JP2008142568A - Ultrasonic diagnostic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic diagnostic apparatus which can objectively, quantitatively, noninvasively, and, further, easily present contraction and expansion functions of cardiac muscles etc. in high accuracy. <P>SOLUTION: The ultrasonic diagnostic apparatus includes a transmission-reception means to scan a subject by ultrasonic waves to obtain reception signals, a means to form ultrasonic images based on the reception signals, a means to calculate motion velocity of tissue coupled to a plurality of points on the ultrasonic image based on the reception signals, a means to extract an area of a site of the heart on the ultrasonic image, a means to correct the motion velocity according to a direction along the outline of the extracted site of the heart, and a means to calculate an index representing contraction-expansion functions of the site of the heart based on the difference of the corrected motion velocity between two points in the plurality of points. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an ultrasonic diagnostic apparatus and an ultrasonic image processing apparatus that estimate the velocity of a living tissue such as a myocardium and process the estimated velocity information to provide information useful for medical diagnosis.

  Objective and quantitative evaluation of the motor function of the heart, that is, the heart function, is very important for the diagnosis of heart disease. Quantitative evaluation methods include left ventricular wall motion analysis method and stress echo method. However, these methods are specialized for ischemic heart disease and are not versatile.

  Further, the left ventricular wall motion analysis method is a method of measuring a temporal change in the wall thickness of the myocardium accompanying the contraction or expansion motion of the heart as an index representing cardiac function, and is not objective. In addition, the left ventricular wall motion analysis method cannot measure extension or contraction in the longitudinal direction of the heart or in the direction along the endocardium or epicardium.

  There is a method called segment shortening as a method to solve such a problem. This method directly embeds several crystals, which are strong ultrasonic reflectors, into the myocardium and changes the distance between the strong reflectors to improve the cardiac function. However, this method is currently limited to animal experiments and is considered impossible to apply to the human body due to its high invasiveness. In other words, at present, it can be said that there is no method for measuring an index related to cardiac function with high accuracy in a non-invasive manner with respect to the human body with the same accuracy as the segment shortening method.

  Also, when calculating an index for evaluating cardiac function, it is important to determine the direction of expansion and contraction of the heart. Since this stretch direction varies depending on the parts of the heart, in order to measure them throughout the heart, all the stretch directions must be set manually for each part of the heart, which is time and labor intensive. It is not practical from the viewpoint.

  An object of the present invention is to provide an ultrasonic diagnostic apparatus and an ultrasonic image processing apparatus that can objectively, quantitatively, non-invasively and easily present a contraction or expansion function of a local myocardium or the like with high accuracy. There is.

  The present invention relates to transmission / reception means for scanning a subject with ultrasonic waves to obtain a reception signal, means for generating an ultrasonic image based on the reception signal, and a plurality of points of the ultrasonic image based on the reception signal. Means for obtaining the motion speed of the tissue; means for extracting a region of the heart part on the ultrasound image; means for correcting the motion speed according to a direction along the contour of the extracted heart part; Means for calculating an index representing a contraction-expansion function of the cardiac region based on the corrected difference in motion speed between two points.

  According to the present invention, for example, an index relating to the motor function of the heart can be easily and objectively and quantitatively evaluated over the entire left ventricle, and information useful for diagnosis can be provided.

  Hereinafter, the present invention will be described by way of preferred embodiments with reference to the drawings. FIG. 1 shows the configuration of the ultrasonic diagnostic apparatus according to the present embodiment. The clock pulse output from the clock pulse generator 5 is frequency-divided by the rate pulse generator 4 to become a rate pulse, which is sent to the transmission pulse generator 2 through the transmission delay circuit 3 as a trigger. The transmission pulse generator 2 repeatedly applies a short pulse voltage having a certain center frequency f0 to the probe 1 having an array transducer in synchronization with the rate pulse. The transmission / reception cycle is given by the reciprocal of the rate frequency. The transmission delay circuit 3 controls the timing of the transmission pulse voltage applied to the plurality of vibration elements, changes the direction of the ultrasonic beam, and focuses the beam. This is hereinafter referred to as beam forming.

