JP3665504B2 - Signal sampling device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a signal sampling apparatus that generates a data sequence by thinning and sampling an original signal data sequence and reducing the number of data.
[0002]
[Prior art]
For example, in an ultrasonic diagnostic apparatus, an ultrasonic wave is transmitted to a subject, and a tomographic image is generated based on the intensity of a reflected wave from each point of the subject. For example, by emitting an ultrasonic pulse once from the probe, an A-mode signal including a reflection signal from each part of the subject on a line scanned by the ultrasonic beam is generated. The A mode signal is represented as a single linear image on the screen, and each point on the line is displayed with a luminance corresponding to the amplitude of the reflected signal. The so-called B-mode image is a tomographic image obtained by sequentially moving the position and angle of the probe little by little. This B-mode image is a two-dimensional image having an axis in the ultrasonic transmission / reception direction and an axis in the movement direction of the probe that the A mode has.
[0003]
The reflected signal obtained as an analog signal is converted into a digital signal by an A / D (analog to digital) conversion circuit, and signal processing is performed using the digital signal. Sampling in this A / D conversion is performed at a relatively high frequency corresponding to the baseband frequency of the transmitted ultrasonic wave. However, the spatial frequency corresponding to the pixel resolution of the image display device is lower than the sampling frequency possible in the A / D conversion circuit. Therefore, when an image of a signal sampled at a high frequency by the A / D conversion circuit is to be displayed, it is necessary to resample at a frequency corresponding to the number of display pixels of the display device.
[0004]
In the conventional method, the ultrasonic reflected signal is passed through an anti-aliasing filter having a frequency corresponding to the number of display pixels as a Nyquist frequency before A / D conversion. Sampling processing is applied. This sampling method includes point sampling and maximum value sampling. FIG. 6 is a schematic diagram showing an example of sampling by these conventional methods. FIG. 5A shows a data string input from the A / D conversion circuit to a circuit that performs re-sampling. The horizontal axis is the time axis, and the vertical direction corresponds to the data value. FIGS. 7B and 7C are diagrams showing the results of point sampling and maximum value sampling for the input data, respectively. In this example, resampling is time t_ThreeThereafter, it is performed every 4 data.
[0005]
In the point sampling shown in FIG. 5B, each time t which is the output timing of resampling._iThe input data at is output as a result of resampling. On the other hand, in the maximum value sampling shown in FIG._iThe maximum value of the input data after the previous resampling timing, that is, t_i-1<T ≦ t_iThe maximum value of the input data in the time axis range is output. These resampled data are held as values representative of the reflected signal until the next resampling timing. By this re-sampling process, the input data string is thinned out in accordance with the resolution of the display device, and a rough change in the reflected signal is extracted.
[0006]
[Problems to be solved by the invention]
Any of the above-described re-sampling methods has a problem that a deviation between the original reflected signal waveform and the reflected signal waveform after re-sampling becomes large.
[0007]
First, in a point sampling method in which band limitation is applied at a Nyquist frequency and then re-sampling is performed at regular intervals, input data between resampling timings is discarded. That is, fine information obtained by ultrasonic transmission / reception is not effectively used. Specifically, if input data such as a maximum value or a minimum value is positioned between resampling timings, there is a problem that important input data representing the characteristics of such a reflected signal is not sampled. Therefore, for example, when the tomographic image is generated by converting the reflected signal into the luminance, the maximum value is not sampled, so that the luminance of the image is lowered and the image is uneven.
[0008]
On the other hand, in the maximum value sampling method, since the maximum value of the input data at each re-sampling interval is held, the luminance of the image does not decrease, but the waveform causes tailing as seen in FIG. End up. This tailing occurs because the timing at which the data reaches the maximum value and the output timing thereof are not synchronized with each other, and the occurrence time difference between adjacent resampling data and the output interval thereof fluctuate. This phenomenon has caused a problem that the resolution in the sampling direction is lowered and the apparent cutoff frequency becomes lower than the original Nyquist frequency.
