TW201907868A - Method and apparatus for measuring viscoelasticity of medium - Google Patents

Abstract

Provided is a method for measuring the viscoelasticity of a medium, comprising: obtaining a detected-wave echo signal of a medium under vibration excitation; obtaining the propagation mode of the detected-wave echo signal, and matching said propagation mode with a propagation mode sample stored in a propagation mode data set to determine the viscoelasticity of the medium; said data set is determined according to the propagation mode samples generated by various medium samples, having different viscoelasticities, under at least one vibration excitation. Said processor is also used for matching the propagation mode with a propagation mode sample stored in the propagation mode data set, and determining the viscoelasticity of the medium.

Description

Method and device for measuring viscoelasticity of medium

The invention relates to the field of measurement technology, and in particular to a method and a device for measuring the viscoelasticity of a medium.

When mechanical vibration or shear wave vibration propagates in the medium, at different moments, the wavefront will reach different positions along the propagation direction, so that the wavefront reaches different positions at different times. This information can form a position time map, in a uniform In the organization, the position time map is usually a straight twill pattern. For such a twill pattern, the slope is determined by the distance traveled by the vibration per unit time, that is, the speed at which the vibration propagates. In a uniform medium, the speed of vibration propagation is related to the viscoelasticity of the medium. Therefore, when vibrating the medium, the viscoelasticity of the medium can be measured by measuring the propagation characteristics of the vibration.

In the prior art, when measuring the viscoelasticity of a medium, it is necessary to select feature points, and linearly fit the feature points at different moments and different positions to obtain quantitative parameters of dynamic ultrasonic viscoelastic imaging. Usually, the feature point is determined by the displacement or strain of the medium when the vibration propagates in the medium. At this time, motion estimation is required to obtain information such as displacement or strain of the medium, and then subsequent operations are performed. However, this method has the problems of large computational complexity and complex feature point selection for motion estimation.

Embodiments of the present invention provide a method and apparatus for measuring the viscoelasticity of a medium. The invention aims to solve the problem that the calculation amount required for motion estimation in the viscoelastic measurement of the medium in the prior art is large, and the feature points are selected to be complicated. In order to have a basic understanding of some aspects of the disclosed embodiments, a brief summary is given below. This generalization is not a general comment, nor is it intended to identify key/critical constituent elements or to describe the scope of protection of these embodiments. Its sole purpose is to present some concepts in a simplified form as a prelude to the following detailed description.

In a first aspect, an embodiment of the present invention provides a method for measuring a viscoelasticity of a medium, comprising: acquiring a detection wave echo signal of a medium under vibration excitation; acquiring a propagation mode of the detection wave echo signal; and using the propagation mode and the propagation mode The propagation mode samples of the media samples of known viscoelastic information stored in the database are matched to determine the viscoelasticity of the medium.

With reference to the first aspect, the embodiment of the present invention provides a first optional implementation manner. Optionally, the vibration excitation is shear wave excitation, and the detection wave echo signal is an ultrasonic echo signal.

In conjunction with the first aspect, an embodiment of the present invention provides a second alternative embodiment, the propagation mode database comprising propagation mode samples generated by at least one vibration excitation according to different media samples of different viscoelasticity.

With reference to the first aspect, the embodiment of the present invention provides a third optional implementation manner, which acquires a propagation mode of a detection wave echo signal, including: acquiring a processing signal, and processing the signal as a filtered detection echo signal; Signal, get the propagation mode.

With reference to the third optional implementation manner of the first aspect, the embodiment of the present invention provides a fourth optional implementation manner. Optionally, the processing signal is a direction-filtered detection wave echo signal; or the processing signal is Detecting wave echo signals after Fourier filtering.

With reference to the first aspect, the embodiment of the present invention provides a fifth optional implementation manner, further comprising: exciting the vibration, detecting the wave echo signal and the viscoelasticity of the medium, and storing the information in the propagation mode database.

In conjunction with the first aspect, an embodiment of the present invention provides a sixth alternative embodiment: The vibration excitation includes: one of continuous or pulsating mechanical vibration and acoustic radiation force pulsation; the range of motion of the medium under vibration excitation is 0.01 micron to 10 mm; the medium moves at a vibration frequency of 20 Hz to 2500 Hz for a duration of 50 microseconds to 1 second.