  An ultrasonic pulse radiated from the probe 1 into the body and reflected at the boundary of the acoustic impedance of the body tissue is received by the same probe 1. This received signal is input to the mixer 9 through the preamplifier 6 and the reception delay circuit 7. The reception delay circuit 7 is for performing beam forming in the same manner as the transmission delay circuit 3. The received signal input to the mixer 9 is frequency-divided from the clock pulse generator 5 and multiplied by the reference signal supplied from the reference signal generator 8, further detected through the low-pass filter 12, and the analog-digital converter (A / A). D) is converted into a digital signal by 16. The output signal of the analog-digital converter 16 is supplied to the imaging circuit 13 to become amplitude information, and further generated by the digital scan converter (DSC) 14 into at least one of a B-mode image and an M-mode image and displayed on the CRT display 15. Is done.

  The output signal of the analog-digital converter 16 is also supplied to the velocity calculation unit 17, where a plurality of sample points (hereinafter simply referred to as “points”) within the scanning range of the ultrasonic beam according to the tissue Doppler imaging method. The velocity relating to the tissue motion such as the myocardium in each is calculated, and this velocity information is generated into a two-dimensional velocity distribution (tissue Doppler image) by the digital scan converter 14 and displayed on the CRT display 15 in color.

  On this image, the “speed correction direction” or “region of interest” is set by the operation of the input unit 11 by the operator. In this region of interest, and based on the velocity obtained by tissue Doppler imaging, the index calculation unit 18 calculates an index that can be a material for determining normality / abnormality of the function of tissue movement such as the myocardium. The index is displayed on the CRT display 15 via the DSC 14.

  By the way, the components for generating a tissue Doppler image mainly excluding some functions of the input unit 11, the index calculation unit 18 and the CPU 10 are already implemented and put into practical use, and details thereof are omitted. The characteristic portions of the present invention will be described in detail below.

  FIG. 2A is a schematic diagram of a long-axis tomogram (tissue morphological image) of the left ventricle of the heart obtained by the apex approach. It is assumed that a two-dimensional velocity distribution (tissue Doppler image) of the myocardial tissue on this tomography is obtained by tissue Doppler imaging (TDI) at the same time that this long-axis tomographic image is taken by an ultrasonic diagnostic apparatus.

  Here, as an index to be obtained, it is required to be effective in the diagnosis of the cardiac stretch function, and has the same significance in clinical diagnosis as the segment shortening that has been confirmed to be effective in animal experiments and the like. It is desirable. In other words, if the myocardium is contracted or expanded in a certain direction on the long-axis tomographic image, the index to be obtained is a non-zero value, the sign of the index value represents contraction or expansion, and the magnitude of the index value is It is preferable to reflect the degree (degree) of contraction and extension. As an index satisfying such a requirement, for example, a speed difference, a speed gradient, a speed differential, a speed difference, and the like can be considered.

  What is important in calculating this index is how to estimate the expansion / contraction direction handled in the calculation. This is because the closer the direction is to the true expansion / contraction direction of the myocardium, the better the accuracy of the index. In this embodiment, this expansion / contraction direction is estimated based on the outline of the left ventricle of the heart.

  First, on the long-axis tomographic image of the left ventricle, the operator manually traces the outline of the myocardium using the input device 11 such as a trackball. The contour trace of the myocardium may be traced between the intima and adventitia, or, as a simpler method, when the operator designates only a few points on the intima and adventitia discretely, these points are You may make it connect by a straight line or a curve approximation. Further, as a completely automated method, the boundary between the heart chamber and the myocardium may be extracted based on the luminance gradient using a method such as the ACT method. The region limited by this trace is treated as the region of interest 19 (FIG. 2B).

  Next, the index calculation unit 18 sets a direction along the inner membrane 20 (or outer membrane) of the left ventricle, for example, a tangential direction, at each point on the inner membrane 20 based on the region of interest. Then, the index calculation unit 18 corrects the angle of the speed data of each point in the region of interest as follows in order to obtain the speed related to the set direction, that is, the true or near speed related to the expansion and contraction of the myocardium at each point. . As is well known, in the Doppler method, not only TDI but also measured velocity data is given as an ultrasonic beam direction component of a true velocity. Therefore, as shown in FIG. 2C, the velocity data V of the point 21 on the intima line 20 is converted into a vector 22 in contact with the local intima curve at the point 21 and a vector representing the direction of the ultrasonic beam. The angle is corrected by “V / cos θ” using the angle (θ) 24 formed by the head 23.

  As shown in FIG. 2D, the angle correction related to the point 25 inside the region of interest (myocardial portion) that is not on the intima line 20 is performed by the perpendicular line drawn toward the intima line 20 and the intima line Applying the direction set at the intersection 26 with 20 and using the angle 29 between the vector 27 in that direction and the vector 28 representing the direction of the ultrasonic beam at the point 25, the speed of the internal point 25 is Similarly, the angle is corrected.