[0009]
7 and 8 are explanatory diagrams for understanding the problem of the above-described conventional resampling process from another aspect, and FIG. 7 is a schematic diagram showing a state in which a sine wave is point-sampled at three different phases. It is. FIG. 8 is a schematic diagram showing a state in which the maximum value of the sine wave is sampled at the same three different phases as in FIG. 7A and FIG. 8A show the case where the resampling timing is positioned at the phase θ of the sine wave θ = 90 ° and 270 °, FIG. 7B and FIG. In the case of = 0 ° and 180 °, FIGS. 7C and 8C show the case of θ = 45 ° and 225 °.
[0010]
The case shown in FIG. 7A regarding the point sampling is a case where the maximum and minimum of the sine wave are captured and there is no problem. However, when the phase shifts from this position, for example, at the position shown in FIG. 5C, the amplitude of the sine wave is underestimated and the contrast is lowered. The case shown in FIG. 5B is an extreme case, and the amplitude does not appear and the signal becomes flat.
[0011]
With regard to maximum value sampling, the maximum value of the sine wave can be correctly captured at any phase, but the amplitude becomes small. For example, when the re-sampling period and the sine wave period are the same as shown here, the amplitude after the re-sampling is ½ of the original sine wave at the maximum (in the case shown in FIG. 8B). In an extreme case, the amplitude does not appear as shown in FIG.
[0012]
From these facts, it is understood that in the conventional resampling process, the amplitude of the hold value varies greatly depending on the phase of resampling even for the same input data string. Such a phenomenon occurs more or less not only in a sine wave but also in a general waveform, and the signal waveform after re-sampling is relatively greatly affected according to the sampling phase. Therefore, there has been a problem that information obtained by the ultrasonic probe is difficult to be faithfully reproduced on the screen.
[0013]
The present invention has been made to solve the above-described problems, and can accurately capture the maximum and minimum of the original waveform, suppress a decrease in luminance caused by point sampling, and resample a signal in the vicinity of the Nyquist frequency. It is an object of the present invention to provide a signal sampling device that can stably capture regardless of the phase, suppress a reduction in resolution caused by maximum value sampling, and can satisfactorily extract the characteristics of the original waveform before re-sampling.
[0014]
[Means for Solving the Problems]
  The signal sampling device according to the present invention isFor each section of the original signal divided into multiple sections,Each sectionCorresponding toA signal sampling device for obtaining a sampling value, wherein an extreme value detecting means for detecting an extreme value of the original signal, and a sampling value determination that determines a value based on the extreme value as the sampling value for the section having the extreme value Means.
[0015]
According to the present invention, the extreme value detecting means checks whether or not the original signal has a maximum or minimum within each section. If there is a local maximum or local minimum in the section, the sampling value determining means determines the sampling value corresponding to the section based on the value of the original signal at any of those points, that is, the local maximum or local minimum. Determine and output. Therefore, since the values reflecting the maximum value and the minimum value of the original signal are captured in sampling, the contrast does not decrease. In addition, by capturing the maximum and minimum values for the original signal in the vicinity of the Nyquist frequency, a sampling data string that varies at the same frequency as the original signal can be obtained. Here, the original signal may be an analog signal or a digital data string. In addition, the sampling value corresponding to the section having the extreme value can be the value itself when there is a single extreme value included in the section, or can be calculated based on a predetermined rule from the extreme value. You can also In addition, when there are a plurality of extreme values, that is, a maximum value and a minimum value at the same time in a section, a predetermined one can be simply selected as a sampling value, or signal values at both ends of the section or adjacent to each other Based on a predetermined determination criterion that also takes into account the signal waveform of the section, it is possible to determine which of the features of the original signal is more suitably represented, and to select the preferable extreme value as the sampling value.
[0016]
In another signal sampling device according to the present invention, the sampling value determining means further determines, as the sampling value, the value of the original signal at a predetermined position in the section for the section not having the extreme value. It is characterized by.
[0017]
According to the present invention, for a section where there is no extreme value, the sampling value determining means determines the value of the original signal at a predetermined position in the section as the sampling value. By sampling at a fixed position in each section, the relationship between the time interval on the original signal of adjacent sampling values and their output timing difference is kept constant unlike the maximum value sampling. That is, in the present invention, basically, as with point sampling, the time when the original signal is sampled and the timing when it is output are synchronized with each other, so that a decrease in resolution such as tailing is suppressed.
