JP6731369B2 - Ultrasonic diagnostic device and program - Google Patents

Description

The present invention relates to an ultrasonic diagnostic apparatus, and particularly to a technique related to measurement of a fetus.

The head and abdomen of the fetus may be measured using an ultrasonic diagnostic apparatus. In the measurement, in order to improve the measurement accuracy, it is desirable to be able to accurately detect the position or region of the measurement target part (for example, the head or the abdomen).

In measuring the fetal head, the tomographic image is transformed into polar coordinates, and the dynamic programming is applied to the image after polar transformation to calculate an ellipse approximating the fetal head, and the ellipse is used for measurement. It may be performed (for example, Patent Document 1).

International Publication No. 2016/190256

As described above, the ellipse corresponding to the fetus head may be calculated and the fetus head may be measured using the ellipse. In order to improve the accuracy of measurement using the ellipse, it is desirable to match the inclination of the ellipse with the inclination of the fetal head. This also applies to the case of measuring the fetal abdomen, and in order to improve the measurement accuracy of the fetal abdomen, it is desirable to match the inclination of the ellipse corresponding to the fetal abdomen with the inclination of the fetal abdomen.

An object of the present invention is to correct the inclination of the ellipse so that the inclination of the ellipse corresponding to the annular portion of the fetus is close to the inclination of the annular portion.

According to the present invention, an ellipse calculation means for calculating an ellipse corresponding to an annular part of the fetus based on a tomographic image obtained by transmitting and receiving ultrasonic waves to and from a fetus in a mother, and the ellipse calculation means. While moving the calculated center of the ellipse in one axis direction of the ellipse, and rotating the reference area extending in the other axis direction of the ellipse at the center after the movement, each position and each position in the one axis direction. At the rotation angle, an evaluation value in the reference area is calculated, and using the evaluation value, an angle correction unit that corrects the angle of the ellipse with respect to the annular portion, and an ultrasonic diagnostic apparatus comprising: is there.

The angle correction means may correct the angle of the ellipse based on the evaluation values obtained at the positions and the rotation angles and the variance of the evaluation values.

The angle correction means moves the center of the ellipse in the one-axis direction, rotates the reference area at the position of the movement destination, and sums the sum of the brightness values in the reference area at each rotation angle. Calculated as an evaluation value, for each position in the one axis direction, the sum of the brightness values in the reference area at each rotation angle is calculated, and for each position in the one axis direction, the brightness at each rotation angle. The variance of the sum of the values is calculated, the position in the one-axis direction having the largest variance is determined, the rotation angle having the largest sum of the brightness values at that position is determined, and the angle of the ellipse is corrected to that rotation angle. May be.

The angle correction means may apply a weighting process according to the amount of movement of the center of the ellipse in the one-axis direction to the variance of the sum of the brightness values.

When the variance at each position in the one-axis direction is less than or equal to a predetermined threshold value, the angle correction means sets the ellipse to the rotation angle at which the sum of the brightness values becomes the largest when the center of the ellipse is not moved. The angle may be corrected.

The annular portion is the head of the fetus, the one axis direction is the minor axis direction of the ellipse, the other axis direction is the major axis direction of the ellipse, the angle correction means, the evaluation value to the Based on this, the angle of the ellipse may be corrected by calculating the direction in which the midline of the head of the fetus extends.

By applying template matching to the tomographic image, position calculating means for calculating a candidate for the central position of the annular portion of the fetus, and the candidate for the central position as an origin of a polar coordinate system, the tomographic image is a polar coordinate. The ellipse calculating means further includes a converting means for converting, a searching means for searching a route from the image after the polar coordinate conversion, and an inverse transforming means for inversely transforming the route, wherein the ellipse calculating means corresponds to the route after the inverse transform. The ellipse may be calculated as an ellipse corresponding to the annular portion.

Further, the present invention provides a computer, an ellipse calculation means for calculating an ellipse corresponding to an annular part of the fetus based on a tomographic image obtained by transmitting and receiving ultrasonic waves to and from the fetus in the mother's body. While moving the center of the ellipse calculated by the ellipse calculation means in one axis direction of the ellipse, and rotating the reference area extending in the other axis direction of the ellipse at the center after the movement, A program that operates as an angle correction unit that calculates an evaluation value in the reference area at each position and each rotation angle, and uses the evaluation value to correct the angle of the ellipse with respect to the annular portion. Is.

According to the present invention, the inclination of the ellipse corresponding to the annular part of the fetus can be made closer to the inclination of the annular part.

It is a block diagram which shows the ultrasonic diagnosing device which concerns on 1st Embodiment. It is a block diagram which shows a position calculation part. It is a block diagram which shows a region calculation part. It is a figure which shows a B-mode tomographic image. It is a figure which shows a template. It is a figure which shows an edge emphasis image. It is a figure which shows the expanded image produced|generated by the polar coordinate conversion. It is a figure which shows the developed image to which the mask was applied. It is a figure which shows the developed image to which the mask was applied. It is a figure which shows the image for demonstrating a route search process. It is a figure which shows a search map. It is a figure which shows the image for demonstrating a route search process. It is a figure which shows the path line produced|generated by the inverse transformation. It is a figure which shows an ellipse. It is a figure which shows a part of B mode tomographic image, and the axis of an ellipse. It is a figure which shows a part of B mode tomographic image, and the axis of an ellipse. FIG. 9 is a diagram showing a developed image according to Modification 1. 9 is a diagram showing a B-mode tomographic image according to Modification 2. FIG. It is a block diagram which shows the ultrasonic diagnosing device which concerns on 2nd Embodiment. It is a figure which shows an example of a median line of a fetal head, and an ellipse approximated to a fetal head. It is a figure which shows an example of a median line of a fetal head, and an ellipse approximated to a fetal head. It is a figure which shows an example of a median line of a fetal head, and an ellipse approximated to a fetal head. It is a figure which shows distribution of dispersion|distribution of the brightness value sum total. It is a figure which shows distribution of a brightness value total. It is a figure which shows the template which concerns on 3rd Embodiment. It is a figure which shows the edge emphasis image which concerns on 3rd Embodiment. It is a figure which shows the developed image in which the mask which concerns on 3rd Embodiment was provided.

<First Embodiment>
Hereinafter, the ultrasonic diagnostic apparatus according to the first embodiment of the present invention will be described with reference to FIG. FIG. 1 shows an ultrasonic diagnostic apparatus according to the first embodiment. FIG. 1 is a block diagram showing the overall configuration. This ultrasonic diagnostic apparatus is used in the medical field and has a function of forming an image of a tissue in a living body by transmitting and receiving ultrasonic waves. As an example, the tissue to be imaged is the fetus. Of course, other tissues may be imaged.

The probe 10 is a transducer that transmits and receives ultrasonic waves. The probe 10 has, for example, a 1D array transducer. The 1D array oscillator is formed by arranging a plurality of vibrating elements one-dimensionally. An ultrasonic beam is formed by the 1D array transducer and repeatedly electronically scanned. As a result, a scanning surface is formed in the living body for each electronic scanning. The scanning plane corresponds to the two-dimensional echo data acquisition space. The probe 10 may have a 2D array transducer formed by arranging a plurality of vibrating elements two-dimensionally instead of the 1D array transducer. When the ultrasonic beam is formed by the 2D array transducer and electronically scanned repeatedly, a scanning surface as a two-dimensional echo data acquisition space is formed for each electronic scanning, and the ultrasonic beam is two-dimensionally scanned. Then, a three-dimensional space as a three-dimensional echo data acquisition space is formed. As the scanning method, sector scanning, linear scanning, convex scanning or the like is used. When performing ultrasonic diagnosis of the fetus, the probe 10 is brought into contact with the surface of the abdomen of the mother, and ultrasonic waves are transmitted and received in that state.

The transceiver 12 functions as a transmission beamformer and a reception beamformer. At the time of transmission, the transmission/reception unit 12 supplies a plurality of transmission signals having a constant delay relationship to a plurality of vibrating elements included in the probe 10. As a result, an ultrasonic transmission beam is formed. At the time of reception, the reflected wave from the inside of the living body is received by the probe 10, whereby a plurality of received signals are output from the probe 10 to the transmission/reception unit 12. The transmission/reception unit 12 forms a reception beam by applying a phasing addition process to a plurality of reception signals. The beam data is output to the signal processing unit 14. That is, the transmission/reception unit 12 performs delay processing on the reception signal obtained from each vibrating element according to the delay processing condition for each vibrating element, and performs addition processing on a plurality of reception signals obtained from a plurality of vibrating elements to receive. Form a beam. The delay processing condition is defined by the reception delay data (delay time). A reception delay data set (a set of delay times) corresponding to the plurality of vibrating elements is supplied from the control unit 30. A technique such as transmission aperture synthesis may be used in transmitting and receiving ultrasonic waves. The transmission/reception unit 12 may also execute parallel reception processing.

The ultrasonic beam (transmission beam and reception beam) is electronically scanned by the action of the transmission/reception unit 12, thereby forming a scanning surface. The scanning plane corresponds to a plurality of beam data, which form reception frame data (RF signal frame data). Each beam data is composed of a plurality of echo data arranged in the depth direction. By repeating the electronic scanning of the ultrasonic beam, a plurality of reception frame data arranged on the time axis are output from the transmission/reception unit 12. They form the received frame sequence.

When the ultrasonic beam is electronically scanned two-dimensionally by the operation of the transmitting/receiving unit 12, a three-dimensional echo data acquisition space is formed, and volume data as an echo data aggregate is formed from the three-dimensional echo data acquisition space. Is obtained. By repeating the electronic scanning of the ultrasonic beam, a plurality of volume data arranged on the time axis is output from the transmitting/receiving unit 12. They form a volume data string.