  Next, angle correction and index calculation methods will be described. As shown in FIG. 2E, two points in the region of interest are A and B, respectively. Velocity data before angle correction of each point is set as VA and VB, and a position vector of B with A as the origin is set as a vector AB. Furthermore, the angles formed by the vectors AB and B from the points A and B and the vector AB are θA and θB. The index calculation unit 18 calculates, for example, a velocity gradient as an index using the following formula.

  Velocity gradient = (VB / cos θB−VA / cos θA) / | AB | The difference in velocity between points A and B is given as part of the numerator of this equation. As is well known, the speeds VA and VB are given positive if each point moves in a direction approaching the probe, and given negative if they move in a direction away from the probe. Therefore, the velocity gradient is given as positive if the myocardium is stretched between two points AB, and is given as negative if it is contracted, and the rate of expansion / contraction is given as a value.

  If this calculation is performed between two adjacent points, it can be taken as a speed difference, and if the distance between two adjacent points is very small, it can be taken as a speed differential. Further, the velocity gradient may be obtained as the gradient by performing a straight line fitting by the least square method from the profiles of velocity data corrected for all two angles. The sign of the index thus obtained can be used to determine whether the tissue is contracting or expanding, and the degree of contraction or expansion can be determined from the size of the index value.

  The index may be obtained at each point in the region of interest, but as shown in FIG. 3, the region of interest is divided into a plurality of minute regions, and one index is obtained for each divided region. good. The minute regions may overlap each other. As shown in FIG. 3A, the region of interest may be divided by dividing a plurality of perpendiculars at equal intervals with respect to the intima and dividing the region of interest by the perpendiculars. As shown in FIG. 5, a plurality of perpendicular lines may be drawn at equal intervals with respect to the major axis, and the region of interest may be divided by the perpendicular lines. Further, as shown in FIG. 3 (c), it may be divided into regions (segments) recommended by ASE (American Society of Echocardiography) and calculated for each region.

  In this way, when the region of interest is divided, it is conceivable that the index is obtained from the average value of the velocities at a plurality of points in each divided region according to the above-described formula. The effect that noise can be removed can be expected.

  In addition to the tangential direction of the myocardial intima (or outer membrane) as described above, the index calculation direction may be unified in parallel with the long axis direction of the heart at all points. In any case, in the speed estimation by TDI in the apex approach or transesophageal approach, measurement with a small Doppler angle and high accuracy can be expected.

  The speed data of the point 26 on the intima line may be represented by taking an average value or the like of a plurality of speed data whose angles are corrected on the vertical line 30, and the region of interest is not limited to the myocardium. The film may be a membrane or an outer membrane, and the velocity data in that case may be data on or near the inner membrane line or the outer membrane line.

  As a display method of the index calculated by the calculation processing unit 18, as shown in FIG. 4A, when a two-dimensional distribution (index map) of the index is displayed in color with a hue corresponding to the value, Easy to understand spatial changes. The color display method is, for example, red when the myocardium contracts in a direction in contact with the inner membrane or the like, and blue when it expands. Various methods such as coloring according to the absolute value of the index are conceivable. It is also important to display the index value itself directly with the numerical value 38. The color display or numerical display may be displayed over the region of interest on the image, but may be displayed in another part.

  Ideally, the index is preferably calculated with sufficient accuracy for all parts on the tomographic image, but the angle between the index calculation direction (speed correction direction) and the ultrasonic beam direction is vertical. Since the angle correction error becomes large at a portion that is close to a predetermined angle or more, such a portion is detected by the index calculation unit 18 and displayed as a non-measurable area 39 in a color different from the index color, or It is desirable not to add an index color. By doing this, it is possible to avoid the risk of misdiagnosis from a portion that may contain a large error. As shown in FIG. 3, when a region of interest is divided and there is a non-measurable region in a certain divided region, the index of the divided region is obtained from the velocity data of points in a range excluding that portion. Calculate it.

  So far, two-dimensional evaluation of cardiac function has been described. In the apex approach or the transesophageal approach, as shown in FIG. 5, if a plurality of tomographic images 41 are collected while rotating the probe 1 around the long axis of the left ventricle, for example, morphological information and velocity throughout the heart Information can be collected. Alternatively, the tomographic plane may be scanned in a fan shape, or a plurality of tomographic images may be collected while being translated. By calculating indices on the acquired tomographic images and interpolating between the tomographic images, local cardiac function information (index) can be obtained over the entire heart.

