JPH1085212A - Ultrasonic diagnostic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively use the dynamic range of an ADC to its maximum by dynamically controlling the gain of an amplifier circuit in front of the ADC according to the level of an input signal. SOLUTION: A digital converting part 14 is provided with a comparator having a threshold that matches the input range of an ADC, and when an input signal from an amplifying part 12 exceeds the threshold, an over-range signal 70 is produced. A gain control part 60 calculates the frequency at which the signals 70 are output, and performs feedback control in which, when the frequency is great, the gain of the amplifying part 12 is reduced, whereas if it is small, the gain is increased, so that the range of the input signal amplified almost equals the dynamic range of the ADC at any time.

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 for performing signal processing after digitizing a received signal, and more particularly to adjusting the gain of an amplifier for amplifying the received signal.

[0002]

2. Description of the Related Art In an ultrasonic diagnostic apparatus, a reception signal from each transducer is converted into an analog signal before phasing and adding reception signals from the transducers of a transducer array to form a reception beam.
Digitizing with a digital converter (ADC)
This has been done conventionally. This solves the problem that noise is increased when the delay of each oscillator in the phasing addition is performed in analog.

Here, the ADC becomes significantly expensive as the dynamic range increases, that is, as the number of bits increases by one bit. For this reason, if a wave phasing addition circuit using the digital delay method is adopted for the ultrasonic receiving circuit, the ADC generally limits the dynamic range of the ultrasonic receiving circuit. That is, an ADC having the minimum number of bits required in the specifications of the device is used.

The ultrasonic diagnostic apparatus includes a plurality of diagnostic modes such as B-mode processing for generating a tomographic image of a living body using the amplitude value of an echo signal and Doppler processing for obtaining blood flow information using phase information. Can be switched. Here, the echo signal from the blood flow is much weaker than that used for the B-mode processing. Therefore, if Doppler processing is performed using the B-mode processing digital signal obtained by, for example, a 10-bit ADC in the above-described mode-switchable ultrasonic diagnostic apparatus, the dynamic range becomes insufficient. As a configuration that solves this problem without increasing the number of bits of the ADC, the dynamic range of a signal targeted by each diagnostic mode is adjusted to the signal input range of the ADC so that the dynamic range is set before the ADC according to the type of the diagnostic mode. A configuration for switching the gain of an amplifying circuit provided has been proposed (Japanese Patent Publication No. 6-14934).

Incidentally, the intensity of the ultrasonic echo returned from the living body depends not only on the magnitude of the difference in acoustic impedance of the living tissue but also on the depth at which the ultrasonic reflection occurs, that is, the propagation distance of the ultrasonic wave. It also depends on the amount of attenuation. In order to correct the difference in attenuation due to the propagation distance, TGC (TiC) that dynamically controls the gain of the amplifier circuit according to the depth is used.
me Gain Compensation) processing is performed. That is, the gain of the amplifier circuit for each transducer at the preceding stage of the ADC is the product of the gain given by the static gain control according to the diagnosis mode and the gain given by the dynamic gain control of the TGC processing. Is determined by

[0006]

SUMMARY OF THE INVENTION As described above, TG
The gain of the C processing is determined according to the depth at which the ultrasonic echo occurs, and the gain according to the diagnostic mode is constant for each diagnostic mode. That is, these gain controls are
Rather than directly considering the received signal level, the dynamic range of the received signal
Control is performed to effectively use the dynamic range of the ADC. However, in practice, the condition is not always satisfied, and there is a problem that the dynamic range of the ADC cannot be effectively used to the utmost. Specifically, if the actual received signal level is lower than the assumed level, the dynamic range of the ultrasonic receiving circuit will be lower than the dynamic range of the ADC, while if it is higher than the expected level, the ADC will overflow. There is a problem that the output waveform is distorted.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and dynamically controls the gain of an amplifier circuit in a preceding stage of an ADC according to the level of a received signal to maximize the dynamic range of the ADC. It is an object of the present invention to provide an ultrasonic diagnostic apparatus including a usable receiving circuit.