The signal processing unit 14 is a module that applies signal processing such as detection and logarithmic compression to the beam data output from the transmission/reception unit 12. The beam data after signal processing may be stored in the memory. Of course, beam data to which such signal processing has not been applied may be stored in the memory, and the above processing may be applied when reading the beam data.

The DSC (digital scan converter) 16 is a module having a conversion function (coordinate conversion function, interpolation processing function, etc.), and generates a tissue display frame sequence based on the reception frame sequence output from the signal processing unit 14. Each tissue display frame sequence is B-mode tomographic image data. The organization display frame sequence is displayed on the display unit 20 such as a monitor via the display processing unit 18. As a result, the B-mode tomographic image is displayed as a moving image in real time.

The display processing unit 18 performs overlay processing of necessary graphic data on the tomographic image and the like to generate a display image. This image data is output to the display unit 20, and one or a plurality of images are displayed side by side in a display mode according to the display mode.

The display unit 20 is composed of a display device such as a liquid crystal display. The display unit 20 may be composed of a plurality of display devices.

The image processing unit 22 has a function of detecting the position and area of the annular portion of the fetus based on the B-mode tomographic image (tissue display frame) and measuring the annular portion based on the detection result. The annular portion is an annular tissue having an edge portion, and is, for example, the head or the abdomen. The image processing unit 22 may perform processing on a B-mode tomographic image obtained from a two-dimensional scanning plane, or may process data corresponding to an arbitrary cross section in volume data obtained from a three-dimensional space. The processing may be performed on the two-dimensional B-mode tomographic image generated based on the above.

The image processing unit 22 includes, for example, a position calculation unit 24, a region calculation unit 26, and a measurement unit 28.

The position calculation unit 24 applies template matching to the B-mode tomographic image to calculate the candidates for the position of the annular part of the fetus (for example, the head of the fetus or the abdomen). For example, the position calculation unit 24 calculates a candidate for the center position of the ring portion of the fetus. The candidate of the center position is used in the area calculation unit 26 described later.

The area calculation unit 26 performs coordinate conversion of the B-mode tomographic image using the candidate for the center position calculated by the position calculation unit 24, and calculates the area of the annular portion of the fetus based on the image after the coordinate conversion. The area calculation unit 26 calculates, for example, an ellipse approximating the annular part.

The measuring unit 28 measures the ring-shaped region of the fetus using the region (for example, an ellipse approximated to the ring-shaped region) of the ring-shaped region calculated by the region calculation unit 26 and the B-mode tomographic image. For example, when the head of the fetus is photographed as an annular portion and a B-mode tomographic image representing the head of the fetus is generated, the measuring unit 28 measures the head of the fetus based on the B-mode tomographic image. When the abdomen of the fetus is imaged as an annular portion and a B-mode tomographic image representing the abdomen of the fetus is generated, the measuring unit 28 measures the abdomen of the fetus based on the B-mode tomographic image.

The control unit 30 has a function of controlling the operation of each component shown in FIG. The control unit 30 may include a region of interest setting unit that sets a region of interest (ROI) on the B-mode tomographic image.

An input unit 32 is connected to the control unit 30. The input unit 32 is configured by an operation panel including input devices such as a trackball, a keyboard, various buttons, and various knobs, for example. The user can use the input unit 32 to specify or input the position of the scanning plane, the position of the cross section, the information on the region of interest, and the like.

In the ultrasonic diagnostic apparatus described above, the configuration other than the probe 10 can be realized by using hardware resources such as a processor and an electronic circuit, and a device such as a memory can be used as necessary in the realization. Good. Further, the configuration other than the probe 10 may be realized by, for example, a computer. That is, all or part of the configuration other than the probe 10 may be realized by the cooperation of the hardware resources such as the CPU, the memory, and the hard disk included in the computer, and the software (program) that defines the operation of the CPU and the like. .. The program is stored in a storage device (not shown) via a recording medium such as a CD or a DVD, or via a communication path such as a network. As another example, the configuration other than the probe 10 may be realized by a DSP (Digital Signal Processor), an FPGA (Field Programmable Gate Array), or the like. Of course, a GPU (Graphics Processing Unit) or the like may be used.

Hereinafter, the ultrasonic diagnostic apparatus according to the first embodiment will be described in detail. In the first embodiment, the ring-shaped part of the fetus is the fetal head, and ultrasonic waves are transmitted/received to/from the fetal head to generate a B-mode tomographic image representing the fetal head.

Hereinafter, the position calculator 24 will be described in detail with reference to FIG. FIG. 2 shows the configuration of the position calculation unit 24. The position calculation unit 24 includes a template generation unit 34, an edge emphasized image generation unit 36, and a matching processing unit 38.

The template generation unit 34 generates a template used for the matching processing by the matching processing unit 38. The template has, for example, a circular ring shape. The template generation unit 34 generates, for example, an annular template having a size (that is, a diameter and a width) based on the number of pregnancy days GD of the fetus. Specifically, the template generation unit 34 calculates an average value (statistical value) of a large head diameter (BPD: Biparietal Diameter) based on the number of pregnancy days GD and its variation (for example, standard deviation SD). , BPD average value (statistical value) as a diameter and a standard deviation SD as a width, an annular template is generated. The BPD average value (statistical value) and standard deviation SD are statistically calculated by the following formula.
BPD average value (statistical value) = -18.3 + 3.85 x 10 ^-1 GD + 1.06 x 10 ^-3 GD ² -3.70 x 10 ^-6 GD ³
SD=1.73+7.96×10 ⁻³ GD

The equations for obtaining the BPD average value and standard deviation SD are statistically obtained equations, and may change depending on, for example, the nationality of the mother.

The information indicating the number of pregnancy days may be input to the ultrasonic diagnostic apparatus by a user such as a doctor, or may be input to the ultrasonic diagnostic apparatus from another apparatus.

The edge-enhanced image generator 36 applies a filter to the B-mode tomographic image to generate an edge-enhanced image in which an edge portion (a portion corresponding to the skull) of the fetal head as an annular portion is emphasized. As the filter, for example, a DoG filter (Difference Of Gaussian filter) is used. By using the DoG filter, the difference between the images having different "blurring" is calculated, and as a result, a portion having high brightness or low brightness with respect to the surroundings is extracted. For example, it is possible to extract a high-luminance portion such as a skull.

When the DoG filter is applied, a positive value and a negative value are obtained, but the negative value is set to zero (0) because only the positive value is used. Further, when the DoG filter is applied, the edge portion (edge portion of the image) of the B-mode tomographic image itself is also emphasized, so that portion may be subjected to mask processing (for example, processing for setting the brightness value to 0). .. As another example, the absolute value of the value obtained by applying the Dog filter may be adopted, or the obtained value may be multiplied by −1 to set the negative value to zero (that is, Substantially the original negative value may be used).

The edge-enhanced image generation unit 36 generates an edge-enhanced image by reducing the size of the B-mode tomographic image to be processed and then applying the DoG filter in order to improve the efficiency of the processing by the matching processing unit 38 described below. You may.

Specifically, the edge-enhanced image generation unit 36 two-dimensionally applies a 5 tap binomial filter having a coefficient of 1:4:6:4:1 to the B-mode tomographic image, and the image after the application. On the other hand, the first image down-sampled on the second floor and the second image down-sampled by one step are generated and the second image is up-sampled by one step, and the difference between the first image and the second image is calculated. As a result, an image to which the DoG filter is applied, that is, an edge emphasized image is generated. Note that the above example is an example, and the types and coefficients of filters, the procedure and the number of times of various sampling processes are not limited to the above example.

The matching processing unit 38 applies a matching process using the template generated by the template generation unit 34 to the edge-emphasized image generated by the edge-emphasized image generation unit 36, and thereby the fetal head position candidate is obtained. Specifically, a candidate for the central position of the fetal head (skull bone) is calculated. The matching processing unit 38 calculates the similarity between the template and the fetal head image (skull bone image) at each position while changing the position of the template on the edge-enhanced image. The matching processing unit 38 identifies the position of the template having the highest degree of similarity, and identifies the center position of the template at that position as a candidate for the center position of the fetal head (skull bone). The matching processing unit 38 may calculate the center position of the fetal head by matching the template with the original B-mode tomographic image without using the edge-enhanced image. In this case, the edge emphasized image generation unit 36 may not be included in the position calculation unit 24.

As described above, the candidates for the central position of the fetal head (skull) are calculated. The candidates for the center position calculated in this way are used for the coordinate conversion performed by the area calculation unit 26.

Hereinafter, the area calculation unit 26 will be described in detail with reference to FIG. FIG. 3 shows the configuration of the area calculation unit 26. The area calculation unit 26 includes a conversion unit 40, a mask setting unit 42, a search unit 44, an inverse conversion unit 46, an ellipse calculation unit 48, a validity determination unit 50, a central mask unit 52, an end determination unit 54, and a central updating unit 56. including.