[0018]
In a preferred aspect of the present invention, the sampling value determining means determines, as the sampling value, the value of the original signal at a predetermined position in the section for the section having the plurality of extreme values.
[0019]
Another preferred aspect of the present invention is a signal sampling device in which the predetermined position is one end of the section. One end of the section is preferable in that it is specified by an easier process than other positions. Another preferred aspect of the present invention is a signal sampling device in which the predetermined position is the center of the section. In this aspect, the difference between the position of the original signal data to be sampled when there is no extreme value in the section and the position in the section when the extreme value exists is less than half of the section width. It is suppressed.
[0020]
  Another preferred aspect of the present invention is the signal sampling apparatus, wherein the sampling value determining means determines the extreme value as the sampling value for the section having a single extreme value. In another preferred aspect of the present invention, the signal sampling apparatus is characterized in that the extreme value is a maximum value.In a further preferred aspect, the sampling value determining means determines the sampling value by using an intermediate signal obtained by modifying the original signal based on the extreme value.
[0021]
  Another signal sampling apparatus according to the present invention is as follows.For each section of the original signal divided into multiple sections of constant width, Each sectionCorresponding toA signal sampling device for obtaining a sampling value, an extreme value detection means for detecting an extreme value of the original signal, and a signal conversion means for generating an intermediate signal by transforming the original signal based on the extreme value;A sampling value that extracts a signal value of the intermediate signal at intervals of the constant width and uses a signal value at a position corresponding to the interval in the extracted signal value of the intermediate signal as a sampling value corresponding to the interval. With decision meansIt is what has.
[0022]
In the above conventional sampling method, the extreme value is suitably reflected in the waveform after sampling according to the sampling phase, or conversely, the extreme value is not reflected at all in the sampling value and the signal waveform and the original represented by the sampling value sequence are used. The problem is that the difference from the signal becomes large. According to the present invention, the intermediate signal is generated by transforming the original signal based on the extreme value. The intermediate signal can be configured such that the extreme value is reflected in the sampling value regardless of the sampling phase. Therefore, even if the sampling value determining means simply performs sampling at regular intervals, the extreme value in the section is reflected in the sampling value.
[0023]
In a preferred aspect of the present invention, the signal value is maintained at the extreme value in a range in which the intermediate signal has the constant width and the position of the extreme value is included. is there.
[0024]
Another preferable aspect of the present invention includes window setting means for moving a window having a width corresponding to the section with the original signal, and the extreme value detection means is included in the window at each window position. The extreme value of the original signal is detected, and the signal conversion means sets the extreme value as a representative value at the window position when the extreme value is detected, and within the window when the extreme value is not detected. The signal sampling apparatus is characterized in that the original signal value at a predetermined position is a representative value, and the intermediate signal is constituted by the representative value.
[0025]
In another preferred aspect of the present invention, the extreme value detection means is based on a change rate detection means for detecting a change rate of the original signal in the window, and a position where the polarity of the change rate changes. An extreme value position determining means for determining an extreme value position is a signal sampling device.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
[Embodiment 1]
Next, embodiments of the present invention will be described with reference to the drawings. The embodiment of the present invention described here is an ultrasonic diagnostic apparatus having a B-mode image display function. The ultrasonic diagnostic apparatus scans the subject with ultrasonic waves emitted from the ultrasonic probe, and the reflected signal of the ultrasonic waves is converted into luminance of the display device and displayed as an image.
[0027]
FIG. 1 is a block diagram showing a main circuit configuration of the ultrasonic diagnostic apparatus according to an embodiment of the present invention. The reflected signal 1 that is an analog signal output from an ultrasonic probe (not shown) is digitally sampled by an A / D converter 2. The A / D converter 2 outputs time series digital data representing a change in the amplitude value of the reflected signal 1. Sampling in the A / D converter 2 is performed at a relatively fast frequency depending on the transmission frequency of the ultrasonic waves.
