JP2017113145A - Ultrasonic observation device, operation method of ultrasonic observation device, and operation program of ultrasonic observation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasonic observation device that allows a user to visually recognize a temporal change in an attenuation rate in an ultrasonic image.SOLUTION: An ultrasonic observation device 1 includes: a frequency analysis part 332 for calculating a plurality of frequency spectra by analyzing a frequency of an ultrasonic signal; a feature amount calculation part 333 for calculating respective feature amounts of the plurality of frequency spectra; an attenuation rate setting part 334 for setting an attenuation rate in a region of interest of the ultrasonic image; a feature amount correction part 335 for calculating a corrected feature amount in the region of interest of the ultrasonic image by performing attenuation correction of the feature amount using the attenuation rate set by the attenuation rate setting part 334; a representative attenuation rate calculation part 336 for calculating a representative attenuation rate of the region of interest defined based on the attenuation rate; an attenuation rate graph generation part 343 for generating an attenuation rate graph indicating a temporal change in the representative attenuation rate; and a display control part 361 for executing control to cause a display device to display the corrected feature amount and the attenuation rate grasp in association with each other.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an ultrasonic observation apparatus that observes a tissue to be observed using ultrasonic waves, an operation method of the ultrasonic observation apparatus, and an operation program of the ultrasonic observation apparatus.

  Conventionally, in an ultrasound observation device that observes the tissue to be observed using ultrasound, the scattered signal attenuation rate (attenuation coefficient) is calculated and displayed along with the scattered waveform features and sound propagation speed in the subject. The technique to do is known (for example, refer patent document 1). In this technique, when a B-mode image is displayed on a display, the information on the characteristic amount of the scattered waveform and the sound propagation speed is color-processed and superimposed on the B-mode image, and the value of the attenuation factor is displayed.

Japanese Patent Laid-Open No. 1-121039

  In the ultrasonic diagnosis, a user such as a doctor often observes while changing the angle of the ultrasonic probe with respect to the subject, so that the observation target region is three-dimensionally grasped and diagnosed in many cases. For this reason, if the change of the attenuation rate according to the change of the cross section can be recognized, it is expected to help a more appropriate diagnosis. However, in the above-described prior art, since only the attenuation rate when the displayed B-mode image is acquired is displayed, it is impossible to visually recognize the temporal change of the attenuation rate.

  The present invention has been made in view of the above, and an ultrasonic observation apparatus, an operation method of the ultrasonic observation apparatus, and an ultrasonic observation apparatus that allow a user to visually recognize a temporal change in attenuation rate in an ultrasonic image, and An object is to provide an operation program of an ultrasonic observation apparatus.

  In order to solve the above-described problems and achieve the object, an ultrasonic observation apparatus according to the present invention includes an ultrasonic transducer that transmits ultrasonic waves to an observation target and receives ultrasonic waves reflected by the observation target. An ultrasonic observation apparatus that generates an ultrasonic image based on an ultrasonic signal acquired by an ultrasonic probe provided, and analyzing the frequency of the ultrasonic signal in the reception depth and reception direction of the ultrasonic signal A frequency analysis unit that calculates a plurality of frequency spectra in response, a feature amount calculation unit that calculates feature amounts of the plurality of frequency spectra, and the ultrasonic wave propagates through the observation target in a region of interest of the ultrasonic image An attenuation rate setting unit that sets an attenuation rate that gives an attenuation characteristic at the time, and the attenuation correction of the feature amount using the attenuation rate set by the attenuation rate setting unit, A feature amount correction unit that calculates a correction feature amount in the region of interest; a representative attenuation rate calculation unit that calculates a representative attenuation rate of the region of interest defined based on the attenuation rate; and a temporal change in the representative attenuation rate. An attenuation rate graph generating unit that generates an attenuation rate graph to be displayed; and a display control unit that performs control to display the correction feature quantity and the attenuation rate graph in association with each other on a display device.

  In the ultrasonic observation apparatus according to the present invention, in the above invention, the attenuation rate setting unit includes a plurality of attenuation rate candidate values that give different attenuation characteristics as attenuation characteristics when the ultrasonic wave propagates through the observation target. The preliminary correction feature quantity of each frequency spectrum for each attenuation rate candidate value is calculated by performing attenuation correction that eliminates the influence of attenuation of the ultrasonic wave on the feature quantity of each frequency spectrum using Based on the plurality of attenuation rate candidate values, an optimum attenuation rate is set for the observation target, and the feature amount correction unit and the representative attenuation rate calculation unit use the optimal attenuation rate to perform the correction. A feature amount and the representative attenuation rate are calculated, respectively.

  In the ultrasonic observation apparatus according to the present invention, in the above invention, the attenuation rate setting unit includes a plurality of unit lengths and units in the ultrasonic wave for each of a plurality of divided regions obtained by dividing the region of interest. By using each of the attenuation rate candidate values per frequency to calculate the preliminary correction feature amount of each frequency spectrum for each attenuation rate candidate value by performing the attenuation correction on the feature amount of each frequency spectrum, Based on the calculation result, the optimal attenuation rate is set from the plurality of attenuation rate candidate values, and the representative attenuation rate calculation unit uses the optimal attenuation rate set in each divided region. A representative attenuation rate is calculated.

  In the ultrasonic observation apparatus according to the present invention, in the above invention, the attenuation rate setting unit calculates a statistical variation of the preliminary correction feature value for each attenuation rate candidate value, and the statistical variation is minimized. A certain attenuation rate candidate value is set as the optimum attenuation rate.

  In the ultrasonic observation apparatus according to the present invention as set forth in the invention described above, the attenuation rate graph generation unit generates the attenuation rate graph by adding information indicating an upper limit value and a lower limit value of the representative attenuation rate. .

  The ultrasonic observation apparatus according to the present invention further includes a storage unit that stores the ultrasonic image, the correction feature amount, and the representative attenuation rate in the above-described invention, and the attenuation rate graph generation unit includes the ultrasonic probe. In the frozen state, the attenuation rate graph corresponding to the set of the reproducible ultrasonic images among the ultrasonic images stored in the storage unit, and corresponding to the ultrasonic images being reproduced on the display device The attenuation rate graph to which information indicating the value of the representative attenuation rate is added is generated.

  In the ultrasonic observation apparatus according to the present invention, in the above invention, the feature amount correction unit accumulates per unit frequency at a sampling point based on an optimum attenuation rate of each divided region set by the attenuation rate setting unit. The correction feature amount of the sampling point is calculated by calculating an attenuation rate and performing attenuation correction of the feature amount using the accumulated attenuation rate.

  In the ultrasonic observation apparatus according to the present invention, in the above invention, the attenuation rate setting unit is a region that is different from a region of interest of the ultrasonic image and is used for calculation for correcting the feature amount. An attenuation factor of a calculation region that is a region located between the region corresponding to the surface of the ultrasonic transducer and the region of interest is further set, and the representative attenuation factor calculation unit determines the attenuation factor of the calculation region. A representative attenuation rate of the calculation region defined based on the calculation region, and the attenuation rate graph generation unit generates an attenuation rate graph further including a temporal change in the representative attenuation rate of the calculation region. To do.

  In the ultrasonic observation apparatus according to the present invention, in the above invention, the attenuation rate setting unit includes a plurality of the ultrasonic regions for each of a plurality of divided regions obtained by dividing the region of interest and the region for calculation. By using each of the unit length and the attenuation rate candidate value per unit frequency, the attenuation correction is performed on the feature quantity of each frequency spectrum, thereby preliminarily correcting each frequency spectrum for each attenuation rate candidate value. A feature amount is calculated, and the optimal attenuation rate is set from the plurality of attenuation rate candidate values based on the calculation result, and the representative attenuation rate calculation unit is configured to set the optimal attenuation rate set in each divided region. At least two representative attenuation rates respectively corresponding to the region of interest and the calculation region are calculated using an attenuation rate.

  In the ultrasonic observation apparatus according to the present invention, in the above invention, the feature amount correction unit is configured to generate per unit frequency at a sampling point based on the attenuation rates of the region of interest and the calculation region set by the attenuation rate setting unit. The correction feature amount of the sampling point is calculated by calculating the attenuation amount of the feature amount using the accumulated attenuation rate.

  In the ultrasonic observation apparatus according to the present invention, in the above invention, the feature amount correction unit may perform the optimum attenuation for each divided region existing between a position corresponding to the surface of the ultrasonic transducer and the sampling point. The cumulative attenuation rate at the sampling point is calculated by cumulatively adding the rate weighted by the round trip distance in the depth direction in each divided region.

  The ultrasonic observation apparatus according to the present invention further includes a feature amount image data generation unit that generates feature amount image data for displaying information on the correction feature amount together with the ultrasonic image in the above invention, and the display control unit includes: The feature amount image corresponding to the feature amount image data and the attenuation rate graph are associated with each other and displayed on the display device.

  In the ultrasonic observation apparatus according to the present invention, in the above invention, the feature amount calculation unit calculates the feature amount by performing a process of approximating the frequency spectrum with an n-order equation (n is a positive integer). It is characterized by.

  An operation method of an ultrasonic observation apparatus according to the present invention is an ultrasonic signal acquired by an ultrasonic probe including an ultrasonic transducer that transmits ultrasonic waves to an observation target and receives ultrasonic waves reflected by the observation target. A method of operating an ultrasonic observation apparatus that generates an ultrasonic image based on the frequency, wherein a frequency analysis unit analyzes a frequency of the ultrasonic signal to thereby analyze a plurality of frequencies according to a reception depth and a reception direction of the ultrasonic signal. A frequency analysis step for calculating the frequency spectrum, a feature amount calculation unit for calculating a feature amount for each of the plurality of frequency spectra, and an attenuation rate setting unit for the region of interest of the ultrasonic image. An attenuation rate setting step for setting an attenuation rate that gives an attenuation characteristic when ultrasonic waves propagate through the observation target, and a feature amount correction unit uses the attenuation rate to correct the attenuation of the feature amount. And performing a feature amount correction step of calculating a correction feature amount in the region of interest of the ultrasound image, and a representative attenuation rate calculation unit calculates a representative attenuation rate of the region of interest defined based on the attenuation rate A representative attenuation factor calculating step, an attenuation factor graph generating unit generating an attenuation factor graph indicating a temporal change in the representative attenuation factor, and a display control unit including the correction feature amount and the attenuation factor. And a display control step for performing control to display the graph on the display device in association with each other.