The conversion unit 40 performs polar coordinate conversion of the B-mode tomographic image by using the candidate for the center position of the fetal head (cranial bone) calculated by the position calculation unit 24 as the origin of the polar coordinate system. The polar coordinate conversion is a process for converting coordinates with the center position candidate as the origin, the vertical axis as the distance (radial r) from the center position candidate, and the horizontal axis as the angle (declination θ). That is, the polar coordinate system after the coordinate conversion is a polar coordinate system having the candidate of the central position of the fetus head as the origin. By this conversion processing, the B-mode tomographic image is developed with the candidate of the center position as the origin, and thereby a developed image (image represented by the polar coordinate system) is generated. In the first embodiment, by using the candidates for the center position calculated by the position calculator 24 (the candidates for the center position obtained by the template matching), the polar coordinate conversion is performed using the position closer to the center position of the fetus head. It becomes possible to improve the accuracy of the route search process and the elliptic calculation which will be described later. Hereinafter, the image after the polar coordinate conversion will be referred to as a “developed image”.

The mask setting unit 42 sets, for the developed image (image after polar coordinate conversion), a mask extending in the radial direction r in a specific region in the direction of the declination θ of the polar coordinate system. The area where the mask is set is an area where the route search processing using the dynamic programming method described later is not performed. As another example, the luminance value in the masked area is set to 0 (zero), and the search process using dynamic programming prevents the route from being searched from the information of the masked area. May be. The specific region is, for example, a region including a portion in which an ultrasonic beam is transmitted/received in parallel with the head of the fetus (skull bone). The luminance value of the portion where the ultrasonic beam is transmitted and received in parallel is likely to be lower than the luminance values of the other portions, and noise is likely to occur. Due to the influence of the noise, an erroneous search may occur in the route search processing described later. By setting the mask in the specific area, it is possible to remove the influence of noise and suppress or prevent the occurrence of false search. For example, normally, noise is likely to occur in the portions corresponding to the front and back of the head of the fetus, so a mask is set in those portions.

The search unit 44 searches for a route from the developed image by applying the route search process to the developed image (image after polar coordinate conversion). This path corresponds to a candidate for the edge portion (the portion corresponding to the skull) of the fetus head. The search unit 44 searches for a route, for example, by applying dynamic programming to the developed image. At this time, the search unit 44 searches the route by excluding the area where the mask is set from the search area in the developed image and applying the dynamic programming to the area where the mask is not set. Further, the search unit 44 estimates a route (for example, a straight route) in the area where the mask is set in the developed image. For example, when there is a mask-set area between a plurality of mask-unset areas, the search unit 44 sets the masks to a plurality of routes in the plurality of mask-unset areas. The entire route is calculated from the developed image by connecting the estimated regions in the set area with the linear route.

The inverse transform unit 46 inversely transforms the route searched by the search unit 44 into the original image space (image space before coordinate conversion).

The ellipse calculation unit 48 calculates an ellipse approximating the head of the fetus using the path after the inverse transformation obtained by the inverse transformation unit 46 and the B-mode tomographic image. As a result, the center position of the ellipse, the length of the short axis, the length of the long axis, and the inclination are obtained as the parameters of the approximate ellipse. Hereinafter, the ellipse calculated by the ellipse calculation unit 48 (ellipse approximated to the fetus head) will be referred to as “approximate ellipse”.

The validity determination unit 50 determines the validity of the approximate ellipse obtained by the ellipse calculation unit 48. The ratio between the length of the major axis and the length of the minor axis of the ellipse is used for determining the validity. The validity determining unit 50 determines that the ratio is valid when the ratio of the length of the major axis and the length of the minor axis of the approximate ellipse calculated by the ellipse calculating unit 48 is within a predetermined allowable range. However, if the ratio is not within the allowable range, it is determined to be invalid. It should be noted that at least one of the size, position, angle, etc. of the ellipse may be used for the validity determination of the ellipse, or a plurality of combinations thereof may be used.

When the validity determination unit 50 determines that the validity is not valid, the central mask unit 52 sets a mask within a predetermined range from the origin for the developed image. The search unit 44 searches again for the developed image for which the mask is set. The B-mode tomographic image showing the fetal head has a high-intensity region called the median line, and the high-intensity region may be erroneously searched as a route in the route search process. In other words, in the route search processing, the purpose is to search for a route corresponding to the skull of the fetus, but there is a possibility that a route passing through the median line may be erroneously searched. Since the median line is assumed to be represented in the central part of the B-mode tomographic image, a mask is set in a range corresponding to the central part and the range is excluded from the route search processing. It is possible to suppress or prevent an erroneous search due to the influence. The mask setting unit 42 may set the mask within a predetermined range from the origin in the developed image without providing the central mask unit 52. In this case, the mask setting unit 42 may set the mask regardless of the determination result by the validity determining unit 50.

The end determination unit 54 determines the end of the processing of each unit of the area calculation unit 26. For example, when the series of processes from the conversion unit 40 to the central updating unit 56 has been performed a predetermined number of times (for example, 3 times), the end determination unit 54 determines that the process has ended. If the predetermined number of processes has not been executed, a series of processes from the conversion unit 40 to the central updating unit 56 is executed. Further, when the fluctuations of the parameters such as the position, size, and angle of the approximate ellipse calculated by the ellipse calculation unit 48 become small (for example, when the approximation ellipse is included within a predetermined allowable range), the end determination unit 54 Alternatively, it may be determined that the processing is completed.

The above processing is summarized as follows. The processing from the conversion unit 40 to the validity determination unit 50 is executed, and when the validity determination unit 50 determines that there is validity, the end determination unit 54 determines. When the validity determining unit 50 determines that the validity is not valid, the processing from the searching unit 44 to the ellipse calculating unit 48 is executed through the processing by the central mask unit 52, and the processing of the validity determining unit 50 is skipped. Then, the end determination unit 54 makes a determination. When the series of processes is not executed a predetermined number of times, the process by the central updating unit 56 is performed. The above-mentioned series of processing is set as one set and the set is executed a predetermined number of times.

When the end determination unit 54 does not determine the end, the center updating unit 56 updates the center position of the approximate ellipse obtained by the ellipse calculation unit 48 as a new origin of the polar coordinate system in the polar coordinate conversion performed by the conversion unit 40. .. After that, a series of processes from the conversion unit 40 to the end determination unit 54 is executed. At this time, the conversion unit 40 uses the center position (updated center position) of the approximate ellipse obtained by the ellipse calculation unit 48 as a new origin of the polar coordinate system to convert the B-mode tomographic image into polar coordinates. As a result, polar coordinate conversion can be performed using a position closer to the center position of the fetus head, and the accuracy of route search processing and elliptic calculation is improved.

When the end determination unit 54 makes the end determination, the measurement unit 28 measures the fetus head using the approximate ellipse and the B-mode tomographic image obtained at the time of the end determination.

Hereinafter, the B-mode tomographic image generated by the ultrasonic diagnostic apparatus according to the first embodiment will be described in detail with reference to FIG. 4. FIG. 4 shows the B-mode tomographic image. A fetal head image 60 is shown in the B-mode tomographic image 58. For example, the position and angle of the probe 10 are adjusted by the user so that the fetal head is represented in the B-mode tomographic image. In FIG. 4, the hatched area indicates a high brightness (echo) area. In the B-mode tomographic image 58 suitable for measurement, the upper part 62, the lower part 64, and the median line 66 of the image in which the ultrasonic beam is easily reflected are easily drawn, and the brightness of these parts is likely to be high. The brightness may increase in the tissues 68 other than those. On the other hand, the side surfaces 70, 72 of the image where the ultrasonic beam is difficult to be reflected (the surfaces corresponding to the front surface and the rear surface of the fetal head in normal ultrasonic diagnosis) (for example, the portions where the ultrasonic beam is transmitted and received in parallel are It is difficult to depict areas including), and the brightness of those parts tends to be low. From such a B-mode tomographic image 58, the measurement unit 28, for example, has a large transverse head diameter (BPD: Biparietal Diameter) and an anterior-posterior diameter (OFD: Occipital-) corresponding to the length in the direction orthogonal to the midline 66. Frontal Diameter), fetal head circumference (HC: Head Circumference), etc. can be measured. Of course, parameters other than these may be measured.

Hereinafter, the template generated by the template generation unit 34 will be described in detail with reference to FIG. FIG. 5 shows an example of the template.

The template 74 is a template (donut-shaped template) having an annular shape generated by the template generation unit 34. The shape of the template 74 is a shape assuming a fetal head (skull bone), and the inside 76 of the ring is a region assuming the inside of the skull. Since it can be assumed that the skull has an elliptical shape close to a circle, template matching uses a template 74 having a circular overall shape. At the stage of performing template matching, the orientation (rotation angle) of the fetal head is not known. Therefore, the accuracy of detecting the central position of the fetal head can be improved by using the circular template 74 having no directionality rather than using the template having directionality such as an ellipse.

For example, the length from the central position O of the template 74 to the central position of the annular portion of the template 74 corresponds to the radius of the template 74, and the length twice the radius corresponds to the diameter A of the template 74. The diameter A is a BPD average value (statistical value) calculated using the number of pregnancy days. The width B of the template 74, that is, the width B of the annular portion is the standard deviation SD of the BPD average value calculated using the number of pregnancy days. As described above, the template 74 is a template in which the size estimated from the number of pregnancy days is reflected. Since the template 74 having such characteristics is a template that reflects the actual size and shape of the skull, by performing template matching using the template 74, a position closer to the center position of the skull is a candidate for the center position. Is easily detected.

Hereinafter, the matching processing by the matching processing unit 38 will be described in detail with reference to FIG. FIG. 6 shows an example of the edge emphasized image.

The edge emphasized image 78 is an image generated by the edge emphasized image generating unit 36. That is, the edge-enhanced image 78 is an image generated by applying the DoG filter to the B-mode tomographic image 58 shown in FIG. In the edge-enhanced image 78, a part corresponding to the skull of the fetus and the like are emphasized.

