JP2003019135A - Ultrasound diagnostic equipment - Google Patents

Abstract

(57) [Problem] To provide an ultrasonic diagnostic apparatus capable of obtaining a higher quality image while avoiding an increase in a coefficient holding memory. SOLUTION: A dynamic filter including two or more FIR filters 1 and 4 connected in series is provided, and control is performed such that the coefficient switching timing of each filter 1 and 4 is different. When each of the filters 1 and 4 performs coefficient switching at appropriate timing, the coefficient holding memories 2 and 5 can be used effectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic diagnostic apparatus including a dynamic filter that dynamically controls the band of an ultrasonic wave reception signal according to the depth in the living body.

[0002]

2. Description of the Related Art An ultrasonic diagnostic apparatus is an apparatus for transmitting an ultrasonic pulse and visualizing and displaying an echo signal reflected at a boundary part in a living body.
This is a method for displaying in-vivo morphological information.

Since the ultrasonic echo is attenuated in the living body, the echo farther from the ultrasonic probe is more attenuated. Furthermore, since this attenuation has a frequency dependent characteristic, the higher the frequency, the stronger the attenuation as the echo is farther. Therefore, the frequency spectrum of the received echo differs between the shallow part and the deep part in the living body. The ultrasonic diagnostic apparatus uses a dynamic filter method that changes the filter characteristics according to the depth, and by performing band limitation in accordance with the band of the received echo, a high-quality ultrasonic image with less noise is obtained. .

Further, with the recent digitization, this dynamic filter is replaced with a non-recursive band pass filter (F
An IR filter) is known. FIR
In the filter, a desired frequency characteristic can be obtained by changing the multiplication coefficient for each tap. Therefore, when changing the characteristics of the FIR filter from the shallow portion to the deep portion, it is possible to realize a dynamic filter by sequentially switching and using the set of coefficients given to each tap.

In an ultrasonic diagnostic apparatus using this type of FIR filter, the characteristics of the bandpass filter for each zone are changed by sequentially reading and setting the filter coefficient stored in the RAM or the like at regular intervals. Bandwidth control was performed.

However, in such a conventional coefficient switching method using a bandpass filter, the intervals between the zones are constant, so that if a smooth image is to be obtained over all depths, the filter coefficients will be unnecessarily large. There was a problem that had to hold.

In order to avoid this problem, an ultrasonic diagnostic apparatus has been proposed in which the switching intervals of the filters given to the bandpass filters are individually set.

Conventionally, this type of ultrasonic diagnostic apparatus defines an FIR filter for receiving an ultrasonic signal, a characteristic information registration unit for registering filter characteristic information defining filter characteristics, and a switching timing of the filter characteristics. A timing registration unit and an instruction switching unit that switches the filter characteristic according to the switching timing are provided, and the switching interval of the filter characteristic is individually set for each FIR filter (Japanese Patent Laid-Open No. 2000-325342).

Further, this type of ultrasonic diagnostic apparatus is provided with a digital IIR filter whose filter coefficient is changed according to the arrival of a received ultrasonic signal to eliminate variations in filter characteristics (Japanese Patent Laid-Open No. 2000-2000). -217825).

[0010]

However, in such a conventional ultrasonic diagnostic apparatus, since the switching intervals of the filters are individually stored and the switching intervals of the zones are not constant,
There is a problem that it is necessary to maintain the same switching interval as the zone to be divided.

In general, when a bandpass filter is constructed, a filter having a longer tap length is required as compared with the case where a single lowpass filter or a single highpass filter is constructed. Then, there is a problem that the number of filter coefficient sets to be stored increases.

That is, in a conventional ultrasonic diagnostic apparatus which uses a bandpass filter and changes the filter characteristics while sequentially switching the filter coefficients, a smooth image cannot be obtained or a large number of coefficient memories are required. was there.

The present invention has been made to solve such a problem, and provides an ultrasonic diagnostic apparatus capable of obtaining a higher quality image while avoiding an increase in the coefficient holding memory.

[0014]

An ultrasonic diagnostic apparatus according to the present invention comprises a dynamic filter including two or more variable coefficient FIR filters connected in series, and the coefficient switching timings of the respective FIR filters differ from each other. And a control means for controlling the switching timing. With this configuration, each filter coefficient can be switched at an appropriate timing, and the coefficient holding memory can be used efficiently, and a high-quality B-mode image with less noise can be obtained particularly at all depths.

