JP2017000547A - Ultrasonic diagnostic equipment - Google Patents

Abstract

In an ultrasonic diagnostic apparatus, delay data in consideration of refraction of ultrasonic waves in an ultrasonic propagation path is generated without causing a significant increase in the amount of calculation.
A controller 46 and a memory 42 are provided for each vibration element. The delay unit computing unit 50 obtains a plurality of delay values corresponding to a plurality of reception focal points according to a calculation formula that does not take into account the refraction of ultrasonic waves. A correction value for taking into account the refraction of the ultrasonic waves is calculated in advance and stored in the correction value memory 52. In the adder 54, the correction value is added to each delay value. As a result, a corrected delay value is obtained. Based on this, the read control circuit 56 controls the read timing of data from the memory 42.
[Selection] Figure 2

Description

  The present invention relates to an ultrasonic diagnostic apparatus, and more particularly to a technique for generating delay data for beam formation.

  The ultrasonic diagnostic apparatus is an apparatus that forms an ultrasonic image based on a reception signal obtained by transmitting / receiving ultrasonic waves to / from a living body. A probe (ultrasonic probe) is used to transmit and receive ultrasonic waves. The probe is provided with an array transducer, one or a plurality of matching layers, an acoustic lens, and the like. As such probes, linear probes, sector probes, convex probes, and the like are known.

  A transmission beam is formed by performing delay processing on a plurality of transmission signals supplied to the array transducer in the probe. For this purpose, a transmission beam former as a transmission circuit is provided in the ultrasonic diagnostic apparatus main body. In the delay processing for transmission, a delay time is given to each transmission signal according to transmission delay data for forming a transmission focus. The transmission delay data includes a plurality of delay values (delay time, delay amount) corresponding to a plurality of vibration elements, that is, a plurality of transmission signals. On the other hand, a plurality of reception signals from the array transducer are delayed and added, that is, a phasing addition process is performed to form a reception beam. For this purpose, a receiving beam former is provided as a receiving circuit in the ultrasonic diagnostic apparatus main body. During reception, reception dynamic focus that dynamically changes the reception focus in the depth direction is usually applied. In the delay processing for reception, for each reception focus, a delay time is given to each reception signal according to reception delay data for forming the reception focus. The delay data for reception is composed of a plurality of delay values (delay time, delay amount) corresponding to a plurality of vibration elements, that is, a plurality of received signals. In the delay processing for reception dynamic focus, a plurality of reception focal points are sequentially formed in the depth direction by sequentially switching reception delay data to be applied.

  Delay data for transmission and delay data for reception are based on probe type (electronic scanning method), physical parameters such as array transducer shape and element arrangement, sound velocity in living tissue (for example, sound velocity 1530 m / s), etc. Is calculated. Typically, it is assumed that there is a uniform medium between each vibration element and the focal point (transmission focal point, receiving focal point), that is, the sound velocity on the ultrasonic propagation path is constant. However, there is an acoustic lens (for example, a sound speed of 1000 m / s, a thickness of 0.8 mm) on the living body side of the array transducer, especially when the curvature is large or thick. In addition, the existence of the fat layer in the living body (for example, sound speed 1420 m / s, thickness 5-30 mm), skull layer (for example, sound speed 2900 m / s, thickness 6 mm), etc. If there is a medium layer with a sound velocity different from that of living tissue on the ultrasound propagation path, a difference in sound velocity will occur on the interface, resulting in the ultrasonic wave. Refraction occurs, which leads to phase aberrations and causes defocus It causes deterioration of image quality of ultrasonic images.

  Patent Document 1 discloses a technique for calculating delay data in consideration of refraction of ultrasonic waves generated on the surface of an acoustic lens, that is, phase aberration. According to the technique, for each individual vibration element, an ultrasonic wave propagation path is specified according to Fermat's principle.

JP-A-11-299780

  However, in the method of calculating the delay value by estimating the actual propagation path for each vibration element according to Fermat's principle, the calculation time is inevitably long. This is because in the reception dynamic focus, it is necessary to obtain a delay value for each vibration element and for each reception focus (sample point).

  An object of the present invention is to improve the image quality of an ultrasonic image. Alternatively, the phase aberration caused by the difference in sound speed is improved without causing a significant increase in the amount of calculation.

