WO2016159395A1 - 공간 스무딩 연산이 간단한 빔포밍 장치, 초음파 이미징 장치 및 빔포밍 방법 - Google Patents
공간 스무딩 연산이 간단한 빔포밍 장치, 초음파 이미징 장치 및 빔포밍 방법 Download PDFInfo
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Definitions
- the present invention relates to beamforming technology.
- Ultrasonic imaging apparatus is an apparatus for obtaining an image of a tomography image, blood flow, or the like for a variety of tissues, structures, and the like inside the object, for example, the human body using ultrasound.
- Such an ultrasound imaging apparatus is relatively small and inexpensive, can display an image in real time, and is widely used in the medical field, for example, the heart, the abdomen, the urology, and the obstetrics and gynecology because there is no risk of exposure by X-rays or the like.
- the ultrasound imaging apparatus irradiates an ultrasound signal toward a target site inside the object, collects an ultrasound echo signal reflected from the target site, and generates an ultrasound image from the collected ultrasound echo signals.
- the ultrasound imaging apparatus performs beamforming for estimating the reflected wave size of a specific space with respect to the plurality of channel data resulting from the ultrasonic echo signal collected through an ultrasonic transducer. Beamforming corrects the time difference of the ultrasonic signals received through the ultrasonic transducer, and adds a predetermined weight, i.e., beamforming coefficient, to each received ultrasonic signal to emphasize the signal at a specific position or relatively attenuate the signal at another position. To focus the ultrasound signal.
- the ultrasound imaging apparatus may generate an ultrasound image suitable for identifying an internal structure of an object and provide the ultrasound image to a user.
- the beamforming apparatus, the ultrasonic imaging apparatus, and the beam for reducing the resource usage of the beamforming apparatus required for beamforming by reducing the amount of computation required for spatial smoothing during beamforming and improving the computation speed Suggest a forming method.
- the beamforming apparatus converts a received signal into another space using a transform function composed of low frequency components, calculates the transformed signal through a spatial smoothing operation using the transform function in transform space, and averages a spatial covariance matrix.
- a spatial smoothing unit for estimating a a weighting unit for calculating a transform signal weight from the averaged spatial covariance matrix estimated through the spatial smoothing operation, and a synthesis unit for generating a beam signal using the transformed signal and the transformed signal weight.
- the spatial smoothing unit converts a received signal into another space by using a conversion function composed of low frequency components remaining after removing low frequency components of the conversion function and removing other high frequency components, thereby generating a converted signal into a plurality of channels. Reduce the dimension of the spatial covariance matrix for each incoming signal.
- the spatial smoothing unit calculates and calculates a converted signal using a characteristic in which a difference between neighboring transformed signals is a difference of the first system and a difference between neighboring differences in the first system is a difference of the second system.
- the spatial covariance matrix is estimated from the transformed signal.
- the transform function is an orthogonal polynomial
- the spatial smoothing unit calculates the transform signal using the characteristic that the orthogonal polynomial is a real number and decreases the order by one each time the differential is different. Estimate the covariance matrix.
- Orthogonal polynomials are Hermite polynomials, Laguerre polynomials, Jacobi polynomials, Jacobi polynomials, Jacobi polynomials, Chebyshev polynomials, or Lezgen polynomials. It can be either.
- the spatial smoothing unit performs a spatial covariance matrix through a spatial smoothing operation. And estimate the estimated spatial covariance matrix silver
- M is the total number of channels
- M-L + 1 is the number of subarrays
- L is the sub-array length
- u l is the conversion signal
- superscript H is Hermit It is a transposition.
- the beamforming apparatus further includes an accumulator configured to accumulate the converted signals corresponding to each sub array, and the combiner calculates the beam signal at one time by combining the converted signal and the weight accumulated through the accumulator.
- the spatial smoothing unit is a modified converted signal in which the converted signal is modified.
- I a modified genre polynomial
- ego ego
- x is the received signal
- subscript l is the starting index of x
- subscript Q is the number of components of the conversion signal selected by the user
- superscript H is the Hermitian transposition
- superscript T is the transposition.
- Modified Rejangre Polynomial The difference of the Rth row of Where d and e are the precomputed real coefficients in d p, q, r or e p, q, r , subscript p is the difference order, and r is the modified transform function Where r is the order of each term in the polynomial, l is the starting index of x, and L is the subarray length.
- the modified Regard de polynomial 2 (Q + 1) multiplications and 2 (Q + 1) addition operations are needed to calculate the difference between the R-th rows of. Each additional step requires one more addition.
- the modified genre polynomial is modified by 2 (Q + 1) multiplication and 3Q + 2 addition. The difference of the R th row of can be calculated.
- the transform function is a Fourier transform basis function
- the spatial smoothing unit calculates a transform function using a Fourier transform basis function and estimates an averaged spatial covariance matrix using the calculated transform function.
- the spatial smoothing unit is a modified conversion signal modified by the conversion signal Creates a, Where is the conversion function Is the modified conversion function, Is, Where x is the received signal, subscript l is the starting index of x, subscript Q is the number of components of the conversion signal selected by the user, and superscript H is the Hermitian transpose.
- the conversion signal u l, m is Where m is the mth row, n is the nth column, l is the starting index of x, and L is the subarray length.
- the beamforming apparatus further includes a channel data averaging unit for averaging a plurality of sample data to generate a received signal in the form of channel data before spatial smoothing.
- the channel data averaging unit may generate a received signal in the form of channel data by beamforming the sample data constituting the sample data set with respect to the sample data received for each sub array of the transducer.
- the channel data averaging unit may generate a received signal in the form of channel data by averaging sample data received for the same depth through elements of the same position of the plurality of sample data sets.
- the spatial smoothing unit may perform spatial smoothing at a time on a received signal having a channel data type in which a plurality of sample data are averaged through the channel data averaging unit.
- the beamforming apparatus further includes a time averaging unit for performing time averaging by collecting the averaged covariance matrices generated through spatial smoothing on sample data having each depth.
