JP5950271B2 - Ultrasonic diagnostic equipment - Google Patents

Description

  The present invention relates to an ultrasonic diagnostic apparatus, and more particularly to an improvement of an apparatus for obtaining a Doppler shift frequency of received ultrasonic waves.

  2. Description of the Related Art Ultrasonic diagnostic apparatuses that measure a blood flow velocity of a subject using a Doppler method are widely used. Examples of such an ultrasonic diagnostic apparatus include a continuous wave Doppler apparatus, a pulse Doppler apparatus, and a color Doppler apparatus. The continuous wave Doppler device transmits ultrasonic waves as a continuous wave toward a subject. Then, based on the Doppler shift frequency component of the ultrasonic wave reflected in the subject and continuously received in time, a Doppler waveform indicating a temporal change in blood flow velocity is displayed.

  The pulse Doppler device transmits pulse-modulated ultrasonic waves toward a subject at a predetermined pulse repetition frequency (PRF: Pulse Repetition Frequency: hereinafter simply referred to as a repetition frequency). Then, the Doppler waveform is displayed based on the Doppler shift frequency component of the ultrasonic wave reflected in the subject and received at a timing corresponding to the depth of the region to be measured.

  Similar to the pulse Doppler device, the color Doppler device transmits pulse-modulated ultrasonic waves to the subject at a predetermined repetition frequency, and obtains Doppler shift frequency components of the ultrasonic waves reflected and received within the subject. . The color Doppler apparatus scans the transmission / reception direction of ultrasonic waves, obtains a Doppler shift frequency component in the scanning plane, and obtains a blood flow velocity distribution on the scanning plane. In general, a color Doppler device acquires tomographic image data in the B mode, and displays the distribution of blood flow velocity with a change in color superimposed on the tomographic image.

  In the pulse Doppler device and the color Doppler device, the measurable Doppler shift frequency, that is, the measurable speed is limited according to the repetition frequency of the pulse modulated wave. Increasing the repetition frequency increases the upper limit of the measurable speed, and decreasing the repetition frequency decreases the upper limit of the measurable speed. If the velocity of the measurement target such as the blood flow velocity exceeds the measurable velocity range, a so-called folding phenomenon occurs and a measurement error occurs.

  The following Patent Document 1 describes a color Doppler device. This color Doppler apparatus obtains a two-dimensional color Doppler image by a pulse Doppler method. Then, for the two-dimensional color Doppler image, it is determined whether or not the number of pixels of the upper limit value of the measurable flow velocity range is a predetermined number or more. The color Doppler device avoids the aliasing phenomenon by changing the repetition frequency and parameters for image display when the number of upper limit pixels is equal to or greater than a predetermined number.

JP-A-11-146879

When the tissue in the subject moves with time, it is difficult to set the repetition frequency appropriately. If the repetition frequency is not appropriate, there is a Turkey cause aliasing phenomenon. In order to extend the measurable range of the Doppler shift frequency and avoid the aliasing phenomenon, it is preferable to increase the repetition frequency. However, when the repetition frequency is increased, the observable depth (field depth) in the subject becomes shallow because the transmitted pulse ultrasound and the received pulse ultrasound must not overlap in time. Problem arises. An object of this invention is to set a repetition frequency appropriately .

The present invention relates to a transmitter that transmits ultrasonic waves at a set repetition frequency while scanning a transmission direction, and receives ultrasonic waves that are transmitted from the transmitter and reflected within the subject, and the received ultrasonic waves A receiving unit that outputs the received data according to the color, a color Doppler operation unit that obtains Doppler shift distribution data on the scanning plane based on the received data sequentially output from the receiving unit according to the scan of the transmitted ultrasonic wave, A repetition frequency setting unit that sets the repetition frequency based on the Doppler shift distribution data obtained by a color Doppler calculation unit, and the Doppler shift distribution data is a Doppler shift frequency for each observation position on the scanning plane. or a data associating the equivalent amount, more the repetition frequency setting unit is determined for scanning over a plurality of times A repetition frequency setting process for setting the repetition frequency based on the Doppler shift distribution data is executed, and the repetition frequency setting process is turned back to any of the plurality of Doppler shift distribution data obtained for a plurality of scans. A process for obtaining a maximum value of a Doppler shift frequency or a corresponding maximum value for each of the plurality of Doppler shift distribution data obtained by scanning a plurality of times, which is executed when no phenomenon occurs, and each of the Doppler shift distributions A process of setting the lower limit value of the repetition frequency based on the maximum one of the maximum values obtained for the data, and setting the repetition frequency to a value larger than the lower limit value and smaller than a predetermined upper limit value And a process to perform. The present invention also includes a transmitter that transmits ultrasonic waves at a set repetition frequency while scanning the transmission direction, and receives ultrasonic waves that are transmitted from the transmitter and reflected within the subject. A reception unit that outputs reception data corresponding to sound waves; a color Doppler calculation unit that obtains Doppler shift distribution data on a scanning plane based on reception data sequentially output from the reception unit in response to scanning of transmitted ultrasonic waves; A repetition frequency setting unit that sets the repetition frequency based on the Doppler shift distribution data obtained by the color Doppler calculation unit, the Doppler shift distribution data for each observation position on the scanning plane, Doppler shift is the frequency or data which associates the corresponding amount, the repetition frequency setting unit is determined for scanning over a plurality of times A repetition frequency setting process for setting the repetition frequency based on a plurality of the Doppler shift distribution data is performed, and the repetition frequency setting process is performed on any of the plurality of Doppler shift distribution data obtained for a plurality of scans. This is executed when the aliasing phenomenon does not occur, and a determination process for determining whether or not the aliasing phenomenon occurs in any of the plurality of Doppler shift distribution data obtained for a plurality of scans is performed. includes processing for searching the repetition frequency, the determination process, among the plurality of observation positions Doppler shift frequency or its corresponding value is indicated by the Doppler shift distribution data, Doppler shift frequency or its corresponding value is equal to or greater than a predetermined threshold value based on the number of observation positions, folded in the Doppler shift distribution data It includes a process for the determination of the elephants has occurred, characterized in that.

