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CN114926394B - Colorectal cancer pathological image segmentation method based on pixel contrast learning - Google Patents

Colorectal cancer pathological image segmentation method based on pixel contrast learning Download PDF

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CN114926394B
CN114926394B CN202210371764.6A CN202210371764A CN114926394B CN 114926394 B CN114926394 B CN 114926394B CN 202210371764 A CN202210371764 A CN 202210371764A CN 114926394 B CN114926394 B CN 114926394B
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杨云
王科龙
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Yunnan University YNU
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Abstract

The invention discloses a rectal cancer pathological image segmentation method based on pixel contrast learning, which belongs to the technical field of image segmentation methods and comprises the following steps of: randomly cutting two subgraphs from an image, and keeping the pixel characteristics corresponding to the subgraphs consistent; a pair of pictures is subjected to two different enhancements and then input into the encoder network and momentum encoder network in the model, both of which are composed of a ResNet connected to a projection head (two 1x1 convolutions interspersed with a batch normalization and Relu activation layer). According to the invention, the encoder is trained through contrast learning to replace the original pre-trained ResNet, an improved pathological image segmentation model can be brought in the aspect of feature extraction performance without additional annotation, and the problem that the traditional contrast learning is inconsistent in downstream segmentation task based on instance-level Loss is solved through introducing the contrast learning of pixel-level Loss.