  The operation program of the ultrasonic observation apparatus according to the present invention is an ultrasonic signal acquired by an ultrasonic probe including an ultrasonic transducer that transmits ultrasonic waves to an observation target and receives ultrasonic waves reflected by the observation target. In the ultrasonic observation apparatus that generates an ultrasonic image based on the frequency, the frequency analysis unit calculates a plurality of frequency spectra corresponding to the reception depth and reception direction of the ultrasonic signal by analyzing the frequency of the ultrasonic signal A frequency analysis step, a feature amount calculation unit calculates a feature amount of each of the plurality of frequency spectra, and an attenuation rate setting unit detects the ultrasonic wave in the region of interest of the ultrasonic image. An attenuation rate setting step for setting an attenuation rate that gives an attenuation characteristic when propagating through an object, and a feature amount correction unit performs attenuation correction of the feature amount using the attenuation rate Therefore, a feature amount correction step for calculating a correction feature amount in the region of interest of the ultrasonic image, and a representative attenuation factor calculation unit that calculates a representative attenuation factor of the region of interest defined based on the attenuation factor An attenuation factor calculating step, an attenuation factor graph generating unit generating an attenuation factor graph indicating a temporal change in the representative attenuation factor, and a display control unit displaying the correction feature amount and the attenuation factor graph. And a display control step of performing control to display the information on the display device in association with each other.

  According to the present invention, it becomes possible for the user to visually recognize the temporal change of the attenuation rate in the ultrasonic image.

FIG. 1 is a block diagram showing a functional configuration of an ultrasonic diagnostic system including an ultrasonic observation apparatus according to Embodiment 1 of the present invention. FIG. 2 is a diagram showing the relationship between the reception depth and the amplification factor in the amplification processing performed by the signal amplification unit of the ultrasonic observation apparatus according to Embodiment 1 of the present invention. FIG. 3 is a diagram showing the relationship between the reception depth and the amplification factor in the amplification correction process performed by the amplification correction unit of the ultrasound observation apparatus according to Embodiment 1 of the present invention. FIG. 4 is a diagram schematically showing a data array in one sound ray of the ultrasonic signal. FIG. 5 is a diagram illustrating an example of a frequency spectrum calculated by the frequency analysis unit of the ultrasonic observation apparatus according to Embodiment 1 of the present invention. FIG. 6 is a diagram schematically illustrating a setting example of divided areas in the display area of the ultrasonic image. FIG. 7 is a diagram showing a straight line having as a parameter the preliminary correction feature amount corrected by the attenuation rate setting unit of the ultrasonic observation apparatus according to Embodiment 1 of the present invention. FIG. 8 is a diagram schematically illustrating an example of distribution of pre-correction feature quantities that have been subjected to attenuation correction based on two different attenuation rate candidate values for the same observation target. FIG. 9 is a flowchart showing an outline of processing performed by the ultrasound observation apparatus according to Embodiment 1 of the present invention. FIG. 10 is a flowchart showing an outline of processing executed by the frequency analysis unit of the ultrasonic observation apparatus according to Embodiment 1 of the present invention. FIG. 11 is a diagram showing an outline of processing performed by the attenuation rate setting unit of the ultrasonic observation apparatus according to Embodiment 1 of the present invention. FIG. 12 is a diagram schematically showing a display example on the display device of all the images generated by the image processing unit of the ultrasonic observation apparatus according to Embodiment 1 of the present invention. FIG. 13 is a diagram showing a display example on the display device of the attenuation rate graph generated by the ultrasonic observation apparatus according to the first modification of the first embodiment of the present invention. FIG. 14 is a diagram showing a display example on the display device of the attenuation rate graph generated by the ultrasonic observation apparatus according to the second modification of the first embodiment of the present invention. FIG. 15 is a diagram schematically illustrating a display example on the display device of all the images generated by the ultrasonic observation apparatus according to the third modification of the first embodiment of the present invention. FIG. 16 is a flowchart showing an outline of processing performed by the ultrasonic observation apparatus according to Embodiment 2 of the present invention. FIG. 17 is a diagram schematically illustrating a setting example of a region of interest and a calculation region in a display region of an ultrasonic image and divided regions of those regions. FIG. 18 is a diagram schematically illustrating a display example on the display device of all the images generated by the image processing unit of the ultrasonic observation apparatus according to the second embodiment of the present invention.

  DESCRIPTION OF EMBODIMENTS Hereinafter, modes for carrying out the present invention (hereinafter referred to as “embodiments”) will be described with reference to the accompanying drawings.

(Embodiment 1)
FIG. 1 is a block diagram showing a functional configuration of an ultrasonic diagnostic system including an ultrasonic observation apparatus according to Embodiment 1 of the present invention. An ultrasonic diagnostic system 1 shown in FIG. 1 transmits an ultrasonic wave to a subject to be observed and receives an ultrasonic wave reflected by the subject, and an ultrasonic endoscope 2. Are provided with an ultrasonic observation device 3 that generates an ultrasonic image based on the ultrasonic signal acquired by the, and a display device 4 that displays the ultrasonic image generated by the ultrasonic observation device 3.

  The ultrasonic endoscope 2 converts an electrical pulse signal received from the ultrasonic observation device 3 into an ultrasonic pulse (acoustic pulse) and irradiates the subject at the tip thereof, and is reflected by the subject. The ultrasonic transducer 21 converts the ultrasonic echo into an electrical echo signal expressed by a voltage change and outputs it. The ultrasonic transducer 21 may be a convex transducer, a linear transducer, or a radial transducer. The ultrasonic endoscope 2 may be one that mechanically scans the ultrasonic transducer 21, or a plurality of elements are provided in an array as the ultrasonic transducer 21, and the elements involved in transmission and reception are electronically arranged. Electronic scanning may be performed by switching or delaying transmission / reception of each element.

  The ultrasonic endoscope 2 usually has an imaging optical system and an imaging device, and is inserted into the digestive tract (esophagus, stomach, duodenum, large intestine) or respiratory organ (trachea, bronchi) of the subject, and the digestive tract. It is possible to image the respiratory organ and surrounding organs (pancreas, gallbladder, bile duct, biliary tract, lymph node, mediastinal organ, blood vessel, etc.). The ultrasonic endoscope 2 has a light guide that guides illumination light to be irradiated onto the subject during imaging. The light guide has a distal end portion that reaches the distal end of the insertion portion of the ultrasonic endoscope 2 into the subject, and a proximal end portion that is connected to a light source device that generates illumination light.

  The ultrasound observation apparatus 3 includes a transmission / reception unit 31, a signal processing unit 32, a calculation unit 33, an image processing unit 34, an input unit 35, a control unit 36, and a storage unit 37.

  The transmission / reception unit 31 is electrically connected to the ultrasonic endoscope 2 and transmits a transmission signal (pulse signal) including a high voltage pulse to the ultrasonic transducer 21 based on a desired waveform and transmission timing. An echo signal, which is an electrical reception signal, is received from the sonic transducer 21 to generate and output digital radio frequency (RF) signal data (hereinafter referred to as RF data). The transmission / reception unit 31 includes a signal amplification unit 311 that amplifies the echo signal. The signal amplification unit 311 performs STC (Sensitivity Time Control) correction in which an echo signal having a larger reception depth is amplified with a higher amplification factor.

FIG. 2 is a diagram illustrating the relationship between the reception depth and the amplification factor in the amplification process performed by the signal amplification unit 311. The reception depth z shown in FIG. 2 is an amount calculated based on the elapsed time from the reception start point of the ultrasonic wave. As shown in FIG. 2, when the reception depth z is smaller than the threshold z _th , the amplification factor β (dB) increases linearly from β ₀ to β _th (> β ₀ ) as the reception depth z increases. The amplification factor β (dB) takes a constant value β _th when the reception depth z is equal to or greater than the threshold value z _th . The value of the threshold value z _th is such a value that the ultrasonic signal received from the observation target is almost attenuated and the noise becomes dominant. More generally, when the reception depth z is smaller than the threshold value z _th , the amplification factor β may increase monotonously as the reception depth z increases. The relationship shown in FIG. 2 is stored in the storage unit 37 in advance.

  The transmission / reception unit 31 performs processing such as filtering on the echo signal amplified by the signal amplification unit 311 and then performs A / D conversion to generate time domain RF data, and the signal processing unit 32 and the calculation unit To 33. When the ultrasonic endoscope 2 is configured to electronically scan the ultrasonic transducer 21 provided with a plurality of elements in an array, the transmission / reception unit 31 is a multi-channel circuit for beam synthesis corresponding to the plurality of elements. Have

  The frequency band of the pulse signal transmitted by the transmission / reception unit 31 may be a wide band that substantially covers the linear response frequency band of the electroacoustic conversion of the pulse signal to the ultrasonic pulse in the ultrasonic transducer 21. In addition, the various processing frequency bands of the echo signal in the signal amplifying unit 311 may be a wide band that substantially covers the linear response frequency band of the acoustoelectric conversion of the ultrasonic transducer 21 into the echo signal of the ultrasonic echo. Accordingly, it is possible to perform accurate approximation when performing frequency spectrum approximation processing, which will be described later.

  The transmission / reception unit 31 transmits various control signals output from the control unit 36 to the ultrasonic endoscope 2 and receives various types of information including an identification ID from the ultrasonic endoscope 2 and receives the control unit 36. It also has a function to transmit to

  The signal processing unit 32 generates digital B-mode reception data based on the RF data received from the transmission / reception unit 31. Specifically, the signal processing unit 32 performs known processing such as a bandpass filter, envelope detection, and logarithmic conversion on the RF data to generate digital B-mode reception data. In logarithmic conversion, a common logarithm of an amount obtained by dividing RF data by a reference voltage is taken and expressed as a decibel value. The signal processing unit 32 outputs the generated B-mode reception data to the image processing unit 34. The signal processing unit 32 is realized by using a general-purpose processor such as a CPU (Central Processing Unit) or a dedicated integrated circuit that executes a specific function such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field Programmable Gate Array). Is done.

  The calculation unit 33 performs a predetermined calculation on the RF data received from the transmission / reception unit 31. The calculation unit 33 includes an amplification correction unit 331, a frequency analysis unit 332, a feature amount calculation unit 333, an attenuation rate setting unit 334, a feature amount correction unit 335, and a representative attenuation rate calculation unit 336. The arithmetic unit 33 is realized by using a general-purpose processor such as a CPU or a dedicated integrated circuit such as an ASIC or FPGA.

