ULTRASONIC BLOOD FLOW IMAGING METHOD AND APPARATUS

Abstract: An ultrasonic blood flow imaging method for two-dimen­ sionally displaying the velocity distribution of a blood flow with­ in a body to be examined is characterized in that the velocity distribution is displayed as a color picture in which the velocity direction is represented by one color when positive and by an­ other different color when negative, and the magnitude of the velocity is represented by varying the brightness of the color concerned. An ultrasonic imaging apparatus for carrying out this method comprises an ultrasonic transmitter/receiver which outputs a tomographic image signal corresponding to a specific region of an object, and an average velocity signal and a velocity deviation signal corresponding to the velocity of blood flow within the specified region. These signals are stored in respective frame memories and then processed by a color processor to produce a color video signal which is input to a color display for displaying a tomographic image, and the ve­ locity and velocity deviation of the blood flow.

Description: This invention relates to an ultrasonic blood flow imaging method and apparatus. An ultrasonic blood flow imaging method and apparatus are known from the U.S.-A-4,205,687. Although this known method and apparatus show an improved displaying of the blood flow velocities, this prior art has the disadvantage that all normal and increased blood flow peak velocity ranges are displayed as a discrete color. Such a displaying however, causes difficulties in showing the essential characteristics of the velocities, for example, as a positive or negative velocity. Therefore, essential characteristics of the blood flow velocity can only be analyzed by persons who are very familiar with this known method and apparatus. Other ultrasonic imaging methods are known wherein an ultrasonic wave beam directed into an object to be examined and an image is formed using the reflected echo produced as a result of differences in acoustic impedance within the object. These methods are advantageous in that they make it possible to observe the interior of an object without adversely affecting its structural make-up and are therefore used, for example, in diagnostic examination of afflicted tissues and organs in humans. These methods have been applied in ultrasonic diagnostic apparatuses and the like. A more sophisticated utilization of ultrasonic waves developed in recent years is the pulse doppler method, wherein the doppler effect that arises when an ultrasonic pulse beam strikes blood flow in a body to be examined is used to determine the velocity of the blood flow. This method has been successfully applied in, for example blood flow velocity meters. Although this velocity distribution has conventionally been displayed as a black-and-white image, it has, with the devices used for this purpose, been difficult to represent the two-dimensional distribution accurately. Thus proposals have been made to improve the situation by use of a color imaging method. The principle of the conventional imaging method is shown in FIG. 1. When the signal representing the movement of the blood flow varies periodically as shown in the figure, six colors (a, b, c, d, e and f) are assigned one each for six velocity bands in the positive direction and six colors (h - m) are assigned for six velocity bands in the negative direction. In this way, colors can be displayed to correspond to the velocity distribution. This conventional system has the advantage to making it possible to judge the velocity distribution at a glance from the colors displayed. On the other hand, however, althrough this conventional method provides a very clear picture when the velocity of the blood flow remains constant, it has the disadvantages that the colors mix to produce a picture that is hard to read when the velocity and the direction of the blood flow repidly vary, especially in blood flow of heart. This method is also disadvantageous in a case like that shown in FIG. 2 where the change with time is not regular and local portions exhibit large deviations within the overall blood flow movement, since in such cases the colors mix throughout the picture making it difficult to read the picture and almost totally impossible to interpret those portions where the positive and negative directions of blood flow are intermingled. US-A-4318413 discloses an ultrasonic apparatus according to the preamble of claim 3 and using a method according to the preamble of claim 1. This ultrasonic diagnostic apparatus is able to supply a first signal for obtaining tomographic image information and second signal for obtaining blood flow information. The tomographic information is obtained by a B mode scanning to read out doppler signals and image obtained by displaying these signals indicate the blood flow velocity information in a state of the displayed tomogram. The tomogram is intended to be modulated and displayed with bright color and different colors are associated to positive and negative directions of the blood flow. However this ultrasonic apparatus is not able to provide and display a deviation signal to the blood flow velocity information and to the tomographic image information in an easily recognizable manner. The object of the present invention is to provide an improved ultrasonic blood flow imaging method and apparatus which are capable of producing a two-dimensional color display of velocity distribution of blood flow that is exceedingly easy to read. This object of the present invention is attained by providing an ultrasonic blood flow imaging method and apparatus as set out in independent claims 1 and 3. In the drawings FIGS. 1 and 2 are diagrams for explaining conventional color display systems. FIG. 3 is a block diagram of the circuit of an ultrasonic diagnostic apparatus employing the ultrasonic blood