JP2005111053A - Ultrasonic image pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic image pickup device for reducing non-continuous changes of the boundary of images at the time of performing multi-stage focusing. <P>SOLUTION: The evaluation parameter value of a depth direction using a pixel value indicating luminance, a frequency spectrum or an autocorrelation function or the like is calculated and the positions of sectioning lines 12, 23, 24 and 32 forming the boundaries of superimposing areas 11, 21, 22 and 31 are set at the positions of the depth direction where the evaluation parameter value is most approximate. Thus, the sectioning lines 12, 23, 24 and 32 are set at the depth direction positions where the luminance, the frequency spectrum or an autocorrelation function value is most approximate, and the non-continuous changes of image quality before and after the sectioning line 42 or 43 forming the boundary of composite image information 40 are reduced. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an ultrasonic imaging apparatus that performs transmission / reception using a multistage focus.

  In imaging of an object using an ultrasonic imaging apparatus, a plurality of probe elements (elements) are transmitted and received with a delay time in order to improve the directivity characteristics of an ultrasonic beam (beam). Focusing is performed at a predetermined depth to obtain a clearer image (see, for example, Non-Patent Document 1).

It is also possible to obtain a plurality of images having different focusing positions in the depth direction, combine these images around the focusing position, and synthesize a clearer image. In this multistage focusing, a clear image focused on the entire image is acquired particularly in an imaging region with little movement.
Yoshinori Iwai, 2 authors, “Medical diagnostic imaging device”, Corona, December 30, 1988, p. 217-219

  However, according to the above background art, when a plurality of images having different focusing positions are combined, the image quality changes discontinuously at the boundary that is a joint between these images. That is, the luminance of the image changes discontinuously, or a discontinuous change of the image texture (texture) caused by different focusing positions occurs.

  In particular, the discontinuous change of the boundary varies depending on the subject and the imaging region of the subject, and the discontinuous change may or may not occur for the operator, resulting in poor image quality. It is a factor to stabilize.

  For these reasons, it is important how to realize an ultrasonic imaging apparatus that reduces discontinuous changes in image boundaries when performing multistage focusing.

  The present invention has been made to solve the above-described problems caused by the background art, and an object of the present invention is to provide an ultrasonic imaging apparatus that reduces discontinuous changes in image boundaries when performing multistage focusing. And

  In order to solve the above-described problem and achieve the object, an ultrasonic imaging apparatus according to the first aspect of the invention includes an ultrasonic transmission / reception in a depth direction inside a subject and the depth direction of the transmission / reception. Image synthesis means for synthesizing one piece of synthesized image information from a plurality of partial image information with different focus positions in the depth direction when transmitting the ultrasonic wave when acquiring B-mode image information by scanning in the orthogonal scanning direction The partial image information includes overlapping regions that overlap each other in the depth direction, and the image composition unit provides a boundary for combining the plurality of partial image information in the overlapping region. Calculating the evaluation parameter values at all the depth positions of the overlapping region for each partial image information, and calculating the depth of the partial image information that approximates the evaluation parameter value most closely. Characterized in that it comprises a setting means for setting the position.

  In the invention according to the first aspect, the setting parameter approximates the evaluation parameter value calculated for each position in the depth direction in the two overlapping regions sharing the boundary by the setting means. Set to position.

  Further, the ultrasonic imaging apparatus according to the invention of the second aspect is characterized in that the evaluation parameter value is an average value of pixel values arranged in a scanning direction of the overlapping region.

  In the invention according to the second aspect, the setting means sets a dividing line at a position where the pixel value of the overlapping region, that is, the luminance is most approximate.

  Moreover, the ultrasonic imaging apparatus according to the invention of the third aspect is characterized in that the evaluation parameter value is a frequency spectrum calculated from pixel values arranged in the scanning direction of the superimposed region.

  According to the third aspect of the invention, the setting means sets a dividing line at a position where the frequency spectrum is closest.

  In the ultrasonic imaging apparatus according to the fourth aspect of the invention, the evaluation parameter value is an autocorrelation average for each depth position in which the autocorrelation function value in the depth direction of the overlapped region is averaged in the scanning direction. It is a value.

  In the fourth aspect of the invention, the setting means sets the boundary at the position where the autocorrelation function value, that is, the redundancy is closest.

  The ultrasonic imaging apparatus according to the invention of the fifth aspect is characterized in that low-pass filter processing for removing noise is performed on the autocorrelation function value.