- the beamforming apparatus may further include a shared memory, and the time averaging unit may be located in the shared memory.
- an ultrasound imaging apparatus includes a transducer for irradiating ultrasound to an object, receiving an ultrasound signal reflected from the object, and converting the received ultrasound to output a plurality of ultrasound signals, and an ultrasound signal received through the transducer Is transformed into another space using a transform function composed of low-frequency components, calculates the transformed signal, generates a beam signal reflecting the weighted value of the transformed signal in the transformed space, and generates a beam signal through spatial smoothing operation using the transform function.
- a beamformer for estimating the averaged spatial covariance matrix to be used, and an image generator for generating an image using a signal output from the beamformer.
- the beamforming unit calculates the converted signal using a characteristic in which a difference between neighboring converted signals is a difference of the first system and a difference between neighboring differences in the first system is a difference of the second system.
- the transform function is an orthogonal polynomial
- the beamforming unit calculates the converted signal by using the characteristic that the orthogonal polynomial is a real number and the order decreases by one for each differential.
- the transform function according to an embodiment is a Fourier transform basis function, and the beamforming unit calculates a transform signal using the Fourier transform basis function.
- a beamforming method includes converting a received signal into another space using a transform function composed of low frequency components to calculate a converted signal, and averaged spatial covariance through spatial smoothing using characteristics of the transform function. Estimating the matrix, calculating a transform signal weight from the averaged spatial covariance matrix, and generating a beam signal reflecting the weight in the transform signal.
- the converted signal is calculated using a characteristic in which a difference between neighboring converted signals is a difference of the first system and a difference between neighboring differences in the first system is a difference of the second system. .
- the transform function is an orthogonal polynomial
- the transform signal in the step of calculating the transform signal, is calculated by using a characteristic in which the orthogonal polynomial is a real number and the order is decreased by one each time the differential is different.
- the weight is calculated through spatial smoothing based on an orthogonal polynomial, and a minimum distributed beam signal is generated from the calculated weight.
- the transform function is a Fourier transform basis function, and the transform signal is calculated using the Fourier transform basis function.
- the weight may be calculated through spatial smoothing based on the Fourier transform basis function, and the beam space adaptive beam signal may be generated from the calculated weight.
- the beamforming method further includes generating a received signal in the form of channel data by averaging a plurality of sample data before spatial smoothing.
- the spatial smoothing operation is simple, and the amount of computation required in the process of generating the beam signal by beamforming the received signal may be reduced.
- various devices for performing beamforming for example, ultrasound imaging apparatuses, may reduce resources required for beamforming.
- spatial smoothing is simplified by calculating transform signals and estimating the averaged spatial covariance matrix using the characteristics of the transform function consisting of Fourier transform basis function or orthogonal polynomial. can do.
- the weights are computed through spatial smoothing based on Fourier transform basis and beam beam adaptive beam signals are generated from the calculated weights, or the weights are calculated through spatial smoothing based on orthogonal polynomials and the least distributed beam signal from the calculated weights. By generating, the beamforming speed for the received signal is increased and the calculation amount can be shortened.
- the spatial smoothing calculation amount can be reduced since the spatial smoothing can be performed at once on the generated channel data.
- performance is improved by temporal averaging in shared memory by collecting the averaged covariance matrices generated through spatial smoothing on sample data having each depth.
- the present invention can be applied to all the various signal processing fields, such as radar, sonar, non-destructive testing, including the ultrasonic diagnostic.
- FIG. 1 is a block diagram of a beamforming apparatus according to an embodiment of the present invention.
- FIG. 2 is a reference diagram illustrating reception channel data to which spatial smoothing is applied according to an embodiment of the present invention
- FIG. 3 is a reference diagram showing that a spatial smoothing calculation amount is simplified when estimating an averaged spatial covariance matrix using characteristics of a Fourier transform function or a transform function composed of an orthogonal polynomial according to an embodiment of the present invention
- FIG. 4 is a data structure diagram illustrating a channel data averaging process according to an embodiment of the present invention.
- FIG. 5 is a data structure diagram illustrating a channel data averaging process according to another embodiment of the present invention.
- FIG. 6 is a block diagram of an ultrasonic imaging apparatus according to an embodiment of the present invention.
- FIG. 8 is a graph comparing continuous wave (CW) beam patterns of the Regenre polynomial-based transform function P according to an embodiment of the present invention with continuous wave (CW) beam patterns of the transform functions of the Fourier transform function B and the PCA MV BF. ,
- FIG. 9 is a flowchart illustrating a beamforming method according to an embodiment of the present invention.
- FIG. 1 is a block diagram of a beamforming apparatus according to an embodiment of the present invention.
- the beamforming apparatus 1 includes a spatial smoothing unit 12, a weight calculator 14, and a synthesizer 16, and includes a channel data averaging unit 10, an accumulator 15, and time.
- the averaging unit 18 may be further included.
- At least some components of the beamforming apparatus 1 illustrated in FIG. 1 may correspond to one or a plurality of processors.
- the processor may be implemented as an array of multiple logic gates, or may be implemented as a combination of a general purpose microprocessor and a memory storing a program that may be executed on the microprocessor.
- a general purpose microprocessor and a memory storing a program that may be executed on the microprocessor.
- the present embodiment may be implemented in other forms of hardware.
- the beamforming apparatus 1 receives a received signal reflected from a subject and forms a received beam therefrom.
- the subject may be, for example, an abdomen, a heart, etc. of the human body
- the received signal may be an ultrasonic signal reflected from the subject, but this is merely an example for helping the understanding of the present invention, but is not limited thereto. .
- the beamforming apparatus 1 transforms a received signal in an element space into a transformed space, which is another space, by using a transform function, and performs signal processing in the transform space.
- a beam signal is generated and output.
- the transform function can be expressed as a transform matrix.
