# Design of a Classification Recognition Model for Bone and Muscle Anatomical Imaging Based on Convolutional Neural Network and 3D Magnetic Resonance

Authors: Ting Pan; Yang Yang
Journal: Applied Bionics and Biomechanics
 (2022)

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## Abstract

In this paper, we use convolutional neural networks to conduct in-depth research and analysis on the classification and recognition of bone and muscle anatomical imaging graphics of 3D magnetic resonance and design corresponding models for practical applications. A series of medical image segmentation models based on convolutional neural networks is proposed. In this paper, firstly, a separated attention mechanism is introduced in the model, which divides the input data into multiple paths, applies self-attention weights to adjacent data paths, and finally fuses the weighted values to form the basic convolutional block. This structure has multiple parallel data paths, which increases the width of the network and therefore improves the feature extraction capability of the model. Then, this paper proposes a bidirectional feature pyramid for medical image segmentation task, which has top-down and bottom-up data paths, and, together with jump connections, can fully interact with feature maps at different scales. After that, a new activation function Mish is introduced, and its advantages over other activation functions are experimentally demonstrated. Finally, for the situation that medical image annotations are not easy to obtain, a semisupervised learning method is introduced in the model training process, and the effectiveness of this method is experimentally demonstrated. The joint network first denoises the input image, then super-resolution mapping is performed on the noise-removed feature map, and finally, the super-resolution 3D-MR image is obtained. We update the network by combining the denoising loss and super-resolution loss during the joint network training process. The experimental results show that the joint network with denoising first and then super-resolution outperforms the joint network with other task order and outperforms the method that performs the two tasks separately and the proposed method in this paper has the optimal performance.


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## Body

## 1. Introduction

Magnetic resonance (MR) imaging is a common diagnostic tool for clinical diagnosis, using the nuclei of hydrogen atoms in water molecules in the human body for imaging. MR images are the main diagnostic basis for MR examinations of patients, and the quality of MR images can directly affect the results of condition analysis for clinical diagnosis. High-quality MR images can provide more detailed information for clinical diagnosis or subsequent image processing, such as the structure of human organs and lesion areas [1, 2]. There are two ways to improve the resolution of low-resolution 3D-MR images, one is to improve the hardware performance of MRI equipment and optimize the parameters, such as increasing the magnetic field strength, increasing the number of receiving coils, and extending the scan time; the other is to perform specialized processing of MR images through image postprocessing techniques; for example, super-resolution techniques can improve the tissue contrast and spatial resolution of MR images. Artificial intelligence (AI) is science oriented discipline. It explores and simulates the function of human brain to expand and expand human intelligence. In recent years, AI technologies have made great strides in several fields such as image recognition and analysis, computer vision, and natural language processing and are widely used in many life scenarios such as education, transportation, retail, medical care, and driverless news. The medical field involves medical image diagnosis, clinical decision making, surgery planning, efficacy assessment, prognosis follow-up, pathology analysis, drug mining, and many other branches [2, 3]. On the one hand, many of these medical processes can generate massive and abundant heterogeneous, structured, and standardized data, which provides a good basis for the evolution and optimization of AI algorithms; on the other hand, under the current situation of resource shortage and long-term lack of professionals in the medical industry, AI algorithms can be integrated into the clinical workflow in a fully automated or semiautomated manner, which can improve the efficiency of doctors and relieve medical pressure, and also provide a good basis for AI research in medical scenarios that provides technical accumulation [4].Accurate segmentation of medical MR images is important in pathophysiological analysis, acquisition of key biomedical indicators, and tissue biophysical model construction. However, in practical applications, because of RF field inhomogeneity, variability between different soft tissues, and partial volume effects, MR image quality is severely degraded and manifested by poor image grayscale uniformity and confounding of the range of pixel grayscale distribution between different tissue structures, which increases the difficulty of segmenting the fine structure of MR images. In addition, the low contrast of the images, the significant diversity of soft tissue structures, and the weak edges also make segmentation difficult [5]. All these problems make the automatic and robust accurate segmentation of MR images still a challenging topic. Some existing MR image segmentation methods suffer from insufficient segmentation accuracy and low robustness. In this paper, we firstly propose an activity contour-based segmentation model to overcome the complex environment of grayscale inhomogeneity, noise, and weak edges in MR data; then, we further integrate the model into a voxel classification joint activity contour evolution segmentation framework to achieve automatic and accurate segmentation of tissue structures with signal overlap [6]. Finally, we redesigned the voxel classification architecture and the information integration of energy generalization within the segmentation framework and applied them to the multiphase segmentation of category unbalanced data with good results.Based on the existing research, we will use the perfect method to design the experiments of this paper and finally analyze and explain the experimental results in depth. The model first performs a preliminary segmentation using multiple cascaded random forests and then provides the preliminary segmentation results as initial contour and shape constraints to the multiphase active contour model using a novel a priori information integration method. Further, the multiscale and multimodal spatial constraint information from MR bulk data is integrated into the energy generalization of the active contour model using a voxel block-based sparse representation technique. Finally, the coupled level set method is used to minimize the energy generalization function to realize the multiphase fine segmentation of MR volume data. This MR bulk data segmentation model achieves satisfactory results on publicly available datasets, and the comparison experiments with current popular segmentation methods show the significant advantages of the model.