  An ultrasonic diagnostic apparatus according to the present invention includes a probe including an array transducer including a plurality of vibration elements that form an ultrasonic beam, and a reception dynamic focus for a plurality of reception signals from the plurality of vibration elements. Delay processing means for performing delay processing for forming a plurality of reception focal points at a plurality of depths, and for the delay processing, a plurality of delay values corresponding to the plurality of reception focal points for each of the vibration elements. Generating means for generating, for each of the vibrating elements, basic delay value calculating means for calculating a plurality of basic delay values under a condition that does not consider refraction in an ultrasonic propagation process, and For each vibration element, a correction value generating means for generating a correction value corresponding to a specific depth as a correction value for taking into account refraction in the ultrasonic wave propagation process, and the correction for the plurality of basic delay values Create value Is allowed, thereby characterized in that it comprises a correction means for generating a plurality of corrected delay value refraction were considered in the ultrasonic propagation process as the plurality of delay values.

  When the medium on the ultrasonic wave propagation path is not uniform and there are multiple medium layers with different sound speeds on the ultrasonic wave propagation path (typically, different layers exist in the biological tissue layer) ), The refraction of the ultrasonic waves occurs at the interface where the sound speed difference occurs. In consideration of such refraction, it is ideal to obtain a plurality of delay values corresponding to all reception focal points arranged in the depth direction for each vibration element. However, for that purpose, quite complicated calculations must be performed many times, which requires a great deal of calculation time. It is possible to calculate it in advance and store the calculation result in the storage unit, but in that case, a huge storage capacity is required. Although it is possible to calculate in real time using a dedicated processor capable of performing calculations at a very high speed, in this case, there is a problem that the cost of the apparatus is increased.

  On the other hand, according to the above configuration, it is possible to obtain a plurality of delay values in consideration of refraction without causing a significant increase in the amount of calculation. Since the refraction is not considered in the calculation for obtaining a plurality of basic delay values, the amount of calculation is remarkably smaller than that in the case of considering refraction. In order to obtain the correction value, any complicated method is required. However, if the correction value is obtained for only one (or a small number) of reception focal points for each vibration element, all of them can be obtained. Compared with the case where the correction value (or delay value) is obtained for the reception focus, the amount of calculation is remarkably small. When correction values are applied to a plurality of basic delay values, for example, simple calculations such as addition and subtraction need only be executed, and the calculation burden does not become a special problem. As described above, it is possible to obtain a delay value sequence (corrected delay value sequence) in which refraction is taken into consideration while suppressing the amount of calculation as the entire delay data calculation. Although the corrected delay value sequence is inferior in delay accuracy to the ideal delay value sequence, as will be described later, by appropriately selecting a specific depth, a practically sufficient delay over the entire depth direction It is possible to ensure accuracy.

  Although it is desirable to use one correction value for all reception focal points, that is, all the depths for one vibration element, it is also possible to use a plurality of correction values corresponding to a plurality of depths. The basic delay value calculated in advance may be stored in the storage unit and read from the storage unit, or the basic delay value may be generated by calculation at a necessary timing each time. Similarly, a correction value calculated in advance may be stored in the storage unit and read from the storage unit, or a correction value may be generated by calculation at a necessary timing. . Usually, since a certain amount of time is required for calculating the correction value, it is desirable to calculate the correction value in advance for each combination of various conditions such as the probe type and store them in the storage unit.

  Preferably, the correction value takes into account a basic delay value corresponding to the specific depth calculated based on a basic calculation formula in which the ultrasonic refraction is not considered, and the ultrasonic refraction. It is a value specified based on the fine delay value corresponding to the specific depth calculated based on the fine calculation formula. Preferably, the correction value corresponds to a difference between the basic delay value and the fine delay value. For convenience of calculation, it is desirable to assume one interface (two medium layers), but two or more interfaces (three or more medium layers) may be assumed.

  Preferably, the basic calculation formula calculates the delay value on the assumption that the first medium layer that generates the first sound velocity is uniformly present on the ultrasonic wave propagation path, and the fine calculation formula is The delay value is calculated on the premise that there is a second medium layer that generates a second sound velocity different from the first sound velocity in addition to the first medium layer on the ultrasonic propagation path. The basic calculation formula includes a calculation formula based on a simple geometric model including an array transducer, and the detailed calculation formula includes a calculation formula according to Fermat's theorem.

