CN109816747A - A kind of metal artifacts reduction method of Cranial Computed Tomography image - Google Patents

A kind of metal artifacts reduction method of Cranial Computed Tomography image Download PDF

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CN109816747A
CN109816747A CN201910136016.8A CN201910136016A CN109816747A CN 109816747 A CN109816747 A CN 109816747A CN 201910136016 A CN201910136016 A CN 201910136016A CN 109816747 A CN109816747 A CN 109816747A
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artifact
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陈茜
谢世朋
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Nanjing Post and Telecommunication University
Nanjing University of Posts and Telecommunications
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Nanjing Post and Telecommunication University
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Abstract

The present invention discloses a kind of metal artifacts reduction method of Cranial Computed Tomography image, including two steps: initially setting up one includes and the database not comprising artifact Cranial Computed Tomography image, using the method for deformable image registration before convolutional neural networks (CNN) training preprocessed data;Secondly, constructing simple 17 layers of CNN framework in training to learn metal artifacts, and accelerate the speed of training data using GPU, improves the learning efficiency of network;Meanwhile the experimental results showed that this method has the ability of good metal artifacts reduction, PSNR and SSIM numerical value also shows that apparent improvement.

Description

A kind of metal artifacts reduction method of Cranial Computed Tomography image
Technical field
The invention belongs to metal artifacts correcting technologies, and in particular to a kind of metal artifacts reduction method of Cranial Computed Tomography image.
Background technique
Computer tomography (computed tomography, CT) be medicine and industrial circle commonly used equipment it One, it obtains sectioning image using specific CT algorithm for reconstructing, plays an important role to medical diagnosis on disease and defect inspection.? In CT scan, metal is much higher than tissue as a kind of attenuation coefficient of highdensity object to X-ray, if scanning In the process, there are the highly attenuating substance of metalloid, when X-ray passes through these objects will sharp-decay, lead to corresponding throwing Shadow data distortion, the image reconstructed just will appear artifact.In by imaging object only single metal when, metal artifacts performance For there are radial artifacts around it;When metal object quantity is more and metallic region area is larger, metal artifacts not only include Radial artifact around metal object, and there is also banding artifacts on metal connecting line direction.
Since CT technology is widely used in medical treatment and industrial circle, the quality of image of reconstruction image is for checking, detecting Effect is most important.It is suggested at present there are many correcting algorithm, the method for metal artifacts reduction can be divided into three in short Class: physical correction, the interpolation and iterative reconstruction of projection domain.Physical correction method between X radiographic source and detector by adding One filter absorbs the lower energy photon of light beam, to reduce artifact;But as the photon of part is absorbed, signal-to-noise ratio It can reduce.Linear interpolation (LI) is a kind of conventional method for reducing metal artifacts, replaces Raw projection data using interpolation technique The middle part influenced by metal, thus achieve the purpose that remove metal artifacts, but this method is easy to generate new artifact, Cause the serious portion structure deformation of metal artifacts.Iterative approximation (LR) is the conventional method of Clinical CT, and this method is due to needing A large amount of to calculate, the performance by experimental facilities is limited.
In conclusion existing hardening artifact bearing calibration is although various, but there is respective limitation in a particular application Property.
Summary of the invention
Goal of the invention: it is an object of the invention to solve the deficiencies in the prior art, a kind of Cranial Computed Tomography image is provided Metal artifacts reduction method, the present invention using based on depth convolutional neural networks residual error study, remove Cranial Computed Tomography image in Metal artifacts, improve calculating speed.
A kind of technical solution: the metal artifacts reduction method of Cranial Computed Tomography image of the invention, comprising the following steps:
(1) database for CNN training is established;Original image is pre-processed using deformable image registration method, And then the Cranial Computed Tomography data comprising artifact and without artifact are obtained to the database of composition;
(2) 17 layers of CNN framework are constructed in CNN training to learn metal artifacts.
Further, the detailed content of the step (1) are as follows:
It (1.1) will include that the CT picture of artifact is set as target image, according to SSIM from the CT image for not including artifact It is worth preliminary screening and goes out the image most like with target image;
(1.2) using image obtained by deformable image registration method processing step (1.1), and then final pairing instruction is obtained Practice data, method particularly includes:
(a) according to the clearly image of multiple groups obtained by step (1.1), feature extraction is carried out;By the input of original image 100*100 Image segmentation extracts the label of characteristic information at the image block of 30*30 from image block;