[0028]
The signal sampling processing unit 4 according to the present invention receives the digital data sequence generated by the A / D converter 2 as an original signal. This original signal data string is input to the maximum value selection circuit 6, the minimum value selection circuit 8, the data delay circuit 10, the subtractor 12, and the selection circuit 14, respectively. Window width data is input to the maximum value selection circuit 6 and the minimum value selection circuit 8. This window width is a parameter that determines the resampling period. That is, as will be described later, the original signal data every window width is output as a re-sampling value in principle, so that, for example, the screen scanning rate and the pixel resolution of the image display device (not shown) of the ultrasonic diagnostic apparatus The window width is determined according to.
[0029]
The maximum value selection circuit 6 is a circuit that outputs the maximum value from the original signal data traced back by the window width to the latest original signal data to the selection circuit 14. On the other hand, the minimum value selection circuit 8 is a circuit that outputs the minimum value from the original signal data traced back by the window width to the latest original signal data to the selection circuit 14.
[0030]
The data delay circuit 10 is a circuit capable of delaying the input original signal data by one sampling clock period of the A / D converter 2 and outputting the delayed signal. The delayed data output from the data delay circuit 10 is input to the subtractor 12.
[0031]
The subtractor 12 obtains a difference between the latest original signal data inputted without delay and the previous original signal data inputted from the data delay circuit 10, and sign data representing the sign of the difference is inputted to the shift register 16. Output to. The inflection point detection circuit 18 monitors the arrangement of the code data in the shift register 16 and detects whether or not the change rate polarity inflection point (inflection point) exists in the original signal data sequence cut out by the window width. To do.
[0032]
When the inflection point detection circuit 18 detects an inflection point from an increase to a decrease in the original signal data, it instructs the selection circuit 14 to select the maximum value data from the maximum value selection circuit 6. When a turning point from decrease to increase is detected, an instruction to select minimum value data from the minimum value selection circuit 8 is issued. When no inflection point is detected, an instruction to select the latest original signal data is issued.
[0033]
In response to this control signal, the selection circuit 14 has three data: the latest original signal data input from the A / D converter 2 and the data input from the maximum value selection circuit 6 and the minimum value selection circuit 8, respectively. Select one of these to output. The data string output from the selection circuit 14 has the same rate as the output of the A / D converter 2. The sampling circuit 20 is a circuit that resamples the data string at a high rate from the selection circuit 14 at a period corresponding to the window width.
[0034]
Next, an operation example of the signal sampling processing unit 4 will be described with reference to the drawings. FIG. 2 is a schematic diagram for explaining a process of generating an intermediate signal data sequence that is an output of the selection circuit 14 from the original signal data sequence. In each of FIGS. 9A to 9K, the horizontal axis is a time t (rightward is positive) and the vertical axis is a data value D (upward is positive). FIG. 4A shows an original signal data string, and FIG. 4K shows an intermediate signal data string. Black circles represent data. Hereinafter, the original signal data and the intermediate signal data at time t are respectively D_O(T), D_P(T). (B) to (j) in FIG. 6 represent data cut out by a window (window width is 5 data here) represented by black circles.
[0035]
Here, a case where the re-sampling interval of the signal sampling processing unit 4 is once per 4 data of the original signal data sequence will be described. That is, the signal sampling processing unit 4 divides the original signal data into four sections and outputs one sampling value for each section.
[0036]
In this apparatus, in order to detect an extreme value, a difference between adjacent data is obtained. Due to this, the window width, which is the number of data used for processing, is set to be one larger than the section width. That is, “5” is designated as the window width here, corresponding to the section width “4” of the resampling. Based on this window width, the maximum value selection circuit 6 and the minimum value selection circuit 8 make the past 5 data including the latest data of the original signal data string the targets of the maximum value selection process or the minimum value selection process.
[0037]
Further, there are four code data generated from the past five data including the latest original signal data. Therefore, when “5” is specified as the window width, the inflection point detection circuit 18 monitors the past four data including the newest code data held in the shift register 16. Here, the sign data has a value “1” when the subtraction result in the subtracter 12 is positive, that is, the change rate of the original signal data is positive (+), whereas the subtraction result is negative, that is, the original signal data When the rate of change is negative (-), the value is defined as "0". Under this definition, each code data is represented by 1 bit. When new code data is input, the shift register 16 shifts the existing stored contents to the left and converts the latest code data to the least significant bit b.₀To store. The inflection point detection circuit 18 reads out the lower 4 bits of the shift register 16 to thereby obtain a 4-bit code data string “b” including the latest code data._Threeb₂b₁b₀Then, the inflection point detection circuit 18 detects the inflection point in the window based on the bit pattern.
