WO2016006288A1 - 超音波観測装置、超音波観測装置の作動方法および超音波観測装置の作動プログラム - Google Patents
超音波観測装置、超音波観測装置の作動方法および超音波観測装置の作動プログラム Download PDFInfo
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B8/00—Diagnosis using ultrasonic, sonic or infrasonic waves
- A61B8/52—Devices using data or image processing specially adapted for diagnosis using ultrasonic, sonic or infrasonic waves
- A61B8/5269—Devices using data or image processing specially adapted for diagnosis using ultrasonic, sonic or infrasonic waves involving detection or reduction of artifacts
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B8/00—Diagnosis using ultrasonic, sonic or infrasonic waves
- A61B8/08—Detecting organic movements or changes, e.g. tumours, cysts, swellings
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B8/00—Diagnosis using ultrasonic, sonic or infrasonic waves
- A61B8/12—Diagnosis using ultrasonic, sonic or infrasonic waves in body cavities or body tracts, e.g. by using catheters
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B8/00—Diagnosis using ultrasonic, sonic or infrasonic waves
- A61B8/13—Tomography
- A61B8/14—Echo-tomography
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B8/00—Diagnosis using ultrasonic, sonic or infrasonic waves
- A61B8/44—Constructional features of the ultrasonic, sonic or infrasonic diagnostic device
- A61B8/4444—Constructional features of the ultrasonic, sonic or infrasonic diagnostic device related to the probe
- A61B8/4461—Features of the scanning mechanism, e.g. for moving the transducer within the housing of the probe
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B8/00—Diagnosis using ultrasonic, sonic or infrasonic waves
- A61B8/46—Ultrasonic, sonic or infrasonic diagnostic devices with special arrangements for interfacing with the operator or the patient
- A61B8/461—Displaying means of special interest
- A61B8/463—Displaying means of special interest characterised by displaying multiple images or images and diagnostic data on one display
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B8/00—Diagnosis using ultrasonic, sonic or infrasonic waves
- A61B8/52—Devices using data or image processing specially adapted for diagnosis using ultrasonic, sonic or infrasonic waves
- A61B8/5207—Devices using data or image processing specially adapted for diagnosis using ultrasonic, sonic or infrasonic waves involving processing of raw data to produce diagnostic data, e.g. for generating an image
Definitions
- 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.
- Ultrasound may be applied to observe the characteristics of the biological tissue or material that is the object of observation. Specifically, ultrasonic waves are transmitted to the observation target, and predetermined signal processing is performed on the ultrasonic echoes reflected by the observation target, thereby acquiring information related to the characteristics of the observation target.
- the intensity of ultrasonic waves is attenuated when propagating through the observation target.
- a technique for determining characteristics of a material to be observed using this attenuation is known (see, for example, Patent Document 1).
- an electrical signal corresponding to an ultrasonic echo is converted into an amplitude spectrum in the frequency domain, and the attenuation is calculated by comparing the amplitude spectrum with a predetermined reference amplitude spectrum.
- the material properties are determined by fitting with a dependent attenuation model.
- the reference amplitude spectrum is made of a material that has the same shape as the observation target and has an ultrasonic velocity equivalent to that of the observation target, but substantially does not attenuate the ultrasonic wave. It is set using a reference object (reference piece).
- the method for determining the characteristics of the observation target using the reference amplitude spectrum set in this way is effective in the case of a material having a regular structure, but is applied to a biological tissue in which the structure itself is irregular. Difficult to do.
- the present invention has been made in view of the above, and it is possible to obtain an attenuation characteristic of an ultrasonic wave suitable for an observation object by simple calculation and to perform an observation using the attenuation characteristic.
- An object is to provide an observation apparatus, an operation method of an ultrasonic observation apparatus, and an operation program of the ultrasonic observation apparatus.
- the ultrasonic observation apparatus converts an ultrasonic echo reflected by the observation target into an electrical signal by transmitting the ultrasonic wave to the observation target.
- a frequency analysis unit that calculates a plurality of frequency spectra by analyzing the frequency of a signal generated based on an echo signal; and a feature amount of each of the plurality of frequency spectra is calculated, and the ultrasonic wave propagates through the observation target Correction of each frequency spectrum by performing attenuation correction that eliminates the influence of attenuation of the ultrasonic wave on the feature quantity of each frequency spectrum in each of a plurality of attenuation rate candidate values that give different attenuation characteristics when performing Calculating a feature amount, and using the corrected feature amount, a feature amount calculation that sets an optimum attenuation rate for the observation target from the plurality of attenuation rate candidate values And a feature amount image data generation unit that generates feature amount image data to be displayed together with the ultrasonic image generated from the
- the feature amount calculation unit calculates the feature amount by performing a process of approximating each frequency spectrum with an n-order equation (n is a positive integer). A statistical variation of the correction feature amount is calculated for each attenuation rate candidate value, and an attenuation rate candidate value having the smallest statistical variation is set as the optimum attenuation rate.
- the feature amount calculation unit approximates a predetermined frequency band in the frequency spectrum by a linear expression, an intercept and an inclination of the linear expression, and an intermediate between the frequency bands.
- One or more of the mid-band fits that are values of the linear expression at a frequency, including one of the slope and the mid-band fit, is calculated as the feature amount, and either the slope or the mid-band fit is calculated.
- the optimum attenuation rate is set based on one of the above.
- the optimum attenuation rate is set based on the inclination, and the midband fit is performed. Is calculated as the feature amount, the optimum attenuation rate is set based on the midband fit.
- the feature amount calculation unit obtains the statistical variation as a function of the attenuation rate candidate value, and the attenuation that minimizes the statistical variation in the function.
- a rate candidate value is set as the optimum attenuation rate.
- the ultrasonic observation apparatus is characterized in that, in the above invention, the feature amount calculation unit sets the optimum attenuation rate in all frames of the ultrasonic image.
- the feature amount calculation unit sets the optimal attenuation rate for each predetermined number of frames larger than 1 of the ultrasonic image, and sets the optimal attenuation rate. For a frame that is not set, the feature amount of each frequency spectrum is calculated using the optimum attenuation rate that was set last before the frame.
