JP5501813B2 - Ultrasonic diagnostic apparatus and control program therefor - Google Patents

Description

  The present invention relates to an ultrasonic diagnostic apparatus that displays an elastic image representing the hardness or softness of a living tissue and a control program therefor.

  For example, Patent Literature 1 discloses an ultrasonic diagnostic apparatus that synthesizes and displays a normal B-mode image and an elastic image representing the hardness or softness of a living tissue. In this type of ultrasonic diagnostic apparatus, the elasticity image is created as follows. First, an ultrasonic probe is pressed against the body surface, and compression and relaxation thereof are repeated, and ultrasonic waves are transmitted and received while deforming a living tissue, thereby obtaining an echo signal. Then, based on the obtained echo signal, a physical quantity related to the elasticity of the living tissue is calculated, and the physical quantity is converted into hue information to create a color elastic image. Incidentally, as a physical quantity related to the elasticity of the living tissue, for example, a strain of the living tissue is calculated.

  Explaining a little more about an example of the calculation method of the physical quantity, first, correlation windows having a width corresponding to a predetermined number of data are respectively set in two echo signals different in time on the same sound ray, and a complex correlation is established between the correlation windows. A physical quantity in each part of the living tissue is calculated by calculating the function. For example, in Patent Document 2, by calculating a complex correlation function between correlation windows, a waveform shift between both echo signals is calculated, and this waveform shift is regarded as distortion.

JP-A-2005-118152 Japanese Patent Laid-Open No. 2008-126079

  A plurality of correlation windows are set on a single sound ray, and a complex correlation function is calculated for each correlation window to calculate a physical quantity in each part of the living tissue. Incidentally, one pixel data in the elastic image is created based on the physical quantity calculated for each correlation window.

  Here, for example, when an elastic image is displayed in a region of interest (ROI) set on the B-mode image, the distortion is calculated from the pixel on the upper end side to the pixel on the lower end side of the region of interest. It is done sequentially. In this case, in one echo signal, a correlation window is set with a portion corresponding to the upper end of the region of interest as a setting start position. When the time from the start point (reception start point) of the one echo signal to the portion corresponding to the upper end of the region of interest is T, the setting start position of the correlation window in the other echo signal is the other echo signal. The time T has elapsed from the start point (reception start point).

  The two echo signals are signals obtained while deforming the living tissue by repeating compression and relaxation thereof, and the other echo signal is compressed or expanded with respect to one of the echo signals. It has a waveform. Therefore, when the setting start position of the correlation window in the two echo signals is the point at which the time T has elapsed from the start point (reception start point) of each echo signal as described above, the biological body in the two echo signals The correlation window cannot be set for the same part of the tissue. Therefore, there is a possibility that a physical quantity that accurately reflects the elasticity of a living tissue cannot be obtained for a pixel that is initially subject to calculation of a physical quantity on one acoustic ray.

  An invention according to a first aspect made to solve the above-described problems includes an ultrasonic probe that transmits / receives ultrasonic waves to / from a living tissue, and the same acoustic line obtained by transmitting / receiving ultrasonic waves by the ultrasonic probe. A physical quantity calculation unit that sets a correlation window for two echo signals different in time and calculates a physical quantity related to the elasticity of a living tissue by calculating a complex correlation function between the correlation windows, and the physical quantity calculation unit. An elastic image creation unit that creates an elastic image based on the physical quantity, and the physical quantity calculation unit sets a plurality of correlation windows for each of the two echo signals in the elastic image creation region. The physical quantity of each pixel is calculated, and the first calculation target pixel for the physical quantity is calculated on one sound ray. In the calculation of the physical quantity, the physical quantity is calculated a predetermined number of times, and in the calculation of the physical quantity for the second and subsequent times, for one echo signal, the correlation window is based on the physical quantity obtained by the calculation of the immediately preceding physical quantity. The setting start position and the window width are determined and the correlation window is reset to calculate a physical quantity, and the elastic image creation unit calculates the physical quantity obtained by the physical quantity calculation for the predetermined number of times for the calculation start pixel. The ultrasonic diagnostic apparatus is characterized in that an elastic image is created based on the above.

  According to the invention of the second aspect, in the invention of the first aspect, the physical quantity calculation unit calculates an imaginary part of a complex correlation function for echo data within a correlation window set in the two echo signals. This is an ultrasonic diagnostic apparatus.