  In the present invention, the Doppler shift distribution data is data in which, for example, the normalized Doppler shift frequency (Doppler shift amount) of the ultrasonic wave reflected at each position on the scanning plane is associated with the coordinates of each reflection position. Here, the standardized Doppler shift frequency is obtained by dividing the Doppler shift frequency by the repetition frequency, or another equivalent amount indicating the Doppler shift frequency (for example, a value converted into a speed), or the like indicating the repetition frequency. It is standardized by dividing by a considerable amount.

Nozomu Mashiku, the process of searching the repetition frequency, the repetition frequency reducing process for setting the repetition frequency to a value smaller than the value set previously, and the determination processing in after said repetition frequency decreases processing, When the determination process is executed and it is determined that no aliasing phenomenon has occurred in any of the plurality of Doppler shift distribution data, a plurality of the Doppler shift distribution data having the aliasing phenomenon occurs. Until the determination is made, the repetition frequency reduction process and the determination process after the repetition frequency reduction process are repeatedly executed, and the execution of the determination process causes a folding phenomenon among a plurality of the Doppler shift distribution data. If it is determined that there is something, the repetition frequency executed together with the determination It includes processing the value before reduction treatment returning the repetition frequency.

Preferably, the repetition frequency setting unit sets the repetition frequency to a predetermined upper limit value, and a folding phenomenon occurs in any of the plurality of Doppler shift distribution data obtained by scanning a plurality of times. An initial determination process for determining whether or not there is a aliasing phenomenon in any of the plurality of Doppler shift distribution data by executing the initial determination process is performed. In the initial determination process, whether or not the aliasing phenomenon occurs based on a comparison between the Doppler shift frequency at each observation position on the scanning plane or its equivalent amount and a predetermined threshold indicated by the Doppler shift distribution data. Including the process of determining whether or not. Preferably, the repetition frequency setting unit performs the repetition frequency setting process when it is determined by the execution of the initial determination process that a folding phenomenon has occurred in any of the plurality of Doppler shift distribution data. Do not execute and maintain the repetition frequency.

Preferably, the determination process is based on the number of observation positions whose Doppler shift frequency or its equivalent amount is equal to or greater than a predetermined threshold among a plurality of observation positions whose Doppler shift frequency or its equivalent amount is indicated by the Doppler shift distribution data. A process for determining that a folding phenomenon has occurred in the Doppler shift distribution data. Preferably, the initial determination process is based on the number of observation positions whose Doppler shift frequency or its equivalent amount is equal to or greater than a predetermined threshold among a plurality of observation positions whose Doppler shift frequency or its equivalent amount is indicated by the Doppler shift distribution data. And a process of determining that a folding phenomenon occurs in the Doppler shift distribution data.

Nozomu Mashiku, the scanning plane is a surface of the subject heart or blood vessels are observed, scanning over a plurality of times in the scanning plane is carried out within a time corresponding to a predetermined heart rate count.

  According to the present invention, an appropriate folding frequency is set based on a change range such as a blood flow velocity at a predetermined number of heartbeats. Thereby, a measurement error based on the folding phenomenon can be avoided.

  In the present invention, when the set value of the repetition frequency is changed, the repetition frequency is set to a value smaller than the previously set value. This shortens the convergence time until an optimum repetition frequency is obtained.

According to the present invention, can it to properly set the repetition frequency.

It is a figure which shows the structure of the ultrasound diagnosing device which concerns on this invention. It is the figure which showed notionally each structure of the beam data for tomographic images, and the beam data for Doppler measurement. It is the figure which showed notionally n doppler shift distribution data memorize | stored in memory. It is a flowchart of the PRF setting process which concerns on 1st Embodiment. It is a flowchart of the PRF setting process which concerns on 2nd Embodiment. It is a flowchart of a PRF search process.

