JPH0716489B2 - Color ultrasonic diagnostic equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention seeks blood flow information in a subject by utilizing the Doppler effect of ultrasonic waves and displays it in a two-dimensional manner. The present invention relates to a sound wave diagnostic apparatus.

(Prior Art) By using the ultrasonic Doppler method and the pulse reflection method together, blood flow information and tomographic image (B-mode image) information can be obtained with one ultrasonic probe, and the tomographic images are overlapped to obtain blood flow information in real time. There is known a color ultrasonic diagnostic apparatus that displays in color. The operation principle when blood flow information is obtained by such a device is as follows.

That is, when an ultrasonic pulse is transmitted to the blood flow flowing in the living body that is the subject, the center frequency fc of this ultrasonic beam is scattered by the flowing blood cells and undergoes Doppler shift to change the frequency fd. Then, this received frequency fo is fo =
It becomes fc + fd. At this time, the frequencies fc and fd are expressed by the following equation.

Here, V: average blood flow velocity Q: angle formed by ultrasonic beam and blood vessel C: speed of sound Therefore, the average blood flow velocity V can be obtained by detecting the Doppler shift fd.

The two-dimensional image display of the average blood flow velocity V thus obtained is performed as follows. First, as shown in FIG. 14, when ultrasonic waves are sequentially transmitted from the ultrasonic probe 1 to the subject in the A, B, C, ... directions to perform sector (or linear) scanning, the ultrasonic pulse Scan control is performed.

When an ultrasonic pulse is first transmitted several times in the A direction, the echo signal that is Doppler-shifted and reflected by the blood flow in the subject is received by the same probe 1, converted into an electrical signal, and received. Sent to the circuit.

Then, the Doppler shift signal is detected by the phase detection circuit. The Doppler shift signal is captured at every 256 sample points set in the ultrasonic pulse transmission direction. The Doppler shift signal captured at each sample point was frequency analyzed by a frequency analyzer and D. equipped with a frame memory.
After being sent to an SC (Digital Scan Converter) and scanned and converted there, the blood flow distribution image in the A direction is sent to the display unit and displayed in real time as a two-dimensional image.

The same operation is repeated for each direction B, C, ..., and the blood flow distribution image (also called color flow mapping (CFM) image) corresponding to each scan direction is displayed. Become.

FIG. 15 shows the relationship between the angle expression and the frequency expression of the average blood flow velocity and the corresponding display colors. Corresponding to −π to + π in the case of the angle expression and −in the case of the frequency expression. fr
Display colors are blue, black, and red corresponding to / 2 to + fr / 2. It should be noted that fr is the repetition frequency of the ultrasonic pulse.

By the way, in the conventional device, since the frame composition period (T _OF ) is longer than the television screen composition period, the temporal smoothing (afterglow effect) processing of the CFM image is performed, and the frame correlation is performed in the temporal smoothing processing. It is used. As shown in FIG. 9, the temporal smoothing processing by the frame correlation is performed in the same coordinate (x, y) when a plurality of continuous CFM images are formed every one frame constituent period (T _OF ). This is a method of taking correlation of blood flow velocity data. In principle, it is a cyclic digital filter as shown in FIG. 10, and is physically a low-pass filter on the time axis (t). By the way CF
When the frame frequency of the M image is represented by f _OF , and the change of the blood flow velocity data due to the frequency representation between adjacent frames is represented by f, if f = f _OF ≧ 1/2 holds, a so-called frame of gradation change The aliasing phenomenon occurs due to the correlation process (see Fig. 11).

(Problems to be Solved by the Invention) Temporal smoothing processing by correlation between data such as B-mode image data (black and white echo data) that has only a gradation change but no sign change is performed as shown in FIG. There is no problem because it is done only on the side.