With reference to the first aspect, the embodiment of the present invention provides a seventh optional implementation manner: the detection wave echo signal is an ultrasonic echo signal; the vibration excitation pulsation repetition frequency is 10 to 20000 Hz; the detection wave echo signal includes At least 100 consecutive frames of detected echo echo data.

In a second aspect, an embodiment of the present invention provides a device for measuring viscoelasticity of a medium, comprising: a probe for acquiring a detection wave echo signal of the medium under vibration excitation; and a processor for acquiring a detection wave acquired by the probe The propagation mode of the echo signal; the memory for storing the propagation mode database, the propagation mode database storing the propagation mode samples of the media samples with known viscoelastic information; the processor, which is also used for the propagation mode and the propagation mode The propagation pattern samples stored in the database are matched to determine the viscoelasticity of the medium.

With reference to the second aspect, the embodiment of the present invention provides a first optional implementation manner, including: a probe, which is also used to acquire an ultrasonic echo signal of a medium under shear wave excitation; a processor, which is also used to acquire a probe. The propagation mode of the ultrasonic echo signal; the memory is also used to store the propagation mode samples of the medium sample with known viscoelastic information under shear wave excitation.

With reference to the second aspect, the embodiment of the present invention provides a second optional implementation manner, where the processor is further configured to: determine a propagation mode according to a propagation mode sample generated by at least one vibration excitation of multiple medium samples of different viscoelasticity database.

With reference to the second aspect, the embodiment of the present invention provides a third optional implementation manner, further including: a filter, configured to acquire a processing signal, and the processing signal is a detection wave echo signal obtained by the filtered probe; It is also used to acquire the propagation mode according to the processing signal acquired by the filter.

With the third optional implementation manner of the second aspect, the embodiment of the present invention provides a fourth optional implementation manner, where the processing signal is a direction-filtered detection wave echo signal; or the processing signal is Fourier-filtered. Detect wave echo signals.

With reference to the second aspect, the embodiment of the present invention provides a fifth optional implementation manner, where the processor is further configured to: excite the vibration, detect the echo signal of the wave and the viscoelasticity of the medium, and store the propagation mode data stored in the memory. In the library.

In the embodiment of the present invention, by establishing a propagation mode database and searching for the propagation mode based on the propagation mode database, the measurement result of the medium viscoelasticity can be obtained without performing motion estimation and feature point selection, and the operation is performed. The amount is greatly reduced and the measurement speed is significantly accelerated.

The above general description and the following detailed description are intended to be illustrative and not restrictive.

The detailed description of the embodiments of the invention are set forth in the description The examples represent only possible variations. Individual components and functions are optional unless explicitly required, and the order of operations may vary. Portions and features of some embodiments may be included or substituted for portions and features of other embodiments. The scope of the embodiments of the present invention includes the entire scope of the claims and all available equivalents of the claims. In this context, various embodiments may be referred to individually or collectively by the term "invention," for convenience only, and if more than one invention is disclosed, it is not intended to automatically limit the scope of the application to any A single invention or inventive concept. Herein, relational terms such as first and second, etc. are used merely to distinguish one entity or operation from another entity or operation, and do not require or imply any actual relationship between these entities or operations or order. Furthermore, the term "comprises" or "comprises" or "comprises" or any other variations thereof is intended to encompass a non-exclusive inclusion, such that a program, method, or device that includes a plurality of elements includes not only those elements but also other items not specifically listed. Elements. The various embodiments herein are described in a progressive manner, and each embodiment focuses on differences from other embodiments, and the same similar parts between the various embodiments may be referred to each other. For the structures, products, and the like disclosed in the embodiments, since they correspond to the parts disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the description of the method parts.

The embodiment of the present invention discloses a method for measuring the viscoelasticity of a medium. As shown in FIG. 1 , the method includes: S101: acquiring a detection wave echo signal of the medium under vibration excitation; S102: acquiring a propagation mode of the detection wave echo signal; S103: Matching the propagation mode to the propagation mode sample of the media sample of the known viscoelastic information stored in the propagation mode database to determine the viscoelasticity of the medium.

Optionally, the propagation mode database includes propagation mode samples generated by the plurality of media samples according to different viscoelasticity under at least one vibration excitation.

