EP0789536A2

EP0789536A2 - Ultrasonic process and circuits for carrying out this process

Info

Publication number: EP0789536A2
Application number: EP95936497A
Authority: EP
Inventors: Volkmar Dr. Uhlendorf; Christian Dr. Hoffmann; Thomas Dr. Fritzsch
Original assignee: Schering AG
Current assignee: Bayer Pharma AG
Priority date: 1994-11-01
Filing date: 1995-10-13
Publication date: 1997-08-20
Also published as: JP2009119299A; CA2204161C; CN1162250A; WO1996013213A3; MX9702842A; CN1154436C; KR970706759A; TW318140B; CA2666047A1; AU3842495A; JP2007283119A; CA2204161A1; IL115832A0; NO972029L; ZA959217B; KR100380126B1; JPH10507672A; NO20072892L; NO325566B1; AU698398B2

Abstract

The invention concerns a process for the selective graphic reproduction and/or the evaluation of the Doppler spectrum of objects, e.g. biological organs and tissue, which offer limited resistance to sound intensities, the process consisting of an ultrasonic process in which a material is introduced into the area under investigation which is to be exposed to acoustic radiation. Radiated ultrasound waves generate non-linear oscillations in the area under investigation, and the signal is evaluated by an ultrasonic transducer. The invention also concerns a circuit for carrying out this process.

Description

Ultrasonic methods and circuits for performing these methods

Summary of the invention

The invention relates to ultrasound methods for imaging and optionally for evaluating a Doppler spectrum of objects with limited resistance to sound intensity, and to circuits for carrying out these methods.

In ultrasound technology, ultrasound waves are radiated into an examination area for the selective imaging and / or evaluation of the Doppler spectrum. Combined transmitter / receiver transducers are typically used in methods and devices for material testing and biological tissue testing. With the help of the crystals of the oscillators and the device electronics, a sound frequency (f ₀ ) is determined, which is the same for sending and for receiving. A typical 5 MHz transducer has a frequency range of approximately 3 MHz to 7 MHz with a maximum at f ₀ = 5 MHz. In the case of pulse echo technology, the reflected and / or backscattered signal is received in the same frequency range. Such devices and methods are also used in the examination of biological tissues using ultrasound contrast agents. Signal components outside the Given the frequency range, such as vibrations, which are in harmonic relation to the transmission frequency, the object is not used in the examination and in other analyzes, such as Doppler measurements. In addition, the previously known methods and device systems use various transducers to cover a larger frequency range, which are exchanged during the examination. EP-A2-0 147 955 describes an ultrasound method in which the object to be examined is exposed to a measurement pulse of high frequency and a pump pulse of low frequency but with a high sound pressure.

In the evaluation, the pressure dependence on the speed of sound is used. The pressure in the object to be examined is changed by the pump pulse. The measuring pulse, which is superimposed on the pump pulse, undergoes a phase change, which is ultimately used for the evaluation. The important factor in this known method is therefore the phase relationship. There is no evaluation of harmonic, subharmonic or superharmonic frequencies.

In addition, in the known method, it is necessary to evaluate a reference signal without a pump pulse in order to be able to measure the phase shift.

A method is known from EP-A3-0 072 330 in which the pressure in the object to be examined is measured. For this purpose, bubbles are generated in the examined object only by exposing it to ultrasonic waves. An ultrasound source of low frequency in the range from below about 100 MHz to typically about 20 MHz down generates vapor bubbles in gas-free liquids in the object to be examined in the low-pressure phase or, if dissolved gases are present, gas bubbles.

The ultrasound power is increased until cavitation bubbles form in the body to be examined. Such bubbles can be very large (easily recognizable by the naked eye ^¬ bar) to remain in the sound field capture and create an embolism risk. If they are produced in the tissue, there are accompanying reactions such as those with pressure reduction complaints go along with expected. Because of the inevitable low frequency ultrasound scattering waves, there is a risk, particularly for lung damage.

