JP4060412B2 - Ultrasonic diagnostic equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic diagnostic apparatus that scans a cross section of a subject with ultrasonic waves and acquires various in-vivo information based on the intensity of an obtained echo signal.
[0002]
[Prior art]
There are various types of medical applications of ultrasound, but the mainstream is an ultrasound diagnostic apparatus that obtains a tomographic image of a soft tissue of a living body using an ultrasonic pulse reflection method. This ultrasonic diagnostic apparatus is a non-invasive examination method and displays a tomographic image of a tissue. Compared to other diagnostic apparatuses such as an X-ray diagnostic apparatus, an X-ray CT apparatus, an MRI, and a nuclear medicine diagnostic apparatus, the ultrasonic diagnostic apparatus is real-time. It has unique features such as display capability, small size, low cost, high safety without exposure to X-rays, and blood flow imaging by ultrasonic Doppler method.
[0003]
This ultrasonic Doppler method includes a continuous wave Doppler method and a pulse Doppler method. Although the continuous wave Doppler method can be measured even at high speed, the pulse Doppler method is the current mainstream because there is no distance resolution and blood flow cannot be identified. It has become. In this pulse Doppler method, a two-dimensional distribution (blood flow image) such as an average velocity can be obtained in real time by using MTI together, and it is very useful, and many of them are standard equipment recently.
[0004]
However, as is well known, this pulse Doppler method has an angle dependency that the measurement speed depends on the angle between the ultrasonic beam and the blood flow, and the absolute velocity of the blood flow cannot be measured. Furthermore, since the Doppler effect is used, there is a problem that the velocity cannot be measured with respect to the blood flow orthogonal to the ultrasonic beam.
[0005]
[Problems to be solved by the invention]
An object of the present invention is to provide an ultrasonic diagnostic apparatus capable of measuring the absolute velocity of blood flow with relatively high accuracy.
[0006]
[Means for Solving the Problems]
The present invention performs a first ultrasonic irradiation that substantially destroys the contrast agent with respect to the fluid in the subject into which the contrast agent has been injected, and a second ultrasonic irradiation after the first transmission and reception, Based on the transmission / reception means for receiving the echo signal, the intensity of the echo signal obtained by the second ultrasonic irradiation, and the time interval between the first ultrasonic irradiation and the second ultrasonic irradiation, the fluid And an estimation means for estimating the speed.
(Function)
The reflection intensity in the fluid itself is low on the order of 10 ^-2 for tissue. Therefore, it is considered that the intensity of the echo signal from the fluid reflects the amount of the contrast agent present in the minute region relatively accurately. Most of such contrast agents, that is, microbubbles, are destroyed by the first transmission / reception. Therefore, if the second transmission / reception is performed after a certain period from the first transmission / reception, the intensity of the echo signal obtained by the second transmission / reception is from the first transmission / reception to the current second transmission / reception. This reflects the inflow amount of the contrast agent that has flowed into the micro area on the fluid flow. This inflow amount mainly depends on the speed of blood flow, the cross-sectional area of the minute region, and the time difference from the previous irradiation to the current irradiation. Of these, the cross-sectional area of the micro area and the time difference from the previous irradiation to the current irradiation are known, so the fluid velocity is estimated from the inflow, that is, the intensity of the current echo signal that reflects it. It can be done.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described by way of preferred embodiments with reference to the drawings. FIG. 1 shows the configuration of an ultrasonic diagnostic apparatus according to this embodiment. The ultrasonic probe 1 is formed by arranging a plurality of micro piezoelectric elements that perform reversible conversion between an electric signal and an ultrasonic wave at a tip portion thereof. The form of the probe 1 is arbitrarily selected from sector correspondence, linear correspondence, convex correspondence, and the like.
[0008]
The rate pulse generator 2 periodically generates rate pulses for determining an ultrasonic transmission rate (number of transmissions per second). The transmission / reception circuit 3 includes a transmission system and a reception system, and the transmission system includes a transmission delay circuit that gives an appropriate delay time to the rate pulse from the rate pulse generator 2, and a probe according to the delayed rate pulse. And a pulsar for supplying a high-frequency (f0) voltage pulse to one piezoelectric element. The piezoelectric element of the probe 1 repeats distortion recovery (vibrates) by this voltage pulse. Thereby, an ultrasonic wave is generated with f0 as the center frequency and transmitted to the subject.