flow imaging method according to this invention. FIG. 4 is a diagram for explaining the operation of the preferred embodiment according to the invention describing in FIG. 3. An embodiment of the present invention as applied to an ultrasonic diagnostic apparatus for producing a tomograph of a desired of a human body is shown in FIG. 3. This ultrasonic diagnostic apparatus produces a black-and-white B-mode tomograph having superposed thereon the velocity distribution of blood flow as determined by the pulse-doppler method. An ultrasonic transmitter/receiver 10 uses an ultrasonic beam to produce a B-mode tomographic signal. Moreover, through the transmission and reception of an ultrasonic pulse beam, it is possible to obtain a blood velocity distribution signal for the blood flow within the plane of the aforesaid B-mode tomograph. That is to say, in the embodiment the ultrasonic transmitter/receiver 10 consists of a combination of an ordinary B-mode echo device and an ultrasonic doppler device and produces the tomograph by either linear or sector electronic scanning. The ultrasonic transmitter/receiver 10 produces three separate signals. The first signal output from terminal A is a tomographic signal, more specifically a B-mode tomographic signal representing a desired tomographic plane. The second signal output from terminal B is a velocity signal produced by the pulse-doppler method, more specifically an average blood flow velocity signal, The third signal output from terminal C is a deviation signal, one kind of velocity signal represent each velocity band. In particular, the method of this invention makes it possible to obtain an exceedingly good two-dimensional color representation in a case where the blood flow in the object under examination makes rapid, irregular movements, for example in heart. As will be clear from the foregoing explanation, in accordance with the present invention, one of two colors is selected depending on whether the movement of the blood flow within the body under examination is fundamentally positive or negative and, therefore, only one of the two colors appears on the screen at any one time. Consequently, as there is no possibility of other colors interfering, it is possible to realize a tremendous improvement over the conventional method which produces an unpleasant picture with complexly intermixed colors. It is preferable for the two selected colors to contrast as strongly as possible in order to give a strong impression of "positive" and "negative". Specifically, it is best to choose colors that give totally opposite impressions such as the yellow and bluish-green used in this embodiment. These two contrasting colors are perceived very differently, one as a warm color and the other as a cool color, making them very easy to distinguish and making the resulting picture very easy to view. Moreover, in this invention, velocity is represented by variation in the brightness of the color concerned, with the brightness increasing in proportion as the velocity increases. Because of this, velocity information, particularly the average flow velocity etc., can be displayed in a very easy-to-read form. In the embodiment described above, not only the average flow velocity but also any velocity deviations at this time can be simultaneously displayed two-dimensionally in color so that even when the velocity and direction of the blood flow varies complexly, for example, in heart blood flow, it is possible to display these complex variations in the two dimensional picture. FIG. 4 shows the relation between the average blood flow velocity and velocity deviations in this invention. The solid-line curve 100 indicates the average flow velocity. As explained above, the display is made in yellow when this average flow velocity 100 is positive and is made in bluish-green when it is negative. The broken-line curves in FIG. 4 indicate deviation from the respective average flow velocities and this deviation is represented in color according to the size of the broken-line band. In this embodiment, it is possible to represent the magnitude of deviation by blending another prescribed color with the color indicating positive or negative velocity in such a way that the previously fixed color indicating the average flow velocity is changed by having the prescribed color blended therewith in a degree corresponding to the magnitude of the deviation. In the embodiment, deviation is represented by varying the amount of green mixed into the yellow for positive velocity and into the bluish-green for indicating negative velocity. In other words, whereas in the representation of only the average flow velocity the values of kr, kg and kb all maintain constant values, in the representation of deviation the value of kg corresponding to green is, in this embodiment, varied according to the deviation. More specifically, when the deviation value stored in frame memory 18 is small, kg is small; when the deviation becomes large, kg becomes large; and when the deviation is minimum, that is when the instantaneous flow velocity and the average flow velocity are equal, kg becomes zero. In this case, the display becomes red when the velocity is positive and becomes blue when the velocity is negative. Moreover, when the deviation value reaches a prescribed maximum value, the value of kg becomes equal to the aforesaid set value of the average flow velocity alone and, as a result, the positive display becomes yellow and the negative display becomes bluish-green. Thus, in considering the deviation, depending on the magnitude of the deviation, the mixing of colors takes place over a range extending from red to yellow in the case of positive velocity and over a range extending from blue to bluish-green in the case of negative velocity so that it is possible to read the deviation from the color mixture displayed. Thus, in accordance with this