The amplification correction unit 331 performs amplification correction on the RF data output from the transmission / reception unit 31 so that the amplification factor is constant regardless of the reception depth. FIG. 3 is a diagram illustrating a relationship between the reception depth and the amplification factor in the amplification correction process performed by the amplification correction unit 331. As shown in FIG. 3, the amplification rate β (dB) in the amplification correction processing performed by the amplification correction unit 331 takes the maximum value β _th −β ₀ when the reception depth z is zero, and the reception depth z is zero to the threshold value z. It decreases linearly until it reaches _th , and is zero when the reception depth z is greater than or equal to the threshold value z _th . Note that the relationship shown in FIG. 3 is stored in the storage unit 37 in advance. The amplification correction unit 331 amplifies and corrects the digital RF signal based on the relationship shown in FIG. 3, so that the influence of STC correction in the signal amplification unit 311 can be canceled and a signal with a constant amplification factor β _th can be output. . Of course, the relationship between the reception depth z and the amplification factor β in the amplification correction unit 331 differs depending on the relationship between the reception depth and the amplification factor in the signal amplification unit 311.

  The reason for performing such amplification correction will be described. STC correction is a correction process that eliminates the influence of attenuation from the amplitude of the analog signal waveform by amplifying the amplitude of the analog signal waveform uniformly over the entire frequency band and with a gain that monotonously increases with respect to the depth. is there. For this reason, when generating a B-mode image to be displayed by converting the amplitude of the echo signal into luminance, and when scanning a uniform tissue, the luminance value is constant regardless of the depth by performing STC correction. become. That is, an effect of eliminating the influence of attenuation from the luminance value of the B-mode image can be obtained.

  On the other hand, when using the result obtained by calculating and analyzing the frequency spectrum of the ultrasonic wave as in the first embodiment, the effect of attenuation accompanying the propagation of the ultrasonic wave cannot always be accurately eliminated even by the STC correction. This is because, although the attenuation amount generally varies depending on the frequency (see Equation (1) described later), the STC correction amplification factor changes only according to the distance and has no frequency dependence. To solve this problem, when generating a B-mode image, output a reception signal subjected to STC correction, while generating an image based on a frequency spectrum, It is conceivable to perform a different new transmission and output a received signal not subjected to STC correction. However, in this case, there is a problem that the frame rate of the image data generated based on the received signal is lowered. Therefore, in the first embodiment, in order to eliminate the influence of the STC correction on the signal subjected to the STC correction for the B-mode image while maintaining the frame rate of the generated image data, the amplification correction unit 331 To correct the amplification factor.

  The frequency analysis unit 332 calculates a plurality of frequency spectra corresponding to the reception depth and reception direction of the ultrasonic signal by analyzing the frequency of the ultrasonic signal. Specifically, the frequency analysis unit 332 generates sample data by sampling RF data (line data) of each sound ray subjected to the amplification correction by the amplification correction unit 331 at a predetermined time interval, and generates the sample data group. By applying a fast Fourier transform (FFT) process, frequency spectra at a plurality of locations (data positions) on the RF data are calculated.

FIG. 4 is a diagram schematically showing a data array in one sound ray of the ultrasonic signal. In the sound ray SR _k shown in the figure, a white or black rectangle means data at one sampling point. In the sound ray SR _k , the data located on the right side is sample data from a deeper location when measured from the ultrasonic transducer 21 along the sound ray SR _k (see the arrow in FIG. 4). The sound ray SR _k is discretized at a time interval corresponding to a sampling frequency (for example, 50 MHz) in A / D conversion performed by the transmission / reception unit 31. FIG. 4 shows the case _where the eighth data position of the sound ray SR _k of number k is set as the initial value Z ^(k) _{0 in} the direction of the reception depth z, but the position of the initial value is arbitrarily set. be able to. The calculation result by the frequency analysis unit 332 is obtained as a complex number and stored in the storage unit 37.

A data group F _j (j = 1, 2,..., K) shown in FIG. 4 is a sample data group to be subjected to FFT processing. In general, in order to perform FFT processing, a sample data group needs to have a power number of 2 data. In this sense, the sample data group F _j (j = 1, 2,..., K−1) is a normal data group with the number of data 16 (= 2 ⁴ ), while the sample data group F _K is Since the number of data is 12, it is an abnormal data group. When performing an FFT process on an abnormal data group, a process for generating a normal sample data group is performed by inserting zero data in an insufficient amount. This point will be described in detail when the processing of the frequency analysis unit 332 is described (see FIG. 10).

  FIG. 5 is a diagram illustrating an example of a frequency spectrum calculated by the frequency analysis unit 332. Here, the “frequency spectrum” means “frequency distribution of intensity at a certain reception depth z” obtained by performing FFT processing on a sample data group. In addition, “intensity” as used herein refers to parameters such as the voltage of the echo signal, the power of the echo signal, the sound pressure of the ultrasonic echo, the acoustic energy of the ultrasonic echo, the amplitude and time integral value of these parameters, and combinations thereof. Points to either.

In FIG. 5, the horizontal axis represents the frequency f. In FIG. 5, the vertical axis represents the common logarithm (decibel expression) I = ₁₀ log ₁₀ (I ₀ / I _c ) obtained by dividing the intensity I ₀ by the reference intensity I _c (constant). In FIG. 5, the reception depth z is constant. It will be described later linear L ₁₀ shown in FIG. Note that the frequency spectrum curve shown in FIG. 5 and FIG. 7 described later and the straight line related to the curve are composed of a set of discrete points.

In the frequency spectrum C ₁ shown in FIG. 5, the lower limit frequency f _L and the upper limit frequency f _H of the frequency band used for the subsequent calculation are the frequency band of the ultrasonic transducer 21 and the frequency band of the pulse signal transmitted by the transmitting / receiving unit 31. For example, f _L = 3 MHz and f _H = 10 MHz. Hereinafter, in FIG. 5, the frequency band determined by the lower limit frequency f _L and the upper limit frequency f _H is referred to as “frequency band U”.

  Generally, when the observation target is a living tissue, the frequency spectrum shows a tendency that varies depending on the properties of the living tissue scanned with ultrasonic waves. This is because the frequency spectrum has a correlation with the size, number density, acoustic impedance, and the like of the scatterer that scatters ultrasonic waves. The “characteristics of the biological tissue” referred to here includes, for example, malignant tumor (cancer), benign tumor, endocrine tumor, mucinous tumor, normal tissue, cyst, vascular vessel and the like.

The feature amount calculation unit 333 calculates the feature amount of each frequency spectrum. Specifically, the feature quantity calculation unit 333 calculates a feature quantity that characterizes the approximated primary expression by performing regression analysis on the frequency spectrum in a predetermined frequency band and approximating it with the linear expression. For example, in the case of the frequency spectrum C ₁ illustrated in FIG. 5, the feature amount calculation unit 333 obtains the approximate straight line L ₁₀ by performing regression analysis in the frequency band U. When the approximate straight line L ₁₀ is expressed by a linear expression I = a ₀ f + b ₀ of the frequency f, the feature amount calculation unit 333 has a slope a ₀ , an intercept b ₀ , and a frequency band U as the feature amount corresponding to the straight line L ₁₀ . A mid-band fit c ₀ = a ₀ f _M + b ₀ which is a value of the intensity I at the center frequency f _M = (f _L + f _H ) / 2 is calculated. Note that the feature amount calculation unit 333 may approximate the frequency spectrum with a second-order or higher polynomial by regression analysis.

Of the three pre-correction feature quantities, the slope a ₀ has a correlation with the size of the ultrasonic scatterer, and it is generally considered that the larger the scatterer, the smaller the slope. The intercept b ₀ has a correlation with the size of the scatterer, the difference in acoustic impedance, the number density (concentration) of the scatterer, and the like. Specifically, the intercept b ₀ has a larger value as the scatterer is larger, has a larger value as the difference in acoustic impedance is larger, and has a larger value as the number density of the scatterers is larger. The midband fit c ₀ is an indirect parameter derived from the slope a ₀ and the intercept b ₀ and gives the intensity of the spectrum at the center of the frequency band U. Therefore, the midband fit c ₀ is considered to have a certain degree of correlation with the brightness of the B-mode image in addition to the size of the scatterer, the difference in acoustic impedance, and the number density of the scatterers.

  The attenuation rate setting unit 334 sets an attenuation rate that gives an attenuation characteristic when the ultrasonic wave propagates through the observation target in the region of interest set for the ultrasonic image. A more specific process of the attenuation rate setting unit 334 will be described. The attenuation rate setting unit 334 first divides the region of interest into a plurality of divided regions. Subsequently, the attenuation rate setting unit 334 uses each of a plurality of unit lengths and attenuation rate candidate values per unit frequency that give different attenuation characteristics when ultrasonic waves propagate through the observation target in each divided region. Thus, the preliminary correction feature quantity of each frequency spectrum for each attenuation rate candidate value is calculated by performing attenuation correction for eliminating the influence of the ultrasonic wave on the feature quantity of each frequency spectrum. Thereafter, the attenuation rate setting unit 334 sets an optimal attenuation rate for the observation target from among a plurality of attenuation rate candidate values based on the calculation result of the preliminary correction feature value.

  FIG. 6 is a diagram schematically illustrating a setting example of divided areas in a region of interest in an ultrasonic image display area. In FIG. 6, only one sound ray is indicated by a broken line, but it goes without saying that a plurality of sound rays are set at predetermined intervals along the scanning angle direction.

FIG. 6 illustrates a case where the region of interest 102 having a substantially fan shape in the image display region 101 is divided into 16 divided regions P _ij (i = 1 to 4, j = 1 to 4). The divided areas P _ij all have the same height H in the depth direction extending radially from the surface position 103 of the ultrasonic transducer 21 in the image display area 101. Information on how to set a divided region for the region of interest is stored in a divided region information storage unit 372 included in the storage unit 37. When the region of interest is set, the attenuation rate setting unit 334 refers to the divided region information storage unit 372 and sets a divided region corresponding to the region of interest. FIG. 6 illustrates the case where the ultrasonic transducer 21 is a convex transducer, but it goes without saying that other types of ultrasonic transducers 21 can similarly set divided areas. Further, the number of divided regions shown in FIG. 6 is merely an example, and it is needless to say that the number of divided regions varies depending on conditions such as the size of the region of interest. It is also possible to set the entire region of the ultrasonic image as one region of interest.