  FIG. 1 shows the configuration of an ultrasonic diagnostic apparatus according to an embodiment of the present invention. The ultrasonic diagnostic apparatus operates in a B mode that displays a tomographic image of a subject or a color Doppler mode that displays a color Doppler image superimposed on the tomographic image. The tomographic image is a cross-section of the tissue of the subject represented by the intensity of the luminance of the image, and the color Doppler image is an image that represents the difference in blood flow velocity by the difference in color. According to the color Doppler mode, the blood flow velocity can be observed together with the cross-sectional shape of the tissue of the subject. Therefore, this ultrasonic diagnostic apparatus is used for diagnosis of the heart, blood vessels, and the like.

  The ultrasonic diagnostic apparatus includes an ultrasonic probe 10, a transmission unit 12, a reception unit 14, a B-mode calculation unit 16, a color Doppler calculation unit 18, an image synthesis unit 20, a display 22, a memory 24, an operation panel 26, and a controller 28. Prepare. The controller 28 controls the transmission unit 12, the reception unit 14, the B mode calculation unit 16, the color Doppler calculation unit 18, and the image composition unit 20 according to the operation setting on the operation panel 26. For example, either the B mode or the color Doppler mode is selected on the operation panel 26, and the controller 28 executes control according to the selection of the operation mode on the operation panel 26.

  The transmission unit 12, the reception unit 14, the B-mode calculation unit 16, the color Doppler calculation unit 18, and the image composition unit 20 execute calculation processing, and each stores information obtained in the calculation process. Have local memory. In addition to storing information in its own local memory, these components store information in the memory 24 through the control of the controller 28, and store the information from the memory 24 as needed through the control of the controller 28. It may be read.

  First, the configuration related to the operation in the B mode and the operation in the B mode will be described. The ultrasonic probe 10 includes a plurality of array transducers arranged on a surface on which ultrasonic waves are transmitted and received. As the ultrasonic probe 10, for example, a probe in which a plurality of array transducers are arranged in a row or a probe in which a plurality of array transducers are arranged in a plurality of rows is used. In the ultrasonic diagnostic apparatus, the one-dimensional scanning plane 30 of the transmission / reception beam 32 by the ultrasonic probe 10 is an observation plane, and a tomographic image on the observation plane is displayed on the display 22. Therefore, the ultrasonic probe 10 is supported in such a posture that the surface on which ultrasonic waves are transmitted and received is directed to the subject and the observation surface is located in the tissue to be diagnosed.

  The transmission unit 12 outputs a pulse-modulated electric signal (pulse modulation signal) to each array transducer of the ultrasonic probe 10. Each array transducer generates pulsed ultrasonic waves based on the pulse modulation signal output from the transmission unit 12. At this time, the transmission unit 12 functions as a beam former of a pulsed ultrasonic wave to be transmitted. That is, the transmission unit 12 controls the delay time of the signal output to each array transducer to form a transmission beam, and performs one-dimensional scanning of the transmission beam.

  Each array transducer of the ultrasonic probe 10 receives pulsed ultrasonic waves reflected in the subject. Each array transducer generates an electrical signal based on the received pulse ultrasonic wave and outputs the electrical signal to the receiving unit 14. The receiving unit 14 functions as a beam former of received pulsed ultrasonic waves. That is, the reception unit 14 forms a reception beam by phasing and adding a plurality of electrical signals output from the plurality of array transducers, and performs one-dimensional scanning of the reception beam in the same direction as the transmission beam.

  The receiving unit 14 generates beam data corresponding to the received pulsed ultrasound. This beam data is data representing on the time axis the intensity of the reflected wave generated on each distance from the ultrasonic probe 10 for a specific transmission / reception beam direction (direction of the transmission beam and the corresponding reception beam). . The receiving unit 14 outputs the beam data generated in this way to the B mode calculation unit 16.

  The transmission unit 12 and the reception unit 14 repeatedly perform one-dimensional scanning of a transmission / reception beam on a subject multiple times. The B mode calculation unit 16 generates tomographic image data for each one-dimensional scan based on the beam data group obtained for each one-dimensional scan, and outputs the tomographic image data to the image composition unit 20. The image composition unit 20 causes the display 22 to sequentially display the tomographic images based on the tomographic image data sequentially output from the B-mode calculation unit 16 by one-dimensional scanning that is repeatedly performed.

  Next, the configuration related to the operation in the color Doppler mode and the operation in the color Doppler mode will be described. The color Doppler mode is a mode in which pulse ultrasound for acquiring a tomographic image and pulse ultrasound for acquiring a color Doppler image are transmitted and received in a time-sharing manner, and color Doppler image data is acquired together with tomographic image data. .