Specifically, in S101, the vibration excitation includes, but is not limited to, mechanical vibration excitation or acoustic radiation force excitation, and the detection wave includes but is not limited to ultrasonic waves or light waves, and may be generated by mechanical vibration, acoustic radiation force or the like. In the way of vibration, after the medium is vibrated and excited, the medium vibrates and the vibration propagates in the medium. Since the velocity of vibration in the medium is limited, it is possible to track the propagation mode of the vibration using ultrasonic waves, light waves or other waves with a relatively fast propagation speed. The detection wave echo signal of the medium under vibration excitation is obtained to reflect the propagation mode of the vibration in the medium. The viscoelasticity of the medium is an important factor in determining the mode of vibration propagation in the medium. When the medium is excited by vibration, a corresponding propagation state will be generated at different times, and the change of the propagation state along time constitutes a propagation mode. The propagation state refers to the state of motion of the medium at a certain moment, and the mode of propagation is the change of the propagation state of the medium along time.

Optionally, when the vibration is excited by one of continuous or pulsating mechanical vibration and acoustic radiation force pulsation, the medium has a motion range of 0.01 micrometer to 10 mm under vibration excitation, and the medium has a motion frequency under vibration excitation. 20 Hz to 2500 Hz with a duration of 50 microseconds to 1 second.

When the medium has different viscoelastic properties, the propagation state is different, and further causes the difference of the detection wave echo signals.

In S103, the database stores the propagation mode samples of the media samples with known viscoelastic information, and finds the propagation mode samples corresponding to the propagation modes in the propagation mode database to determine the corresponding medium viscoelasticity.

Alternatively, the medium viscoelasticity may include a combination of at least one or more of shear modulus, Young's modulus, shear viscoelasticity, shear viscosity, mechanical impedance, mechanical relaxation time, and anisotropy.

Optionally, the viscoelasticity includes at least one of viscosity and elasticity. Illustratively, when the viscoelasticity is viscous, the viscoelastic information may include viscous information, or viscous information and elastic information. Illustratively, when the viscoelasticity is elastic, the viscoelastic information may include elastic information, or viscous information and elastic information. Illustratively, when viscoelasticity is viscous and elastic, the viscoelastic information can include viscous information and elastic information.

Optionally, after S103, the method further includes: S104: exciting the vibration, detecting the wave echo signal and the viscoelasticity of the medium, and storing the information in the database.

Specifically, the stored vibration excitation, detecting the wave echo signal and the viscoelasticity of the medium can be used for searching and matching in the subsequent measurement of the viscoelasticity of the medium.

The embodiment of the invention can find the medium sample with the highest degree of similarity to the medium to be measured in the propagation mode database, and determine the viscoelasticity of the medium to be measured by the propagation mode sample of the medium sample under vibration excitation, and can perform motion estimation and When the feature points are selected, the measurement results of the viscoelasticity of the medium are obtained, and the amount of calculation is greatly reduced, and the measurement speed is remarkably accelerated.

Exemplarily, when the vibration excitation is a shear wave excitation, the detection wave is an ultrasonic wave, and the detection wave echo signal is an ultrasonic echo signal, the embodiment of the present invention also discloses another method for measuring the viscoelasticity of the medium, as shown in FIG. 2 . The method includes: S201: acquiring an ultrasonic echo signal of the medium under shear wave excitation; S202: acquiring a propagation mode of the ultrasonic echo signal; S203: acquiring known viscoelastic information stored in the propagation mode and the propagation mode database The propagation mode samples of the media samples are matched to determine the viscoelasticity of the medium.

Optionally, the propagation mode database includes propagation mode samples generated by the plurality of media samples of different viscoelasticity under at least one vibration excitation.

Optionally, the propagation mode database can also be obtained in advance by experiment or simulation analysis, and stored in a local server or a cloud server, so that the data information can be read or called conveniently when used. .

Optionally, when the detection wave echo signal is an ultrasonic echo signal, the vibration excitation pulsation repetition frequency is 10 to 20,000 Hz, and the detection wave echo signal includes at least 100 consecutive frame detection wave echo data.

Optionally, after S203, the method further includes: S204: exciting the shear wave, the ultrasonic echo signal, and the viscoelasticity of the medium, and storing the data in the propagation mode database.