[0038]
For example, when the code data string is “1111” and “0000”, the original signal data is monotonically increasing and monotonically decreasing in the window, and has no inflection point. On the other hand, when the code data string is “1110”, “1100”, or “1000”, there is only one inflection point where the rate of change changes from positive to negative, that is, one local maximum point. On the other hand, when the code data string is “0001”, “0011”, or “0111”, there is only one inflection point where the rate of change changes from negative to positive, that is, a minimum point in the window. The inflection point detection circuit 18 controls the selection circuit 14 as described above based on the detection result of the inflection point.
[0039]
In the case of other bit patterns such as “0110”, a plurality of inflection points exist in the window. In this case, in this apparatus, a weighted criterion is required as to which inflection point to select and sample. Whether or not the extreme value is captured by performing the process of determining such a weighting criterion can be arbitrarily selected depending on the application. In general, resampling will not be performed at frequencies where such multiple inflection points occur in a single window. In consideration of this, in this apparatus, when a plurality of inflection points are detected, the processing load is reduced and the circuit configuration is simplified by treating them as if no inflection points exist.
[0040]
Now, time t_FiveThe window contains the time t₁~ T_FiveAre extracted (FIG. 2B). The maximum value selection circuit 6 and the minimum value selection circuit 8 each have a maximum value D in this window._O(t_Five), Minimum value D_O(t₁) Is output. The data delay circuit 10 has original signal data one older than the latest original signal data, that is, D_O(t_Four) Is output. The subtractor 12 is “D_O(t_Five-D_O(t_Four) ”Is generated, and new code data is generated and output to the shift register 16. Since the code data string is“ 1111 ”at this time, the inflection point detection circuit 18 determines that there is no inflection point. The pole detection circuit 18 controls the selection circuit 14 so as to select the latest original signal data._O(t_Five) Is intermediate signal data D_P(t_Five) Is output.
[0041]
Time t₆In FIG. 2, there is no inflection point in the window (FIG. 2C). Therefore, time t_FiveBy the same operation, the latest original signal data D_O(t₆) And intermediate signal data D_P(t₆) Is output.
[0042]
Time t₇The window contains the time t_Three~ T₇Are extracted (FIG. 2 (d)). In this case, the latest original signal data D_O(t₇) As the last D_O(t₆A smaller value is entered. Therefore, the output of the subtractor 12 changes to “0”, and the code data string output to the inflection point detection circuit 18 becomes “1110”. Based on this code data string, the inflection point detection circuit 18 determines that a local maximum point exists in the window. Then, the inflection point detection circuit 18 controls the selection circuit 14 so as to select the output from the maximum value selection circuit 6. Maximum value selection circuit 6 is time t_Three~ T₇Maximum value D at_O(t₆) Is output. Therefore, the selection circuit 14 receives this D_O(t₆) Is intermediate signal data D_P(t₇) Is output.
[0043]
Time t shown in FIGS. 2 (e) and 2 (f)₈, T₉In FIG. 4, code data “0” is sequentially input to the shift register 16 in accordance with newly input original signal data. As a result, the code data strings change to “1100” and “1000”, respectively, but both include inflection points from positive to negative. In other words, the state where there is a local maximum point in the window is the time t₇Has not changed since. Therefore, at these times, the time t₇By the same operation, the output from the maximum value selection circuit 6 is selected. From the maximum value selection circuit 6, the time t₇Since then, D continues_O(t₆) Is output, and intermediate signal data D_P(t₈), D_P(t₉) As D_O(t₆) Is output continuously.
[0044]
Time t shown in FIGS. 2 (g) to (i)_Ten~ T₁₂Since the code data string is “0000”, the inflection point detection circuit 18 determines that there is no inflection point in the window. The selection circuit 14 selects and outputs the latest original signal data based on the control signal from the inflection point detection circuit 18. Therefore, intermediate signal data D_P(t_Ten), D_P(t₁₁), D_P(t₁₂) As D_O(t_Ten), D_O(t₁₁), D_O(t₁₂) Are output in order.