  Preferably, the specific depth is a pre-selected depth, a transmission focus depth, or a depth representative of the region of interest. For example, the specific depth may be obtained in advance by simulation so that the delay error is reduced for the entire reception focal points arranged in the depth direction.

  In the ultrasonic diagnostic apparatus, the method according to the present invention delays each vibration element for delay processing on a plurality of transmission signals supplied to the plurality of vibration elements or a plurality of reception signals output from the plurality of vibration elements. A method of generating a value, a step of calculating in advance a correction value corresponding to a specific depth as a correction value for taking into account refraction in an ultrasonic wave propagation process for each of the vibration elements; A step of calculating a basic delay value under a condition that does not take into account refraction in an ultrasonic propagation process for each vibration element, and adding the correction value to the basic delay value, whereby ultrasonic propagation is performed as the delay value. Generating a corrected delay value that takes into account refraction in the process. If correction using a correction value that takes into account ultrasonic refraction is performed for either or one of transmit beamforming and receive beamforming, the image quality of the ultrasound image can be improved without causing a significant increase in the amount of computation. It is done.

  According to the present invention, the image quality of an ultrasonic image can be improved. Alternatively, problems due to phase aberration can be improved without causing a significant increase in the amount of computation.

1 is a block diagram showing a preferred embodiment of an ultrasonic diagnostic apparatus according to the present invention. It is a block diagram which shows the structural example of a delay circuit. It is a figure which shows the ultrasonic wave propagation path in a convex probe. It is a figure which shows the ultrasonic wave propagation path in a linear probe. It is a figure which shows the delay error before and behind correction | amendment about the 1st vibration element and the 10th vibration element. It is a figure which shows the delay error before and behind correction | amendment about the 20th vibration element and the 30th vibration element. It is a figure which shows the change of the depth direction about the delay error before and behind correction | amendment.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings.

  FIG. 1 shows a preferred embodiment of an ultrasonic diagnostic apparatus according to the present invention, and FIG. 1 is a block diagram showing the overall configuration thereof. This ultrasonic diagnostic apparatus is installed in a medical institution and is used for ultrasonic diagnosis of a living body.

  In FIG. 1, an array transducer 10 is provided in a probe not shown. The array transducer 10 includes a plurality of vibration elements 10a. They form an ultrasonic beam. The ultrasonic beam is scanned electronically. As such methods, an electronic linear scanning method, an electronic sector scanning method, and the like are known. The convex scanning method applies an electronic linear scanning method to an arc-shaped array transducer. In addition to the array transducer 10, the probe includes one or a plurality of matching layers, an acoustic lens, a backing, and the like. In particular, in the micro convex probe, the curvature of the acoustic lens is large, and the problem of phase aberration cannot be ignored. Therefore, the correction described later is applied.

  The transmission unit 12 includes a generator array 16, a transmission delay processing unit 18, and an amplifier array 20. A transmission signal is generated in each generator 22. The transmission delay processing unit 18 includes a plurality of delay circuits 24. Each delay circuit 24 performs a delay process on the transmission signal. The transmission delay processing unit 18 performs a delay process according to the delay data for forming the transmission focus. The delay data is composed of a plurality of delay values given to a plurality of vibration elements 10a, that is, a plurality of transmission signals. The amplifier row 20 includes a plurality of amplifiers 26. Each amplifier 26 is a power amplifier. Delay data is calculated whenever necessary by an arithmetic circuit included in the transmission delay processing unit 18. In FIG. 1, the D / A converter row and the like included in the transmission unit 12 are not shown.

  The receiving unit 14 includes an amplifier array 28, an A / D converter array 30, a reception delay processing unit 32, and an adder 34. The amplifier row 28 includes a plurality of amplifiers 36, and the A / D converter row 30 includes a plurality of A / D converters 38. The reception delay processing unit 32 has a plurality of delay circuits 40. The reception delay processing unit 32 performs a series of delay processes for sequentially forming reception focal points in the depth direction on a plurality of reception signals output from the plurality of vibration elements 10a for reception dynamic focus. . Delay processing according to the delay data is executed for each reception focus. The delay data is composed of a plurality of delay values arranged in the element arrangement direction. From another viewpoint, in the reception dynamic focus, a plurality of delay values (delay value sequences) corresponding to a plurality of reception focal points arranged in the depth direction are used for each vibration element. In the present embodiment, it is possible to use a corrected delay value sequence that takes into account the refraction of ultrasonic waves caused by layers such as an acoustic lens as the delay value sequence. In addition, the corrected delay value sequence can be obtained with relatively few calculations. This will be described in detail later.