On the other hand, in the CFM image, the Doppler shift signal is discretely sampled at the repetition frequency fr of the ultrasonic pulse. Therefore, when the blood flow velocity V (t) becomes fr / 2 or more or −fr / 2 or less, “by sampling "Foldback phenomenon" occurs. For this reason,
As shown in Fig. 13, in reality, the blood flow velocity V as shown by X
Despite the change in (t), due to the "sampling-back phenomenon", as shown by the ● mark in the latter half, the data 2a and later turn back, and shift from red to blue and from blue to red. When the folding phenomenon due to sampling occurs in this way, when frame correlation processing is performed between different codes such as data 2a and 2b and data 2c and 2d, smoothing is performed as shown in processing result 2. The blood flow velocity V (t) changes so as to cross the frequency zero line. Since black is assigned to this zero-crossing part 3, if the CFM image is frozen (still image display) there, the part becomes black on the display image even though there is a high-speed blood flow part actually. It is displayed as if there is no blood flow.

The present invention eliminates the above-mentioned drawbacks, and an object of the present invention is to eliminate the black display of the high blood flow portion when the folding phenomenon occurs due to sampling, thereby enabling an appropriate blood flow distribution image display. The present invention is to provide a color ultrasonic diagnostic apparatus.

[Structure of the Invention] (Means for Solving the Problems) The present invention relates to a transmitting / receiving means for transmitting / receiving ultrasonic pulses to / from a subject, and a sampling frequency by the transmitting / receiving means.
Detecting means for detecting blood flow velocity data of the subject based on the received data obtained by fr, smoothing processing means for subjecting the blood flow velocity data to temporal smoothing processing by frame correlation, and this smoothing processing means In the color ultrasonic diagnostic apparatus having a display unit for displaying the processing result of 1., the smoothing processing unit has different signs of the old and new blood flow rate data input in the range of −fr / 2 to + fr / 2. In this case, the absolute value of the difference between the data values is compared with the threshold value, and when the absolute value is greater than the threshold value, the maximum of the old data in the blood flow direction is replaced with the result of the temporal smoothing process. It is characterized by giving a value equal to the gradation.

(Operation) According to the present invention, the blood flow velocity of the blood flow distribution image data is −fr / 2.
When the aliasing development by sampling exceeding + fr / 2 is generated, the smoothing processing means performs the temporal smoothing processing in the direction not crossing the frequency zero line in the frequency expression of the blood flow velocity. Therefore, it is possible to eliminate the black display of the high blood flow velocity portion when the folding phenomenon occurs.

(Examples) Hereinafter, the present invention will be specifically described with reference to Examples.

FIG. 1 shows an embodiment of the present invention.

10 is an ultrasonic probe formed by arranging a plurality of ultrasonic transducers in an array, 11 is a transmission / reception unit that transmits and receives ultrasonic pulses through the ultrasonic probe 10, and 12 is an ultrasonic echo. The receiver 13 performs envelope detection, converts it to a digital signal, and outputs it.
Is a white / black frame memory in which the output of is written. Further, 14 is a quadrature detection unit that performs quadrature detection of ultrasonic echoes, and 15 is a CFM that performs CFM (color flow mapping) processing.
Reference numeral 16 is a unit, and 16 is a color frame memory in which this CFM processing output is written. This color frame memory
16 and the subsequent stage of the white / black frame memory 13, a synthesis processing unit 17 for synthesizing read data from both memories is arranged,
Further, an RGB monitor 18 that displays the color of the output of the synthesis processing is arranged at the subsequent stage of the synthesis processing unit 17.

Here, the CFM unit 15 is configured as follows.

Reference numeral 19 is an A / D (analog / digital) converter, and the output of the quadrature detector 14 is converted into a digital signal by the A / D converter 19. This A / D converter 1
An MTI filter 20 for removing the clutter component is arranged in the subsequent stage of 9, and a CFM calculator 21 for calculating the average blood flow velocity (), total power (), and dispersion () is provided in the subsequent stage of the filter 20. Further, smoothing processing means 22 for performing temporal smoothing processing of the blood flow distribution image by frame correlation is arranged at the subsequent stage of the CFM calculation unit 21. Here, in the smoothing processing means 22, when the blood flow velocity of the blood flow distribution image data exceeds -fr / 2 to + fr / 2, the smoothing processing means 22 does not cross the frequency zero line in the frequency expression of the blood flow information. The blood flow distribution image is subjected to temporal smoothing processing, which is one of the characteristic points of the apparatus of this embodiment.

