JPS59174147A - Ultrasonic photographing apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an ultrasonic imaging device using a split transducer, for example, an ultrasonic tomographic imaging device for diagnosis.

[Prior art]

In the wave reception section of an ultrasonic imaging device using a split transducer, the signals received by each transducer element are A/D converted, temporarily written to a digital memory, read out again, and phased and summed to achieve one reception. The A/D conversion eaves-to-wall method for forming the system is an effective method for realizing an imaging system with high spatial resolution because it provides a large delay time and allows free real-time dynamic focus reception.

When implementing this method, the setting of the quantization resolution of the A/D converter is very important in practice, since it has a great effect on the performance and cost of the device.

Therefore, first, the S/N ratio of the imaging system will be explained. FIG. 1 to FIG. 3 explain the establishment of a reception system spatial response function in the pulse echo method using a split transducer. Figure 1 shows one oscillator
This shows an example of the two-dimensional spatial response function of C, which has a value only on the circular arc (hatched area) with a thickness corresponding to the pulse length, and has a value of O in the other region B. F is a focal point, but with one element there is no particular peak. FIG. 2 shows the tolerance function when only three elements, ElsBa and En, of the elements constituting the divided vibrator array are operated and phasing and addition processing is performed. The three arcs corresponding to the three elements overlap in the vicinity of the focal point F, are added in the same phase, and strengthen each other to form a peak P. Figure 3 is a schematic diagram of the response function when n elements (El to E,) are operated.The arcs corresponding to each element overlap each other, and the peak P and butterfly A type plateau-like region S is formed. Here, the value of the area of S (this is called acoustic noise) with respect to the peak value of the focal point F is roughly estimated to be on the order of l/n. However, the values of side lobes and grating lobes were excluded from this estimate. In an actual device, in addition to this acoustic noise, noise known as electrical noise, which exists even when the received sound pressure is infinitesimal, appears on the entire screen. This is due to thermal noise of the amplifier, etc., and appears in the area on the screen corresponding to area B, and determines the dynamic range of the receiving system. The above is
This is a consideration when configuring a receiving system without quantizing the amplitude axis.

As shown above, the original 8/N ratio without amplitude quantization is
Since the region S in the case of FIG. 3 is different from other regions, the influence of quantization noise due to amplitude doji conversion can also be evaluated separately for the above two regions.

In the conventional A/D conversion conversion phase method, the magnitude of the amplifier input equivalent of the width axis quantization unit is set equally over the entire conversion range, so the generated quantization noise is uniform regardless of whether it is inside or outside the region S. It was the size of . In this case, the required resolution R0 of the A/Di converter is determined by the reciprocal of the required electrical noise level, that is, the required receiving system dynamic range D, as shown in the following equation.

Ro = v'T; 1/D/ 2 =-・"-(1)
Here, n is the number of receiving elements, and R is determined so that the probability that quantization noise exceeding a set electrical noise level will appear is 5% or less.

Specifically, taking as an example the case where n=16 and the dynamic range is 60d13, that is, n=10'', the A required by the conventional method is
/D converter resolution R is determined by the following formula: % Formula % (2) Therefore, the required number of A/D converter bits is 8 to 9.

[Summary of the invention]

In contrast, in the present invention, the number of required A/D converter bits is reduced by varying the set noise level inside and outside the region S of the diagram. The noise level outside the region S, that is, the electrical noise level, is also determined by the dynamic range D0 when focusing on one A/D converter. The relationship between Do and the dynamic range D of the receiving system is calculated by taking the reciprocal of equation (1) as follows: D0=2D/-VT'ii...
...(3) On the other hand, the noise level caused by quantization in S, that is, the newly added acoustic noise level, is 1
When focusing on each A/D converter, it is determined by its relative accuracy, that is, the ratio of the quantization error to the true signal value. The relationship between the relative accuracy E0 and the expected root mean square value E of the acoustic noise newly added to the receiving system is E"EO/v'Dingsei...
(4) In order to reduce the probability that the newly added acoustic noise level exceeds the original acoustic noise level by quantization to 5% or less, the following equation should be satisfied.

2E (1/n ・・・・・・・・・・・・・・・
-Song (5) Therefore, from (4) and (5), the EO required for the A/D converter is determined as follows.

EO=V'E 〒/2 ・・・・・・・・・・・・・・・
・(6) Specifically, for the same example as before, when determining the characteristics required of the A/D converter, Do = 290. E0=0.22...-(7) In order to find the required number of A/D converter bits from the value of equation (7), perform the following conversion steps at the A/D converter input. Consider an example of how to make a decision.

That is, from the origin to the upper limit of the conversion range, the quantization steps are xl s xt m...,Xk,...,X
When m, ...... (8) The range from the origin to the lower limit of the conversion range is determined symmetrically with equation (8). Specifically, when calculating the example of equation (7), m=14. To illustrate the meaning of equation (9), it is p1 logarithmic characteristic as shown in FIG. Here, the total number of quantization steps is 2m+1=29=24-'...
(10) Therefore, the required number of A/D conversion bits is 5. Again, it can be seen that in this example, the number of conversion bits is reduced by 3 to 4 according to the present invention. A to ultrasound
Since the circuit scale and cost of a flash-type high-speed A/D converter convenient for /DK conversion are approximately proportional to the total number of quantization steps, the present invention reduces the A/D converter cost to 1/16 to 1/16. It is reduced to 1/8 times.