## 2. Related Works

Among many image segmentation methods, the energy generalized function-based segmentation method; i.e., the active contour model-based segmentation method is a hot research problem, which was originally used as a numerical technique for tracking boundaries and shapes and has been increasingly applied to image segmentation in the past decade [7, 8]. The basic idea of the active contour model is to describe the target contour with a continuous curve/surface, and then define the energy generalization function with this curve/surface as the independent variable, then the segmentation process is transformed into finding the minimal value of the energy generalization function, and its numerical implementation can be formalized and solved by the well-established mathematical theory, including variational and partial differential equations [9]. The active contour model has many advantages over other image segmentation methods. The energy generalization function can be defined in a continuous state, so the final contour of the target obtained has high accuracy. The target contour has smooth constraints, and the a priori information can be integrated into the energy generalization function, so the active contour model has strong robustness [10]. The active contour model uses closed curves or surfaces to represent the contours, so even for the case of non-closed contours such as the target due to occlusion, the model can still extract the closed contours, thus avoiding the preprocessing or postprocessing required by many traditional segmentation methods [11]. The numerical computation of the curves/surfaces involved can be performed in a deterministic Cartesian grid without the need for parameterization of the target [12].The proposed level set with the Gaussian selectable filter norm selective binary and Gaussian filtering regularized level set (SBGFRLS) method is a classical local segmentation method based on a local approximation of the symbolic distance function [13]. The method approximates the symbolic distance function as a finite chain of integers and improves the traditional curvature smoothing term to smooth the active contour using a Gaussian function. The model can likewise characterize arbitrary regional information in a localized form while controlling the active contour using a narrow band around the zero-level set [14]. To cope with the grayscale inhomogeneity problem encountered in medical image segmentation, the SBGFRLS model is improved by a velocity function based on local statistical information, and better segmentation results are obtained for grayscale inhomogeneous images [15]. The back-propagation algorithm was used to update the weights of the neural network model, and this research was applied to handwritten digit recognition [16]. However, due to the small number of neural network layers at that time, the trained model did not converge well and lacked a rigorous theoretical basis and mathematical derivation, the neural network development entered a low point again.The traditional convolutional neural network (CNN) is limited by the fact that the fully connected layer at the end of the CNN can only obtain one-dimensional feature vectors, and the final category information obtained is only the probability of classification, which cannot achieve pixel-level classification. The fully convolutional networks for semantic segmentation (FCN) inherits the feature extraction ability of the traditional convolutional neural network, and by replacing the last fully connected layer with a convolutional layer, the limitation that the fully connected layer can only obtain fixed-length feature vectors is broken, and by adding the deconvolutional layer, the size of the output image is unified with the input image, and the pixel-level classification of the image is realized. The emergence of FCN formally brought image semantic segmentation into the era of pixel-level classification, and thus, image segmentation entered a high-speed development stage. While the development of image segmentation at the pixel level was gradually improved, the question of whether neural networks could be extended to detect multiple individuals of the same kind of objects simultaneously was raised. The research for this problem is known as instance segmentation. Our method is more efficient and accurate than existing methods and is simpler to use and easier to apply in practice. The objective is to achieve automatic segmentation and labeling of hand skeletal structures while training the segmentation of hand skeletal structures using the U-Net model, a segmentation network commonly used in medical images, to compare the effects of two different algorithms in hand DR image segmentation.


## 3. Analysis of Convolutional Neural Network and 3D Magnetic Resonance for Classification and Identification Model of Bone and Muscle Anatomy Imaging

### 3.1. Convolutional Neural Network for 3D MRI of Bone and Muscle Anatomy Image Classification and Recognition Algorithm Design

The ordinary neural network consists of a series of fully connected layers cascaded back and forth, and the convolutional neural network upgrades it by introducing a unique convolutional layer and a pooling layer on top of it. The motivation for introducing convolutional layers is that for an image with a high resolution, the number of pixel points increases [17, 18]. For example, a color RGB image with a resolution of 500×500 has 750,000 feature points, and using a fully connected layer for image feature extraction would result in a network with a huge number of parameters and a huge increase in computation. The introduction of the convolutional layer alleviates these problems gracefully. Adding a pooling layer to the network structure can further reduce the number of parameters and computation and improve the feature extraction capability of the network.The convolution operation in the convolution layer is done by sliding the convolution kernel through the input image or feature map. The intermediate result of the original input image obtained by operations such as convolution or pooling is called the feature map. The convolution kernel is composed of a set of two-dimensional matrices equal in number to the number of channels of the input data, usually of square odd values ranging in size from1×1 to 7×7. Because odd values more directly determine the centroid of the convolution kernel, a large kernel can lead to a significant increase in the number of parameters and computation time.As shown in Figure1, the convolution kernel is slid on the feature map of the previous layer from top to bottom, and the area where the kernel covers the feature map to be convolved is called the sliding window. Each time the window is slid, the values in the sliding window are weighted and summed with the corresponding values of the convolution kernel, and a series of values are obtained [19]. These values are arranged as a two-dimensional matrix in the order of the sliding windows, which is the result of the convolution operation. The operation is shown in
(1)Xl=ConcatWkl−1∗Xl−bkl+1,where Wkl−1 denotes the parameters of the kth group of convolutional kernels acting in the layer l−1 network, Xl is the feature map of the layer l network, bkl+1 is the bias parameter corresponding to Wkl−1 the final combination of the convolutional results of all convolutional kernels, and the feature map Xl of the layer U network is obtained.Figure 1