- the beamforming apparatus 1 leaves low frequency components and removes other high frequency components among the components constituting the conversion function. At this time, the low frequency components are found to be the low frequency frequency components in the lateral direction (lateral direction). Then, the received signal is converted into another space by using a conversion function composed of the remaining low frequency components. In this case, the dimension of the spatial covariance matrix R for each of the received signals input to the plurality of channels can be reduced. This also simplifies the calculation of the inverse matrix R -1 of the covariance matrix required for the transform signal weight calculation.
- the spatial smoothing unit 12 of the beamforming apparatus 1 receives the received signal X 126 and converts the received received signal X 126 by using a predetermined conversion function V to convert the converted signal U 120.
- Create The received signal X 126 may be composed of a channel data set input through a plurality of channels. That is, it may be a collection of a plurality of channel data.
- the conversion signal U 120 may also be a set of conversion signals of a plurality of channels outputted in the plurality of channels.
- the dimension of the converted signal U 120 is smaller than the dimension of the received signal X 126.
- the transform function is given by the matrix of (M ⁇ N)
- the formula of M> N is established and the received signal X 126 is given by (M ⁇ 1), i.e.
- the conversion signal U 120 which is the result of the calculation, is given by (N x 1) so that the dimension of the conversion signal U 120 becomes smaller than the reception signal X 126.
- the dimension is reduced in this way, the amount of computation is relatively reduced, and the convenience and speed of the computation may be improved.
- the spatial smoothing unit 12 performs spatial smoothing using the characteristics of the transform function proposed by the present invention, the amount of spatial smoothing is reduced. Spatial smoothing is to prevent signal canceling due to coherence of channel signals.
- the spatial smoothing unit 12 obtains the converted signal U 120 using a transform function, and converts the converted signal U. From (120) (122), Spatial covariance matrix averaged from 122 Estimate 124.
- the spatial smoothing unit 12 separates the arrays of transducers into a plurality of sub-arrays that overlap each other.
- M is the total number of channels
- M-L + 1 is the number of subarrays
- the spatial smoothing unit 12 averages the spatial covariance matrices corresponding to each sub array. (124) is obtained. Embodiments of M and L of the transducer array will be described once more with reference to FIG. 2 to be described later.
- the spatial smoothing unit 12 calculates the transform signal U 120 using the characteristics of the Fourier transform basis function.
- the spatial smoothing unit 12 calculates the converted signal U 120 using the characteristics of the transform function composed of an orthogonal polynomial.
- the orthogonal polynomial may be a normalized orthogonal polynomial.
- the spatial smoothing unit 12 calculates the conversion signal U 120 using a characteristic in which an orthogonal polynomial is a real number and decreases by one for each differential. In this case, the amount of calculation of the converted signal U 120 is simplified.
- An embodiment of calculating spatial smoothing using a transform function composed of an orthogonal polynomial such as the Regenre polynomial will be described later with reference to Equations 21 to 29.
- an embodiment of calculating spatial smoothing using the characteristics of the Fourier transform basis function will be described later with reference to Equations 30 to 32.
- the beamforming method of the beamforming apparatus 1 is various.
- the beamforming apparatus 1 uses a beam space adaptive beamforming (hereinafter, referred to as BA BF) method.
- BA BF method converts a received signal of an element space into another space using a transform function that is an orthonormal basis matrix, and performs signal processing such as approximation that leaves only an important component in the transformed space.
- the dimension of the spatial covariance matrix for each of the received signals input to the plurality of channels is reduced. As a result, the inverse matrix calculation of the covariance matrix can be made very simple.
- the spatial smoothing unit 12 uses a transformation function composed of an orthogonal polynomial during spatial transformation.
- Orthogonal polynomials are a series of polynomials that satisfy an orthogonal relationship.
- Orthogonal polynomials include, for example, Hermite polynomials, Laguerre polynomials, Jacobi polynomials, Gegenbauer polynomials, Chebyshev polynomials, or Chebyshev polynomials Legendre polynomial).
- Hermite polynomials Laguerre polynomials
- Jacobi polynomials Jacobi polynomials
- Gegenbauer polynomials Chebyshev polynomials
- Chebyshev polynomials Legendre polynomial Chebyshev polynomials Legendre polynomial
- the spatial smoothing unit 12 uses an orthonormal matrix composed of a Legendre polynomial as a transform function.
- the spatial smoothing unit 12 may use the L'Genre polynomial as a transform function in a minimum variance beamforming method (hereinafter, referred to as MV BF).
- MV BF minimum variance beamforming method
- performance can be maintained while greatly reducing the calculation amount of MV BF.
- a method of using a matrix made of the Regenre polynomial as a transform function for converting the received signal of the element space into the transform space is based on the Regenre polynomial least distributed beamforming (LP MV BF, hereinafter referred to as LP MV BF) method.
- LP MV BF method can be used to approximate MV BF more precisely than BA BF, and to perform PCA-based least-distributed beamforming (MV BF method based on principal component analysis). Similar performance can be achieved.
- the beamforming apparatus 1 beamforms the MV BF method in transform space, by using only a few components that are important in transform space, the amount of computation required for inverse matrix computation of the spatial covariance matrix can be greatly reduced.
- the dimension of the spatial covariance matrix is reduced by taking only a few first columns of the transformation matrix and transforming the received signal. The first few columns of the transformation matrix represent the important components of the MV BF operation.
- the spatial smoothing unit 12 can only use the first few columns of a Fourier transform matrix.
- the first few columns represent low frequency components, which correspond to focal point directions and beam components close to the focal point. Assuming that interference mainly occurs near the frontal direction, using only these columns can effectively reduce the dimension of the spatial covariance matrix.
- the spatial smoothing unit 12 uses only the first few columns of a transform function made of an orthogonal polynomial.
- the columns of this transform function represent high frequency components from low frequency components, so the first few columns correspond to the low frequency components, just like the Fourier transform function.
- Spatial smoothing of the MV BF can eliminate the long side lobes of the X shape observed in the delay-and-sum beamforming (hereinafter referred to as DAS BF) method.
