JP4191812B2 - Ultrasonic diagnostic equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic diagnostic apparatus that displays a spectrum of a frequency shifted due to the Doppler effect as a time waveform (periodogram).
[0002]
[Prior art]
The frequency spectrum can be evaluated by the frequency resolution and the time resolution that define the fineness of display of the frequency spectrum, that is, the fineness of the periodogram display. These frequency resolution and time resolution are determined by parameters such as the rate frequency fPRF, the number of FFT data N, and the scroll speed S. Conventionally, for example, when the rate frequency fPRF is changed, the time resolution changes. There was a problem that it was very difficult to see as a periodogram.
[0003]
To solve this problem, when a certain parameter is changed or changed, the ratio of the frequency resolution ΔY to the time resolution ΔX (the aspect ratio; ΔY / ΔX) is adjusted by adjusting the number of FFT data N and the window weight Ww. The technology has been developed to stabilize the periodogram display while maintaining a constant value, and is now mainstream.
[0004]
However, in this aspect ratio stabilization technique, for example, if the rate frequency fPRF is lowered in order to improve the low flow velocity detection capability and accurately observe a relatively slow blood flow such as the abdomen, the time resolution increases. Accordingly, since it functions to increase the frequency resolution by changing the number of FFT data N and the window weight Ww, the minimum unit constituting the periodogram (the number of pixels in the vertical direction is the frequency resolution, the number of pixels in the horizontal direction is (Defined by temporal resolution) becomes very large and rough, and there is a problem that it is difficult to capture subtle changes in speed, fine temporal responses, and the like.
[0005]
[Problems to be solved by the invention]
An object of the present invention is to provide an ultrasonic diagnostic apparatus capable of adjusting a frequency resolution and a time resolution in accordance with an observer's request as much as possible.
[0006]
[Means for Solving the Problems]
According to a first aspect of the present invention, an ultrasonic wave is transmitted to a subject, the obtained echo signal is frequency-analyzed to generate a frequency spectrum, the frequency spectrum is a time waveform, the vertical axis is the frequency axis, the horizontal axis In the ultrasonic diagnostic apparatus displaying the axis as a time axis, the ratio resolution mode for changing the frequency resolution of the frequency spectrum and the time resolution while keeping the ratio of the two constant, and the frequency resolution with the time resolution fixed. The time resolution priority mode to be changed and the frequency resolution priority mode to change the time resolution while the frequency resolution is fixed can be selected. The time resolution ΔX and the frequency resolution ΔY are respectively ΔX = (D X × N × K × M) / (f PRF × S), ΔY = D Y / (N × W w), D X; horizontal axis of the display range of the periodogram ( The number of data of the frequency analysis K;; between axis) the number of pixels D Y; vertical axis of the display range of the periodogram (frequency axis) direction of the number N of pixels alternately stages M; thinning rate f PRF; rate frequency S; scroll speed W w ; defined by window weight, and in the time resolution priority mode , at least among the number D Y of pixels in the frequency axis direction of the periodogram display range related to frequency resolution, the number N of frequency analysis data, and the window weight W w Even if one changes and the frequency resolution fluctuates, the number of pixels D X in the time axis direction, the number of alternating stages K, the thinning rate M, the rate frequency f PRF , and the scroll speed S of the periodogram display range other than the number of data N At least one of them is changed, and the temporal resolution is maintained at a predetermined value.