The matching processing unit 38 applies a matching process using the template 74 to the edge-enhanced image 78 to calculate a candidate for the center position of the fetal head (skull bone). Specifically, the matching processing unit 38 changes the position of the template 74 on the edge-enhanced image 78 as shown by an arrow 80, and the similarity between the template 74 and the fetus head image (skull image) at each position. Calculate the degree. As a result, a two-dimensional map of similarity (similarity map) is generated. The similarity is calculated by the following equation (1).

Here, I(i,j) is the brightness (0 to 255) of the edge emphasized image 78 (DoG image). T(x,y) is the brightness (0 or 1) of the template 74.

The matching processing unit 38 may apply filter processing to the similarity map described above. For example, two types of filters are used. The first filter is, for example, a Gaussian filter of (5×5), σ=2.0, and the second filter is, for example, a Gaussian filter having a size half the horizontal size×the vertical size of the image. The first filter is a filter for removing the local high brightness value and smoothing the peripheral area so that the candidate is detected also in the peripheral area having the high brightness value. Assuming that the observation target is located near the center of the B-mode tomographic image as a characteristic of the B-mode tomographic image, the second filter makes it difficult for candidates to be detected from the end of the B-mode tomographic image. , A filter that slightly weights the central portion of the B-mode tomographic image. Of course, these filters may not be applied.

The matching processing unit 38 detects the position where the degree of similarity is maximum in the above similarity map as a candidate for the central position of the fetal head (skull bone). This candidate for the center position is used in polar coordinate conversion described later.

Hereinafter, the processing by the area calculation unit 26 will be described in detail with reference to FIGS. 7 to 15.

FIG. 7 shows an example of a developed image generated by polar coordinate conversion. The developed image 82 is an image generated by the polar coordinate conversion performed by the conversion unit 40. Specifically, the expanded image 82 is obtained by polar-transforming the B-mode tomographic image 58 shown in FIG. 4 using the candidate for the center position of the fetal head (skull bone) obtained by the matching processing unit 38. It is an image generated in. The horizontal axis represents the angle θ (declination θ) of the polar coordinate system, and the vertical axis represents the distance r (radius r) of the polar coordinate system. The origin (θ=0, r=0) of the developed image 82 is a position corresponding to the candidate of the central position of the fetal head (skull bone) obtained by the matching processing unit 38. An image 84 in the developed image 82 is an image corresponding to the upper portion 62, the lower portion 64, and the median line 66 shown in the B-mode tomographic image 58, and the image 86 corresponds to the tissue 68 shown in the B-mode tomographic image 58. The corresponding image.

FIG. 8 shows an example of the developed image to which the mask is applied. A mask 88 is set by the mask setting unit 42 on the developed image 82. For example, in the developed image 82, masks 88 having a width of ±45° in the angle θ direction are set at positions where the angle θ is 90° and −90°. Of course, the width of the angle is merely an example, other values may be used, and the width may be changed by the user. The mask 88 has a shape extending from the position at the distance r=0 in the direction of the distance r. The position where the angle θ is ±90° is usually a position corresponding to the anterior surface and posterior surface of the fetal head, and the ultrasonic beam is easily transmitted and received in parallel to that portion, so that portion is difficult to visualize. If the portion is included in the route search target area, an erroneous search may occur in the route search processing. Further, if another tissue with high brightness is drawn near the part where the skull is hard to be drawn, an erroneous search may occur in the route search process. In order to cope with this, a mask 88 having a width in the direction of the angle θ is set in a portion where the skull is difficult to be drawn (position where the angle θ is ±90°). As a result, that portion is excluded from the route search area, so that the occurrence of false search can be suppressed or prevented. For example, when the image 86 shown in FIG. 7 exists near the angle θ of ±90°, there is a possibility that a part of the image 86 is extracted as a path and a part other than the skull is extracted as a path. .. By setting the mask, such an erroneous search can be prevented.

Hereinafter, the route search process by the search unit 44 will be described in detail. A developed image 82 is shown in FIG. 9. The search unit 44 searches the developed image 82 for a route such that the sum of the brightness values on the route is maximum. Any method may be used to search for a route that maximizes the sum of brightness values, but the search unit 44 searches for a route using dynamic programming as an example. At this time, the search unit 44 excludes the area in which the mask 88 is set from the path search area and searches for the path. The route 90 shown by the solid line in FIG. 9 is the route searched by applying the dynamic programming. Path 90 is along image 84. The search unit 44 also estimates the route 92 in the area where the mask 88 is set. The search unit 44 calculates the entire route by, for example, connecting the ends of the plurality of routes 90 searched by the dynamic programming method with a linear route 92 (a route indicated by a broken line). The path 92 is a linear path in the area where the mask 88 is set. Note that the search unit 44 searches for a route having r coordinates close to each other at the left and right ends of the developed image 82 so that the searched route becomes a closed curve in the original image space (image space before coordinate conversion). May be.

The dynamic programming will be described below with reference to FIGS. 10 to 12. 10 and 12 show images for explaining the route search process. FIG. 11 shows an example of the search map.

First, as shown in FIG. 10, the searching unit 44 adds the brightness value of the pixel having the maximum brightness value to the target pixel 94 among the three pixels 96 arranged on the left side of the target pixel 94. .. The search unit 44 performs this process from the upper end to the lower end of the image, and then from the left end to the right end of the image to generate a two-dimensional search map. In the search map, a higher brightness portion corresponds to an area having a larger total brightness value.

FIG. 11 shows an example of the search map obtained as described above. The search unit 44 detects the pixel 98 having the maximum brightness from the right end of the search map.

Next, as shown in FIG. 12, the search unit 44 selects a pixel having the maximum luminance value among the three pixels 102 arranged on the left side of the current pixel 100 (the above pixel 98), This process is repeated up to the left edge of the image. After the route reaches the left end of the image, the search unit 44 compares the r coordinate of the search start point with the r coordinate of the search end point, and when the difference is large (for example, when the difference is equal to or larger than the threshold), the search map. The pixel having the second highest luminance value from the right end of is selected as the search start point, and the search is performed again. The search unit 44 repeats this process until the difference between the search start point and the search end point falls within a predetermined allowable range.

The search unit 44 searches for the route having the maximum sum of the brightness values by the above process. The search unit 44 uses, as parameters other than the brightness value, at least one parameter selected from a parameter group such as brightness gradient information, edge amount, entropy, likelihood, Hog, SaliencyMap, L1, L2 norm, and the like. Alternatively, the route may be searched using a combination of a plurality of selected parameters. Further, depending on the parameters used, minimization or optimization may be performed instead of maximization. Further, the search map generation direction may be the opposite direction to the example described above.

When the route is searched by the search unit 44 as described above, the inverse transformation unit 46 inversely transforms the route into the original image space (image space before coordinate transformation). FIG. 13 shows the path line 104 generated by the inverse transformation. Note that FIG. 13 also shows the B-mode tomographic image 58 before the coordinate conversion shown in FIG. 4, and the path line 104 is shown superimposed on the B-mode tomographic image 58.

When the path line 104 is generated by the inverse transformation, the ellipse calculator 48 uses the path line 104 and the B-mode tomographic image 58 to calculate an ellipse approximating the fetal head (approximate ellipse). Hereinafter, this process will be described in detail. First, the ellipse calculation unit 48 extracts, from all the pixels on the path line 104, a certain proportion of pixels having higher brightness (for example, 50% of pixels). This extraction processing is to improve the accuracy of the ellipse approximation by extracting and using the pixels existing on the skull among the pixels existing on the path. Next, the ellipse calculation unit 48 randomly selects five or more candidate points from the extracted pixel group and applies an ellipse to these candidate point groups. As an ellipse fitting method, for example, a Hough transform, a least squares method, an optimization method using a polynomial, or the like can be used. In FIG. 14, an ellipse 106 fitted to the candidate point group is shown. Next, the ellipse calculation unit 48 calculates the distance between the ellipse calculated by the fitting and the extracted pixel group (pixel group extracted from all the pixels on the path line 104), and the distance is calculated in advance. The number of pixels within a predetermined threshold (for example, the number of pixels whose distance is within 5 pixels) is calculated as the number of pixels on the ellipse. The ellipse calculation unit 48 performs these processes a predetermined number of times (for example, 100 times) and employs the ellipse having the largest number of pixels on the ellipse as an ellipse approximating the head of the fetus (approximate ellipse). As a result, the center position of the approximate ellipse, the length of the minor axis, the length of the major axis, and the angle are specified.

The validity determination unit 50 determines the validity of the approximate ellipse adopted by the ellipse calculation unit 48 as described above. When the ratio between the length of the major axis and the length of the minor axis of the approximate ellipse is within the predetermined allowable range, the validity determining unit 50 determines that the ratio is valid and the ratio is within the allowable range. If not included, it is determined to be invalid. When it is determined that there is no validity, the search unit 44 performs the search again.

If the end determination unit 54 has not determined that the process has ended, that is, if the process has not been performed a predetermined number of times, the center updating unit 56 determines the approximate ellipse adopted by the ellipse calculation unit 48. The center position is updated as a new origin of the polar coordinate system in the polar coordinate conversion by the conversion unit 40. When the processing is performed a predetermined number of times, for example, the approximate ellipse obtained in the last processing may be adopted as the ellipse for measurement by the measuring unit 28, or the position, size, and angle of the ellipse. An ellipse with the smallest variation in parameters such as may be adopted as the ellipse for measurement.