  According to a third aspect of the invention, in the first or second aspect of the invention, the physical quantity calculation unit calculates a previous delay from the setting start position of the correlation window previously set on one sound ray, by calculating the immediately preceding physical quantity. The ultrasonic diagnostic apparatus is characterized in that the setting start position of the correlation window in the one echo signal is determined by using the physical quantity obtained in (1).

  According to a fourth aspect of the invention, in the invention of the third aspect, the previously set correlation window is an initial correlation window that is initially set on one sound ray. It is.

  A fifth aspect of the invention is the ultrasonic diagnostic apparatus according to the third or fourth aspect of the invention, wherein the advance delay increases as the physical quantity obtained by the calculation of the immediately preceding physical quantity increases. .

  The invention of the sixth aspect is the invention of any one of the first to fifth aspects, wherein the window width of the correlation window to be reset becomes smaller as the physical quantity obtained by the calculation of the immediately preceding physical quantity becomes larger. Is an ultrasonic diagnostic apparatus.

  In the invention of the seventh aspect, in the invention of any one of the first to sixth aspects, when the number of echo data in the echo signals in each correlation window to be calculated by the complex correlation function is not equal, the number is The ultrasonic diagnostic apparatus is characterized in that the echo data in the smaller correlation window is interpolated based on other echo data to calculate a complex correlation function.

  The invention according to the eighth aspect provides a computer with a correlation window for two temporally different echo signals on the same sound ray obtained by transmission / reception of ultrasonic waves by an ultrasonic probe that transmits / receives ultrasonic waves to / from a living tissue. A physical quantity calculation function for setting and calculating a physical quantity related to the elasticity of a living tissue by performing a complex correlation function between the correlation windows, and an elastic image for creating an elastic image based on the physical quantity calculated by the physical quantity calculation unit The physical quantity calculation function calculates a physical quantity of each pixel in the elasticity image by setting a plurality of correlation windows for each of the two echo signals in the elasticity image creation area. In the calculation of the physical quantity for the calculation start pixel which is the first calculation target of the physical quantity on one sound ray, In the calculation of the physical quantity of the number of times, and in the calculation of the physical quantity for the second and subsequent times, the setting start position and the window width of the correlation window are determined based on the physical quantity obtained by the previous physical quantity calculation for one echo signal. A physical quantity is calculated by resetting a correlation window, and the elasticity image creation function creates an elasticity image for the calculation start pixel based on the physical quantity obtained by the physical quantity calculation for the predetermined number of times. Is a control program of the ultrasonic diagnostic apparatus.

  According to the invention of the above aspect, in the calculation of the physical quantity for the calculation start pixel that is the calculation target of the physical quantity for the first time on one acoustic ray, the physical quantity is calculated a predetermined number of times, and the second and subsequent times. In the calculation of the physical quantity, for one echo signal, the correlation window setting start position and the window width are determined based on the physical quantity obtained by the calculation of the previous physical quantity, and the correlation window is reset to calculate the physical quantity. Therefore, a physical quantity that more accurately reflects the elasticity of the living tissue can be calculated for the calculation start pixel.

It is a block diagram which shows an example of schematic structure of embodiment of the ultrasonic diagnosing device which concerns on this invention. It is explanatory drawing of creation of physical quantity data. It is a figure for demonstrating calculation of a physical quantity. It is a block diagram which shows the structure of the display control part in the ultrasonic diagnosing device shown in FIG. It is a figure which shows an example of the display of the display part in the ultrasonic diagnosing device shown in FIG. It is a figure which shows the flowchart about the calculation of the distortion on one sound ray. It is a figure for demonstrating the pixel located in the highest in a region of interest, and a pixel other than that. It is a figure for demonstrating the setting of the first correlation window about the pixel located in the highest position of a region of interest. It is a figure for demonstrating the concept of the calculation of a complex correlation function. It is a figure for demonstrating reset of the correlation window about the pixel located in the highest position of a region of interest. It is a figure for demonstrating the interpolation of the echo data in the reset correlation window. It is a figure for demonstrating the setting of the correlation window at the time of calculating the distortion about the following pixel.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 includes an ultrasonic probe 2, a transmission / reception unit 3, a B-mode data creation unit 4, a physical quantity data creation unit 5, a display control unit 6, a display unit 7, a control unit 8, and an operation unit 9. Prepare.

  The ultrasonic probe 2 transmits an ultrasonic wave to a living tissue and receives an echo thereof. With the ultrasonic wave transmission / reception surface of the ultrasonic probe 2 in contact with the body surface, for example, based on an echo signal obtained by performing ultrasonic wave transmission / reception while repeating compression and relaxation, elasticity is obtained as described later. An image is created.