  In the fifth aspect of the invention, the autocorrelation function value is subjected to low-pass filter processing to remove noise components.

  The ultrasonic imaging apparatus according to the invention of the sixth aspect is characterized in that the autocorrelation function value is a value obtained by subtracting an average value of all the depth positions.

  In the invention according to the sixth aspect, the autocorrelation function value removes the components that the organs included in the image of the superimposed region generally have.

  In the ultrasonic imaging apparatus according to the seventh aspect of the invention, the setting unit may be configured such that the setting unit is between a position in the depth direction of the boundary that is initially set and a position in the depth direction that the evaluation parameter value approximates most. A manual setting means for manually setting the boundary is provided.

  In the seventh aspect of the invention, the setting means manually sets the boundary between the initial position of the boundary in the depth direction and the position in the depth direction where the evaluation parameter value is most approximated by the manual setting means. Set.

  Further, in the ultrasonic imaging apparatus according to the invention of the eighth aspect, the setting means calculates two average values of pixel values arranged in the scanning direction at a position where the evaluation parameter value of the superimposition region is closest. One of the partial image information is corrected so that the calculation is performed for each of the overlapping regions and the average value approximates the two overlapping regions.

  In the invention of the eighth aspect, the setting means prevents the luminance of the composite image information from changing discontinuously at the boundary position.

  As described above, according to the present invention, the evaluation parameter value calculated for each position in the depth direction of the two overlapping regions that share the boundary by the setting means is determined by the setting unit. Set to the closest position, combine the image at the position where the pixel value or image texture is the closest, and reduce the discontinuity of image quality before and after the depth direction of the boundary of the combined image information Instability of image quality can be improved.

  The best mode for carrying out an ultrasonic imaging apparatus according to the present invention will be described below with reference to the accompanying drawings. Note that the present invention is not limited thereby.

  First, the overall configuration of the ultrasonic imaging apparatus according to the present embodiment will be described. FIG. 1 shows an overall configuration of an ultrasonic imaging apparatus according to an embodiment of the present invention. Ultrasonic waves are applied to a subject 1 and are linearly scanned electronically to acquire B-mode image information. An example of an ultrasonic imaging apparatus is shown.

  The ultrasonic imaging apparatus includes a probe unit 101, a transmission / reception unit 102, an image synthesis unit 90, a screen display control unit 105, a display unit 106, an input unit 107, and a controller unit 108. The image synthesizing unit 90 includes a B mode processing unit 103 and a frame processing unit 104.

  In the probe unit 101, piezoelectric elements for transmitting and receiving ultrasonic waves are arranged in a linear shape at the tip, and the piezoelectric elements are brought into close contact with the surface of the subject 1 to image the inside of the subject 1. Here, the piezoelectric element is a portion that performs electronic scanning while irradiating the imaging range of the subject 1 with ultrasonic waves while receiving ultrasonic echoes (echo) reflected from the subject 1. The probe unit 101 includes piezoelectric elements arranged in an array, and also includes a switching circuit that selectively drives the piezoelectric elements.

  The transmission / reception unit 102 is connected to the probe unit 101 by a coaxial cable and generates an electric signal for driving the piezoelectric element of the probe unit 101, and at the same time, amplifies the received ultrasonic echo signal at the first stage. It is a part to do.

  The B-mode processing unit 103 is a part that performs processing for generating B-mode image information in real time from the ultrasonic echo signal amplified by the transmission / reception unit 102. Specific processing contents include, for example, delay addition processing of received ultrasonic echo signals, A / D (analog / digital) conversion processing, and processing for generating digital information after conversion as B-mode image information. Etc.

  The frame processing unit 104 performs frame processing on the B-mode image information from the B-mode processing unit 103, for example, image information combining processing described later, and outputs the image information to the screen display control unit 105. Note that the B-mode processing unit 103 and the frame processing unit 104 constitute an image synthesizing unit 90 when synthesizing synthesized image information described later.

  The screen display control unit 105 is also called a scan converter, converts display frame rate of the B-mode image information generated by the B-mode processing unit 103, linear, convex, or sector. This is a part for converting the image display form such as (sector) and controlling the display position of these images.

  The input unit 107 is composed of a keyboard, a mouse, or the like. The input unit 107 provides operation input information by the operator, for example, input information such as personal information, ID number, or imaging position of the subject 1 to the controller unit 108. is there.