[0008]

According to a first aspect of the present invention, there is provided an ultrasonic diagnostic apparatus for transmitting and receiving ultrasonic waves, amplifying a received signal from the transmitting and receiving means, and outputting the amplified received signal. Amplifying means for adjusting the gain, and converting the received signal from the amplifying means into a digital received signal,
Digital conversion means for outputting an overrange signal when a received signal exceeding an overrange determination value is input from the amplification means, and dynamic range control for feedback-controlling the gain of the amplification means in response to the overrange signal Means.

According to the present invention, the dynamic range control means increases or decreases the gain of the amplifying means according to the overrange signal output from the digital conversion means. The overrange determination value is determined based on the maximum input signal level that can be converted by the digital conversion means. As a preferable mode, the maximum input signal level itself or a level lower by a certain value is set. You.

[0010] In the ultrasonic diagnostic apparatus according to the second invention, the dynamic range control means performs the feedback control of the gain in accordance with the output frequency of the overrange signal.

According to the present invention, the gain of the amplifying means is increased or decreased in accordance with the number of occurrences of the overrange signal in a certain time range or a certain spatial region scanned by, for example, an ultrasonic beam. For example, when the output frequency of the over-range signal is larger than the reference value using a certain value or two values consisting of an upper limit and a lower limit as a reference value, the gain of the amplifying means is reduced by a certain amount. When it is smaller, the dynamic range control means controls to increase the gain of the amplification means by a certain amount. Thus, the dynamic range of the received signal amplified by the amplifying unit is maintained in a substantially constant relationship with the dynamic range of the digital converting unit.

An ultrasonic diagnostic apparatus according to a third invention is the ultrasonic diagnostic apparatus according to the second invention, wherein the dynamic range control means includes a frequency determination means for determining the output frequency, and the output frequency falls within a predetermined target range. A comparison determination unit that outputs a gain decrease signal that decreases the gain when the output frequency exceeds the upper limit of the target range, and outputs a gain increase signal that increases the gain when the output frequency falls below the lower limit of the target range. It is characterized by having.

According to the present invention, the dynamic range control means performs feedback control of the gain of the amplification means based on the target range given for the output frequency of the overrange signal. Thus, the dynamic range of the received signal amplified by the amplifying means always falls within a certain range. The relationship between the dynamic range of the received signal and the dynamic range of the digital conversion means is always realized by effectively using the dynamic range of the digital conversion means by adjusting the overrange determination value and the target range as parameters. Can be set to

According to a fourth aspect of the present invention, in the ultrasonic diagnostic apparatus according to the third aspect, the transmitting / receiving means includes a plurality of transducers provided in parallel for outputting the received signals, and the amplifying means comprises: The digital conversion means includes a plurality of variable gain amplifiers provided for each of the vibrators, the digital conversion means includes a plurality of analog-to-digital converters provided for each of the variable gain amplifiers, the dynamic range control means The frequency determination means determines the output frequency based on a total value of the number of times of the overrange signal output from a part or all of the plurality of analog / digital converters.

In a preferred aspect of the fourth invention, the amplification means sets a common gain value to each of the variable gain amplifiers as the gain. Also,
In another preferred aspect, the amplification means sets an individual gain value for each of the variable gain amplifiers as the gain. In another preferred aspect, the dynamic range control means generates a logical sum of the overrange signals output from some or all of the plurality of analog / digital converters, and It is characterized by having a logical sum operator for outputting to the frequency determining means.

According to a fifth aspect of the present invention, in the ultrasonic diagnostic apparatus according to the first aspect of the present invention, the frequency determining means determines the number of times of the overrange signal generated within a gate range set along a beam direction of the ultrasonic wave. The output frequency is determined.

