JP2007068731A - Ultrasonic diagnostic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily perform a tracking process using a plurality of ultrasonic beams. <P>SOLUTION: As for a beam #3 as a criterion of a plurality of ultrasonic beams 40, and a beam #2 as a related beam thereto, this apparatus detects a position on the beam #2 corresponding to a tracking point A3 of the beam #3 by specifying a partial echo signal string of the beam #3 based on the correlation between mutual partial echo signal strings and sets a tracking point A2 of the beam #2 at the detected position. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an ultrasonic diagnostic apparatus, and more particularly to an ultrasonic diagnostic apparatus that executes tracking processing using a plurality of ultrasonic beams.

  In an ultrasonic diagnostic apparatus, an echo tracking method for tracking a blood vessel wall or the like based on an echo signal obtained from an ultrasonic beam is known. By the echo tracking method, the displacement of the blood vessel wall or the like can be measured with an accuracy of about several μm below the wavelength of the ultrasonic wave (see Patent Documents 1 to 3).

  For example, in Patent Document 2, while observing a B-mode image of a blood vessel, tracking points are manually set on the blood vessel front wall side and the rear wall side on a specific ultrasonic beam, and the manually set front wall side In addition, an echo tracking method has been proposed in which the displacement of the blood vessel diameter is measured with high accuracy by tracking the tracking point on the rear wall side. By applying this technique, various blood vessel elasticity indices can be measured from changes in blood pressure and blood vessel diameter.

JP 2002-17728 A JP 2001-218768 A JP-A-2005-268

  When measuring the blood vessel diameter with one ultrasonic beam using the echo tracking method, the diameter of only a specific position of the blood vessel is measured. For this reason, for example, when obtaining an average elasticity index in a certain range along the blood vessel extension direction, it is necessary to measure the blood vessel diameter with a plurality of ultrasonic beams at different positions. In this case, it is troublesome to set a tracking start point for each ultrasonic beam.

  Incidentally, measurement software for obtaining a blood vessel diameter from a B-mode image is known in order to obtain an average elasticity index along the blood vessel elongation direction. However, in blood vessel measurement using B-mode image processing, the measurement accuracy is on the order of about 0.1 mm, so that the measurement accuracy is insufficient when the change in blood vessel diameter is small due to arteriosclerosis or the like.

  The present invention has been made in such a background, and an object of the present invention is to provide a technique for easily executing tracking processing using a plurality of ultrasonic beams.

  In order to achieve the above object, an ultrasonic diagnostic apparatus according to a preferred aspect of the present invention includes a transmission / reception unit that forms a plurality of ultrasonic beams and acquires an echo signal for each ultrasonic beam, and a plurality of ultrasonic units. A tracking point setting means for setting a tracking point of another ultrasonic beam based on a tracking point set as a reference beam of the acoustic beam, and a feature point of an echo signal corresponding to the tracking point for each ultrasonic beam. Tracking means for tracking, and the tracking point setting means for the reference beam and the related beam of the plurality of ultrasonic beams, from the correlation between the partial echo signal sequences of each other, the partial echo signal sequence of the reference beam By identifying the partial echo signal sequence of the related beam corresponding to, the position on the related beam corresponding to the tracking point of the reference beam Setting the tracking point of the associated beam detected position detecting, characterized in that.

  In the above configuration, tracking points of other ultrasonic beams are set based on the tracking points set for the reference beam. The initial position of the reference beam tracking point is set, for example, on the blood vessel wall by the user. In the ultrasonic diagnostic apparatus having the above configuration, for example, based on the tracking point of the reference beam set by the user, the apparatus automatically detects the position on the related beam corresponding to the tracking point, and the related beam is detected at the detected position. Set tracking points. For this reason, the user operation in the case of performing tracking processing using a plurality of ultrasonic beams is greatly simplified.

  In the ultrasonic diagnostic apparatus according to a preferred aspect, the tracking point setting means extracts the partial echo signal sequence of the related beam in a stepwise manner while moving along the related beam, and a predetermined position on the reference beam for each step. Calculating a cross-correlation value with a partial echo signal sequence of the reference beam, and identifying a partial echo signal sequence of the related beam corresponding to the partial echo signal sequence of the reference beam from a comparison of a plurality of cross-correlation values obtained in stages. Features.