  The display unit 106 is a part for visually displaying image information whose display frame rate conversion, image display form conversion, and display position are controlled by the screen display control unit 105 to the operator.

  The controller unit 108 is a unit for controlling the operation of each unit of the above-described ultrasonic imaging apparatus based on the operation input information given from the input unit 107 and the program (program) and data (data) stored in advance. .

  Next, the configurations of the B-mode processing unit 103 and the frame processing unit 104 that form the image composition unit 90 are shown in FIG. FIG. 2 is a block diagram schematically showing the configuration of the B mode processing unit 103 and the frame processing unit 104. The B mode processing unit 103 includes a memory 201 and setting means 202, and the frame processing unit 104 includes a calculation unit 212 and a memory 211.

  The B mode processing unit 103 reads a plurality of B mode image information (hereinafter referred to as partial image information) having different transmission focus positions in the depth direction from the transmission / reception unit 102 into the memory 201. In this partial image information, three pieces of partial image information 10, partial image information 20, and partial image information 30 are acquired in order from a shallow transmission focus position in the depth direction, and the imaging positions in the depth direction are different from each other. The reception focus position is set to a common position in the partial image information 10 to 30. Further, the number of partial image information is not limited to three, and may be two or four.

  The setting unit 202 performs calculation such as calculation of a correlation function value or spectrum (spectrum) from the partial image information 10 to 30, and calculation of the position of the dividing line which is synthesis information. Then, the frame processing unit 104 creates the composite image information 40 from the partial image information 10 to 30 from the memory 201 and the position information of the dividing line from the setting unit 202, and sends it to the screen display control unit 105. Send.

  FIG. 3 is a diagram schematically illustrating a process in which the synthesized image information 40 is synthesized from the partial image information 10 to 30. The partial image information 10 to 30 includes pixels that are two-dimensionally arranged in the scanning direction that is the arrangement direction of the piezoelectric elements and the depth direction that is the traveling direction of the ultrasonic waves. Here, as for the partial image information 10-30, the position of the acquired image information in the depth direction is different, and the image information at a deeper position is acquired in numerical order.

  In FIG. 3, the coordinates of the depth direction position form a common coordinate axis in the partial image information 10 to 30 and the composite image information 40, the partial image information 10 from the shallowest, the intermediate depth is the partial image information 20, The deeper one corresponds to the partial image information 30.

  The partial image information 10 has an overlapping region 11 that overlaps the partial image information 20 in the depth direction. Similarly, the partial image information 20 has an overlapping region 21 that overlaps the partial image information 10. The overlapping regions 11 and 21 have exactly the same number of pixels in the scanning direction and the depth direction. Note that the partial image information 20 and the partial image information 30 also have overlapping regions 22 and 31 in exactly the same manner.

  When combining the partial image information 10 to 30 to generate the combined image information 40, the calculation unit 212 performs partial image information at the positions of the dividing lines 12, 23, 24, and 32 that form the boundary of the partial image information 10 to 30. Divide 10-30. Here, the calculation unit 212 rejects the image information portion consisting only of the overlapping region, and performs image composition using the other image information portion. Accordingly, the positions of the dividing lines 42 and 43 that form the boundary, which is the bonding position of the composite image information 40, coincide with the positions in the depth direction of the dividing lines 12 and 23 and the dividing lines 24 and 32. Note that the dividing lines 42 and 43 forming the boundary of the composite image information 40 shown in FIG. 3 merely indicate the composite position of the image and are not displayed in the image.

  As for the position in the depth direction of the dividing lines 12 and 23 and 24 and 32 that form a boundary at the time of composition, the optimum setting is selected from the overlapping regions 11 and 21 and the overlapping regions 22 and 32. Is selected.

  Next, the operation of the setting unit 202 according to the present embodiment will be described with reference to FIG. FIG. 4 is a diagram schematically showing an operation of determining the dividing line position from the overlapping regions 11 and 21 of the partial image information 10 and 20 using the setting unit 202. The setting unit 202 selects an optimum dividing line position in the depth direction from the overlapping regions 11 and 21 and the overlapping regions 22 and 32. Here, the setting means 202 calculates an evaluation parameter (parameter) value in the depth direction of the overlapping regions 11, 21, 22, and 32, and the evaluation parameter is calculated in the overlapping regions 11 and 21 and the overlapping regions 22 and 32. The position in the depth direction where the values most closely match is the position of the separator lines 12 and 23 and the position of the separator lines 24 and 32.