- DAS BF delay-and-sum beamforming
- the MV BF using the L'Genrede polynomial-based conversion function is very effective for the MV BF even though the dimensionality reduction that deals with the side lobe components close to the front and removes the other high frequency components. I can keep it well. It can be seen with reference to FIG. 7 to be described later that the high frequency components are removed only through spatial smoothing.
- the weight calculation unit 14 is an averaged spatial covariance matrix generated through spatial smoothing based on the transform signal U 120 through the spatial smoothing unit 12. Weight from 124 Calculate 140. weight The method for calculating 140 is as described in Equation 11 described later.
- the accumulator 15 accumulates the converted signal U 120 for each sub array and accumulates the converted signal accumulated value.
- Generate 150, and the synthesis unit 160 converts the converted signal 150 and weights And synthesize the beam signal Z ( 160 may be generated.
- the accumulator 15 may accumulate M-L + 1 converted signals U which are the number of sub arrays. Accumulated value of converted signal by accumulating converted signal U 120 corresponding to each sub array Generating 150 and calculating the beam signal Z 160 at one time simplifies the spatial smoothing operation.
- the beamforming apparatus 1 includes a channel data averaging unit 10.
- the channel data averaging unit 10 generates a received signal X 126 in the form of channel data by averaging a plurality of sample data before spatial smoothing through the spatial smoothing unit 12.
- channel data is generated by beamforming sample data constituting the sample data set with respect to the sample data set received for each sub array of the transducer. An embodiment thereof will be described later with reference to FIG. 4.
- the channel data averaging unit 10 generates channel data by averaging sample data received for the same depth through elements at the same position of the transducer for a plurality of sample data sets. An embodiment thereof will be described later with reference to FIG. 5. Averaging can be done through data summation.
- the spatial smoothing unit 12 may perform spatial smoothing at a time on the received signal X 126 in the form of averaged channel data, thereby reducing the amount of spatial smoothing.
- the averaging process of the channel data averaging unit 10 described above can be used in spatial compounding and synthetic aperture.
- the beamforming apparatus 1 includes a time averaging unit 18.
- the time averaging unit 18 performs time averaging by collecting the averaged covariance matrix generated through spatial smoothing on sample data having depths.
- the quality of the image may not be good due to the fact that a lot of speckle noise is included in the actual ultrasound image or a part of the image is missing.
- speckle noise which is often found in homogeneous regions of varying brightness of pixel values, is an obstacle for the system to automatically analyze and recognize an image. Therefore, the time averaging section 18 uses the time average to reduce the speckle noise.
- the time averaging unit 18 according to an embodiment is located in the shared memory. The use of shared memory can improve the time averaging performance of the time averaging unit 18.
- the DAS BF method may be used to focus the ultrasound beam in a desired direction in the ultrasound diagnostic apparatus.
- DAS BF to lower the level of clutter caused by echo signals from unwanted directions, appropriate weights should be applied to received signals from array elements. In this case, there is a constraint that the sacrifice of widening the width of the main lobe (main lobe).
- MV BF also called capon beamforming, named after the inventor
- the MV BF calculates and applies an optimal weight, i.e., apodization function, for each receive focal point based on the input data to gain 1 (unity gain). Pass and the signal from the other direction can be optimally reduced. Therefore, unlike the DAS BF, it is possible to reduce the clutter level and at the same time reduce the width of the main lobe, thereby simultaneously improving the spatial resolution and the contrast resolution.
- MV BF Planar Biharmonic BF
- the MV BF method may require a large amount of computation because the inverse of the spatial covariance matrix needs to be obtained. Therefore, if possible, it is desired to reduce the calculation amount without degrading the performance of the MV BF.
- the most computationally necessary step in MV BF is to find the inverse of the spatial covariance matrix.
- the dimension of the spatial covariance matrix is L ⁇ L
- the operation of O (L 3 ) is required to find its inverse.
- transform the input data from element space into another space and then remove components in that space that have less effect on the performance of the MV BF, significantly reducing the dimension of the spatial covariance matrix and consequently simply covariance.
- the BA BF based on Fourier transform can be used.
- the spatial smoothing unit 12 uses an orthogonal polynomial as a basis matrix for spatial transformation. Using orthogonal polynomials, when the dimensions of the spatial covariance matrix are equally reduced, the approximation error due to dimension reduction is less or similar to that of the BA BF and PCA MV BF methods.
- FIG. 2 is a reference diagram illustrating reception channel data to which spatial smoothing is applied according to an embodiment of the present invention.
- the spatial smoothing unit 12 separates the array of transducers into a plurality of sub-arrays overlapping each other.
- M is the total number of channels
- M-L + 1 is the number of subarrays
- L is the sub-array length.
- the number M of the total channels is 10
- the length L of the sub array is 5
- the number M-L + 1 of the sub array is 6.
- the spatial smoothing unit 12 averages the spatial covariance matrices corresponding to each sub array. Will be calculated.
- FIG. 3 is a reference diagram illustrating a simplified amount of spatial smoothing operation when estimating an averaged spatial covariance matrix using characteristics of a Fourier transform function or a transform function composed of an orthogonal polynomial according to an embodiment of the present invention.
- ⁇ 1 , 4 (320) in FIG. 3 is ⁇ 1 , 3 (300) plus ⁇ 2 , 4 (310)
- U 4 340 is U 3 330 and ⁇ 1 , 4 Plus 320.
- the difference between neighboring transformed signals corresponds to the difference of the first system
- the difference between neighboring differences of the first system corresponds to the difference of the second system.
- FIG. 4 is a data structure diagram illustrating a channel data averaging process according to an embodiment of the present invention.
- channel data is generated by beamforming sample data constituting the sample data set with respect to the sample data set received for each sub array of the transducer.
- a plurality of sample data sets are received through sub array 1 40-1 and sub array 2 40-2 of the transducer, respectively.
- a sample data set is beamformed on the sample data constituting the sample data set to generate a received signal 126-1 in the form of channel data.