Convolution principle.Local connectivity is where improvements are made for full connectivity. In an image, more critical image edges, corner points, and other features occupy only a small region of the image, and only the values near the key feature pixel points interact more significantly, which is called the local relevance of the image. It is because of this property that we can maintain the feature extraction capability of the network by making local connections in the spatial direction of the image [20]. In addition, feature extraction by full connectivity requires pulling two-dimensional images into a one-dimensional data format, which has the major disadvantage of ignoring the spatial correlation between pixel points. The convolution operation can well uncover the spatial relationships between pixel points by using a two-dimensional convolution kernel sliding over the image to extract features.Equivariant representation means that if a part of the image is spatially shifted since the convolutional kernel weights are shared, the associated eigenvalues of the feature map in the subsequent neural network layers will also be shifted. This way the element values on the feature map will also have spatial characteristics, which is significant for image segmentation. Moreover, the spatial position of some parts of the image is transformed so that the convolutional kernel can still perform accurate recognition and the results of tasks such as image classification do not change much. So, the covariant representation is also another representation of translation invariance in convolutional neural networks.The pooling operation is essentially a downsampling operation, which serves to complete the compression and downsampling of features, reduce the number of neural network parameters, and avoid overfitting during training. The pooling operation is also performed on the input image X in a sliding manner, and the activation values of the neurons in the area covered by each pooling kernel are selected as representative values according to some rules and output.This approach reduces the problem of gradient disappearance and allows the gradient values to be back-propagated more deeply. The Xavier initialization works very well for the tanh activation function, but the improvement is not so obvious for the more used ReLU activation function. The Xavier initialization satisfies the following equation’s uniform distribution:(2)W~U8nk−nk−1,8nk+nk−1,where W is the parameter of the current network layer, nk denotes the input dimension of the layer where W is located, and nk−1 denotes the dimension of the layer after W, which is also the dimension of the layer where W is located.Methionine sulfoxide reductase A (MSRA) initialization, also known as He initialization, is an initialization method proposed for the ReLU activation function. After the input value is passed through the ReLU function, it will output more 0 values, and the variance will change more. The improvement of MRSA over Xavier is that the value of Xavier initialization can be multiplied by2/mn, which is the dimension of the previous layer of the network so that the initial value of the parameter can be avoided to being too large or too small. For activation functions such as ReLU, the results are much better, so this initialization is now in higher use.In the MSRA initialization approach, the parameter distribution for the rectified linear unit (ReLU) activation function, considered in the forward propagation approach, satisfies the following equation:(3)W~N0,4fanin.For the leaky ReLU activation function, the following equation is satisfied:(4)W~N0,41−a2fanin,where fanin denotes the dimension of the current input layer and a is the slope of the Leaky ReLU on the negative half-axis. The left half is the encoder, where the input image is downsampled every two convolutional layers, and there are 4 downsampling processes in total. The right half is the decoder, which also follows two convolutional layers for decoding after each upsampling. During the upsampling process, the network combines the image information with the feature maps from the sibling encoders through a jump connection. The feature map of the last layer of the decoder is processed by a convolutional kernel of size 1×1 so that the number of channels equals the number of categories [21].After the fully connected layer at the very end of the network, the softmax function is used as the output layer. In AlexNet, the convolutional kernel size is reduced from11×11 to 5×5 and then to 3×3, by decreasing the convolutional kernel size layer by layer to control the appropriate receptive field and focus on specific regions in the input from coarse to fine. In addition, the local connectivity property of the convolutional neural network enables it to maintain translation and rotation invariance to the input. And the weight sharing can effectively reduce the network parameters and improve the training efficiency. The convolutional neural network also adopts the supervised training mode and uses the back-propagation algorithm to implement the parameter updating process, as shown in Figure 2.Figure 2
Schematic diagram of U-net structure.The commonly used FCN model usually consists of an encoder and a decoder. The encoder often consists of multiple convolutional layers connected, and this part often borrows from some classical CNN networks and removes the fully connected layers from them to complete the extraction of abstract features and output the feature map. The decoder, on the other hand, upsamples the compressed feature map to reduce it to the original output size and obtain the semantic segmentation image.In this step, the low-dimensional feature map needs to be mapped to the high-dimensional original space, and this process is done by a special convolutional layer, i.e., the deconvolutional layer, which can also be called the transposed convolutional layer. For an arbitrary high-dimensional inputX, the low-dimensional feature map output by the convolution operation is represented as Y. The relationship between the two can be expressed as:
(5)Y=w⋅X,where w denotes the weight. Then, based on the above equation, it is known that
(6)X=wT⋅Y,where wT represents an inverted matrix. The encoder in the FCN-32s model is composed of a combination of 5 group convolutional and pooling layers connected, and the output feature map is reduced to the 1/2,1/4,1/8,1/16,1/32 source input in turn after each substructure operation. The decoder, on the other hand, consists of only one layer of deconvolution layers, and the compressed feature maps are reduced to the original output size in one go. Finally, the softmax function is used to perform pixel-by-pixel category prediction and to complete the image segmentation. In terms of network performance, the structure of FCN-32s is relatively simple and involves only one layer of deconvolution, which often results in rough segmentation edges due to insufficient detail filling.The encoder of U-net adopts a structure like that of FCN-32 and undergoes four pooling cycles involving 5, a total of four different feature dimensions [22]. The decoder of U-net adopts the same symmetric structure as its encoder and uses a deconvolution layer to gradually complete the expansion process of compressed features. Unlike the pixel-by-pixel addition in the FCN network, U-net adopts the skip connection mechanism, which directly splices the encoded features and decoded features in the same feature dimension. This method fuses features of different scales, improves data reuse, and maximizes the extraction of boundary contours in the segmentation target. Therefore, U-net can show good segmentation performance on small sample grayscale datasets and has been regarded as a classic basic model in medical image segmentation tasks.