Specifically, the saved shear wave excitation, the ultrasonic echo signal, and the viscoelasticity of the medium can be used for matching matching in the subsequent measurement of the viscoelasticity of the medium.

Optionally, the propagation mode database may be obtained by means of simulation calculation, or may be obtained by statistical summarization of a large amount of experimental data or measured data, or may be a combination of the two methods.

S203 may further include: S2031: acquiring a target propagation mode sample that matches a propagation mode of the ultrasonic echo signal in the propagation mode database; S2032: determining a viscoelasticity of the target medium sample corresponding to the target propagation mode sample as a medium.

The propagation mode database can store multiple sets of data. Each set of data records the acquisition and processing results of dynamic imaging information of a medium sample over time under a vibration excitation, that is, the propagation mode of the detected echo signals. Specifically, the propagation mode database may store at least one medium sample, a propagation mode sample generated by at least one shear wave excitation, and a propagation mode database, or a medium sample including a viscoelasticity of the medium sample. A variety of attribute parameters have been pre-stored. Therefore, when the technical solution disclosed in the embodiment of the present invention is implemented by a person skilled in the art, the specific shear wave used in the measurement process and the obtained propagation mode of the ultrasonic echo signal can be used in the propagation mode data. A matching target propagation mode sample is found in the library, the target medium sample corresponding to the target propagation mode sample is determined, and then the target medium sample viscoelasticity is determined as the medium viscoelasticity to be measured.

Optionally, the method for matching the obtained propagation mode and the propagation mode sample to determine the target propagation mode sample may be any one of the pattern matching methods, which is not limited by the embodiment of the present invention.

Another embodiment of the present invention discloses a method for measuring the viscoelasticity of a medium, as shown in FIG. 3, comprising: S301: acquiring a detection wave echo signal of the medium under vibration excitation; S302: acquiring a processing signal, wherein the processing signal is processed The filtered echo signal is filtered; S303: acquiring the propagation mode according to the processing signal; S304: matching the propagation mode with the propagation mode sample stored in the propagation mode database to determine the viscoelasticity of the medium. The propagation mode database is determined according to the propagation mode samples generated by the plurality of medium samples of different viscoelasticity under at least one vibration excitation.

In S302, the processing signal may be a direction-filtered detection wave echo signal, or may be a Fourier-filtered detection wave echo signal, or other manner, the filtered detection echo signal, which is used in the embodiment of the present invention. Not limited.

In S304, the propagation mode database stores the correspondence between the propagation mode and the viscoelasticity of the medium under vibration excitation. According to the vibration excitation and propagation mode, the corresponding medium viscoelasticity can be determined by searching in the propagation mode database.

The embodiment of the invention is based on the database. By searching and comparing the propagation modes, the measurement results of the viscoelasticity of the medium can be obtained without performing motion estimation and feature point selection, and the calculation amount is greatly reduced, and the measurement speed is significantly accelerated. At the same time, by filtering the detected wave echo signal, the processing signal is obtained, and the propagation mode is obtained according to the processing signal, so that the propagation mode of the detection wave echo signal can be obtained more quickly and accurately.

Illustratively, when the vibration excitation is a shear wave excitation, the detection wave is an ultrasonic wave, and the detection wave echo signal is an ultrasonic echo signal, and the database is a propagation mode database, the embodiment of the present invention also discloses another medium viscosity. The elastic measurement method, as shown in FIG. 4, includes: S401: acquiring an ultrasonic echo signal of the medium under shear wave excitation; S402: acquiring a processing signal, wherein the processing signal is a filtered ultrasonic echo signal; S403 Obtaining a propagation mode according to the processing signal; S404: matching the propagation mode with a propagation mode sample stored in the propagation mode database to determine a viscoelasticity of the medium, wherein the propagation mode database is based on a plurality of media samples of different viscoelasticity The propagation mode samples generated under at least one vibration excitation are determined.

Optionally, the propagation mode database can also be obtained in advance by experiment or simulation analysis, and stored in a local server or a cloud server, so that the information information can be conveniently completed when using the propagation mode database. Read or call.

S404 may further include: S4041: obtaining a target propagation mode sample that matches the propagation mode in the propagation mode database; S4042: determining that the target media sample viscoelasticity corresponding to the target propagation mode sample is the medium viscoelasticity.

Optionally, after S404, the method further includes: S405: exciting the shear wave, the propagation mode, and the viscoelasticity of the medium in the propagation mode database.