EP-A2-0 068 399 describes a method for determining the ultrasound damping or absorption coefficient in the tissue. For this purpose, the change in the mean frequency of the backscattered spectrum over time or the spatial change therein is determined in the direction of progression. Because of the approximately frequency-proportional attenuation, the middle frequency shifts slowly towards lower frequencies as the distance of the ultrasonic energy pulse increases. The shift from f _τ to f _c and f _R is relatively small.

In the method according to US Pat. No. 3,640,271, the blood pressure and the flow rate are measured. For this purpose, individual bubbles of a controlled size are injected within a range of 10 to 100 μm in diameter and their resonance frequency is determined before and after the injection. This is done either with a damped transducer and a frequency sweep, or with shock excitation from a weakly damped transducer. Depending on the size of the bubbles, frequencies in the range from 60 to 600 kHz, i.e. with wavelengths from 2.5 to 25 mm, must be used. The bubbles used are large so that they cannot pass through the capillaries. The speed of the bubbles is measured using the Doppler effect or determined from the time it takes to pass between two points.

From the literature used, L. Germain, JON Cheeke, J. Acoust. Soc. At the. 83 (1988) 942 it is known to improve the image quality in an ultrasound microscope by using harmonic multiples of the excitation frequency. For this purpose, however, ultrasound waves of very large amplitude have to be radiated in order to generate non-linear vibrations on the way into the examination area, the energy from the vibrations having the fundamental frequency, which as a result of this non-linearity converts into higher harmonic vibrations becomes. This literature reference, like the literature reference Journal of the Acoustical Society of America, Volume 69, No. 4, April 1981, pages 1212, WK Law, inter alia, relates to the nonlinear progression of ultrasound in water and tissue only occurs at high intensities.

In the case of non-linear progression, no subharmonic vibrations occur and harmonic vibrations only occur after a minimum running distance of several cm in the medium. However, these processes cannot be used in the ultrasound examination, which uses frequencies of, for example, in the order of magnitude of 1 to 10 MHz, of objects that do not resist high sound intensities, such as biological tissue in particular. The problem on which the invention is based is to extend the field of application of the ultrasound methods to objects with limited resistance to sound intensity, especially to biological tissue, for the selective imaging and evaluation of the Doppler spectrum and to create circuits for carrying out these methods.

The present method solves the problem. By introducing materials or media that produce a non-linearity into the examination area that is to be exposed to low sound intensities that are not harmful, you get - in addition to the excitation frequency - intense and significantly frequency-shifted scattering and / or transmission signals. These scattering and / or transmission signals are especially for the harmonics (2 f _o , 3 f ...), the subharmonics (1/2 f _o , 1/3 f _o , 3/4 f _Q ) and the superharmonics (2nd / 3 f _Q , 5/4 f _Q ...) of the excitation frequency intense. With this method, low frequencies can be irradiated, so that a greater depth of penetration is achieved, and received signals of higher frequency can be evaluated. the selective evaluation of the signal components influenced by the materials or media that have been introduced and the selective representation of these areas filled with these means are advantageously possible without - as was previously required - to find the difference between two or more conditions that were registered before and after the introduction of the materials or media. In particular, the Doppler effect that has been generated can be evaluated free of artifacts.

Advantageously, nonlinear scattering bodies are introduced into the examination area, but nonlinear ultrasound contrast media in the form of a solution or suspension and especially microbubbles or agents that produce microbubbles can also be introduced into the examination area.

Suitable nonlinear ultrasound contrast agents are, for example, the agents described in EP 0 365 457, which are incorporated by reference into the disclosure and which are based on galactose particles which contain fatty acid.

However, under certain conditions - which will be described in more detail later - such contrast agents as are described in DE 38 03 972, WO 93/25242 and WO 94/07539 and which are introduced here by reference can also be used. These agents contain microparticles that consist of a gas core and a polymer shell and show an ambivalent behavior. At low sound pressure they show a behavior with linear scatter, at higher ones

Sound pressures (whose strength is still in the diagnostic range) show a non-linear one

Backscattering behavior. According to the invention, they can therefore be used in the non-linear range.

The introduction of a microbubble suspension having a concentration of 10 ^{~ 3} wt% to 30 wt% dry matter in the suspension medium gives good results. The method according to the invention and the circuit according to the invention surprisingly reach the low lower limit of 10 ^"3 % by weight.