### 3.2. Experimental Design for the Classification of Bone and Muscle Anatomical Figures by Dimensional Magnetic Resonance

In this paper, when the migration learning is carried out in the experiment because the pretraining model of the COCO dataset is invoked, the JSON data format obtained by VIA data annotation is not uniform with the training data format of the COCO dataset; to ensure that the training data can participate in training normally, the JSON data format exported after the completion of VIA annotation needs to be converted to the JSON in COCO dataset format in the COCO dataset. The specific operation to realize the conversion of the two JSON file data formats is to expand the dict in the VIA format JSON file layer by layer and put it into the dict in the COCO dataset format according to the corresponding data location, as shown in Figure3.Figure 3
Flowchart of active shape model segmentation.The network training structure of the experiments in this chapter is based on the Reset-101 network with the introduction of bottleneck structure; firstly, the pretraining model is loaded, and the pretraining model of the COCO dataset is used for the training of this dataset; and the network weights are retained to speed up the convergence speed of the network, and the network performance is further improved by the subsequent adjustment of some training parameters.Combined with the object of this experiment and the hardware conditions, the batch size value is set to 2; at the same time, to obtain a better network segmentation model, this experiment will take 50 and 100 two values for epoch, respectively, each to complete an experiment, and compare the performance of the two models. Mask R-CNN in the original experiment, and the learning rate is initially set to 0.02, but because the experiments in this chapter are built on the TensorFlow framework structure, 0.02 the learning rate is prone to gradient explosion, so the learning rate is chosen 0.001 for the experiments in this chapter, the momentum term coefficient is 0.9 set to, and the weight decay value is set to 0.0001.The automatic segmentation and labeling model of hand skeletal structure based on Mask R-CNN framework completes the image segmentation based on the classification task and labels each segmented skeletal structure at the same time. To evaluate the effectiveness of the segmentation model trained in this chapter, the mapped value, i.e., the average of the predicted AP values for each hand skeletal category segmentation, is used as the evaluation index [23]. The AP value is based on the area under the PR curve formed by the precision and recall of the model prediction in the right-angle coordinate system, where the precision is the y-axis and the recall is the x-axis, and the precision and recall are calculated as follows:
(7)Precision=TPTP‐FP,(8)Recall=TPTP‐FN.In this paper, the experiments were first conducted with the original Mask R-CNN for automatic segmentation and labeling of hand skeletal structures, and then, the improved Mask R-CNN was used to improve the network structure for the problems exhibited during the experiments. With the same training samples and other training parameters set the same, the training results of the two methods are shown in Table1. Table 1 shows that the improved Mask R-CNN has a higher mAP value and faster detection speed; i.e., it can automatically segment and label the skeletal structures of the hand faster and more accurately.Table 1
Configuration of the experimental platform.
ParameterConfigurePython video memory3.6GPU16GTensorFlowNVIDIA 396.82Keras1.12.0In this study, 10 (KKI33-KKI42) T1-weighted image 3D MRI images from the publicly available clinical real dataset, Kirby dataset, with a resolution of1×1×1.2 mm3 and an image size of 170×256×256 were used as the training set data. This study used the Bratsk dataset containing gliomas as well as the Brainweb dataset to test the trained network model. Among them, BraTS was tested using T1-weighted images and T2-weighted images published in 2015 with a resolution of 1×1×1 mm3 and an image size of 240×240×155, which is a real clinical dataset; T1-weighted images from the Brainweb dataset were tested with a resolution of 1×1×1 mm3 and an image size of 181 × 217 × 181, which is a simulated dataset.The traditional live wire algorithm uses Dijkstra’s algorithm to calculate the cost function when performing the steps related to path search, and the calculation process starts from the seed point and expands outward, and each round goes to calculate the eight-neighborhood cost function value for the minimum point of the cost function on the edge of the region that has been calculated, so the edge of the calculated region needs to be found before each round of expanding the cost function. The traditional algorithm implements this part by first traversing the whole image to find the target edges before each round of computation, and the time complexity of this operation isON∗M, where N and M are the image length and width. However, considering that the edge update of the computed region in each round only occurs in the eight neighborhoods of the minimum cost function points, and the rest of the boundary points remain untouched, it can be optimized here to make full use of the boundary information of the previous round, examine the local update of the boundary and the computed region, and derive the updated edge for the next round of computation, as shown in Figure 4.Figure 4
Improved boundary search strategy.The left side of the figure shows an example of the state after one round of cost function calculation, the gray dots and black dots are the pixel points for which the cost function has been calculated, the gray dots are the points in the region, and the black dots are the edge points [24–29]. The white dots are the pixel points for which the cost function has not been computed yet. The center of the dashed rectangle is the target pixel with the smallest cost function to the edge pixel, and the eight surrounding points are the eight neighborhoods, where a new round of cost function calculation is performed. The cost function of the uncomputed pixels in the eight neighborhoods is computed first, and the edge update operation is performed based on the edge pixels (the coordinates of the pixel points have been stored in a chain table in this round before the next round of cost function computation).


## 3.1. Convolutional Neural Network for 3D MRI of Bone and Muscle Anatomy Image Classification and Recognition Algorithm Design