In general, the ultrasonic attenuation A (f, z) is attenuation that occurs while the ultrasonic waves reciprocate between the reception depth 0 and the reception depth z, and the intensity change before and after the reciprocation (difference in decibel expression). ). The attenuation amount A (f, z) is empirically known to be proportional to the frequency in a uniform tissue, and is expressed by the following equation (1).
A (f, z) = 2αzf (1)
Here, the proportional constant α is an amount called an attenuation rate, and gives an attenuation amount of ultrasonic waves per unit length and unit frequency. Z is the ultrasonic reception depth, and f is the frequency. When the observation target is a living body, a specific value of the attenuation rate α is determined according to the part of the living body. The unit of the attenuation rate α is, for example, dB / cm / MHz.

The attenuation rate setting unit 334 sets an optimal attenuation rate from a plurality of attenuation rate candidate values. At this time, the attenuation rate setting unit 334 uses the attenuation rate candidate value α to perform the following with respect to the feature amounts (slope a ₀ , intercept b ₀ , midband fit c ₀ ) calculated by the feature amount calculation unit 333. Preliminary correction feature amounts a, b, and c are calculated by performing attenuation correction according to equations (2) to (4).
a = a ₀ + 2αz (2)
b = b ₀ (3)
c = c ₀ + A (f _M , z) = c ₀ + 2αzf _M (= af _M + b) (4)
As is clear from the equations (2) and (4), the attenuation rate setting unit 334 performs correction with a larger correction amount as the ultrasonic reception depth z increases. Further, according to the equation (3), the correction related to the intercept is an identity transformation. This is because the intercept is a frequency component corresponding to a frequency of 0 (Hz) and is not affected by attenuation.

FIG. 7 is a diagram illustrating a straight line having the preliminary correction feature amounts a, b, and c corrected by the attenuation rate setting unit 334 as parameters. The equation for the straight line L ₁ is
I = af + b = (a ₀ + 2αz) f + b ₀ (5)
It is represented by As is clear from this equation (5), the straight line L ₁ has a larger slope (a> a ₀ ) and the same intercept (b = b ₀ ) compared to the straight line L ₁₀ before attenuation correction. is there.

  The attenuation rate setting unit 334 sets the attenuation rate candidate value having the smallest statistical variation of the preliminary correction feature value calculated for each attenuation rate candidate value as the optimal attenuation rate in each divided region. In the first embodiment, dispersion is applied as an amount indicating statistical variation. In this case, the attenuation rate setting unit 334 sets the attenuation rate candidate value that minimizes the variance as the optimal attenuation rate. Two of the three preliminary correction feature values a, b, and c described above are independent. In addition, the preliminary correction feature amount b does not depend on the attenuation rate. Therefore, when setting an optimal attenuation rate for the preliminary correction feature amounts a and c, the attenuation rate setting unit 334 may calculate the variance of one of the preliminary correction feature amounts a and c.

However, when the attenuation rate setting unit 334 sets an optimal attenuation rate using the preliminary correction feature amount a, the dispersion of the preliminary correction feature amount a is applied and the optimal attenuation rate is set using the preliminary correction feature amount c. When setting, it is more preferable to apply the variance of the preliminary correction feature quantity c. This is because the equation (1) that gives the attenuation amount A (f, z) is merely ideal, and the following equation (6) is more appropriate in reality.
A (f, z) = 2αzf + 2α ₁ z (6)
Α _{1 in} the second term on the right-hand side of equation (6) is a coefficient representing the magnitude of the change in signal intensity in proportion to the ultrasonic reception depth z. It is a coefficient representing a change in signal intensity caused by a change in the number of channels at the time of synthesis. Since the second term on the right side of Equation (6) exists, when setting the optimal attenuation rate using the preliminary correction feature quantity c, the attenuation is more accurately corrected by applying the variance of the preliminary correction feature quantity c. (See equation (4)). On the other hand, when the optimum attenuation rate is set using the preliminary correction feature quantity a that is a coefficient proportional to the frequency f, the second term on the right side of the equation (6) is more suitable when the variance of the preliminary correction feature quantity a is applied. It is possible to correct the attenuation accurately by eliminating the influence of.

  Here, the reason why the optimum attenuation rate can be set based on statistical variation will be described. When the optimum attenuation rate is applied to the observation target, the feature amount is converged to a value unique to the observation target regardless of the distance between the observation target and the ultrasonic transducer 21, and the statistical variation is considered to be small. On the other hand, when the attenuation rate candidate value that does not match the observation target is set as the optimal attenuation rate, the attenuation correction is excessive or insufficient, and thus the feature amount is shifted depending on the distance from the ultrasonic transducer 21. It is considered that the statistical variation of the feature amount is increased. Therefore, it can be said that the attenuation rate candidate value having the smallest statistical variation is the optimum attenuation rate for the observation target.

FIG. 8 is a diagram schematically illustrating an example of distribution of pre-correction feature quantities that have been subjected to attenuation correction based on two different attenuation rate candidate values for the same observation target. In FIG. 8, the horizontal axis represents the preliminary correction feature amount, and the vertical axis represents the frequency. The two distribution curves N ₁ and N ₂ shown in FIG. 8 have the same total frequency. In the case shown in FIG. 8, the distribution curve N ₁ has a small statistical variation (small variance) in the feature amount compared to the distribution curve N _2, and has a steep mountain shape. Therefore, when the attenuation rate setting unit 334 sets an optimum attenuation rate from the two attenuation rate candidate values corresponding to the two distribution curves N ₁ and N ₂ , the attenuation rate setting unit 334 sets the attenuation rate candidate value corresponding to the distribution curve N _1. Set as the optimum attenuation rate.

The feature amount correction unit 335 calculates a correction feature amount in the region of interest of the ultrasonic image by performing attenuation correction of the feature amount using the attenuation rate set by the attenuation rate setting unit 334. The feature amount correcting unit 335 accumulates per unit frequency at the sampling point by using the optimum attenuation rate of the divided region existing between the surface of the ultrasonic transducer and the sampling point among the optimum attenuation rate for each divided region. An attenuation factor (hereinafter also simply referred to as a cumulative attenuation factor) is calculated, and attenuation correction of the feature amount is performed using the cumulative attenuation factor. The cumulative attenuation rate at an arbitrary sampling point is calculated by using the distance from the surface of the ultrasonic transducer 21 and the optimum attenuation rate in the divided area existing therebetween. The distance from the boundary closer to the ultrasonic transducer 21 is h (0 <h ≦ H) in the divided region P _IJ (1 ≦ I ≦ i _max , 1 ≦ J ≦ j _max ; I and J are constants). cumulative attenuation factor gamma _IJ (h) is at the sampling points S _IJ (h) as,
γ _IJ (h) = [Σ _{j = 1,2,..., J-1} (2H · α (P _Ij ))] + 2h · α (P _IJ )
... (7)
It is expressed. Here, Σ _{j = 1, 2,..., J−1} means that the sum of j = _{1 to J−1} is taken, and α (P _Ij ) represents the optimum attenuation rate in the divided region P _Ij . Yes. The first term on the right-hand side of Equation (7) is the sum of the ultrasonic round-trip distance 2H for each divided region multiplied by the optimum attenuation rate α (P _Ij ). The second term of the right side of formula (7), the optimum damping ratio in ultrasonic reciprocating distance 2h the divided area P _IJ to the sampling points S _IJ (h) in the divided area P _IJ alpha a (P _IJ) It is multiplied. In this way, the feature amount correction unit 335 calculates the cumulative attenuation rate γ _IJ (h) by accumulating the attenuation rate from the surface of the ultrasonic transducer 21. When the optimum unit of attenuation rate is dB / cm / MHz, the unit of cumulative attenuation rate is dB / MHz.

For example, FIG. 6 illustrates the case where I = 2 and J = 3 (where i _max = j _max = 4) in the equation (7). In this case, the cumulative attenuation rate γ ₂₃ (h) at the sampling point S ₂₃ (h) is obtained from the equation (7):
γ ₂₃ (h) = 2H · α (P ₂₁ ) + 2H · α (P ₂₂ ) + 2h · α (P ₂₃ ) (8)
It becomes.

The feature amount correction unit 335 performs attenuation correction of the feature amount at the sampling point S _IJ (h) using the accumulated attenuation rate γ _IJ (h) as follows.
a _IJ (h) = a ₀ + 2γ _IJ (h) (9)
b _IJ (h) = b ₀ (10)
c _IJ (h) = c ₀ + 2f _M γ _IJ (h) (11)

  The representative attenuation factor calculation unit 336 calculates the representative attenuation factor of the region of interest using the optimum attenuation factor set in each divided region. The representative attenuation rate is, for example, an average value of optimum attenuation rates of the respective divided regions in the region of interest. Note that a statistic such as a maximum value, a median value, or a mode value when a set of optimal attenuation rates in all divided regions is a population may be used as the representative attenuation rate. Further, in the set of optimal attenuation rates of all the divided regions, a frequency distribution is generated by dividing each attenuation rate value by a certain width, and an average value of the attenuation rate of each section up to a predetermined rank with high frequency, The maximum value, the median value, or the mode value may be used as the representative attenuation rate. Further, in the set of optimum attenuation factors of all the divided regions, a group of intermediate values excluding the maximum value and the minimum value may be used as the representative attenuation factor. The number of representative attenuation factors is desirably set in consideration of visibility in an attenuation factor graph described later. For example, the number of representative attenuation factors is preferably less than or equal to the number of divided regions. Further, the input unit 35 may accept the input of the switching instruction signal and switch the setting of the representative attenuation rate.

  When the region of interest is not divided, in other words, when the region of interest is composed of one divided region, the optimum attenuation rate and the representative attenuation rate of the region of interest match. Therefore, when the region of interest is not divided, the representative attenuation rate calculation unit 336 calculates the optimum attenuation rate set by the attenuation rate setting unit 334 as the representative attenuation rate.

  The image processing unit 34 generates various image data. Specifically, the image processing unit 34 includes a B-mode image data generation unit 341, a feature amount image data generation unit 342, and an attenuation rate graph generation unit 343. The image processing unit 34 is realized using a general-purpose processor such as a CPU or a dedicated integrated circuit such as an ASIC or FPGA.

