CN105534479A - Multi-modal microwave breast imaging method and system - Google Patents

Abstract

The invention relates to a multi-modal microwave breast imaging method and system. Pixel points of one image in a radar detection image and a tomography image are mapped into the other image, the relevant pixel points of the two images are consistent at spatial positions, and then the two images are fused. When a patient suffering from early-stage cancer is diagnosed, advantage complementing can be conducted through different imaging modals, the two technologies are successfully fused to form the multi-modal microwave breast imaging system, and the purpose of imaging advantage and disadvantage complementing is achieved.

Description

A kind of multi-modal microwave breast formation method and system

Technical field

The present invention relates to a kind of fusion method and system of image, particularly relate to fusion method and the system of a kind of radar detection image and tomoscan image.

Background technology

In medical testing process, generally include X-ray and take the photograph sheet, color ultrasound, magnetic resonance and histology.It is high that X-ray takes the photograph chip resolution, but along with ionizing radiation and the compression to breast, be not suitable for the generaI investigation of patient.Color ultrasound detects "dead" infringement, but can not show part cancer sufferer, calcification point and burr poplar structure, and large by inspecting doctor's experience influence.Costly, imaging time is of a specified duration, and histological examination also needs accurate location in magnetic resonance, as molybdenum target be inducted into pin, color ultrasound guidance enters pin etc.Therefore, these current detection meanss are not also suitable for the examination of large-scale cancer sufferer, especially for the rural area that China is vast, medical facilities are with under universal very unbalanced condition, and the Clinical detection of microwave imaging have, effect low without ionizing radiation, cost and X-ray quite, can long term monitoring feature, the important tool that I crosses extensive examination can be become.

In microwave Imaging Technique, include two kinds of technology, microwave radar imaging and microwave Tomography, the former is for contrasting breast tissue clearly, can be good at finding strong scattering region, meet X-ray and ultrasonic and judgement that is MRI, very fine and close breast is difficult to understand, and for benign tumor, or some tissue cakings, equally can provide and misread, microwave Tomography then can judge the dense type of tissue, can judge the region of different tissues, two kinds of formation methods respectively have advantage but are difficult to unified simultaneously.

Summary of the invention

The technical problem that the present invention solves is: build a kind of multi-modal microwave breast formation method and system, overcoming the single detection means of prior art can not carry out unified technical problem to two kinds of images.

Technical scheme of the present invention is: provide a kind of multi-modal microwave breast formation method, comprise the steps:

Microwave Scanning: to breast area generation microwave broadband pulse signal to be measured and microwave single-frequency coherent signal; Receive microwave broadband pulse echo signal and microwave single-frequency echo-signal;

Imaging respectively: generate radar detection image, according to microwave single-frequency echo signal form tomoscan image according to microwave broadband pulse echo signal;

Image co-registration: the pixel of piece image in described radar detection image and described tomoscan image is mapped in another piece image and merges.

Further technical scheme of the present invention is: be mapped in another piece image by the pixel of piece image in described radar detection image and described tomoscan image, make the related pixel point of two width images on locus, reach the fusion unanimously completing this two width image.

Further technical scheme of the present invention is: in described radar detection image and described tomoscan image, the characteristic point place of image carries out labelling, the image tagged coincidence of described radar detection image and described tomoscan image is merged described radar detection image and described tomoscan image, the image tagged of described radar detection image and described tomoscan image is identified, then recognition image is carried out image co-registration as boundary mark.

Further technical scheme of the present invention is: in image co-registration step, and the image pixel weighted average of described radar detection image and described tomoscan image correspondence position is completed image co-registration.

Further technical scheme of the present invention is: be optimized image after carrying out labelling.

Technical scheme of the present invention is: build a kind of multi-modal microwave breast imaging system, comprise microwave signal generating unit, microwave signal receiving element, radar imagery unit, Tomography unit, fusion treatment unit, described microwave signal generating unit is to breast area generation microwave broadband pulse signal to be measured and microwave single-frequency coherent signal, described microwave signal receiving element receives microwave broadband pulse echo signal and microwave single-frequency echo-signal, described radar imagery unit generates radar detection image according to microwave broadband pulse echo signal, described Tomography unit is according to microwave single-frequency echo signal form tomoscan image, described radar detection image and described tomoscan image merge by described fusion treatment unit.