  The transmission / reception unit 3 drives the ultrasonic probe 2 under a predetermined scanning condition to perform ultrasonic scanning for each sound ray. The transmission / reception unit 3 performs signal processing such as phasing addition processing on the echo received by the ultrasonic probe 2. The echo signal signal-processed by the transmission / reception unit 3 is output to the B-mode data creation unit 4 and the physical quantity data creation unit 5.

  Incidentally, the transmission / reception unit 3 separately performs a B-mode image scan for creating a B-mode image and an elastic image scan for creating an elastic image. As elastic image scanning, at least two scans are performed on the same sound ray in a region (elastic image creation region) in which an elastic image is created in the subject.

  The B-mode data creation unit 4 performs B-mode processing such as logarithmic compression processing and envelope detection processing on the echo signal output from the transmission / reception unit 3 to create B-mode data.

  The physical quantity data creation unit 5 creates physical quantity data related to the elasticity of each part in the living tissue based on the echo signal output from the transmission / reception unit 3 (physical quantity calculation function). More specifically, the elasticity data creation unit 5 calculates the strain St of each part in the living tissue caused by the compression and relaxation of the ultrasonic probe 2 as a physical quantity related to the elasticity of each part in the living tissue. Create physical quantity data. As shown in FIG. 2, the physical quantity data creation unit 5 creates physical quantity data by calculating distortion St based on two echo signals on the same sound ray belonging to two temporally different frames (i) and (ii). To do. The physical quantity data creation unit 5 is an example of an embodiment of a physical quantity calculation unit in the present invention.

  Specifically, as shown in FIG. 3, the physical quantity data creation unit 5 sets a correlation window W1 for the echo signal belonging to the frame (i) and sets a correlation window W2 for the echo signal belonging to the frame (ii). . Then, the physical quantity data creation unit 5 calculates the distortion St by calculating the imaginary part of the complex correlation function between the correlation windows W1 and W2. The calculation of the imaginary part of the complex correlation function will be described later.

  In FIG. 3, the frames (i) and (ii) are made up of echo signals acquired on a plurality of sound rays. In FIG. 3, five sound lines L1a, L1b, L1c, L1d, and L1e are shown as a part of the plurality of sound lines in the frame (i), and the sound lines L1a to L1e in the frame (ii) are shown. As sound lines corresponding to L1e, sound lines L2a, L2b, L2c, L2d, and L2e are shown. That is, the sound ray L1a and the sound ray L2a, the sound ray L1b and the sound ray L2b, the sound ray L1c and the sound ray L2c, the sound ray L1d and the sound ray L2d, the sound ray L1e and the sound ray. L2e corresponds to the same sound ray belonging to two different frames. In FIG. 3, R (i) and R (ii) indicate regions corresponding to a region of interest R in which an elastic image is displayed, as will be described later.

  For example, it is assumed that a correlation window W1c is set as the correlation window W1 in the echo signal on the sound ray L1c, and a correlation window W2c is set as the correlation window W2 in the echo signal on the sound ray L2c. The elasticity data creation unit 5 performs a correlation calculation between the correlation windows W1c and W2c and calculates a strain St. The elastic data creation unit 5 sequentially sets correlation windows W1c and W2c from the upper end 100 to the lower end 101 of the regions R (i) and R (ii) on the sound rays L1c and L2c, and calculates the strain St. . Further, the physical quantity data creation unit 5 calculates the distortion St in the same manner for other sound rays in the regions R (i) and R (ii). Thereby, physical quantity data for one frame composed of distortion St data is obtained. Further details will be described later.

  The display control unit 6 is input with B-mode data from the B-mode data creation unit 4 and elasticity data from the elasticity data creation unit 5. The display control unit 6 includes a B-mode image data creation unit 61, an elastic image data creation unit 62, and a synthesis unit 63, as shown in FIG.

  The B-mode image data creation unit 61 and the elastic image data creation unit 62 have a scan converter. The B-mode image data creation unit 61 converts the B-mode data into B-mode image data having luminance information corresponding to the echo signal intensity. The elastic image data creation unit 62 converts the physical quantity data into color elastic image data having hue information corresponding to distortion (elastic image creation function). The elastic image data creation unit 62 is an example of an embodiment of the elastic image creation unit in the present invention.