(b) according to the feature tag extracted, by the image segmentation containing artifact at the progress of an equal amount of image block Match;
(c) image block matched is merged into complete image, carried out image procossing (i.e. picture enhancing), final Clearly image after to registration.
In the above process, input picture is registrated according to the target image containing artifact, selects registration effect Fruit is best, that is, takes out after registration closest to the data of target image, forms one group with the original image containing artifact Data pair.In short, eliminating the slight displacement in CT image in mini piece between pixel using deformable image registration method.? After completing registration, image data gets out be sent to training in network.
Further, the detailed process of the step (2) are as follows:
(2.1) construct convolutional neural networks: the depth of the convolutional neural networks is D layers, including three kinds of network layers: (A) volume Product network+amendment linear unit (ReLU);(B) convolutional network+crowd standardization (BN)+ReLU;(C) convolutional network;
In Type (A), the filter that 64 sizes are 3 × 3 × 1 is for generating 64 Feature Mappings;This layer is added ReLU is pre-processed, i.e., using Element-Level operation will all pixels value in sketch map less than 0 be set as 0;
Type (B) be from the second layer to D-1 layer, using 64 having a size of 3 × 3 × 64 filter;In convolutional network and Normalization unit BN is criticized in introducing on the basis of correcting linear unit, and BN is added between convolution sum ReLU;Number will be trained using BN According to thoroughly upsetting, and training speed is greatly improved, allows bigger learning rate;
Type (C) is convolutional layer, the filter that convolutional layer is 3 × 3 × 64 using size, for rebuilding output;
(2.2) residual error learn, i.e., using CNN network residual error study analysis CT image in artifact, it is intended to by original image with From the middle school's acquistion of CT image to artifact subtract each other, finally obtain and clearly correct image;
The model of CT image is f=x+n, and wherein the artifact in n representative image, a mapping function is trained using CNN Then F (f)=n obtains the image without artifact that can be estimatedIt is instructed using the difference and network of reconstruction image The Averaged Square Error of Multivariate between artifact after white silk needs to restore the loss function of image as measurement;Formula is as follows:
WhereinIt indicates N group data pair, is made of true picture and the image containing artifact;μ (f) represents CNN Mapping.In order to ensure the quality of the image recovered, it is necessary to the parameter in training network, so that parameter value appropriate is obtained, Mean square error is minimized to obtain.
The artifacts obtained by CNN network, according to formulaObtain final clearly image.
The utility model has the advantages that the present invention initially sets up one includes and the database not comprising artifact Cranial Computed Tomography image.In the step In rapid, using the method for deformable image registration before CNN training preprocessed data.Secondly, in CNN training, building one A simple 17 layers of CNN framework learns metal artifacts.The experimental results showed that this method has good metal artifacts reduction Ability, PSNR and SSIM also show that apparent improvement.
Detailed description of the invention
Fig. 1 is overall flow figure of the invention.
Fig. 2 is the process schematic of deformable registration method in the present invention.
Fig. 3 is the structure chart of depth convolutional neural networks in embodiment.
Fig. 4 is in embodiment using the process of CNN network removal artifact.
Fig. 5 is that artifact process schematic in CT image is corrected in embodiment.
Fig. 6 is four kinds of comparative result schematic diagrams in embodiment after different artifact correction methods.
Specific embodiment
Technical solution of the present invention is described in detail below, but protection scope of the present invention is not limited to the reality Apply example.
Due to the presence of metal charge, metal artifacts always affect the effect of computed tomography (CT) inspection.Cause This, removal metal artifacts are still one of the main problem in clinical Cranial Computed Tomography image.In order to reduce the tooth regions of CT image In metal artifacts, as shown in Figures 1 to 4, the metal artifacts reduction method of a kind of Cranial Computed Tomography image of invention, including following Step:
(1) database for CNN training is established;Original image is pre-processed using deformable image registration method, And then the Cranial Computed Tomography data comprising artifact and without artifact are obtained to the database of composition;
It (1.1) will include that the CT picture of artifact is set as target image, according to SSIM from the CT image for not including artifact It is worth preliminary screening and goes out the image most like with target image (by comparing the size of the SSIM value of image, from the CT for being free of artifact In image, preliminary screening goes out most like with target image);
(1.2) using image obtained by deformable image registration method processing step (1.1), and then final pairing instruction is obtained Practice data;Method particularly includes:
(a) according to the clearly image of multiple groups obtained by step (1.1), feature extraction is carried out;By the input of original image 100*100 Image segmentation extracts the label of characteristic information at the image block of 30*30 from image block;
(b) according to the feature tag extracted, by the image segmentation containing artifact at the progress of an equal amount of image block Match;