- the feature amount calculation unit calculates an optimum attenuation rate equivalent value corresponding to the optimum attenuation rate in all frames of the ultrasound image, and is greater than 1.
- the optimum attenuation rate is set based on the value corresponding to the optimum attenuation rate calculated in a predetermined number of frames.
- the ultrasonic observation apparatus is characterized in that, in the above invention, the feature image data includes information on the optimum attenuation rate.
- the ultrasonic observation apparatus is characterized in that, in the above-described invention, the ultrasonic observation apparatus further includes a display unit for displaying a feature amount image corresponding to the feature amount image data.
- the ultrasonic observation apparatus further includes an input unit that receives a setting input of a target region in which the frequency analysis unit calculates the frequency spectrum in the above invention, and the frequency analysis unit is reflected by the target region.
- the frequency spectrum is calculated based on the ultrasonic echo.
- the ultrasonic observation apparatus is the ultrasonic observation apparatus according to the above aspect, wherein the feature amount calculation unit uses data having a dynamic range wider than a dynamic range of data used by the feature amount image data generation unit. It is characterized by setting.
- the frequency analysis unit generates the ultrasonic wave transmitted to the observation target based on the echo signal obtained by converting the ultrasonic echo reflected by the observation target into an electrical signal.
- An output step, and a feature amount image data generation unit that generates feature amount image data to be displayed together with the ultrasound image generated from the
- the operation program of the ultrasonic observation apparatus is generated based on an echo signal in which an ultrasonic wave transmitted from the frequency analysis unit to the observation target is converted into an electrical signal from the ultrasonic echo reflected by the observation target.
- Correction of each frequency spectrum by performing attenuation correction that eliminates the influence of attenuation of the ultrasonic wave on the feature quantity of each frequency spectrum in each of a plurality of attenuation rate candidate values that give different attenuation characteristics when performing A feature amount is calculated, and an optimum attenuation rate is set for the observation target from the plurality of attenuation rate candidate values using the corrected feature amount.
- a feature amount image data generation unit that generates the feature amount image data to be displayed together with the ultrasonic image generated from the echo signal in association with the visual information with the corrected feature amount based on the optimum attenuation rate. And causing the ultrasonic observation apparatus to execute the feature quantity image data generation step.
- an optimal attenuation rate is set for an observation target from among a plurality of attenuation rate candidate values that give different attenuation characteristics when ultrasonic waves propagate through the observation target, and the optimal attenuation rate is used. Since the characteristic amount of each frequency spectrum is calculated by performing attenuation correction, the attenuation characteristic of the ultrasonic wave suitable for the observation target can be obtained by simple calculation, and observation using the attenuation characteristic can be performed. .
- FIG. 1 is a block diagram showing a configuration of an ultrasonic observation apparatus according to an embodiment of the present invention.
- FIG. 2 is a diagram illustrating a 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 the embodiment of the present invention.
- 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 of the ultrasonic observation apparatus according to the embodiment 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 the embodiment of the present invention.
- FIG. 6 is a diagram showing a straight line having as a parameter the correction feature amount corrected by the attenuation correction unit of the ultrasonic observation apparatus according to the embodiment of the present invention.
- FIG. 7 is a diagram schematically illustrating a distribution example of correction feature amounts that have been attenuation-corrected based on two different attenuation rate candidate values for the same observation target.
- FIG. 8 is a flowchart showing an outline of processing performed by the ultrasonic observation apparatus according to the embodiment of the present invention.
- FIG. 9 is a flowchart showing an outline of processing executed by the frequency analysis unit of the ultrasonic observation apparatus according to the embodiment of the present invention.
- FIG. 10 is a diagram illustrating an outline of processing performed by the optimum attenuation rate setting unit of the ultrasonic observation apparatus according to the embodiment of the present invention.
- FIG. 11 is a diagram schematically illustrating a display example of the feature amount image on the display unit of the ultrasonic observation apparatus according to the embodiment of the present invention.
- FIG. 12 is a diagram illustrating an outline of processing performed by the optimum attenuation rate setting unit of the ultrasonic observation apparatus according to the first modification of the embodiment of the present invention.
- FIG. 1 is a block diagram showing a configuration of an ultrasonic observation apparatus according to an embodiment of the present invention.
- An ultrasonic observation apparatus 1 shown in the figure is an apparatus for observing an observation object using ultrasonic waves.
- the ultrasonic observation apparatus 1 outputs an ultrasonic pulse to an observation target, and receives an ultrasonic echo reflected by the observation target, and an electric signal between the ultrasonic probe 2 and the ultrasonic probe 2.
- a transmission / reception unit 3 for performing transmission / reception, a calculation unit 4 for performing a predetermined calculation on an electrical echo signal obtained by converting an ultrasonic echo into an electrical signal, and generation of image data corresponding to the electrical echo signal It is realized using the image processing unit 5 and a user interface such as a keyboard, a mouse, a touch panel, etc., and is realized using an input unit 6 that receives input of various information, and a display panel made up of liquid crystal or organic EL (Electro Luminescence).
- the display unit 7 for displaying various information including the image generated by the image processing unit 5, the storage unit 8 for storing various information necessary for ultrasonic observation, and the operation control of the ultrasonic observation apparatus 1 are performed.
- the ultrasonic observation apparatus 1 is a process in which the ultrasonic probe 2 provided with the ultrasonic transducer 21 and the ultrasonic probe 2 are detachably connected, and the above-described portions other than the ultrasonic probe 2 are provided.
- Device processing
- the ultrasound probe 2 is in the form of an external probe that irradiates ultrasound from the body surface of the living body, in a lumen such as the digestive tract, the bile pancreatic duct, and a blood vessel.
- any of a form of a miniature ultrasonic probe provided with a long-axis insertion part to be inserted into an ultrasonic endoscope and a form of an ultrasonic endoscope further provided with an optical system in the intraluminal ultrasonic probe may be employed.
- an ultrasonic transducer 21 is provided at the distal end side of the insertion portion of the intraluminal ultrasonic probe, and the intraluminal ultrasonic probe is located at the proximal end side. Removably connected to the processing device.