  Note that a pixel value representing a luminance, a frequency spectrum, an autocorrelation function, or the like is used as the evaluation parameter value. Therefore, first, the case where the pixel value representing the luminance is set as the evaluation parameter value is described below.

  FIG. 4 is a diagram illustrating an example in which a pixel value is used as the evaluation parameter value. The setting means 202 obtains an average value in the scanning direction for each position in the depth direction with respect to the pixel values of the overlapping regions 11 and 21. 4, the average values P1, P2,... In the scanning direction are obtained sequentially from the shallow position in the superimposing region 11, and the average values Q1, Q2,. Ask. In FIG. 4, the pixel positions to be averaged are schematically indicated by the arrows in the overlapping regions 11 and 21, but the order of averaging indicated by the direction of the arrows is not particularly limited.

  After that, the setting unit 202 obtains the difference between the average values of the overlapping regions 11 and 21 having the same depth direction position, Pi-Qi (i is a parameter indicating the depth direction position), and the depth with the smallest difference. The vertical position i is the position of the dividing lines 12 and 23. Note that the positions of the dividing lines 24 and 32 are determined in the same manner for the overlapping regions 22 and 31 as well.

  Further, a frequency spectrum in the scanning direction can also be used as the evaluation parameter value. In this case, instead of the average values P1, P2... Or Q1, Q2... Shown in FIG. 4, the frequency spectrums SP1, SP2... SQ1, SQ2. Is used. Then, instead of the difference Pi-Qi, for example, the difference SPi-SQi of the frequency spectrum added in the scanning direction sets the smallest depth direction position i as the positions of the dividing lines 12 and 23.

  Also, an autocorrelation function in the depth direction can be used as the evaluation parameter value. It is mathematically known that the autocorrelation function is a parameter representing the redundancy of image data and is equivalent to a difference between pixel values in the depth direction. Therefore, the setting means 202 obtains an autocorrelation function value at the position in the depth direction for each position in the scanning direction of the overlapping regions 11 and 21. Here, an average value of the pixel values in the depth direction of the superimposed regions 11 and 21 is obtained, and a difference from the average value for each position in the depth direction is set as an autocorrelation function value. Thereafter, an autocorrelation average value obtained by averaging the autocorrelation function values in the scanning direction is used as an evaluation parameter value.

  FIG. 5 shows an example of the autocorrelation average value. 5A is a diagram illustrating an autocorrelation average value over the entire partial image information 10, and FIG. 5B is a diagram illustrating an autocorrelation average value over the entire partial image information 20. Here, the horizontal axis indicates the position in the depth direction, and the vertical axis indicates the autocorrelation average value. In FIGS. 5A and 5B, the autocorrelation average value exists in both the overlapping regions 11 and 21, and the position in the depth direction where the autocorrelation average value approximates most in this region is indicated by the dividing line 12. And 23 positions. For the partial image information 20 and 30, the positions of the separator lines 24 and 32 can be determined in exactly the same manner.

  As described above, in the present embodiment, the positions of the dividing lines 12, 23, 24, and 32 that form the boundaries in the overlapping regions 11, 21, 22, and 31 are represented by pixel values that represent luminance, frequency spectra, or autocorrelation functions. The evaluation parameter value in the depth direction using, etc. is calculated and set to the position in the depth direction where this evaluation parameter value is closest to the depth, so that the brightness, frequency spectrum, or autocorrelation function value is the closest depth Separation lines 12, 23, 24, and 32 are set at the directional positions, and as a result, discontinuous changes in image quality before and after the separation line 42 or 43 that forms the boundary of the composite image information 40 can be reduced.

  In the present embodiment, the evaluation parameter values are calculated for each position in the depth direction in the overlapping regions 11, 21, 22, and 31, but in each overlapping region 11, 21, 22, and 31, all the depths are calculated. It is also possible to obtain an average value of the evaluation parameter values in the vertical direction and correct the evaluation parameter value with this average value. As a result, when an organ having a size covering the overlapping region is included, the contribution to the evaluation parameter value unique to the organ can be reduced.

  Further, in the present embodiment, when obtaining the autocorrelation function value, the average or difference is performed on the partial image information 10 to 30, but the average or difference is obtained after low-pass filter processing is performed on the partial image information 10 to 30. Can also be done. Thereby, an evaluation parameter value with little influence of noise can be obtained.