According to a second aspect of the present invention, ultrasonic waves are transmitted to a subject, the obtained echo signal is subjected to frequency analysis, a frequency spectrum is generated, the frequency spectrum is a time waveform, the vertical axis is the frequency axis, the horizontal axis In the ultrasonic diagnostic apparatus displaying the axis as a time axis, the ratio resolution mode for changing the frequency resolution of the frequency spectrum and the time resolution while keeping the ratio of the two constant, and the frequency resolution with the time resolution fixed. The time resolution priority mode to be changed and the frequency resolution priority mode to change the time resolution while the frequency resolution is fixed can be selected. The time resolution ΔX and the frequency resolution ΔY are respectively ΔX = (D X × N × K × M) / (f PRF × S), ΔY = D Y / (N × W w), D X; horizontal axis of the display range of the periodogram ( The number of data of the frequency analysis K;; between axis) the number of pixels D Y; vertical axis of the display range of the periodogram (frequency axis) direction of the number N of pixels alternately stages M; thinning rate f PRF; rate frequency S; scroll speed W w ; defined by window weight. In the frequency resolution priority mode, the number of pixels D X in the time axis direction , the number K of alternating steps, the thinning rate M, the rate frequency f PRF , and the scroll speed in the periodogram display range related to the time resolution Even if at least one of S changes and the time resolution changes, the number of pixels D Y , the number of data N, and the window weight W w in the frequency axis direction of the periodogram display range are not changed, and both resolutions are related. If the data number N is changed, child maintain frequency resolution by changing at least one of the frequency number of pixels axis D Y and Madoomomi W w of the display range of the periodogram at a constant value The features.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an ultrasonic diagnostic apparatus according to the present invention will be described with reference to the drawings according to preferred embodiments. FIG. 1 shows the configuration of an ultrasonic diagnostic apparatus according to this embodiment. A plurality of piezoelectric elements for mutual conversion between an electrical signal and an acoustic signal are arranged at the distal end portion of the ultrasonic probe 1. A transmission / reception circuit (T & R) 2 is connected to the ultrasonic probe 1. The transmission / reception circuit 2 includes a transmission part, a reception part, and a quadrature detection part. In the transmission part, first, a clock from a clock generator is divided to generate a rate pulse of about 4 kHz to 50 kHz. The frequency of this rate pulse is called a rate frequency or a pulse repetition frequency. Here, it is assumed to be referred to as a rate frequency and represented by the symbol “fPRF”. After the rate pulse is appropriately delayed, a voltage pulse is applied from the pulser to the piezoelectric element of the probe 1 as a trigger. By this application, the piezoelectric element of the probe 2 mechanically vibrates and generates an ultrasonic pulse.
[0008]
This ultrasonic wave propagates inside the subject, is reflected by a discontinuous surface of acoustic impedance in the middle thereof, returns to the probe 1, and mechanically vibrates the piezoelectric element. As a result, a weak electric signal is generated from the piezoelectric element. This electric signal is taken into the receiving part, amplified by a preamplifier, converted into a digital signal by an analog-digital converter, and added through a process corresponding to delay by a so-called digital beamformer. The output signal from the reception part includes a frequency component shifted due to the Doppler effect of a moving body such as a blood cell, and this is detected by the quadrature detection part.
[0009]
The output signal of the transmission / reception circuit 2, that is, the Doppler quadrature detection signal, is mainly reflected by a high-frequency component that has undergone frequency shift due to reflection by a fast moving body such as blood cells, and mainly by a slow moving body such as a heart wall. The low-frequency component subjected to frequency shift due to the above-mentioned, generally the clutter component, is contained, so the high-frequency clutter filter 3 attenuates the low-frequency component and extracts the high-frequency component. The high frequency component extracted in 3 is subjected to audio processing by the audio circuit 6 so that the observer can hear it as a Doppler sound from the speaker 7.
[0010]
The high-frequency component extracted by the clutter filter 3 is frequency-analyzed by a fast Fourier transform processor (FFT) 4 and the frequency spectrum is displayed on the display device 5 as a time waveform, that is, a periodogram.
[0011]
Incidentally, the control device (CPU) 8 can selectively adjust the frequency resolution and time resolution in three types of modes. These three modes are a constant aspect ratio mode in which the resolution can be adjusted while maintaining a constant ratio of frequency resolution to time resolution as shown in FIG. 2A, and FIG. The time resolution priority mode in which the frequency resolution can be adjusted while keeping the time resolution as shown in FIG. 2 and the frequency in which the time resolution can be adjusted while keeping the frequency resolution as shown in FIG. There is a resolution priority mode.
[0012]
Each of these modes will be described in turn. First, a method for calculating the time resolution ΔX and the frequency resolution ΔY will be described. The time resolution ΔX and the frequency resolution ΔY are calculated by the following equations (1) and (2).