  Incidentally, the luminance information in the B-mode image data and the hue information in the color elastic image data have predetermined gradations (for example, 256 gradations).

  The B-mode data before being converted into B-mode image data and the physical quantity data before being converted into color elastic image data are referred to as raw data.

  The synthesizing unit 63 synthesizes the B-mode image data and the color elastic image data by adding them, and creates image data of a two-dimensional ultrasonic image displayed on the display unit 7. The image data is displayed on the display unit 7 as a two-dimensional ultrasonic image G in which a monochrome B-mode image BG and a color elastic image EG are combined as shown in FIG. In this example, the elastic image EG is displayed in the region of interest R in a translucent manner (with the background B-mode image transparent). The display unit 7 is an example of an embodiment of a display unit in the present invention. The region of interest R is a region (elastic image creation region) in which an elastic image of a living tissue is created.

  The control unit 8 is constituted by a CPU (Central Processing Unit), reads a control program stored in a storage unit (not shown), and executes functions in each unit of the ultrasonic diagnostic apparatus 1. The operation unit 9 includes a keyboard and a pointing device (not shown) for the operator to input instructions and information.

  Now, the operation of the ultrasonic diagnostic apparatus 1 of this example will be described. First, the transmission / reception unit 3 transmits an ultrasonic wave from the ultrasonic probe 2 to a living tissue of a subject and acquires an echo signal thereof. At this time, the ultrasonic probe 2 transmits and receives ultrasonic waves while deforming the living tissue by repeatedly pressing and relaxing the subject, for example.

  When the echo signal is acquired, the B-mode data creation unit 4 creates B-mode data, and the physical quantity data creation unit 5 creates physical quantity data. Based on the B-mode data and physical quantity data, the B-mode image data creation unit 61 and the elastic image data creation unit 62 create B-mode image data and color elastic image data. An ultrasonic image G based on the combined image data is displayed on the display unit 7.

  The creation of the physical quantity data will be described in detail. The physical quantity data creating unit 5 sets a correlation window for echo signals on each sound ray in the region of interest R, calculates distortion St, and creates physical quantity data. The calculation of the distortion St on one sound ray will be described based on the flowchart of FIG.

  In the flowchart of FIG. 6, steps S1 to S4 are processes for the calculation start pixel pa that is the first calculation target of the distortion St on one sound ray, and steps S5 to S7 are other than the calculation start pixel pa. This process is for the pixel pb.

  In this example, the calculation start pixel pa is a pixel located at the highest position in the region of interest R. In FIG. 7, the pixels indicated by diagonal lines are the calculation start pixels pa, and the other pixels are the pixels pb. On one sound ray, first, the distortion St is calculated for the calculation start pixel pa, and then the distortion is sequentially calculated for the pixel pb toward the lower end 101 of the region of interest R. Hereinafter, the processing of steps S1 to S7 will be specifically described.

  First, in step S1, as shown in FIG. 8, correlation windows W1 and W2 are set for echo signals r (t) and s (t) on the same sound ray. The correlation windows W1 and W2 are set with a window width WD corresponding to a predetermined time width from a predetermined setting start position sp in the echo signals r (t) and s (t). The setting start position sp is a position on the earliest time phase (on the ultrasonic probe 2 side) of both ends of the correlation windows W1 and W2 in the echo signals r (t) and s (t).

  Incidentally, in FIG. 8, only a part of the echo signals r (t) and s (t) is shown. Further, the echo signals r (t) and s (t) become echo signals from the deep part of the living tissue as they go downward in FIG. 8 (the same applies to FIG. 10).

  The setting start position sp in the echo signal r (t) is a position corresponding to the upper end 100 of the region of interest R in the echo signal r (t). In the echo signal r (t), if the time from the start point (reception start point, not shown) of the echo signal r (t) to the portion corresponding to the upper end 100 of the region of interest R is T, the echo signal The setting start position sp in the signal s (t) is a portion where time T has elapsed from the start point (reception start point, not shown) of the echo signal s (t). Accordingly, the setting start position sp in the echo signal r (t) and the setting start position sp in the echo signal s (t) have the same depth from the transmission / reception surface (surface of the biological tissue) of the ultrasonic probe 2. It is a part corresponding to. However, since the echo signals r (t) and s (t) are acquired in a state where the living tissue is stretched, the setting start position in the echo signals r (t) and s (t). sp corresponds to a different part of the living tissue.