- each of the sample data sets 42-1 and 42-2 for the sub array 1 40-1 and the sub array 2 40-2 may be data received at the same time.
- each of the sample data sets 42-1 and 42-2 for the sub array 1 40-1 and the sub array 2 40-2 may be data received at different times.
- the above-described process is repeated for each sub array of the transducer to finally generate the received signal 126-1 in the form of channel data.
- the received signal 126-1 in the form of channel data is provided to the spatial smoothing unit 12.
- FIG. 5 is a data structure diagram illustrating a channel data averaging process according to another embodiment of the present invention.
- a plurality of sample data sets are subjected to averaging of sample data received for the same depth through elements at the same position of the transducer to form channel data. Generate the received signal.
- the sample data sets 42-3 and 42-4 of FIG. 5 are sample data sets received at different times t o and t 1 through the transducer array 40, respectively.
- 40 is composed of a plurality of elements. Among them, the first sample data 400-1 of the first sample data set 42-3 and the first sample data set 42-3 received through the first element 400 of the transducer array 40. The second sample data 400-2 of the second sample data set 42-4 received through the first element 400 of the transducer array 40 at a different time from the transducer array 40.
- the above-described process is repeated with respect to the other elements of the transducer array 40 to finally generate the received signal 126-2 in the form of channel data.
- the received signal 126-2 in the form of generated channel data is provided to the spatial smoothing unit 12.
- FIG. 6 is a configuration diagram of an ultrasonic imaging apparatus according to an embodiment of the present invention.
- the ultrasound imaging apparatus 6 may include a transducer 600, a beamformer 610, an image generator 620, a display unit 630, a storage unit 640, and an output unit 650. Include.
- the beamforming unit 610 illustrated in FIG. 6 corresponds to an embodiment of the beamforming apparatus 1 illustrated in FIG. 1. Accordingly, since the above description with reference to FIG. 1 is also applicable to the ultrasound imaging apparatus shown in FIG. 6, redundant description thereof will be omitted.
- the ultrasound imaging apparatus 6 provides an image of a subject.
- the diagnostic image indicating the subject is displayed, or a signal indicating the diagnostic image of the subject is output to an external device displaying the diagnostic image indicating the subject.
- the diagnostic image may be an ultrasound image, but is not limited thereto.
- the transducer 600 transmits and receives a signal with the subject.
- the transducer 600 transmits an ultrasonic signal to a subject and receives an ultrasonic echo signal reflected from the subject.
- the beamformer 610 calculates a weight to be applied to the ultrasound echo signal reflected from the subject by using the basis vectors, applies the weight to the ultrasound echo signal reflected from the subject, and synthesizes the weighted signals.
- the basis vectors may be stored in the beamforming unit 610 or in the storage unit 640. Accordingly, the beamformer 610 may beamform using at least some of the stored basis vectors. In this case, the number of at least some basis vectors may be determined by the user.
- the beamformer 610 may calculate the weight using the plurality of basis vectors, and apply the calculated weight to perform beamforming with a reduced computation amount.
- the beamformer 610 according to an embodiment generates and outputs a beam signal from a weight obtained through a spatial smoothing operation.
- the image generator 620 generates an image using the signals output from the beamformer 610.
- the image generator 620 may include a digital signal processor (DSP) and a digital scan converter (DSC). According to an embodiment, the DSP performs a predetermined signal processing operation on the signal output from the beamformer 610, and the DSC scan-converts the image data formed by using the signal on which the predetermined signal processing operation is performed.
- DSP digital signal processor
- DSC digital scan converter
- the display unit 630 displays an image generated by the image generator 620.
- the display unit 630 includes all output devices such as a display panel, a mouse, an LCD screen, a monitor, and the like provided in the ultrasound imaging apparatus.
- the ultrasound imaging apparatus 6 does not include the display unit 630, and may include an output unit 650 for outputting an image generated by the image generator 620 to an external display device. Those skilled in the art to which the present embodiment pertains may be known.
- the storage unit 640 stores the image generated by the image generator 620 and data generated while the operation of the ultrasound imaging apparatus 6 is performed.
- the output unit 650 may transmit and receive data with an external device through a wired, wireless network or wired serial communication.
- the external device may be another medical imaging system, a general purpose computer system, a facsimile, or the like located remotely.
- the storage unit 640 and the output unit 650 according to an embodiment further includes an image reading and retrieval function may be integrated into a form such as PACS (Picture Archiving Communication System) Those skilled in the art can know.
- the ultrasound imaging apparatus 6 may generate a real time high resolution image.
- the beamforming process of the ultrasonic diagnostic apparatus may be expressed as Equation 1.
- Equation 1 x m [n] is a received signal of each channel to which a focusing delay is applied, m is a channel index, n is a time index, and w m [n] is The weights, z [n], to be applied to the signal of each channel, also called apodization, is the output of the beamforming apparatus.
- M may be the number of receiving channels participating in beamforming or the number of receiving sub-arrays participating in beamforming.
- M may be the number of receiving channels, and m may be the m th channel among the M channels.
- M may be the number of receiving subarrays, and m may be the m th subarray of the M subarrays.
- the MV BF finds w for minimizing the variance, i.e., power of z [n] while maintaining the gain of the front signal at 1 in a signal having a desired direction, for example, a focusing delay.
- w [n] [w 0 [n], w 1 [n],... , w m - 1 [n]] H. Accordingly, it is possible to minimize the contribution of the signal from the unwanted direction to the output without distorting the signal in the desired direction. This problem is represented by the equation below.
- Equation 3 E [ ⁇ ] is the expectation operator, w [n] H is the Hermitian transpose of w [n], a is the steering vector, and x m [n] is Since the focus is applied to the delay signal, the elements are all composed of ones.
- R [n] is a spatial covariance matrix as shown in Equation 3.
- R [n] needs to be estimated, and spatial smoothing, or sub-average averaging, is used to avoid signal canceling due to coherence of each channel signal while estimating. -aperture averaging). Then, temporal averaging is performed to improve statistical characteristics of the speckle pattern of the resultant image. Estimated Is shown in Equation 5 below.