Next, a configuration example for realizing the function of the smoothing processing means 22 will be described.

FIG. 2 shows a detailed configuration of the smoothing processing means 22.

Reference numeral 25 is a coefficient ROM (read only memory) that multiplies the blood flow velocity signal V (t) from the CFM calculator 21 of FIG. 1 by (1-a), and the output of this coefficient ROM 25 is arranged in the subsequent stage. Adder 2
Taken in 6 and in the adder 26, the coefficient ROM described later
After being added to the output of 29, it is taken into the image memory 28 via the MPX (multiplexer) 27. Here, a means a coefficient in the frame correlation process. MP
X27 has a function of selectively transmitting the output of the adder 26 and the output of the initial condition ROM 30 to the image memory 28, and which is selected depends on the selection signal SEL from the initial condition ROM 30. Initial condition
The ROM 30 compares the output of the image memory 28 with the input signal V (t), and sends the selection signal SEL and the initial condition to the MPX 27 according to the comparison result. The initial condition and the MPX27 selection logic will be described later in detail.

The image memory 28 is a two-dimensional memory having a storage capacity of M rasters in the azimuth direction and N pixels in the distance direction, as shown in FIG. The memory controller 31 performs switching between data read operation from the memory 28 and addressing. Then, the memory controller 31 has a 1-frame configuration periodic signal OFO and a CMF scan raster head signal IN.
The transfer clock DEPIXCK from the ITO and CFM calculation units is input. Further, in the subsequent stage of the image memory 28, a coefficient ROM 29 for multiplying the output of the image memory 28 by a is arranged. Then, the coefficient ROMs 25 and 29 have the host of FIG.
A coefficient selection signal from a CPU (central processing unit) 23 is taken in. The value of the coefficient a is determined by this signal. That is, the value of the coefficient a in the coefficient ROMs 25 and 29 is determined under the control of the host CPU 23. Also MPX27
Is output to the color frame memory 16 of FIG. 1 as the output of the smoothing processing means 22.

FIG. 8 shows the selection logic of the MPX 27, which will be described below.

The current data is V (n), and the data one frame before this V (n) is V (n + 1). This V (n), V
When the signs of (n + 1) are equal, the selection signal SEL is not output from the initial condition ROM 30, and the MPX 27 selects the output of the adder 26 (continuation of frame correlation processing). Also, V (n), V (n
When the signs of +1) are different and the absolute value of the difference is equal to or higher than the threshold level TH, the frame correlation process is temporarily stopped and the initial condition is given.
That is, in this case, the selection signal SEL from the initial condition ROM 30
And the initial condition are output, and the MPX 27 selects the initial condition from the initial condition ROM 30 and sends it to the image memory 28 and the color frame memory 16. Furthermore, V (n), V (n + 1)
If the sign of is different and the absolute value of the difference is smaller than the threshold level TH, the initial condition RO
The selection signal SEL is not output from M30, and the MPX27 selects the output of the adder 26 (frame correlation processing continues). Here, the threshold level TH is normally set to fr / 2 (fr is the repetition frequency of the ultrasonic pulse), but it can be adjusted from 0 to fr as necessary. Also, the initial condition is + fr / 2 when V (n + 1) is positive, and conversely V
When (n + 1) is negative, it is -fr / 2.

Next, the operation of the embodiment apparatus having the above configuration will be described.