Under certain conditions, especially when the agents described in DE 38 03 972, WO 93/25242 or WO 94/07539 are used, there is a further increase in the

Sensitivity possible. These means surprisingly show a disproportionate increase in the level of the temporary backscatter signals with an increase in the amplitude of the emitted signal above a certain threshold. This disproportionate level increase can occur not only at the frequency of the emitted signal (f ₀ ), but especially at 1/2 f _Q , 3/2 f _Q , 2 f ₀ , 5/2 f _o , 3 f ₀ , 7/2 f _o and 4 f ₀ can be observed. Since the backscatter signal at 2 f almost reaches the intensity of f ₀ when the excitation is above the threshold value, that signal is preferably detected. Detection of individual particles or gas bubbles is possible due to excitation in the diagnostic range that is above the threshold value. The dose required for space-filling contrasting can be reduced in the area examined to a particle concentration (gas bubble concentration) of 10 ppb. If the relative density of 1 ppb is taken into account, this concentration corresponds to about 1000 particles, preferably 100 to 1000 particles, per cm ^{3 of} the examined body area. Concentrations of 1000 to 100,000 particles per cm ³ can also be used. The reduction in the contrast agent concentration results in a reduction in the acoustic damping which is caused by the contrast medium, as a result of which the penetration depth of the irradiated ultrasound signal into the tissue is increased. Sonographic examination of the lower parts of the body is also possible.

This effect is further enhanced by the fact that the irradiation of ultrasound with an energy above the threshold value causes the particles to be destroyed (or the gas bubbles to burst), so that the concentration of the particles (bubbles) in the tissue is constant over the course of the examination decreases. In this case, the particles (bubbles) that are closest to the sound source are destroyed first. As the examination time increases, the ultrasound signal also penetrates to the layers below it, which enables uniform contrast formation through all tissue layers (organ layers). Because these processes, especially in the areas of the smallest contrast medium concentration, take place in very short periods of time run, the recording of the received signals by modern data acquisition storage techniques is particularly preferred. The energy required to destroy the particles (bubbles) changes as a function of the contrast medium selected. In the case of the contrast agents described in EP 0 365 467, the energy must be above a threshold value of 0.03 MPa, in the case of the contrast agents described in WO 93/25242 and WO 94/07539 above a threshold value of 0.1 MPa. The energy required for other contrast agents can be easily determined by a person skilled in the art and is generally in the range from 0.01 to 1 MPa, and the threshold increases with increasing stability of the bubbles.

The reduction of the contrast agent concentration possible by the method according to the invention further enables the imaging of areas of the body which do not have enough particles, for example those which do not belong to the RES. Thus, among other things The tissue flow is represented by the detection of the contrast agent in very fine blood vessels, which due to their small cross-section can only absorb very small amounts of contrast agent (e.g. in the heart muscle, in the liver, in the kidney, in the muscles, in the skin , in the base of the eye, in lymphatic vessels, in lymph nodes, in the urinary tract, in tubes and in small and large body cavities). The advantages of the method according to the invention are particularly clear if location-, structure- or tissue-specific contrast agents can be determined. Such specific contrast agents are described, for example, in WO 94/07539. Since, in the case of specific contrast media, in general only a small part of the administered dose adheres to the desired target tissue (organ), a determination by conventional ultrasound methods is problematic. However, the detection of these small amounts of contrast medium is possible without problems by using the method and the circuits according to the invention, in particular if the contrast medium is irradiated with an energy above its threshold value.

Due to the significant increase in sensitivity of the The method according to the invention in combination with the contrast media mentioned makes it possible to image all areas of the body with the exception of the lungs, cartilage areas and bones. To utilize the special sensitivity of the method according to the invention in combination with one of the contrast agents described in patent applications EP 0 365 457, WO 93/25242, DE 38 03 972 or WO 94/07539, excitation frequencies in the range from 1 to 22 MHz, preferably from 2 up to 5 MHz applied. The necessary

Sound pressure amplitudes are in the range from 0.01 to 5 MPa, preferably from 0.03 to 0.2 MPa. In this case, the HF sound impulses have 1 to 50 pulses, preferably 2 to 8 pulses.