The ordinary neural network consists of a series of fully connected layers cascaded back and forth, and the convolutional neural network upgrades it by introducing a unique convolutional layer and a pooling layer on top of it. The motivation for introducing convolutional layers is that for an image with a high resolution, the number of pixel points increases [17, 18]. For example, a color RGB image with a resolution of 500×500 has 750,000 feature points, and using a fully connected layer for image feature extraction would result in a network with a huge number of parameters and a huge increase in computation. The introduction of the convolutional layer alleviates these problems gracefully. Adding a pooling layer to the network structure can further reduce the number of parameters and computation and improve the feature extraction capability of the network.The convolution operation in the convolution layer is done by sliding the convolution kernel through the input image or feature map. The intermediate result of the original input image obtained by operations such as convolution or pooling is called the feature map. The convolution kernel is composed of a set of two-dimensional matrices equal in number to the number of channels of the input data, usually of square odd values ranging in size from1×1 to 7×7. Because odd values more directly determine the centroid of the convolution kernel, a large kernel can lead to a significant increase in the number of parameters and computation time.As shown in Figure1, the convolution kernel is slid on the feature map of the previous layer from top to bottom, and the area where the kernel covers the feature map to be convolved is called the sliding window. Each time the window is slid, the values in the sliding window are weighted and summed with the corresponding values of the convolution kernel, and a series of values are obtained [19]. These values are arranged as a two-dimensional matrix in the order of the sliding windows, which is the result of the convolution operation. The operation is shown in
(1)Xl=ConcatWkl−1∗Xl−bkl+1,where Wkl−1 denotes the parameters of the kth group of convolutional kernels acting in the layer l−1 network, Xl is the feature map of the layer l network, bkl+1 is the bias parameter corresponding to Wkl−1 the final combination of the convolutional results of all convolutional kernels, and the feature map Xl of the layer U network is obtained.Figure 1
Convolution principle.Local connectivity is where improvements are made for full connectivity. In an image, more critical image edges, corner points, and other features occupy only a small region of the image, and only the values near the key feature pixel points interact more significantly, which is called the local relevance of the image. It is because of this property that we can maintain the feature extraction capability of the network by making local connections in the spatial direction of the image [20]. In addition, feature extraction by full connectivity requires pulling two-dimensional images into a one-dimensional data format, which has the major disadvantage of ignoring the spatial correlation between pixel points. The convolution operation can well uncover the spatial relationships between pixel points by using a two-dimensional convolution kernel sliding over the image to extract features.Equivariant representation means that if a part of the image is spatially shifted since the convolutional kernel weights are shared, the associated eigenvalues of the feature map in the subsequent neural network layers will also be shifted. This way the element values on the feature map will also have spatial characteristics, which is significant for image segmentation. Moreover, the spatial position of some parts of the image is transformed so that the convolutional kernel can still perform accurate recognition and the results of tasks such as image classification do not change much. So, the covariant representation is also another representation of translation invariance in convolutional neural networks.The pooling operation is essentially a downsampling operation, which serves to complete the compression and downsampling of features, reduce the number of neural network parameters, and avoid overfitting during training. The pooling operation is also performed on the input image X in a sliding manner, and the activation values of the neurons in the area covered by each pooling kernel are selected as representative values according to some rules and output.This approach reduces the problem of gradient disappearance and allows the gradient values to be back-propagated more deeply. The Xavier initialization works very well for the tanh activation function, but the improvement is not so obvious for the more used ReLU activation function. The Xavier initialization satisfies the following equation’s uniform distribution:(2)W~U8nk−nk−1,8nk+nk−1,where W is the parameter of the current network layer, nk denotes the input dimension of the layer where W is located, and nk−1 denotes the dimension of the layer after W, which is also the dimension of the layer where W is located.Methionine sulfoxide reductase A (MSRA) initialization, also known as He initialization, is an initialization method proposed for the ReLU activation function. After the input value is passed through the ReLU function, it will output more 0 values, and the variance will change more. The improvement of MRSA over Xavier is that the value of Xavier initialization can be multiplied by2/mn, which is the dimension of the previous layer of the network so that the initial value of the parameter can be avoided to being too large or too small. For activation functions such as ReLU, the results are much better, so this initialization is now in higher use.In the MSRA initialization approach, the parameter distribution for the rectified linear unit (ReLU) activation function, considered in the forward propagation approach, satisfies the following equation:(3)W~N0,4fanin.For the leaky ReLU activation function, the following equation is satisfied:(4)W~N0,41−a2fanin,where fanin denotes the dimension of the current input layer and a is the slope of the Leaky ReLU on the negative half-axis. The left half is the encoder, where the input image is downsampled every two convolutional layers, and there are 4 downsampling processes in total. The right half is the decoder, which also follows two convolutional layers for decoding after each upsampling. During the upsampling process, the network combines the image information with the feature maps from the sibling encoders through a jump connection. The feature map of the last layer of the decoder is processed by a convolutional kernel of size 1×1 so that the number of channels equals the number of categories [21].After the fully connected layer at the very end of the network, the softmax function is used as the output layer. In AlexNet, the convolutional kernel size is reduced from11×11 to 5×5 and then to 3×3, by decreasing the convolutional kernel size layer by layer to control the appropriate receptive field and focus on specific regions in the input from coarse to fine. In addition, the local connectivity property of the convolutional neural network enables it to maintain translation and rotation invariance to the input. And the weight sharing can effectively reduce the network parameters and improve the training efficiency. The convolutional neural network also adopts the supervised training mode and uses the back-propagation algorithm to implement the parameter updating process, as shown in Figure 2.Figure 2
Schematic diagram of U-net structure.The commonly used FCN model usually consists of an encoder and a decoder. The encoder often consists of multiple convolutional layers connected, and this part often borrows from some classical CNN networks and removes the fully connected layers from them to complete the extraction of abstract features and output the feature map. The decoder, on the other hand, upsamples the compressed feature map to reduce it to the original output size and obtain the semantic segmentation image.In this step, the low-dimensional feature map needs to be mapped to the high-dimensional original space, and this process is done by a special convolutional layer, i.e., the deconvolutional layer, which can also be called the transposed convolutional layer. For an arbitrary high-dimensional inputX, the low-dimensional feature map output by the convolution operation is represented as Y. The relationship between the two can be expressed as:
(5)Y=w⋅X,where w denotes the weight. Then, based on the above equation, it is known that
(6)X=wT⋅Y,where wT represents an inverted matrix. The encoder in the FCN-32s model is composed of a combination of 5 group convolutional and pooling layers connected, and the output feature map is reduced to the 1/2,1/4,1/8,1/16,1/32 source input in turn after each substructure operation. The decoder, on the other hand, consists of only one layer of deconvolution layers, and the compressed feature maps are reduced to the original output size in one go. Finally, the softmax function is used to perform pixel-by-pixel category prediction and to complete the image segmentation. In terms of network performance, the structure of FCN-32s is relatively simple and involves only one layer of deconvolution, which often results in rough segmentation edges due to insufficient detail filling.The encoder of U-net adopts a structure like that of FCN-32 and undergoes four pooling cycles involving 5, a total of four different feature dimensions [22]. The decoder of U-net adopts the same symmetric structure as its encoder and uses a deconvolution layer to gradually complete the expansion process of compressed features. Unlike the pixel-by-pixel addition in the FCN network, U-net adopts the skip connection mechanism, which directly splices the encoded features and decoded features in the same feature dimension. This method fuses features of different scales, improves data reuse, and maximizes the extraction of boundary contours in the segmentation target. Therefore, U-net can show good segmentation performance on small sample grayscale datasets and has been regarded as a classic basic model in medical image segmentation tasks.


## 3.2. Experimental Design for the Classification of Bone and Muscle Anatomical Figures by Dimensional Magnetic Resonance

