Two-dimensional coding and decoding methods for ultrasonic synthetic aperture imaging

Abstract

This application provides a two-dimensional encoding and decoding method for ultrasonic synthetic aperture imaging. The method includes: generating an order Hadamard matrix for an ultrasonic transducer array with n elements, where is a multiple of 8; generating an order serial encoding matrix according to the requirements of axial resolution and near-field dead zone; performing co-encoded transmission and acquisition using n two-dimensional encoding matrices generated by matrix multiplication of the Hadamard matrix and the serial encoding matrix, where ; performing dual decoding of the acquired echo data based on the two-dimensional encoding matrices; and using the decoded data for synthetic aperture imaging. This application can improve the depth and contrast of ultrasonic synthetic aperture imaging.

Description

Technical Field

[0001] This application relates to the field of ultrasonic imaging and signal processing technology, and in particular to a two-dimensional encoding and decoding method for ultrasonic synthetic aperture imaging. Background Technology

[0002] Ultrasonic imaging technology has wide applications in deep-sea exploration, non-destructive testing, and medical diagnostics. In all these applications, the resolution, contrast, and signal-to-noise ratio of ultrasound images are three crucial parameters. Improving these three parameters can further enhance the practical value of ultrasound imaging.

[0003] Synthetic aperture imaging (SAP) is an advanced imaging technique. It involves independently exciting each element in an ultrasonic transducer array in a round-robin fashion, simultaneously acquiring data from all elements to obtain a large volume of echo data (referred to as synthetic aperture data or complete data). Due to the sheer volume and rich information of synthetic aperture data, and the flexibility allowed for post-processing algorithms, SAP theoretically offers high resolution and contrast. Because it does not rely on specific array geometry or Huygens' principle for emission focusing, this technique is particularly suitable for three-dimensional ultrasonic imaging based on two-dimensional sparse arrays.

[0004] However, the energy of the polling independent transmission mode is very weak, resulting in an extremely low signal-to-noise ratio (SNR) for the echo signal. Therefore, conventional synthetic aperture imaging (SAP) has significant limitations in terms of SNR and imaging depth. In practice, the transmission energy is usually increased by encoding the transmission, and high SNR synthetic aperture data is recovered using decoding algorithms. Existing technologies typically perform encoding and decoding in isolation along the time or spatial dimensions, and the resulting SNR gain remains limited. Summary of the Invention

[0005] The purpose of this application is to provide a two-dimensional encoding and decoding method for ultrasonic synthetic aperture imaging, which can solve at least one technical problem mentioned in the prior art.

[0006] One aspect of this application provides a two-dimensional encoding and decoding method for ultrasonic synthetic aperture imaging. The method includes: for a... An array of ultrasonic transducers with individual elements generates a... Hadamard matrix ,in, It is a multiple of 8; based on the requirements of axial resolution and near-field dead zone range, it generates Level serial encoding matrix Using the aforementioned Hadamard matrix and the serial encoding matrix Generated by matrix multiplication Two-dimensional encoding matrix , to conduct Secondary encoding transmission and acquisition, among which... The acquired echo data is dual-decoded according to the two-dimensional coding matrix; the decoded data is then used for synthetic aperture imaging.

[0007] Furthermore, the Hadamard matrix Each row corresponds to a coding template of one element dimension; the serial coding matrix Each row corresponds to a clock dimension encoding template.

[0008] Furthermore, based on the requirements of axial resolution and near-field dead zone range, the generation... Level serial encoding matrix This includes: determining the number of levels of the serial encoding matrix based on the requirements for axial resolution and near-field dead zone range. ; Generate according to the iterative replication method The serial encoding matrix of level .

[0009] Furthermore, the number of levels of the serial encoding matrix is ​​determined according to the following formula. :

[0010] ,

[0011] ,

[0012] in, Represents the number of cycles of the excitation pulse unit. This represents rounding down. This represents the requirement for axial resolution. This represents the center frequency of the transducer. Represents the length of the near-field dead zone. The estimated sound velocity constant represents the imaging medium.