  The transmitter 12 outputs a pulse modulation signal for tomographic image acquisition to each array transducer, and then outputs a plurality of pulse modulation signals for Doppler measurement to each array transducer at a repetition frequency PRF. The pulse modulation signal for Doppler measurement is a pulse modulation signal for acquiring a color Doppler image, and differs in pulse time width, signal level, and the like from the pulse modulation signal for tomographic image acquisition. The repetition frequency PRF is a frequency set by the controller 28 and will be described in detail later.

  Each array transducer of the ultrasonic probe 10 generates a plurality of pulsed ultrasonic waves for Doppler measurement at a repetition frequency PRF following the pulsed ultrasonic waves for acquiring a tomographic image. At this time, the transmission unit 12 forms a transmission beam by controlling the delay time of the signal output to each array transducer, and performs one-dimensional scanning of the transmission beam.

  Each array transducer receives a pulsed ultrasound for acquiring a tomographic image and a plurality of pulsed ultrasounds for Doppler measurement reflected in the subject. Each array transducer generates an electrical signal based on the received ultrasonic wave and outputs the electrical signal to the receiving unit 14. At this time, the receiving unit 14 forms a reception beam by phasing and adding a plurality of electrical signals output from the plurality of array transducers, and performs one-dimensional scanning of the reception beam in the same direction as the transmission beam. The receiving unit 14 outputs tomographic image beam data corresponding to the tomographic image acquisition pulse ultrasound to the B-mode computing unit 16. Then, the Doppler measurement beam data corresponding to the pulsed ultrasound for Doppler measurement is output to the color Doppler calculation unit 18.

  FIG. 2 conceptually shows the configuration of the tomographic image beam data 38 and the configuration of the Doppler measurement beam data 40. These data correspond to one transmission / reception beam 32 on the one-dimensional scanning plane 30 in FIG. The horizontal axis indicates the time when data is generated in the receiving unit 14. The time indicated on the horizontal axis corresponds to the distance from the ultrasonic probe 10 in the transmission / reception beam direction. Each section 42 represents digital data representing the level of ultrasound received. In the example shown in FIG. 2, a plurality of Doppler measurement beam data 40 is arranged at a time interval of the reciprocal frequency PRF after one tomographic image beam data 38.

  The transmission unit 12 and the reception unit 14 repeatedly perform one-dimensional scanning of the transmission / reception beam a plurality of times. The B mode calculation unit 16 generates tomographic image data for each one-dimensional scan based on the tomographic image beam data group obtained for each one-dimensional scan, and outputs the tomographic image data to the image composition unit 20. .

  On the other hand, the color Doppler computing unit 18 generates color Doppler image data for each one-dimensional scan based on the Doppler measurement beam data group obtained for each one-dimensional scan, and the color Doppler image data is converted into an image composition unit. 20 is output.

  Based on the tomographic image data and the color Doppler image data, the image composition unit 20 generates tomographic color Doppler image data indicating an image in which the color Doppler image is superimposed on the tomographic image, and causes the display 22 to display the tomographic color Doppler image. With such a configuration and processing, the tomographic color Doppler image data is obtained every time the transmission / reception beam is scanned one-dimensionally, and the tomographic color Doppler image is displayed on the display 22.

  A process in which the color Doppler calculation unit 18 generates color Doppler image data will be specifically described. The color Doppler calculation unit 18 obtains Doppler shift distribution data for the one-dimensional scanning plane based on the Doppler measurement beam data group acquired by the one-dimensional scanning. Here, the Doppler shift distribution data is obtained by associating the normalized Doppler shift frequency (Doppler shift amount) of the ultrasonic wave reflected at each position on the one-dimensional scanning plane with the coordinates of each reflection position. The Doppler shift distribution data consists of a set of pixels, and one pixel corresponds to one reflection position. The standardized Doppler shift frequency is obtained by dividing the Doppler shift frequency by the repetition frequency PRF, or another equivalent amount indicating the Doppler shift frequency (for example, a value converted into a speed), and other values indicating the repetition frequency PRF. Divided by a considerable amount and standardized.

  Since the Doppler shift frequency obtained based on the beam data for Doppler measurement is a value of −0.5 PRF or more and 0.5 PRF or less, the normalized Doppler shift frequency is a value of −0.5 or more and 0.5 or less. .

  Note that normalization by dividing the Doppler shift frequency by the repetition frequency PRF is an example. That is, another normalization process in which the original Doppler shift frequency is converted to a value within a predetermined range and the converted value is defined to indicate the original Doppler shift frequency may be used.