Further technical scheme of the present invention is: described fusion treatment unit also comprises image tagged module, the characteristic point place of described image tagged module image in described radar detection image and described tomoscan image carries out labelling, the image tagged coincidence of described radar detection image and described tomoscan image is merged described radar detection image and described tomoscan image.

Further technical scheme of the present invention is: described fusion treatment unit also comprises image tagged identification module, and the image tagged of described radar detection image and described tomoscan image identifies by described image tagged identification module.

Further technical scheme of the present invention is: also comprise image optimization module, and described image optimization module is optimized the image after labelling.

Further technical scheme of the present invention is: microwave signal generating unit is multiple, respectively microwave broadband pulse signal and microwave single-frequency coherent signal occurs; Or microwave signal generating unit is one, alternately there is microwave broadband pulse signal and microwave single-frequency coherent signal.

Technique effect of the present invention is: build a kind of multi-modal microwave breast formation method and system, by being mapped in another piece image by the pixel of piece image in described radar detection image and described tomoscan image, make the related pixel point of two width images on locus, reach the fusion unanimously completing this two width image.Can have complementary advantages by using different image modes in the process of diagnosis earlier stage cancer patients, microwave radar imaging utilizes ultra-wideband microwave signal to obtain the high-resolution of target scattering center in distance, then doppler information is utilized, obtain the high-resolution of scattering center in lateral separation, both combine two dimension or the dimensional resolution that can obtain target, thus the multidigit high-resolution of target is achieved.Microwave Tomography is by low power microwave directive testee, under the excitation of microwave, measured object produces a scattered field, this scattered field distributes relevant with the complex dielectric permittivity of measured object inside, by the measurement to this scattering, obtain the relative dielectric constant of measured object and the distribution of electrical conductivity, the microwave wave circuits and systems of measured object internal object after carrying out corresponding information processing, can be obtained.By these two kinds of technology successful fusion in the present invention, form a set of multi-mode microwave breast imaging system, reach the good and bad complementary object of imaging.

Accompanying drawing explanation

Fig. 1 is structural representation of the present invention.

Fig. 2 is structure chart of the present invention.

Fig. 3 is fusion flow chart of the present invention.

Detailed description of the invention

Below in conjunction with specific embodiment, technical solution of the present invention is further illustrated.

As shown in Figure 1, the specific embodiment of the present invention is: provide a kind of multi-modal microwave breast formation method, comprise the steps:

Microwave Scanning: to breast area generation microwave broadband pulse signal to be measured and microwave single-frequency coherent signal; Receive microwave broadband pulse echo signal and microwave single-frequency echo-signal;

Specific implementation process is as follows: microwave generating unit by microwave antenna to breast area generation microwave broadband pulse signal to be measured, microwave broadband pulse signal irradiates the focal area in imaging region, produce scattering on surface, focal area, receive the microwave broadband pulse echo signal from focus surface scattering with the scanning of several microwave antennas.Microwave generating unit is by microwave antenna to breast area generation microwave single-frequency coherent signal to be measured, and microwave antenna scanning receives and records the microwave single-frequency echo-signal of position.Microwave antenna alternately realizes signal transmitting and receiving; Or microwave transmitting antenna and microwave antenna are arrayed, carry out launched microwave signal simultaneously and receive microwave echoes signal, microwave signal generating unit is multiple signal generator, for system provides microwave broadband pulse signal and microwave single-frequency coherent signal respectively simultaneously.

Imaging respectively: generate radar detection image, according to microwave single-frequency echo signal form tomoscan image according to microwave broadband pulse echo signal.

Specific implementation process is as follows: microwave radar image-forming principle utilizes theory of SAR, using a miniature antenna as single radiating element, the continuous motion scan in direction along a straight line, in movement, select some positions to transmit, receive the echo-signal of corresponding transmitting site, the amplitude of storage Received signal strength and phase place.Received the time of microwave scattering signal by microwave antenna record, can time delay be calculated, and the distance of microwave transmitting antenna and focus is fixed, therefore the distance of micro-transmitting antenna to focus can be obtained, thus carry out accurate imaging.Microwave wave circuits and systems method is similar to computed tomography (CT), it is a kind of THE INVERSE ELECTROMAGNETIC SCATTERING method, by scattering object external observation to electromagnetic field carry out the electromagnetic signature parameter distribution in inversion imaging region, thus judge the information such as position, shape and size distribution of scattering object target.By the microwave single-frequency echo-signal received, generate tomoscan image according to the position of electromagnetic signature parameter distribution and scattering object target, shape and size distributed intelligence.