- Equation 5 Corresponds to this space smoothing, This corresponds to time averaging.
- M is the total number of channels
- M-L + 1 is the number of subarrays
- L is the sub-array length. Spatial smoothing separates the entire M channels into redundant M-L + 1 subarrays, with each subarray of length L. In this case, the spatial covariance matrix for each sub array This is how you average them.
- x [n] is a received signal
- x l [n] means a starting index of x.
- Equation 7 tr () is a trace operator, and ⁇ is a constant called a diagonal loading factor.
- Equation 8 To obtain the MV BF output from the MV weights obtained through spatial smoothing, Equation 8 is used.
- Equation 8 M is the number of total channels, M-L + 1 is the number of subarrays, and L is the sub-array length. At this time, the weight w [n] is Is calculated from
- Equation 8 is rearranged to Equation 1, Equation 9 is obtained.
- the apodization function of the standard MV BF corresponding to w m of Equation 1 is r k , that is, a convolution form of a rectangular window of length M-L + 1 and w [n] H. It can be seen that. It is well known that the continuous wave beam pattern in the focal plane is the Fourier transform pair of the apodization function, and consequently the beam pattern of the apodization function of the standard MV BF is the Fourier transform pair of the rectangular window. That is, it is expressed as the product of the Fourier transform pairs of w [n] H obtained from the sink function and the minimum variance. Since the sink function decreases gradually as it moves away from the center as a whole, it can be estimated that the space smoothing can attenuate the clutter far from the main lobe to some extent.
- FIG. 7 is a graph showing that high frequency components are removed only through spatial smoothing according to an embodiment of the present invention.
- FIG. 7A illustrates a point target image of a DAS BF apodized by a rectangular window
- FIG. 7B illustrates w [n] as a rectangular function. function
- the MV BF method of converting the MV BF into another space instead of applying the original space of x, that is, the element space, and performing minimum distributed beamforming in the transform space will be described below.
- any weight w in Equation 4 is expressed as a linear combination of the columns of V as follows. Can be.
- the MV BF solution is found as follows.
- R 1 may be defined as an expected value for the transpose of u and u, and V 1 is a modified steering vector.
- Equation 11 is the MV BF solution in the space where x is converted into V H.
- Equation 14 The output of the beamforming apparatus considering spatial smoothing is expressed by Equation 14.
- MV BF methods in transform space use only a few components that are particularly important in transform space.
- the amount of computation required for inverse matrix operation can be greatly reduced. Since the first few columns of V represent important components in MV BF operation, by converting the received signal x using only those columns Can reduce the dimension. Therefore, its inverse computation amount can be further reduced.
- This Fourier transform matrix transforms element space into transformed space.
- the first few of these columns represent low-frequency components, corresponding to the focal point direction and the beam components close to it. Assuming that interference mainly occurs near the frontal direction, the dimension can be reduced efficiently by using only these columns. Furthermore, as described above, spatial smoothing has the effect of reducing interference from far away from the front.
- a beamforming apparatus may use a Lesgard polynomial-based least-dispersion beamforming method using a matrix made of a Lesmel polynomial as a transform function for converting an element space signal into a transformed space.
- LP MV BF LP MV BF
- the first few columns of the transform function created by the L'Genre polynomial can faithfully represent low frequency components.
- the Gram-Schmidt orthonormalization process is a series of polynomials ⁇ 1, n, n 2 ,. , n it can be used in each column V of the Legendre polynomial obtained by applying the L- 1 ⁇ .
- V P
- P [P 0 , P 1 ,... A 1] -, P L.
- P k is the k-th column of P
- P k [P 0k , P 1k ,... , P (L-1) k ] T , again to be. Is determined by the Gram-Schmid unit orthogonalization process.
- P 2 is equal to Equation 20.
- the columns of P in turn represent high frequency components from low frequency components.
- FIG. 8 is a graph comparing continuous wave (CW) beam patterns of the Regenre polynomial-based transform function P according to an embodiment of the present invention with continuous wave (CW) beam patterns of the transform functions of the Fourier transform function B and the PCA MV BF. to be.
- CW continuous wave
- FIG. 8 illustrates the second column of P, that is, the CW beam pattern of P 1 , using the Fourier transform function B and the PCA MV BF transform function. This is compared with the continuous wave (CW) beam patterns of the second columns of.
- CW beam pattern also CW beam pattern of the columns of Is a weighted sum. It can be seen that the CW beam pattern from P has a pattern very similar to the CW beam pattern of the transform function of PCA MV BF.
- P 1 has a lower frequency component than the second column b 1 of B, unlike the case of the b 1, the absolute value of the beam pattern is symmetrical about 0 degrees.
- the direction of the null point in the CW beam pattern of one column of B is also the null point direction in the CW beam pattern of another column, but in the case of P, as shown in FIG.
- Q 2
- P 1 cannot contribute in that direction.
- This is almost the same when using the conversion function of PCA MV BF, which may be a serious disadvantage of P when using continuous waves.
- a null point does not appear clearly in the beam pattern, which is not a problem.
- LP MV BF One of the advantages of LP MV BF is that the conversion function consists only of real numbers. BA BF or PAC MV BF should in principle be complex. Therefore, the LP MV BF simplifies the conversion operation.
- Polynomials such as the Legendre polynomial, used as a conversion function, are reduced by one order each time there is a difference.
- the present invention can simply calculate the spatial smoothing utilizing the above-described characteristics. For example, in equation 17 Is expressed as shown in Equation 21.
- Equation 21 may be represented as Equation 22 again.
- ⁇ 1, l +1,0 u l + 1,0 -u l, o .
- ⁇ p, q, r ⁇ p-1, q, r - ⁇ p-1, q-1, r for p ⁇ 2.
- ⁇ 2, l +2,2 ⁇ 1, l +2,2 - ⁇ 1, l +1,2 .
- L is the length of the sub-array.