  The plurality of received signals after the delay processing are added in the adder 34. Since addition is performed for a plurality of reception focal points arranged in the depth direction, a reception beam is electronically formed as a result. Beam data corresponding to the received beam is output from the adder 34. Along with electronic scanning of the ultrasonic beam, a plurality of beam data constituting the scanning surface are sequentially output from the adder 34.

  The signal processing unit 41 applies known signal processing such as detection processing and logarithmic conversion processing to individual beam data. The image forming unit 44 includes a digital scan converter having a coordinate conversion function, a pixel interpolation function, and the like, and forms a display frame based on a plurality of beam data. One display frame constitutes one B-mode tomographic image. This is displayed on the display 46. The control unit 48 controls the operation of each component in the ultrasonic diagnostic apparatus. It consists of a CPU and an operation program. The input unit 49 is an operation panel.

  FIG. 2 shows a configuration example of the reception delay processing unit 32. In the illustrated example, a plurality of memories 42 and a plurality of controllers 46 are provided corresponding to a plurality of vibration elements, that is, a plurality of received signals. The configuration is merely an example. Each controller 46 controls reading and writing of each memory 42. By controlling the timing of reading from each memory 42, a delay amount is given to the data stored therein. The read data is temporarily stored on the register 44. A plurality of data read from the plurality of registers is sent to the adder.

  As described above, the memory 42 and the controller 46 are provided for each individual reception channel. The controller 46 includes a write control circuit 48, a delay value calculator 50, a correction value memory 52, an adder 54, and a read control circuit 56. In the adder 54, the correction value output from the correction value memory 52 is added to the delay value (basic delay value) calculated for each reception focus in the delay value calculator 50. A common correction value that acts on a plurality of reception focal points arranged in the depth direction is prepared for each vibration element. The adder 54 sequentially adds the same correction value to a plurality of delay values (basic delay values) corresponding to a plurality of reception focal points. Thereby, a plurality of corrected delay values corresponding to a plurality of reception focal points are obtained. The read control circuit 56 reads data at a timing based on the corrected delay value for each reception focus. The memory 42 is composed of, for example, a FIFO. When viewed as the entire reception delay processing unit 32, a plurality of delay values arranged in the element arrangement direction are generated in units of reception focus. They constitute delay data (delay curve). When viewed in units of reception channels, a plurality of delay values arranged in the depth direction are sequentially generated in units of vibration elements. With these delay values, a delay value string (basic delay value string before correction) can be considered.

The delay value calculator 50 calculates a basic delay value t ₀ (r) for each depth r in accordance with a model or calculation formula that does not consider the refraction of ultrasonic waves on the ultrasonic wave propagation path. In the configuration shown in FIG. 2, the controller 46 is provided for each vibration element. However, a single delay data calculator corresponding to a plurality of controllers 46 may be provided. The correction value t _h is calculated for a specific depth h according to a model or calculation formula that takes into account the refraction of the ultrasonic wave on the ultrasonic wave propagation path. A correction value corresponding to a specific depth h is shared for a plurality of depths. In this embodiment, according to a delay value corresponding to a specific depth calculated according to a calculation formula that does not consider the refraction of ultrasonic waves on the ultrasonic propagation path, and a calculation formula that considers refraction of ultrasonic waves on the ultrasonic propagation path. A correction value corresponding to the specific depth is obtained as a difference from the calculated delay value corresponding to the specific depth. The calculation formula for that will be described in detail later. It is the correction value calculator 58 that performs such calculation. In the illustrated example, a correction value calculator 58 is provided outside the controller 46. A correction value calculator 58 may be provided in the controller 46.

  The delay value calculator 50 calculates individual delay values based on the probe type (electronic scanning method), the physical form and element arrangement of the array transducer, the speed of sound in the living tissue, the speed of sound in the layer of interest, and the like. To do. In the present embodiment, each delay value is calculated according to equation (1) described later. In that case, an approximation method based on the recurrence formula (1) or the PWL (Piece-Wise Linear) method may be used. The correction value calculator 58 also calculates a correction value based on the above information. In the present embodiment, the correction value is calculated in accordance with equation (9) or (10), equation (13), and the like described later. The delay value calculator 50 calculates a delay value for each reception focus, whereas the correction value calculator 58 calculates a correction value only for the representative depth. However, a plurality of correction values corresponding to a plurality of representative depths may be calculated and used selectively.