Image co-registration: the pixel of piece image in described radar detection image and described tomoscan image is mapped in another piece image, makes the related pixel point of two width images reach the fusion unanimously completing this two width image on locus.

Specific implementation process is as follows: image co-registration comprises multiple method: a kind of method is labelling method, in described radar detection image and described tomoscan image, the characteristic point place of image carries out labelling, the image tagged coincidence of described radar detection image and described tomoscan image is merged described radar detection image and described tomoscan image, when image co-registration, the image tagged of described radar detection image and described tomoscan image is identified, then recognition image is carried out image co-registration as boundary mark, recognition image marker characteristic, image co-registration can be made more accurate.In specific embodiment, after carrying out labelling, image is optimized, after segmentation, image co-registration is carried out to cut zone.Image tagged software design becomes the boundary mark of the Feature point recognition of image as Images uniting.Image tagged software according to described radar detection image and tomoscan image to the labelling of tissue identification, the labelling of lymph node identification and the labelling of characteristic, coordinate axes forms coincide point, complete the fusion of described radar detection image and tomoscan image, the method is equally applicable to two dimension that other modes combine or three-dimensional breast image.Further comprises the display to multi-modal microwave breast image, the two and three dimensions information of display breast, to the labelling of focal area.Another kind method is pixel weighted mean method, that is: the image pixel weighted average of described radar detection image and described tomoscan image correspondence position is completed image co-registration.

Below for labelling method:

Image registration

By using the process means such as coupling, superposition, the same target in multiple image being kept same position in the picture, making it have the process of identical space coordinates.

In the registration of microwave tomoscan image and microwave radar image, using metastable microwave tomoscan image as with reference to visual I, using microwave radar image as floating image II, carry out the image registration of the maximum mutual information method based on pixel, flow chart as shown in Figure 3 under:

Rigid body translation comprises transformation of scale, in two-dimensional image I I, and point (x ₁, y ₁) through rigid transformation to point (x ₂, y ₂) application of formula is:

$\left[\begin{array}{c}{x}_2\\ y_2\end{array}\right]=K\left[\begin{array}{cc}cos\mathrm{\α}& \±sin\mathrm{\α}\\ \sin \mathrm{\α}& \±cos\mathrm{\α}\end{array}\right]\left[\begin{array}{c}{x}_1\\ y_1\end{array}\right]---\left(1\right)$

Wherein, α is the anglec of rotation, and K is scale parameter.

Mutual information relevance evaluation.Regard the gray value of two images subject to registration as two stochastic variable A and B respectively, scope 0 to 255, marginal probability distribution is respectively P _a(a) and P _bb (), joint probability distribution is P _aB(a, b), then edge entropy and the combination entropy that can obtain A and B are respectively: H (A), H (B) and H (A, B).Then have:

$\left\{\begin{array}{c}H\left(A\right)=-\underset{a}{\Σ}{P}_A\left(a\right){\mathrm{logP}}_A\left(a\right)\\ H\left(B\right)=-\underset{b}{\Σ}{P}_B\left(b\right){\mathrm{logP}}_B\left(b\right)\\ H(A,B)=-\underset{a}{\Σ}\underset{b}{\Σ}{P}_{AB}(a,b){\mathrm{logP}}_{AB}(a,b)\end{array}\right.,a,b\∈\[0.255\]---\left(2\right)$

Normalized mutual information dependent evaluation function I (A, B) of stochastic variable A and B, for:

$I(A,B)=\frac{H\left(A\right)+H\left(B\right)}{H(A,B)}---\left(3\right)$

When two width reach optimal registration based on the image of common anatomical structure, gray scale cross-correlation value of information I (A, B) of their respective pixel should reach maximum.

Registration is optimized.After rigid body translation completes, a kind of similarity side degree need be found further to weigh the similarity degree of two width images, need constantly conversion parameter alpha and K, make similar side degree reach optimum, wherein scale parameter K excursion is 0 to 1, and rotation angle range is 0 to 180 degree.