- Equation 29 Generally of The final difference of the first row is shown in Equation 29.
- Equation 29 in d p, q, r or e p, q, r , d and e are precomputed real coefficients, and the subscripts p and r mean the same as in ⁇ p, q, r , but The subscript q means the order of each term in the polynomial.
- Equations 30 to 32 x is a received signal, subscript l is a start index of x, subscript Q is the number of components of a conversion signal selected by the user, and superscript H is Hermitian transpose.
- m is the mth row, n is the nth column, and L is the subarray length.
- FIG. 9 is a flowchart illustrating a beamforming method according to an embodiment of the present invention.
- the beamforming apparatus converts a received signal of an element space into a transform space, which is another space, using a transform function, and calculates a transform signal in the transform space (900).
- a conversion function composed of low frequency components may be used.
- the beamforming apparatus uses a transform function configured as an orthogonal polynomial at the time of transform signal calculation 900.
- Orthogonal polynomials are a series of polynomials that satisfy an orthogonal relationship.
- Orthogonal polynomials can be, for example, Hermit polynomials, Lager polynomials, Jacobian polynomials, Guggenbauer polynomials, Chebyshev polynomials or Legendre polynomials.
- the least-distributed beamforming (MV BF) method may be used as the transform function. At this time, performance can be maintained while significantly reducing the calculation amount of MV BF.
- the beamforming apparatus beamforms using an orthogonal polynomial-based least distributed beamforming scheme, it is possible to select a low frequency component and discard high frequency components among the orthogonal polynomial components constituting the transform function, and the first few columns are Fourier transform functions. Likewise, it corresponds to the low frequency component.
- the beamforming apparatus calculates a transform signal by using a characteristic of a Fourier transform basis function or a transform function composed of a polynomial.
- the transformed signal is calculated using the characteristic that the order is reduced by one each time the orthogonal polynomial differs. In this case, the amount of conversion signal calculation is simplified.
- the beamforming apparatus estimates the averaged spatial covariance matrix through spatial smoothing using the characteristics of the transform function (910). Subsequently, the beamforming apparatus calculates a transform signal weight from the averaged spatial covariance matrix, and generates a beam signal in which the weight is reflected in the transform signal (920).
- the beamforming apparatus generates a received signal in the form of channel data by averaging a plurality of sample data before spatial smoothing.
- the received data in the form of channel data is generated by averaging the sample data constituting the sample data set for each sample data set.
- a received signal in the form of channel data is generated by averaging the sample data received through the same element of the transducer for a plurality of sample data sets. Accordingly, spatial smoothing can be performed at a time on a received signal having a plurality of sample data averaged, thereby reducing the amount of computation.
- the beamforming apparatus may perform a time averaging by collecting averaged covariance matrices generated through spatial smoothing on sample data having respective depths.
- the time averaging performance may be improved by performing time averaging in the shared memory.
- the present invention can be applied not only to an ultrasonic diagnostic apparatus but also to various array signal processing fields such as radar, sonar, and non-destructive testing.
Abstract
Description
Claims (32)
- 저주파수 성분들로 구성된 변환함수를 이용하여 수신신호를 다른 공간으로 변환하고 변환 공간에서 상기 변환함수를 이용한 공간 스무딩 연산을 통해 변환신호를 계산하고 평균화된 공간 공분산 행렬을 추정하는 공간 스무딩부;상기 공간 스무딩 연산을 통해 추정된 평균화된 공간 공분산 행렬로부터 변환신호 가중치를 연산하는 가중치 연산부; 및변환신호 및 변환신호 가중치를 이용하여 빔 신호를 생성하는 합성부;를 포함하는 것을 특징으로 하는 빔포밍 장치.
- 제 1 항에 있어서, 상기 공간 스무딩부는변환함수의 저주파수 성분들은 남기고 다른 고주파 성분들은 제거한 후 남겨진 저주파수 성분들로 구성된 변환함수를 이용하여 수신신호를 다른 공간으로 변환하여 변환신호를 생성함에 따라 복수의 채널로 입력되는 각각의 수신신호에 대한 공간 공분산 행렬의 차원을 감소시키는 것을 특징으로 하는 빔포밍 장치.
- 제 1 항에 있어서, 상기 공간 스무딩부는이웃한 변환신호 간의 차가 제1계의 차분(difference)이고, 제1계의 이웃한 차분 간의 차가 제2계의 차분인 특성을 이용하여 변환신호를 계산하고 계산된 변환신호로부터 공간 공분산 행렬을 추정하는 것을 특징으로 하는 빔포밍 장치.
- 제 1 항에 있어서,상기 변환함수는 직교 다항식(orthogonal polynomial)이며,상기 공간 스무딩부는직교 다항식이 실수이며 미분(differential) 때마다 차수가 하나씩 감소하는 특성을 이용하여 변환신호를 계산하고 계산된 변환신호로부터 공간 공분산 행렬을 추정하는 것을 특징으로 하는 빔포밍 장치.
- 제 4 항에 있어서,상기 직교 다항식은 에르미트 다항식(Hermite polynomial), 라게르 다항식(Laguerre polynomial), 야코비 다항식(Jacobi polynomial), 구겐바우어 다항식(Gegenbauer polynomial), 체비쇼프 다항식(Chebyshev polynomial) 또는 르장드르 다항식(Legendre polynomial) 중 어느 하나인 것을 특징으로 하는 빔포밍 장치.
- 제 1 항에 있어서, 상기 빔포밍 장치는각 서브 어레이에 해당하는 변환신호를 누적시키는 누적부;를 더 포함하며,상기 합성부는상기 누적부를 통해 누적된 변환신호와 가중치를 합성하여 한 번에 빔 신호를 계산하는 것을 특징으로 하는 빔포밍 장치.
- 제 1 항에 있어서,상기 변환함수는 푸리에 변환 기저함수(Fourier transform basis function)이고,상기 공간 스무딩부는상기 푸리에 변환 기저함수를 이용하여 변환함수를 계산하는 것을 특징으로 하는 빔포밍 장치.