  As for the calculation start pixel pa, as described later, the correlation window W2 is set a plurality of times and the distortion calculation is performed a plurality of times. The setting start position sp in step S1 is referred to as an initial setting start position fsp, and the correlation window W2 set in step S1 is referred to as an initial correlation window W2f.

  Here, the echo signals r (t) and s (t) in FIG. 8 are represented as analog signals for convenience of explanation, but actual processing is assumed to be performed with digital data. The window width WD of the correlation window W1 is equal to the window width WD of the initial correlation window W2f. The number of data of the echo signal r (t) in the correlation window W1 and the echo signal s ( The number of data of t) is equal.

  Next, in step S2, the strain St is calculated. Specifically, the imaginary part of the complex correlation function of the echo data in the correlation windows W1 and W2 in the echo signals r (t) and s (t) is calculated (refer to Patent Document 2 for a specific calculation formula). Here, the imaginary part of the complex correlation function represents the shift amount (shift amount) of the waveforms of both echo signals r (t) and s (t), and this is set as the distortion St.

Here, the concept of the calculation of the complex correlation function will be described with reference to FIG. When the number of data in the correlation windows W1 and W2 is n, the complex correlation function means (Equation 1) below.
r (1) .s ^* (1) + r (2) .s ^* (2) + r (3) .s ^* (3)
+ ... + r (n-1) .s ^* (n-1) + r (n) .s ^* (n) (Formula 1)
That is, the complex correlation function of the echo signals r (t) and s (t) is obtained by using the data r (n) in the echo signal r (t) and the data s in the echo signal s (t) in the correlation windows W1 and W2. It means the sum Ad of the product M _n = r (n) · s ^* (n) with the conjugate complex number s ^* (n) of (n). Incidentally, “*” means a conjugate complex number, and n means the nth data.

The data of the echo signals r (t) and s (t) are represented by complex numbers. That is, the data in the echo signal r (t) is r (n) = a _n + b _n i, and the data in the echo signal s (t) is s (n) = c _n + d _n i. Since the conjugate complex number s ^* (n) of the data s (n) is s ^* (n) = c _n −d _n i, (Equation 1) becomes (Equation 2) below.
(A ₁ + b ₁ i) (c ₁ −d ₁ i) + (a ₂ + b ₂ i) (c ₂ −d ₂ i)
+ (A ₃ + b ₃ i) (c ₃ −d ₃ i) +.
+ (A _n-1 + b _n-1 i) (c _n-1 -d _n-1 i)
+ ( _An + b _n i) (c _n −d _n i) (Expression 2)
Therefore, the physical quantity data creation unit 5 calculates the imaginary part of (Equation 2).

  Here, the accuracy of the distortion St obtained by setting the correlation window W1 and the initial correlation window W2f will be described in relation to the setting positions of the correlation window W1 and the initial correlation window W2f. In this example, the echo signal s (t) is an echo signal acquired in a state where the living tissue is compressed from the time when the echo signal r (t) is acquired. Therefore, as shown in FIG. 8, the waveform of the echo signal r (t) is a waveform obtained by compressing the waveform of the echo signal s (t).

  A portion A indicated by a broken line in the echo signal s (t) is a portion corresponding to a portion where the correlation window W1 is set in the echo signal r (t). In other words, a portion where the correlation window W1 is set in the echo signal r (t) and a portion A indicated by a broken line in the echo signal s (t) are signals from the same portion of the living tissue. Therefore, when the correlation window W2 is set in this portion A and the imaginary part of the complex correlation function is calculated, a strain St that accurately reflects the elasticity of the living tissue can be obtained.

  Incidentally, the real part of the complex correlation function is a correlation coefficient C, which is a measure of how well the echo signals r (t) and s (t) match in the correlation windows W1 and W2. This includes not only the amount of deviation between the two signals but also the signal waveform. Here, it is assumed that the correlation coefficient C is 0 ≦ C ≦ 1, and the closer to 1, the higher the coincidence of the echo signals r (t) and s (t), and the distortion St that accurately reflects the elasticity of the living tissue. Can be calculated. Accordingly, when the correlation window W2 is set in the portion A indicated by the broken line in the echo signal s (t), the correlation coefficient of the complex correlation function is 1, and the strain St that accurately reflects the elasticity of the living tissue is calculated. Is done.