  In situations where the array transducer can be regarded as a single medium, or in situations where the curvature and thickness of a special layer such as an acoustic lens are so small that refraction and sound speed can be ignored, correction of the delay value is omitted. It is also possible. That is, whether or not the delay value is corrected may be switched depending on the situation. Normally, different correction values are stored in the plurality of correction value memories 52 provided in the plurality of controllers 46. However, for example, the same correction value may be stored in the two correction value memories using the symmetry in the reception aperture. The write control circuit 48 executes control for sequentially writing the sequentially input data to the memory 42. The read control circuit 56 executes control to read data from the memory 42 at the timing based on the corrected delay value as described above.

  For example, the specific depth h may be obtained by a prior simulation so as to reduce the delay error in the entire depth direction. A common depth h may be set between a plurality of receiving channels, or an optimum depth h may be set for each receiving channel.

  According to the above configuration, since the refraction is not considered in the generation stage of the basic delay value, the calculation amount can be reduced, that is, the calculation time can be shortened. In calculating the correction value, since refraction is usually taken into consideration, it takes a considerable calculation time to calculate one correction value, but basically only one correction value needs to be calculated per reception channel. Therefore, if attention is focused on the entire depth direction, the calculation amount of the correction value can be reduced. In addition, the correction value can be calculated in advance, and in that case, the storage capacity for the storage may be small. Even when the delay value and the correction value are added by the adder 54, no complicated processing is required. Therefore, it is possible to obtain an advantage that a corrected delay value considering refraction in a relatively short time can be obtained. Thereby, the phase aberration can be greatly improved, so that the image quality of the ultrasonic image can be improved.

  In the present embodiment, corrected delay data that takes refraction into account is used in the reception delay process, and delay data that does not take into account refraction as in the prior art is used in the transmission delay process. In the transmission delay process, corrected delay data calculated in the same manner as described above may be used. As shown in FIG. 2, when a delay value string is calculated in advance in the delay value calculator 50, a delay value corresponding to a specific depth h in the calculation result is calculated as a correction value calculator 58. You may make it pass to.

  Next, calculation of the basic delay value, the correction value, and the corrected delay value will be described with reference to FIGS.

FIG. 3 schematically shows a convex probe. The array transducer includes a plurality of vibration elements arranged in an arc shape. The radius of curvature is R. An acoustic lens having a certain thickness exists on the living body side of the array transducer. The curvature radius of the surface on the living body side is R1. The thickness of the acoustic lens is (R1-R). The element of interest is identified by E in the array transducer. The angle formed between the direction connecting the element of interest E and the center of curvature Q and the center line (dashed line) is φ. The depth of the reception focus F viewed from the origin O is indicated by r. Φ is a beam deflection angle when performing spatial compounding. When the sound velocity c1 in the acoustic lens is different from the sound velocity c in the living tissue, the ultrasonic wave is refracted at the interface (acoustic lens surface) between them. For example, the ultrasonic wave emitted from the reception focal point F is refracted at the point S and reaches the element of interest E. The distance b and distance d in FIG. 3 are expressed by the following expressions (1) and (2).

FIG. 4 schematically shows a linear probe. The array transducer is composed of a plurality of vibration elements arranged in a straight line, and an acoustic lens is provided on the front side thereof. Its thickness is L. The angle formed by the direction connecting the origin O and the reception focus F with respect to the center line (dashed line) is θ. θ is the beam deflection angle when performing spatial compounding or sector scanning. The depth of the reception focal point F viewed from the origin is indicated by r. The distance between the element of interest E and the origin O is x. When the sound velocity c1 in the acoustic lens is different from the sound velocity c in the living tissue, the ultrasonic wave is refracted at the interface (acoustic lens surface) between them. For example, the ultrasonic wave emitted from the reception focal point F is refracted at the point S and reaches the element of interest E. The distance b and distance d in FIG. 4 are expressed by the following equations (3) and (4).

Based on the above two models, the case where the refraction of the ultrasonic wave on the surface of the acoustic lens is not considered will be examined. In the receive beamformer, the delay time to given to the received signal output from the element of interest E is expressed by the following (5).