  The B-mode image data generation unit 341 generates B-mode image data that is an ultrasonic image to be displayed by converting the amplitude of the echo signal into luminance. Specifically, the B-mode image data generation unit 341 performs signal processing using known techniques such as gain processing and contrast processing on the B-mode reception data received from the signal processing unit 32, and also displays the display device. The B-mode image data is generated by thinning out the data according to the data step width determined according to the image display range in 4. The B-mode image is a grayscale image in which values of R (red), G (green), and B (blue), which are variables when the RGB color system is adopted as a color space, are matched.

  The B-mode image data generation unit 341 performs coordinate conversion on the B-mode reception data so that the scanning range can be spatially represented correctly, and then performs interpolation processing between the B-mode reception data to perform B-mode image data. A gap between received data is filled to generate B-mode image data. The B-mode image data generation unit 341 outputs the generated B-mode image data to the feature amount image data generation unit 342.

The feature amount image data generation unit 342 generates feature amount image data for displaying information related to the corrected feature amount calculated by the feature amount correction unit 335. Specifically, the feature amount image data generation unit 342 superimposes visual information related to the corrected feature amount calculated by the feature amount correction unit 335 on each pixel of the image in the B-mode image data, thereby generating a feature amount image. Generate data. For example, the feature amount image data generation unit 342 applies the sample data group F to a pixel region corresponding to the data amount of one sample data group F _j (j = 1, 2,..., K) illustrated in FIG. Visual information corresponding to the characteristic amount of the frequency spectrum calculated from _j is assigned. The feature amount image data generation unit 342 generates feature amount image data by associating a hue as visual information with any one of the above-described inclination, intercept, and midband fit, for example. Note that the feature amount image data generation unit 342 generates the feature amount image data by associating the hue with one of the two feature amounts selected from the inclination, the intercept, and the midband fit, and by associating the light and dark with the other. May be. As visual information related to the feature amount, in addition to hue and brightness (brightness), a predetermined color system such as saturation, luminance value, R (red), G (green), and B (blue) is configured. List color space variables.

  The attenuation rate graph generation unit 343 generates an attenuation rate graph indicating the temporal change of the representative attenuation rate over a predetermined period. When the attenuation rate graph generation unit 343 acquires the latest representative attenuation rate calculated by the representative attenuation rate calculation unit 336, the attenuation rate graph generation unit 343 deletes the data of the oldest attenuation rate within the period and generates an attenuation rate graph.

  The input unit 35 receives input of various types of information including an operation instruction signal for the ultrasound observation apparatus 3. For example, the input unit 35 receives a setting input of a region of interest that is a partial region divided by a specific depth width and sound ray width in an ultrasound image. The input unit 35 is configured using a user interface such as a keyboard, a mouse, a trackball, and a touch panel.

  The control unit 36 controls the operation of the entire ultrasound diagnostic system 1. The control unit 36 includes a display control unit 361 that controls display on the display device 4. The display control unit 361 displays the ultrasound image data generated by the B-mode image data generation unit 341, the feature amount image data generated by the feature amount image data generation unit 342, and the attenuation rate graph generated by the attenuation rate graph generation unit 343. Control for displaying the corresponding images on the display device 4 is performed. In the first embodiment, the display control unit 361 performs control to display at least the feature amount image data and the attenuation rate graph on the display device 4 in association with each other.

  The control unit 36 is realized using a general-purpose processor such as a CPU having arithmetic and control functions, or a dedicated integrated circuit such as an ASIC or FPGA. When the control unit 36 is realized by a general-purpose processor or FPGA, various programs and various data stored in the storage unit 37 are read from the storage unit 37 and various arithmetic processes related to the operation method of the ultrasound observation apparatus 3 are executed. Thus, the ultrasonic observation apparatus 3 is controlled in an integrated manner. When the control unit 36 is configured using an ASIC, various processes may be performed alone, or various processes may be performed by using various data stored in the storage unit 37. The control unit 36 may be configured using a general-purpose processor or a dedicated integrated circuit that is common to the signal processing unit 32, the calculation unit 33, and the image processing unit 34.

  The storage unit 37 stores various types of information including information necessary for the operation of the ultrasound observation apparatus 3. The storage unit 37 includes an image data storage unit 371 that stores at least temporarily data of an ultrasonic image such as a B-mode image and a feature amount image, a divided region information storage unit 372 that stores information about divided regions, and a frequency analysis. A spectrum information storage unit 373 that stores the information of the frequency spectrum calculated by the unit 332 together with the reception depth and the reception direction, and information on the feature amount calculated by the feature amount calculation unit 333 and the corrected feature amount corrected by the feature amount correction unit 335. A feature amount information storage unit 374 to store, an optimum attenuation rate set for each divided region by the attenuation rate setting unit 334, a cumulative attenuation rate for each sampling point calculated by the feature amount correction unit 335, and a representative attenuation rate calculation unit 336 And an attenuation rate information storage unit 375 that stores information on the representative attenuation rate calculated by.

  In addition to the above, the storage unit 37 has information necessary for amplification processing (relationship between the amplification factor and the reception depth shown in FIG. 2) and information necessary for amplification correction processing (the amplification factor and the reception depth shown in FIG. 3). ), Information necessary for the attenuation correction process (see equation (1)), information on window functions (Hamming, Hanning, Blackman, etc.) necessary for the frequency analysis process, and the like are stored.

  In addition, the storage unit 37 stores various programs including an operation program for executing the operation method of the ultrasound observation apparatus 3. The operation program can be recorded on a computer-readable recording medium such as a hard disk, a flash memory, a CD-ROM, a DVD-ROM, or a flexible disk and widely distributed. The various programs described above can also be obtained by downloading via a communication network. The communication network here is realized by, for example, an existing public line network, a LAN (Local Area Network), a WAN (Wide Area Network) or the like, and may be wired or wireless.

  The storage unit 37 having the above configuration is realized using a ROM (Read Only Memory) in which various programs and the like are installed in advance, and a RAM (Random Access Memory) that stores calculation parameters and data of each process. .

  FIG. 9 is a flowchart showing an outline of processing performed by the ultrasound observation apparatus 3 having the above configuration. The flowchart shown in FIG. 3 is for setting the region of interest in an ultrasonic image after the transmission / reception unit 31 starts transmitting a transmission drive wave and the ultrasonic transducer 21 starts transmitting an ultrasonic wave in the ultrasonic diagnostic system 1. Shows the processing when is completed.

  First, the ultrasonic observation device 3 receives an echo signal as a measurement result of an observation target by the ultrasonic transducer 21 from the ultrasonic endoscope 2 (step S1).

  The signal amplifying unit 311 that has received the echo signal from the ultrasonic transducer 21 amplifies the echo signal (step S2). Here, the signal amplifying unit 311 performs amplification (STC correction) of the echo signal based on the relationship between the amplification factor and the reception depth shown in FIG. 2, for example.

  Subsequently, the B-mode image data generation unit 341 generates B-mode image data using the echo signal amplified by the signal amplification unit 311 (step S3). The display control unit 361 performs control to display the B mode image corresponding to the B mode image data on the display device 4 (step S4).

  The amplification correction unit 331 performs amplification correction on the RF data output from the transmission / reception unit 31 so that the amplification factor is constant regardless of the reception depth (step S5). Here, the amplification correction unit 331 performs amplification correction based on, for example, the relationship between the amplification factor and the reception depth shown in FIG.

  Thereafter, the frequency analysis unit 332 calculates frequency spectra for all the sample data groups by performing frequency analysis by FFT on the RF data of each sound ray after amplification correction, and stores the frequency spectrum in the spectrum information storage unit 373. (Step S6). FIG. 10 is a flowchart showing an overview of the processing performed by the frequency analysis unit 332 in step S6. Hereinafter, the frequency analysis processing will be described in detail with reference to the flowchart shown in FIG.

First, the frequency analysis unit 332 sets a counter k for identifying a sound ray to be analyzed as k ₀ (step S31).

Subsequently, the frequency analysis unit 332 sets an initial value Z ^(k) ₀ of a data position (corresponding to a reception depth) Z ^(k) that represents a series of data groups (sample data group) generated for the FFT calculation. (Step S32). For example, FIG. 4 shows a case _where the eighth data position of the sound ray SR _k is set as the initial value Z ^(k) ₀ as described above.

  Thereafter, the frequency analysis unit 332 acquires a sample data group (step S33), and causes the window function stored in the storage unit 37 to act on the acquired sample data group (step S34). By applying the window function to the sample data group in this way, it is possible to avoid the sample data group from becoming discontinuous at the boundary and to prevent the occurrence of artifacts.

Subsequently, the frequency analysis unit 332 determines whether or not the sample data group at the data position Z ^(k) is a normal data group (step S35). As described with reference to FIG. 4, the sample data group needs to have the number of powers of two. Hereinafter, the number of data in the normal sample data group is 2 ⁿ (n is a positive integer). In the first embodiment, the data position Z ^(k) is set as much as possible to the center of the sample data group to which Z ^(k) belongs. Specifically, since the number of data in the sample data group is 2 ⁿ , Z ^(k) is set to the 2 ⁿ / 2 (= 2 ^n-1 ) th position close to the center of the sample data group. In this case, the sample data group is normal, (a = N) 2 ^n-1 -1 to the shallow side of the data position Z ^(k) there are pieces of data, deep from the data position Z ^(k) This means that there are 2 ^n-1 (= M) data on the side. In the case shown in FIG. 4, the sample data group F _j (j = 1, 2,..., K−1) is normal. FIG. 4 illustrates the case of n = 4 (N = 7, M = 8).

If the result of determination in step S35 is that the sample data group at data position Z ^(k) is normal (step S35: Yes), the frequency analysis unit 332 proceeds to step S37 described later.

If the result of determination in step S35 is that the sample data group at the data position Z ^(k) is not normal (step S35: No), the frequency analysis unit 332 inserts zero data for the shortage to obtain a normal sample data group. Generate (step S36). A window function is applied to the sample data group determined to be not normal in step S35 (for example, the sample data group F _{K in} FIG. 4) before adding zero data. For this reason, even if zero data is inserted into the sample data group, discontinuity of data does not occur. After step S36, the frequency analysis unit 332 proceeds to step S37 described later.

  In step S37, the frequency analysis unit 332 obtains a frequency spectrum that is a frequency distribution of amplitude by performing an FFT operation using the sample data group (step S37).

Subsequently, the frequency analysis unit 332 changes the data position Z ^(k) by the step width D (step S38). It is assumed that the step width D is stored in advance in the storage unit 37. FIG. 4 illustrates a case where D = 15. The step width D is desirably matched with the data step width used when the B-mode image data generation unit 341 generates B-mode image data. However, if the amount of calculation in the frequency analysis unit 332 is to be reduced, the step width D A value larger than the data step width may be set as the width D.