1. be the unit vector of coordinate axes: c by the set of α and K transformation range _i=e (i=1,2 ..., N);

2. recording initial value position vector is P ₀=(α ₀, K ₀);

3. to i=1,2 ..., N, by P _{i ?1}move to object function I (A, B) and prolong c _ithe maximum position in direction, writes down this P _i;

4. to i=1,2 ..., N, by c _i+1be assigned to c _i, juxtaposition c _n=P _n?P ₀;

5. by P _nmove to object function I (A, B) at c _nmaximum point on direction, and the P recording this point ₀;

6. repeat step 2. to arrive 5., until functional value I (A, B) no longer increases.

The preferred embodiment of the present invention is: also comprised before carrying out image co-registration and carry out Image semantic classification.

Microwave tomoscan image preprocess method is as follows: large by external interference factor based on microwave Tomography, Image semantic classification we utilize point processing to carry out the expansion of contrast, make clear picture, feature is obvious, assuming that original image f (x, y) tonal range is [a, b], what the tonal range of the image g (x, y) after conversion was linear extends to [c, d], then there is grey linear transformation expression formula is:

$g(x,y)=\frac{d-c}{b-a}\×\[f(x,y)-a\]+c$

When the grey level distribution of pixel most of in image is in interval [a, b], f _maxfor the maximum gray scale of former figure, only have the gray level of a very little part to exceed this interval, then in order to improve reinforced effects, Wo Menling

$g(x,y)=\left\{\begin{array}{cc}c& 0\≤f(x,y)\≤a\\ \frac{d-c}{b-a}\×\[f(x,y)-a\]+c& a\≤f(x,y)\≤b\\ d& b\≤f(x,y)\≤f_{max}\end{array}\right.$

By the linear stretch to image, can effectively improve picture contrast effect.

Microwave radar image pre-processing method is as follows: because microwave radar imaging is except the intrinsic problem speckle noise existed, and also there is the random bright spot high-frequency noise occurred, we utilize low pass Recursive filtering method to carry out pretreatment to it simultaneously.

Suppose the grey decision-making x of each pixel in the n-th width microwave radar image _n(i, j) represents, α is correlation coefficient, then the image y after process _n(i, j) is

y _n(i，j)＝α*y _n‐1(i，j)+(1‐α)*x _n(i，j)(4)

Can be learnt by formula (4), the value of current each pixel only depends on the input of this pixel and the output of last time, has nothing to do with the value of other pixels, and we analyze its frequency characteristic by the transform method of one dimension, analyze the frequency response of each pixel self, namely have:

y(n)＝α*y(n‐1)+(1‐α)*x(n)(5)

Its transfer function is,

H(z)＝Y(z)/X(z)＝(1‐α)/(1‐αz ^‐1)(6)

In l-G simulation test, value α is the amplitude-frequency characteristic of 0.2,0.6 and 0.8, and α value is larger, and radio-frequency component is repressed more severe, weakens speckle noise more obvious.

As Fig. 1, shown in Fig. 2, the specific embodiment of the present invention is: the present invention builds a kind of multi-modal microwave breast imaging system, comprise microwave signal generating unit 1, microwave signal receiving element 2, radar imagery unit 3, Tomography unit 4, fusion treatment unit 5, described microwave signal generating unit 1 is to breast area generation microwave broadband pulse signal to be measured and microwave single-frequency coherent signal, described microwave signal receiving element 2 receives microwave broadband pulse echo signal and microwave single-frequency echo-signal, described radar imagery unit 3 generates radar detection image according to microwave broadband pulse echo signal, described Tomography unit 4 is according to microwave single-frequency echo signal form tomoscan image, the pixel of piece image in described radar detection image and described tomoscan image is mapped in another piece image and merges by described fusion treatment unit 5.