Hereinafter, the processing performed by the measuring unit 28 will be described in detail with reference to FIGS. 15 and 16. 15 and 16, a part of the B-mode tomographic image 58 and the axis of the ellipse are shown. As shown in FIG. 15, the minor axis 108 and major axis 110 of the ellipse (approximate ellipse) (measurement ellipse) approximated to the head of the fetus are obtained by the above processing. The measurement unit 28 detects intersections 112, 114, 116, 118 of the short axis 108 of the approximate ellipse and the outer and inner sides of the fetal skull image (the upper portion 62 and the lower portion 64). This is because there are two methods for measuring the head of the fetus: one is to measure the length between the upper outer side and the lower inner side, and the other is to measure the length between the upper outer side and the lower outer side. For example, the intersection is detected by using a gradient. For the calculation of the gradient, for example, a difference value, a Sobel filter, a Laplacian filter, or a Brewett filter can be used.

Hereinafter, with reference to FIG. 16, a case where the Sobel filter is used will be described as an example. The measuring unit 28 sets a search range on a straight line 120 that is an extension of the short axis 108 of the approximate ellipse (measurement ellipse). The search range includes an upper outer search range 122, an upper inner search range 124, a lower inner search range 126, and a lower outer search range 128. Next, the measurement unit 28 calculates the gradient strength at each point indicated by a black circle in FIG. 16, and detects the point where the gradient strength is the maximum in each search range as the intersection point. As a result, the intersection 112 is detected within the search range 122, the intersection 114 is detected within the search range 124, the intersection 116 is detected within the search range 126, and the intersection 118 is detected within the search range 128. It

In addition, the measuring unit 28 may calculate the outer peripheral ellipse 130 of the fetal head (skull bone) shown in FIG. 15 by performing the above processing in a plurality of directions. In this case, the measuring unit 28 may calculate the perimeter of the outer peripheral ellipse 130 as the head perimeter HC and the length of the major axis 110 as the fetal head front-back diameter OFD.

When the fetal head is measured by the measuring unit 28, the measurement result is displayed on the display unit 20, for example.

As described above, in the first embodiment, the candidate for the central position of the fetal head is obtained by performing the matching process using the template that approximates the shape of the fetal head (cranial bone). By performing polar coordinate conversion using the candidate of the center position, it is possible to perform polar coordinate conversion that reflects a more accurate center position, so the accuracy of the route search process using the expanded image generated by polar coordinate conversion, that is, , The accuracy of elliptic approximation is improved. Since an ellipse that is closer to the fetal head (skull) is obtained, the measurement accuracy of the fetal head using the ellipse is improved. As described above, in the first embodiment, in order to improve the accuracy of the route search process on the image after the polar coordinate conversion, the center position of the fetal head is subjected to template matching as a preprocess of the polar coordinate conversion based on the route search process. Calculate the candidate of.

(Modification 1)
Modification 1 will be described below with reference to FIG. FIG. 17 shows an example of the developed image. The developed image 82 shown in FIG. 17 is the same image as the developed image 82 shown in FIG.

In the first modification, the mask setting unit 42 applies weighting processing to the developed image 82 instead of setting the mask on the developed image 82. For example, in the developed image 82, weighting regions 132 having a width of ±45° in the angle θ direction are set at positions where the angle θ is 90° and −90°. The weighting region 132 has a shape extending in the distance r direction from the position of the distance r=0. In the weighting region 132, the weighting coefficient at the position of ±90° is set to be the smallest, and the larger the weighting coefficient is assigned to the position further away from the position of ±90° in the angle θ direction. The mask setting unit 42 multiplies the brightness value of each pixel of the developed image 82 by a weighting coefficient, and the search unit 44 performs the route search process using the brightness value multiplied by the weighting coefficient. As a result, the luminance value of the portion where the skull is difficult to detect becomes difficult to use in the route search process, so that it is possible to suppress or prevent the influence of noise in that portion. The mask setting unit 42 may perform weighting processing on the entire developed image 82. Also in this case, the weighting factor is set to the smallest at the position of ±90°, and a larger weighting factor is assigned to the position further away from the position of ±90° in the angle θ direction.

(Modification 2)
Modification 2 will be described below with reference to FIG. FIG. 18 shows an example of the B-mode tomographic image. The B-mode tomographic image 58 shown in FIG. 18 is the same image as the B-mode tomographic image 58 shown in FIG.

In the second modification, the mask setting unit 42 sets a mask corresponding to the type of the probe 10 in the developed image. Since the transmission/reception direction of the ultrasonic beam changes depending on the type of the probe 10, the mask setting unit 42 sets the mask corresponding to the transmission/reception direction in the developed image. The mask setting unit 42 includes, for example, a direction orthogonal to the transmission/reception direction of the ultrasonic beam indicated by the arrow 134 with the candidate of the ellipse center position calculated by the position calculation unit 24 as a reference position, and has a predetermined width. A mask is set in the region 136 which is included. In practice, a mask is set in the area corresponding to the area 136 in the developed image generated by the polar coordinate conversion. In such a region 136, since the ultrasonic beam is easily transmitted and received in parallel with the fetal skull, it is difficult to visualize the skull. By setting a mask in this area 136, it is possible to suppress or prevent an erroneous search for a route due to noise in the area 136. Since the position and size of the region 136 change depending on the type of the probe 10, the mask setting unit 42 changes the position and size of the region 136 according to the type of the probe 10.

For example, mask information indicating the position and size of the region 136 corresponding to the type of each probe 10 is recorded in advance in the ultrasonic diagnostic apparatus. When the probe 10 is connected to the ultrasonic diagnostic apparatus body, the mask setting unit 42 acquires information indicating the probe type from the probe 10, acquires mask information associated with the type, and a developed image according to the mask information. Set the mask to.

<Second Embodiment>
Hereinafter, an ultrasonic diagnostic apparatus according to the second embodiment of the present invention will be described with reference to FIG. FIG. 19 shows an ultrasonic diagnostic apparatus according to the second embodiment. FIG. 19 is a block diagram showing the overall structure.

The ultrasonic diagnostic apparatus according to the second embodiment includes an image processing unit 22A instead of the image processing unit 22 of the ultrasonic diagnostic apparatus according to the first embodiment. The image processing unit 22A further includes an angle correction unit 138 in addition to the configuration included in the image processing unit 22. Since the configuration other than the angle correction unit 138 is the same as the configuration of the ultrasonic diagnostic apparatus according to the first embodiment, the angle correction unit 138 will be described below, and the description of the other configurations will be omitted.

The angle correction unit 138 corrects the angle of an ellipse (approximate ellipse) that is approximated to the fetal head (skull bone) calculated by the region calculation unit 26. As shown in FIG. 4, in the B-mode tomographic image showing the fetal head, a high-intensity region called a midline 66 extending in the front-back direction of the fetal head is drawn. In order to improve the measurement accuracy of the fetal head, it is desirable that the long axis of the ellipse (approximate ellipse) that approximates the fetal head be in the same direction as the median line. Therefore, the angle correction unit 138 corrects the angle of the approximate ellipse so that the major axis direction of the ellipse approximating the head of the fetus (approximate ellipse) matches the direction of the median line. Hereinafter, the angle correction processing by the angle correction unit 138 will be described in detail.

FIG. 20 shows an example of a midline of the fetal head and an ellipse (approximate ellipse) that approximates the fetal head. The high-intensity region 140 corresponds to the image representing the midline of the head of the fetus (the midline 66 in FIG. 4). The approximate ellipse 142 is an ellipse approximating the fetal head calculated by the processing of the first embodiment described above. The minor axis straight line 144 is a straight line extending the minor axis of the approximate ellipse 142, and the major axis straight line 146 is a straight line extending the major axis of the approximate ellipse 142. The center position 148 is the center position of the approximate ellipse 142.

First, the angle correction unit 138 sets the movement range 150 of the center position 148 on the short-axis straight line 144. The movement range 150 is a range in which the center position 148 can move in the minor axis direction. The length of the movement range 150 in the short axis direction is, for example, a predetermined length of 2 L, and the movement range 150 is set within a range of ±L in the short axis direction with reference to the center position 148 before the movement. There is. The length L is, for example, a% (for example, 2.5%) of the length of the short axis of the approximate ellipse 142. The length of the moving range 150 is specified for the efficiency of processing. Of course, the moving range 150 may be set to the entire range of the short axis of the approximate ellipse 142.

Next, the angle correction unit 138 sets the reference area 152 on the long-axis straight line 146. The reference area 152 has a rectangular shape having a length M extending in the major axis direction and a width W in the minor axis direction. The length M is, for example, b% (for example, 80%) of the length of the long axis of the approximate ellipse 142. Of course, the length M may be the length of the major axis of the approximate ellipse 142 itself. The width W is, for example, a length of c pixels (for example, a length of 5 pixels). Of course, the width W may be the length of one pixel.

Next, the angle correction unit 138 moves the center position 148 in the movement range 150 and rotates the reference area 152 extending in the long-axis direction at the center position 148 after movement and the center position 148 after movement. The evaluation value in the reference area 152 is calculated at each position and each rotation angle in the movement range 150 while rotating the center of the long axis straight line 146 as a reference within the rotation angle ±α. The evaluation value is, for example, the sum of the brightness values in the reference area 152. The rotation angle α is, for example, 20°. Of course, the value of the rotation angle α is merely an example, and another value may be used, and the angle correction unit 138 determines that the reference area covers the range of the rotation angle ±90° (that is, the range of all the rotation angles). The 152 may be rotated. The angle correction unit 138 moves the center position 148 by a predetermined number of pixels (for example, one pixel at a time) within the movement range 150, and within a range of the rotation angle ±α, the angle correction unit 138 is predetermined. The evaluation value in the reference area 152 is calculated while rotating the reference area 152 each time (for example, 1° each). Of course, the amount of movement (number of pixels) is only an example, and other amounts of movement may be used. Moreover, the angle is only an example, and another angle may be used.