[0045]
Time t₁₃The window contains the time t₉~ T₁₃Original signal data is cut out (FIG. 2 (j)). In this case, the latest original signal data D_O(t₁₃) As the last D_O(t₁₂A value greater than) is entered. Therefore, the output of the subtractor 12 changes from “0” to “1” so far, and the code data string output to the inflection point detection circuit 18 becomes “0001”. Based on this code data string, the inflection point detection circuit 18 determines that a minimum point exists in the window. Then, the inflection point detection circuit 18 controls the selection circuit 14 so as to select the output from the minimum value selection circuit 8. The minimum value selection circuit 8 receives the time t₉~ T₁₃Minimum value D at_O(t₁₂) Is output. Therefore, the selection circuit 14 receives this D_O(t₁₂) Is intermediate signal data D_P(t₁₃) Is output.
[0046]
The intermediate signal data string generated by the above processing is shown in FIG. This intermediate signal data is the time t when the maximum of the original signal data string is detected.₇The maximum value D of the original signal data over the following 3 data_O(t₆). Therefore, this causes time t₆Including four data equal to the sampling interval width D_O(t₆) Will be held. Similarly, the intermediate signal data is time t₁₃When the minimum of the original signal data string is detected, the minimum value D of the original signal data_O(t₁₂).
[0047]
FIG. 3 is a schematic diagram illustrating a process in which a resampled data sequence is generated from the intermediate signal data sequence. 2A to 2F, the horizontal axis corresponds to time t and the vertical axis corresponds to the data value D, as in FIG. FIG. 4A shows an original signal data string, which is shown for comparison. FIG. 5B shows an intermediate signal data string generated by the above-described processing. When this intermediate signal data string is resampled every section width 4, there are four sampling phases. FIGS. 9C to 9F show the four types of resampling results. Each n is an integer, and FIG._P(t_i) (I = 4n + 1) is sampled, FIG._P(t_i) (I = 4n) is sampled, (e) in FIG._P(t_i) (I = 4n-1) is sampled, FIG._P(t_i) (I = 4n−2) is sampled.
[0048]
As described above, when a plurality of inflection points do not exist within one window width, the intermediate signal data sequence is based on the waveform of the original signal data sequence, but in the vicinity of the extreme value, the extreme value The waveform is modified so that is continuous by a number equal to the resampling interval. Therefore, the extreme value is always sampled regardless of the phase of the intermediate signal data string. For example, in the phase shown in FIG. 3C, the resampled intermediate signal data D_P(t₉) Is the maximum value D of the original signal data_O(t₆), And in the same figure (d) to (f), the resampled intermediate signal data D_P(t₈), D_P(t₇), D_P(t₆) Is the maximum value D of the original signal data_O(t₆).
[0049]
Therefore, the sampling circuit 20 can simply adopt a simple circuit configuration for sampling every four data.
[0050]
FIG. 4 is a schematic diagram showing the waveform of the original signal data sequence and the output waveform obtained by each sampling method in order to compare the re-sampling result of this apparatus with the results of conventional point sampling and maximum value sampling. It is. 4A to 4C are the same as FIGS. 6A to 6C used in the description of the prior art. FIG. 4D shows the result of inflection point detection sampling by this apparatus. The output of this device is the time t₉It can be understood from the figure that the local maximum value at can be captured and that tailing like the maximum value sampling does not occur.
[0051]
This tailing will be examined in more detail. D with resampled data_RThis is expressed as (t). Note that t represents the timing at which the resampled data is output, not the generation timing in the original signal data. For maximum value sampling, for example, D_R(t₇) = D_O(t₇), D_R(t₁₁) = D_O(t₉), D_R(t₁₅) = D_O(t₁₁). Comparing the output timing of the sampled data with the generation timing of the data, the maximum value sampling does not deviate from the output timing and generation timing at the front end of the waveform, but the output timing occurs at the rear end It can be delayed by as much as the resampling interval from the timing. This is recognized as a phenomenon called tailing.