invention, the blood velocity information is displayed in one or the other of two colors depending on the direction of the velocity and the magnitude of the velocity is displayed as the brightness of the color concerned so that velocity information can be read most clearly. Moreover, as in the embodiment, the velocity information and the deviation information can be displayed independently or together as desired and as the changes in velocity and the changes in deviation are represented as changes within the same color system, it is possible to distinguish the changes in the picture with ease. Further, when the information pertaining to the blood flow is displayed as superposed on the image of the surrounding stationary part in the manner of this embodiment, it becomes most easy to grasp the interrelation between the blood flow and stationary part. In particular, when this invention is used in conjunction with an ultrasonic diagnostic apparatus or the like, it becomes possible to observe the flow of blood etc. within an organ with reference to a tomograph thereof and thus to obtain a huge quantity of diagnostic data. It should be noted that although in the embodiment described the average blood flow velocity is displayed alone in yellow or bluish-green, it is also possible to select other colors as desired. For example, it is possible in displaying only the average flow velocity to eliminate the signal for displaying green and to use only the two colors red and green. Although it is possible to use an ordinary arithmetic circuit for the color processor 26, it is preferable to further provide a ROM for storing according to the pulse-doppler method, which includes information on the deviation of the instantaneous velocity from the average velocity. For this third signal is used, for example, one with a dispersion value corresponding to the standard deviation or to the square of the standard deviation. The aforesaid three signals are produced as digital signals within the transmitter/receiver 10 by conversion from the analog reflection echo signal. The transmitter/receiver 10 also outputs from terminal D a transmission repetition pulse, a clock pulse or an address signal corresponding to the direction of transmission/reception of the ultrasonic beam. The signal from the terminal D is fed to a synchronization controller 12 which produces a synchronization signal required for memory operation and display as will be explained later. The three signals from the transmitter/receiver 10 are written into respective frame memories 14, 16, 18 and the addresses at which these signals are written is determined by the synchronization signal from the synchronization controller 12. Therefore, tomographic, average velocity and deviation signals for the tomographic plane are respectively stored at the same addresses in the frame memories 14, 16, 18. The data stored in the frame memories 14, 16, 18 are supplied to a color processor 26 through selector switches 20, 22, 24. The selector switches 20, 22, 24 are ON/OFF controlled so as to include only desired portions of the detected data in the video display. The color processor 26 converts the input data into color video signals in accordance with a prescribed processing method. In this embodiment, color processor 26 processes and outputs three color video signals corresponding respectively to three primary colors: red (R), green (G) and blue (B). These three color video signals are supplied to the input terminal of a color display 34 through D/A converters 28, 30, 32. In the embodiment, the color display 34 is a color CRT to which the D/A converters 28, 30, 32 supply R, G and B inputs respectively. As the synchronization signal from the synchronization controller 12 is supplied to the color display 34 as sweep input, the color display 34 is able to display the data stored at specific addresses in the frame memories 14, 16, 18 as a two-dimensional color image. The present invention is characterized by the fact that the color display 34 displays the velocity distribution two-dimensionally in color, the color image displayed in the case of the embodiment being that of a combination of the average blood flow velocity and the deviation therefrom. When the RGB inputs applied to the display 34 are of equal voltage, the color displayed is white. This white display is varied in brightness in accordance with the variation in brightness input at this time, so that the desired tomograph is displayed in black-and-white. Therefore, if only the selector switch 20 is ON or if the transmitter/receiver 10 produces only a tomographic signal, the B-mode tomograph will be displayed on the color display 34 in white. Next, in respect of the average flow velocity data from the frame memory 16, the color processor 26 specifies one or the other of two predetermined colors depending on whether the velocity is positive or negative and also varies the brightness of the specified color in accordance with the velocity data at that time. The positive and negative directions of movement of the blood flow are defined in advance, as by calling velocities which bring the moving member closer to the probe which sends and receives the beam in accordance with the pulse-doppler method to be positive and velocities which move it away therefrom to be negative. Thus, the velocity data stored in the frame memory 16 includes both the magnitude of the velocity and its sign (positive or negative) for each time of measurement. Here, denoting the velocity data as V and the voltages applied to the R, G and B terminals of the color display 34 as E R , E G and E B , the color processor 26 carries out the operations indicated by the following formulas on the average blood flow velocity data. In the case where the average flow velocity is positive: E R = krV E G = kgV E B = O And in the case where the average flow velocity is negative: E R = O E G = kgV