- the ultrasonic transducer 21 converts an electrical pulse signal received from the transmission / reception unit 3 into an ultrasonic pulse (acoustic pulse), and converts an ultrasonic echo reflected from an external observation target into an electrical echo signal.
- the ultrasonic probe 2 may be one that mechanically scans the ultrasonic transducer 21, or a plurality of elements are arranged 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. In the present embodiment, it is possible to select and use any one of a plurality of different types of ultrasonic probes 2 as the ultrasonic probe 2.
- the transmission / reception unit 3 is electrically connected to the ultrasound probe 2 and transmits an electrical pulse signal to the ultrasound probe 2, and an echo that is an electrical reception signal from the ultrasound probe 2. Receive a signal. Specifically, the transmission / reception unit 3 generates an electrical pulse signal based on a preset waveform and transmission timing, and transmits the generated pulse signal to the ultrasound probe 2.
- the transmission / reception unit 3 includes a signal amplification unit 31 that amplifies the echo signal.
- the signal amplifier 31 performs STC (Sensitivity Time Control) correction that amplifies an echo signal having a larger reception depth with a higher amplification factor.
- FIG. 2 is a diagram illustrating a relationship between the reception depth and the amplification factor in the STC correction process performed by the signal amplification unit 31.
- 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.
- the amplification factor ⁇ (dB) increases linearly from ⁇ 0 to ⁇ th (> ⁇ 0 ) as the reception depth z increases.
- the amplification factor ⁇ (dB) takes a constant value ⁇ 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 ⁇ may increase monotonously as the reception depth z increases.
- the transmission / reception unit 3 performs processing such as filtering on the echo signal amplified by the signal amplification unit 31 and then performs A / D conversion to generate a time-domain digital high frequency (RF) signal. Output.
- the transmission / reception unit 3 has a plurality of beams for beam synthesis corresponding to the plurality of elements.
- a channel circuit is included.
- the calculation unit 4 performs amplification correction on the digital RF signal generated by the transmission / reception unit 3 so as to make the amplification factor ⁇ constant regardless of the reception depth, and the digital RF signal subjected to amplification correction at high speed.
- a frequency analysis unit 42 that calculates a frequency spectrum by performing Fourier analysis (FFT: Fast Fourier Transfom) and performs a frequency analysis, and a feature amount calculation unit 43 that calculates a feature amount of the frequency spectrum are included.
- the calculation unit 4 is realized by using a CPU (Central Procuring Unit), various calculation circuits, and the like.
- FIG. 3 is a diagram illustrating the relationship between the reception depth and the amplification factor in the amplification correction process performed by the amplification correction unit 41.
- the amplification rate ⁇ (dB) in the amplification process performed by the amplification correction unit 41 takes the maximum value ⁇ th ⁇ 0 when the reception depth z is zero, and the reception depth z is zero from the threshold z th. Decreases linearly until reaching 0 and is zero when the reception depth z is greater than or equal to the threshold z th .
- the amplification correction unit 41 amplifies and corrects the digital RF signal with the amplification factor determined in this way, thereby canceling the influence of STC correction in the signal amplification unit 31 and outputting a signal with a constant amplification factor ⁇ th. .
- the relationship between the reception depth z and the amplification factor ⁇ performed by the amplification correction unit 41 is different depending on the relationship between the reception depth and the amplification factor in the signal amplification unit 31.
- 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.
- the STC correction cannot accurately eliminate the influence of attenuation accompanying the propagation of the ultrasonic wave. 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.
- the amplification correction unit 41 Correct the gain.
- the frequency analysis unit 42 performs a fast Fourier transform on each sound ray (line data) of a signal obtained by amplifying and correcting a digital RF signal based on an echo signal, and performing a fast Fourier transform on a plurality of amplitude data groups sampled at a predetermined time interval. A frequency spectrum at a location (data position) is calculated.
- FIG. 4 is a diagram schematically showing a data array in one sound ray of the ultrasonic signal.
- a white or black rectangle means one piece of data.
- 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 3.
- FIG. 4 shows a case where the first 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 42 is obtained as a complex number and stored in the storage unit 8.
- the amplitude data group needs to have a power number of 2 data.
- a process for generating a normal amplitude 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 42 is described (see FIG. 9).
- FIG. 5 is a diagram illustrating an example of a frequency spectrum calculated by the frequency analysis unit 42.
- the “frequency spectrum” means “frequency distribution of intensity at a certain reception depth z” obtained by performing fast Fourier transform (FFT operation) on the amplitude data group.
- FFT operation fast Fourier transform
- intensity 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.
- the horizontal axis represents the frequency f.
- the reception depth z is constant. It will be described later linear L 10 shown in FIG. In the present embodiment, the curve and the straight line are composed of a set of discrete points.
- the lower limit frequency f L and the upper limit frequency f H of the frequency band used for the subsequent calculations are the frequency band of the ultrasonic transducer 21 and the frequency band of the pulse signal transmitted by the transmitting / receiving unit 3.
- f L 3 MHz
- f H 10 MHz.
- the frequency band determined by the lower limit frequency f L and the upper limit frequency f H is referred to as “frequency band F”.
- the frequency spectrum shows a tendency that varies depending on the properties (attributes) 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 living tissue” referred to here are, for example, malignant tumor (cancer), benign tumor, endocrine tumor, mucinous tumor, normal tissue, vascular and the like.
- the feature amount calculation unit 43 calculates the feature amounts of a plurality of frequency spectra, respectively.
- the feature amount calculation unit 43 A correction feature amount of each frequency spectrum is calculated by performing attenuation correction that eliminates the influence of ultrasonic attenuation on the amount (hereinafter referred to as a pre-correction feature amount), and a plurality of attenuation rates are calculated using the correction feature amount.
- the optimal attenuation rate is set for the observation target from the candidate values.
- the feature amount calculating unit 43 approximates the frequency spectrum with a straight line to calculate an uncorrected feature amount of the frequency spectrum, and a plurality of attenuation rate candidate values for the uncorrected feature amount calculated by the approximating unit 431.