  The color Doppler calculation unit 18 obtains beam direction velocity data using a plurality of Doppler measurement beam data obtained at the repetition frequency PRF for each transmission / reception beam direction. Here, the beam direction velocity data is data in which the normalized Doppler shift frequency of the ultrasonic wave reflected at each position in a specific transmission / reception beam direction is associated with the coordinates of each reflection position. In the processing for obtaining the beam direction velocity data, a wall filter process for reducing clutter noise and the like are performed together with autocorrelation processing for a plurality of Doppler measurement beam data obtained at the repetition frequency PRF, and the Doppler shift frequency at each reflection position is determined. Desired. Then, the obtained Doppler shift frequency is normalized by the repetition frequency PRF. In this process, another equivalent amount indicating the Doppler shift frequency may be obtained, and the obtained equivalent amount of the Doppler shift frequency may be normalized by another equivalent amount indicating the repetition frequency PRF. The color Doppler calculation unit 18 sets a set of beam direction velocity data obtained for each transmission / reception beam direction on the one-dimensional scanning plane as Doppler shift distribution data for the one-dimensional scanning plane.

  The color Doppler calculation unit 18 obtains color Doppler image data by replacing each normalized Doppler frequency indicated by the Doppler shift distribution data with a corresponding color identification value. That is, the color Doppler calculation unit 18 stores a color identification value table in which the normalized Doppler shift frequency and an identification value (color identification value) for identifying a color displayed on the display 22 are associated with each other, and the Doppler shift distribution data indicates For each normalized Doppler frequency, a corresponding color identification value is acquired. Then, each normalized Doppler frequency indicated by the Doppler shift distribution data is replaced with a corresponding color identification value. Through such processing, the color Doppler calculation unit 18 generates color Doppler image data for each one-dimensional scan, and outputs the color Doppler image data to the image composition unit 20.

  In the color identification value table, as an example, for the positive normalized Doppler shift frequency, the larger the normalized Doppler shift frequency is associated with the color identification value of the longer wavelength, and the negative normalized Doppler shift frequency is As the normalized Doppler shift frequency increases in the negative direction, the color identification value of a color having a shorter wavelength is associated. By this association, different colors are displayed depending on the difference in the normalized Doppler shift frequency.

  Instead of storing such a color identification value table, the color Doppler calculation unit 18 may execute an algorithm for obtaining a color identification value by giving a normalized Doppler shift frequency.

  According to such processing, a color identification value is assigned to the standardized Doppler shift frequency, and color Doppler image data is obtained. As a result, even if the possible range of the observed Doppler shift frequency changes due to a change in the diagnosis status, a color identification value can be appropriately assigned to the observed Doppler shift frequency. Therefore, the visibility of the tomographic color Doppler image can be improved regardless of the diagnosis status.

  The color Doppler calculation unit 18 stores Doppler shift distribution data sequentially obtained by one-dimensional scanning that is repeatedly performed in the memory 24 under the control of the controller 28. FIG. 3 conceptually shows n Doppler shift distribution data stored in the memory 24. Addresses 0 to n−1 are assigned to areas in which each Doppler shift distribution data is stored. In the following description, the Doppler shift distribution data stored in the areas of addresses 0 to n−1 are referred to as Doppler shift distribution data D0 to Dn−1, respectively.

  The innermost Doppler shift distribution data Dn-1 stored in the area of address n-1 is the data stored first, and the foremost Doppler shift distribution data D0 stored in the area of address 0 Is the Doppler shift distribution data stored last.

  In the memory 24, every time one piece of Doppler shift distribution data is newly input, the Doppler shift distribution data Dn-1 stored in the area of the address n-1 is erased. Then, n−1 pieces of Doppler shift distribution data stored in the areas of addresses 0 to n−2 are shifted and stored in the back by one address. Further, newly input Doppler shift distribution data is stored in the area of address 0.

  As will be described below, all of n pieces of Doppler shift distribution data stored in the memory 24 or any one of them is used for processing for setting the repetition frequency PRF.

  A process in which the PRF setting unit 34 included in the controller 28 sets the repetition frequency PRF will be described. FIG. 4 shows a flowchart showing the PRF setting process. This flowchart is executed when the controller 28 recognizes that the operation of the speed range automatic setting switch has been performed on the operation panel 26.

  The PRF setting unit 34 sets the repetition frequency PRF to a predetermined frequency upper limit value MX (S101). The controller 28 controls the transmission unit 12 and the reception unit 14 so that pulsed ultrasonic waves for Doppler measurement are transmitted and received at the repetition frequency PRF set in step S101 (S102). At this time, the controller 28 controls the transmission unit 12 and the reception unit 14 to repeatedly perform one-dimensional scanning of the transmission / reception beam. As a result, the memory 24 sequentially stores Doppler shift distribution data obtained for each one-dimensional scan. That is, the Doppler shift distribution data stored first is erased from the memory 24 for each one-dimensional scan, and newly acquired Doppler shift distribution data is stored in the memory 24 for each one-dimensional scan.

  The PRF setting unit 34 has the absolute value of the normalized Doppler shift frequency equal to or greater than a predetermined threshold for each of the j pieces of Doppler shift distribution data D0 to Dj-1 stored in the area of addresses 0 to j-1 of the memory 24. The number of pixels, that is, boundary pixels is obtained (S103). Here, j is the number of data used in the PRF setting process, and is an arbitrary number from 1 to n.