[0013] Furthermore, the method of generating according to iterative replication... The serial encoding matrix of level Includes the following steps:

[0014] Step 1: Generate a 2nd order Hadamard matrix , as the initial serial encoding matrix ,make ;

[0015] Step Two: After being divided equally in all directions, it is represented by a block matrix, denoted as . ,generate and order ;

[0016] Step 3: Repeat step 2 until... equal That is, to obtain The serial encoding matrix of level .

[0017] Furthermore, the size of each of the two-dimensional coding matrices is Each row represents the encoding method of the array element direction at each excitation time, and each column represents the encoding method of each array element in the excitation time direction.

[0018] Furthermore, the two-dimensional encoding matrix is ​​generated in pairs as follows:

[0019] ,

[0020] ,

[0021] in, Less than odd numbers, and Represent The first order of the Hadamard matrix row and number OK, , , , Represent The serial encoding matrix of level In the block matrix representation, the vectors at the top left, bottom left, top right, and bottom right are... , , , They are , , , The transpose of .

[0022] Furthermore, the elements of the two-dimensional encoding matrix include only two encodings: +1 and -1. The +1 encoding represents that the excitation pulse unit is emitted with a positive sign, and the -1 encoding represents that the excitation pulse unit is emitted after inverting its sign.

[0023] Furthermore, the dual decoding of the acquired echo data based on the two-dimensional coding matrix includes: first performing serial decoding on the acquired echo data based on the two-dimensional coding matrix, and then performing array element decoding.

[0024] Furthermore, the execution of serial decoding includes the following steps:

[0025] Step 1: Perform a Fourier transform on the acquired echo data to obtain the common echo signal. Frame rate domain data, making ;

[0026] Step Two: Select the first Frame and the Frame echo data, making ;

[0027] Step 3: Proceed to the next step The serial decoding process involves adding two frames of data and subtracting them, then multiplying by a timing advance factor. This yields two new frames of data;

[0028] Step 4: Let And repeat step three until the total is completed. Serial decoding;

[0029] Step 5: Let Perform steps two through four until all processes are complete. Frame echo data.

[0030] Furthermore, the aforementioned time advance factor Determined by the following formula:

[0031] ,

[0032] in, Represents the number of cycles of the excitation pulse unit. This represents the center frequency of the transducer.

[0033] Furthermore, the execution of array element decoding includes the following steps:

[0034] Step 1: Let ;

[0035] Step 2: Extract the data obtained from serial decoding The first frame of echo data The data corresponding to each array element are concatenated to form a... , where, The number of sampling points representing the echo;

[0036] Step 3: Put Data frame left multiplication The transpose of the Hadamard matrix of order X That is, to obtain the first Each array element corresponds to the echo data emitted by all array elements;

[0037] Step 4: Let Repeat steps two and three to obtain complete frequency domain synthetic aperture data.

[0038] The two-dimensional encoding and decoding method for ultrasonic synthetic aperture imaging in this application combines serial encoding (time dimension) and array element encoding (spatial dimension) to form a two-dimensional encoded transmission to improve transmission energy, and performs decoding in the frequency domain through a simple linear transformation to obtain ultrasonic synthetic aperture data with a high signal-to-noise ratio, thereby improving the depth and contrast of ultrasonic synthetic aperture imaging. Attached Figure Description

[0039] Figure 1 This is a flowchart illustrating a two-dimensional encoding and decoding method for ultrasonic synthetic aperture imaging according to an embodiment of this application.

[0040] Figure 2 This is an embodiment of the present application showing the 8-element encoding template corresponding to an 8-element linear array and an 8th-order Hadamard matrix.

[0041] Figure 3 Generate a 3-level serial encoding matrix for one embodiment of this application The specific process.

[0042] Figure 4 This is a schematic diagram illustrating the encoding and transmission of a 4-element linear array under a given two-dimensional encoding matrix, according to an embodiment of this application.

[0043] Figure 5 A two-dimensional encoding matrix of one embodiment of this application The specific generation method.

[0044] Figure 6 This is a schematic diagram illustrating the serial decoding process of two frames of echo data according to an embodiment of this application. Detailed Implementation

[0045] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numerals in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses consistent with some aspects of this application as detailed in the appended claims.