- Attenuation correction unit 432 that calculates a correction feature quantity by performing attenuation correction based on each of the above, and a plurality of variations based on statistical variation of the correction feature quantity calculated for all frequency spectra by attenuation correction unit 432
- An optimum attenuation rate setting unit 433 for setting an optimum attenuation rate from among the attenuation rate candidate values.
- the approximating unit 431 performs a regression analysis of the frequency spectrum in a predetermined frequency band and approximates the frequency spectrum with a linear expression (regression line), thereby calculating a pre-correction feature quantity characterizing the approximated primary expression.
- the approximating unit 431 obtains a regression line L 10 by performing regression analysis in the frequency band F and approximating the frequency spectrum C 1 with a linear expression.
- (Mid-band fit) c 0 a 0 f M + b 0 is calculated as a feature amount before correction.
- 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 mid-band 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 in the effective frequency band. 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. Note that the feature quantity calculation unit 43 may approximate the frequency spectrum with a second-order or higher polynomial by regression analysis.
- 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) 2 ⁇ zf (1)
- the proportionality constant ⁇ is an amount called an attenuation rate.
- Z is the ultrasonic reception depth
- f is the frequency.
- the attenuation correction unit 432 performs attenuation correction on each of a plurality of attenuation rate candidate values in order to set an attenuation rate (optimum attenuation rate) that best suits the observation target. Details of the plurality of attenuation rate candidate values will be described later with reference to FIGS. 8 and 10.
- the attenuation correction unit 432 performs attenuation correction according to the following equations (2) to (4) on the pre-correction feature values (slope a 0 , intercept b 0 , midband fit c 0 ) extracted by the approximation unit 431. By doing so, the correction feature amounts a, b, and c are calculated.
- the attenuation correction unit 432 performs correction with a larger correction amount as the ultrasonic reception depth z is larger.
- 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. 6 is a diagram illustrating a straight line having the correction feature amounts a, b, and c corrected by the attenuation correction unit 432 as parameters.
- the optimum attenuation rate setting unit 433 sets the attenuation rate candidate value having the smallest statistical variation of the correction feature amount calculated for each attenuation rate candidate value by the attenuation correction unit 432 for all frequency spectra as the optimum attenuation rate. Set. In this embodiment, dispersion is applied as an amount indicating statistical variation. In this case, the optimum attenuation rate setting unit 433 sets the attenuation rate candidate value that minimizes the variance as the optimum attenuation rate. Two of the three correction feature values a, b, and c described above are independent. In addition, the correction feature amount b does not depend on the attenuation rate. Therefore, when setting an optimal attenuation rate for the correction feature amounts a and c, the optimal attenuation rate setting unit 433 may calculate the variance of one of the correction feature amounts a and c.
- the correction feature amount used when the optimum attenuation rate setting unit 433 sets the optimum attenuation rate is the same type as the correction feature amount used when the feature amount image data generation unit 52 generates the feature amount image data. It is preferable. That is, when the feature amount image data generation unit 52 generates feature amount image data using the inclination as the correction feature amount, the distribution of the correction feature amount a is applied, and the feature amount image data generation unit 52 sets the correction feature amount to mid. When generating feature amount image data using band fitting, it is more preferable to apply the variance of the corrected feature amount 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.
- Attenuation can be corrected. For example, when the unit of the attenuation rate ⁇ is dB / cm / MHz, the unit of the coefficient ⁇ 1 is dB / cm.
- the reason why the optimum attenuation rate can be set based on statistical variation will be described.
- 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.
- 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. 7 is a diagram schematically illustrating a distribution example of correction feature amounts that have been attenuation-corrected based on two different attenuation rate candidate values for the same observation target.
- the horizontal axis is the correction feature amount
- the vertical axis is the frequency.
- the two distribution curves N 1 and N 2 shown in FIG. 7 have the same total frequency.
- the distribution curve N 1 has a smaller statistical variation in feature quantity (small variance) and a steep mountain compared to the distribution curve N 2 .
- the optimum attenuation rate setting unit 433 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 candidate value corresponding to the distribution curve N 1 is set. Is set as the optimum attenuation factor.
- the image processing unit 5 converts the amplitude of the echo signal into luminance and displays the B-mode image data generation unit 51 that generates B-mode image data that is an ultrasonic image to be displayed, and the optimum attenuation rate setting unit 433. And a feature amount image data generation unit 52 that generates feature amount image data to be displayed together with the B-mode image in association with the feature amount based on the attenuation rate.
- the B-mode image data generation unit 51 performs signal processing using a known technique such as a bandpass filter, logarithmic conversion, gain processing, contrast processing, and the like on the digital signal, and also according to the image display range on the display unit 7.
- B-mode image data is generated by thinning out data in accordance with the data step width determined in advance.
- 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 feature amount image data generation unit 52 generates 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 other with light and dark. May be.
- visual information related to the feature amount for example, variables in a color space constituting a predetermined color system such as hue, saturation, brightness, luminance value, R (red), G (green), and B (blue) are included. Can be mentioned.
- the storage unit 8 associates a plurality of feature amounts calculated by the attenuation correction unit 432 for each frequency spectrum in accordance with the attenuation rate candidate values, and a variance that gives statistical variation of the plurality of feature amounts with the attenuation rate candidate values. And a feature amount information storage unit 81 for storing the information.
- the storage unit 8 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.
- the storage unit 8 stores various programs including an operation program for executing the operation method of the ultrasonic observation apparatus 1.
- 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, LAN (Local Area Network), WAN (Wide Area Network), etc., and may be wired or wireless.
- the storage unit 8 having the above configuration is realized using a ROM (Read Only Memory) in which various programs are installed in advance, and a RAM (Random Access Memory) that stores calculation parameters and data of each process. .
- ROM Read Only Memory
- RAM Random Access Memory
- the control unit 9 is realized by using a CPU (Central Procuring Unit) having various calculation and control functions, various arithmetic circuits, and the like.
- the control unit 9 performs overall control of the ultrasound observation apparatus 1 by reading information stored and stored in the storage unit 8 from the storage unit 8 and executing various arithmetic processes related to the operation method of the ultrasound observation apparatus 1. To do.
- the control unit 9 and the calculation unit 4 may be configured using a common CPU or the like.
- FIG. 8 is a flowchart showing an outline of processing performed by the ultrasonic observation apparatus 1 having the above configuration.