  The data number j is, for example, the number of Doppler shift distribution data acquired in a time corresponding to a predetermined number of heartbeats of the subject. For example, when only 30 pieces of Doppler shift distribution data are obtained in a time per heartbeat, the number of data j is 30. In this case, the controller 28 acquires a pulse signal synchronized with the heartbeat by the heartbeat detector 36. Then, the data number j is set based on the number of Doppler shift distribution data obtained in a predetermined cycle of the acquired pulse signal. The controller 28 uses a plurality of tomographic image data generated in the past by the B-mode calculation unit 16 or the past generated by the color Doppler calculation unit 18 instead of using the pulse signal acquired by the heartbeat detector 36. Based on a plurality of Doppler shift distribution data, the number of Doppler shift distribution data (number of images) corresponding to a predetermined number of heartbeats may be obtained, and the number of data j may be set.

  The number of boundary pixels for each of the Doppler shift distribution data D0 to Dj-1 may be obtained when each Doppler shift distribution data is obtained and stored in the memory 24 in advance. In this case, the PRF setting unit 34 reads the number of boundary pixels for each of the Doppler shift distribution data D0 to Dj−1 from the memory 24 in Step S103.

  The PRF setting unit 34 determines whether or not there are any number of boundary pixels in the Doppler shift distribution data D0 to Dj-1 that is greater than or equal to a predetermined number (S104).

  Here, the technical significance of step S104 will be described. In general, in an ultrasonic diagnostic apparatus using a pulse Doppler method, when pulsed ultrasonic waves for Doppler measurement are transmitted and received at a repetition frequency PRF, the measurable Doppler shift frequency range is −0.5 PRF or more and 0.5 PRF or less. Become. When the frequency fd is a frequency of −0.5 PRF or more and 0.5 PRF or less, the actual Doppler shift frequency fd ± k · PRF is measured as the frequency fd, and the measured Doppler shift frequency is ± k · PRF. Error occurs. Here, k is an arbitrary natural number 1, 2, 3,. Such an error is referred to as a folding error, and a phenomenon in which such an error occurs is referred to as a folding phenomenon.

  Under such a pulse Doppler method, the larger the number of boundary pixels included in the Doppler shift distribution data, the higher the possibility that the aliasing phenomenon occurs. Therefore, in the PRF setting process shown in the flowchart of FIG. 4, if there are more than a predetermined number of boundary pixels in the Doppler shift distribution data D0 to Dj−1, it is assumed that the aliasing phenomenon has occurred. When S110 is executed and no Doppler shift distribution data D0 to Dj-1 has a boundary pixel number equal to or larger than the predetermined number, the processing after Step S105 is executed assuming that the aliasing phenomenon does not occur.

  That is, when there is Doppler shift distribution data in which the number of boundary pixels is equal to or greater than a predetermined number, the PRF setting unit 34 maintains the value of the repetition frequency PRF set in step S101 (S110). On the other hand, when there is no Doppler shift distribution data in which the number of boundary pixels is equal to or greater than the predetermined number, the PRF setting unit 34 sets the maximum absolute value of the normalized Doppler shift frequency for each of the Doppler shift distribution data D0 to Dj-1. The Doppler shift maximum value DM is obtained (S105). Then, the maximum one of the j maximum Doppler shift values DM obtained for each of the Doppler shift distribution data D0 to Dj-1 is determined as the peak frequency Fp (S106), and the value obtained by doubling the peak frequency Fp is repeatedly set as the lower frequency limit. Value L is set (S107).

  The Doppler shift maximum value DM for each of the Doppler shift distribution data D0 to Dj-1 may be obtained when each Doppler shift distribution data is obtained and stored in the memory 24 in advance. In this case, the PRF setting unit 34 reads the Doppler shift maximum value DM for each of the Doppler shift distribution data D0 to Dj-1 from the memory 24 in Step S105.

  The PRF setting unit 34 sets a new repetition frequency PRF in a range that is larger than the repetition frequency lower limit value L and smaller than the frequency upper limit value MX set as the initial value (S108). For example, the new repetition frequency PRF is set as PRF = L + α · (MX−L). Here, α is an arbitrary adjustment coefficient larger than 0 and smaller than 1. The controller 28 controls the transmission unit 12 and the reception unit 14 so that pulsed ultrasonic waves for Doppler measurement are transmitted and received at the repetition frequency PRF set in step S108 (S109).

  According to such a PRF setting process, the repetition frequency PRF is set to a value as small as possible to avoid the folding phenomenon except when the folding phenomenon occurs when the repetition frequency PRF is set to the frequency upper limit value MX (S110). Obtain (S105 to S108).