[0052]
On the other hand, according to the sampling of this device, for example, D_R(t₇) = D_O(t₇), D_R(t₁₁) = D_O(t₉), D_R(t₁₅) = D_O(t₁₅). As described above, in the sampling by this apparatus, the output timing of the sampled data and the generation timing of the data are basically synchronized with each other at the front end and the rear end of the waveform. That is, there is no difference between the output timing and the generation timing at both positions. This means that the sampling of the device does not cause tailing.
[0053]
FIG. 5 is a schematic diagram showing a state in which a sine wave is sampled at three different phases by this apparatus. This corresponds to FIGS. 7 and 8 relating to the conventional sampling, and FIGS. 5A to 5C show the case where the resampling timings are sine wave phases θ = 90 ° and 270 °, respectively. , Θ = 0 °, 180 °, and θ = 45 °, 225 °. As shown in this figure, according to this apparatus, the maximum value and the minimum value are correctly captured at any resampling phase, and the amplitude of the waveform after resampling is equal to the waveform of the original signal. In addition, the fluctuation of the data value having the same period as the original signal is always reproduced regardless of the sampling phase, and the original signal having a frequency close to the Nyquist frequency can be sampled appropriately.
[0054]
[Embodiment 2]
In the above-described apparatus, the inflection point detection circuit 18 is configured to detect both an inflection point where the original signal data changes from increase to decrease and an inflection point where the original signal data changes from decrease to increase. Correspondingly, both the maximum value and the minimum value of the original signal data sequence are held over the sampling interval width in the intermediate signal data sequence.
[0055]
On the other hand, the inflection point detection circuit 18 can be configured to detect only one of the inflection points. For example, when the inflection point detection circuit 18 is configured to detect only inflection points at which the original signal data changes from increase to decrease, only the maximum value is held in the intermediate signal data string. The maximum value is always captured in the result of re-sampling the intermediate signal data string. On the other hand, in this configuration, there is no guarantee that the minimum value is captured. That is, the effect of raising the resampling value as a whole occurs. This means that the amplitude is underestimated, but when applied to an ultrasound image, the contrast and frequency characteristics are maintained moderately while there is no maximum sampling loss and the brightness is increased in a brighter direction. The obtained image is obtained.
[0056]
Here, the ultrasonic image represents the shape of the structure by a collection of small points having different luminances. If there are bright and dark spots in a relatively uniform brightness area in the image, even if the brightness difference between them is about the same, the dark spot is visually Is more prominent than a bright spot. Such conspicuous dark spots appear as noise to the eyes of the image observer and give the impression that the S / N ratio is reduced.
[0057]
According to the present apparatus, since the decrease in the re-sampling value corresponding to such a low-brightness point is suppressed, noise is not noticeable and the image quality of the ultrasonic image is improved.
[0058]
On the other hand, in the configuration in which only the inflection point from the decrease of the original signal data string to the increase is detected, the minimum value is always sampled, but there is no guarantee that the maximum value is sampled. Such sampling may also be suitable depending on the field of use.
[0059]
[Other embodiments]
In the above-described configuration, the latest original signal data is sampled unless there is only one extreme value in the resampling interval. That is, the rear end of the re-sampling interval is sampled in principle, and only when there is only one extreme value in the interval, the sampling position is changed to the position of the extreme value in the interval. However, the basic sampling position need not be limited to the rear end of the section, but may be a predetermined position in the section.
[0060]
In the maximum value sampling, when an extreme value exists, the sampling position is not only a point in the middle of the section, but if it is monotonically increasing, it is sampled at the rear end of the section, and if it is monotonically decreasing, it is sampled at the front end of the section. Will be. Such fluctuation of the sampling position causes tailing. Therefore, tailing is prevented by preventing the sampling interval from fluctuating. In the present invention, in principle, sampling is performed at a predetermined interval by sampling at a predetermined position in the sampling section, and thus tailing can be prevented. That is, in order to prevent tailing, the sampling position may be a fixed position in the section in principle, and it does not matter whether it is an end.