In the method according to the invention, the sound transducer is advantageously excited with the aid of a function generator, by means of which RF sound impulses with an adjustable amplitude and an adjustable mean frequency (f _τ ) in the range from 0.3 MHz to 22 MHz, preferably from 1 MHz to 11 MHz, and with 0.5 to 20 periods, preferably with 1 to 5 periods. It has been found to be particularly advantageous to evaluate frequencies that are lower than the average frequency f _{τ of} the sound transducer (transmitter).

In the evaluation, it is advantageous to select at least one time period with the aid of a computer-controlled gate circuit and to determine the assigned frequency spectrum in an analog or digital manner. This procedure adjusts the length of the time window and the number of periods per shock between optimal frequency resolution and optimal room resolution. By using the method according to the invention, it is advantageously possible to evaluate Doppler effects in the case of harmonics of the excitation frequency and in the case of mixed products such as the upper sideband in the case of 2-frequency excitations. This allows relatively slow flows to be reproduced without interference from vessel wall movements.

In addition, when evaluating harmonic signal components or signals in the upper sideband receive improved penetration depth and / or spatial resolution, which is particularly advantageous in the representation and in Doppler measurements.

The circuit according to the invention for performing the method described above comprises a function generator, the output of which is connected via a T / R switch (transmitter / receiver, transmitter / receiver) which is synchronized by the function generator and, seen in the message flow direction, behind which a signal processing device is connected to the oscillator of an acoustically highly damped, electrically adapted, broadband transducer element.

In another embodiment of the circuit, the function generator is connected to the input of a converter, the output of which is connected to a signal processing system.

In the former case, when the T / R switch is set to "transmit", the surge excitation generated by the function generator is applied to the oscillator of the converter, and when the T / R switch is set to "receive" that by the Transducer received signal passed on to the evaluation system. In the second case, the input and the output of the converter are separated, so that a T / R switch is not necessary.

It is particularly advantageous to use a transducer element whose average frequency f _{τ is} higher than the upper one

Working area limit. The transducer element is constructed so that the sound intensity emitted by it, as a function of frequency, is in the frequency range below the

Excitation or center frequency f _{τ has} a positive first derivative according to the frequency, this derivative being approximately constant, particularly in the working area, or that the sound intensity itself has a constant value in the working area. Because of this approximately linear

Frequency response in the work area can have a similar frequency response, especially an attenuation, in the

Large-scale examination area exposed to ultrasonic waves

Scope to be balanced. As a result of this circuit and the transmission used, it is possible for the Change the frequency used without changing the transducer. In addition, the optimal ratio of spatial resolution and frequency resolution can be selected when evaluating spectra for material characterization, especially for tissue characterization.

The method according to the invention can advantageously be carried out with the aid of a circuit which carries out a multi-element converter with converter elements which receive signals in a phase-delayed manner in order to carry out a phase series or a dynamically focused process. In this circuit, the output of a function generator using an n-way signal divider, n computer-controlled time delay circuits and n T / R switches, which are controlled by the function generator or by a computer, with the inputs of n acoustically highly damped, electrically adapted, broadband transducer elements connected, the outputs of which are each connected to an m-way signal divider via the n T / R switches. These m-way signal dividers are each connected via m time delay circuits and m fixed or variable frequency band selection circuits and also via a circuit for phase correct summation and, if appropriate, for signal division to a system for the selective further processing of m frequency bands.

In a further solution to the problem on which the invention is based, a material is introduced into the examination area to be exposed to the ultrasonic waves, by means of which non-linear vibrations are generated in this area by the interspersed ultrasonic waves; A broadband, acoustically highly damped, electrically adapted ultrasonic transducer with one or more transducer elements, which can be controlled individually or in groups, is excited with the aid of two RF impulse excitations, the excitation frequencies of which are different and lower than half _the upper limit frequency of the working range ; and there are signal combinations of the two excitation frequencies, specifically their sum frequency or their difference frequency, evaluated from the ultrasound signal received by the ultrasound transducer, which was reflected from the examination area or backscattered from this area. To achieve the threshold level mentioned above, it is preferred that at least one of the two frequencies lies above the threshold level.