Thereafter, the frequency analysis unit 332 determines whether or not the data position Z ^(k) is larger than the maximum value Z ^(k) _max in the sound ray SR _k (step S39). When the data position Z ^(k) is larger than the maximum value Z ^(k) _max (step S39: Yes), the frequency analysis unit 332 increments the counter k by 1 (step S40). This means that the processing is shifted to the next sound ray. On the other hand, when the data position Z ^(k) is equal to or less than the maximum value Z ^(k) _max (step S39: No), the frequency analysis unit 332 returns to step S33.

After step S40, the frequency analysis unit 332 determines whether or not the counter k is greater than the maximum value k _max (step S41). When the counter k is larger than the maximum value k _max (step S41: Yes), the frequency analysis unit 332 ends a series of frequency analysis processing. On the other hand, when the counter k is equal to or less than the maximum value k _max (step S41: No), the frequency analysis unit 332 returns to step S32. The maximum value k _max is a value arbitrarily input by a user such as an operator through the input unit 35 or a value preset in the storage unit 37.

In this way, the frequency analysis unit 332 performs the FFT operation a plurality of times for each of (k _max −k ₀ +1) sound rays in the analysis target region. The frequency spectrum obtained as a result of the FFT operation is stored in the spectrum information storage unit 373 together with the reception depth and the reception direction.

  In the above description, the frequency analysis unit 332 performs the frequency analysis process on all the areas where the ultrasonic signal is received. However, the frequency analysis process may be performed only in the region of interest. It is.

Following the frequency analysis processing in step S6 described above, the feature amount calculation unit 333 calculates the feature amount of the frequency spectrum at the sampling points included in the region of interest (step S7). Specifically, the feature amount calculation unit 333 approximates by a linear expression I = a ₀ f + b ₀ by performing regression analysis on a frequency spectrum of a predetermined frequency band, and the gradient a ₀ and intercept b as the feature amount. ₀ , midband fit c ₀ is calculated. For example, a straight line L ₁₀ shown in FIG. 5 is a regression line approximated by the feature amount calculation unit 333 to the frequency spectrum C ₁ of the frequency band U by regression analysis.

Thereafter, the attenuation rate setting unit 334 sets the attenuation rate candidate value α to be applied when performing attenuation correction described later to a predetermined initial value α ₀ (step S8). The initial value α ₀ is stored in advance in the attenuation rate information storage unit 375. The input unit 35 may be configured to accept an input of a setting change of the initial value α ₀ of the attenuation rate candidate value.

Subsequently, the attenuation rate setting unit 334 calculates a preliminary correction feature amount by performing attenuation correction on the feature amount approximated to each frequency spectrum by the feature amount calculation unit 333 using the attenuation rate candidate value as α. Then, it is stored in the feature amount information storage unit 374 together with the attenuation rate candidate value α (step S9). A straight line L ₁ illustrated in FIG. 7 is an example of a straight line obtained by the attenuation rate setting unit 334 performing attenuation correction processing.

In step S9, the attenuation rate setting unit 334 obtains the data position Z = (f _sp / 2v) obtained using the sound ray data array of the ultrasonic signal at the reception depth z in the above-described equations (2) and (4). _s ) A preliminary correction feature value is calculated by substituting Dn. Here, f _sp is the data sampling frequency, v _s is the sound velocity, D is the data step width, and n is the number of data steps from the first data of the sound ray up to the data position of the sample data group to be processed. For example, _assuming that the data sampling frequency f _sp is 50 MHz, the sound velocity vs is 1530 m / sec, the data arrangement shown in FIG. 4 is employed, and the step width D is 15, Z = 0.295n (mm).

  The attenuation factor setting unit 334 calculates the variance of one preliminary correction feature value selected from a plurality of preliminary correction feature values obtained by the attenuation factor setting unit 334 performing attenuation correction on each frequency spectrum, and the attenuation factor. It is stored in the feature amount information storage unit 374 in association with the candidate value α (step S10). For example, when the preliminary correction feature amount is the slope a and the midband fit c, as described above, the attenuation rate setting unit 334 calculates the variance of one of the preliminary correction feature amounts a and c. As described above, when the feature amount image data generation unit 342 generates feature amount image data using the corrected feature amount a (h) in the subsequent processing, the dispersion of the preliminary correction feature amount a in the region of interest is applied. It is preferable to do this. In addition, when the feature amount image data generation unit 342 generates feature amount image data using the corrected feature amount c (h) in the subsequent processing, the variance of the preliminary correction feature amount c in the region of interest is applied. preferable. The preliminary correction feature value for calculating the variance may be set in advance, or may be set by inputting an instruction signal for instructing a desired preliminary correction feature value from the input unit 35 by the user. .

Thereafter, the attenuation rate setting unit 334 increases the attenuation rate candidate value α by Δα (step S11), and compares the increased attenuation rate candidate value α with a predetermined maximum value α _max (step S11). S12). As a result of the comparison in step S12, when the attenuation rate candidate value α is larger than the maximum value α _max (step S12: Yes), the ultrasound observation apparatus 3 proceeds to step S13. On the other hand, if the attenuation rate candidate value α is equal to or less than the maximum value α _max as a result of the comparison in step S12 (step S12: No), the ultrasound observation apparatus 3 returns to step S9. Note that the input unit 35 may be configured to accept an input of setting change of the increase rate Δα and the maximum value α _max of the attenuation rate candidate value.

  In step S13, the attenuation rate setting unit 334 refers to the variance of the preliminary correction feature amount for each attenuation rate candidate value stored in the feature amount information storage unit 374 with respect to the region of interest, and the attenuation rate candidate having the minimum variance The value is set as the optimum attenuation rate (step S13).

FIG. 11 is a diagram illustrating an outline of processing performed by the attenuation rate setting unit 334. Attenuation rate candidate value α and variance S when α ₀ = 0 (dB / cm / MHz), α _max = 1.0 (dB / cm / MHz), and Δα = 0.2 (dB / cm / MHz) It is a figure which shows the example of a relationship with ((alpha)). In the case shown in FIG. 11, when the attenuation rate candidate value α is 0.2 (dB / cm / MHz), the dispersion takes the minimum value S (α) _min . Therefore, in the case shown in FIG. 11, the attenuation rate setting unit 334 sets α = 0.2 (dB / cm / MHz) as the optimum attenuation rate. Note that after the characteristic amount calculation unit 333 performs regression analysis to calculate a curve for interpolating the value of the variance S (α) in the attenuation rate candidate value α, the attenuation rate setting unit 334 determines that the attenuation rate candidate value is in the definition area. The minimum value of the curve may be set as the optimum attenuation rate.

  Thereafter, the ultrasound observation apparatus 3 performs the process related to the feature image (steps S14 to S17) and the process related to the attenuation rate graph (steps S18 to S20) in parallel.

  First, processing related to a feature amount image will be described. The feature amount correcting unit 335 calculates the cumulative attenuation rate at the sampling points in the region of interest using the optimum attenuation rate set for the region of interest by the attenuation rate setting unit 334 (step S14). For example, the cumulative attenuation rate γ (h) at the sampling point S (h) in the region of interest 102 shown in FIG. 6 is given by Expression (7).

Subsequently, the feature amount correction unit 335 calculates a correction feature amount by performing attenuation correction on the feature amount of the sampling point in the region of interest using the cumulative attenuation rate (step S15). For example, the feature amount correction unit 335 corrects the corrected feature amounts a ₂₃ (h), b ₂₃ of the slope a ₀ , the intercept b ₀ , and the midband fit c ₀ at the sampling point S ₂₃ (h) of the region of interest 102 shown in FIG. (H) and c ₂₃ (h) are calculated according to the equations (9) to (11), respectively.

  The feature amount image data generation unit 342 performs visual information (for example, hue) associated with the corrected feature amount calculated in step S14 for each pixel in the region of interest in the B mode image data generated by the B mode image data generation unit 341. ) To generate feature amount image data (step S16). Thereafter, the display control unit 361 performs control to display the feature amount image corresponding to the generated feature amount image data on the display device 4 (step S17).

  Next, processing related to the attenuation rate graph will be described. The representative attenuation rate calculation unit 336 calculates the representative attenuation rate of the region of interest using the attenuation rate of each divided region in the region of interest (step S18).

  Subsequently, the attenuation rate graph generation unit 343 generates an attenuation rate graph using the representative attenuation rate calculated in step S18 (step S19). Thereafter, the display control unit 361 performs control to display the generated image of the attenuation rate graph on the display device 4 (step S20).

  After steps S17 and S20, the ultrasound observation apparatus 3 ends a series of processes. The ultrasound observation apparatus 3 periodically repeats the processes of steps S1 to S20.

  FIG. 12 is a diagram schematically illustrating a display example of all images generated by the image processing unit 34 on the display device 4. The display screen 201 shown in the figure includes an information display area 211 for displaying patient information such as ID, name, and sex, and feature quantity information, a first image display area 212, a second image display area 213, and an attenuation rate. And an attenuation rate graph display area 214 for displaying a graph.

  A B-mode image 221 is displayed in the first image display area 212, and a feature amount image 222 is displayed in the second image display area 213. The feature amount image 222 is a feature amount image for the region of interest 223. It is also possible to set the entire image as a region of interest. When the display device 4 displays the B-mode image 221 and the feature amount image 222 side by side, the user can accurately grasp the tissue properties in the region of interest.

The attenuation factor graph display area 214, the representative decay curve 231 showing a time change of a representative attenuation factor alpha _ROI is displayed. The representative attenuation rate curve 231 gives a temporal change in the representative attenuation rate α _ROI in a certain period, and the latest calculation result is the rightmost point. In the representative attenuation rate curve 231, each point moves from right to left with time, disappears from the left side in order from the old point, and new points appear from the right side.

  In the first embodiment, the display control unit 361 may control the display device 4 so that at least the feature amount image 222 and the representative attenuation rate curve 231 are associated and displayed on the same screen. More generally, the display control unit 361 may control the display device 4 to display the correction feature amount of the region of interest and the attenuation rate graph in association with each other.

  According to the first embodiment of the present invention described above, the attenuation rate graph indicating the temporal change of the representative attenuation rate in the region of interest of the ultrasonic image and the attenuation-corrected feature amount are associated with each other and displayed on the display device. The user can visually recognize the temporal change of the attenuation rate in the ultrasonic image.