However, in the case of a convex probe, x and θ in the above equation (5) are expressed as follows.

  In the above equation (5), the r / c term on the right side represents the propagation time in the propagation path OF at the time of transmission, and the next term (route term) represents the propagation time in the propagation path EF at the time of reception. The content of the above equation (5) is very simple, and even if the delay time is calculated for each r for each individual vibration element, it does not take much time. Depending on the actual device configuration, the minus between the first term and the second term may be positive in the equation (5).

On the other hand, when refraction at the acoustic lens surface is assumed, the propagation path between the element of interest E and the reception focal point F is a route specified by the ESF. The propagation time T in the route is expressed by the following equation (8).

  B and d in the formula (8) are as shown in the formula (1), the formula (2), the formula (3), and the formula (4). Fermat's principle is that the sound wave follows the path of the shortest propagation time. Specifically, if the condition for minimizing T for the target pixel E is found, the refractive propagation path can be specified with it. Become. A calculation formula according to Snell's law may be used.

In the case of a convex probe, if ψ where ∂T / ∂ψ in the following equation (9) is 0, the S point on the interface can be specified.

On the other hand, in the case of a linear probe, if y is obtained such that ∂T / ∂y in the following equation (10) is 0, the S point on the interface can be specified with that y.

The solutions of the above equations (9) and (10) are obtained by repeating numerical calculation. If ψ or y is known, b and d are also known, T is determined from the equation (8), and the delay time t given to the received signal from the element of interest E is the following equation (11) as in the equation (5): And (12).

  The first term on the right side of each equation is the transmission propagation time from the center of the aperture to the focal point, corresponding to the first term on the right side in equation (5), and the next term T is the root term in equation (5). Correspond. Appropriate time is required to solve the above equations (9) and (10).

  In consideration of this, in the present embodiment, correction values are not obtained individually for all depths, but are obtained only for specific representative depths. That is, the number of times of specifying the route satisfying the shortest propagation time condition is greatly reduced. Basically, only one correction value is obtained for each vibration element when one reception beam is formed. The correction value is shared by a plurality of reception focal points arranged in the depth direction.

  The correction value is a value that acts in common on a plurality of delay values (basic delay value sequence) calculated without considering refraction, and specifically, is added (or subtracted) in common to them. It is a value corresponding to a specific depth. Specifically, for a specific depth h, the delay value (true delay value) obtained by considering the refraction of ultrasound (or layer structure) and the refraction of ultrasound (or layer structure) are considered. A correction value is obtained as a difference between the delay value obtained without the calculation.

Specifically, the correction value th for a specific depth h is expressed as the following equation (13).

Correction of the delay value by the correction value is expressed as the following equation (14).

  Ideal correction can be performed at a specific depth h. For other depths, a delay error occurs, but as described below, the delay error is practically not a problem.

  5 to 7 show the computer simulation results. In the simulation, a micro convex probe was assumed. The curvature radius R of the array transducer was 14 mm, the number of elements was 80, and the element pitch was 0.32 mm. The thickness (R1-R) of the acoustic lens layer was 0.78 mm, and the sound velocity c1 in the acoustic lens layer was 1000 m / s. The sound velocity c in the living tissue was set to 1530 m / s. The deflection angle Φ was 0 °. 55 mm was selected as the specific depth h.

  5 and 6, reference numeral 62 indicates the simulation result for the first vibration element, reference numeral 64 indicates the simulation result for the tenth vibration element, and reference numeral 66 indicates the twentyth vibration element. No. 68 shows the simulation result for the 30th vibration element. As shown in the figure, the left end corresponds to No. 1 and the right end corresponds to No. 80. Graphs 62b, 64b, 66b, and 68b show delay errors before correction. Graphs 62a, 64a, 66a and 68a show the corrected delay errors. In each graph, the horizontal axis indicates the depth, and the vertical axis indicates the delay error. By applying a correction value corresponding to a specific depth to the graph before correction, the delay error of the entire graph after correction is greatly reduced.

  FIG. 7 shows simulation results 70, 72, 74 and 76. Reference numeral 70 indicates an observation result at a depth of 20 mm, reference numeral 72 indicates an observation result at a depth of 40 mm, and reference numeral 74 indicates an observation result at a depth of 80 mm. Reference numeral 76 indicates an observation result at a position having a depth of 120 mm. Graphs 70b, 72b, 74b, and 76b show delay errors before correction. Graphs 70a, 72a, 74a, and 76a show delay errors after correction. In each graph, the horizontal axis indicates the element position, and the vertical axis indicates the delay time error.