In the described method, the irradiation of two separate signals produces a stronger received signal, the frequency of which is a combination of the frequencies of the irradiated signals, in particular their sum frequency or difference frequency. The sum frequency is of particular interest in view of the higher spatial resolution that can be achieved. In this method, the one transducer element can be excited by means of two RF excitation pulses, but it is also possible to excite two separate transducer elements each with a single RF excitation pulse, the mean frequencies of these RF excitation pulses being different and lower than half the upper limit frequency of the working range. Because of the non-linearity that is generated according to the invention, the use of, for example, two low-frequency signals, for example f _o ~ f ~ 2 MHz, leads to a stronger received signal at f _o + f, that is to say at about 4 MHz, compared to a signal , which is obtained when with the same total power I ₀ , I only a single transmission signal

Frequency f + f is used. This phenomenon enables a greater depth of penetration at high observation frequencies.

The same materials and means used in the method for evaluating the harmonic frequencies of the excitation frequency can be used as materials or means which produce the nonlinearity. It is possible to use essentially the same circuit elements, but with the addition of a second RF generator. In the event that the circuit has a multi-element converter, the second signal is always emitted in the direction of the first signal and begins for the purpose of reducing the average power radiated into the examination area approximately 1 to 2 periods earlier and continues until the end of the first excitation pulse signal. To achieve this, the second signal from the second generator is influenced by suitable delay circuits in such a way that after passing through the T / R switch it runs to the same transducer elements in the transducer and is emitted in the same direction as the first transmission signal. The circuit matrix then receives signals at the sum frequency. The T / R switch is controlled by the second transmit signal, which takes longer.

Embodiments of the invention are described in the following description with reference to the figures shown in the drawings. Show it:

1 shows a block diagram;

2 shows a schematic sectional view of a sample vessel; Fig. 3 shows a curve of the sound power as

Function of the frequency of a transmitter; Fig.n 4-9 graphical representations of backscattered signals;

10 shows a further block diagram; Fig.n 11

-13 graphical representations of the backscattered

Signals (time resolution) and their spectra (frequency resolution) at different

Sound intensities using a

Contrast agent as described in WO 93/25242;

14 shows a graphic representation of the scatter signals at 2 f as a function of the sound intensity

Use of a contrast agent as described in WO 93/25242.

To generate the signals shown in FIGS. 4 to 9, which are ready for further processing, the

_S circuit according to FIG. 1 together with the sample vessel according to FIG.

2 used, the broadband transducer

3 has performance characteristics. A function generator 1, which is controlled by a central computer 15, periodically repeats electrical transmission pulses - RF impulses - variable frequency f _Q in the working range f ₀ min to f ₀ max (f ₀ min = 0.3 MHz <f _o <f _o max = 22 MHz) and of variable bandwidth, given by the number of sine periods per pulse: 0.5 <n <20, generated with adjustable amplitude. The central computer 15 controls both the course of the measurement and its evaluation. The output 2 of the generator 1 leads to a transmitter / receiver switch referred to as a T / R switch 3, which, as shown schematically, is synchronized by the generator 1. The T / R switch 3 can also be controlled directly by the computer 15. The output of the T / R switch 3 is connected to a broadband, adapted and focused converter element 4. The special properties of the converter element 4 are shown schematically in FIG. 3. The converter is a very broadband converter without interference in the work area; it also has good electrical and acoustic impedance matching and a medium transmission frequency f _τ > f _o max. In the example described, f _τ = 17 MHz. The transducer can also have spatially and electrically separate transmitter and receiver transducer elements. In this case, the T / R switch 3 is unnecessary. Another converter element for emitting a second, independent high-frequency signal is advantageously present.

The signal received by the converter element 4 is sent via the switched T / R switch to a broadband preamplifier 16, behind which an anti-alias filter 17 is connected in the case of digital frequency analysis. The broadband preamplifier 16 has a bandwidth> f _o max. The filter 17 has a cut-off frequency of 10 MHz, for example. A fast A / D converter 18 follows the filter, in which the signal is digitized, for example with a Nyquist frequency of 12.5 MHz. The further processing of the signal is carried out in a digital storage oscilloscope and in the central computer. A plotter 19 is connected behind the A / D converter 18.