In this paper, when the migration learning is carried out in the experiment because the pretraining model of the COCO dataset is invoked, the JSON data format obtained by VIA data annotation is not uniform with the training data format of the COCO dataset; to ensure that the training data can participate in training normally, the JSON data format exported after the completion of VIA annotation needs to be converted to the JSON in COCO dataset format in the COCO dataset. The specific operation to realize the conversion of the two JSON file data formats is to expand the dict in the VIA format JSON file layer by layer and put it into the dict in the COCO dataset format according to the corresponding data location, as shown in Figure3.Figure 3
Flowchart of active shape model segmentation.The network training structure of the experiments in this chapter is based on the Reset-101 network with the introduction of bottleneck structure; firstly, the pretraining model is loaded, and the pretraining model of the COCO dataset is used for the training of this dataset; and the network weights are retained to speed up the convergence speed of the network, and the network performance is further improved by the subsequent adjustment of some training parameters.Combined with the object of this experiment and the hardware conditions, the batch size value is set to 2; at the same time, to obtain a better network segmentation model, this experiment will take 50 and 100 two values for epoch, respectively, each to complete an experiment, and compare the performance of the two models. Mask R-CNN in the original experiment, and the learning rate is initially set to 0.02, but because the experiments in this chapter are built on the TensorFlow framework structure, 0.02 the learning rate is prone to gradient explosion, so the learning rate is chosen 0.001 for the experiments in this chapter, the momentum term coefficient is 0.9 set to, and the weight decay value is set to 0.0001.The automatic segmentation and labeling model of hand skeletal structure based on Mask R-CNN framework completes the image segmentation based on the classification task and labels each segmented skeletal structure at the same time. To evaluate the effectiveness of the segmentation model trained in this chapter, the mapped value, i.e., the average of the predicted AP values for each hand skeletal category segmentation, is used as the evaluation index [23]. The AP value is based on the area under the PR curve formed by the precision and recall of the model prediction in the right-angle coordinate system, where the precision is the y-axis and the recall is the x-axis, and the precision and recall are calculated as follows:
(7)Precision=TPTP‐FP,(8)Recall=TPTP‐FN.In this paper, the experiments were first conducted with the original Mask R-CNN for automatic segmentation and labeling of hand skeletal structures, and then, the improved Mask R-CNN was used to improve the network structure for the problems exhibited during the experiments. With the same training samples and other training parameters set the same, the training results of the two methods are shown in Table1. Table 1 shows that the improved Mask R-CNN has a higher mAP value and faster detection speed; i.e., it can automatically segment and label the skeletal structures of the hand faster and more accurately.Table 1
Configuration of the experimental platform.
ParameterConfigurePython video memory3.6GPU16GTensorFlowNVIDIA 396.82Keras1.12.0In this study, 10 (KKI33-KKI42) T1-weighted image 3D MRI images from the publicly available clinical real dataset, Kirby dataset, with a resolution of1×1×1.2 mm3 and an image size of 170×256×256 were used as the training set data. This study used the Bratsk dataset containing gliomas as well as the Brainweb dataset to test the trained network model. Among them, BraTS was tested using T1-weighted images and T2-weighted images published in 2015 with a resolution of 1×1×1 mm3 and an image size of 240×240×155, which is a real clinical dataset; T1-weighted images from the Brainweb dataset were tested with a resolution of 1×1×1 mm3 and an image size of 181 × 217 × 181, which is a simulated dataset.The traditional live wire algorithm uses Dijkstra’s algorithm to calculate the cost function when performing the steps related to path search, and the calculation process starts from the seed point and expands outward, and each round goes to calculate the eight-neighborhood cost function value for the minimum point of the cost function on the edge of the region that has been calculated, so the edge of the calculated region needs to be found before each round of expanding the cost function. The traditional algorithm implements this part by first traversing the whole image to find the target edges before each round of computation, and the time complexity of this operation isON∗M, where N and M are the image length and width. However, considering that the edge update of the computed region in each round only occurs in the eight neighborhoods of the minimum cost function points, and the rest of the boundary points remain untouched, it can be optimized here to make full use of the boundary information of the previous round, examine the local update of the boundary and the computed region, and derive the updated edge for the next round of computation, as shown in Figure 4.Figure 4
Improved boundary search strategy.The left side of the figure shows an example of the state after one round of cost function calculation, the gray dots and black dots are the pixel points for which the cost function has been calculated, the gray dots are the points in the region, and the black dots are the edge points [24–29]. The white dots are the pixel points for which the cost function has not been computed yet. The center of the dashed rectangle is the target pixel with the smallest cost function to the edge pixel, and the eight surrounding points are the eight neighborhoods, where a new round of cost function calculation is performed. The cost function of the uncomputed pixels in the eight neighborhoods is computed first, and the edge update operation is performed based on the edge pixels (the coordinates of the pixel points have been stored in a chain table in this round before the next round of cost function computation).


## 4. Analysis of Results

### 4.1. Convolutional Neural Network Algorithm Performance Results Analysis

We evaluate the proposed network model using T1-weighted and T2-weighted images on the DHCP dataset, comparing algorithms including five methods, bicubic interpolation (bicubic), and four deep learning methods, SRCNN-3D, FSRCNN-3D, ReCNN-3D, and DCSRN, respectively. We compute the mean and variance of the T1- and T2-weighted images in the test dataset. We calculated the mean and variance of PSNR and SSIM for T1- and T2-weighted images in the test dataset.The test results of each algorithm on T1-weighted images are shown in Figure5. Among them, DCACNN has the best performance among all the compared algorithms with PSNR value 51.80 and SSIM value. As 0.97015 can be observed from the figure, the deep learning-based super-resolution algorithm significantly outperforms the bicubic interpolation algorithm, with both PSNR values being 2 dB higher and SSIM values being higher 0.02. Our proposed DCACNN is 0.35 dB higher in PSNR value and higher 0.059 in SSIM value than the best performing existing super-resolution algorithm, ReCNN-3D, with good reconstruction results. Figure 4 shows the subjective visual plots of different algorithms on the test set, from which the reconstruction of DCACNN outperforms the other algorithms for both 3D-MR images and its 2D slices.Figure 5
Test results of the algorithm on T1- and T2-weighted images.The test results on T2-weighted images are shown in Figure4, the PSNR value of DCACNN is 49.36, and the SSIM value is 0.9746, which is still the best performance among all the algorithms. The PSNR value of DCACNN on T2-weighted images is still 4 dB higher than that of the bicubic interpolation algorithm, and 0.35 dB higher than that of CNN, the best 3D MRI super-resolution reconstruction algorithm. From this, our proposed DCACNN has good performance on multimodal data.The deep learning-based super-resolution algorithms used in the experimental process can be broadly classified into two categories, one is to use upsampling to enlarge the image at the beginning of the network, e.g., SRCNN-3D and ReCNN-3D, and the other is to use upsampling to enlarge the image at the end of the network, e.g., fast super-resolution by convolutional neural network-3D (FSRCNN-3D), distributed control system (DCS), certified associate convolutional neural network (DCACNN), and sample rate convertor convolutional neural network (SRCNN). SRCNN-3D and ReCNN-3D have a smaller number of parameters, but their computational complexity is higher than the latter algorithms.In this section, we also study the performance of joint and separate tasks. We first perform the joint strategy for the two tasks mentioned above and then perform the separate tasks separately. The tests were performed with a super-resolution factor of 2 and a noise level of 0.2, and the quantitative comparison results are shown in Figure6. The joint scheme generally outperforms the scheme without the joint strategy for the same task order case. As in the above experiments, the numerical performance of the reconstructed images decreases sharply when denoising is not performed first. As can be seen from the third row of Figure 6, the model that performs denoising and super-resolution alone also obtains good performance when denoising is performed first, which also justifies the order in which we go in for the joint task. It can be seen from the last two rows that the joint execution of denoising and super-resolution tasks outperforms the other solutions under large networks. In addition, we can further improve the performance using the additional denoising loss ℒ𝑑𝑒𝑛𝑜𝑖𝑠𝑒, which also verifies the effectiveness of our use of the joint loss function.Figure 6
Quantitative comparison of denoising and super-resolution mixing problems.The reconstructed images have severe artifacts if the super-resolution task is performed first for either the joint task or the separate task. Next, a new super-resolution reconstruction algorithm for neonatal 3D-MR images was constructed using an attention mechanism and a two-domain learning strategy. Using the discrete cosine transform for the interconversion of the spatial and frequency domains of the data, the 3D-MR image imaging process itself is in the frequency domain, and the network can make the features rich and diverse by using the information in the frequency domain of the images themselves in the process of feature extraction. The attention mechanism can make the network learn the feature information more efficiently and only learn the part that needs attention, which not only reduces the computational load of the network but also improves the learning efficiency of the network and lays the foundation for the subsequent upsampling reconstruction process.