The angle correction unit 138 corrects the angle of the approximate ellipse 142 with respect to the fetal head (skull bone) using the sum of the brightness values obtained at each position and each rotation angle and the variance of the sum of the brightness values. Specifically, the angle correction unit 138 calculates the sum of the brightness values in the reference area 152 at each rotation angle for each position in the movement range 150, and the brightness at each rotation angle for each position in the movement range 150. Calculates the variance of value sums. Next, the angle correction unit 138 determines the position with the largest variance, determines the rotation angle with the largest sum of luminance values at that position, and corrects the angle of the approximate ellipse 142 to that rotation angle.

Hereinafter, the angle correction processing by the angle correction unit 138 will be described in more detail with reference to specific examples.

FIG. 20 shows the approximate ellipse 142 before the center position 148 moves. The center position 148 at this time is arranged at the initial position (position A1) within the movement range 150. The angle correction unit 138, in the state where the center position 148 is located at the position A1, sets the reference area 152 within the range of the rotation angle ±α with respect to the long axis straight line 146 (for example, within the range of the rotation angles φ1 to φn). While rotating with, the total brightness value in the reference area 152 is calculated at each rotation angle. As a result, at the position A1, the brightness value sums T1 to Tn for the respective rotation angles φ1 to φn are obtained. The angle correction unit 138 calculates the variance S1 of the brightness value sums T1 to Tn obtained at the position A1.

Next, the angle correction unit 138 moves the center position 148 along the minor axis straight line 144 within the movement range 150. FIG. 21 shows the approximate ellipse 142 after the center position 148 has moved. At this time, the center position 148 is assumed to be located at the position A2 within the movement range 150. The angle correction unit 138, in the state where the central position 148 is located at the position A2, sets the reference area 152 within the range of the rotation angle ±α (within the range of the rotation angles φ1 to φn) with respect to the long axis straight line 146. While rotating, the sum of the brightness values in the reference area 152 is calculated at each rotation angle. As a result, at the position A2, the brightness value sums T1 to Tn for the respective rotation angles φ1 to φn are obtained. The angle correction unit 138 calculates the variance S2 of the brightness value sums T1 to Tn obtained at the position A2.

For example, when the positions A1 to An are set within the movement range 150, the angle correction unit 138 moves the center position 148 to each of the positions A1 to An, and performs the above processing at each of the positions A1 to An. Thus, the brightness value sums T1 to Tn and the variance are calculated at the positions A1 to An, respectively. Thereby, the variances S1 to Sn at the positions A1 to An are obtained.

The angle correction unit 138 identifies the largest variance among the variances S1 to Sn obtained at the positions A1 to An. For example, the variance Sc is the largest variance among the variances S1 to Sn. Next, the angle correction unit 138 identifies the position (referred to as position Ac) within the movement range 150 where the variance Sc is obtained. Next, the angle correction unit 138 specifies the largest sum of the brightness values (referred to as the sum of brightness values Tc) among the brightness value sums T1 to Tn obtained at the position Ac. The angle correction unit 138 identifies the rotation angle (referred to as the rotation angle φc) at which the total brightness value Tc is obtained. As a result, the position Ac at which the variance Sc is obtained and the rotation angle φc at which the luminance value sum Tc is obtained at that Ac are specified.

The angle correction unit 138 matches the angle of the major axis of the approximate ellipse 142 with the rotation angle φc. That is, the angle correction unit 138 rotates the approximate ellipse 142 to match the inclination of the major axis of the approximate ellipse 142 with the inclination of the straight line having the rotation angle φc. Thereby, the angle of the approximate ellipse 142 is corrected. FIG. 22 shows the approximate ellipse 142 with the angle corrected. The short-axis straight line 153 is a straight line that extends the short axis of the approximate ellipse 142 in the angle-corrected state, and the long-axis straight line 154 is a straight line that extends the long axis of the approximate ellipse 142 in the angle-corrected state. The inclination of the long-axis straight line 154 matches the inclination of the straight line having the rotation angle φc. As shown in FIG. 22, the major axis (major axis straight line 154) of the angle-corrected approximate ellipse 142 is arranged in parallel or substantially parallel (with a slight angular difference) to the high-intensity region 140 representing the median line.

The large dispersion of the brightness value sums T1 to Tn indicates that the brightness value sums T1 to Tn have large variations. The brightness value sum increases as the reference area 152 matches the midline, and the brightness value sum decreases as the reference area 152 does not match the midline. The small variance (small variation) of the luminance value sum total at a position Ax indicates that the luminance value sum totals T1 to Tn have a small variation within the rotation angle range of φ1 to φn at the position Ax. There is. If a part or all of the median line is included in the range of the rotation angles φ1 to φn at the position Ax, the total brightness value becomes large at the rotation angle at which the reference area 152 intersects the median line (intersection). It is assumed that the larger the area is, the larger the total brightness value becomes, and the smaller the total brightness value is at the rotation angle where the reference area 152 does not intersect the midline, the larger the dispersion of the total brightness value is. On the other hand, when the median line does not exist in the range of the rotation angles φ1 to φn, it is estimated that the sum of the brightness values at each rotation angle becomes small. Therefore, when the variation of the sum of brightness values T1 to Tn, that is, the dispersion becomes small. Guessed. As described above, when some or all of the median lines are included in the range of the rotation angles φ1 to φn at a certain position Ax, it is estimated that the variance of the brightness value sums T1 to Tn obtained in the range becomes large. To be done. From this, it can be inferred that the median line is highly likely to exist within the range of the rotation angles φ1 to φn at the position Ax where the dispersion of the brightness value sums T1 to Tn is large.

Further, the more the reference area 152 coincides with the midline, the larger the total brightness value becomes. Therefore, the total brightness value becomes maximum within the range of the rotation angles φ1 to φn at the position Ax where the dispersion of the total brightness values T1 to Tn becomes large. It can be inferred that the rotation angle is closer to the angle in the direction in which the midline extends.

To summarize the above, it is estimated that the rotation angle φc at which the brightness value sum is maximum at the position Ac where the variance of the brightness value sums T1 to Tn is maximum is the direction in which the median line extends, and the angle correction unit 138 matches the angle of the approximate ellipse with its rotation angle. As a result, the angle of the approximate ellipse is corrected, and the inclination of the approximate ellipse becomes close to the inclination of the fetal head (skull bone).

FIG. 23 shows the variance of the brightness value sums T1 to Tn at each position. The horizontal axis represents the position in the short axis direction (the position within the range of +L to −L), and the vertical axis represents the variance of the luminance value sums T1 to Tn at each position in the short axis direction. For example, when the dispersion curve 156 is obtained, the position Ac at which the dispersion is maximum in the dispersion curve 156 is specified.

FIG. 24 shows the luminance value sums T1 to Tn at the position Ac. The horizontal axis represents the rotation angle (range from +α to −α), and the vertical axis represents the total brightness value. For example, when the brightness value total curve 160 is obtained at the position Ac, the rotation angle φc at which the brightness value total curve 160 is maximum is specified in the brightness value total curve 160. This rotation angle φc is estimated to be the angle in the direction in which the midline extends, and the angle correction unit 138 corrects the angle of the approximate ellipse to the rotation angle φc.

As described above, according to the second embodiment, the direction in which the median line of the fetal head extends is detected, and the direction of the major axis of the approximate ellipse matches the direction in which the median line extends. The angle of the approximate ellipse is corrected. Therefore, the inclination of the approximate ellipse is close to the inclination of the fetal head (skull bone), and the measurement accuracy of the fetal head is further improved.

The angle correction unit 138 may weight the dispersion curve 156 according to the position in the short axis direction. For example, the angle correction unit 138 reduces the weighting coefficient as it moves away from the original center position 148 (position A1) before the movement, multiplies the weighting coefficient by the dispersion curve 156, and distributes the weighted dispersion curve. You may specify the position Ac which becomes maximum. That is, the angle correction unit 138 applies weighting processing to the dispersion curve according to the amount of movement of the center position 148. Since the central position 148 before the movement is evaluated to be a position closer to the central position of the fetus head, the closer to the central position 148 before the movement, the more likely the midline direction is detected. There is. Therefore, the direction of the median line can be detected with higher accuracy by increasing the weighting factor for the position closer to the center position 148 before the movement.

Further, when the maximum value of the dispersion is equal to or smaller than the predetermined threshold value Sth as in the dispersion curve 158 shown in FIG. 23, the angle correction unit 138 obtains the maximum value at the position Ac. The rotation angle at which the maximum brightness value sum is obtained from the brightness value sums T1 to Tn obtained at the initial position A1 (the center position 148 that is not moving) without using the obtained brightness value sums T1 to Tn. Alternatively, the angle of the approximate ellipse may be corrected.

Further, as in the brightness value sum curve 162 shown in FIG. 24, in the brightness value sum curve showing the brightness value sums T1 to Tn obtained at the position Ac where the variance is maximum, the maximum value of the brightness value sums If is less than or equal to a predetermined threshold Tth, the angle correction unit 138 does not have to correct the angle of the approximate ellipse. This is because no significant rotation angle was detected.

