue segment thickness.  FIG.  14 A  illustrates example measured retina thickness from the first study. In particular, group 3 and group 4 in the top right barograph show smaller thickness compared to group 1 and group 2. This observation may suggest that there may be toxicity that affects the normal pathology of the retina. By contrast, the thicknesses for the four groups look similar for the rest of the barographs.  FIG.  14 B  illustrates example measured retina thickness from the second study. 
     As can be seen, the embodiments disclosed herein may be beneficial for a variety of application when the tissues of interest are composed of multiple layers (e.g., the retina) because of the intrinsic ability of the embodiments disclosed herein to detect changes in the thickness of specific layers. 
       FIG.  15    illustrates an example computer system  1500 . In particular embodiments, one or more computer systems  1500  perform one or more steps of one or more methods described or illustrated herein. In particular embodiments, one or more computer systems  1500  provide functionality described or illustrated herein. In particular embodiments, software running on one or more computer systems  1500  performs one or more steps of one or more methods described or illustrated herein or provides functionality described or illustrated herein. Particular embodiments include one or more portions of one or more computer systems  1500 . Herein, reference to a computer system may encompass a computing device, and vice versa, where appropriate. Moreover, reference to a computer system may encompass one or more computer systems, where appropriate. 
     This disclosure contemplates any suitable number of computer systems  1500 . This disclosure contemplates computer system  1500  taking any suitable physical form. As example and not by way of limitation, computer system  1500  may be an embedded computer system, a system-on-chip (SOC), a single-board computer system (SBC) (such as, for example, a computer-on-module (COM) or system-on-module (SOM)), a desktop computer system, a laptop or notebook computer system, an interactive kiosk, a mainframe, a mesh of computer systems, a mobile telephone, a personal digital assistant (PDA), a server, a tablet computer system, or a combination of two or more of these. Where appropriate, computer system  1500  may include one or more computer systems  1500 ; be unitary or distributed; span multiple locations; span multiple machines; span multiple data centers; or reside in a cloud, which may include one or more cloud components in one or more networks. Where appropriate, one or more computer systems  1500  may perform without substantial spatial or temporal limitation one or more steps of one or more methods described or illustrated herein. As an example and not by way of limitation, one or more computer systems  1500  may perform in real time or in batch mode one or more steps of one or more methods described or illustrated herein. One or more computer systems  1500  may perform at different times or at different locations one or more steps of one or more methods described or illustrated herein, where appropriate. 
     In particular embodiments, computer system  1500  includes a processor  1502 , memory  1504 , storage  1506 , an input/output (I/O) interface  1508 , a communication interface  1510 , and a bus  1512 . Although this disclosure describes and illustrates a particular computer system having a particular number of particular components in a particular arrangement, this disclosure contemplates any suitable computer system having any suitable number of any suitable components in any suitable arrangement. 
     In particular embodiments, processor  1502  includes hardware for executing instructions, such as those making up a computer program. As an example and not by way of limitation, to execute instructions, processor  1502  may retrieve (or fetch) the instructions from an internal register, an internal cache, memory  1504 , or storage  1506 ; decode and execute them; and then write one or more results to an internal register, an internal cache, memory  1504 , or storage  1506 . In particular embodiments, processor  1502  may include one or more internal caches for data, instructions, or addresses. This disclosure contemplates processor  1502  including any suitable number of any suitable internal caches, where appropriate. As an example and not by way of limitation, processor  1502  may include one or more instruction caches, one or more data caches, and one or more translation lookaside buffers (TLBs). Instructions in the instruction caches may be copies of instructions in memory  1504  or storage  1506 , and the instruction caches may speed up retrieval of those instructions by processor  1502 . Data in the data caches may be copies of data in memory  1504  or storage  1506  for instructions executing at processor  1502  to operate on; the results of previous instructions executed at processor  1502  for access by subsequent instructions executing at processor  1502  or for writing to memory  1504  or storage  1506 ; or other suitable data. The data caches may speed up read or write operations by processor  1502 . The TLBs may speed up virtual-address translation for processor  1502 . In particular embodiments, processor  1502  may include one or more internal registers for data, instructions, or addresses. This disclosure contemplates processor  1502  including any suitable number of any suitable internal registers, where appropriate. Where appropriate, processor  1502  may include one or more arithmetic logic units (ALUs); be a multi-core processor; or include one or more processors  1502 . Although this disclosure describes and illustrates a particular processor, this disclosure contemplates any suitable processor. 