[0046] The two-dimensional encoding and decoding method for ultrasonic synthetic aperture imaging of this application will be described in detail below with reference to the accompanying drawings. Unless otherwise specified, the features in the following embodiments and implementations can be combined with each other.

[0047] Figure 1 A schematic flowchart illustrating a two-dimensional encoding and decoding method for ultrasonic synthetic aperture imaging according to an embodiment of this application is provided. Figure 1As shown, a two-dimensional encoding and decoding method for ultrasonic synthetic aperture imaging according to an embodiment of this application may include the following steps S1 to S5.

[0048] Step S1: For a given... An array of ultrasonic transducers with individual elements generates a... Hadamard matrix ,in, It is a multiple of 8.

[0049] Hadama matrix Each row corresponds to a coding template for one array element dimension.

[0050] Figure 2 This application discloses an embodiment of the encoding template for the 8 elements of an 8-element linear array, corresponding to an 8th-order Hadamard matrix. For example... Figure 2 As shown, white elements represent +1 encoding, and black elements represent -1 encoding. These encoding templates represent the cooperative transmission modes of all elements in the array. These different cooperative transmissions all have higher transmission energy than independent rotational transmissions, thus achieving a preliminary improvement in the echo signal-to-noise ratio.

[0051] Return to reference Figure 1 Step S2: Generate based on the requirements of axial resolution and near-field dead zone range. Level serial encoding matrix .

[0052] Serial encoding matrix Each row corresponds to a clock-dimensional encoding template. Encoding is performed in the time dimension to further improve transmission energy, and this encoding method consists of a serial encoding matrix. To express it.

[0053] When using time coding, the near-field echo signal is submerged in the lengthened excitation signal, resulting in meaningless artifacts in the near field of the image, known as the near-field dead zone. To control the size of the near-field dead zone, the length of the time code must be limited. Furthermore, imaging generally requires axial resolution, which is affected by the number of cycles of the excitation pulse unit. A larger number of cycles results in poorer resolution. Therefore, both factors must be considered when determining the serial coding matrix. .

[0054] In some embodiments, step S2 generates [the required parameters] based on the requirements of axial resolution and near-field dead zone range. Level serial encoding matrix It may further include the following steps S21 and S22.

[0055] Step S21: Determine the number of levels in the serial coding matrix based on the requirements for axial resolution and near-field dead zone. .

[0056] First, calculate the number of cycles of the excitation pulse unit. Based on the relationship between axial resolution and pulse length, the following can be derived:

[0057] ,

[0058] in, This represents rounding down. This represents the requirement for axial resolution. This represents the center frequency of the transducer.

[0059] Next, considering that the dead zone range is the coverage depth of the sound wave round trip within the total excitation time, and the relationship between the serial coding matrix and its coding length, the series of the serial coding matrix can be derived. As shown below:

[0060] ,

[0061] in, Represents the length of the near-field dead zone. The estimated sound velocity constant represents the imaging medium.

[0062] Step S22: Generate according to the iterative replication method. Level serial encoding matrix .

[0063] In some embodiments, step S22 generates the product according to the iterative replication method. Level serial encoding matrix It may further include the following steps S221 to S223.

[0064] Step S221: Generate a 2nd order Hadamard matrix , as the initial serial encoding matrix ,make .

[0065] Step S222: After being divided equally in all directions, it is represented by a block matrix, denoted as . ,generate and order .

[0066] Step S223: Repeat step S222 until... equal That is, to obtain Level serial encoding matrix .

[0067] Figure 3This application discloses an embodiment of generating a 3-level serial encoding matrix. The specific process.

[0068] Continue to refer to Figure 1 Step S3: Use the Hadamard matrix and serial encoding matrix Generated by matrix multiplication Two-dimensional encoding matrix , to conduct Secondary encoding transmission and acquisition, among which... .

[0069] The elements of the two-dimensional coding matrix include only two codes: +1 and -1. The +1 code represents that the excitation pulse unit is emitted with a positive sign, and the -1 code represents that the excitation pulse unit is emitted with the sign reversed.