[Embodiments of the invention]

FIG. 5 is a block diagram showing the configuration of an embodiment of the present invention. The signal received by the transducer element E passes through the preamplifier PA and the bandpass filter BPF to the fourth
After passing through an amplifier LA with logarithmic input/output characteristics as in the example shown in the figure, an A/D converter AD with a uniform quantization step
The signal is A/D converted by C and written to line memory LMI or LM2. Note that SWl and SW2 are switches. On the other hand, the data read from the line memory is subcoded by a decoder DEC having an exponential input/output characteristic as in the example of FIG. 6, that is, a characteristic corresponding to the inverse function of FIG. It is input to the phase adder Σ. However, like FIG. 4, FIG. 6 also shows the upper half of the origin, and the lower half is symmetrical to that point. This decoder can be realized at low cost by using the ROM address as input data and the contents as output data, for example, as shown in FIG. Although a configuration in which the decoder DEC is placed before the line memories LMI and LM2 is conceivable, the configuration shown in FIG. 5 is advantageous in that the line memory capacity can be reduced. When the filter BPF is inserted into the amplifier system, it must be inserted before the amplifier LA, as shown in FIG.

This is because, due to the compressive characteristics of the amplifier LA, the amplifier LA
This is because harmonic components exist as signal effective components in the output. An amplifier LA having vertically symmetrical logarithmic characteristics can be constructed, for example, by combining commercially available logarithmic amplifiers LQG as shown in FIG. In other words, the input signal is
One is directly connected to the logarithmic amplifier LQG and the other is connected to the logarithmic LQG through the signal inverter INV, and the sum of the outputs of the two-wire logarithmic amplifier LQG is obtained by the adder Σ.

Fluctuations in the characteristics of the individual amplifiers LA can be corrected by measuring the characteristics of the individual amplifiers LA and providing the inverse characteristics to the corresponding decoders DEC.

FIG. 8 is a block diagram showing the configuration of another embodiment.

The difference from the case shown in FIG.
DC' is used. A/ in the example of equation (7)
The input/output characteristics of the D converters A and DC' may be as shown in FIG. 4.

Such characteristics can be realized, for example, by changing the resistance value of the resistance ladder that determines the quantization step of the flash type A/D converter as shown in FIG.

FIG. 10 shows another embodiment, in which the A/D converter ADC'
This is an example of the input/output characteristics of Figure 4.

Different from the case of FIG. 4, the manner in which the quantization step interval increases from the origin to the upper limit of the conversion range is a geometric series with a common ratio of 2.

This simplifies the quantization step setting of the p, A/Df converter, and also makes the input/output relationship of the decoder DEC simple as shown in the table shown in FIG. If the relationship is as shown in the table above, you do not necessarily need to use RQM,
It can be looked at using a simple logic circuit.

〔Effect of the invention〕

As described above, according to the present invention, an ultrasonic imaging device using the A/D conversion phasing method can be realized with a significant reduction in cost without deteriorating performance.

Therefore, the industrial significance of the present invention is significant.

[Brief explanation of the drawing]

Figures 1, 2, and 3 show the two-dimensional spatial response of the reception wave when one transducer element, three elements, and all elements constituting a split transducer array are manufactured, respectively. FIG. 4 is a diagram showing an example of input/output characteristics of A/D conversion in the second embodiment of the present invention, and FIG. 5 is a block diagram showing another embodiment of the present invention. 6 is a diagram showing the input/output characteristics of the decoder, FIG. 7 is a diagram showing the configuration of the logarithmic amplifier, FIG. 8 is a block diagram showing another embodiment of the present invention, and FIG. 9 is a diagram showing the A of the decoder. FIG. 10 is a diagram showing the ratio of the resistance values between the steps of the resistance ladder that concludes the quantization step of the /D conversion step. The figure shown in FIG. 11 is a diagram similarly showing an input-to-input correspondence table of the decoder. Agent Patent Attorney Akira Tsutsuhashi Tsuki K

Claims (1)

[Claims] 1. A split transducer, an amplifier for amplifying the signal received by each transducer element, and A for A/D converting the output signal.
1. An ultrasonic imaging apparatus comprising: a /D converter, a decoder that decodes the digital output of each A/D converter, and a phasing adder that phasing and adding the output signals of each decoder. 2. In the apparatus according to claim 1, the interval of the quantization step converted to the amplifier input is set such that the interval for the large amplitude signal is set larger than the interval for the small amplitude signal, and the doji conversion step is made non-uniform. It is characterized by compensating for the non-linear characteristics caused by the decoder by giving its inverse characteristics to the decoder input/output characteristics, and keeping the relationship between the amplifier input analog signal and the phasing adder digital signal linear excluding error components. device to do. 3. Range of % Permission Required The device according to item 2, characterized in that the input/output characteristic of the amplifier is a logarithmic characteristic, and the input/output characteristic corresponding to an index function that is an inverse function of the input/output characteristic is given to the decoder. A device that does this. 4. In the device according to claim 2, the A
/D7 A device characterized in that the size of the quantization unit of the exchange is set to increase stepwise from near the origin to the upper and lower limits of the operating range. 5. The device according to claim 4, wherein the A
A device characterized in that the operating range of the /D converter is divided into N stages on one side symmetrically about the origin, and the size of the quantization unit is set to increase stepwise from near the origin to the upper and lower limits of the operating range. .