According to the present invention, the depth in the ultrasonic beam direction corresponds to the gate range, and the gain of the amplifying means is set so that the dynamic range of the digital conversion means is effectively used in the depth range of interest for observation. Can be adjusted. For example, if it is desired to observe only a relatively deep region with high accuracy, if the gate range is set so as to exclude a shallower region, a shallow region in which an overrange signal is likely to be generated due to a strong received signal strength close to the transmitting and receiving means. The dynamic range of the digital conversion means can be adjusted to the received signal from the depth region of interest without being affected.

The ultrasonic diagnostic apparatus according to a sixth aspect of the present invention is the ultrasonic diagnostic apparatus according to the above aspect, wherein the transmission and reception of the ultrasonic waves are repeatedly performed.
The frequency determining means has an averaging means for calculating an addition value obtained by adding the number of times of the overrange signal generated by each of the transmissions and receptions over a plurality of continuous transmissions and receptions. It is characterized by doing.

According to the present invention, the averaging means smoothes the output frequency of the overrange signal by performing, for example, a moving average between a plurality of ultrasonic beams. Thus, for example, when a tomographic image is formed by a plurality of ultrasonic beams, a change in gain in the image is suppressed, and an easy-to-view image is obtained.

In a preferred aspect of the present invention, the lower limit of the target range in the comparing and judging means is zero.

[0021]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic block diagram of an ultrasonic diagnostic apparatus according to an embodiment of the present invention. This ultrasonic diagnostic apparatus performs reception dynamic focus,
The received signal is processed to display a B-mode tomographic image of a living tissue or a color Doppler image of a blood flow.

Each of the transducers 4 constituting the transducer array 2 arranged in the probe receives a transmission signal 8 generated by the transmission section 6 and emits an ultrasonic pulse into a living body.
Then, the ultrasonic pulse generates a reflection having an intensity corresponding to the change in the acoustic impedance of the tissue in the living body. Each transducer 4 detects this reflected wave, and a plurality of channels corresponding to each transducer 4 are output from the transducer array 2. Is received. The received signal 10 is amplified by an amplifier 12 and is converted to a digital converter 14
Is converted into a digital reception signal 16. Amplifier 1
2. Each of the digital conversion units 14 includes a plurality of preamplifiers 18 and a digital conversion circuit 20.

The digital reception signal 16 is supplied to the phasing addition circuit 3
Input to 0. The phasing addition circuit 30 includes a digital delay unit 32 provided for each channel and capable of controlling a delay amount, and an adder 34 for adding their outputs.
Each digital delay unit 32 receives a control signal from the scanning control unit 36 and adjusts the delay amount according to the direction of the ultrasonic beam and the focus position. By the way, the digital delay 32 is
For example, it is constituted by a shift register.

The added received signal 38 is input to an I / Q generation circuit 40, where an I signal and a Q signal, which are complex signal components used for Doppler processing, are generated. The tissue tomographic echo processor 42 and the color Doppler processor 44 process this complex signal. The tissue tomographic echo processing unit 42 calculates the power of the signal from the complex signal and forms a B-mode image or an M-mode image. The color Doppler processing unit 44 performs an autocorrelation process to form a Doppler image. Each of these processing units 42 and 44 converts the formed image data into a DSC (Di
gital Scan Converter) 46. DSC46
Synthesizes these image data, and the display 48 displays the DSC4
From 6, image data is read out at a predetermined frame rate and displayed.

The feature of the present apparatus lies in gain control for the amplifier 12. This gain control is performed by the digital conversion unit 14.
The control is performed by a feedback loop including the gain control unit 60 and the gain control unit 60. FIG. 2 is a block diagram illustrating a circuit configuration of a feedback loop including the amplifier 12, the digital converter 14, and the gain controller 60. In this figure, control signals such as a clock for operating each block are omitted. Each digital conversion circuit 20 is a set of a comparator receiving an analog input and an ADC. A threshold corresponding to the input range of the ADC, that is, a threshold corresponding to the upper limit of the voltage that can be converted by the ADC is set in the comparator, and a pulse is generated when the input received signal exceeds the threshold. This is the overrange signal 70. The overrange signal 70 output from the comparator of the digital conversion circuit 20 of each channel is input to the gain control unit 60.