  As described above, the echo signals r (t) and s (t) are not the same waveform, but a waveform in which the echo signal s (t) is compressed more than the echo signal r (t). Accordingly, the point at which the setting start position sp of the correlation window W1 and the initial setting start position fsp of the initial correlation window W2f have passed the same time T from the start points (reception start points) of the echo signals r (t) and s (t). If this is the case, the correlation window W1 and the initial correlation window W2f cannot be set in the same portion of the living tissue of the echo signals r (t) and s (t). Therefore, a value close to 1 cannot be obtained as the correlation coefficient C of the complex correlation function, and it is difficult to obtain a strain St that accurately reflects the elasticity of the living tissue. As the distortion St, a distortion larger than the actual elasticity is calculated because the deviation amount of the waveform of the echo signals r (t) and s (t) in the correlation window W1 and the initial correlation window W2f is large. Therefore, as described later, the distortion St is calculated by resetting the correlation window W2 to the echo signal s (t).

  Next, in step S3, it is determined whether or not the distortion calculation in step S2 is the Xth time. X is a natural number set in advance. If it is determined in step S3 that it is not the Xth time (NO in step S3), the process proceeds to step S4. Then, an elasticity image is created using the distortion obtained at the Xth time as physical quantity data of the calculation start pixel pa. On the other hand, if it is determined in step S3 that it is the Xth time (YES in step S3), the process proceeds to step S5.

  In step S4, the correlation window W2 is reset to the echo signal s (t) based on the distortion St calculated in step S2 (distortion St obtained by the previous distortion calculation). However, only the correlation window W2 is reset, and the correlation window W1 is not reset. The echo signal s (t) is an example of an embodiment of one echo signal in the present invention.

In resetting the correlation window W2, the setting start position sp and the window width WD are calculated. Specifically, the setting start position sp is determined from the initial setting start position fsp, as shown in FIG. 10, based on the distortion St calculated in step S2 (distortion St obtained by the previous distortion calculation). Is obtained by calculating the prior delay Dm corresponding to the time of
_Dm = _Dm-1 + St / (1-St) ... (Formula 3)
The subscript m means m-th distortion calculation, and D _m−1 is a prior delay used in the (m−1) -th distortion calculation, that is, the previous distortion calculation. Incidentally, in the case of the second distortion calculation, D _m−1 is zero. In addition, when the distortion St = 0, D _m = D _m−1 and the same prior delay as the immediately preceding prior delay is used.

Here, it is assumed that the strain St can take either a positive value or a negative value. When the strain St is negative (St <0), the living tissue is contracted due to compression by the ultrasonic probe 2, while when the strain St is positive (St> 0), the ultrasonic probe In this state, the compression by 2 is relaxed and the living tissue is stretched. Incidentally, FIG. 8 and FIG. 10 show echo signals when the living tissue contracts. In any case of St <0 and St> 0, the larger the absolute value of the strain St, the more the living tissue is distorted. Pre delay D _m becomes larger as the distortion St calculated in step S2 is increased, whereas the strain St calculated in step S2 is as smaller decrease in (although, | St | <1).

If the window width of the correlation window W2 is WD2, the window width WD2 is calculated using the following (Equation 4) based on the distortion St calculated in step S2.
WD2 = {1.0 / (1-St)} × WD1 (Formula 4)
WD1 is the window width of the correlation window W1.

  From the above (Equation 4), when St <0, the window width WD2 decreases as the distortion St calculated in step S2 increases, while the window width WD2 increases as the distortion St calculated in step S2 decreases. Become. When St> 0, the window width WD2 increases as the distortion St calculated in step S2 increases, while the window width WD2 decreases as the distortion St calculated in step S2 decreases.

  When the correlation window W2 is reset in step S4, the process returns to step S2, and the imaginary part of the complex correlation function is calculated between the reset correlation window W2 and the correlation window W1, and distortion St Ask for.

  Here, for example, as shown in FIG. 11, the number of echo data of the echo signal s (t) in the correlation window W2 that has been reset is the number of echo data of the echo signal r (t) in the correlation window W1. May be less than the number. In FIG. 11, the number of echo data in the correlation window W1 is n, whereas the number of echo data in the correlation window W2 is (n−4). In this case, after interpolating four pieces of echo data based on the echo data in the echo signal s (t), the imaginary part of the complex correlation function is calculated. In this way, when the number of echo data in the correlation windows W1 and W2 is not equal, the echo data in the smaller correlation window is interpolated from other data, and the complex correlation function is calculated.