(c) image block matched is merged into complete image, carried out image procossing (i.e. picture enhancing), final Clearly image after to registration;
(2) 17 layers of CNN framework are constructed in CNN training to learn metal artifacts;
(2.1) construct convolutional neural networks: the depth of the convolutional neural networks is D layers, including three kinds of network layers: (A) volume Product network+amendment linear unit (ReLU);(B) convolutional network+crowd standardization (BN)+ReLU;(C) convolutional network;
In Type (A), the filter that 64 sizes are 3 × 3 × 1 is for generating 64 Feature Mappings;This layer is added ReLU is pre-processed, i.e., using Element-Level operation will all pixels value in sketch map less than 0 be set as 0;
Type (B) be from the second layer to D-1 layer, using 64 having a size of 3 × 3 × 64 filter;In convolutional network and Normalization unit BN is criticized in introducing on the basis of correcting linear unit, and BN is added between convolution sum ReLU;Number will be trained using BN According to thoroughly upsetting, and training speed is greatly improved, allows bigger learning rate;
Type (C) is convolutional layer, the filter that convolutional layer is 3 × 3 × 64 using size, for rebuilding output;
(2.2) residual error learn, i.e., using CNN network residual error study analysis CT image in artifact, it is intended to by original image with From the middle school's acquistion of CT image to artifact subtract each other, finally obtain and clearly correct image;
The model of CT image is f=x+n, and wherein the artifact in n representative image, a mapping function is trained using CNN Then F (f)=n obtains the image without artifact that can be estimatedIt is instructed using the difference and network of reconstruction image The Averaged Square Error of Multivariate between artifact after white silk needs to restore the loss function of image as measurement;Formula is as follows:
WhereinIt indicates N group data pair, is made of true picture and the image containing artifact;μ (f) represents CNN Mapping.In order to ensure the quality of the image recovered, it is necessary to the parameter in training network, so that parameter value appropriate is obtained, Mean square error is minimized to obtain.
The artifacts obtained by CNN network, according to formulaObtain final clearly image.
The training parameter setting of above-described embodiment is as follows:
It is trained using Adam optimizer, learning rate is set as 1e-4 to 1e-5.Epoch in network is set as 190, the size of input picture is set as 100 × 100.MatConvNet work in this Web vector graphic MATLAB 2017a environment Have case, is realized using GTX 1080Ti graphics processor and i7-6850K CPU (3.60HZ).
The speed for being accelerated training data using GPU is enabled the training time of CNN shorten within one day, improves study Efficiency.Simultaneously by test, proof of algorithm is carried out using CPU, every picture is detected and needs one minute or so time, and is made In the case where GPU, detection every only needs one second, and speed is obviously improved.
In the above process, learn the Cranial Computed Tomography figure containing artifact and without artifact in the present invention using residual error learning method Mapping as between, the method for residual error study focus on residual image (train difference) between only comprising artifact and Noise, not comprising other significant anatomical structures.So (containing and without belonging to metal artifacts by two CT images ) it is used as training to, needing to carry out registration work before, because registration can be minimized the structural difference of training pair.
For the tooth regions in Cranial Computed Tomography image, image is further registrated using the method for deformable image registration. As shown in Fig. 2, input picture is registrated according to the target image containing artifact, it is best to select registration effect, It is exactly the data taking-up after being registrated closest to target image, forms one group of data pair with the original image containing artifact.Always It, deformable image registration method attempts to eliminate the slight displacement in CT image in mini piece between pixel.Complete registration Afterwards, image data gets out be sent to training in network.
Embodiment 1:
For experimental result as shown in figure 5, the left side is the input picture with artifact, the right is by metal artifacts reduction Export image, it can be seen that the artifact in CT image has obtained good correction.
Meanwhile the present embodiment uses beam hardening correcting (BHC) method and linear interpolation (LI) method as comparing.Fig. 6 exhibition Shown using four kinds of comparison results after different artifact correction methods (display window is [- 1,000 1000]).Fig. 6 (a) be using The reference picture obtained after the method for deformable image registration, Fig. 6 (b) are the original images containing artifact;Fig. 6 (c) be using Correction image Fig. 6 (d) after BHC method is the correction image using LI method;Fig. 6 (e) is corrected using our method Image.
Table 1 lists the SSIM value in Fig. 6 (c)-(e) about reference Fig. 5.Table 2 lists correction image relative to reference The PSNR of image.In contrast, there is highest accuracy using the CNN image obtained after the present invention and realizes maximum PSNR value.
Table 1
Table 2
In short, the present invention proposes a kind of artifact correction algorithm based on depth convolutional neural networks, the DIR method of use The use of the CNN network architecture of 17 layers of cooperation can effectively remove artifact, and accelerate the speed of training data using GPU Degree, improves the learning efficiency of network;Meanwhile the experimental results showed that this method have good metal artifacts reduction ability, PSNR and SSIM also shows that apparent improvement.