The overrange signal 70 input to the gain control unit 60 is first ORed by the OR circuit 100 and bundled into one signal. Hereinafter, the circuit for determining the gain of the amplification unit 12 determines the gain at the time of tissue tomographic echo processing for generating a B-mode tomographic image or the like (hereinafter, referred to as B-mode and at the time of B-mode processing). And a circuit for determining a gain during color Doppler processing (hereinafter, referred to as D mode processing).
The circuit configurations are the same. The gain determined in each case is selected and used according to the type of the mode.
Here, first, the functions common to them will be described using the block configuration of the gain determination circuit at the time of the B mode processing in FIG. 2, and then the details of each gain determination circuit will be described.

Now, the gain of the amplifying unit 12 is optimized and A
The in-vivo depth range in which the DC dynamic range is to be used effectively is referred to as a target depth range. The scanning controller 36 controls the gate signal 1 for each ultrasonic beam in synchronization with a period in which a reception signal from the target depth range is obtained.
02 is generated. The gate circuit 104 opens in response to the gate signal 102, and allows only one of the overrange signals input from the OR circuit 100, which is generated by the reception signal of the one ultrasonic beam in the target depth range.

The counter 106 counts up the overrange signal passing through the gate circuit 104 for each ultrasonic beam. That is, the counter 106 sequentially outputs the number of overrange signals generated in the target depth range on each ultrasonic beam. The subtractor 108 counts the count value A of the counter 106 for the current ultrasonic beam.
_i and a predetermined number (m
Book. ) Count value A for previous ultrasonic beam
_im and the difference A _i −A _im is output.
Note that the digital delay unit 110 is a memory that performs a FIFO operation.

The integrator 112 accumulates and adds the difference data sequentially output from the subtractor 108 in the transmission / reception cycle of the ultrasonic beam. As can be readily seen, the value output from the integrator 112, the sum of the count value A _i Recent m duty, that is, _{A i + A i-1 +} ... + A i-m + 1. Thus, the digital delay unit 110, the subtractor 108, and the integrator 112
This is an averaging means for performing a moving average process over m ultrasonic beams. This moving average indicates the output frequency of how much the received signal has overflowed the input range of the ADC within the target depth range of the m beams. Therefore, up to the integrator 112 of the gain control unit 60 functions as a frequency determination unit that determines the output frequency.

The moving average value, which is the output frequency, is input to a comparator 114, which is a comparison determining means. A target range of the output frequency is set in the comparator 114. For example, the upper limit of the target range is set to a certain finite positive value, and the lower limit is set to zero. When the output frequency exceeds the upper limit value, the comparator 114 outputs a countdown signal DN for decreasing the count of the next counter 116. On the other hand, when the output frequency is 0, the comparator 114 outputs a countup signal UP for increasing the count. Output. The operation of the comparator is performed in synchronization with the transmission / reception cycle of the ultrasonic beam.

The count of the counter 116 is converted into an analog signal by the digital / analog converter 118 at, for example, the period of the ultrasonic beam or the period of the frame.
This is fed back to the amplifier 12 as a gain signal 120. The functions described above are common to the gain determination circuits for the B mode processing and the D mode processing. As described above, the gain control unit 60 controls the amplifying unit 12 so that the output frequency of the overrange signal converges to its target range.
Dynamic range control means for feedback-controlling the gain of each preamplifier 18 in the section. That is, the gain controller 60 controls the dynamic range of the received signal to match the dynamic range of the ADC in the digital conversion circuit 20, that is, the maximum value of the received signal approaches the upper limit of the input range of the ADC. It is possible to maximize the effective use of the range.