[0009]
This ultrasonic wave propagates in the living body, is reflected one after another at a discontinuous surface of acoustic impedance in the middle, and returns one after another to the probe 1 to vibrate the piezoelectric element. As a result, a voltage signal is generated with an amplitude corresponding to the intensity of the echo. In the receiving system, this voltage signal is first amplified by a preamplifier, and an appropriate delay time is given by a reception delay circuit and then added to obtain an echo signal having directivity. The echo signal is detected and logarithmically amplified, and then supplied to the digital scan converter (DSC) 4 as a digital signal.
[0010]
In the digital scan converter 4, the echo signal is scan-converted into an interlaced television system of 30 Hz / sec and output as a one-dimensional data string representing a tissue cross-sectional image (B-mode image). In accordance with this data string, the monitor 8 displays the B-mode image in shades.
[0011]
Further, the data circuit output from the digital scan converter 4 is subjected to a range gate at an arbitrary timing and an arbitrary time width by a gate circuit 5 to extract only data in a sample volume at an arbitrary position and size. This is supplied to the speed calculation processing unit 6. Based on the data in the sample volume extracted by the gate circuit 5, that is, the intensity of the echo signal, the velocity calculation processing unit 6 estimates the absolute velocity of the fluid (blood flow) in the sample volume with relatively high accuracy. .
[0012]
The absolute velocity of the blood flow estimated here is displayed on the same screen as the B-mode image via the image synthesis unit 7, as a numerical value, as a graph representing temporal changes, and further at the position of the sample volume of the B-mode image. According to the quantity, it is displayed with an appropriate hue.
[0013]
The absolute speed estimation method will be described in detail below. First, the relationship between the amount of contrast medium present in the bloodstream and the intensity of the echo signal, and the behavior of the contrast medium due to ultrasonic irradiation will be described.
[0014]
In order to estimate the absolute velocity of the blood flow, a contrast medium (microbubbles) is continuously injected into the blood vessel of the subject for a certain period of time in a constant amount per unit time. Then, the transmission / reception of ultrasonic waves is repeated with respect to the blood flow mixed with this contrast agent. Here, as is well known, the reflection intensity at the blood flow itself (mainly blood cells) The reflection intensity is on the order of 10 ^-2 , or even a fraction of that for the contrast intensity of the contrast agent. Therefore, the echo signal from the blood flow part in which the contrast agent is mixed. It is considered that the intensity of the light reflects the existing amount of the contrast medium at the time of irradiation relatively accurately. The correlation between the existing amount of the contrast agent and the intensity of the echo signal can be expressed by the relationship shown in FIG.
[0015]
FIG. 3 schematically shows the behavior of the contrast agent by two successive ultrasonic irradiations, and most of the contrast agent existing in the sample volume immediately before the ultrasonic irradiation collapses due to the ultrasonic irradiation. Then, the contrast effect is lost (FIGS. 3A and 3B), and in the period until the next irradiation, a contrast medium newly flows into the sample volume (FIG. 3C). Most of the contrast agent that has flowed in collapses (FIG. 3D).
[0016]
FIG. 4 shows a temporal change in the existing amount of contrast agent due to repetition of such ultrasonic irradiation. In FIG. 4, Δt represents a repetition period (1 / PRF) in which ultrasonic waves are repeatedly applied to the same ultrasonic scanning line in which the sample volume exists.
[0017]
As described above, the intensity of the echo signal reflects the abundance of the contrast agent, and most of the contrast agent is destroyed by the previous irradiation, so the intensity of the echo signal obtained by the current irradiation is During the time Δt from the irradiation to immediately before the current irradiation, the inflow amount of the contrast agent newly flowing into the sample volume is reflected.
[0018]
Thus, the inflow amount of the contrast agent that can be estimated from the intensity of the echo signal is determined mainly depending on the absolute velocity of the blood flow, the cross-sectional area of the sample volume, and the inflow time Δt. Among these, since the cross-sectional area of the sample volume and the inflow time Δt are known, if the inflow amount is known as described above, the absolute velocity of the blood flow can be estimated.