  In the ultrasonic diagnostic apparatus according to a preferred aspect, the tracking point setting means extracts the partial echo signal sequence of the related beam in a stepwise manner while moving along the related beam, and a predetermined position on the reference beam for each step. Calculate the SAD (Sum of Absolute Difference) value with the partial echo signal sequence of and identify the partial echo signal sequence of the related beam corresponding to the partial echo signal sequence of the reference beam from the comparison of multiple SAD values obtained in stages It is characterized by.

  In order to achieve the above object, an ultrasonic diagnostic apparatus according to a preferred aspect of the present invention is a transmitter / receiver that forms a plurality of ultrasonic beams arranged in the direction of blood vessel extension and acquires an echo signal for each ultrasonic beam. A wave point, a tracking point setting unit for setting a tracking point of another ultrasonic beam based on a tracking point corresponding to a blood vessel wall set as a reference beam among a plurality of ultrasonic beams, and for each ultrasonic beam And an echo tracking means for detecting and tracking a zero-cross point of the echo signal corresponding to the tracking point.

  Moreover, in the ultrasonic diagnostic apparatus according to a preferred aspect, the tracking point setting unit is configured to determine a partial echo signal of the reference beam from a correlation between the partial echo signal sequences of the reference beam and the related beam among the plurality of ultrasonic beams. By identifying the partial echo signal sequence of the related beam corresponding to the sequence, the position on the related beam corresponding to the tracking point of the reference beam is detected, and the tracking point of the related beam is set to the detected position. And

  According to the present invention, it is possible to easily perform tracking processing using a plurality of ultrasonic beams.

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

  FIG. 1 shows a preferred embodiment of an ultrasonic diagnostic apparatus according to the present invention, and FIG. 1 is an overall configuration diagram thereof. The array probe 10 is an ultrasonic probe, and an ultrasonic probe used in contact with the body surface of the subject is preferable. Of course, an ultrasonic probe used by being inserted into the subject may be used. The array probe 10 forms an ultrasonic beam 40 toward the blood vessel 50 in the body of the subject. The array probe 10 is preferably a linear electronic scan probe (linear probe) that electronically scans the ultrasonic beam 40, but may use a method such as sector electronic scan. The blood vessel 50 to be diagnosed is, for example, the carotid artery.

  The transmission / reception unit 12 controls the array probe 10 to electronically scan the ultrasonic beam 40 within the tomographic plane (the cut surface of the blood vessel 50 shown in FIG. 1). When the array probe 10 is a linear probe, for example, 120 ultrasonic beams 40 (only five ultrasonic beams for echo tracking, which will be described in detail later) are electronically scanned one after another, An echo signal is acquired for each ultrasonic beam 40. The acquired plurality of echo signals are output to the tomographic image forming unit 18, and the tomographic image forming unit 18 forms a tomographic image (B-mode image) of the blood vessel 50 based on the plurality of echo signals. The formed tomographic image of the blood vessel 50 is displayed on the display 30 via the display image forming unit 28.

  The echo signal acquired by the transmission / reception unit 12 is also output to the echo tracking processing unit 20. The echo tracking processing unit 20 performs so-called echo tracking processing in which a signal portion corresponding to the blood vessel wall is extracted from each echo signal and tracked. For the echo tracking process, for example, a technique detailed in Japanese Patent Laid-Open No. 2001-309918 is used. For example, five tracking echo signals are used for the echo tracking process. The tracking echo signal may be selected from echo signals (for example, 120 echo signals) used for tomographic image formation, or five tracking echoes separately from the tomographic image forming beam. A signal may be formed.

  Each of the five ultrasonic beams 40 shown in FIG. 1 is a beam for acquiring a tracking echo signal. The inspector inputs an instruction regarding ultrasonic transmission / reception to the transmission / reception control unit 14 via the operation panel 16, and the transmission / reception control unit 14 controls the transmission / reception unit 12 based on the instruction of the inspector. Thereby, the ultrasonic beam 40 for acquiring the tracking echo signal is transmitted to the blood vessel 50 based on the instruction of the examiner.