- 제 1 항에 있어서, 상기 빔포밍 장치는공간 스무딩 이전에, 다수의 샘플 데이터를 평균화하여 채널 데이터 형태의 수신신호를 생성하는 채널 데이터 평균화부;를 더 포함하는 것을 특징으로 하는 빔포밍 장치.
- 제 16 항에 있어서, 상기 채널 데이터 평균화부는트랜스듀서의 서브 어레이 별로 수신한 샘플 데이터 셋을 대상으로 샘플 데이터 셋을 구성하는 샘플 데이터들을 빔포밍하여 채널 데이터 형태의 수신신호를 생성하는 것을 특징으로 하는 빔포밍 장치.
- 제 16 항에 있어서, 상기 채널 데이터 평균화부는다수의 샘플 데이터 셋을 대상으로 트랜스듀서의 동일한 위치의 엘리먼트를 통해 동일한 깊이에 대해 수신한 샘플 데이터끼리를 평균화하여 채널 데이터 형태의 수신신호를 생성하는 것을 특징으로 하는 빔포밍 장치.
- 제 16 항에 있어서, 상기 공간 스무딩부는상기 채널 데이터 평균화부를 통해 다수의 샘플 데이터가 평균화된 채널 데이터 형태의 수신신호를 대상으로 한 번에 공간 스무딩을 수행하는 것을 특징으로 하는 빔포밍 장치.
- 제 1 항에 있어서, 상기 빔포밍 장치는각 깊이를 가지는 샘플 데이터를 대상으로 공간 스무딩을 거쳐 생성된 평균화된 공분산 행렬들을 모아서 시간 평균화를 수행하는 시간 평균화부;를 더 포함하는 것을 특징으로 하는 빔포밍 장치.
- 제 20 항에 있어서, 상기 빔포밍 장치는공유 메모리;를 더 포함하고,상기 시간 평균화부는 공유 메모리에 위치하는 것을 특징으로 하는 빔포밍 장치.
- 대상체로 초음파를 조사하고 대상체로부터 반사되는 초음파 신호를 수신하며 수신된 초음파를 변환하여 복수의 초음파 신호를 출력하는 트랜스듀서;상기 트랜스듀서를 통해 수신된 초음파 신호를 저주파수 성분들로 구성된 변환함수를 이용하여 다른 공간으로 변환하여 변환신호를 계산하고 변환된 공간에서 변환신호에 가중치를 반영한 빔 신호를 생성하며, 상기 변환함수를 이용한 공간 스무딩 연산을 통해 빔 신호 생성에 사용될 평균화된 공간 공분산 행렬을 추정하는 빔포밍부; 및상기 빔포밍부에서 출력된 신호를 이용하여 영상을 생성하는 영상 생성부;를 포함하는 초음파 이미징 장치.
- 제 22 항에 있어서, 상기 빔포밍부는이웃한 변환신호 간의 차가 제1계의 차분이고, 제1계의 이웃한 차분 간의 차가 제2계의 차분인 특성을 이용하여 변환신호를 계산하는 것을 특징으로 하는 초음파 이미징 장치.
- 제 22 항에 있어서,상기 변환함수는 직교 다항식이며,상기 빔포밍부는직교 다항식이 실수이며 미분(differential) 때마다 차수가 하나씩 감소하는 특성을 이용하여 변환신호를 계산하는 것을 특징으로 하는 초음파 이미징 장치.
- 제 22 항에 있어서,상기 변환함수는 푸리에 변환 기저함수이고,상기 빔포밍부는상기 푸리에 변환 기저함수를 이용하여 변환신호를 계산하는 것을 특징으로 하는 초음파 이미징 장치.
- 저주파수 성분으로 구성된 변환함수를 사용하여 수신신호를 다른 공간으로 변환하여 변환신호를 계산하는 단계;변환함수의 특성을 이용한 공간 스무딩을 통해 평균화된 공간 공분산 행렬을 추정하는 단계; 및평균화된 공간 공분산 행렬로부터 변환신호 가중치를 계산하고 변환신호에 가중치를 반영한 빔 신호를 생성하는 단계;를 포함하는 것을 특징으로 하는 빔포밍 방법.
- 제 26 항에 있어서, 상기 변환신호를 계산하는 단계는이웃한 변환신호 간의 차가 제1계의 차분이고, 제1계의 이웃한 차분 간의 차가 제2계의 차분인 특성을 이용하여 변환신호를 계산하는 것을 특징으로 하는 빔포밍 방법.
- 제 26 항에 있어서,상기 변환함수는 직교 다항식이며,상기 변환신호를 계산하는 단계는상기 직교 다항식이 실수이고 미분(differential) 때마다 차수가 하나씩 감소하는 특성을 이용하여 변환신호를 계산하는 것을 특징으로 하는 빔포밍 방법.
- 제 28 항에 있어서, 상기 빔 신호를 생성하는 단계는직교 다항식에 기반한 공간 스무딩을 거쳐 가중치를 계산하고 계산된 가중치로부터 최소분산 빔 신호를 생성하는 것을 특징으로 하는 빔포밍 방법.
- 제 26 항에 있어서,상기 변환함수는 푸리에 변환 기저함수이고,상기 변환신호를 계산하는 단계는상기 푸리에 변환 기저함수를 이용하여 변환신호를 계산하는 것을 특징으로 하는 빔포밍 방법.
- 제 30 항에 있어서, 상기 빔 신호를 생성하는 단계는푸리에 변환 기저함수에 기반한 공간 스무딩을 거쳐 가중치를 계산하고 계산된 가중치로부터 빔 공간 적응형 빔 신호를 생성하는 것을 특징으로 하는 빔포밍 방법.
- 제 26 항에 있어서, 상기 빔포밍 방법은,공간 스무딩 이전에, 다수의 샘플 데이터를 평균화하여 채널 데이터 형태의 수신신호를 생성하는 단계;를 더 포함하는 것을 특징으로 하는 빔포밍 방법.
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