- the ultrasonic observation apparatus 1 first measures a new observation target with the ultrasonic probe 2 (step S1). Specifically, the ultrasonic transducer 21 of the ultrasonic probe 2 converts an electrical pulse signal into an ultrasonic pulse and sequentially transmits it to the observation target. The ultrasonic pulse is reflected by the observation object, and an ultrasonic echo is generated. The ultrasonic transducer 21 converts ultrasonic echoes into electrical echo signals.
- the frequency band of the pulse signal 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. Thus, it is possible to perform accurate approximation in the frequency spectrum approximation process described later.
- the signal amplifying unit 31 that has received the echo signal from the ultrasonic probe 2 amplifies the echo signal (step S2).
- the signal amplifying unit 31 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.
- the various processing frequency bands of the echo signal in the signal amplifying unit 31 may be a wide band that substantially covers the linear response frequency band of the acoustoelectric conversion to the echo signal of the ultrasonic echo by the ultrasonic transducer 21. This is also because it is possible to perform accurate approximation in the frequency spectrum approximation processing described later.
- the B-mode image data generation unit 51 generates B-mode image data using the echo signal amplified by the signal amplification unit 31 (step S3). Thereafter, the control unit 9 causes the display unit 7 to display a B mode image corresponding to the generated B mode image data (step S4).
- the amplification correction unit 41 performs amplification correction on the signal output from the transmission / reception unit 3 so that the amplification factor is constant regardless of the reception depth (step S5).
- the amplification correction unit 41 performs amplification correction based on, for example, the relationship between the amplification factor and the reception depth shown in FIG.
- FIG. 9 is a flowchart showing an outline of the processing executed by the frequency analysis unit 42 in step S6.
- the frequency analysis process will be described in detail with reference to the flowchart shown in FIG.
- the frequency analysis unit 42 sets a counter k for identifying a sound ray to be analyzed as k 0 (step S21).
- the frequency analysis unit 42 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 (amplitude data group) acquired for FFT calculation.
- FIG. 4 shows a case where the first data position of the sound ray SR k is set as the initial value Z (k) 0 as described above.
- the frequency analysis unit 42 acquires the amplitude data group to which the data position Z (k) belongs (step S23), and applies the window function stored in the storage unit 8 to the acquired amplitude data group (step S24). .
- the window function By applying the window function to the amplitude data group in this way, it is possible to avoid the amplitude data group from becoming discontinuous at the boundary and to prevent occurrence of artifacts.
- the frequency analysis unit 42 determines whether or not the amplitude data group at the data position Z (k) is a normal data group (step S25).
- the amplitude data group needs to have a data number of a power of two.
- the number of data in the normal amplitude data group is 2 n (n is a positive integer).
- step S25 If the result of determination in step S25 is that the amplitude data group at data position Z (k) is normal (step S25: Yes), the frequency analysis unit 42 proceeds to step S27 described later.
- step S25 when the amplitude data group at the data position Z (k) is not normal (step S25: No), the frequency analysis unit 42 inserts zero data as much as the deficient amount into the normal amplitude data group. Generate (step S26). A window function is applied to the amplitude data group determined to be not normal in step S25 (for example, the amplitude data groups F 1 and F K in FIG. 4) before adding zero data. For this reason, discontinuity of data does not occur even if zero data is inserted into the amplitude data group. After step S26, the frequency analysis unit 42 proceeds to step S27 described later.
- step S27 the frequency analysis unit 42 performs an FFT operation using the amplitude data group to obtain a frequency spectrum that is a frequency distribution of the amplitude (step S27).
- FIG frequency spectrum C 1 shown in 5 is an example of the resulting frequency spectrum as a result of step S27.
- the frequency analysis unit 42 changes the data position Z (k) by the step width D (step S28). It is assumed that the step width D is stored in advance in the storage unit 8.
- the step width D is desirably matched with the data step width used when the B-mode image data generation unit 51 generates the B-mode image data. A value larger than the data step width may be set as the width D.
- the frequency analysis unit 42 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 S29).
- the frequency analysis unit 42 increases the counter k by 1 (step S30). This means that the processing is shifted to the next sound ray.
- the frequency analysis unit 42 returns to step S23.
- the frequency analysis unit 42 performs an FFT operation on [(Z (k) max ⁇ Z (k) 0 +1) / D + 1] amplitude data groups for the sound ray SR k .
- [X] represents the maximum integer not exceeding X.
- step S30 the frequency analysis unit 42 determines whether or not the counter k is larger than the maximum value k max (step S31). When the counter k is greater than k max (step S31: Yes), the frequency analysis unit 42 ends the series of FFT processing. On the other hand, when the counter k is equal to or less than k max (step S31: No), the frequency analysis unit 42 returns to step S22.
- the frequency analysis unit 42 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 analysis unit 42 performs frequency analysis processing on all areas where the ultrasonic signal is received.
- the input unit 6 is interested in being divided by a specific depth width and sound ray width. It is also possible to accept the setting input of the region and perform the frequency analysis process only within the set region of interest.
- the feature amount calculation unit 43 calculates pre-correction feature amounts of a plurality of frequency spectra, and gives different attenuation characteristics when the ultrasonic wave propagates through the observation target.
- the correction feature quantity of each frequency spectrum is calculated by performing attenuation correction that eliminates the influence of ultrasonic attenuation on the pre-correction feature quantity of each frequency spectrum, and the correction feature
- the optimum attenuation rate for the observation target is set from a plurality of attenuation rate candidate values using the quantity (steps S7 to S13).
- steps S7 to S13 will be described in detail.
- step S7 the approximating unit 431 calculates a pre-correction feature amount corresponding to each frequency spectrum by performing regression analysis on each of the plurality of frequency spectra calculated by the frequency analyzing unit 42 (step S7). Specifically, the approximating unit 431 approximates each frequency spectrum with a linear expression by regression analysis, and calculates a slope a 0 , an intercept b 0 , and a midband fit c 0 as pre-correction feature values.
- the straight line L 10 shown in FIG. 5 is a regression line approximated by the approximation unit 431 to the frequency spectrum C 1 of the frequency band F by regression analysis.