Further, the ultrasonic diagnostic apparatus of the present invention has a structure in which the dynamic filter includes at least one high pass filter and at least one low pass filter. With this configuration, the optimum band limitation is applied to the echo signal from the short distance to the long distance.

In the ultrasonic diagnostic apparatus of the present invention, among the FIR filters included in the dynamic filter,
At least one FIR filter switches the coefficients up to the middle of the acoustic line, and at least one FIR filter has a control means for controlling the coefficients to switch from the middle of the acoustic line. With this configuration, the first FI
The R filter and the second FIR filter can suppress the increase in the number of taps by performing only high-pass filtering or only low-pass filtering.

In the ultrasonic diagnostic apparatus of the present invention, among the FIR filters included in the dynamic filter,
It has a configuration in which a control unit for controlling the coefficient switching of at least two FIR filters is provided alternately.
With this configuration, it is possible to reduce simultaneous switching and smooth changes in filter characteristics.

The ultrasonic diagnostic apparatus of the present invention has a configuration in which the coefficient switching timings are set at unequal intervals. With this configuration, a smooth image can be obtained over all depths while reducing the amount of coefficient holding memory.

Further, the ultrasonic diagnostic apparatus of the present invention has a structure in which the coefficient switching interval is an interval represented by a geometric progression. With this configuration, the coefficient switching is performed more frequently in the short-distance region, and the band control here is made precise.

Further, the ultrasonic diagnostic apparatus of the present invention has a structure in which the coefficient switching interval is an interval represented by a geometric progression. With this configuration, the band setting in the region of interest becomes precise.

Further, the ultrasonic diagnostic apparatus of the present invention is the above-mentioned F
The coefficient switching interval of the IR filter and the set of filter coefficients given to the FIR filter have different configurations depending on the selected ultrasonic probe. With this configuration, optimum coefficient switching processing is performed according to the type of ultrasonic probe.

Further, the ultrasonic diagnostic apparatus of the present invention has a structure in which the filter coefficient is a difference value from the previous filter coefficient. With this configuration, it is possible to suppress an increase in the coefficient holding memory.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. [First Embodiment] As shown in FIG. 1, the first embodiment of the present invention
The ultrasonic diagnostic apparatus according to the embodiment of the present invention is configured so that the dynamic filter including two or more variable coefficient FIR filters 1 and 4 connected in series and the coefficient switching timing of each FIR filter 1 and 4 are different from each other. The CPU for controlling the switching timing of the above, the coefficient holding memories 2 and 5, and the address generators 3 and 6 are provided. here,
Variable coefficient FIR filters 1 and 4 for the received echo are set to 2
The stages are connected in series.

In FIG. 1, an FIR filter 1 is a non-recursive filter including a delay element such as a flip-flop (FF), a multiplier, and an adder, and performs an operation with a filter coefficient given by a coefficient holding memory 2. The coefficient holding memory 2 is a general RAM and holds coefficient data for each zone. Here, the zone represents a period in which a set of filter coefficients is held and applied to the FIR filter. The FIR filter 4 and the coefficient holding memory 5 also have the same configurations as described above. The address generator 3 is a block that generates a read address of the coefficient memory 2,
The address generator 6 is a block that generates a read address of the coefficient memory 5. As described above, it is important to independently provide the address generating units 3 and 6 with respect to the two coefficient holding memories 2 and 5, respectively.

The configuration of the address generator 3 will be described in detail with reference to FIG. In this embodiment, inputs to the address generator 3 are a system clock, an echo start signal, a first zone period, and another zone period. Here, the echo start signal indicates the beginning of a reception echo, and is a control signal sent in synchronization with the beginning of the echo signal of each acoustic line. The "first zone period" is a control signal for setting a first zone period and the "other zone period" is a period common to the second and subsequent zones, which is set by a CPU (not shown).