  Further, according to the first embodiment, the temporal change of the attenuation rate, which is an intermediate parameter for calculating the correction feature value, is displayed on the display device, so that the tissue characteristics of the subject can be grasped more accurately. Can provide significant information.

  In the above description, the case where the feature amount image is generated for the region of interest has been described, but the feature amount image for the entire region of the ultrasonic image including the region other than the region of interest can also be generated. In this case, the correction feature amount may be obtained for the entire region.

(Modification 1)
FIG. 13 is a diagram illustrating a display example on the display device 4 of the attenuation rate graph generated by the ultrasonic observation apparatus according to the first modification of the first embodiment. A representative attenuation rate display curve 232 shown in the figure is a freeze operation performed by the ultrasonic endoscope 2, and the user selects a desired image from past images temporarily stored in the image data storage unit 371. A display example in the case of performing cine memory playback for playback display is shown. At this time, in the attenuation rate graph display area 214, a display image bar 233 indicating which image is reproduced and displayed among images temporarily stored in the image data storage unit 371 is displayed. Thereby, the user can visually recognize the value of the representative attenuation rate α _ROI in the currently displayed feature value image. Note that the value of the representative attenuation rate α _ROI at the time at which the representative attenuation rate display curve 232 and the display image bar 233 intersect may be displayed numerically in the attenuation rate graph display area 214.

(Modification 2)
FIG. 14 is a diagram illustrating a display example on the display device 4 of the attenuation rate graph generated by the ultrasonic observation apparatus according to the second modification of the first embodiment. In addition to the representative attenuation rate display curve 234, the attenuation rate graph display area 214 shown in the figure has an upper limit value 235a and a lower limit value 235b that indicate the upper and lower limits of the representative attenuation rate α _{ROI that} can be taken by the observation target (for example, a living body), respectively. Is shown. FIG. 14 shows an example in which the upper limit of the representative attenuation rate α _ROI is 1.0 (dB / MHz / cm) and the lower limit is 0.3 (dB / MHz / cm). The upper and lower limit values may be set and changed by the user through input from the input unit 35. By displaying the upper limit value and the lower limit value of the representative attenuation rate in this way, the user can intuitively grasp the validity of the numerical value of the representative attenuation rate curve and easily determine whether there is an abnormality in the image. .

(Modification 3)
In the ultrasonic observation apparatus according to the third modification of the first embodiment, the input unit 35 has a function of receiving a designation input of a desired point in the region of interest, and the representative attenuation rate of the divided region including the designated point The graph is displayed on the display device 4. FIG. 15 is a diagram schematically illustrating a display example on the display device 4 of all images generated by the ultrasonic observation apparatus according to the third modification. In the display screen 202 shown in the figure, the same reference numerals are given to the same parts as those of the display screen 201 described in the first embodiment.

  In the feature amount image 222 displayed in the second image display region 213 of the display screen 202, two points 241 and 242 are displayed in the region of interest 223. These points 241 and 242 are points where the input unit 35 has received a setting input.

  In the attenuation rate graph display area 214, representative attenuation rate curves 236 and 237 of the divided areas including the two points 241 and 242 are displayed. The two representative attenuation rate curves 236 and 237 are displayed in a manner distinguishable from each other. In the case shown in FIG. 15, the line types of the two curves are changed and displayed, but other line colors, thicknesses, etc. may be displayed. Further, the number of points that accept designation within the region of interest is not limited to two, and may be one or three or more.

  According to the modified example 3 described above, since the attenuation rate graph that gives the time change of a plurality of attenuation rates is generated, the user can make an accurate diagnosis even for a non-uniform tissue. In addition, since the user can visually recognize the temporal change in the representative attenuation rate of a desired region in the region of interest, the user can more accurately acquire information for diagnosis.

(Embodiment 2)
The ultrasound observation apparatus according to the second embodiment of the present invention generates an attenuation rate graph that displays temporal changes in the representative attenuation rate in the calculation region to be calculated among the region of interest and the region outside the region of interest. It is characterized by that. The functional configuration of the ultrasonic observation apparatus according to the second embodiment is the same as the functional configuration of the ultrasonic observation apparatus 3 described in the first embodiment.

  FIG. 16 is a flowchart showing an outline of processing performed by the ultrasonic observation apparatus according to Embodiment 2 of the present invention. In the flowchart illustrated in FIG. 16, the processes in steps S51 to S56 sequentially correspond to the processes in steps S1 to S6 described in the first embodiment.

In step S57, the feature amount calculation unit 333 calculates the feature amount of the frequency spectrum at the sampling points respectively included in the region of interest and the calculation region (step S57). FIG. 17 is a diagram schematically illustrating a setting example of a region of interest and a calculation region in a display region of an ultrasonic image and divided regions of those regions. In the image display area 104 shown in FIG. 17, a region of interest 105 and a calculation region 107 located between the surface position 106 of the ultrasonic transducer 21 and the region of interest are set. The region of interest 105 is surrounded by a total of four boundary lines: two boundary lines each extending linearly along the depth direction from the surface position 106 and two boundary lines each arcing along the scanning angle direction. It is an area. The calculation area 107 is in contact with the surface position 106 and the region of interest 105. In addition, two boundary lines extending linearly along the depth direction from the surface position 106 among the boundary lines of the calculation area 107 are respectively linear along the depth direction from the surface position 106 in the region of interest 105. Are included in the same straight line as one of the two boundary lines extending to In the image display region 104, the region of interest 105 is divided into eight divided regions R _ij (i = 1 to 2, j = 1 to 4), and the calculation region 107 is divided into four divided regions Q _k (k = 1 to 4), it is only an example. For example, the calculation may be performed with the region of interest 105 and the calculation region 107 as one region.

  The processes in steps S58 to S63 sequentially correspond to the processes in steps S8 to S13 described in the first embodiment. However, the second embodiment is different in that the attenuation rate setting unit 334 performs processing for setting an optimum attenuation rate for the calculation region in addition to the region of interest.

In the second embodiment, the attenuation rate candidate value is calculated on the assumption that both the region of interest and the calculation region have the same initial value α ₀ , increase amount Δα, and maximum value α _max . An initial value, an increase amount, and / or a maximum value may be individually set for each region.

  The processing related to the feature amount image in steps S64 to S67 sequentially corresponds to steps S14 to S17 described in the first embodiment.

  The processes related to the attenuation rate graph in steps S68 to S70 correspond to steps S18 to S20 described in the first embodiment in order. However, the attenuation rate graph generation unit 343 also generates a representative attenuation rate curve of the calculation area.

  FIG. 18 is a diagram schematically illustrating a display example on the display device 4 of all images generated by the ultrasound observation apparatus 3 according to the second embodiment. In the display screen 203 shown in the figure, the same parts as those of the display screen 201 described in the first embodiment are denoted by the same reference numerals.

  In the feature amount image 222 displayed in the second image display region 213 of the display screen 203, the region of interest 224 and the calculation region 225 are displayed in an identifiable manner. Specifically, the region of interest 224 is displayed with a solid line, and the calculation region 225 is displayed with a broken line.

  In the attenuation rate graph display area 214, a representative attenuation rate curve 238 in the region of interest 224 and a representative attenuation rate curve 239 in the calculation area 225 are displayed. Note that the attenuation rate graph generation unit 343 may generate an attenuation rate graph that displays a plurality of representative attenuation rates equal to or less than the number of divided regions in each region as the representative attenuation rates of the region of interest and the calculation region.

  According to the second embodiment of the present invention described above, as in the first embodiment, it becomes possible for the user to visually recognize the temporal change of the attenuation rate in the ultrasonic image, and the tissue characteristics of the subject can be further improved. Significant information for accurately grasping can be provided.

  In addition, according to the second embodiment, the user can also grasp information related to the attenuation rate of the calculation area that is indispensable for the calculation of the correction feature value, among the areas outside the region of interest. Therefore, the user can make an accurate diagnosis even when diagnosing uneven tissue properties.

  In FIG. 17, the region of interest 105 and the calculation region 107 are in contact with each other, but it may be set so that a part of the region of interest 105 intersects. For example, two regions may be set such that a portion having a small depth in the region of interest 105 and a portion having a large depth in the calculation region 107 have a band-like overlap along the scanning angle direction.

  In the second embodiment, the attenuation rate setting unit 334 may set the attenuation rate of the calculation area as a uniform value.

(Other embodiments)
The embodiments for carrying out the present invention have been described so far, but the present invention should not be limited only by the above-described first and second embodiments. For example, the image processing unit 34 generates an attenuation rate image that displays the optimum attenuation rate of each divided region in the region of interest in a visually identifiable manner, and displays it on the display device 4 together with the feature amount image and the attenuation rate graph. You may make it make it. In this case, the optimum attenuation rate may be displayed in a manner that can be identified for each divided region in the calculation region.

  The attenuation rate setting unit 334 may set an optimal attenuation rate at a predetermined frame interval of the ultrasonic image. Thereby, the amount of calculation can be reduced significantly. In this case, the most recently set optimum attenuation value may be used until the next optimum attenuation rate is set.

  Further, as an amount giving statistical variation, for example, any one of standard deviation, a difference between the maximum value and the minimum value of the feature amount in the population, and a half-value width of the distribution of the feature amount can be applied. It is conceivable to apply the reciprocal of the variance as an amount that gives statistical variation. In this case, however, it is needless to say that the attenuation rate candidate value having the maximum value is the optimum attenuation rate.

  In addition, the attenuation rate setting unit 334 can calculate statistical variations of a plurality of types of preliminary correction feature amounts, and can set the attenuation rate candidate value having the smallest statistical variation as the optimal attenuation rate. It is.

  Further, the attenuation rate setting unit 334 may attenuate the frequency spectrum using a plurality of attenuation rate candidate values, and perform a regression analysis on the frequency spectrum after the attenuation correction to calculate the preliminary correction feature amount. Good.

  Further, the present invention can be applied to an ultrasonic probe other than the ultrasonic endoscope. As the ultrasonic probe, for example, a thin ultrasonic miniature probe without an optical system may be applied. Ultrasonic miniature probes are usually inserted into the biliary tract, bile duct, pancreatic duct, trachea, bronchi, urethra, ureter, and used to observe surrounding organs (pancreas, lung, prostate, bladder, lymph nodes, etc.). Further, as the ultrasonic probe, an external ultrasonic probe that irradiates ultrasonic waves from the body surface of the subject may be applied. The extracorporeal ultrasonic probe is usually used for observing an abdominal organ (liver, gallbladder, bladder), breast (particularly mammary gland), and thyroid gland.