Specifically, the saved shear wave excitation, the propagation mode, and the viscoelasticity of the medium can be used for matching matching in the subsequent measurement of the viscoelasticity of the medium.

The embodiment of the present invention further discloses a medium viscoelasticity measuring device 50, as shown in FIG. 5, comprising: a probe 501 for acquiring a detection wave echo signal of the medium under vibration excitation; and a processor 503 for acquiring The propagation mode of the detection wave echo signal obtained by the probe; the memory 502 for storing the propagation mode database, the propagation mode database storing the propagation mode samples of the media sample with the known viscoelastic information; the processor 503, also used for The propagation mode is matched with the propagation mode samples stored in the propagation mode database to determine the viscoelasticity of the medium.

Optionally, the probe 501 is further configured to obtain an ultrasonic echo signal of the medium under the excitation of the shear wave; the processor 503 may also be configured to acquire a propagation mode of the ultrasonic echo signal acquired by the probe; the memory 502, further It can be used to store a propagation mode sample of a medium sample with known viscoelastic information under shear wave excitation; the processor 503 can also be used to match the propagation mode with the propagation mode sample stored in the propagation mode database, and determine The viscoelastic properties of the medium.

Optionally, the processor 503 is further configured to determine a database according to the propagation mode samples generated by the plurality of media samples of different viscoelasticity under the excitation of at least one shear wave.

Optionally, the processor 503 may further determine a propagation mode sample according to the ultrasonic echo signal samples generated by the plurality of media samples of different viscoelasticity under the at least one vibration excitation; and determine the propagation mode database according to the propagation mode samples.

Optionally, the processor 503 is further configured to obtain a target propagation mode sample that matches the propagation mode in the propagation mode database, and determine that the target media sample viscoelasticity corresponding to the target propagation mode sample is the medium viscoelasticity.

It should be noted that the measuring device shown in FIG. 5 can be used to perform all the steps in the measuring methods shown in FIG. 1 and FIG. 2, and the related content has been described in the foregoing embodiment, and is no longer described here. Narration.

The embodiment of the present invention further discloses a medium viscoelasticity measuring device 60, as shown in FIG. 6, comprising: a probe 601 for acquiring a detection wave echo signal of the medium under vibration excitation; and a filter 602 for acquiring Processing the signal, wherein the processing signal is the detection wave echo signal acquired by the filtered probe 601; the processor 604 is configured to acquire the propagation mode according to the processing signal acquired by the filter 602.

The memory 603 is configured to store a propagation mode database, wherein the propagation mode database stores a propagation mode sample of the medium sample with known viscoelastic information under vibration excitation; the processor 604 is further configured to use the propagation mode The propagation mode samples stored in the propagation mode database are matched to determine the viscoelasticity of the medium.

Optionally, the probe 601 can also be used to obtain an ultrasonic echo signal of the medium under shear wave excitation; the filter 602 can also be used to acquire a processing signal, wherein the processing signal is the ultrasonic wave acquired by the filtered probe 601. The echo signal; the processor 604 is further configured to obtain a propagation mode according to the processing signal acquired by the filter 602.

The memory 603 can also be used to store a propagation mode database, wherein the propagation mode database stores a propagation mode sample of the medium sample with known viscoelastic information under shear wave excitation; the processor 604 can also be used for The propagation mode is matched with the propagation mode samples stored in the propagation mode database to determine the viscoelasticity of the medium.

Optionally, the processor 604 is further configured to determine a propagation mode sample according to the ultrasonic echo signal samples generated by the plurality of media samples of different viscoelasticity under the at least one vibration excitation, and determine the data base according to the propagation mode samples.

Optionally, the processor 604 is further configured to obtain a target propagation mode sample that matches the propagation mode in the propagation mode database, and determine that the target media sample viscoelasticity corresponding to the target propagation mode sample is the medium viscoelasticity.

Optionally, the processor 604 can also be used to excite the shear wave, process the signal and the viscoelasticity of the medium, and store the data in the propagation mode database stored in the memory 603.

It should be noted that the measuring device shown in FIG. 6 can be used to perform all the steps in the measuring methods shown in FIG. 3 and FIG. 4, and the related content has been described in the foregoing embodiment, and is no longer described here. Narration.