[0070] The size of each two-dimensional encoding matrix is Each row represents the encoding method of the array element direction at each excitation time, and each column represents the encoding method of each array element in the excitation time direction. Figure 4 This illustration reveals a schematic diagram of a 4-element linear array being encoded and transmitted under a given two-dimensional coding matrix, according to an embodiment of this application.

[0071] In some embodiments, two-dimensional encoding matrices are generated in pairs as follows:

[0072] ,

[0073] ,

[0074] in, Less than odd numbers, and Represent The first order of the Hadamard matrix row and number OK, , , , Represent Level serial encoding matrix In the block matrix representation, the vectors at the top left, bottom left, top right, and bottom right are... , , , They are , , , The transpose of .

[0075] Figure 5 This application discloses a two-dimensional encoding matrix according to an embodiment. The specific generation method.

[0076] Step S4: Perform dual decoding on the acquired echo data according to the two-dimensional coding matrix.

[0077] In some embodiments, dual decoding of the acquired echo data based on the two-dimensional coding matrix may include: first performing serial decoding on the acquired echo data based on the two-dimensional coding matrix, and then performing array element decoding.

[0078] Figure 6 A schematic flowchart illustrating the serial decoding process of two frames of echo data according to an embodiment of this application is disclosed. (Referring to...) Figure 6 As shown, in some embodiments, performing serial decoding may include the following steps S411 to S415.

[0079] Step S411: Perform Fourier transform on the acquired echo data to obtain the common echo signal. Frame rate domain data, making .

[0080] Step S412: Select the first Frame and the Frame echo data, making .

[0081] Step S413: Proceed to the first The serial decoding process involves adding two frames of data and subtracting them, then multiplying by a timing advance factor. This yields two new frames of data.

[0082] Time advance factor It can be determined by the following formula:

[0083] ,

[0084] Step S414: Let And repeat step S413 until the total is completed. Serial decoding.

[0085] Step S415: Let Execute steps S412 to S414 until all processes are completed. Frame echo data.

[0086] In some embodiments, performing array element decoding may include the following steps S421 to S424.

[0087] Step S421: Let .

[0088] Step S422: Extract the data obtained from serial decoding The first frame of echo data The data corresponding to each array element are concatenated to form a... , where, This represents the number of sampling points for the echo.

[0089] Step S423: ... Data frame left multiplication transpose of an 1 / 2 Hadamard matrix That is, to obtain the first Each array element corresponds to the echo data emitted by all array elements.

[0090] Step S424: Let Repeat steps S422 and S423 to obtain complete frequency domain synthetic aperture data.

[0091] Continue to refer to Figure 1 Step S5: Use the decoded data to perform synthetic aperture imaging.

[0092] The two-dimensional encoding and decoding method for ultrasonic synthetic aperture imaging in this application combines serial encoding (time dimension) and array element encoding (spatial dimension) to form a two-dimensional encoded transmission to improve transmission energy, and performs decoding in the frequency domain through a simple linear transformation to obtain ultrasonic synthetic aperture data with a high signal-to-noise ratio, thereby improving the depth and contrast of ultrasonic synthetic aperture imaging.

[0093] The two-dimensional encoding and decoding method for ultrasonic synthetic aperture imaging provided in the embodiments of this application has been described in detail above. Specific examples have been used to illustrate the two-dimensional encoding and decoding method for ultrasonic synthetic aperture imaging in the embodiments of this application. The descriptions of the embodiments above are only for helping to understand the core ideas of this application and are not intended to limit this application. It should be noted that those skilled in the art can make several improvements and modifications to this application without departing from the spirit and principles of this application, and these improvements and modifications should all fall within the protection scope of the appended claims.

Claims

1. A two-dimensional encoding and decoding method for ultrasound synthetic aperture imaging, characterized in that, Comprising: For an ultrasonic transducer array having elements, a Hadamard matrix of order is generated wherein is a multiple of 8; According to the requirements of axial resolution and near-field dead-zone range, generate Stage serial encoding matrix ; using the hadamard matrix and the serial encoding matrix generated by matrix multiplication two-dimensional encoding matrices , a co coding transmission and acquisition, wherein ; double decoding the acquired echo data according to the two-dimensional encoding matrix; using the decoded data to perform synthetic aperture imaging.