As described above, with regard to the calculation start pixel pa, initially, the degree of coincidence of the correlation windows W1 and W2 in the echo signals r (t) and s (t) is low (correlation coefficient is small), and distortion larger than actual. St is calculated. Therefore, when resetting the correlation windows W2, first has a large pre-delay D _m, also set as window width WD is reduced is performed, the correlation window W2 is to approach the portion A indicated by broken lines in FIG. 8 Will be reset to Then, as the correlation window W2 is reset by repeating the loop of steps S2 to S4, the correlation window W2 approaches the portion A and the correlation windows W1, W2 in the echo signals r (t), s (t). The degree of coincidence becomes higher (the correlation coefficient becomes larger), and the calculated strain St becomes a strain that more accurately reflects the elasticity of the living tissue.

  Therefore, the numerical value X, which is the determination criterion in step S3, is set to a value such that the degree of coincidence between the correlation windows W1 and W2 is as high as possible, and a correlation coefficient as close to 1 as possible is obtained in the calculation of the complex correlation function.

  As the physical quantity data of the calculation start pixel pa, the elasticity image is created using the distortion obtained at the Xth time in step S2. Thereby, an elasticity image accurately reflecting the elasticity of the living tissue can be obtained for the calculation start pixel pa.

  In step S3, when it is determined that the calculation of distortion is the Xth time and the process proceeds to step S5, correlation windows W1 and W2 are set. By calculating the imaginary part of the complex correlation function for the correlation windows W1 and W2 set in step S5 as described later, the distortion St is calculated for the pixel pb.

  The setting of correlation windows W1 and W2 in step S5 will be described with reference to FIG. First, the setting of the correlation window W1 for the echo signal r (t) will be described. In FIG. 12, a correlation window W1 ′ is a correlation window set by the previous calculation, that is, the calculation performed on the calculation start pixel pa. The correlation window W1 is set by moving a certain amount from the correlation window W1 ′. Specifically, the correlation window W1 is set with the end of the correlation window W1 ′ as a setting start position sp. The correlation window W1 'and the correlation window W1 have the same window width WD, and the number of echo data in the correlation window W1 is n.

Next, the setting of the correlation window W2 for the echo signal s (t) will be described. In FIG. 12, a correlation window W2 ′ is a correlation window set by the immediately preceding calculation, that is, the calculation performed last for the pixel pa. Unlike the correlation window W1, the correlation window W2 is set using the distortion St obtained by the immediately preceding calculation, that is, the calculation of the imaginary part of the complex correlation function for the correlation windows W1 ′ and W2 ′. And the window width WD is calculated and set. Specifically, the prior delay from the initial setting start position fsp based on (Equation 3) using the distortion St obtained by the calculation of the imaginary part of the complex correlation function for the correlation windows W1 ′ and W2 ′ Dm is calculated to set the setting start position sp, and the window width WD2 is calculated based on (Equation 4). Incidentally, since the distortion St obtained by the last calculation for the pixel pa is a more accurate value (the correlation coefficient is 1 or a value close to 1), the prior delay D _m obtained in step S5 is The value is such that the correlation window W2 is set at a position where the relationship number is close to 1 or a position where the relationship number is 1.

  Next, in step S6, the imaginary part of the complex correlation function is calculated for the echo data in the correlation windows W1 and W2 set in step S5, and the distortion St for the pixel pb is calculated.

  Next, in step S7, it is determined whether or not the pixel pb for which distortion St is to be calculated next is a pixel in the region of interest R. If pixel pb for which distortion is to be calculated next is a pixel in region of interest R (YES in step s7), it is a pixel for which distortion St is to be calculated, and the processing returns to step S5 to return to the next correlation window W1, After setting W2, distortion St is calculated in step S6. On the other hand, when the pixel pb for which distortion St is to be calculated next is not a pixel in the region of interest R (NO in step S7), the processing is terminated, not the pixel for which distortion St is to be calculated. Thereby, the calculation of the distortion St up to the lower end 101 of the region of interest R on one sound ray ends.

  The processing of steps S1 to S7 described above is performed for each sound ray in the region of interest R to calculate the distortion St, and physical quantity data in the region of interest R is created.

  As mentioned above, although this invention was demonstrated by each said embodiment, of course, this invention can be variously implemented in the range which does not change the main point. For example, in the present invention, the calculation start pixel that is the first physical quantity calculation target is not limited to the uppermost pixel of the region of interest R. For example, on one sound ray, the correlation windows W1 and W2 are sequentially set from the upper end 100 side to the lower end 101 side of the region of interest R to calculate the physical quantity, and the calculation is interrupted and the physical quantity is changed again. In the case of performing the calculation, it is assumed that the pixel that is the first physical quantity calculation target after the interruption is also included in the calculation start pixel in the present invention.