In FIG. 2, the zone counter 21 counts the period within one zone and notifies the transition of the zone. The zone counter 21 is composed of, for example, a down counter, and loads the “first zone period” or the “other zone period” by an echo start signal or a zone switching signal generated by the zone counter 21, and counts down until it reaches 0. To do. The address counter 22 is an up counter which is cleared to 0 by an echo start signal and is incremented by 1 in response to a zone switching signal from the zone counter 21, and generates an address to be given to the coefficient holding memory 2. The address counter 22 stops counting up at the maximum value.

The address generating section 6 is a block for generating an address to be given to the coefficient holding memory 4, and its configuration is the same as that of the address generating section 3.

Next, the operation of the dynamic filter of this embodiment will be described with reference to FIGS. When updating the coefficient of the dynamic filter and the zone control information when the power is turned on or the probe is switched, the filter coefficient for each zone is sent from the CPU to the coefficient holding memories 2 and 4, and the "first zone period" and the "other zone" Information of “period” is sent to the registers of the address generators 3 and 6. Here, the first zone periods given to the address generators 3 and 6 are p1 and q, respectively.
1, and the other zone periods are p2 and q2.

In synchronization with the echo start signal, p1 is loaded in the zone counter 21 and q1 is loaded in the address counter 22, and the count is decremented by 1 until it becomes 0 every clock. Zone counter 21, address counter 22
Generates a zone switching signal when each count value becomes 0, loads other zone period information p2 and q2, and starts counting down. After that, when the count value becomes 0, a zone switching signal is generated and p
2. Load q2.

The address counter 22 is cleared to 0 by the echo start signal and counted up by the zone switching signal from the zone counter 21. When the address count value reaches the maximum value, it is held until the next echo start.

FIG. 3 shows memory addresses generated by the address generators 3 and 6. For simplification, the address is 3 bits, and 0 to 7. The horizontal axis represents time, and the echo starts at time 0 and one echo ends at the right end of FIG.

FIGS. 3A and 3B show addresses generated by the address generators 3 and 6, respectively.
In FIG. 3A, the zone is switched after p1 from the echo start, and then the zone is switched every p2 until the address becomes 7. In FIG. 3B, the zones are switched q1 after the echo start, and thereafter, the zones are switched every q2 until the address becomes 7. Based on the addresses thus generated, the coefficient sets to be set in the FIR filter 1 and the FIR filter 2 are read from the coefficient holding memories 2 and 5, respectively, and filtered.

As described above, the ultrasonic diagnostic apparatus according to the present embodiment limits the band according to the depth, but the character is different between the shallow portion and the deep portion. Since a sufficient echo level can be obtained in the shallow region, the emphasis is placed on improving the image quality quality rather than improving the S / N ratio, and the dynamic filter is used for positive waveform shaping. For this purpose, processing for suppressing the low frequency component of the echo signal is used. On the other hand, in a deep part, the echo level becomes extremely low, so that the emphasis is on improving the S / N ratio rather than the quality of the image, and it is important to remove the noise contained in the high frequency components.

Now, assuming that the FIR filter 1 performs high-pass filter processing and the FIR filter 2 performs low-pass filter processing, the address generation as shown in FIG. 3 meets this purpose. That is, the FIR filter
At 1, the high-pass filter performs waveform shaping from the short distance to the middle distance, and at the FIR filter 2, the noise is reduced by the low-pass filter from the middle distance to the long distance. Since the FIR filters 1 and 2 only perform high-pass or low-pass filtering, they do not need so many taps,
Can be composed of small filters.

As described above, the ultrasonic diagnostic apparatus according to the first embodiment of the present invention includes a dynamic filter including two or more variable coefficient FIR filters 1 and 4 connected in series, and each FIR filter 1, 4 and the CPU for controlling the switching timing of the coefficients so that the switching timings of the coefficients are different from each other, the coefficient zones of the FIR filters 1 and 4 are individually controlled, and the high-pass filter is used for a short distance. Finer coefficient control is possible, and the low-pass filter is capable of finer coefficient control at a long distance. Therefore, it is possible to obtain an image of high quality and high S / N ratio by effective band limitation with a small memory amount.