     In particular embodiments, memory  1504  includes main memory for storing instructions for processor  1502  to execute or data for processor  1502  to operate on. As an example and not by way of limitation, computer system  1500  may load instructions from storage  1506  or another source (such as, for example, another computer system  1500 ) to memory  1504 . Processor  1502  may then load the instructions from memory  1504  to an internal register or internal cache. To execute the instructions, processor  1502  may retrieve the instructions from the internal register or internal cache and decode them. During or after execution of the instructions, processor  1502  may write one or more results (which may be intermediate or final results) to the internal register or internal cache. Processor  1502  may then write one or more of those results to memory  1504 . In particular embodiments, processor  1502  executes only instructions in one or more internal registers or internal caches or in memory  1504  (as opposed to storage  1506  or elsewhere) and operates only on data in one or more internal registers or internal caches or in memory  1504  (as opposed to storage  1506  or elsewhere). One or more memory buses (which may each include an address bus and a data bus) may couple processor  1502  to memory  1504 . Bus  1512  may include one or more memory buses, as described below. In particular embodiments, one or more memory management units (MMUs) reside between processor  1502  and memory  1504  and facilitate accesses to memory  1504  requested by processor  1502 . In particular embodiments, memory  1504  includes random access memory (RAM). This RAM may be volatile memory, where appropriate. Where appropriate, this RAM may be dynamic RAM (DRAM) or static RAM (SRAM). Moreover, where appropriate, this RAM may be single-ported or multi-ported RAM. This disclosure contemplates any suitable RAM. Memory  1504  may include one or more memories  1504 , where appropriate. Although this disclosure describes and illustrates particular memory, this disclosure contemplates any suitable memory. 
     In particular embodiments, storage  1506  includes mass storage for data or instructions. As an example and not by way of limitation, storage  1506  may include a hard disk drive (HDD), a floppy disk drive, flash memory, an optical disc, a magneto-optical disc, magnetic tape, or a Universal Serial Bus (USB) drive or a combination of two or more of these. Storage  1506  may include removable or non-removable (or fixed) media, where appropriate. Storage  1506  may be internal or external to computer system  1500 , where appropriate. In particular embodiments, storage  1506  is non-volatile, solid-state memory. In particular embodiments, storage  1506  includes read-only memory (ROM). Where appropriate, this ROM may be mask-programmed ROM, programmable ROM (PROM), erasable PROM (EPROM), electrically erasable PROM (EEPROM), electrically alterable ROM (EAROM), or flash memory or a combination of two or more of these. This disclosure contemplates mass storage  1506  taking any suitable physical form. Storage  1506  may include one or more storage control units facilitating communication between processor  1502  and storage  1506 , where appropriate. Where appropriate, storage  1506  may include one or more storages  1506 . Although this disclosure describes and illustrates particular storage, this disclosure contemplates any suitable storage. 
     In particular embodiments, I/O interface  1508  includes hardware, software, or both, providing one or more interfaces for communication between computer system  1500  and one or more I/O devices. Computer system  1500  may include one or more of these I/O devices, where appropriate. One or more of these I/O devices may enable communication between a person and computer system  1500 . As an example and not by way of limitation, an I/O device may include a keyboard, keypad, microphone, monitor, mouse, printer, scanner, speaker, still camera, stylus, tablet, touch screen, trackball, video camera, another suitable I/O device or a combination of two or more of these. An I/O device may include one or more sensors. This disclosure contemplates any suitable I/O devices and any suitable I/O interfaces  1508  for them. Where appropriate, I/O interface  1508  may include one or more device or software drivers enabling processor  1502  to drive one or more of these I/O devices. I/O interface  1508  may include one or more I/O interfaces  1508 , where appropriate. Although this disclosure describes and illustrates a particular I/O interface, this disclosure contemplates any suitable I/O interface. 