- the optimum attenuation rate setting unit 433 sets the attenuation rate candidate value ⁇ to be applied when performing attenuation correction, which will be described later, to a predetermined initial value ⁇ 0 (step S8).
- the initial value ⁇ 0 may be stored in advance in the storage unit 8 and the optimum attenuation rate setting unit 433 may refer to the storage unit 8.
- the attenuation correction unit 432 calculates a correction feature amount by performing attenuation correction on the pre-correction feature amount approximated to each frequency spectrum by the approximation unit 431 by using the attenuation rate candidate value as ⁇ , and attenuates the attenuation. It is stored in the feature amount information storage unit 81 together with the rate candidate value ⁇ (step S9).
- a straight line L 1 illustrated in FIG. 6 is an example of a straight line obtained by the attenuation correction unit 432 performing the attenuation correction process.
- f sp is the data sampling frequency
- v s is the sound speed
- D is the data step width
- n is the number of data steps from the first data of the sound ray up to the data position of the amplitude data group to be processed.
- the sampling frequency f sp data and 50 MHz, the sound velocity v s and 1530 m / sec, when a 15 step width D employs a data sequence shown in FIG. 4, a z 0.2295n (mm).
- the optimum attenuation rate setting unit 433 calculates the variance of the representative correction feature amount among a plurality of correction feature amounts obtained by the attenuation correction unit 432 performing attenuation correction on each frequency spectrum, and sets the attenuation rate candidate value. It is stored in the feature amount information storage unit 81 in association with ⁇ (step S10).
- the optimum attenuation rate setting unit 433 calculates the variance of one of the correction feature amounts a and c.
- step S10 when the feature amount image data generation unit 52 generates the feature amount image data using the inclination, the feature amount image data is generated by applying the variance of the corrected feature amount a and using the midband fit. In this case, it is preferable to apply the variance of the correction feature value c.
- the optimum attenuation rate setting unit 433 increases the value of the attenuation rate candidate value ⁇ by ⁇ (step S11), and compares the increased attenuation rate candidate value ⁇ with a predetermined maximum value ⁇ max (Ste S12).
- the ultrasound observation apparatus 1 proceeds to step S13.
- the attenuation rate candidate value ⁇ is equal to or less than the maximum value ⁇ max as a result of the comparison in step S12 (step S12: No)
- the ultrasound observation apparatus 1 returns to step S9.
- the optimum attenuation rate setting unit 433 refers to the variance for each attenuation rate candidate value stored in the feature amount information storage unit 81, and sets the attenuation rate candidate value having the smallest variance as the optimum attenuation rate ( Step S13).
- FIG. 10 is a diagram illustrating an outline of processing performed by the optimum attenuation rate setting unit 433.
- the attenuation rate candidate value ⁇ is 0.2 (dB / cm / MHz)
- the feature amount image data generation unit 52 provides visual information associated with the corrected feature amount based on the optimum attenuation rate set in step S13 for each pixel in the B mode image data generated by the B mode image data generation unit 51.
- the feature amount image data is generated by superimposing the hue) and adding the information of the optimum attenuation rate (step S14).
- FIG. 11 is a diagram schematically illustrating a display example of the feature amount image on the display unit 7.
- a feature amount image 101 shown in FIG. 1 includes a superimposed image display unit 102 that displays an image in which visual information related to a feature amount is superimposed on a B-mode image, and observation target identification information and an attenuation rate set as an optimal attenuation rate.
- an information display unit 103 that displays information on candidate values.
- the information display unit 103 may further display feature amount information, approximate expression information, image information such as gain and contrast, and the like.
- a B-mode image corresponding to the feature amount image may be displayed side by side with the feature amount image. Moreover, it is good also as a structure which the input part 6 can receive the instruction
- step S4 In the series of processes described above (steps S1 to S15), the process of step S4 and the processes of steps S5 to S13 may be performed in parallel.
- an optimum attenuation rate is set for the observation target from among a plurality of attenuation rate candidate values that give different attenuation characteristics when ultrasonic waves propagate through the observation target. Since the feature amount of each of the plurality of frequency spectra is calculated by performing attenuation correction using the optimal attenuation rate, the attenuation characteristic of the ultrasonic wave suitable for the observation target can be obtained by simple calculation. Observation using attenuation characteristics can be performed.
- an optimum attenuation rate can be set even when the attenuation rate suitable for the observation target is unknown.
- FIG. 12 is a diagram illustrating an outline of processing performed by the optimum attenuation rate setting unit of the ultrasonic observation apparatus according to the first modification of the present embodiment.
- the value of the dispersion S ( ⁇ ) in (/ MHz) is the same as that in FIG.
- the approximation unit 431 performs a regression analysis to interpolate the value of the variance S ( ⁇ ) in the attenuation rate candidate value ⁇ . R is calculated.
- the optimum attenuation rate setting unit 433 calculates a minimum value S ( ⁇ ) ′ min at 0 (dB / cm / MHz) ⁇ ⁇ 1.0 (dB / cm / MHz) for the curve R,
- the value ⁇ ′ of the attenuation rate candidate value at that time is set as the optimum attenuation rate.
- the optimum attenuation rate ⁇ ′ takes a value between 0 (dB / cm / MHz) and 0.2 (dB / cm / MHz).
- the optimum attenuation rate setting unit 433 sets an optimum attenuation rate with a dynamic range wider than the dynamic range for displaying as a feature amount image.
- the feature amount calculation unit 43 performs an attenuation calculation with a dynamic range (for example, 100 dB) larger than the dynamic range (70 dB).
- a dynamic range for example, 100 dB
- the feature amount calculation unit 43 uses a 32-bit floating point method to calculate a feature amount and set an optimum attenuation rate. Including attenuation calculation processing.
- the calculation accuracy can be improved as compared with the attenuation calculation process using the fixed-point method.
- An optimal attenuation rate can be calculated with high accuracy by generating a quadratic curve based on variance from the calculation of the feature amount before correction.
- the optimum attenuation rate setting unit 433 calculates an optimum attenuation rate equivalent value corresponding to the optimum attenuation rate in all frames of the ultrasonic image, and a predetermined number of optimum values including the optimum attenuation rate equivalent value in the latest frame.