[Second Embodiment] FIG. 4 shows a second embodiment of the present invention.
7 shows the timing of address generation in the embodiment. This is different from the first embodiment in that at least two FIR filters among the FIR filters 1, 44, 44a included in the dynamic filter are controlled to alternately switch the coefficients and the coefficient holding memories 2, 45. , 45a and address generators 43, 46, 49 are provided. According to this configuration, it is possible to obtain the effect of suppressing the occurrence of horizontal stripes on the B-mode image and further reducing the simultaneous switching.

As shown in FIG. 5, in this embodiment, three variable coefficient FIR filters 1, 44, 44 connected in series are used.
A dynamic filter including 44a is provided. In addition,
Since the configuration and operation of each block (FIR filter, coefficient holding memory, address generation unit) are the same as those in the first embodiment, description thereof will be omitted, and the address generation timing for switching filter coefficients shown in FIG. explain.

Now, the first zone periods given to the address generators 43, 46 and 49 are respectively given different values, t1, t2,
When t3 is set and the other zone setting periods are set to be the same t4, the address switching timing is
Each has an alternate relationship. Therefore, the three filters are not switched at the same time, and the change in the filter characteristic becomes smoother. This makes it possible to suppress the occurrence of horizontal stripes on the B-mode image and reduce simultaneous switching.

[Third Embodiment] FIG. 6 shows a third embodiment of the present invention.
2 is a block diagram of a main part of the embodiment of FIG. This is different from the first embodiment in that the coefficient switching interval of the FIR filter is an interval represented by an arithmetic sequence. With this configuration, it is possible to obtain the effect that the filter coefficient can be switched more frequently in the short-distance region and the band control can be performed more finely.

In FIG. 6, the zone counter 61 has a first
This is a down counter similar to that of the embodiment (shown in FIG. 2), and the signal from the cumulative adder 64 is used as the "other zone period" setting signal in the first embodiment. The cumulative adder 64 takes in the first term 65 by the load signal, and thereafter, the tolerance 66 by the zone switching signal generated by the zone counter 61.
Is added and output. The address counter 62 is also the first
The configuration is similar to that of the embodiment (shown in FIG. 2).

Next, the address generating operation in this embodiment will be described. For the first zone, the first
This is the same as the embodiment. The zone lengths after the second zone are defined by the cumulative adder 64. This cumulative adder 64
Is a zone switching signal indicating the end of the first zone,
The first term 65 is loaded and stored in the internal register. After that, by accumulating the tolerance 66 cumulatively for each zone switching signal,
Zones can be set to intervals represented by arithmetic progressions. FIG. 7 shows how an address is generated when the zone gradually expands. Here, if the first zone interval is p0, the first term is a0, and the tolerance is d, the first zone interval is p0,
The interval of the second zone is a0, the interval of the third zone is "a0
+ D ”, hereafter“ a0 + 2d ”,“ a0 + 3d ”,“ a
0 + 4d ". Of course, it is also possible to give a negative value as the tolerance d. In this case, as shown in FIG.
As shown in, the zone interval is set to be gradually narrowed.

As described above, by setting the zone switching interval to the arithmetic progression, it becomes possible to switch the filter coefficient more frequently in the short distance area where the band control is desired to be performed more finely, and the coefficient holding memory (see FIG. 1). (Corresponding to 2, 5) can be utilized more effectively.

[Fourth Embodiment] FIG. 9 shows a fourth embodiment of the present invention.
The principal part front view of embodiment of FIG. This is different from the first embodiment in that the coefficient switching interval of the FIR filter is
The difference is that the intervals are represented by geometric progressions.
According to this configuration, the effect that the band setting can be controlled more finely in the region of interest is also obtained.

In FIG. 9, the zone counter 81 has a first
The down counter is the same as that in the second embodiment (shown in FIG. 2), and the "other zone period" setting signal in the first embodiment is used as the signal from the cumulative adder 80. The cumulative multiplier 80 gives the zone counter 81 a common ratio r instead of the common difference d used in the third embodiment.
As a result, the zone intervals generated by the zone counter 81 as shown in FIG. 10 are p0, a0, “a0 * r”, and “a0.
The zone intervals can be set to form a geometric progression such as * r ^ 2 ”and“ a0 * r ^ 3 ”, and the band setting can be controlled more finely in the region of interest.