  Further, in the present embodiment, in the overlapping regions 11, 21, 22, and 31, the separation lines 12, 23, 24, and 32 that form boundaries are provided at positions where the evaluation parameter values are closest to each other, and the partial image information 10 to 30 Although the composition is performed, the brightness of the partial image information 10 to 30 can be corrected at the time of composition, and the brightness before and after the dividing lines 42 and 43 of the composite image information 40 can be continuously changed. For example, when combining the partial image information 10 and 20, the average value of the pixel values on the dividing line 12 and the average value of the pixel values on the dividing line 23 are obtained, and the correction coefficient is determined from the ratio of these average values. Then, all pixel values of the partial image information 10 or 20 are corrected.

  In the present embodiment, the setting unit 202 automatically sets the positions of the dividing lines 12, 23, 24, and 32 that form the boundary. However, the setting unit 202 manually allows the operator to manually set the dividing lines. Setting means can also be provided. According to this, the manual setting means sets the separator lines 42 and 43 of the composite image information 40 according to the preference of the operator, for example, between the default separator line position and the automatically set separator line position.

  In the present embodiment, an example of B-mode image information by linear scanning has been described. However, the present invention is not limited to this, and sector-type, convex-type electronic scanning or mechanical scanning, and further B-mode image information. It can also be used for color flow mapping that overwrites blood flow information.

It is a block diagram which shows the whole structure of an ultrasonic imaging device. It is a block diagram which shows the B mode process part and frame process part of embodiment. It is a figure which shows the process of synthesize | combining synthetic | combination image information from the partial image information of embodiment. It is a figure which shows an example at the time of using a pixel value as an evaluation parameter value of embodiment. It is a figure which shows an example at the time of using an autocorrelation function as an evaluation parameter value of embodiment.

Explanation of symbols

1 Subject 10, 20, 30 Partial image information 11, 21, 22, 31 Superimposition region 12, 23, 24, 32, 42, 43 Separation line 40 Composite image information 90 Image composition means 101 Probe unit 102 Transceiver 103 B mode processing unit 104 Frame processing unit 105 Screen display control unit 106 Display unit 107 Input unit 108 Controller unit 201, 211 Memory 202 Setting means 212 Calculation unit

Claims (8)

When acquiring B-mode image information by transmitting / receiving ultrasonic waves in the depth direction inside the subject and scanning in the scanning direction orthogonal to the depth direction of the transmission / reception, when transmitting the ultrasonic waves, An ultrasonic imaging apparatus comprising image combining means for combining one piece of combined image information from a plurality of partial image information having different focus positions,
The partial image information has overlapping regions that overlap each other in the depth direction,
The image synthesizing unit provides a boundary for synthesizing the plurality of partial image information in the overlap region, and evaluates the depth direction position of the boundary at all depth positions of the overlap region for each partial image information. An ultrasonic imaging apparatus comprising: setting means for calculating a parameter value and setting the parameter value to a depth position of the partial image information that approximates the evaluation parameter value most closely.   The ultrasonic imaging apparatus according to claim 1, wherein the evaluation parameter value is an average value of pixel values arranged in a scanning direction of the overlapping region.   The ultrasonic imaging apparatus according to claim 1, wherein the evaluation parameter value is a frequency spectrum calculated from pixel values arranged in a scanning direction of the overlapping region.   2. The ultrasonic wave according to claim 1, wherein the evaluation parameter value is an autocorrelation average value for each depth position that averages an autocorrelation function value in the depth direction of the superimposed region in a scanning direction. Imaging device.   The ultrasonic imaging apparatus according to claim 4, wherein the autocorrelation function value is subjected to low-pass filter processing for removing noise.   The ultrasonic imaging apparatus according to claim 4, wherein the autocorrelation function value is a value obtained by subtracting an average value of all the depth positions.   The setting means includes manual setting means for manually setting the boundary between a position in the depth direction of the boundary that is initially set and a position in the depth direction that the evaluation parameter value is closest to. The ultrasonic imaging apparatus according to any one of claims 1 to 6.   The setting means calculates an average value of pixel values arranged in the scanning direction at a position where the evaluation parameter value of the superimposition area is the closest, for each of the two superimposition areas, and the average value is equal to the two superimposition values. The ultrasonic imaging apparatus according to claim 1, wherein any one of the partial image information is corrected so as to be approximated by a region.

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