[0019]
Note that the contrast medium existing amount (inflow amount) may be calculated from the intensity of the echo signal, and the absolute velocity of the blood flow may be calculated from the inflow amount, the cross-sectional area of the sample volume, and the inflow time Δt. Actually, the relationship between the intensity of the echo signal and the absolute velocity of the blood flow (see FIG. 5) is calculated in advance or measured using a phantom or the like, and this relationship is converted into, for example, a ROM and real-time. It may be preferable to allow processing.
[0020]
As described above, according to the present embodiment, the absolute velocity of the blood flow without angle dependency is estimated from the intensity of the echo signal by skillfully utilizing the property of the contrast agent such that the contrast agent is disrupted by ultrasonic irradiation. be able to. Moreover, since this is obtained for each repetition period (1 / PRF), it is possible to observe a change in the absolute velocity of the blood flow over time. The absolute velocity of the blood flow can theoretically be estimated for each pixel. However, considering the S / N ratio, practically, as described above, the data of a plurality of pixels included in the sample volume is considered. It can be said that it is preferable to estimate using the sum or the average value.
[0021]
The present invention is not limited to the embodiments described above, and can be implemented with various modifications. For example, a plurality of sample volumes may be set in the cross section to generate a spatial distribution of absolute velocities. Furthermore, using the nonlinear phenomenon that is a feature of contrast agents, only the harmonic components peculiar to contrast agent reflections contained in the echo signal are extracted, and the absolute velocity is estimated with higher accuracy based on the intensity of the harmonic components. You may do it.
[0022]
【The invention's effect】
According to the present invention, the absolute velocity of a kinetic fluid such as a blood flow can be measured with relatively high accuracy.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an ultrasonic diagnostic apparatus according to an embodiment of the present invention.
FIG. 2 is a correlation diagram between the intensity of an echo signal and the amount of contrast medium present.
FIG. 3 is a diagram showing the behavior of a contrast medium in a sample volume from the previous irradiation to the current irradiation.
FIG. 4 is a view showing temporal changes in the amount of contrast agent in a sample volume when ultrasonic waves are repeatedly irradiated at a constant period Δt.
FIG. 5 is a correlation diagram between an inflow amount of a contrast medium newly flowing into a sample volume and a blood flow velocity during an ultrasonic irradiation period Δt.
[Explanation of symbols]
1 ... ultrasonic probe,
2 ... Rate pulse generator,
3. Transmission / reception circuit,
4 ... Digital scan converter,
5 ... Gate circuit,
6 ... Speed calculation processing part,
7: Image composition unit,
8: Monitor.

Claims (9)

The first ultrasonic irradiation that substantially destroys the contrast agent with respect to the fluid in the subject into which the contrast agent is injected, and the second ultrasonic irradiation after the first transmission / reception, and receives the echo signal Transmitting and receiving means,
Estimating means for estimating the velocity of the fluid based on the intensity of the echo signal obtained by the second ultrasonic irradiation and the time interval between the first ultrasonic irradiation and the second ultrasonic irradiation;
An ultrasonic diagnostic apparatus comprising:   The ultrasonic diagnostic apparatus according to claim 1, wherein the transmission / reception unit performs the first ultrasonic irradiation and the second ultrasonic irradiation on the same minute region.   The estimation means estimates an inflow amount of a contrast agent between the first ultrasonic irradiation and the second ultrasonic irradiation, and the fluid is based on the estimated inflow amount and the size of the minute region. The ultrasonic diagnostic apparatus according to claim 2, wherein the speed of the ultrasonic diagnostic apparatus is estimated.   The ultrasonic diagnostic apparatus according to claim 1, wherein the contrast agent is continuously injected in a substantially constant amount per unit time.   The ultrasonic diagnostic apparatus according to claim 1, wherein the estimation unit includes a unit that averages the intensity of the echo signal in the minute region.   The ultrasonic diagnostic apparatus according to claim 1, wherein the estimation unit includes a unit that extracts a harmonic component whose main component is an echo component of the contrast agent from the echo signal.   The ultrasonic diagnostic apparatus according to claim 1, wherein the estimating means includes means for individually estimating the velocity of the fluid with respect to a plurality of minute regions in a cross section of the subject.   The ultrasonic diagnostic apparatus according to claim 1, wherein the estimation unit estimates the velocity of the fluid based on luminance given according to the intensity of the echo signal.   2. The ultrasonic diagnostic apparatus according to claim 1, further comprising means for numerically displaying the estimated fluid velocity.

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