Claims (3)

1. a kind of metal artifacts reduction method of Cranial Computed Tomography image, it is characterised in that: the following steps are included:
(1) database for CNN training is established;Original image is pre-processed using deformable image registration method, in turn The Cranial Computed Tomography data comprising artifact and without artifact are obtained to the database of composition;
(2) 17 layers of CNN framework are constructed in CNN training to learn metal artifacts.
2. the metal artifacts reduction method of Cranial Computed Tomography image according to claim 1, it is characterised in that: the step (1) Detailed content are as follows:
It (1.1) will include that the CT picture of artifact is set as target image, according at the beginning of SSIM value from the CT image for not including artifact Step filters out the image most like with target image;
(1.2) using image obtained by deformable image registration method processing step (1.1), and then final pairing training number is obtained According to, method particularly includes:
(a) according to the clearly image of multiple groups obtained by step (1.1), feature extraction is carried out;By the input picture of original image 100*100 point It is cut into the image block of 30*30, the label of characteristic information is extracted from image block;
(b) according to the feature tag extracted, the image segmentation containing artifact is matched at an equal amount of image block;
(c) image block matched is merged into complete image, carries out image procossing, the clearly figure after finally obtaining registration Picture.
3. the metal artifacts reduction method of Cranial Computed Tomography image according to claim 1, it is characterised in that: the step (2) Detailed process are as follows:
(2.1) construct convolutional neural networks: the depth of the convolutional neural networks is D layers, including three kinds of network layers: (A) convolution net Network+amendment linear unit (ReLU);(B) convolutional network+crowd standardization (BN)+ReLU;(C) convolutional network;
In Type (A), the filter that 64 sizes are 3 × 3 × 1 is for generating 64 Feature Mappings;This layer be added ReLU into Row pretreatment, i.e., using Element-Level operation will all pixels value in sketch map less than 0 be set as 0;
Type (B) be from the second layer to D-1 layer, using 64 having a size of 3 × 3 × 64 filter;In convolutional network and amendment Crowd normalization unit BN is introduced on the basis of linear unit, and BN is added between convolution sum ReLU;It is using BN that training data is thorough Upset at bottom;
Type (C) is convolutional layer, the filter that convolutional layer is 3 × 3 × 64 using size, for rebuilding output;
(2.2) residual error learns, i.e., using the artifact in the residual error study analysis CT image of CNN network;
The model of CT image is f=x+n, and wherein the artifact in n representative image, a mapping function F (f) is trained using CNN =n, the image without artifact then estimatedUtilize the artifact after the difference and network training of reconstruction image Between Averaged Square Error of Multivariate, need to restore the loss function of image as measurement;Formula is as follows:
WhereinIt indicates N group data pair, is made of true picture and the image containing artifact;μ (f) represents reflecting for CNN It penetrates;
The artifacts obtained by CNN network, according to formulaObtain final clearly image.
CN201910136016.8A 2019-02-25 2019-02-25 A kind of metal artifacts reduction method of Cranial Computed Tomography image Pending CN109816747A (en)

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN111754436A (en) * 2020-06-24 2020-10-09 上海联影医疗科技有限公司 Acceleration method for medical image artifact correction, computer device and storage medium
CN113706643A (en) * 2020-09-09 2021-11-26 南京邮电大学 Homomorphic adaptation learning-based head CT metal artifact correction method
CN113744155A (en) * 2021-09-04 2021-12-03 重庆大学 Rock and ore sample CT image metal artifact correction method based on triple convolution network

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
XIA HUANG等: "Metal artifact reduction on cervical CT images by deep residual learning", 《BIOMEDICAL ENGINEERING ONLINE》 *

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN111754436A (en) * 2020-06-24 2020-10-09 上海联影医疗科技有限公司 Acceleration method for medical image artifact correction, computer device and storage medium
CN111754436B (en) * 2020-06-24 2024-05-03 上海联影医疗科技股份有限公司 Acceleration method for medical image artifact correction, computer device and storage medium
CN113706643A (en) * 2020-09-09 2021-11-26 南京邮电大学 Homomorphic adaptation learning-based head CT metal artifact correction method
CN113706643B (en) * 2020-09-09 2023-06-30 南京邮电大学 Head CT metal artifact correction method based on homomorphic adaptation learning
CN113744155A (en) * 2021-09-04 2021-12-03 重庆大学 Rock and ore sample CT image metal artifact correction method based on triple convolution network
CN113744155B (en) * 2021-09-04 2023-09-26 重庆大学 Triple convolution network-based rock-mineral sample CT image metal artifact correction method

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Application publication date: 20190528