- the average value, median value, or mode value of the attenuation rate equivalent values may be set as the optimal attenuation rate. In this case, compared with the case where the optimum attenuation rate is set in each frame, the change in the optimum attenuation rate is reduced, and the value can be stabilized.
- the optimum attenuation rate setting unit 433 may set an optimum 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.
- the target area for calculating the statistical variation may be set for each sound ray, or the reception depth may be an area having a predetermined value or more. It is good also as a structure which the input part 6 can receive the setting of these area
- the optimum attenuation rate setting unit 433 may individually set optimum attenuation rates within the set region of interest and outside the region of interest.
- the input unit 6 may be configured to accept an input of setting change of the initial value ⁇ 0 of the attenuation rate candidate value.
- an amount giving statistical variation for example, any one of standard deviation, a difference between the maximum value and minimum value of the feature amount in the population, and a half-value width of the distribution of the feature amount can be applied.
- a difference between the maximum value and minimum value of the feature amount in the population, and a half-value width of the distribution of the feature amount can be applied.
- distribution is applied as an amount which gives statistical dispersion
- the optimum attenuation rate setting unit 433 may calculate statistical variations of a plurality of types of correction feature amounts, and may set an attenuation rate candidate value when the statistical variation is minimum as an optimal attenuation rate. Is possible.
- the approximation unit 431 calculates a correction feature amount by performing regression analysis on each frequency spectrum after the attenuation correction. You may do it.
- the ultrasonic observation apparatus, the operation method of the ultrasonic observation apparatus, and the operation program of the ultrasonic observation apparatus according to the present invention can determine the attenuation characteristic of the ultrasonic wave suitable for the observation object by simple calculation. At the same time, it is useful for observation using the attenuation characteristics.
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Abstract
Description
A(f,z)=2αzf ・・・(1)
ここで、比例定数αは減衰率と呼ばれる量である。また、zは超音波の受信深度であり、fは周波数である。減衰率αの具体的な値は、観測対象が生体である場合、生体の部位に応じて定まる。減衰率αの単位は、例えばdB/cm/MHzである。本実施の形態において、減衰補正部432は、観測対象に最も適合する減衰率(最適な減衰率)を設定するために、複数の減衰率候補値に対してそれぞれ減衰補正を行う。複数の減衰率候補値の詳細については、図8および図10を参照して後述する。
a=a0+2αz ・・・(2)
b=b0 ・・・(3)
c=c0+A(fM,z)=c0+2αzfM(=afM+b) ・・・(4)
式(2)、(4)からも明らかなように、減衰補正部432は、超音波の受信深度zが大きいほど、補正量が大きい補正を行う。また、式(3)によれば、切片に関する補正は恒等変換である。これは、切片が周波数0(Hz)に対応する周波数成分であって減衰の影響を受けないためである。
I=af+b=(a0+2αz)f+b0 ・・・(5)
で表される。この式(5)からも明らかなように、直線L1は、減衰補正前の直線L10と比較して、傾きが大きく(a>a0)、かつ切片が同じ(b=b0)である。
A(f,z)=2αzf+2α1z ・・・(6)
式(6)の右辺第2項のα1は、超音波の受信深度zに比例して信号強度が変化する大きさを表す係数であり、観測対象の組織が不均一であることや、ビーム合成時のチャンネル数の変更などに起因して発生する信号強度の変化を表す係数である。式(6)の右辺第2項が存在するため、補正特徴量cを用いて特徴量画像を生成する場合は、補正特徴量cの分散を適用した方が正確に減衰を補正することができる(式(4)を参照)。一方、周波数fに比例する係数である補正特徴量aを用いて特徴量画像を生成する場合は、補正特徴量aの分散を適用した方が、右辺第2項の影響を排除して正確に減衰を補正することができる。例えば、減衰率αの単位がdB/cm/MHzである場合、係数α1の単位はdB/cmである。