2. The two-dimensional encoding and decoding method of claim 1, wherein, The Hadama matrix Each row corresponds to a coding template of one element dimension; the serial coding matrix Each row corresponds to a clock dimension encoding template.

3. The two-dimensional encoding and decoding method of claim 1, wherein, The generating is according to the requirement of axial resolution and near field dead zone range Stage serial encoding matrix Comprising: determining the number of stages of the serial encoding matrix according to the axial resolution and the near field dead zone range requirements ; According to the iterative copy method, generate level said serial encoding matrix .

4. The two-dimensional encoding and decoding method of claim 3, wherein, The number of stages of the serial encoding matrix is determined according to the following formula : , , wherein, representing a number of cycles of the excitation pulse unit, representing a floor function, representing a requirement for axial resolution, representing a center frequency of the transducer, representing a length of a near field dead zone range, representing an estimated speed of sound constant of the imaging medium.

5. The two-dimensional encoding and decoding method of claim 3, wherein, said generating according to the iterative duplication method said serial encoding matrix of the level comprising the steps of: Step one: Generate a 2x2 Hadamard matrix as the initial serial encoding matrix Let ; Step Two: After being divided equally in all directions, it is represented by a block matrix, denoted as . ,generate and order ; Step three: repeat step two until is equal to i.e. we obtain the serially encoded matrix of level .

6. The two-dimensional encoding and decoding method of claim 5, wherein, The size of each two-dimensional encoding matrix is wherein each row represents the encoding mode of the element direction at each excitation moment, and each column represents the encoding mode of the element in the excitation time direction.

7. The two-dimensional encoding and decoding method of claim 6, wherein, generating the two-dimensional encoding matrix in pairs in the following way: , , wherein is an odd integer smaller than , and represent the th row and the th row of a Hadamard matrix of order , , , , represent the th row of the serial encoding matrix the upper left, lower left, upper right, lower right vectors in the block matrix representation, , , , are the transposes of , , , .

8. The two-dimensional encoding and decoding method of claim 1, wherein, the elements of the two-dimensional encoding matrix only include two kinds of encoding of +1 and -1, wherein the +1 encoding represents that the excitation pulse unit transmits in a positive symbol, and the -1 encoding represents that the excitation pulse unit transmits after inverting the symbol.

9. The two-dimensional encoding and decoding method of claim 1, wherein, the double decoding the acquired echo data according to the two-dimensional encoding matrix comprises: first performing serial decoding and then performing array element decoding on the acquired echo data according to the two-dimensional encoding matrix.

10. The two-dimensional encoding and decoding method of claim 9, wherein, the performing serial decoding comprises the following steps: Step one: Fourier transform the collected echo data to get the common frame frequency domain data, let ; Step two: select the first frame and the first frame echo data, let ; Step three: Perform a first order serial decoding, add the two frames of data, and subtract the two frames of data and multiply by a time advance factor to get new two frames of data ​​ Step four: Let and repeat step three until a total of level serial decoding; Step five: Let Steps two through four are executed until all frame echo data has been processed.

11. The two-dimensional encoding and decoding method of claim 10, wherein, The time advance factor is determined by the equation: , wherein, represents the number of cycles of the excitation pulse unit, represents the center frequency of the transducer.

12. The two-dimensional encoding and decoding method of claim 10, wherein, the performing array element decoding comprises the following steps: Step one: Let ; Step 2: Extract the data obtained from serial decoding The first frame of echo data The data corresponding to each array element are concatenated to form a... The data frame, in which, The number of sampling points representing the echo; Step 3: Put Data frame left multiplication The transpose of the Hadamard matrix of order X That is, to obtain the first Each array element corresponds to the echo data emitted by all array elements; Step four: Let Steps two and three are repeated to obtain the complete frequency domain synthetic aperture data.

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