  As described above, the present invention can include various embodiments without departing from the technical idea described in the claims.

DESCRIPTION OF SYMBOLS 1 Ultrasonic diagnostic system 2 Ultrasound endoscope 3 Ultrasound observation apparatus 4 Display apparatus 21 Ultrasonic transducer 31 Transmission / reception part 32 Signal processing part 33 Calculation part 34 Image processing part 35 Input part 36 Control part 37 Storage part 101,104 Image display area 102, 105, 223, 224 Area of interest 103, 106 Surface position 107, 225 Calculation area 201, 202, 203 Display screen 211 Information display area 212 First image display area 213 Second image display area 214 Attenuation rate graph Display area 221 B mode image 222 Feature amount image 231, 232, 234, 236, 237, 238, 239 Representative attenuation rate curve 233 Display image bar 235 a Upper limit value 235 b Lower limit value 311 Signal amplification unit 331 Amplification correction unit 332 Frequency analysis unit 333 Feature amount calculation unit 334 Attenuation rate setting unit 335 Feature amount correction unit 336 Representative attenuation rate calculation unit 341 B-mode image data generation unit 342 Feature amount image data generation unit 343 Attenuation rate graph generation unit 361 Display control unit 371 Image data storage unit 372 Division region information storage unit 373 Spectrum information storage unit 374 Feature value information storage unit 375 Attenuation rate information storage unit

Claims (15)

An ultrasonic observation apparatus that generates an ultrasonic image based on an ultrasonic signal acquired by an ultrasonic probe including an ultrasonic transducer that transmits ultrasonic waves to an observation target and receives ultrasonic waves reflected by the observation target Because
A frequency analyzer that calculates a plurality of frequency spectra according to a reception depth and a reception direction of the ultrasonic signal by analyzing the frequency of the ultrasonic signal;
A feature amount calculation unit for calculating the feature amounts of the plurality of frequency spectra respectively;
An attenuation rate setting unit for setting an attenuation rate that gives an attenuation characteristic when the ultrasonic wave propagates through the observation target in the region of interest of the ultrasonic image;
A feature amount correction unit that calculates a correction feature amount in the region of interest of the ultrasonic image by performing attenuation correction of the feature amount using the attenuation rate set by the attenuation rate setting unit;
A representative attenuation rate calculation unit for calculating a representative attenuation rate of the region of interest defined based on the attenuation rate;
An attenuation rate graph generating unit for generating an attenuation rate graph showing a time change of the representative attenuation rate;
A display control unit that performs control for associating the correction feature amount and the attenuation rate graph with a display device; and
An ultrasonic observation apparatus comprising: The attenuation rate setting unit
Using each of a plurality of attenuation rate candidate values that give different attenuation characteristics as attenuation characteristics when the ultrasonic waves propagate through the observation object, the influence of the attenuation of the ultrasonic waves on the feature amount of each frequency spectrum is eliminated. By performing attenuation correction, a preliminary correction feature amount of each frequency spectrum for each attenuation rate candidate value is calculated, and an optimum attenuation for the observation target is selected from the plurality of attenuation rate candidate values based on the calculation result. Set the rate,
The feature amount correction unit and the representative attenuation rate calculation unit are:
The ultrasonic observation apparatus according to claim 1, wherein the correction feature amount and the representative attenuation rate are respectively calculated using the optimum attenuation rate. The attenuation rate setting unit
By using each of a plurality of unit lengths and attenuation rate candidate values per unit frequency in the ultrasonic wave for each of a plurality of divided regions obtained by dividing the region of interest, a feature amount of each frequency spectrum is obtained. Preliminary correction feature values of each frequency spectrum for each attenuation rate candidate value are calculated by applying the attenuation correction to the attenuation rate candidate value, and the optimum attenuation value is selected from the plurality of attenuation rate candidate values based on the calculation result. Set the rate,
The representative attenuation rate calculation unit includes:
The ultrasonic observation apparatus according to claim 2, wherein the representative attenuation rate is calculated using the optimum attenuation rate set in each divided region. The attenuation rate setting unit
3. The statistical variation of the preliminary correction feature value is calculated for each attenuation rate candidate value, and the attenuation rate candidate value having the smallest statistical variation is set as the optimum attenuation rate. The ultrasonic observation apparatus described in 1. The attenuation rate graph generation unit
The ultrasonic observation apparatus according to claim 1, wherein the attenuation rate graph is generated by adding information indicating an upper limit value and a lower limit value of the representative attenuation rate. A storage unit that stores the ultrasonic image, the correction feature amount, and the representative attenuation rate;
The attenuation rate graph generation unit
When the ultrasonic probe is in a frozen state, the attenuation rate graph corresponding to a set of the ultrasonic images that can be reproduced among the ultrasonic images stored in the storage unit, and being reproduced on the display device The ultrasonic observation apparatus according to claim 1, wherein the attenuation rate graph to which information indicating the value of the representative attenuation rate corresponding to an ultrasonic image is added is generated. The feature correction unit
Based on the optimum attenuation rate of each of the divided areas set by the attenuation rate setting unit, a cumulative attenuation rate per unit frequency at the sampling point is calculated, and attenuation correction of the feature amount is performed using the accumulated attenuation rate. The ultrasonic observation apparatus according to claim 2, wherein the correction feature amount of the sampling point is calculated as described above. The attenuation rate setting unit
A region that is different from the region of interest of the ultrasonic image and is used for calculation for correcting the feature value, and is located between the region corresponding to the surface of the ultrasonic transducer and the region of interest Further set the attenuation rate of the calculation area,
The representative attenuation rate calculation unit includes:
Further calculating a representative attenuation rate of the calculation region defined based on the attenuation rate of the calculation region;
The attenuation rate graph generation unit
The ultrasonic observation apparatus according to claim 1, wherein an attenuation rate graph further including a temporal change in the representative attenuation rate of the calculation area is generated. The attenuation rate setting unit
For each of a plurality of divided regions obtained by dividing the region of interest and the calculation region, respectively, by using each of a plurality of unit lengths and attenuation rate candidate values per unit frequency in the ultrasonic wave, By performing the attenuation correction on the feature amount of the frequency spectrum, a preliminary correction feature amount of each frequency spectrum for each attenuation rate candidate value is calculated, and based on the calculation result, the plurality of attenuation rate candidate values are calculated. Set the optimum attenuation factor from the inside,
The representative attenuation rate calculation unit includes:
9. The ultrasonic wave according to claim 8, wherein at least two representative attenuation rates respectively corresponding to the region of interest and the calculation region are calculated using the optimal attenuation rate set in each divided region. Observation device. The feature correction unit
Based on the attenuation rates of the region of interest and the calculation region set by the attenuation rate setting unit, a cumulative attenuation rate per unit frequency at a sampling point is calculated, and attenuation correction of the feature amount is performed using the cumulative attenuation rate The ultrasonic observation apparatus according to claim 8, wherein the correction feature amount of the sampling point is calculated by performing the following. The feature correction unit
By accumulatively adding the optimum attenuation rate for each divided region existing between the position corresponding to the surface of the ultrasonic transducer and the sampling point, weighted by the round-trip distance in the depth direction in each divided region The ultrasonic observation apparatus according to claim 10, wherein the cumulative attenuation rate at the sampling point is calculated. A feature amount image data generation unit for generating feature amount image data for displaying information on the corrected feature amount together with the ultrasonic image;
The display control unit
The ultrasound observation apparatus according to claim 1, wherein a feature amount image corresponding to the feature amount image data and the attenuation rate graph are displayed in association with each other on the display device. The feature amount calculation unit includes:
The ultrasonic observation apparatus according to claim 1, wherein the feature amount is calculated by performing a process of approximating the frequency spectrum with an n-order equation (n is a positive integer). An ultrasonic observation apparatus that generates an ultrasonic image based on an ultrasonic signal acquired by an ultrasonic probe including an ultrasonic transducer that transmits ultrasonic waves to an observation target and receives ultrasonic waves reflected by the observation target The operation method of
A frequency analysis step in which a frequency analysis unit calculates a plurality of frequency spectra according to the reception depth and reception direction of the ultrasonic signal by analyzing the frequency of the ultrasonic signal;
A feature amount calculating unit that calculates feature amounts of the plurality of frequency spectra, respectively;
An attenuation rate setting unit that sets an attenuation rate that gives an attenuation characteristic when the ultrasonic wave propagates through the observation target in the region of interest of the ultrasonic image; and
A feature amount correcting unit that calculates a correction feature amount in the region of interest of the ultrasonic image by performing attenuation correction of the feature amount using the attenuation rate;
A representative attenuation factor calculating unit that calculates a representative attenuation factor of the region of interest defined based on the attenuation factor; and
An attenuation factor graph generation unit generates an attenuation factor graph indicating a time change of the representative attenuation factor; and
A display control step in which a display control unit performs control to display the correction feature quantity and the attenuation rate graph in association with each other on a display device;
A method for operating an ultrasonic observation apparatus, comprising: An ultrasonic observation apparatus that generates an ultrasonic image based on an ultrasonic signal acquired by an ultrasonic probe including an ultrasonic transducer that transmits ultrasonic waves to an observation target and receives ultrasonic waves reflected by the observation target In addition,
A frequency analysis step in which a frequency analysis unit calculates a plurality of frequency spectra according to the reception depth and reception direction of the ultrasonic signal by analyzing the frequency of the ultrasonic signal;
A feature amount calculating unit that calculates feature amounts of the plurality of frequency spectra, respectively;
An attenuation rate setting unit that sets an attenuation rate that gives an attenuation characteristic when the ultrasonic wave propagates through the observation target in the region of interest of the ultrasonic image; and
A feature amount correcting unit that calculates a correction feature amount in the region of interest of the ultrasonic image by performing attenuation correction of the feature amount using the attenuation rate;
A representative attenuation factor calculating unit that calculates a representative attenuation factor of the region of interest defined based on the attenuation factor; and
An attenuation factor graph generation unit generates an attenuation factor graph indicating a time change of the representative attenuation factor; and
A display control step in which a display control unit performs control to display the correction feature quantity and the attenuation rate graph in association with each other on a display device;
A program for operating an ultrasonic observation apparatus, characterized in that