図12は、本実施の形態の変形例1に係る超音波観測装置の最適減衰率設定部が行う処理の概要を示す図である。図12では、α0=0(dB/cm/MHz)、αmax=1.0(dB/cm/MHz)、Δα=0.2(dB/cm/MHz)とした場合の減衰率候補値αと分散S(α)との関係の例を示しており、減衰率候補値α=0、0.2、0.4、0.6、0.8、1.0(いずれもdB/cm/MHz)における分散S(α)の値は、図10とそれぞれ同じである。本変形例1では、最適減衰率設定部433が最適な減衰率を設定する前に、近似部431が回帰分析を行うことによって減衰率候補値αにおける分散S(α)の値を補間する曲線Rを算出する。その後、最適減衰率設定部433は、この曲線Rに対し、0(dB/cm/MHz)≦α≦1.0(dB/cm/MHz)における最小値S(α)’minを算出し、そのときの減衰率候補値の値α’を最適な減衰率として設定する。図12に示す場合、最適な減衰率α’は、0(dB/cm/MHz)と0.2(dB/cm/MHz)の間の値となる。
次に、本発明の実施の形態の変形例2について説明する。本変形例では、最適減衰率設定部433が、特徴量画像として表示する際のダイナミックレンジよりも広いダイナミックレンジで最適な減衰率を設定する。
2 超音波探触子
3 送受信部
4 演算部
5 画像処理部
6 入力部
7 表示部
8 記憶部
9 制御部
21 超音波振動子
31 信号増幅部
41 増幅補正部
42 周波数解析部
43 特徴量算出部
51 Bモード画像データ生成部
52 特徴量画像データ生成部
81 特徴量情報記憶部
101 特徴量画像
102 重畳画像表示部
103 情報表示部
431 近似部
432 減衰補正部
433 最適減衰率設定部
C1 周波数スペクトル
Claims (14)
- 観測対象に対して送信した超音波が前記観測対象によって反射された超音波エコーを電気信号に変換したエコー信号に基づいて生成される信号の周波数を解析することによって複数の周波数スペクトルを算出する周波数解析部と、
前記複数の周波数スペクトルの特徴量をそれぞれ算出し、前記超音波が前記観測対象を伝播する際の互いに異なる減衰特性を与える複数の減衰率候補値の各々において、各周波数スペクトルの特徴量に対して前記超音波の減衰の影響を排除する減衰補正を行うことによって前記各周波数スペクトルの補正特徴量を算出し、該補正特徴量を用いて前記複数の減衰率候補値の中から前記観測対象に最適な減衰率を設定する特徴量算出部と、
前記最適な減衰率に基づく前記補正特徴量を視覚情報と関連づけて前記エコー信号から生成された超音波画像とともに表示する特徴量画像データを生成する特徴量画像データ生成部と、
を備えたことを特徴とする超音波観測装置。 - 前記特徴量算出部は、
前記各周波数スペクトルをn次式(nは正の整数)で近似する処理を行うことによって前記特徴量を算出し、
前記減衰率候補値ごとに前記補正特徴量の統計的なばらつきを算出し、該統計的なばらつきが最小である減衰率候補値を前記最適な減衰率として設定することを特徴とする請求項1に記載の超音波観測装置。 - 前記特徴量算出部は、
前記周波数スペクトルにおける所定の周波数帯域を一次式で近似し、前記一次式の切片および傾き、ならびに前記周波数帯域の中間周波数における前記一次式の値であるミッドバンドフィットのうち、前記傾きおよび前記ミッドバンドフィットのいずれか一方を含む一つまたは複数を前記特徴量として算出し、
前記傾きおよび前記ミッドバンドフィットのいずれか一方に基づいて前記最適な減衰率を設定することを特徴とする請求項2に記載の超音波観測装置。 - 前記特徴量算出部は、
前記傾きを前記特徴量として算出する場合は前記傾きに基づいて前記最適な減衰率を設定し、前記ミッドバンドフィットを前記特徴量として算出する場合は前記ミッドバンドフィットに基づいて前記最適な減衰率を設定することを特徴とする請求項3に記載の超音波観測装置。 - 前記特徴量算出部は、
前記統計的なばらつきを前記減衰率候補値の関数として求め、
前記関数において前記統計的なばらつきが最小となる減衰率候補値を前記最適な減衰率として設定することを特徴とする請求項2に記載の超音波観測装置。 - 前記特徴量算出部は、
前記超音波画像の全てのフレームで前記最適な減衰率を設定することを特徴とする請求項1に記載の超音波観測装置。 - 前記特徴量算出部は、
前記超音波画像の1より大きい所定数のフレームごとに前記最適な減衰率を設定し、
前記最適な減衰率を設定しないフレームでは、該フレーム以前で最後に設定された前記最適な減衰率を用いて前記各周波数スペクトルの特徴量を算出することを特徴とする請求項1に記載の超音波観測装置。 - 前記特徴量算出部は、
前記超音波画像の全てのフレームで前記最適な減衰率に相当する最適減衰率相当値を算出し、1より大きい所定数のフレームで算出した前記最適減衰率相当値をもとに前記最適な減衰率を設定することを特徴とする請求項1に記載の超音波観測装置。 - 前記特徴量画像データは、前記最適な減衰率に関する情報を含むことを特徴とする請求項1に記載の超音波観測装置。
- 前記特徴量画像データに対応する特徴量画像を表示する表示部をさらに備えたことを特徴とする請求項1に記載の超音波観測装置。
- 前記周波数解析部が前記周波数スペクトルを算出する対象領域の設定入力を受け付ける入力部をさらに備え、
前記周波数解析部は、前記対象領域で反射された前記超音波エコーをもとに前記周波数スペクトルを算出することを特徴とする請求項1に記載の超音波観測装置。 - 前記特徴量算出部は、前記特徴量画像データ生成部が用いるデータのダイナミックレンジよりも広いダイナミックレンジのデータを用いて前記最適な減衰率の設定を行うことを特徴とする請求項1に記載の超音波観測装置。
- 周波数解析部が、観測対象に対して送信した超音波が前記観測対象によって反射された超音波エコーを電気信号に変換したエコー信号に基づいて生成される信号の周波数を解析することによって複数の周波数スペクトルを算出する周波数解析ステップと、
特徴量算出部が、前記複数の周波数スペクトルの特徴量をそれぞれ算出し、前記超音波が前記観測対象を伝播する際の互いに異なる減衰特性を与える複数の減衰率候補値の各々において、各周波数スペクトルの特徴量に対して前記超音波の減衰の影響を排除する減衰補正を行うことによって前記各周波数スペクトルの補正特徴量を算出し、該補正特徴量を用いて前記複数の減衰率候補値の中から前記観測対象に最適な減衰率を設定する特徴量算出ステップと、
特徴量画像データ生成部が、前記最適な減衰率に基づく前記補正特徴量を視覚情報と関連づけて前記エコー信号から生成された超音波画像とともに表示する特徴量画像データを生成する特徴量画像データ生成ステップと、
を有することを特徴とする超音波観測装置の作動方法。 - 周波数解析部が、観測対象に対して送信した超音波が前記観測対象によって反射された超音波エコーを電気信号に変換したエコー信号に基づいて生成される信号の周波数を解析することによって複数の周波数スペクトルを算出する周波数解析ステップと、
特徴量算出部が、前記複数の周波数スペクトルの特徴量をそれぞれ算出し、前記超音波が前記観測対象を伝播する際の互いに異なる減衰特性を与える複数の減衰率候補値の各々において、各周波数スペクトルの特徴量に対して前記超音波の減衰の影響を排除する減衰補正を行うことによって前記各周波数スペクトルの補正特徴量を算出し、該補正特徴量を用いて前記複数の減衰率候補値の中から前記観測対象に最適な減衰率を設定する特徴量算出ステップと、
特徴量画像データ生成部が、前記最適な減衰率に基づく前記補正特徴量を視覚情報と関連づけて前記エコー信号から生成された超音波画像とともに表示する特徴量画像データを生成する特徴量画像データ生成ステップと、
を超音波観測装置に実行させることを特徴とする超音波観測装置の作動プログラム。
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US11559287B2 (en) * | 2018-10-11 | 2023-01-24 | Shenzhen Mindray Bio-Medical Electronics Co., Ltd. | Transducer spectral normalization |
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