  As shown in FIGS. 5 to 7, even with uniform correction using a correction value corresponding to a specific depth, it is possible to significantly improve the delay error as a whole in the depth direction and the element arrangement direction. . As the distance from both ends of the array transducer increases, the error increases particularly near the array transducer. However, in normal dynamic focus, the control to narrow the reception aperture is applied near the array transducer. The problem of increased error is unlikely to occur.

  For example, if the center frequency in the frequency band of the probe is 3.2 MHz, for example, if the absolute value of the delay error is 1/8 or less (approximately 40 ns or less) of the period of the nominal frequency, the delay error can be tolerated. Conceivable. As shown in FIGS. 5 to 7, the corrected delay error is 40 ns or less except for the elements close to the end of the array transducer and the shallow portion. During reception, a variable aperture is normally performed as described above. The closer the reception distance is, the smaller the reception aperture is, and no element near the end of the probe is used, or in the case of reception weighting, the weight is decreased. doing. Further, the smaller the radius of curvature of the probe, the smaller the reception aperture. Therefore, according to this embodiment, a sufficiently practical technique can be provided.

  The specific depth is preferably determined as a depth determined in advance by simulation, a depth of a transmission focus, a center depth of a region of interest of interest, or the like.

  18 transmission delay processing unit, 32 reception delay processing unit, 50 delay value calculator, 52 correction value memory, 54 adder, 56 readout control circuit, 58 correction value calculator.

Claims (6)

A probe having an array transducer composed of a plurality of transducer elements for forming an ultrasonic beam;
Delay processing means for performing delay processing for forming a plurality of reception focal points at a plurality of depths for reception dynamic focus on a plurality of reception signals from the plurality of vibration elements;
Generating means for generating a plurality of delay values corresponding to the plurality of reception focal points for each of the vibration elements for the delay processing;
Including
The generating means includes
Basic delay value calculation means for calculating a plurality of basic delay values under conditions that do not consider refraction in an ultrasonic wave propagation process for each of the vibration elements,
Correction value generating means for generating a correction value corresponding to a specific depth as a correction value for considering refraction in an ultrasonic wave propagation process for each vibration element;
Correction means for causing the correction values to act on the plurality of basic delay values, thereby generating a plurality of corrected delay values in consideration of refraction in an ultrasonic propagation process as the plurality of delay values;
An ultrasonic diagnostic apparatus comprising: The apparatus of claim 1.
The correction value is calculated based on a basic calculation formula that does not consider the refraction of the ultrasonic wave and is calculated based on a basic delay value corresponding to the specific depth and a fine calculation formula that takes into account the refraction of the ultrasonic wave. A fine delay value corresponding to the specific depth calculated based on, and a value specified based on
An ultrasonic diagnostic apparatus. The apparatus of claim 2.
The correction value corresponds to a difference between the basic delay value and the fine delay value.
An ultrasonic diagnostic apparatus. The apparatus of claim 2.
The basic calculation formula is to calculate the delay value on the assumption that the first medium layer that causes the first sound velocity on the ultrasonic wave propagation path exists uniformly,
The fine calculation formula calculates the delay value on the premise that there is a second medium layer that generates a second sound velocity different from the first sound velocity in addition to the first medium layer on the ultrasonic propagation path. To do,
An ultrasonic diagnostic apparatus. The apparatus of claim 1.
The specific depth is a preselected depth, a transmission focus depth, or a depth representative of the region of interest.
An ultrasonic diagnostic apparatus. In the ultrasonic diagnostic apparatus, a delay value is generated for each vibration element for delay processing on a plurality of transmission signals supplied to the plurality of vibration elements or a plurality of reception signals output from the plurality of vibration elements. And
For each vibration element, as a correction value for taking into account refraction in an ultrasonic wave propagation process, a step of calculating in advance a correction value corresponding to a specific depth;
For each vibration element, calculating a basic delay value under conditions that do not consider refraction in an ultrasonic wave propagation process;
Adding the correction value to the basic delay value, thereby generating a corrected delay value taking into account refraction in an ultrasonic propagation process as the delay value;
A method comprising the steps of:

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