The reflected component of the ultrasonic pulse transmitted from the ultrasonic probe 10 toward the subject is again the ultrasonic probe.
Envelope detection received by the receiver 12 via the transmitter / receiver 11 and converted into a digital signal is transferred to the white / black frame memory 13 and written therein. . The stored contents of the white / black frame memory 13 are read at the timing of the monitor system and transmitted to the RGB monitor 18 via the composition processing unit 17.

On the other hand, the pulse echo obtained by transmitting and receiving the ultrasonic pulse for obtaining the Doppler information is subjected to quadrature detection in the quadrature detection unit 14, and the detection output thereof is sent to the CFM unit 15. Then, the quadrature detection output is converted into a digital signal by the A / D converter 19, and after the clutter component is removed by the MTI filter 20, the quadrature detection output is taken into the CFM calculation unit 21, where the average blood flow velocity (), the total power ( ) And variance (). Then, the calculation result in the CFM calculator 21 is taken into the smoothing processing means 22, and the smoothing processing means 22 performs temporal smoothing processing by frame correlation,
The processing result is the color frame memory 16 and the composition processing unit
It is transmitted to the RGB monitor 18 via 17 and is displayed superimposed on the monochrome B-mode image.

Here, details of this temporal smoothing processing will be described.

As shown in FIG. 9, the temporal smoothing process by frame correlation is a process between frames of one frame constituting period (every OF period) of a CFM image.

3 and 4 show the CFM output timing,
FIG. 3 is a data output timing chart in the azimuth direction, and FIG. 4 is a data output timing chart in the distance direction.

M (M is a positive integer) CFM scan raster head signals (INITO) are generated in the CFM1 frame configuration cycle (OFO signal cycle). Further, the same raster is scanned several times at a rate frequency (PRF) period in order to obtain data for one raster of the CFM image. The CFM output signal V (t) thus obtained is output at the timing shown by the shaded area in FIG. Also CFM1
The data 1 ', 2', 3 '..., N'in the distance direction in the output signal V (t) for the raster are sequentially output within one rate as shown in FIG.

FIG. 6 shows the frame correlation processing timing of pixel (m, n), and FIG. 7 shows the Ta portion of FIG. 6 in an enlarged manner.

As shown in FIG. 6, the address of the image memory 28 is the memory RD.
Incremented in synchronization with the signal, (m, 1), (m,
2), ... (m, n-1), (m, n), ...
After this memory address is fixed, the data stored in the image memory 28 up to 10F cycles before is read and processed together with the currently fetched data, and the result of this processing is read again by the memory WR signal. Written on 28. Details of the correlation processing for this pixel (m, n) are as follows.

That is, as shown in FIG. 7, the old data at the address (m, n) is read from the image memory 28, multiplied by a by the coefficient ROM 29 and taken into the adder 26, and the current input data V
When (t) is multiplied by (a-1) in the coefficient ROM 25 and taken into the adder 26, both data are added by the adder 26, and the addition result is the new data of the address (m, n). As M
It is written in the image memory 28 via the PX27 (data update). Then, almost simultaneously with this writing, new (m, n) data is transferred to the color frame memory 16 (FIG. 1). Such processing is performed for all pixels of the CFM image.

Here, the data (old data) read from the image memory 28 is transferred to the coefficient ROM 29 and also to the initial condition ROM 30. This data is V (n + 1). At this time, the newly fetched data V (t) (this is V
(If (n)) and the old data V (n + 1) have the same sign, or if they have different signs and | V (n) −V (n + 1) | <TH holds, Since the output of the adder 26 is selected by the MPX 27, the above frame correlation processing is continued (see FIG. 8). However, if V (n) and V (n + 1) have different signs, and | V (n) -V (n + 1) | ≧ TH holds, the initial condition ROM30 indicates that the initial condition is selected together with the selection signal SEL. The MPX27 outputs this selection signal SEL.
By inputting, the initial condition of the initial condition ROM 30 is selected (see FIG. 8). Here, the initial condition is + fr / 2 when V (n + 1) is positive, and conversely, −fr when V (n + 1) is negative.
/ 2. That is, instead of the output of the adder 26, a value equal to the highest gradation in each blood flow direction is given to the image memory 28 and the color frame memory 16.