[0013]
ΔX = (DX × N × K × M) / (fPRF × S) (1)
ΔY = DY / (N × Ww) (2)
DX: Number of pixels in the horizontal axis (time axis) direction of the periodogram display range DY: Number of pixels in the vertical axis (frequency axis) direction of the periodogram display range N: FFT data number K: Alternating stage number M; Decimation rate fPRF; rate frequency S; scroll speed Ww; window weight The window weight Ww is as follows. As is well known, the number of FFT data N is limited to a power of 2, but in many cases, the number of data calculated to achieve the target frequency resolution is not a power of 2. Therefore, for the number N of FFT data, the power of 2 that is the closest to the number of calculation data is selected, and the mismatch between the selected number of FFT data N and the number of calculation data is indicated in the FFT window. The window weight Ww is a parameter that determines the size of the window (window width). For example, when the calculation data number is 320, 512 is selected as the FFT data number N. In this case, the window weight Ww is set to 5/8. In FIG. 3, the aspect ratio is constant. The concept of the control method for realizing the mode is shown, and given the rate frequency fPRF, the scroll speed S, the alternating stage number K, the thinning-out number M, and DY, to maintain the desired aspect ratio Pr of the observer The number N of FFT data and the window weight Ww are calculated. That is, for example, when the rate frequency fPRF changes (when the time resolution changes), the frequency resolution is changed by adjusting the FFT data number AA accordingly, and the aspect ratio is made constant. This data number AA is obtained by the following equation (3).
[0014]
AA = (fPRF * DY * S) / (Pr * K * M * DX) (3)
The FFT data number AA thus calculated is not necessarily a power of 2 that can be handled by the FFT, as described above. Therefore, as described above, the power of 2 closest to the calculated data number AA is selected, and the selected FFT data number N and the window weight Ww for filling the mismatch between the two are selected. In practice, this processing is often realized by a ROM table.
[0015]
With such processing, even if parameters such as the rate frequency change, the ratio of the frequency resolution ΔY to the time resolution ΔX can be kept constant.
Next, in the time resolution priority mode, at least one of parameters related to frequency resolution, that is, the number of pixels DY in the vertical axis (frequency axis) direction of the periodogram display range, the number of FFT data N, and the window weight Ww is changed. Thus, even if the frequency resolution fluctuates, processing is performed to fix the time resolution to a constant value desired by the observer, that is, when the number of data N related to both resolutions changes, the above equation (1) , The number of pixels DX in the horizontal axis (time axis) direction of the display range of the periodogram, the number of alternating stages K, the thinning rate M, the rate frequency fPRF, the scroll speed S, for example, The time resolution is maintained at a constant value by changing the scroll speed S.
[0016]
In the frequency resolution priority mode, parameters related to time resolution, that is, the number of pixels DX in the horizontal axis (time axis) direction of the periodogram display range other than the number of data N related to both resolutions, the number of alternating stages K, the thinning rate M, Even if at least one of the rate frequency fPRF and the scroll speed S changes and the time resolution changes, the vertical axis (frequency) of the periodogram display range is fixed so that the frequency resolution is fixed to a constant value desired by the observer. If the number of pixels DY, the number of data N, and the window weight Ww in the (axis) direction remain unchanged and the number of data N related to both resolutions changes, the frequency axis direction of the periodogram display range changes. The frequency resolution is maintained at a constant value by changing at least one of the number of pixels DY and the window weight Ww.
[0017]
FIG. 4 shows how the actually displayed periodogram changes depending on the mode with respect to the true periodogram.
Since these three types of modes are prepared, for example, when the constant aspect ratio mode is initially used and the time resolution is too large or too small to be observed, the time resolution priority mode is selected and the frequency resolution is selected. When it is difficult to observe due to excessive or reduced magnification, it is possible to select the frequency resolution priority mode, which makes it difficult to observe subtle changes in velocity, or conversely, the unit region is too fine to observe temporal response. It can solve problems that have become difficult.
It goes without saying that the present invention is not limited to the above-described embodiments and can be implemented with various modifications.