Fig. 1 shows that the A / D converter from the function generator 1 is triggered.

The digitized signal is stored and processed in a manner known per se. It is specifically for required

Corrections available. It is also possible that a signal is branched off before the A / D conversion and is only digitized after further analog processing.

Fig. 2 shows schematically the geometry of a vessel with which the measurement results given below were obtained.

2, the transducer 4 is arranged in a sample container 20. It is a 17 MHz transducer that is broadband, matched and focused. The sample vessel 20 contains water. Two films 21 delimit a sample area in which 10 mg of ultrasound contrast medium are dissolved in 3 ml of H ₂ O. The signals reflected or backscattered in the measuring area between the films 21 contain certain components which are obtained by mutual action of the transmission pulse (with f ₀ ) and the non-linear contrast medium introduced into the measurement object. Fig. 3 shows schematically the frequency band of the transducer element in the transducer. It can be seen that the frequency response of the oscillator in the transducer is quasi-linear in the working area. The frequency response in the work area can be used to compensate for an identical frequency response in the tested sample, but the frequency response in the tested sample can also be subsequently corrected by weighting.

A time span of interest in the time range is selected for the measurement with the aid of a computer-controlled gate circuit (not shown). You can also choose different time periods. The assigned spectrum is calculated using an FFT circuit (Fast Fourier Transformation), and examples of such spectra are shown in FIGS. 4 to 9. By choosing a suitable length of the time window, it is possible to choose between optimal frequency resolution and optimal spatial resolution. Figures 4 to 8 each show the spectrum over the time window. To the spectral components in these figures To show clearly, a long time window, and thus a poor spatial resolution, was chosen. Fig. 4 shows the change in the transmission pulse after reflection at the coupling window over time without contrast medium, f O = 4, '0 MHz,' + 15 dBm at the transducer. A clear signal can be seen at 4 MHz. The signal shown in the upper part of FIG. 4 is a medium power spectrum which was obtained behind the low-pass filter with a Nyquist frequency of 50 MHz.

5 shows the backscatter signal from the sample chamber without ultrasound contrast medium. FIG. 6 shows the backscatter signal 7 minutes after the addition of 10 mg of contrast medium in 3 ml of H ₂ 0. A clear peak can be seen at 2 ^· f _o .

FIG. 7 shows a measurement after 21 minutes under the conditions given in FIG. 5. A frequency f ₀ = 3 MHz was used. The recorded spectrum clearly shows the first and second harmonics at 6.0 MHz and 9.0 MHz. Fig. 8 shows the backscatter signal 15 minutes after the addition of an ultrasound contrast agent in a small concentration. A frequency f of 4 MHz + 20 dBm was used on the transducer. The spectrum shown in the upper part of FIG. 8 shows the subharmonic at 1/2 f _o , the superharmonic at 3/2 f _o and the first harmonic at 2 f _Q with a relatively high frequency resolution.

Fig. 9 shows the backscatter signal from the linear ultrasound contrast medium at f _Q = 4 MHz + 15 dBm at the transducer. The spectrum shows backscattering only at the excitation frequency.

It can be seen that the spectra shown have clear amplitudes in frequency ranges which do not occur in the transmitted spectrum if there has been an interaction with nonlinear contrast media. It is possible to evaluate spectral changes that are based on a Doppler effect. In order to use the circuit used in the described embodiments for representing ultrasound processes, additional components are present in the case of a transducer of the type with phases arranged in rows, or a dynamically focused transducer is used. A corresponding one Circuit diagram is shown in Fig. 10.