E B = kbV (where kr, kg, kb are constants). From the foregoing explanation, it will be understood that based on the average flow velocity data stored in the frame memory 16 the color processor 26 mixes red and green to produce yellow in the case where the velocity is positive and mixes blue and green to produce bluish-green in the case where the velocity is negative and that in either case the brightness of the color concerned is varied in proportion to the velocity. When, as in the embodiment described above, positive velocity is indicated by a warm color (yellow) and negative velocity is indicated by a cool color (bluish-green), it becomes very easy to distinguish positive and negative velocities. Moreover, as velocity magnitude is represented by varying the brightness of the color concerned, much less effort is needed to distinguish velocities than is required in the conventional method in which a different color is used to the predetermined condition of the processing operation so that processing can be carried out at high speed. Further, it should be noted that it is not absolutely necessary to provide the selector switches describes in connection with the above embodiment although these switches are convenient since they make it possible to combine the information from the frame memories in various ways. Furthermore, widely used conventional color-TV and VTR can be used to display the color image by reading out the output signals from the frame memories 14, 16 and 18 in synchronizing manner to scanning signals for the TV and VTR. Again, although in the embodiment described the output of the color processor is used to control the grid voltage of a color picture tube, it is possible instead to use it to phase modulate a sub-carrier as in an ordinary television set and then to use the demodulation voltage thereof control the RGB voltage. As will be clear from the foregoing, this invention makes it possible to effectively utilize a color display device to obtain a two-dimensional display of the velocity distribution of blood flow within a body under examination and, in particular, makes it possible to obtain a very easily readable display even when the moving member moves rapidly.

Claims: Ultrasonic blood flow imaging method for two-dimensionally displaying the velocity distribution of blood flow within a body under examination, wherein the velocity distribution is displayed as a color picture wherein a positive velocity direction which is defined as a velocity direction which brings the blood flow closer to an ultrasonic probe is represented by one color and wherein a negative velocity direction which is defined as velocity direction which moves the blood flow away from the ultrasonic probe is represented by another different color, and wherein the magnitude of the blood flow velocity is represented by varying the brightness of the color concerned, characterized in , that the color selected depending on whether the velocity direction of the blood flow is positive or negative is mixed with still another color in accordance with a velocity deviation of the blood flow, that velocity deviation is provided as the deviation of the instantaneous velocity from the average velocity, and that the mixing is done proportionally to the magnitude of a deviation signal, whereby the velocity deviation in the direction of the blood flow concerned is represented by a change in color. Ultrasonic blood flow imaging method according to claim 1 wherein the form of the stationary portions in the vicinity of the blood flow is displayed in black-and-white as superposed on the color picture of the velocity distribution. Ultrasonic blood flow imaging apparatus comprising an ultrasonic transmitter/receiver (10) for outputting a tomographic image signal (A) produced by sending an ultrasonic beam into a specific region of a body under examination and electrically detecting the reflected echo from said region, and a velocity signal said velocity corresponding to the velocity of movement of a blood flow member within said region as determined by a pulse-doppler method; a color processor (26) for producing a color video-signal; and a color display (34) for displaying a tomographic image of said region using said color video signal, said color display (34) displaying said tomographic image in black-and-white, displaying positive directions of the velocity of the blood flow in one color and negative directions in another different color and displaying the magnitude of the velocity by varying the brightness of the color concerned wherein positive directions are defined as directions which bring the blood flow closer to an ultrasonic probe and negative directions are defined vice versa, characterized in that said velocity signal comprises an average velocity signal (B) and a velocity deviation signal (C) provided as the deviation of an instantaneous velocity signal from the average velocity signal (B),; the apparatus comprises three frame memories (114,16,18), one for storing each of said signals;, from which said color processor produces said color video-signal; and said color display (34) is provided for displaying the tomographic image, velocity and deviation as superposed one on the others by mixing still another color with the color selected depending on whether the velocity is positive or negative, the colors being mixed proportionally to the magnitude of the deviation signal. Apparatus according to claim 3, wherein said color processor (26), in the case where the velocity is positive, e.g., mixes the color signals of red and green to produce a yellow color signal and mixes e.g. the blue color signal and green color signal to produce a bluish-green signal in the case where the velocity is negative.

Inventors: NAMEKAWA, KOROKU
Applicants: ALOKA CO. LTD.
Application year: 1983
Main classification: A61B8
IPC codes: G01N29, G01S7, G01H3, A61B8, G01S15