[0018]
【The invention's effect】
According to the present invention, when the three types of modes are used properly, for example, in the constant aspect ratio mode, it is difficult to see the periodogram, for example, when it is difficult to observe a subtle speed change, the mode for fixing the time resolution and the frequency resolution Can be selected to make it easy to observe the periodogram.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an ultrasonic diagnostic apparatus according to a preferred embodiment of the present invention.
FIG. 2 is an explanatory diagram regarding three types of display modes according to the present embodiment.
FIG. 3 is a conceptual diagram of local processing in a constant aspect ratio mode.
4 is a diagram showing how a periodogram looks in each mode of FIG. 2 in comparison with a true periodogram. FIG.
[Explanation of symbols]
1 ... ultrasonic probe,
2. Transmission / reception circuit (T & R),
3 ... Clutter filter,
4 ... Fast Fourier transform processor (FFT),
5 ... display device,
6 ... Audio circuit,
7 ... Speaker,
8 ... Control device,
9 ... Console.

Claims (2)

Ultrasound is transmitted to the subject, the obtained echo signal is frequency-analyzed, and a frequency spectrum is generated. This frequency spectrum is displayed as a time waveform with the vertical axis representing the frequency axis and the horizontal axis representing the time axis. In the ultrasonic diagnostic equipment,
Fixed frequency ratio mode that changes the frequency resolution and time resolution of the frequency spectrum while keeping the ratio between them constant, fixed time resolution mode that changes the frequency resolution while fixing the time resolution, and fixed frequency resolution It is configured to be able to select the frequency resolution priority mode that changes the time resolution as it is,
The time resolution ΔX and the frequency resolution ΔY are respectively
ΔX = (DX × N × K × M) / (fPRF × S)
ΔY = DY / (N × Ww)
DX: Number of pixels in the horizontal axis (time axis) direction of the periodogram display range DY; Number of pixels N in the vertical axis (frequency axis) direction of the periodogram display range; Number of data K in frequency analysis; Rate fPRF; rate frequency S; scroll speed Ww; defined by window weight,
In the time resolution priority mode, at least one of the number of pixels DY in the frequency axis direction, the number of frequency analysis data N, and the window weight Ww in the periodogram display range related to the frequency resolution changes, and the frequency resolution changes. The time resolution is set to a predetermined value by changing at least one of the number of pixels DX in the time axis direction of the periodogram display range other than the number of data N, the number of alternating steps K, the thinning rate M, the rate frequency fPRF, and the scroll speed S. An ultrasonic diagnostic apparatus characterized in that the apparatus is maintained. Ultrasound is transmitted to the subject, the obtained echo signal is frequency-analyzed, and a frequency spectrum is generated. This frequency spectrum is displayed as a time waveform with the vertical axis representing the frequency axis and the horizontal axis representing the time axis. In the ultrasonic diagnostic equipment,
Fixed frequency ratio mode that changes the frequency resolution and time resolution of the frequency spectrum while keeping the ratio between them constant, fixed time resolution mode that changes the frequency resolution while fixing the time resolution, and fixed frequency resolution It is configured to be able to select the frequency resolution priority mode that changes the time resolution as it is,
The time resolution ΔX and the frequency resolution ΔY are respectively
ΔX = (DX × N × K × M) / (fPRF × S)
ΔY = DY / (N × Ww)
DX: Number of pixels in the horizontal axis (time axis) direction of the periodogram display range DY; Number of pixels N in the vertical axis (frequency axis) direction of the periodogram display range; Number of data K in frequency analysis; Rate fPRF; rate frequency S; scroll speed Ww; defined by window weight,
In the frequency resolution priority mode, at least one of the number of pixels DX in the time axis direction, the number of alternating stages K, the thinning rate M, the rate frequency fPRF, and the scroll speed S of the periodogram display range related to the time resolution is changed. If the number of pixels DY, the number of data N, and the window weight Ww in the frequency axis direction of the periodogram display range do not change, and the number of data N related to both resolutions changes, An ultrasonic diagnostic apparatus characterized in that the frequency resolution is maintained at a constant value by changing at least one of the number of pixels DY in the frequency axis direction of the display range and the window weight Ww.

Images