  The blood vessel wall of the blood vessel 50 has a three-layer structure of an outer membrane, a middle membrane, and an inner membrane. In the case of performing echo tracking processing of a blood vessel wall, for example, the boundary between the media and the outer membrane becomes a tracking target. For this reason, the inspector sets a tracking start point (tracking point) at the boundary between the media and the outer membrane for one ultrasonic beam 40 serving as a reference while observing the B-mode image. The tracking point is set by the inspector via the operation panel 16.

  The echo tracking processing unit 20 dramatically improves the extraction accuracy by detecting a zero cross point as a feature point of each echo signal and tracking the zero cross point. The zero cross point is detected as the timing at which the polarity of the echo signal is inverted from positive to negative or from negative to positive in the vicinity of the set tracking point. When a zero cross point is detected, a tracking gate is set around that point. Next, in the echo signal acquired from the same part next time, the zero cross point is detected within the set tracking gate period. In this manner, the zero cross point is tracked as a blood vessel wall for each echo signal (for each ultrasonic beam 40).

  In the present embodiment, the tracking point of another ultrasonic beam 40 is automatically set by the apparatus based on the tracking point manually set for one ultrasonic beam 40 serving as a reference by the examiner. Accordingly, a tracking point setting process for a plurality of ultrasonic beams 40 will be described next. 1 are used in the following description as well.

  FIG. 2 is a diagram for explaining the tracking point setting process, and shows a B-mode image of the long-axis cross section of the blood vessel 50 in FIG. 1 and five ultrasonic beams 40 for echo tracking. The five ultrasonic beams 40 are arranged at substantially equal intervals in the extending direction of the blood vessel 50, and the distance between the beams # 1 and # 5 is, for example, about several centimeters.

  First, on the central beam # 3, the tracking point A3 on the front wall side and the tracking point P3 on the rear wall side of the blood vessel 50 are set manually. That is, the inspector manually sets the tracking point A3 and the tracking point P3 via the operation panel 16 while observing the B-mode image of the long-axis cross section of FIG. The position of the set point A3 and the position of the point P3 are stored in the apparatus. For example, it is stored in the memory 22.

  When the point A3 and the point P3 are set to the beam # 3, the tracking point setting unit 24 moves forward and backward from the position of each point on the beam # 3 with respect to the positions of the points A3 and P3 (beam The echo signal in the region of Δz is extracted as a partial echo signal sequence. The echo signal may be RF data before detection processing or detection data after detection processing. Thus, a partial echo signal sequence on the front wall side centered on the point A3 and a partial echo signal sequence on the rear wall side centered on the point P3 are extracted from the beam # 3.

  Next, the tracking point setting unit 24, on each of the beams # 2 and # 4 closest to the beam # 3, as a calculation start center point, points A2 ′ and P2 ′ on the beam # 2. And point A4 ′ and point P4 ′ are set on beam # 4. That is, with respect to the beam # 2, the points A2 ′ and P2 ′ are set as start center points at the same positions (the same positions in the beam depth direction) as the points A3 and P3 set for the beam # 3. Also, with respect to the beam # 4, the point A4 ′ and the point as the starting center point are located at the same position (same position in the beam depth direction) as the point A3 and the point P3 set for the beam # 3. P4 ′ is set.

  Next, the tracking point setting unit 24 extracts, from the beam # 2, the echo signal in the region Δz before and after (in the beam depth direction) Δz around the position of the point A2 ′ as a partial echo signal sequence on the front wall side. Then, the tracking point setting unit 24 calculates the correlation (similarity) between the partial echo signal sequence on the front wall side extracted from the beam # 3 and the partial echo signal sequence on the front wall side extracted from the beam # 2. To do. For the evaluation of the correlation, calculation of a cross correlation value or the like is used. Specific operations will be described in detail later.