Description

Colorectal cancer pathological image segmentation method based on pixel contrast learning
Technical Field
The invention belongs to the technical field of image segmentation methods, and particularly relates to a rectal cancer pathological image segmentation method based on pixel contrast learning.
Background
At present, diagnosis of the rectal cancer needs to be analyzed through pathological images, and a pathologist evaluates the cancer cell load by quantitatively analyzing the area of a pathological tissue area in the images, so as to specify a diagnosis and treatment plan. However, manual observation is time consuming and laborious and requires a long experience accumulation. Therefore, the automatic segmentation of the lesion tissue area is realized, and the diagnosis and treatment efficiency can be greatly improved.
With the successful application of deep learning in the medical field, the pathological image field is also continuously developed. However, due to insufficient data, the segmentation model often adopts natural image pre-trained ResNet for feature extraction, and thus the learned feature mapping is often not optimal. Therefore, how to improve the feature extraction capability of the model is a urgent problem to be solved.
The self-supervision learning mode can be used without additional labels by contrast learning. The main idea is to pull the mapping distance between different samples (negative examples) by pulling the distance of similar samples (positive examples) in the mapping space. In this field, a pre-task (pre tasks) is generally set to construct positive and negative examples, for example, in the image field, an original image is a base sample, an enhanced (converted) version thereof serves as a positive example, and the rest of images in a batch or training data serve as a negative example, so many experiments in the natural image segmentation field have proved that such a method can improve the performance of a feature extractor, so as to better assist a downstream task.
The existing pathological image segmentation model has the following defects:
(1) Because of the lack of labeling data, an image net pre-training model is often adopted by an encoder of a segmentation network, but the model is trained on a natural image and only has sub-good feature mapping for a pathological image.
(2) Most of contrast learning is mainly performed through instance-level differences, while image segmentation is mainly based on pixel-level features, which causes dislocation of upstream and downstream tasks.
(3) Although the contrast learning positive example construction capability is greatly improved by benefiting from various powerful image enhancement modes, the designs are mainly aimed at natural images, and do not have excessive research on the enhancement of pathological images.
Disclosure of Invention
The invention aims at: in order to solve the problems of the background technology, a rectal cancer pathological image segmentation method based on pixel contrast learning is provided.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
a rectal cancer pathological image segmentation method based on pixel contrast learning specifically comprises the following steps:
s1, pixel contrast learning: randomly cutting two subgraphs from an image, and keeping the pixel characteristics corresponding to the subgraphs consistent;
s2, a pair of pictures is subjected to two different enhancements and then is input into an encoder network and a momentum encoder network in a model, wherein the encoder network and the momentum encoder network are both formed by connecting a projection head (two 1x1 convolutions and a batch normalization and Relu activation layer is interposed between the two projection heads) by ResNet;
s3, randomly cutting out two sub-feature images from the feature images of the two different enhanced images, and then calculating the consistency loss between the two sub-images so as to pull up the mapping representation distance;
s4, based on S3, the spatial distance judgment is also reflected, namely, the spatial distance of the pixel set between the two characteristic subgraphs is calculated, if the distance between the two characteristic subgraphs exceeds a set threshold valueThe loss is not calculated and if the threshold is not exceeded, the situation that all pixels in the image are finally attributed to one value can be prevented by calculating the loss;
s5, introducing a new image enhancement mode: the method has the advantages that the RandAugment is introduced, the original enhancement mode is added into the RandAugment, the property of the RandAugment limits the enhancement strength and the number of enhancement methods used, and the defect of excessive enhancement modes is avoided;
s6, image segmentation: extracting features of the image by using an encoder, and then performing segmentation mask prediction on the image by using a decoder;
and S7, the encoder part transfers the characteristic encoder obtained by contrast learning training to an encoder module of the U-Net to replace the original image Net pre-trained encoder, and then inputs the pathological image slice into a network to finish segmentation.
As a further description of the above technical solution:
in the step S1, the purpose is to pull up the mapping representation of different sub-pixels with similar distances for learning.
As a further description of the above technical solution:
in S2, unlike the conventional contrast learning method, the pixel contrast learning maps the feature into a feature map, and the conventional method maps the feature into a vector.
As a further description of the above technical solution:
in the S1-S4, two losses are proposed in the pixel contrast learning, one isFor calculating pixel loss between subgraphs, the other is +.>For calculating the loss after projection through pixel propagation.
As a further description of the above technical solution:
the saidOne is a conventional encoder with a pixel propagation module for generating smooth features; the other is a momentum encoder without a propagation module, a conventional encoder with a pixel propagation module and a momentum encoder without a propagation module are used for calculation, the distances of two different encoders are shortened, the distance is equivalent to that x in the second image is mapped again to obtain y (similar to the effect of a projection head, nonlinear mapping is performed), and then the loss is calculated by y and x' in the momentum encoder.
As a further description of the above technical solution:
in the step S5, two enhancement modes of contrast learning are set, one is the improved RandAugment, the other is the enhancement mode in the original Simclr, and different enhancement modes can explore more proper changes in the contrast learning.
As a further description of the above technical solution:
in S6, the skipped connection between the encoder and decoder combines the low-level feature map with the high-level feature map, resulting in a more accurate segmentation result.
In summary, due to the adoption of the technical scheme, the beneficial effects of the invention are as follows:
1. in the invention, the encoder is trained through contrast learning to replace the original pre-trained ResNet, and an improved pathological image segmentation model can be brought in the aspect of feature extraction performance without additional annotation.
2. The problem that the traditional contrast learning is inconsistent in downstream segmentation tasks based on instance level Loss is solved by introducing the contrast learning of pixel level Loss.
3. The positive characteristic construction of the traditional contrast learning is designed for natural images and is different from pathological images, so that the invention provides a positive example construction method which is more suitable for the pathological image field.
To sum up:
1. by introducing pixel contrast learning, the model can be better adapted to downstream segmentation tasks.
2. The method is used for constructing the positive example with WSIRANdAug, and solves the problem that the traditional contrast learning is used for constructing the positive example aiming at the natural image.
Drawings
FIG. 1 is a network flow chart of a rectal cancer pathological image segmentation method based on pixel contrast learning;
fig. 2 is a network structure diagram of a rectal cancer pathological image segmentation method based on pixel contrast learning.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Referring to fig. 1-2, the present invention provides a technical solution: a rectal cancer pathological image segmentation method based on pixel contrast learning specifically comprises the following steps:
s1, pixel contrast learning: two subgraphs are randomly cut from an image, and pixel characteristics corresponding to the subgraphs are kept consistent, wherein in the S1, the aim is to enable different subgraphs with similar distances to draw mapping characterization for learning;
s2, a pair of pictures is subjected to two different enhancements and then is input into an encoder network and a momentum encoder network in a model, wherein the encoder network and the momentum encoder network are both formed by connecting a projection head (two 1x1 convolutions with a batch normalization and a Relu activation layer interposed therebetween) by ResNet, and in S2, unlike a traditional contrast learning mode, pixel contrast learning can map features into a feature map mode, and the traditional method maps features into a vector;
s3, randomly cutting out two sub-feature images from the feature images of the two different enhanced images, and then calculating the consistency loss between the two sub-images so as to pull up the mapping representation distance;
s4, based on S3, the spatial distance judgment is also reflected, namely, the spatial distance of the pixel set between the two characteristic subgraphs is calculated, if the distance between the two characteristic subgraphs exceeds a set threshold valueThe loss is not calculated and if the threshold is not exceeded, it is prevented that all pixels in the image will eventually fall to a value, as shown in the formula:
in this embodiment, in the S1-S4, the pixel contrast learning provides two losses, one isFor calculating pixel loss between subgraphs, the other is +.>For calculating the loss after projection through pixel propagation, < >>Similar to example contrast learning, the formula is as follows:
where i represents a pixel in both subgraphs,representing positive and negative pixel sets, x, respectively, located in the second sub-image i ,x′ j For the pixel characteristic vector in the two subgraphs, τ is a scalar value of 0.3, the loss is calculated twice on the shared pixels of the first subgraph and the second subgraph, and finally the average is taken;
the saidOne is a conventional encoder with a pixel propagation module for generating smooth features; the other is a momentum encoder without a propagation module. The calculation is performed with a conventional encoder with a pixel propagation module and a momentum encoder without a propagation module, pulling the distances of the two different encoders. The method is equivalent to mapping x in the second graph again to obtain y (similar to the effect of a projection head, performing nonlinear mapping), and then calculating the loss by using y and x' in a momentum encoder;
by introducing both losses, the upstream and downstream tasks are made more consistent.
The whole loss is composed of three parts, and besides the two traditional example contrast learning losses:
wherein the method comprises the steps ofThe learning penalty is compared for the conventional example.
S5, introducing a new image enhancement mode: introducing RandAugment, adding the original enhancement mode into the RandAugment together, limiting the enhancement strength and the number of enhancement methods used by the properties of the enhancement mode, and avoiding the defect of excessive enhancement modes, wherein in S5, two enhancement modes of contrast learning are set, one is the improved RandAugment, the other is the enhancement mode in the original Simclr, and the different enhancement modes can be used for exploring more proper changes in the contrast learning;
s6, image segmentation: performing feature extraction on the image by using an encoder and then performing segmentation mask prediction on the image by using a decoder, wherein in S6, a skip connection between the encoder and the decoder combines the low-level feature map with the high-level feature map, thereby generating a more accurate segmentation result;
and S7, the encoder part transfers the characteristic encoder obtained by contrast learning training to an encoder module of the U-Net to replace the original image Net pre-trained encoder, and then inputs the pathological image slice into a network to finish segmentation.
The foregoing is only a preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art, who is within the scope of the present invention, should make equivalent substitutions or modifications according to the technical scheme of the present invention and the inventive concept thereof, and should be covered by the scope of the present invention.