According to such processing, when aliasing development by sampling occurs, temporal smoothing processing by frame correlation is performed in a direction that does not cross the frequency zero line in the frequency representation of blood flow information. That is, when the folding phenomenon occurs due to sampling, in the conventional apparatus, the smoothing is performed in the direction intersecting the frequency zero line as shown by the solid line 2 in FIG. 13, whereas in the apparatus of this embodiment, as shown by the broken line 4. It is smoothed in the direction that does not cross the zero frequency line. According to this, the zero crossing portion 3 does not exist even if smoothing is performed when the folding development by sampling occurs, and therefore, even when the CFM image is frozen, the high speed blood flow portion is displayed in black. Does not happen.

The present invention is not limited to the above embodiment.

In the above-described embodiment, the initial condition (+ fr / 2 and -fr / 2) is given from the initial condition ROM 30 under a constant condition, but a method equivalent to the method of resetting with the coefficient a = 1 is adopted. You can also In this case, the output data of the image memory 28 remains as it is under the initial condition RO.
Pass M30 and select it with MPX27.

In the above embodiment, the smoothing processing means 2 is provided in the CFM unit 15.
Although the description has been given of the case where 2 is provided, since the frame correlation processing can also be performed by using the color frame memory 16 of FIG. 1, the smoothing processing means can be arranged at the subsequent stage of the CFM unit 15.

[Effects of the Invention] As described in detail above, according to the present invention, blood flow distribution (CFM)
A color ultrasonic diagnostic apparatus capable of eliminating the black display of the high blood flow velocity portion when the aliasing phenomenon occurs in the temporal smoothing processing by the frame correlation of the image and enabling an appropriate blood flow distribution display. Can be provided.

[Brief description of drawings]

FIG. 1 is a block diagram of an apparatus according to an embodiment of the present invention. FIG. 2 is a detailed configuration block diagram of a main part of the apparatus, FIG. 3, FIG.
FIGS. 6, 6 and 7 are operation timing charts of the apparatus of the present embodiment, FIG. 5 is a format diagram of an image memory in the same apparatus, FIG. 8 is an explanatory diagram of MPX data selection logic in the same apparatus, and FIG. FIG. 10 is an explanatory diagram of data sampling in frame correlation processing, FIG. 10 is a block diagram of a cyclic filter that executes frame correlation processing, FIG. 11 is a characteristic diagram of frame correlation processing, and FIG. 12 is based on frame correlation of unsigned data. Explanatory diagram of temporal smoothing process, FIG. 13 is an explanatory diagram of temporal smoothing process by frame correlation of CFM image data,
FIG. 14 is a pattern diagram of an ultrasonic scan, and FIG. 15 is an explanatory diagram of the relationship between the angle expression and frequency expression of the average blood flow velocity and the corresponding display color. 10 ... Ultrasonic probe, 15 ... CFM unit, 18 ... RGB monitor, 21 ... CFM calculator, 22 ... Smoothing processing means.

Claims (1)

[Claims] 1. A transmitting / receiving means for transmitting / receiving an ultrasonic pulse to / from a subject, and a detecting means for detecting blood flow velocity data of the subject based on received data obtained at the sampling frequency fr by the transmitting / receiving means. A color ultrasonic diagnostic apparatus comprising: smoothing processing means for subjecting the blood flow velocity data to temporal smoothing processing by frame correlation; and display means for displaying the processing result of the smoothing processing means in color. When the signs of the old and new blood flow rate data input in the range of −fr / 2 to + fr / 2 are different, the processing means compares the absolute value of the difference between the data values with the threshold value, and determines the absolute value. When the value is larger than a threshold value, a value equivalent to the highest gradation in the blood flow direction of the old data is given instead of the processing result of the temporal smoothing processing.