### 4.2. Experimental Results of Anatomical Pattern Classification of Bone and Muscle by Dimensional Magnetic Resonance

The angular error box line diagram of the test data is shown in Figure7. Where SAX is the short-axis plane, 4 chamber is the four-chamber core plane, 3 chamber is the three-chamber core plane, and 2 chamber is the two-chamber core plane, all of which have the same meaning in the following graphs. Of all the angular errors, SAX has a median of 2.2°, with a minimum value of 0.2°. 4 chamber has a median of 3.73°, which is slightly higher than SAX. 3 chamber has a median of 3.41°, which is slightly lower than 4 chamber, but has a maximum value of 7.70°. 2 chamber has a median of 3.79°, which is moderate. The overall positioning effect is moderate. From the figure, we can observe that the short-axis plane has the smallest mean angular error concerning the other planes, and the 3-chamber center plane has the largest mean angular error among all planes.Figure 7
Angle error box line diagram.The median of SAX is 0.81 mm, which is the lowest among all planes. The median value of 4 chamber is 0.89 mm, which is slightly larger than SAX, but the overall error distribution is reduced. 3 chamber and 2 chamber both have a median value of 1.21 mm, but the former has a lower mean error value than the latter. From the above data, in the short-axis plane positioning, there are more cases with good positioning effect, but there are cases with large position offset; the two-chamber and four-chamber planes have moderate position errors, and the three-chamber plane has the best overall performance.The proposed method has the largest angular and positional errors in the plane, where the mean and standard deviation of angular errors are8.6±9.7, 19.2±8.5, 12.3±11.0, and 18.9±2.1 for SAX, 4 chamber, 3 chamber, and 2 chamber, respectively, and the mean and standard deviation of positional errors are 11.7±20.6, 5.7±8.5, 4.6±7.7, and 6.6±8.8, respectively. Since the traditional method is not accurate enough in modeling, it will lead to the poor localization effect of the method because the shape of that slice is not standard enough to fit the real data situation when acquiring a certain slice in the model, and then, there will be a large deviation in finding the geometric relationship of the plane.Figure8 shows the segmentation results of the automatic segmentation model of the ablation region after multiphase phacoemulsification on an independent test set. The Dice coefficients of this model for segmentation of ablation region in venous phase and arterial phase CT images are 89.06% and 82.83% with F1 scores of 0.73 and 0.74, respectively. So far, few deep-learning-based automatic segmentation algorithms have been applied to the task of automatic segmentation of postablation ablation regions in images. And the accurate segmentation of the postablation ablation region can help to evaluate the ablation procedure treatment effect. This step has a significant impact on the prognosis of patients with malignant liver tumors and can directly influence the subsequent treatment plan. As shown in Figure 8, the results of preoperative tumor segmentation and postoperative ablation region segmentation for a group of the same cases are shown schematically.Figure 8
Graphical recognition of splitting results.In the feature selection process, expert experience only qualitatively observed to select the optimal layer, and precise mathematical evaluation metrics are still lacking. In addition, the integration network and feature selection workflow proposed in this paper should apply to more deep learning frameworks and clinical scenarios. In the future, we will continue to explore the flexibility and scalability of the multiscale fusion model in this chapter and validate it in more medical images or diseases with different modalities.Indeed, a longer follow-up time would improve the diagnostic accuracy of physicians and reinforce the credibility of the automatic diagnostic algorithm. Moreover, during the feature selection process, expert experience selects the optimal layer by qualitative observation-only, and precise mathematical evaluation metrics are still lacking. In addition, the integrated network and feature selection workflow proposed in this paper should apply to more deep learning frameworks and clinical scenarios. In the future, we will continue to explore the flexibility and scalability of the multiscale fusion model in this chapter and validate it in more medical images or diseases with different modalities.


## 4.1. Convolutional Neural Network Algorithm Performance Results Analysis

We evaluate the proposed network model using T1-weighted and T2-weighted images on the DHCP dataset, comparing algorithms including five methods, bicubic interpolation (bicubic), and four deep learning methods, SRCNN-3D, FSRCNN-3D, ReCNN-3D, and DCSRN, respectively. We compute the mean and variance of the T1- and T2-weighted images in the test dataset. We calculated the mean and variance of PSNR and SSIM for T1- and T2-weighted images in the test dataset.The test results of each algorithm on T1-weighted images are shown in Figure5. Among them, DCACNN has the best performance among all the compared algorithms with PSNR value 51.80 and SSIM value. As 0.97015 can be observed from the figure, the deep learning-based super-resolution algorithm significantly outperforms the bicubic interpolation algorithm, with both PSNR values being 2 dB higher and SSIM values being higher 0.02. Our proposed DCACNN is 0.35 dB higher in PSNR value and higher 0.059 in SSIM value than the best performing existing super-resolution algorithm, ReCNN-3D, with good reconstruction results. Figure 4 shows the subjective visual plots of different algorithms on the test set, from which the reconstruction of DCACNN outperforms the other algorithms for both 3D-MR images and its 2D slices.Figure 5
Test results of the algorithm on T1- and T2-weighted images.The test results on T2-weighted images are shown in Figure4, the PSNR value of DCACNN is 49.36, and the SSIM value is 0.9746, which is still the best performance among all the algorithms. The PSNR value of DCACNN on T2-weighted images is still 4 dB higher than that of the bicubic interpolation algorithm, and 0.35 dB higher than that of CNN, the best 3D MRI super-resolution reconstruction algorithm. From this, our proposed DCACNN has good performance on multimodal data.The deep learning-based super-resolution algorithms used in the experimental process can be broadly classified into two categories, one is to use upsampling to enlarge the image at the beginning of the network, e.g., SRCNN-3D and ReCNN-3D, and the other is to use upsampling to enlarge the image at the end of the network, e.g., fast super-resolution by convolutional neural network-3D (FSRCNN-3D), distributed control system (DCS), certified associate convolutional neural network (DCACNN), and sample rate convertor convolutional neural network (SRCNN). SRCNN-3D and ReCNN-3D have a smaller number of parameters, but their computational complexity is higher than the latter algorithms.In this section, we also study the performance of joint and separate tasks. We first perform the joint strategy for the two tasks mentioned above and then perform the separate tasks separately. The tests were performed with a super-resolution factor of 2 and a noise level of 0.2, and the quantitative comparison results are shown in Figure6. The joint scheme generally outperforms the scheme without the joint strategy for the same task order case. As in the above experiments, the numerical performance of the reconstructed images decreases sharply when denoising is not performed first. As can be seen from the third row of Figure 6, the model that performs denoising and super-resolution alone also obtains good performance when denoising is performed first, which also justifies the order in which we go in for the joint task. It can be seen from the last two rows that the joint execution of denoising and super-resolution tasks outperforms the other solutions under large networks. In addition, we can further improve the performance using the additional denoising loss ℒ𝑑𝑒𝑛𝑜𝑖𝑠𝑒, which also verifies the effectiveness of our use of the joint loss function.Figure 6
Quantitative comparison of denoising and super-resolution mixing problems.The reconstructed images have severe artifacts if the super-resolution task is performed first for either the joint task or the separate task. Next, a new super-resolution reconstruction algorithm for neonatal 3D-MR images was constructed using an attention mechanism and a two-domain learning strategy. Using the discrete cosine transform for the interconversion of the spatial and frequency domains of the data, the 3D-MR image imaging process itself is in the frequency domain, and the network can make the features rich and diverse by using the information in the frequency domain of the images themselves in the process of feature extraction. The attention mechanism can make the network learn the feature information more efficiently and only learn the part that needs attention, which not only reduces the computational load of the network but also improves the learning efficiency of the network and lays the foundation for the subsequent upsampling reconstruction process.