  In an ultrasonic diagnostic apparatus using the pulse Doppler method, it is preferable to increase the repetition frequency PRF in order to expand the measurable range of the Doppler shift frequency and avoid the aliasing phenomenon. However, when the repetition frequency PRF is increased, the range that can be taken by the normalized Doppler shift frequency indicated by the Doppler shift distribution data is reduced. This causes a problem that the color change width of the color Doppler image is reduced, and the blood flow velocity is difficult to grasp. Further, when the repetition frequency PRF is increased, the depth (field depth of view) that can be observed in the subject is shallow because the transmitted pulse ultrasound and the received pulse ultrasound must not overlap in time. Problem arises.

  Therefore, in the PRF setting process according to the present embodiment, except for the case where the aliasing phenomenon occurs when the repetition frequency PRF is set to the frequency upper limit value MX (S110), the repetition frequency PRF is set to a value as small as possible to avoid the aliasing phenomenon. Can be set (S105 to S108). As a result, the folding phenomenon can be avoided as much as possible, the visibility of the color Doppler image can be improved, and the depth of field can be increased.

  The frequency upper limit value MX, the threshold value for specifying the boundary pixel in step S103, the number of boundary pixels serving as the determination condition in step S104, and the like are determined in advance according to the diagnostic part and stored in the memory 24. May be. These numerical values may be input by operating the operation panel 26.

  Next, PRF setting processing according to the second embodiment will be described. FIG. 5 shows a flowchart thereof. The same processes as those shown in FIG. 4 are denoted by the same reference numerals and description thereof is omitted.

  The PRF setting unit 34 executes Steps S101 to S104 by the same process as the PRF setting process shown in FIG. In step S104, if there is no Doppler shift distribution data in which the number of boundary pixels is equal to or larger than the predetermined number, PRF search processing (S201) for searching for an optimum repetition frequency is executed. FIG. 6 shows a flowchart of the PRF search process. The PRF setting unit 34 sets a value obtained by subtracting a predetermined step frequency Δ from the previously set repetition frequency PRF as a new repetition frequency PRF (S201-1). The controller 28 controls the transmission unit 12 and the reception unit 14 so that pulsed ultrasonic waves for Doppler measurement are transmitted and received at the set repetition frequency PRF (S201-2). At this time, the controller 28 controls the transmission unit 12 and the reception unit 14 to repeatedly perform one-dimensional scanning of the transmission / reception beam. As a result, the memory 24 sequentially stores Doppler shift distribution data obtained for each one-dimensional scan. That is, the Doppler shift distribution data stored first is erased from the memory 24 for each one-dimensional scan, and newly acquired Doppler shift distribution data is stored in the memory 24 for each one-dimensional scan.

  The PRF setting unit 34 obtains the number of boundary pixels for which the absolute value of the normalized Doppler shift frequency is equal to or greater than a predetermined threshold for each of the Doppler shift distribution data D0 to Dj−1 (S201-3).

  The PRF setting unit 34 determines whether or not the number of boundary pixels is greater than or equal to a predetermined number among the Doppler shift distribution data D0 to Dj−1 (S201-4). Then, when there is no Doppler shift distribution data in which the number of boundary pixels is a predetermined number or more, the process returns to step S201-1.

  On the other hand, if there is Doppler shift distribution data in which the number of boundary pixels is a predetermined number or more, the PRF setting unit 34 newly adds a value obtained by adding the step frequency Δ to the value of the repetition frequency PRF set in step S201-1. Is set to a repetitive frequency PRF (S201-5), and the process proceeds to step S109 in FIG.

  According to such a PRF setting process, the repetition frequency PRF is set to a value as small as possible to avoid the folding phenomenon except when the folding phenomenon occurs when the repetition frequency PRF is set to the frequency upper limit value MX (S110). (S201). As a result, similar to the PRF setting process according to the first embodiment, the aliasing phenomenon can be avoided as much as possible, the visibility of the color Doppler image can be improved, and the depth of field can be increased.

  In the PRF setting process according to the first and second embodiments, the initial value of the repetition frequency PRF is set to the frequency upper limit value MX, and the repetition frequency PRF is changed to a value smaller than that value. This shortens the convergence time until the optimum repetition frequency PRF is obtained.

  DESCRIPTION OF SYMBOLS 10 Ultrasonic probe, 12 Transmission part, 14 Reception part, 16 B mode calculation part, 18 Color doppler calculation part, 20 Image composition part, 22 Display, 24 Memory, 26 Operation panel, 28 Controller, 30 One-dimensional scanning plane, 32 Transmit / receive beam, 34 PRF setting unit, 36 heart rate detector, 38 tomographic image beam data, 40 Doppler measurement beam data.