  The calculation of the correlation is performed for each stage while shifting the position of the point A2 ′ set for the beam # 2 by δ. That is, the partial echo signal sequence of beam # 2 is extracted stepwise while moving along beam # 2, and the correlation between the partial echo signal sequences of beam # 3 and beam # 2 is determined for each step. Calculated. Thus, the partial echo signal sequence of the beam # 2 having the highest similarity with the partial echo signal sequence of the beam # 3 is detected from a plurality of correlation calculation results obtained in stages. The tracking point setting unit 24 sets the tracking point A2 on the front wall side of the beam # 2 at the center position of the partial echo signal sequence of the beam # 2 having the highest similarity.

  Further, the tracking point setting unit 24 extracts, from the beam # 2, an echo signal in the region Δz before and after (in the depth direction of the beam) around the position of the point P2 ′ as a partial echo signal sequence on the rear wall side. The tracking point setting unit 24 calculates a correlation (similarity) between the partial echo signal sequence on the rear wall side extracted from the beam # 3 and the partial echo signal sequence on the rear wall side extracted from the beam # 2. To do. The calculation of the correlation is performed at each stage while shifting the position of the point P2 ′ of the beam # 2 by δ. Thus, as in the case of the front wall side, the partial echo signal sequence of the beam # 2 having the highest similarity with the partial echo signal sequence of the beam # 3 from the calculation results of a plurality of correlations obtained in stages. Is detected, and the tracking point P2 on the rear wall side of the beam # 2 is set at the center position of the partial echo signal sequence of the beam # 2 having the highest similarity.

  The tracking point setting unit 24 sets a tracking point on the front wall side and a tracking point on the rear wall side for the beam # 4 in the same manner as in the case of the beam # 2. That is, a partial echo signal sequence on the front wall side centered on the position of the point A4 ′ is extracted from the beam # 4, and the correlation with the partial echo signal sequence on the front wall side extracted from the beam # 3 is stepped. The tracking point A4 on the front wall side of the beam # 4 is set at the center position of the partial echo signal sequence having the highest similarity. Further, a partial echo signal sequence on the rear wall side centered on the position of the point P4 ′ is extracted from the beam # 4, and the correlation with the partial echo signal sequence on the rear wall side extracted from the beam # 3 is stepped. The tracking point P4 on the rear wall side of the beam # 4 is set at the center position of the partial echo signal sequence having the highest similarity.

  Thus, based on the front wall-side echo tracking point A3 and the rear wall-side echo tracking point P3 manually set by the inspector with respect to the beam # 3, the tracking point setting unit 24 performs the front-side echo tracking point P3 with respect to the beam # 2. The echo tracking point A2 on the wall side and the echo tracking point P2 on the rear wall side are automatically set, and the echo tracking point A4 on the front wall side and the echo tracking point P4 on the rear wall side are automatically set for the beam # 4. .

  The tracking point setting unit 24 sets a tracking point on the front wall side and a tracking point on the rear wall side for the beam # 1 and the beam # 5 in the same manner as in the case of the beam # 2 and the beam # 4. . That is, for beam # 1, a partial echo signal sequence is extracted from each of beam # 1 and beam # 3 with reference to the positions of points A3 and P3 set for beam # 3, and beam # 1. The partial echo signal sequence of beam # 3 is moved stepwise, the correlation with the partial echo signal sequence of beam # 3 is calculated, and the partial echo signal sequence having the highest similarity is detected. A tracking point A1 on the wall side and a tracking point P1 on the rear wall side are set. Similarly, a tracking point A5 on the front wall side and a tracking point P5 on the rear wall side of the beam # 5 are set by comparison with the partial echo signal sequence of the beam # 3.

  Thus, based on the front wall-side echo tracking point A3 and the rear wall-side echo tracking point P3 manually set by the inspector with respect to the beam # 3, the tracking point setting unit 24 uses the beam # 1 and the beam # 2. For each of beam # 4 and beam # 5, the front wall side echo tracking points (A1, A2, A4, A5) and the rear wall side echo tracking points (P1, P2, P4, P5) are automatically set. To do.