  Of course, the index may be calculated after interpolation of the speed data. If the information of the entire left ventricle thus obtained is displayed as a normal three-dimensional image as shown in FIG. 6 and an arbitrary cross section can be cut out, for example, which infarct site is It can be easily grasped three-dimensionally whether it has a degree of expansion.

  In addition, as shown in FIG. 7 (a), a pulls eye map used in nuclear medicine, that is, a development view as seen from the viewpoint inside the heart, can be displayed. Information can be displayed at once.

  In addition, as shown in FIG. 7B, if the index for each divided region is displayed in a bull's eye map, the cardiac function can be determined for each dominant region of each coronary artery. In the boundary portion where the cardiac function is lowered, it is expected that the index value of each divided region is affected by the way of setting the divided region. Therefore, the index map obtained without dividing the area and the obtained index map obtained by dividing the area are displayed together or are displayed simultaneously in parallel as shown in FIG. Is displayed as a guide, the dividing line 44 is linked, and if one of them is moved, the other can be moved accordingly. At this time, it is desirable to recalculate and display the index of each divided area in real time in accordance with the movement of the dividing line 44.

  As described above, based on the myocardial contour, it has been explained that the index is calculated with respect to the direction in contact with the endocardium or epicardium. However, after setting the region of interest, the tangential direction in contact with the intimal contour is completely It can be automated, and the labor of the operator can be greatly reduced.

  On the other hand, in the case of a short-axis tomogram of the heart, it is conceivable to calculate an index related to the wall thickness change by angle-correcting the measurement speed in the direction from each point of the myocardium toward the center of gravity of the short-axis tomogram. . Hereinafter, this method will be described.

  FIG. 8A is a schematic diagram of a short-axis tomogram of the left ventricle of the heart. It is assumed that this is displayed on the CRT display 15. First, the intima 45 of the myocardium of the left ventricular short-axis tomogram is traced by the operation of the input instrument 11 by the operator (FIG. 8B). The tracing method may be to trace the intima, or as a simpler method, if the operator specifies only a few points discretely on the intima, the points are connected by a straight line or a curve approximation You may make it connect with. Further, as a completely automated method, the boundary between the heart chamber and the myocardium may be extracted based on the luminance gradient using a method such as the ACT method. The outer membrane 46 is traced in the same manner as the inner membrane. Alternatively, a curve away from each point on the intima by a certain distance may be used as the outer membrane, or the similarity of the intima shape may be enlarged.

  When the intima and adventitia are traced in this way, the index calculation unit 18 calculates the position of the center of gravity from the contour coordinates of the intima or adventitia, or from the area center of gravity of the myocardial part surrounded by the intima and adventitia The center of gravity 47 is specified (FIG. 8C). At each point of the myocardium that is the region of interest, an index calculation direction is set in the direction 48 toward the center of gravity, and calculation is performed (FIG. 8D).

  Furthermore, when dividing the region of interest into segments recommended by ASE, it is possible to automatically draw the dividing line 49 in multiple regions of interest by drawing the dividing lines 49 radially around the center of gravity. Thus, the operator's trouble can be saved (FIG. 8 (e)). When calculating the index in the thickness direction of the myocardium, a direction 50 perpendicular to the intima curve may be obtained for each portion of the traced intima as shown in FIG. After setting the direction, the speed difference, speed gradient, speed differential, and speed difference may be calculated. In this case, these indicators are related to the wall thickness change rate.

  As described above, when calculating the index indicating tissue contraction / extension, using the contour information of the region of interest, setting the calculation direction, dividing the region of interest, etc., the operator's operation sets the region of interest. Thus, it is possible to measure the index very easily and more accurately. In addition, if the index calculation direction is displayed at any point in the region of interest when necessary and can be adjusted, the operator can confirm and change the direction set by the index calculation unit 18. . After the change, the index calculation unit 18 again performs angle correction and index calculation based on the changed direction.

  As shown in FIG. 9, the setting of the region of interest and the calculation and display of the index are separated from the ultrasonic diagnostic apparatus by a computer 51 such as a PC or a workstation equipped with the function of the measurement processing unit of FIG. You can go. Data such as a tomographic image and a two-dimensional velocity distribution output from the DSC 14 may be sent to the computer 51, and the calculated result may be displayed on a monitor attached to the computer or may be displayed on the CRT 15 of the diagnostic apparatus. The present invention is not limited to the above-described embodiment, and can be implemented with various modifications.