Claims (7)

A transmitter that transmits ultrasonic waves at a set repetition frequency while scanning the transmission direction;
A receiving unit that receives the ultrasonic waves transmitted from the transmitting unit and reflected in the subject, and outputs received data corresponding to the received ultrasonic waves;
A color Doppler operation unit that obtains Doppler shift distribution data on the scanning surface based on reception data sequentially output from the reception unit in accordance with scanning of transmitted ultrasonic waves;
A repetition frequency setting unit for setting the repetition frequency based on the Doppler shift distribution data obtained by the color Doppler calculation unit,
The Doppler shift distribution data is data in which a Doppler shift frequency or an equivalent amount thereof is associated with each observation position on the scanning plane,
The repetition frequency setting unit performs a repetition frequency setting process for setting the repetition frequency based on a plurality of the Doppler shift distribution data obtained for scanning over a plurality of times,
The repetition frequency setting process is executed when no aliasing phenomenon occurs in any of the plurality of Doppler shift distribution data obtained for a plurality of scans,
For each of the plurality of Doppler shift distribution data obtained by scanning over a plurality of times, a process for obtaining the maximum value of the Doppler shift frequency or the maximum value thereof,
A process of setting a lower limit value of the repetition frequency based on the maximum one of the maximum values obtained for each of the Doppler shift distribution data;
A process of setting the repetition frequency to a value larger than the lower limit value and smaller than a predetermined upper limit value,
An ultrasonic diagnostic apparatus. A transmitter that transmits ultrasonic waves at a set repetition frequency while scanning the transmission direction;
A receiving unit that receives the ultrasonic waves transmitted from the transmitting unit and reflected in the subject, and outputs received data corresponding to the received ultrasonic waves;
A color Doppler operation unit that obtains Doppler shift distribution data on the scanning surface based on reception data sequentially output from the reception unit in accordance with scanning of transmitted ultrasonic waves;
A repetition frequency setting unit for setting the repetition frequency based on the Doppler shift distribution data obtained by the color Doppler calculation unit,
The Doppler shift distribution data is data in which a Doppler shift frequency or an equivalent amount thereof is associated with each observation position on the scanning plane,
The repetition frequency setting unit performs a repetition frequency setting process for setting the repetition frequency based on a plurality of the Doppler shift distribution data obtained for scanning over a plurality of times,
The repetition frequency setting process is executed when no aliasing phenomenon occurs in any of the plurality of Doppler shift distribution data obtained for a plurality of scans, and is obtained for a plurality of scans. Including a process of searching for the repetition frequency while performing a determination process for determining whether or not a folding phenomenon occurs in any of the plurality of Doppler shift distribution data,
The determination process includes
Based on the number of observation positions where the Doppler shift frequency or its equivalent amount is greater than or equal to a predetermined threshold among a plurality of observation positions whose Doppler shift frequency or its equivalent amount is indicated by the Doppler shift distribution data, the Doppler shift distribution data has a folding phenomenon. An ultrasonic diagnostic apparatus comprising: a process for determining that it has occurred. The ultrasonic diagnostic apparatus according to claim 2,
The process of searching for the repetition frequency includes:
Performing a repetition frequency reduction process for setting the repetition frequency to a value smaller than a previously set value, and the determination process after the repetition frequency reduction process,
When it is determined by the execution of the determination processing that no folding phenomenon has occurred in any of the plurality of Doppler shift distribution data, it is determined that there is a folding phenomenon among the plurality of Doppler shift distribution data. Until the repetition frequency reduction process and the determination process after the repetition frequency reduction process are repeatedly executed,
When it is determined by the execution of the determination process that there is an aliasing phenomenon among a plurality of the Doppler shift distribution data, the repetition frequency is set to a value before the repetition frequency reduction process performed together with the determination. Including processing to return
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to any one of claims 1 to 3,
The repetition frequency setting unit includes:
An initial determination process for determining whether or not a folding phenomenon occurs in any of the plurality of Doppler shift distribution data obtained by scanning a plurality of times after setting the repetition frequency to a predetermined upper limit value. Run,
When it is determined by the execution of the initial determination process that no aliasing phenomenon has occurred in any of the plurality of Doppler shift distribution data, the repetition frequency setting process is executed,
The initial determination process includes:
A process of determining whether or not a folding phenomenon occurs based on a comparison between a Doppler shift frequency at each observation position on the scanning plane or an equivalent amount thereof and a predetermined threshold indicated by the Doppler shift distribution data.
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 4,
The repetition frequency setting unit includes:
If it is determined by the execution of the initial determination process that a folding phenomenon occurs in any of the plurality of Doppler shift distribution data, the repetition frequency setting process is not performed, and the repetition frequency is maintained.
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 4 or 5,
The initial determination process includes:
Based on the number of observation positions where the Doppler shift frequency or its equivalent amount is greater than or equal to a predetermined threshold among a plurality of observation positions whose Doppler shift frequency or its equivalent amount is indicated by the Doppler shift distribution data, the Doppler shift distribution data has a folding phenomenon. An ultrasonic diagnostic apparatus comprising: a process for determining that it has occurred. The ultrasonic diagnostic apparatus according to any one of claims 1 to 6 ,
The scanning surface is a surface on which the heart or blood vessel of the subject is observed,
A plurality of scans on the scan plane are performed within a time corresponding to a predetermined number of heartbeats.
An ultrasonic diagnostic apparatus.

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