Claims (7)

1. The rectal cancer pathological image segmentation method based on pixel contrast learning is characterized by comprising the following steps of:
s1, pixel contrast learning: randomly cutting two subgraphs from an image, and keeping the pixel characteristics corresponding to the subgraphs consistent;
s2, a pair of pictures is subjected to two different enhancements and then is input into an encoder network and a momentum encoder network in a model, wherein the encoder network and the momentum encoder network are both formed by connecting a projection head (two 1x1 convolutions and a batch normalization and Relu activation layer is interposed between the two projection heads) by ResNet;
s3, randomly cutting out two sub-feature images from the feature images of the two different enhanced images, and then calculating the consistency loss between the two sub-images so as to pull up the mapping representation distance;
s4, based on S3, the spatial distance judgment is also reflected, namely, the spatial distance of the pixel set between the two characteristic subgraphs is calculated, if the distance between the two characteristic subgraphs exceeds a set threshold valueThe loss is not calculated and if the threshold is not exceeded, the situation that all pixels in the image are finally attributed to one value can be prevented by calculating the loss;
s5, introducing a new image enhancement mode: the method has the advantages that the RandAugment is introduced, the original enhancement mode is added into the RandAugment, the property of the RandAugment limits the enhancement strength and the number of enhancement methods used, and the defect of excessive enhancement modes is avoided;
s6, image segmentation: extracting features of the image by using an encoder, and then performing segmentation mask prediction on the image by using a decoder;
and S7, the encoder part transfers the characteristic encoder obtained by contrast learning training to an encoder module of the U-Net to replace the original image Net pre-trained encoder, and then inputs the pathological image slice into a network to finish segmentation.
2. The method for segmenting a pathological image of rectal cancer based on pixel contrast learning according to claim 1, wherein in S1, the purpose is to make different sub-pixels close to each other in distance map representation for learning.
3. The method for segmenting a pathological image of rectal cancer based on pixel contrast learning according to claim 1, wherein in S2, unlike the conventional contrast learning method, the pixel contrast learning maps features into a feature map form, and the conventional method maps features into a vector.
4. The method for segmenting a pathological image of rectal cancer based on pixel contrast learning according to claim 1, wherein in the S1-S4, the pixel contrast learning proposes two losses, one is thatFor calculating pixel loss between subgraphs, the other is +.>For calculating the loss after projection through pixel propagation.
5. The method for segmenting a pathological image of rectal cancer based on pixel contrast learning according to claim 4, wherein the steps ofOne is a conventional encoder with a pixel propagation module for generating smooth features; the other is a momentum encoder without a propagation module, a conventional encoder with a pixel propagation module and a momentum encoder without a propagation module are used for calculation, the distances of two different encoders are shortened, the distance is equivalent to that x in the second image is mapped again to obtain y (similar to the effect of a projection head, nonlinear mapping is performed), and then the loss is calculated by y and x' in the momentum encoder.
6. The method for segmenting a pathological image of rectal cancer based on pixel contrast learning according to claim 1, wherein in S5, two enhancement modes of contrast learning are set, one is an improved randagament and the other is an original enhancement mode in Simclr, and different enhancement modes can be used for exploring more proper changes in contrast learning.
7. A method of segmentation of a pathological image of rectal cancer based on pixel contrast learning according to claim 1, wherein in S6, the skipped connection between encoder and decoder combines the low-level feature map with the high-level feature map, thereby yielding a more accurate segmentation result.
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