1 is a block diagram of an ultrasonic diagnostic apparatus according to a preferred embodiment of the present invention. (A) is a diagram showing a long-axis tomographic image of the heart obtained by an apex approach, (b) is a diagram showing a region of interest set by manual or automatic myocardial tracing, and (c) is a point on a point on the myocardium. An explanatory diagram of angle correction, (d) is an explanatory diagram of angle correction regarding a point inside the myocardium, and (e) is an explanatory diagram of a method of calculating an index such as a velocity gradient between two points. (A) is a diagram showing a region of interest divided by the first method, (b) is a diagram showing a region of interest divided by the second method, and (c) is a diagram showing a region of interest divided by the third method. . (A) is a display example of the index map calculated for each point, (b) is a diagram showing a display example of the index map calculated for each divided region. The figure which shows the example of the three-dimensional scanning by the apex approach. The figure which shows the example of a display of the three-dimensional image of a parameter | index. (A) is a diagram showing a bullseye map display example of a 3D image of an index calculated for each point, (b) is a diagram showing a bullseye map display example of a 3D image of an index calculated for each divided region, (c) FIG. 4 is a diagram showing an example of simultaneous display of a bullseye map image of an index calculated for each point and each divided region. (A) is a diagram showing a short-axis tomogram of the left ventricle of the heart, (b) is a diagram showing a trace of the intima of the left ventricle of the heart, and (c) is a trace of the epicardium of the heart left ventricle and the center of gravity of the short-axis cross section. (D) is a diagram showing the calculation direction of the stretch index centered on the center of gravity, (e) is a diagram showing a method of dividing the region of interest radially from the center of gravity, and (f) shows the direction of the myocardial thickness. Figure. The block diagram regarding the modification of this invention.

Explanation of symbols

1 ... probe,
2 ... Pulse generator,
3 ... transmission delay circuit,
4 ... Rate pulse generator,
5 ... Clock generator,
6 ... Preamp,
7: Reception delay circuit,
8: Reference signal generator,
9 ... Mixer,
10 ... CPU,
11 ... Input device,
12 ... Low-pass filter,
13: Imaging circuit,
14 ... Digital scan converter,
15 ... CRT display,
16: Analog to digital converter,
17 ... speed calculation part,
18: Index calculation unit,
51. Computer.

Claims (11)

Transmitting and receiving means for scanning a subject with ultrasound to obtain a received signal;
Means for generating an ultrasound image based on the received signal;
Means for determining a tissue motion speed for a plurality of points of the ultrasound image based on the received signal;
Means for extracting a region of the heart part on the ultrasound image;
Means for correcting the speed of motion according to a direction along a contour of the extracted heart portion;
An ultrasonic diagnostic apparatus comprising: means for calculating an index representing a contraction / expansion function of the cardiac region based on the corrected difference in motion speed between two points of the plurality of points. Means for inputting ultrasonic image data of a subject and movement speed data of a tissue related to a plurality of points of the ultrasonic image;
Means for extracting a region of the heart part on the ultrasound image;
Means for correcting the movement speed according to a direction according to an outline of the extracted heart part;
Means for calculating an index representing a contraction / expansion function of the cardiac region based on the corrected difference in motion speed between two points of the plurality of points. . 3. The apparatus according to claim 1, wherein the correction unit sets the direction along the endocardium or epicardium on a tomographic image of the heart. The apparatus according to claim 1, further comprising means for displaying an angle formed by the direction and the ultrasonic beam. 3. The apparatus according to claim 1, further comprising means for displaying an angle formed by the direction and the ultrasonic beam in a color superimposed on the heart region. The apparatus according to claim 1, further comprising index display means for displaying the index calculated by the index calculation means over a plurality of positions in two dimensions or three dimensions. The apparatus according to claim 6, wherein the index display means displays the index in a color corresponding to an index value. 3. The apparatus according to claim 1, wherein the index calculating means includes means for dividing the region of the heart region into a plurality of divided areas, and calculates the index for each of the divided areas. . The apparatus according to claim 8, wherein the correction unit sets the direction one by one for each divided region. 3. The apparatus according to claim 1, wherein the correction unit calculates an index representing a contraction / expansion function of the cardiac region based on the corrected average of the motion speed. The apparatus according to claim 1, wherein the calculation unit calculates the index based on a distance between two points along a contour of a part of a heart image in the plurality of points.

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