     In particular embodiments, communication interface  1510  includes hardware, software, or both providing one or more interfaces for communication (such as, for example, packet-based communication) between computer system  1500  and one or more other computer systems  1500  or one or more networks. As an example and not by way of limitation, communication interface  1510  may include a network interface controller (NIC) or network adapter for communicating with an Ethernet or other wire-based network or a wireless NIC (WNIC) or wireless adapter for communicating with a wireless network, such as a WI-FI network. This disclosure contemplates any suitable network and any suitable communication interface  1510  for it. As an example and not by way of limitation, computer system  1500  may communicate with an ad hoc network, a personal area network (PAN), a local area network (LAN), a wide area network (WAN), a metropolitan area network (MAN), or one or more portions of the Internet or a combination of two or more of these. One or more portions of one or more of these networks may be wired or wireless. As an example, computer system  1500  may communicate with a wireless PAN (WPAN) (such as, for example, a BLUETOOTH WPAN), a WI-FI network, a WI-MAX network, a cellular telephone network (such as, for example, a Global System for Mobile Communications (GSM) network), or other suitable wireless network or a combination of two or more of these. Computer system  1500  may include any suitable communication interface  1510  for any of these networks, where appropriate. Communication interface  1510  may include one or more communication interfaces  1510 , where appropriate. Although this disclosure describes and illustrates a particular communication interface, this disclosure contemplates any suitable communication interface. 
     In particular embodiments, bus  1512  includes hardware, software, or both coupling components of computer system  1500  to each other. As an example and not by way of limitation, bus  1512  may include an Accelerated Graphics Port (AGP) or other graphics bus, an Enhanced Industry Standard Architecture (EISA) bus, a front-side bus (FSB), a HYPERTRANSPORT (HT) interconnect, an Industry Standard Architecture (ISA) bus, an INFINIBAND interconnect, a low-pin-count (LPC) bus, a memory bus, a Micro Channel Architecture (MCA) bus, a Peripheral Component Interconnect (PCI) bus, a PCI-Express (PCIe) bus, a serial advanced technology attachment (SATA) bus, a Video Electronics Standards Association local (VLB) bus, or another suitable bus or a combination of two or more of these. Bus  1512  may include one or more buses  1512 , where appropriate. Although this disclosure describes and illustrates a particular bus, this disclosure contemplates any suitable bus or interconnect. 
     Herein, a computer-readable non-transitory storage medium or media may include one or more semiconductor-based or other integrated circuits (ICs) (such, as for example, field-programmable gate arrays (FPGAs) or application-specific ICs (ASICs)), hard disk drives (HDDs), hybrid hard drives (HHDs), optical discs, optical disc drives (ODDs), magneto-optical discs, magneto-optical drives, floppy diskettes, floppy disk drives (FDDs), magnetic tapes, solid-state drives (SSDs), RAM-drives, SECURE DIGITAL cards or drives, any other suitable computer-readable non-transitory storage media, or any suitable combination of two or more of these, where appropriate. A computer-readable non-transitory storage medium may be volatile, non-volatile, or a combination of volatile and non-volatile, where appropriate. 
     Herein, “or” is inclusive and not exclusive, unless expressly indicated otherwise or indicated otherwise by context. Therefore, herein, “A or B” means “A, B, or both,” unless expressly indicated otherwise or indicated otherwise by context. Moreover, “and” is both joint and several, unless expressly indicated otherwise or indicated otherwise by context. Therefore, herein, “A and B” means “A and B, jointly or severally,” unless expressly indicated otherwise or indicated otherwise by context. 
     The scope of this disclosure encompasses all changes, substitutions, variations, alterations, and modifications to the example embodiments described or illustrated herein that a person having ordinary skill in the art would comprehend. The scope of this disclosure is not limited to the example embodiments described or illustrated herein. Moreover, although this disclosure describes and illustrates respective embodiments herein as including particular components, elements, feature, functions, operations, or steps, any of these embodiments may include any combination or permutation of any of the components, elements, features, functions, operations, or steps described or illustrated anywhere herein that a person having ordinary skill in the art would comprehend. Furthermore, reference in the appended claims to an apparatus or system or a component of an apparatus or system being adapted to, arranged to, capable of, configured to, enabled to, operable to, or operative to perform a particular function encompasses that apparatus, system, component, whether or not it or that particular function is activated, turned on, or unlocked, as long as that apparatus, system, or component is so adapted, arranged, capable, configured, enabled, operable, or operative. Additionally, although this disclosure describes or illustrates particular embodiments as providing particular advantages, particular embodiments may provide none, some, or all of these advantages.