Next, the gain determining circuits used in the B mode processing and the D mode processing will be described. B
At the time of mode processing, an image is formed based on the amplitude value of the received signal. Therefore, if the gain changes between beams in one frame of an image formed by beam scanning, the image becomes difficult to see. Therefore, at the time of the B mode processing, it is necessary to increase the number m of beams on which the moving average processing is performed to a certain extent or more. For example, the gain determination circuit at the time of the B mode processing determines the output frequency of the overrange signal in units of frames using beams of one or more frames, and performs control such that the gain for the amplification unit 12 is changed in units of frames. Further, as another method of solving the above-described image inconsistency due to a gain variation between beams,
At the time of image formation in the tissue tomographic echo processing unit 42, it is conceivable to correct the luminance value by performing inverse conversion according to the gain adjustment before analog-digital conversion.

The gate circuit 102 of the gain determination circuit at the time of the B-mode processing is intended to remove a region of no interest in observation as described above and to optimally adjust a dynamic range in the region of interest. Therefore, when observing the whole area, it may not be necessary.

At the time of the D mode processing, the frequency analysis of the received signal is performed, and an image is formed based on the phase shift amount of the received signal. For example, based on the Doppler shift of the frequency, an image is displayed in which the magnitude of the blood flow velocity is associated with the color. Here, the received signal from the blood flow to be processed is extremely small as compared with a signal from another living tissue, for example, a heart wall. In order to adjust the dynamic range of the ADC to a small signal from the blood flow, a large signal from another tissue becomes excessively input.
The gate signal for 4D is generated to satisfy not only the condition of the target depth range but also the condition of excluding the existing range of other tissues. Such processing can be performed, for example, by using a tomographic image information of a living tissue obtained by the B-mode processing to mask a region where strong reflection occurs. Also, a clutter removing circuit for removing a signal from a stationary echo source, for example, an MTI (moving
A gate signal to the gate circuit 104D may be generated by using a target indication) circuit or the like so as to mask a portion where an input and an output have a difference, that is, a removed portion. Thus, the gate circuits 104D and B
If a region of interest for observation is specified using the gate circuit 104 or the like at the time of mode processing, the gain control unit 60 performs AD control on the received signal in that region by feedback control.
The gain is automatically adjusted to match the dynamic range of C, and high-precision analog-to-digital conversion is realized. Since the amplitude value of the received signal is not represented in the image obtained by the D-mode processing, there is no problem even if the moving average is not performed for each frame.
A configuration without the averaging means including the 0D, the subtractor 108, and the integrator 112D is also possible.

In the above description, the lower limit of the comparator 114 is set to 0.
And This lower limit is determined by the overrange determination value set in the comparator in the digital
Is particularly preferable when the upper limit of the convertible voltage itself is close to or close to the upper limit. It is also possible to set the overrange determination value to a lower value and perform suitable gain control by setting the lower limit value of the comparator 114 to a positive value smaller than the upper limit value.

It is also possible that the OR circuit 100 takes a logical OR of only a part of the overrange signals of all the channels instead of a logical OR. At this time, some of the channels may be selected according to the beam direction. Further, a gain control unit may be individually provided for each channel without providing the OR circuit 100.

The gain control unit 60 has different gain signals for the B mode processing and the D mode processing, but the same value is set for each preamplifier 18. On the other hand, in the gain control unit 60, for example, it is possible to multiply the count value of the counter 116 by a factor for each channel, and to apply an individual gain signal to each preamplifier 18. For example, among the TGC processes for correcting the difference between the depth and the amount of attenuation different between the channels, the correction between the channels can be realized by incorporating the above factors.

[0038]

According to the ultrasonic diagnostic apparatus of the present invention, AD
The gain of an amplifier circuit such as a preamplifier provided in the stage preceding C is dynamically controlled in accordance with the level of the received signal, and the received signal is amplified so as to match the input range of the ADC. As a result, the dynamic range of the ADC is used to the utmost, the analog-to-digital conversion of the received signal is performed with good accuracy, and the effect of improving the dynamic range of the device is obtained.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram of an ultrasonic diagnostic apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a circuit configuration of a feedback loop for gain control.