It is to be understood that the invention is not to be construed as being limited to The scope of the invention is limited only by the scope of the appended claims.

S101, S102, S103, S201, S202, S203, S204, S301, S302, S303, S304, S401, S402, S403, S404‧‧

50, 60‧‧‧ measuring devices

501, 601‧‧ ‧ probe

502, 603‧‧‧ memory

503, 604‧‧‧ processor

602‧‧‧ filter

The accompanying drawings, which are incorporated in the specification of FIG 1 is a flow chart of a method for measuring viscoelasticity of a medium according to an embodiment of the present invention; FIG. 2 is a flow chart of another method for measuring viscoelasticity of a medium disclosed in an embodiment of the present invention; FIG. 4 is a flow chart of another method for measuring the viscoelasticity of a medium disclosed in the embodiment of the present invention; FIG. 5 is a flow chart of a medium disclosed in an embodiment of the present invention; A schematic diagram of an elastic measuring device; FIG. 6 is a schematic view of another medium viscoelastic measuring device disclosed in the embodiment of the present invention.

Claims (14)

A method for measuring a viscoelasticity of a medium, comprising: acquiring a detection wave echo signal of the medium under vibration excitation; acquiring a propagation mode of the detection wave echo signal; and using the propagation mode and a propagation mode The propagation mode samples of a medium sample of known viscoelastic information stored in the database are matched to determine the viscoelasticity of the medium. The method of claim 1, wherein the vibration excitation is a shear wave excitation, and the detection wave echo signal is an ultrasonic echo signal. The method of claim 1, wherein: the propagation mode database comprises a propagation mode sample generated by the plurality of medium samples of different viscoelasticity under at least one vibration excitation. The method of claim 1, wherein the acquiring the propagation mode of the detection echo signal comprises: acquiring a processing signal, wherein the processing signal is the filtered echo signal; according to the processing Signal to get the propagation mode. The method of claim 4, wherein the processing signal is a direction-filtered detection echo signal; or the processing signal is a Fourier-filtered detection echo signal. The method of claim 1, further comprising: storing the vibration excitation, the detection wave echo signal, and the viscoelasticity of the medium in the propagation mode database. The method of claim 1, wherein: the vibration excitation comprises: one of a mechanical vibration and a radiation force pulsation in a continuous or pulsating manner; the medium has a range of motion of 0.01 under the vibration excitation Micron to 10 mm; The medium is excited by this vibration at a frequency of 20 Hz to 2500 Hz for a duration of 50 microseconds to 1 second. The method of claim 1, wherein: the detection wave echo signal is an ultrasonic echo signal; the vibration excitation pulsation repetition frequency is 10 to 20,000 Hz; the detection wave echo signal includes at least continuous The collected 100 frame detection wave echo data. A device for measuring viscoelasticity of a medium, comprising: a probe for acquiring a detection wave echo signal of the medium under vibration excitation; and a processor for acquiring the detection wave obtained by the probe a propagation mode of the wave signal; a memory for storing a propagation mode database, the propagation mode database storing a propagation mode sample of a media sample having known viscoelastic information; the processor is further configured to The propagation mode matches the propagation mode samples stored in the propagation mode database to determine the viscoelasticity of the medium. The measuring device of claim 9, wherein the probe is further configured to acquire an ultrasonic echo signal of the medium under a shear wave excitation; the processor is further configured to acquire the acquired by the probe a propagation mode of the ultrasonic echo signal; the memory is further configured to store a propagation mode sample of a medium sample of known viscoelastic information under the excitation of the shear wave. The measuring device according to claim 9, wherein the processor is further configured to: determine the propagation mode database according to a propagation mode sample generated by the plurality of medium samples of different viscoelasticity under at least one vibration excitation . The measuring device of claim 9, further comprising: a filter for acquiring a processing signal, wherein the processing signal is the filtered echo signal obtained by the filtered probe; the processor And is further configured to acquire the propagation mode according to the processing signal obtained by the filter. The measuring device of claim 12, wherein the processing signal is a direction-filtered detection echo signal; or the processing signal is a Fourier-filtered detection echo signal. The measuring device of claim 9, wherein the processor is further configured to: store the vibration excitation, the detection wave echo signal and the viscoelasticity of the medium in the propagation mode stored in the memory In the database.