  The tracking points of beam # 1 and beam # 5 may be set with reference to the tracking points of beam # 2 and beam # 4. That is, with respect to the beam # 1, the points A1 ′ and P1 ′ are set as start center points at the same positions (the same positions in the beam depth direction) as the points A2 and P2 set for the beam # 2. The partial echo signal sequence is extracted from each of the beam # 1 and the beam # 2 for each of the front wall side and the rear wall side, and the partial echo signal sequence of the beam # 1 is moved stepwise while being set. By calculating the correlation with the partial echo signal sequence of # 2, and detecting the partial echo signal sequence having the highest similarity with the partial echo signal sequence of beam # 2, the front wall side of beam # 1 The tracking point A1 and the tracking point P1 on the rear wall side may be set.

  Similarly, with respect to the beam # 5, the points A5 ′ and P5 ′ are set as the starting center points at the same positions (the same positions in the beam depth direction) as the points A4 and P4 set for the beam # 4. And for each of the front wall side and the rear wall side, a partial echo signal sequence is extracted from each of the beams # 4 and # 5, and the partial echo signal sequence of the beam # 5 is moved stepwise. By calculating the correlation with the partial echo signal sequence of beam # 4 and detecting the partial echo signal sequence having the highest similarity with the partial echo signal sequence of beam # 4, the front wall of beam # 5 is detected. The tracking point A5 on the side and the tracking point P5 on the rear wall side may be set.

  It should be noted that the tracking point such as the beam # 2 that has been automatically set may be determined whether or not the tracking point that has been automatically set is adopted after the inspector finally confirms its position on the image. .

Next, calculation of correlation (similarity) between partial echo signal sequences will be described. For the correlation calculation, for example, a cross-correlation function is used. Let x (n) be an echo signal in the vicinity of the tracking point of the reference beam (for example, a partial echo signal string on the front wall side of beam # 3 in FIG. 2). When this signal and a related beam signal (for example, a partial echo signal sequence on the front wall side of beam # 2 in FIG. 2) are y (n), the cross-correlation function is defined by the following equation.
Here, L is a time shift amount (shift amount in the beam depth direction), and is calculated using data in a range of −N to N. The greater the cross-correlation value r _xy (L) obtained by Equation 1, the higher the similarity between both signals x (n) and y (n). By changing L, that is, by moving the partial echo signal sequence of the related beam (for example, beam # 2) stepwise, calculating the cross-correlation value and searching for the maximum L, the highest similarity is obtained. A partial echo signal sequence can be detected.

Note that multiplication is used in the cross-correlation function, but in general, multiplication is computationally expensive. In order to reduce this load, SAD (Sum of Absolute Difference) defined by the following equation may be used when evaluating the similarity between both signals x (n) and y (n).
SAD represents the sum of the absolute values of the differences between the two signals. The smaller the SAD, the higher the similarity. In other words, the partial echo signal sequence having the highest similarity can be detected by calculating SAD while changing L and searching for L having the minimum value. Since SAD is subtraction and absolute value calculation, the amount of calculation is small compared to the calculation using the cross-correlation function, and it is suitable for high-speed calculation of large data.

  Returning to FIG. 1, when the tracking point setting unit 24 sets the tracking points of the five echo tracking ultrasonic beams 40, the echo tracking processing unit 20 sets the blood vessel 50 for each ultrasonic beam 40. The front and rear walls are tracked. Thereby, the blood vessel diameter which is the distance between the front wall and the rear wall is measured for each ultrasonic beam 40. The measurement result of the blood vessel diameter is supplied to the averaging calculation unit 26 via the memory 22.

  The averaging calculation unit 26 averages the measurement results of the blood vessel diameter obtained from each of the five ultrasonic beams 40 having different spatial positions, and, for example, the five ultrasonic beams 40 are formed based on the average result. An average blood vessel diameter change waveform of the region thus formed is formed. That is, a change waveform indicating a time change with respect to the average value of the blood vessel diameter obtained from the five ultrasonic beams 40 is formed.