In each of the above embodiments, the FI
The coefficient switching interval of the R filter and the set of filter coefficients given to the FIR filter may be set differently depending on the selected ultrasonic probe. With this configuration,
A high quality ultrasonic image can be displayed according to the selected ultrasonic probe. Further, the filter coefficient may be a difference value from the previous filter coefficient. With this configuration, it is possible to suppress an increase in the coefficient holding memory.

In each of the above-described embodiments, the coefficient holding memories 2, 5, 45, 45a and the address generators 3, 6, 43, 46, 4 are stored.
9. A CPU or the like constitutes the control means.

[0047]

As described above, according to the present invention, two or more variable coefficient FIR filters for ultrasonic reception signals are connected in series, and the switching timing of each filter coefficient is individually controlled to reduce the memory capacity. Thus, it is possible to provide an ultrasonic diagnostic apparatus having an excellent effect of enabling effective band limitation and displaying an ultrasonic image with high quality and less noise.

[Brief description of drawings]

FIG. 1 is a block diagram of a main part (dynamic filter) of an ultrasonic diagnostic apparatus according to a first embodiment of the present invention.

FIG. 2 is a block diagram of a main part (address generation part) of the ultrasonic diagnostic apparatus according to the first embodiment of the present invention.

FIG. 3 is a timing chart of address generation according to the first embodiment of this invention.

FIG. 4 is a timing chart of address generation according to the second embodiment of the present invention.

FIG. 5 is a block diagram of a main part (dynamic filter) of the ultrasonic diagnostic apparatus according to the second embodiment of the present invention.

FIG. 6 is a block diagram of a main part (address generating part) of an ultrasonic diagnostic apparatus according to a third embodiment of the present invention.

FIG. 7 is a timing chart of address generation (when the zone gradually expands) according to the third embodiment of this invention.

FIG. 8 is a timing chart of address generation (when the zone is gradually narrowed) according to the third embodiment of this invention.

FIG. 9 is a block diagram of a main part (address generating part) of an ultrasonic diagnostic apparatus according to a fourth embodiment of the present invention.

FIG. 10 is a timing chart of address generation according to the fourth embodiment of the present invention.

[Explanation of symbols]

1, 4, 44, 44a FIR filter 2, 5, 45, 45a coefficient holding memory 3, 6, 43, 46, 49 Address generator 21, 61, 81 zone counter 22, 62, 82 Address counter 64 cumulative adder 80 cumulative multiplier

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 2G047 EA10 EA14 GG09 GG16 GG17                       GG41 GH07 GH08                 4C301 AA01 CC01 EE07 EE11 JB02                       JB11 JB17 JB35 JB42 LL05

Claims (9)

[Claims] 1. A variable coefficient FI in which two or more are connected in series.
An ultrasonic diagnostic apparatus comprising: a dynamic filter including an R filter; and control means for controlling the coefficient switching timing so that the coefficient switching timing of each FIR filter is different. 2. The ultrasonic diagnostic apparatus according to claim 1, wherein the dynamic filter includes at least one high pass filter and at least one low pass filter. 3. The F included in the dynamic filter
Among the IR filters, at least one FIR filter is provided with control means for performing coefficient switching up to the middle of the acoustic line, and at least one FIR filter is provided with control means for controlling the coefficient switching from the middle of the acoustic line. Claim 1
Alternatively, the ultrasonic diagnostic apparatus according to item 2. 4. The F included in the dynamic filter
The ultrasonic diagnostic apparatus according to claim 1 or 2, further comprising: a control unit that controls so as to alternately switch the coefficients of at least two FIR filters among the IR filters. 5. The ultrasonic diagnostic apparatus according to claim 1, wherein the coefficient switching timings are set at unequal intervals. 6. The ultrasonic diagnostic apparatus according to claim 5, wherein the coefficient switching interval is an interval represented by a geometric progression. 7. The ultrasonic diagnostic apparatus according to claim 5, wherein the coefficient switching interval is an interval represented by a geometric progression. 8. The coefficient switching interval of the FIR filter and the set of filter coefficients given to the FIR filter are:
The ultrasonic diagnostic apparatus according to claim 1, wherein the ultrasonic diagnostic apparatus is set to be different depending on the selected ultrasonic probe. 9. The ultrasonic diagnostic apparatus according to claim 1, wherein the filter coefficient is a difference value from a previous filter coefficient.