Since the center position of the approximate ellipse calculated by the area calculation unit 26 is estimated to be a position close to the center position of the fetus head, the angle correction unit 138 does not correct the center position 148 of the approximate ellipse 142. .. In the example shown in FIG. 22, the center position 148 of the approximate ellipse 142 is not corrected, and the center position 148 of the approximate ellipse 142 in the angle-corrected state is the center position of the approximate ellipse 142 in the state before the angle is corrected. It is the same position as 148. This makes it possible to make the inclination of the approximate ellipse 142 close to the inclination of the fetal head with the center position 148 of the approximate ellipse 142 being arranged at or near the center position of the fetal head. Of course, the angle correction unit 138 may correct the center position 148. For example, the above position Ac may be adopted as the center position 148.

In the above example, the sum of luminance values is used, but as a correction method, pattern matching, angle estimation by principal component analysis, or the like may be used. Further, although the variance of the total luminance value is used, another value (for example, standard deviation or the like) may be used as an index indicating the variation. Further, the angle correction may be performed by using the maximum value of the total brightness values without using the variance.

In the second embodiment, the approximate ellipse calculated by the processing according to the first embodiment is targeted, but the ellipse that is the target of the angle correction processing by the angle correction unit 138 is the processing according to the first embodiment. It may be an ellipse calculated by processing other than. For example, when an ellipse approximating the head of the fetus is calculated by applying a known technique, the angle correction process may be applied to the ellipse. In this case, the image processing unit 22A does not have to include the position calculation unit 24 and the region calculation unit 26, and the angle correction unit 138 applies the angle correction processing to the ellipse calculated by processing other than these. For example, when the approximate ellipse is obtained by applying the elliptic approximation technique according to the known technique, the angle correction unit 138 corrects the angle of the approximate ellipse by applying the angle correction process to the approximate ellipse. You may.

<Third Embodiment>
Hereinafter, an ultrasonic diagnostic apparatus according to the third embodiment of the present invention will be described. In the third embodiment, it is assumed that the ring-shaped region of the fetus is the abdomen of the fetus, and ultrasonic waves are transmitted and received to and from the abdomen of the fetus to generate a B-mode tomographic image representing the abdomen of the fetus. The ultrasonic diagnostic apparatus according to the third embodiment has the same configuration as the ultrasonic diagnostic apparatus according to the first embodiment.

In the third embodiment as well, as in the first embodiment, the position calculation unit 24 applies template matching to the B-mode tomographic image to obtain a candidate for the position of the fetal abdomen (for example, a candidate for the central position). Calculate The area calculation unit 26 performs polar coordinate conversion of the B-mode tomographic image using the candidate for the center position calculated by the position calculation unit 24, and an ellipse (approximation approximated to the fetal abdomen based on the image (developed image) after the polar coordinate conversion. Calculate an ellipse). The measuring unit 28 measures the fetal abdomen based on the B-mode tomographic image using the approximate ellipse. The measurement unit 28 includes, for example, an anterior trunk diameter (APTD: Antero Posterior Trunk Diameter), a lateral trunk diameter (TTD: Transverse Trunk Diameter), an abdominal circumference (AC: Abdominal Circumference), and a fetal trunk area (FTA: Fetal Trunk cross-). sectional area), etc. can be measured. Of course, parameters other than these may be measured.

Hereinafter, the ultrasonic diagnostic apparatus according to the third embodiment will be described in detail.

The template generation unit 34 generates, for example, an annular template having a diameter and a width based on the number of pregnancy days GD of the fetus. Specifically, the template generation unit 34 calculates an average value (statistical value) of the diameter R of the fetal abdomen and its variation (for example, standard deviation SD) based on the number of pregnancy days GD, and calculates the average value of the diameter R. An annular template (for example, the template 74 shown in FIG. 5) having (statistical value) as the diameter A and having the standard deviation SD as the width B is generated. As the average value (statistical value) of the diameter R of the abdomen of the fetus, for example, the average value (statistical value) of the transverse trunk diameter (TTD) is used, and the variation in the average value of the diameter R (for example, standard deviation SD) For example, a variation in the TTD average value (statistical value) (for example, standard deviation SD) may be used.

Similar to the first embodiment, the edge-enhanced image generation unit 36 applies the DoG filter to the B-mode tomographic image, for example, to generate the edge-enhanced image in which the edge of the fetal abdomen is emphasized.

Although a positive value is used in the processing using the DoG filter described above, the abdomen of the fetus has less bone than the head of the fetus, and the information of the edge portion is extremely difficult to be drawn. Therefore, when some edge portions are strong or when there are a large number of weak edge portions, the edge portions of the fetal abdomen are difficult to be properly rendered due to the influence of those portions. Therefore, the edge-enhanced image generation unit 36 calculates the average value of the positive values obtained by applying the DoG filter, and sets the value of the pixel having the brightness value equal to or higher than the average value to “1”, The value of a pixel having a brightness value less than the average value is set to "0". In this way, the edge-enhanced image generation unit 36 binarizes the image to which the DoG filter has been applied. As a result, the weak edge portion is removed. Next, the edge-enhanced image generation unit 36 applies a median filter (1×3) to the binarized image in the horizontal direction to fill the void portion generated by the binarization process. Next, the edge-enhanced image generation unit 36 applies weighting processing to the central portion of the image to which the median filter has been applied. The weighting function is, for example, a function (normal distribution) in which the weighting coefficient at the center of the image is 1.0 and the value decreases toward the edge of the image. As a result, it is possible to emphasize the portion that is likely to become a circle that exists near the center of the image.

Similar to the first embodiment, the matching processing unit 38 applies the matching process using the above template to the edge-enhanced image, so that the fetal abdominal position candidate, specifically, the fetal abdominal position is detected. Calculate the candidates for the center position.

Also in the third embodiment, as in the first embodiment, polar coordinate conversion by the conversion unit 40, mask processing by the mask setting unit 42, route search processing by the search unit 44, inverse conversion by the inverse conversion unit 46, and ellipse calculation unit. Ellipse calculation processing by 48 is performed. The conversion unit 40 performs polar coordinate conversion of the B-mode tomographic image using the candidate for the center position of the fetal abdomen. The processing by the validity determining unit 50 and the processing by the central mask unit 52 may be executed.

The measurement unit 28 measures the fetal abdomen using the approximate ellipse and the B-mode tomographic image obtained by the above processing.

In the above example, the matching process is performed using the annular template 74 (see FIG. 5), but a template having another shape may be used. The abdomen of the fetus has less bone than the head of the fetus, and it is extremely difficult to visualize the information of the edge part. In addition to that, as described in the first embodiment, the B-mode tomographic image has a portion where the edge portion is difficult to be drawn (for example, an area in which the deviation angle θ direction is ±90° in the polar coordinate system). Information from that part may be noise.

Therefore, in the third embodiment, a template having a shape in which a part of the ring is cut off (a shape in which a part of the ring is cut) may be used. FIG. 25 shows an example of the template. The template 164 is a template generated by the template generation unit 34. The shape of the template 164 is a shape assuming a fetal abdomen. The template 164 includes an upper arch portion 166 and a lower arch portion 168 having an arc shape. The upper arch portion 166 and the lower arch portion 168 are arranged in directions opposite to each other. Spaces 170 and 172 are formed between both end portions of the upper arch portion 166 and both end portions of the lower arch portion 168. The positions of the spaces 170 and 172 correspond to the portion where the edge portion is difficult to be drawn in the B-mode tomographic image, that is, the area where the deviation angle θ direction is ±90° in the polar coordinate system. A region 174 surrounded by the upper arch portion 166 and the lower arch portion 168 is a region assuming the inside of the fetal abdomen. Since it can be assumed that the fetal abdomen has an elliptical shape close to a circle, template matching uses a template 164 simulating that shape. When the template 164 is regarded as an annular shape including the spaces 170 and 172, the diameter A of the annular shape is the average value (statistical value) of the diameter R calculated using the number of pregnancy days (for example, the TTD average value). (Statistical value)), and the width B of the ring, that is, the width B of the upper arch portion 166 and the lower arch portion 168 is the standard deviation of the diameter R average value (statistical value) calculated using the number of pregnancy days. It is SD. As described above, the template 164 is a template in which the size estimated from the number of pregnancy days and the variation in the size are reflected. Further, in the template 164, since the spaces 170 and 172 are formed in the portion where the edge portion is difficult to be drawn in the B-mode tomographic image, noise is difficult to be detected in the matching process. The template 164 having such characteristics reflects the actual size and shape of the fetal abdomen, and has a shape in which noise is difficult to be detected. Therefore, template matching is performed using the template 164 to detect the fetal abdomen. A position closer to the center position of is easily detected as a candidate for the center position.

Hereinafter, the matching process using the template 164 will be described in detail with reference to FIG. FIG. 26 shows an example of the edge emphasized image.

For example, the position and angle of the probe 10 are adjusted by the user so that the fetal abdomen is represented in the B-mode tomographic image, and a B-mode tomographic image representing the fetal abdomen is generated. From the B-mode tomographic image, the edge emphasized image generation unit 36 generates the edge emphasized image 176. In FIG. 26, the hatched area indicates a high brightness area. The abdomen of the fetus has less bones than the head of the fetus, and the edge portion of the abdomen of the fetus is difficult to be depicted in the edge-enhanced image 176 (B-mode tomographic image). In the example shown in FIG. 26, an image 178 representing a part of the abdomen of the fetus (upper part and lower part) is shown in the edge-enhanced image 176, but since many other tissues are also drawn, compared with the fetal head. Therefore, it is difficult to identify the abdomen of the fetus. Further, as described above, the ultrasonic beam is transmitted/received in parallel to the side surface of the fetal abdomen (the region where the deviation angle θ direction is ±90° in the polar coordinate system), so that part thereof is difficult to visualize. In order to deal with this, in addition to DoG filter processing, median filter processing and weighting processing are performed on the B-mode tomographic image so that a region having a shape close to a circle can be easily drawn. Further, the template 164 is used so that noise is hardly detected in the matching process.