[Explanation of symbols]

2 transducer array, 4 transducers, 10 received signals, 12
Amplifying unit, 14 digital conversion unit, 16 digital reception signal, 18 preamplifier, 20 digital conversion circuit, 3
0 phasing addition circuit, 32 digital delay unit, 34 adder, 42 tissue tomographic echo processing unit, 44 color Doppler processing unit, 46 DSC, 48 display, 60 gain control unit, 70 overrange signal, 100 OR circuit,
104 gate circuit, 106, 116 counter, 108
Subtracter, 110 digital delay, 112 integrator,
114 comparator, 118 digital-to-analog converter.

Claims (10)

[Claims] 1. A transmission / reception unit for transmitting and receiving an ultrasonic wave, a gain-adjustable amplification unit for amplifying a reception signal from the transmission / reception unit and outputting an amplified reception signal, and a reception signal from the amplification unit To a digital reception signal, and a digital conversion unit that outputs an overrange signal when a reception signal exceeding an overrange determination value is input from the amplification unit, and the amplification unit responds to the overrange signal. And a dynamic range control means for performing feedback control of the gain of the ultrasonic diagnostic apparatus. 2. The ultrasonic diagnostic apparatus according to claim 1, wherein said dynamic range control means performs feedback control of said gain in accordance with an output frequency of said overrange signal. 3. The dynamic range control means includes: frequency determination means for determining the output frequency; and the gain when the output frequency exceeds an upper limit of the target range so that the output frequency falls within a predetermined target range. 3. An ultrasonic wave according to claim 2, further comprising: a comparing and judging means for outputting a gain decreasing signal for decreasing, and outputting a gain increasing signal for increasing the gain when the output frequency falls below a lower limit of a target range. Diagnostic device. 4. The transmitting and receiving means includes a plurality of transducers provided in parallel for outputting the received signal, and the amplifying means includes a plurality of variable gain amplifiers provided for each of the transducers. Wherein the digital conversion means includes a plurality of analog-to-digital converters provided for each of the variable gain amplifiers, wherein the frequency determination means of the dynamic range control means includes a plurality of the analog-to-digital converters. 4. The ultrasonic diagnostic apparatus according to claim 3, wherein the output frequency is determined based on a total value of the number of times of the overrange signal output from a part or all of the ultrasonic diagnostic apparatus. 5. 5. The ultrasonic diagnostic apparatus according to claim 4, wherein said amplification means sets a common gain value for each of said variable gain amplifiers as said gain. 6. The ultrasonic diagnostic apparatus according to claim 4, wherein said amplification means sets an individual gain value for each of said variable gain amplifiers as said gain. 7. The dynamic range control means generates a logical sum of the overrange signals output from a part or all of the plurality of analog-to-digital converters and outputs the logical sum to the frequency determination means. The ultrasonic diagnostic apparatus according to claim 4, further comprising a logical sum operation unit. 8. The frequency determination unit according to claim 3, wherein the frequency determination unit determines the output frequency based on the number of times of the overrange signal generated within a gate range set along the beam direction of the ultrasonic wave. An ultrasonic diagnostic apparatus according to any one of claims 1 to 7. 9. The transmission / reception of the ultrasonic wave is repeatedly performed, and the frequency determination unit obtains an added value obtained by adding the number of times of the overrange signal generated by each transmission / reception over a plurality of continuous transmission / receptions. The ultrasonic diagnostic apparatus according to any one of claims 3 to 8, further comprising averaging means, wherein the output frequency is determined based on the added value. 10. The ultrasonic diagnostic apparatus according to claim 3, wherein a lower limit of the target range in the comparison / determination means is zero.