  The average blood vessel diameter change waveform is displayed on the display 30 via the display image forming unit 28. For example, the display image forming unit 28 forms a display image in which a B-mode image including the blood vessel 50 and an average blood vessel diameter change waveform related to the blood vessel 50 are simultaneously displayed and displayed on the display 30. The averaging calculator 26 may calculate various vascular elasticity indices from the average vascular diameter and blood pressure data.

  The preferred embodiment of the present invention has been described above. However, according to the above-described embodiment, the displacement of the average blood vessel diameter in a certain spatial region can be obtained. Since variations in spatial blood vessel diameter are averaged, variations in measurement results and the like are reduced. Further, the cross-correlation method estimates the tracking point of the related beam close to the echo characteristic of the tracking point of the reference beam set manually, and the tracking point on a plurality of beams can be automatically set. For this reason, the operation by the inspector becomes simple. In addition, since the echo tracking method is used, the displacement of the blood vessel wall is measured with extremely high accuracy on the order of several μm.

  The above-described embodiments are merely examples in all respects, and do not limit the scope of the present invention. For example, in the above-described embodiment, a blood vessel is a diagnosis target, but the ultrasound diagnostic apparatus of FIG. 1 may be used when tracking the surface of a bone with a plurality of ultrasound beams. Further, the number of beams is not limited to five, and the beam interval is not limited to an equal interval.

1 is a block diagram showing an overall configuration of an ultrasonic diagnostic apparatus according to the present invention. It is a figure for demonstrating the setting process of a tracking point.

Explanation of symbols

  20 echo tracking processing unit, 24 tracking point setting unit, 26 averaging calculation unit.

Claims (5)

A wave transmitting / receiving means for forming a plurality of ultrasonic beams and obtaining an echo signal for each ultrasonic beam;
Tracking point setting means for setting a tracking point of another ultrasonic beam based on a tracking point set as a reference beam among a plurality of ultrasonic beams;
Tracking means for tracking feature points of the echo signal corresponding to the tracking points for each ultrasonic beam;
Have
The tracking point setting means includes a partial echo signal sequence of a related beam corresponding to a partial echo signal sequence of the reference beam from a correlation between the partial echo signal sequences of the reference beam and the related beam of the plurality of ultrasonic beams. By detecting the position on the related beam corresponding to the tracking point of the reference beam, the tracking point of the related beam is set at the detected position.
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 1,
The tracking point setting means extracts the partial echo signal sequence of the related beam in stages while moving along the related beam, and calculates a cross-correlation value with a partial echo signal sequence at a predetermined position on the reference beam for each step. Calculating and identifying a partial echo signal sequence of the related beam corresponding to the partial echo signal sequence of the reference beam from a comparison of a plurality of cross-correlation values obtained in stages;
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 1,
The tracking point setting means extracts the partial echo signal sequence of the related beam in a stepwise manner while moving along the related beam, and performs SAD (Sum of Sum of the partial echo signal sequence of a predetermined position on the reference beam for each step (Absolute Difference) value is calculated, and the partial echo signal sequence of the related beam corresponding to the partial echo signal sequence of the reference beam is identified from a comparison of a plurality of SAD values obtained in stages.
An ultrasonic diagnostic apparatus. A wave transmitting / receiving means for forming a plurality of ultrasonic beams arranged in the direction of blood vessel elongation and acquiring an echo signal for each ultrasonic beam;
Tracking point setting means for setting a tracking point of another ultrasonic beam based on a tracking point corresponding to a blood vessel wall set as a reference beam among a plurality of ultrasonic beams;
Echo tracking means for detecting and tracking the zero cross point of the echo signal corresponding to the tracking point for each ultrasonic beam;
Having
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 4,
The tracking point setting means includes a partial echo signal sequence of a related beam corresponding to a partial echo signal sequence of the reference beam from a correlation between the partial echo signal sequences of the reference beam and the related beam of the plurality of ultrasonic beams. By detecting the position on the related beam corresponding to the tracking point of the reference beam and setting the tracking point of the related beam at the detected position,
An ultrasonic diagnostic apparatus.