## 4.2. Experimental Results of Anatomical Pattern Classification of Bone and Muscle by Dimensional Magnetic Resonance

The angular error box line diagram of the test data is shown in Figure7. Where SAX is the short-axis plane, 4 chamber is the four-chamber core plane, 3 chamber is the three-chamber core plane, and 2 chamber is the two-chamber core plane, all of which have the same meaning in the following graphs. Of all the angular errors, SAX has a median of 2.2°, with a minimum value of 0.2°. 4 chamber has a median of 3.73°, which is slightly higher than SAX. 3 chamber has a median of 3.41°, which is slightly lower than 4 chamber, but has a maximum value of 7.70°. 2 chamber has a median of 3.79°, which is moderate. The overall positioning effect is moderate. From the figure, we can observe that the short-axis plane has the smallest mean angular error concerning the other planes, and the 3-chamber center plane has the largest mean angular error among all planes.Figure 7
Angle error box line diagram.The median of SAX is 0.81 mm, which is the lowest among all planes. The median value of 4 chamber is 0.89 mm, which is slightly larger than SAX, but the overall error distribution is reduced. 3 chamber and 2 chamber both have a median value of 1.21 mm, but the former has a lower mean error value than the latter. From the above data, in the short-axis plane positioning, there are more cases with good positioning effect, but there are cases with large position offset; the two-chamber and four-chamber planes have moderate position errors, and the three-chamber plane has the best overall performance.The proposed method has the largest angular and positional errors in the plane, where the mean and standard deviation of angular errors are8.6±9.7, 19.2±8.5, 12.3±11.0, and 18.9±2.1 for SAX, 4 chamber, 3 chamber, and 2 chamber, respectively, and the mean and standard deviation of positional errors are 11.7±20.6, 5.7±8.5, 4.6±7.7, and 6.6±8.8, respectively. Since the traditional method is not accurate enough in modeling, it will lead to the poor localization effect of the method because the shape of that slice is not standard enough to fit the real data situation when acquiring a certain slice in the model, and then, there will be a large deviation in finding the geometric relationship of the plane.Figure8 shows the segmentation results of the automatic segmentation model of the ablation region after multiphase phacoemulsification on an independent test set. The Dice coefficients of this model for segmentation of ablation region in venous phase and arterial phase CT images are 89.06% and 82.83% with F1 scores of 0.73 and 0.74, respectively. So far, few deep-learning-based automatic segmentation algorithms have been applied to the task of automatic segmentation of postablation ablation regions in images. And the accurate segmentation of the postablation ablation region can help to evaluate the ablation procedure treatment effect. This step has a significant impact on the prognosis of patients with malignant liver tumors and can directly influence the subsequent treatment plan. As shown in Figure 8, the results of preoperative tumor segmentation and postoperative ablation region segmentation for a group of the same cases are shown schematically.Figure 8
Graphical recognition of splitting results.In the feature selection process, expert experience only qualitatively observed to select the optimal layer, and precise mathematical evaluation metrics are still lacking. In addition, the integration network and feature selection workflow proposed in this paper should apply to more deep learning frameworks and clinical scenarios. In the future, we will continue to explore the flexibility and scalability of the multiscale fusion model in this chapter and validate it in more medical images or diseases with different modalities.Indeed, a longer follow-up time would improve the diagnostic accuracy of physicians and reinforce the credibility of the automatic diagnostic algorithm. Moreover, during the feature selection process, expert experience selects the optimal layer by qualitative observation-only, and precise mathematical evaluation metrics are still lacking. In addition, the integrated network and feature selection workflow proposed in this paper should apply to more deep learning frameworks and clinical scenarios. In the future, we will continue to explore the flexibility and scalability of the multiscale fusion model in this chapter and validate it in more medical images or diseases with different modalities.


## 5. Conclusion

The segmentation of the target region of the MRI image data also includes preprocessing of the MRI image data before segmentation. The preprocessing includes noise processing and isotropic processing. Noise processing is used to smooth the acquired MRI data; isotropic processing is used to adjust the MRI layer spacing to eliminate anisotropy. The 3D-MR image imaging process itself is in the frequency domain, and the network uses the information in the frequency domain of the image itself in the process of feature extraction, which can make the features rich and diverse. The attention mechanism can make the network learn the feature information more efficiently and only learn the part that needs attention, which not only reduces the computational effort of the network but also improves the learning efficiency of the network and lays the foundation for the subsequent upsampling reconstruction process. The first step performs the denoising task, which calculates the loss of the image after noise removal with the noise-free low-resolution image, and the second step performs the super-resolution reconstruction, which calculates the loss of the image after super-resolution with the high-resolution original image, and the two parts of the loss are jointly back-propagated to update the network. In the future, we will conduct further research based on this research.



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*Source: 4393154-2022-05-20.xml*