Specific implementation process is as follows: described microwave signal generating unit 1 is to breast area generation microwave broadband pulse signal to be measured and microwave single-frequency coherent signal, and described microwave signal receiving element 2 receives microwave broadband pulse echo signal and microwave single-frequency echo-signal.Described microwave signal generating unit 1 comprises microwave generator and microwave transmitting antenna, and described microwave signal receiving element 2 comprises microwave antenna, and microwave antenna comprises microwave transmitting antenna and microwave antenna.Microwave signal generating unit 1 by microwave antenna to breast area generation microwave broadband pulse signal to be measured, microwave broadband pulse signal irradiates the focal area in imaging region, produce scattering on surface, focal area, receive the signal from focus surface scattering with the scanning of several microwave antennas.Microwave signal generating unit 1 is by microwave antenna to breast area generation microwave single-frequency coherent signal to be measured, and microwave antenna scanning receives and records the microwave broadband pulse echo signal of position.Microwave transmitting antenna and microwave antenna can be same microwave antenna, are used alternatingly; Microwave transmitting antenna and microwave antenna also can be respectively different microwave antenna, carry out launched microwave signal respectively and receive microwave echoes signal using.Microwave signal generating unit is multiple, respectively microwave broadband pulse signal and microwave single-frequency coherent signal occurs; Or microwave signal generating unit is one, alternately there is microwave broadband pulse signal and microwave single-frequency coherent signal.Microwave radar image-forming principle utilizes theory of SAR, using a miniature antenna as single radiating element, the continuous motion scan in direction along a straight line, selects some positions to transmit in movement, receive the echo-signal of corresponding transmitting site, the amplitude of storage Received signal strength and phase place.Received the time of microwave broadband pulse echo signal by microwave antenna record, can time delay be calculated, and the distance of microwave transmitting antenna and focus is fixed, therefore the distance of micro-transmitting antenna to focus can be obtained, thus carry out accurate imaging.Microwave wave circuits and systems method is similar to computed tomography (CT), it is a kind of THE INVERSE ELECTROMAGNETIC SCATTERING method, by scattering object external observation to electromagnetic field carry out the electromagnetic signature parameter distribution in inversion imaging region, thus judge the information such as position, shape and size distribution of scattering object target.By the microwave single-frequency echo-signal received, generate tomoscan image according to the position of electromagnetic signature parameter distribution and scattering object target, shape and size distributed intelligence.The pixel of piece image in described radar detection image and described tomoscan image is mapped in another piece image by described fusion treatment unit 5, makes the related pixel point of two width images on locus, reach the fusion unanimously completing this two width image.

Image co-registration comprises multiple method: a kind of method is labelling method, described fusion treatment unit 5 also comprises image tagged module 51, image tagged identification module 52, image optimization module 53, the characteristic point place of described image tagged module 51 image in described radar detection image and described tomoscan image carries out labelling, the image tagged coincidence of described radar detection image and described tomoscan image is merged described radar detection image and described tomoscan image.The image tagged of described radar detection image and described tomoscan image identifies by described image tagged identification module 52.Described image optimization module is optimized the image after labelling, after segmentation, carries out image co-registration to cut zone.When image co-registration, the image tagged of described radar detection image and described tomoscan image is identified, then recognition image is carried out image co-registration as boundary mark.In specific embodiment, after carrying out labelling, image is optimized.Image tagged software design becomes the boundary mark of the Feature point recognition of image as Images uniting.Image tagged software according to described radar detection image and tomoscan image to the labelling of tissue identification, the labelling of lymph node identification and the labelling of characteristic, coordinate axes forms coincide point, complete the fusion of described radar detection image and tomoscan image, the method is equally applicable to two dimension that other modes combine or three-dimensional breast image.Further comprises the display to multi-modal microwave breast image, the two and three dimensions information of display breast, to the labelling of focal area.Another kind method is pixel weighted mean method, that is: the image pixel weighted average of described radar detection image and described tomoscan image correspondence position is completed image co-registration.

The preferred embodiment of the present invention is: described microwave antenna forms aerial array.Aerial array can meet the demand of microwave radar imaging and microwave Tomography simultaneously, and aerial array entirety turns to towards 32 of half ball center dual-mode antenna unit in hemispherical.Aerial array is divided into transmitting and receiving unit, alternately arrange at equal intervals, corresponding two receiving elements of transmitting element, staggered transmitting-receiving, by microwave control unit control antenna array to measured target sequential filming microwave radar detectable signal, control mode is single pole multiple throw.Microwave control unit provides cline frequency ripple to microwave switch aerial array, and operating frequency range is 1 to 30GHz.