  In addition, the physical quantity data creation unit 5 may calculate a displacement due to deformation of the living tissue, an elastic modulus, etc. instead of strain as a physical quantity related to the elasticity of the living tissue.

DESCRIPTION OF SYMBOLS 1 Ultrasonic diagnostic apparatus 2 Ultrasonic probe 5 Physical quantity data creation part (physical quantity calculation part)
62 Elastic image data creation unit (elastic image creation unit)
W1, W2 Correlation window EG Elastic image R Region of interest (elastic image creation region)
pa calculation start pixel sp setting start position WD window width D _m prior delay

Claims (8)

An ultrasound probe that transmits and receives ultrasound to and from biological tissue;
A correlation window is set for two temporally different echo signals on the same sound ray obtained by transmitting and receiving ultrasonic waves by the ultrasonic probe, and a complex correlation function is calculated between the correlation windows to relate to the elasticity of biological tissue. A physical quantity calculation unit for calculating a physical quantity;
An elastic image creation unit that creates an elastic image based on the physical quantity calculated by the physical quantity calculation unit,
The physical quantity calculation unit calculates a physical quantity of each pixel in the elastic image by setting a plurality of correlation windows for each of the two echo signals in the elastic image creation region. In the calculation of the physical quantity for the calculation start pixel that is the calculation target of the physical quantity, the physical quantity is calculated a predetermined number of times, and in the calculation of the physical quantity for the second and subsequent times, for one echo signal, the physical quantity of the previous physical quantity is calculated. Based on the physical quantity obtained in the calculation, the correlation window setting start position and window width are determined, the correlation window is reset, and the physical quantity is calculated.
The ultrasound diagnostic apparatus, wherein the elasticity image creation unit creates an elasticity image for the calculation start pixel based on the physical quantity obtained by the physical quantity calculation for the predetermined number of times.   The ultrasonic diagnostic apparatus according to claim 1, wherein the physical quantity calculation unit calculates an imaginary part of a complex correlation function for echo data within a correlation window set for the two echo signals.   The physical quantity calculation unit calculates a prior delay from the setting start position of the correlation window previously set on one sound ray by using the physical quantity obtained by the previous physical quantity calculation, and in the one echo signal The ultrasonic diagnostic apparatus according to claim 1, wherein a setting start position of the correlation window is determined.   The ultrasonic diagnostic apparatus according to claim 3, wherein the previously set correlation window is an initial correlation window set first on one sound ray.   The ultrasonic diagnostic apparatus according to claim 3 or 4, wherein the advance delay increases as the physical quantity obtained by the calculation of the immediately preceding physical quantity increases.   The ultrasonic diagnostic apparatus according to claim 1, wherein a window width of the correlation window to be reset becomes smaller as a physical quantity obtained by the calculation of the immediately preceding physical quantity becomes larger.   If the number of echo data in the echo signal in each correlation window to be calculated by the complex correlation function is not equal, the echo data in the smaller correlation window is interpolated based on other echo data, The ultrasonic diagnostic apparatus according to claim 1, wherein a complex correlation function is calculated. On the computer,
A correlation window is set between two temporally different echo signals on the same sound line obtained by transmission / reception of ultrasonic waves by an ultrasonic probe that transmits / receives ultrasonic waves to / from a living tissue, and a complex correlation function is set between the correlation windows. A physical quantity calculation function for calculating a physical quantity related to the elasticity of the living tissue by performing the calculation of
An elastic image creation function for creating an elastic image based on the physical quantity calculated by the physical quantity calculation unit;
The physical quantity calculation function calculates a physical quantity of each pixel in the elastic image by setting a plurality of correlation windows for each of the two echo signals in the elastic image creation region. In the calculation of the physical quantity for the calculation start pixel that is the calculation target of the physical quantity, the physical quantity is calculated a predetermined number of times, and in the second and subsequent calculation of the physical quantity, the previous physical quantity is calculated for one echo signal. Based on the physical quantity obtained in step 1, the setting start position and window width of the correlation window are determined, the correlation window is reset, and the physical quantity is calculated.
The control program for an ultrasonic diagnostic apparatus, wherein the elasticity image creation function creates an elasticity image for the calculation start pixel based on a physical quantity obtained by the predetermined physical quantity calculation.

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