Similar to the first embodiment, the matching processing unit 38 applies the matching processing using the template 164 to the edge-emphasized image 176 to calculate the candidate for the central position of the fetal abdomen. Specifically, the matching processing unit 38 calculates the similarity between the template 164 and the fetal abdominal image at each position while changing the position of the template 164 on the edge-enhanced image 176, as indicated by the arrow 180. As a result, a two-dimensional map of similarity (similarity map) is generated. The similarity is calculated by the above equation (1). The matching processing unit 38 may perform filter processing using two types of filters, as in the first embodiment. The matching processing unit 38 detects a position where the degree of similarity is maximum in the similarity map as a candidate for the center position of the fetal abdomen. This candidate for the center position is used in polar coordinate conversion.

The area calculation unit 26 calculates the ellipse (approximate ellipse) that approximates the abdomen of the fetus by performing polar coordinate conversion, mask processing, route search processing, inverse conversion, and ellipse calculation processing using the above-described candidates for the center position. To do. The measuring unit 28 measures the fetal abdomen using the approximate ellipse and the B-mode tomographic image.

As described above, according to the third embodiment, the candidate for the central position of the fetal abdomen is obtained by performing the matching process using the template that approximates the shape of the fetal abdomen. By performing the polar coordinate conversion using the candidate of the center position, the polar coordinate conversion in which the more accurate center position is reflected can be performed, so that the accuracy of the ellipse approximation is improved. As a result, an ellipse that is closer to the fetal abdomen is obtained, and the measurement accuracy of the fetal abdomen using the ellipse is improved.

As described above, the abdomen of the fetus has less bone than the head of the fetus, and it is difficult to visualize the edge portion. Therefore, the region to which the route search process is applied may be narrowed in the expanded image by the mask process. FIG. 27 shows an example of a developed image to which the mask is applied. The expanded image 182 is an image generated by the polar coordinate conversion by the conversion unit 40. Specifically, the developed image 182 is an image generated by performing polar coordinate conversion of the B-mode tomographic image using the candidate for the center position of the fetal abdomen obtained by the matching processing unit 38. The origin (θ=0, r=0) of the developed image 182 is a position corresponding to the candidate of the central position of the abdomen of the fetus obtained by the matching processing unit 38. The image 184 in the developed image 182 is an image corresponding to the image 178 shown in the B-mode tomographic image.

Masks 186, 188, and 190 are set in the developed image 182 by the mask setting unit 42. Similar to the first embodiment, in the developed image 182, the mask 186 having a width of ±45° in the angle θ direction is set at the position where the angle θ is 90° and the position where it is −90°. The mask 186 has a shape extending in the distance r direction from the position of the distance r=0. The position where the angle θ is ±90° is a position corresponding to the side surface of the abdominal part of the fetus, and the ultrasonic beam is easily transmitted and received in parallel to that part, so that part is difficult to visualize. If the portion is included in the route search target area, an erroneous search may occur in the route search processing. Further, if another tissue having high brightness is drawn in a portion where the abdomen of the fetus is hard to be drawn, an erroneous search may occur in the route search processing. In order to cope with this, a mask 186 having a width in the angle θ direction is set in a portion where the fetal abdomen is difficult to be drawn (position where the angle θ is ±90°). As a result, that portion is excluded from the route search area, so that the occurrence of false search can be suppressed or prevented.

Further, the mask setting unit 42 estimates a range in which there is a high possibility that the edge portion (boundary) of the fetal abdomen does not exist based on the diameter R average value (statistical value) of the fetal abdomen estimated from the number of pregnancy days, and Masks 188 and 190 are set in the range. The mask 188 is a mask (mask set in a range of 0 to a) set within a predetermined range (distance a) from the position of the distance r=0, and the mask 190 is an edge part of the fetal abdomen. It is a mask set in a range assumed to be outside (a mask set in a range of Ra). By setting the mask in this way, it is possible to suppress or prevent the occurrence of erroneous search by removing noise from a region where the edge portion of the fetal abdomen is not supposed to exist.

Note that the mask setting unit 42 may apply weighting processing to the developed image instead of setting the mask, as in the first modification of the first embodiment, or the modification of the first embodiment. Similar to 2, the mask corresponding to the type of the probe 10 may be set in the developed image.

The ultrasonic diagnostic apparatus according to the third embodiment may have the same configuration as the ultrasonic diagnostic apparatus according to the second embodiment. In this case, the angle correction unit 138 corrects the angle of the ellipse approximated to the fetal abdomen. For example, the angle may be corrected with the spine of the fetus as a reference.

The template 164 used in the third embodiment may be used in the first embodiment. As described above, in the B-mode tomographic image, the side surface of the fetal head is difficult to be drawn, and in the calculation processing of the candidate for the central position of the fetal head, there is a case where it is affected by noise caused by that part. By using the template 164 in which a part of the circular ring is missing, it is possible to reduce the influence of noise on the side surface of the fetal head, so that the detection accuracy of the candidate for the central position of the fetal head is increased. Further, the masks 188 and 190 shown in FIG. 27 may be set in the developed image according to the first embodiment.

22 image processing unit, 24 position calculation unit, 26 region calculation unit, 28 measurement unit, 34 template generation unit, 36 edge enhanced image generation unit, 38 matching processing unit, 40 conversion unit, 42 mask setting unit, 44 search unit, 46 Inverse transforming unit, 48 Ellipse calculating unit, 50 Validity determining unit, 52 Central masking unit, 54 End determining unit, 56 Center updating unit, 138 Angle correcting unit.

Claims (8)

Based on the tomographic image obtained by transmitting and receiving ultrasonic waves to and from the fetus in the mother's body, an ellipse calculating means for calculating an ellipse corresponding to the annular portion of the fetus,
While moving the center of the ellipse calculated by the ellipse calculating means in one axis direction of the ellipse, and rotating the reference area extending in the other axis direction of the ellipse at the center after the movement, the one axis direction At each position and each rotation angle, an evaluation value in the reference area is calculated, and using the evaluation value, an angle correction unit that corrects the angle of the ellipse with respect to the annular portion,
An ultrasonic diagnostic apparatus comprising: The ultrasonic diagnostic apparatus according to claim 1,
The angle correction means corrects the angle of the ellipse based on the evaluation value obtained at each of the positions and the rotation angles and the variance of the evaluation value,
An ultrasonic diagnostic apparatus characterized by the above. The ultrasonic diagnostic apparatus according to claim 2,
The angle correction means moves the center of the ellipse in the one-axis direction, rotates the reference area at the position of the movement destination, and sums the sum of the brightness values in the reference area at each rotation angle. Calculated as an evaluation value, for each position in the one axis direction, the sum of the brightness values in the reference area at each rotation angle is calculated, and for each position in the one axis direction, the brightness at each rotation angle. The variance of the sum of the values is calculated, the position in the one-axis direction having the largest variance is determined, the rotation angle having the largest sum of the luminance values at that position is determined, and the angle of the ellipse is corrected to the rotation angle. ,
An ultrasonic diagnostic apparatus characterized by the above. The ultrasonic diagnostic apparatus according to claim 3,
The angle correction means applies weighting processing according to the amount of movement of the center of the ellipse in the one-axis direction to the variance of the sum of the luminance values,
An ultrasonic diagnostic apparatus characterized by the above. The ultrasonic diagnostic apparatus according to claim 3 or 4,
When the variance at each position in the one-axis direction is less than or equal to a predetermined threshold value, the angle correction means sets the ellipse to the rotation angle at which the sum of the luminance values becomes maximum when the center of the ellipse is not moved. Correct the angle of
An ultrasonic diagnostic apparatus characterized by the above. The ultrasonic diagnostic apparatus according to claim 1,
The annular portion is the head of the fetus,
The one-axis direction is the minor axis direction of the ellipse,
The other axis direction is the major axis direction of the ellipse,
The angle correction means corrects the angle of the ellipse by calculating the direction in which the midline of the head of the fetus extends based on the evaluation value.
An ultrasonic diagnostic apparatus characterized by the above. The ultrasonic diagnostic apparatus according to any one of claims 1 to 6,
By applying template matching to the tomographic image, a position calculation means for calculating a candidate for the central position of the annular portion of the fetus,
Transform means for polar coordinate transforming the tomographic image by using the candidate of the center position as the origin of the polar coordinate system,
Search means for searching a route from the image after the polar coordinate conversion,
Inverse conversion means for inversely converting the path,
Further including,
The ellipse calculation means calculates an ellipse corresponding to the path after the inverse transformation as an ellipse corresponding to the annular portion,
An ultrasonic diagnostic apparatus characterized by the above. Computer,
Ellipse calculation means for calculating an ellipse corresponding to the annular portion of the fetus, based on a tomographic image obtained by transmitting and receiving ultrasonic waves to and from the fetus in the mother's body,
While moving the center of the ellipse calculated by the ellipse calculating means in one axis direction of the ellipse, and rotating the reference area extending in the other axis direction of the ellipse at the center after the movement, the one axis direction At each position and each rotation angle, an evaluation value in the reference area is calculated, and the evaluation value is used to correct the angle of the ellipse with respect to the annular portion.
A program characterized by making it function as.