[0061]
In the above configuration, a window that moves on the original signal data string is introduced. In this configuration, an intermediate signal data sequence having the same rate as the original signal data sequence is once generated, and the data sequence is resampled. However, a configuration that does not use a window that moves data one by one is also possible. For example, it is possible to divide the original signal data sequence into predetermined sampling sections and select one sampling value directly from each section. In this configuration, when it is detected that an extreme value exists in the section, the extreme value is sampled, and when no extreme value exists, the original signal data at a fixed position in the section is sampled.
[0062]
【The invention's effect】
According to the signal sampling device of the present invention, it is detected whether or not the original signal has an extreme value within the sampling interval, and if present, the value based on the extreme value is sampled. Thereby, the sampling reflecting the extreme value of the original signal is performed, and the effect that the contrast does not decrease is obtained. Also, by capturing the maximum and minimum values for the original signal near the Nyquist frequency, a sampling data string that varies at the same frequency as the original signal can be obtained, and the cut-off frequency can be raised to the Nyquist frequency. An effect is also obtained.
[0063]
Further, according to the signal sampling device of the present invention, the value of the original signal at a predetermined position in the interval is sampled for the sampling interval having no extreme value, thereby preventing a phenomenon such as tailing and lowering the resolution. The effect which is prevented is acquired.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a main circuit configuration of the ultrasonic diagnostic apparatus according to an embodiment of the present invention.
FIG. 2 is a schematic diagram illustrating a process in which an intermediate signal data sequence is generated from an original signal data sequence.
FIG. 3 is a schematic diagram illustrating a process in which a resampled data sequence is generated from an intermediate signal data sequence.
FIG. 4 is a schematic diagram showing a waveform of an original signal data sequence, a conventional sampling waveform, and a sampling waveform by this apparatus.
FIG. 5 is a schematic diagram showing a state in which a sine wave is sampled at three different phases by this apparatus.
FIG. 6 is a schematic diagram showing an example of sampling by a conventional method.
FIG. 7 is a schematic diagram showing a state in which a sine wave is point-sampled at three different phases.
FIG. 8 is a schematic diagram showing a state where a sine wave is sampled at a maximum value at three different phases.
[Explanation of symbols]
2 A / D converter, 4 signal sampling processing unit, 6 maximum value selection circuit, 8 minimum value selection circuit, 10 data delay circuit, 12 subtractor, 14 selection circuit, 16 shift register, 18 inflection point detection circuit, 20 sampling circuit.

Claims (3)

An ultrasonic diagnostic apparatus for obtaining a sampling value corresponding to each section for each section of the original signal divided into a plurality of sections of a certain width, using a received signal obtained by scanning ultrasound as an original signal,
Window setting means for moving a window having a width corresponding to the section with the original signal;
Extreme value detection means for detecting an extreme value of the original signal included in the window at each window position;
Have
When the extreme value is detected, the extreme value is set as a representative value at the window position, and when the extreme value is not detected, the original signal value at a predetermined position in the window is set as the representative value at each window position. A corresponding representative value is set, and a representative value at a position corresponding to each section among a plurality of representative values corresponding to a plurality of window positions is set as a sampling value corresponding to each section.
An ultrasonic diagnostic apparatus. A signal sampling device for obtaining a sampling value corresponding to each section for each section of the original signal divided into a plurality of sections having a constant width,
Extreme value detection means for detecting an extreme value of the original signal;
Signal converting means for generating an intermediate signal by modifying the original signal based on the extreme value;
A sampling value that extracts a signal value of the intermediate signal at intervals of the constant width and uses a signal value at a position corresponding to the interval in the extracted signal value of the intermediate signal as a sampling value corresponding to the interval. A determination means;
Window setting means for moving a window having a width corresponding to the section with the original signal;
Have
The extreme value detecting means detects an extreme value of the original signal included in the window at each window position,
When the extreme value is detected, the signal converting means sets the extreme value as a representative value at the window position, and when the extreme value is not detected, the signal conversion means sets the original signal value at a predetermined position in the window as a representative value. The intermediate signal is constituted by the representative value,
A signal sampling device. The signal sampling device according to claim 2, wherein
The extreme value detecting means includes
Change rate detecting means for detecting a change rate of the original signal within the window;
Extreme value position determining means for determining the position of the extreme value based on the position where the polarity of the rate of change changes;
A signal sampling device comprising:

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