Technique effect of the present invention is: build a kind of multi-modal microwave breast formation method and system, by being mapped in another piece image by the pixel of piece image in described radar detection image and described tomoscan image, make the related pixel point of two width images on locus, reach the fusion unanimously completing this two width image.Can have complementary advantages by using different image modes in the process of diagnosis earlier stage cancer patients, microwave radar imaging utilizes ultra-wideband microwave signal to obtain the high-resolution of target scattering center in distance, then doppler information is utilized, obtain the high-resolution of scattering center in lateral separation, both combine two dimension or the dimensional resolution that can obtain target, thus the multidigit high-resolution of target is achieved.Microwave Tomography is by low power microwave directive testee, under the excitation of microwave, measured object produces a scattered field, this scattered field distributes relevant with the complex dielectric permittivity of measured object inside, by the measurement to this scattering, obtain the relative dielectric constant of measured object and the distribution of electrical conductivity, the microwave wave circuits and systems of measured object internal object after carrying out corresponding information processing, can be obtained.By these two kinds of technology successful fusion in the present invention, form a set of multi-mode microwave breast imaging system, reach the good and bad complementary object of imaging.

Above content is in conjunction with concrete preferred implementation further description made for the present invention, can not assert that specific embodiment of the invention is confined to these explanations.For general technical staff of the technical field of the invention, without departing from the inventive concept of the premise, some simple deduction or replace can also be made, all should be considered as belonging to protection scope of the present invention.

Claims (10)

1. a multi-modal microwave breast formation method, comprises the steps:

Microwave Scanning: to breast area generation microwave broadband pulse signal to be measured and microwave single-frequency coherent signal; Receive microwave broadband pulse echo signal and microwave single-frequency echo-signal;

Imaging respectively: generate radar detection image, according to microwave single-frequency echo signal form tomoscan image according to microwave broadband pulse echo signal;

Image co-registration: the pixel of piece image in described radar detection image and described tomoscan image is mapped in another piece image and merges.

2. multi-modal microwave breast formation method according to claim 1, it is characterized in that, the pixel of piece image in described radar detection image and described tomoscan image is mapped in another piece image, makes the related pixel point of two width images on locus, reach the fusion unanimously completing this two width image.

3. multi-modal microwave breast formation method according to claim 1, it is characterized in that, in described radar detection image and described tomoscan image, the characteristic point place of image carries out labelling, the image tagged coincidence of described radar detection image and described tomoscan image is merged described radar detection image and described tomoscan image, the image tagged of described radar detection image and described tomoscan image is identified, then recognition image is carried out image co-registration as boundary mark.

4. multi-modal microwave breast formation method according to claim 1, is characterized in that, in image co-registration step, the image pixel weighted average of described radar detection image and described tomoscan image correspondence position is completed image co-registration.

5. multi-modal microwave breast formation method according to claim 1, is characterized in that, be optimized after carrying out labelling to image.

6. a multi-modal microwave breast imaging system, it is characterized in that, comprise microwave signal generating unit, microwave signal receiving element, radar imagery unit, Tomography unit, fusion treatment unit, described microwave signal generating unit is to breast area generation microwave broadband pulse signal to be measured and microwave single-frequency coherent signal, described microwave signal receiving element receives microwave broadband pulse echo signal and microwave single-frequency echo-signal, described radar imagery unit generates radar detection image according to microwave broadband pulse echo signal, described Tomography unit is according to microwave single-frequency echo signal form tomoscan image, the pixel of piece image in described radar detection image and described tomoscan image is mapped in another piece image and merges by described fusion treatment unit.

7. multi-modal microwave breast imaging system according to claim 6, it is characterized in that, described fusion treatment unit also comprises image tagged module, the characteristic point place of described image tagged module image in described radar detection image and described tomoscan image carries out labelling, the image tagged coincidence of described radar detection image and described tomoscan image is merged described radar detection image and described tomoscan image.

8. multi-modal microwave breast imaging system according to claim 7, it is characterized in that, described fusion treatment unit also comprises image tagged identification module, and the image tagged of described radar detection image and described tomoscan image identifies by described image tagged identification module.

9. multi-modal microwave breast imaging system according to claim 7, it is characterized in that, also comprise image optimization module, described image optimization module is optimized the image after labelling.

10. multi-modal microwave breast imaging system according to claim 6, it is characterized in that, microwave signal generating unit is multiple, respectively microwave broadband pulse signal and microwave single-frequency coherent signal occurs; Or microwave signal generating unit is one, alternately there is microwave broadband pulse signal and microwave single-frequency coherent signal.