The transmission signal from the function generator 1 (frequency f) is given by the output 2 to an n-way signal divider 5. The signal is divided into one branch per converter element. In the embodiment shown, there are n converter elements 4. The converter elements 4.1 ... 4.n receive the signal via delay circuits 7.1 ... 7.n and via the T / R switches 3.1 ... 3.n, which are controlled by the generator or the computer. The computer sets the time delay for each transducer element so that the desired directional characteristic is generated on the transducer at the selected transmission frequency. The same directional characteristic is set by the computer in the receiver part through corresponding time delays. The signal received at the transducers 4.1 ... 4.n is sent via the T / R switches 3.1 ... 3.n to broadband preamplifiers 6.1 ... 6.n, each of which sends a signal to an m-path Signal divider 10 supplies, to the message current below suitably controlled or adjusted delay circuits 11 are connected, feed the circuits 12 for frequency band selection. Behind them are circuits for the phase correct summation of the frequency bands and, if appropriate, for the signal division. This is followed by the selective further processing of the individual frequency bands with the aid of methods known per se.

Specifically, the evaluation of frequencies that are not identical frequencies to f ₀ , for example 1/2 f ₀ and 2 f ₀ , is carried out.

The delay circuits can be variable or fixed. The distribution of the received signals on the m-way signal divider generates the desired number of frequency bands, the position and width of which are adjusted with the aid of band filters. Alternatively, the division can take place in such a way that the received signal is mixed with an auxiliary signal which is derived from the original signal and deviates depending on the frequency band in such a way that the individual bands can work with uniform components in the subsequent stages. The frequency band around f _Q gives the usual results, while the other bands largely frequency-shifted and non-linear signal components from the interaction of the

Contain transmission signal with the non-linear ultrasound contrast agents.

The further processing steps and signal analyzes can be carried out in any desired frequency channel or in different parallel frequency channels in accordance with known procedures. In order to use two transmission frequencies f ₀ and f, there is a second generator 1 shown on the right in FIG. 10, which is connected to the T / R switches 3.1 ... 3.n via signal dividers and delay lines. The second generator 1 makes it possible to expose the ultrasonic waves to at least that spatial area of the examined object which is determined by the directional characteristic at that time and the receiver gate. The construction can be such that, in addition to the broadband transducer elements described, the transducer contains at least one further, likewise broadband transmit transducer, which is preferably electrically separated from the others and is fed by the second, independent transmit generator 1. However, the two transmission signals can also be electrically superimposed on one another in such a way that the same transducer element is used. Fig. 11 shows (in the upper half of the figure) in

Time range the backscatter signal, which is caused by a contrast medium, as described in WO 93/55242, with weak excitation with a 5 MHz burst with an amplitude of 0.1 MPa.

The power spectrum of this signal is shown in the lower half of the figure. The signal with the excitation frequency f _o (5 MHz) is clearly recognizable; Harmonics, subharmonics and superharmonics are lost statically.

Fig. 12 shows the backscatter signal at an excitation with an _A mplitude of 0.34 MPa under otherwise identical test conditions as for Fig. 11. In this case, the larger backscattering portion of the contrast agent in the time domain can be clearly recognized. In the frequency resolution, the signals can be clearly determined at 2 f _Q and 3 f _o . 13 shows the backscatter signal with an excitation with an amplitude of 1 MPa. The backscattering portion of the contrast medium is evidently higher in the time domain (upper half of the figure) than the reflections of the transmission pulses, and it should be noted that 1 scale marking in the ordinate corresponds to 5 mV. In the power spectrum (lower half of the figure, the signals can be clearly recognized at 1/2 f ₀ , f _o , 3/2 f ₀ , 2 f ₀ , 5/2 f ₀ 3 f 0, '7 /' 2 fo and 4 fo Surprisingly, the signal at 2 f _{0 has} an intensity approximately equal to the echo de emitted frequency (f ₀ ).

14 shows the strength of the backscattered signal be 2 f as a function of the emitted sound pressure at different excitation frequencies (f _o ) of 2, 3 and 4 MHz. In this case too, a contrast medium was used, as described in WO 93/25242. Surprisingly, the strength of the backscattered signal rises above the threshold value of about 40 dB, and that disproportionately to the excitation strength. This behavior is also observed in an analogous manner for other contrast medium preparations, for example for microparticles which are based on fatty acid-containing galactose particles, or microparticles which consist of a gas core and a biodegradable polymer scarf, with an optional molecule location, structure and / or tissue-specific properties is bound. The entire disclosure of all applications, patents, and publications listed above and below are incorporated herein by reference.

From the foregoing description, those skilled in the art can easily ascertain the essential features of the invention and, without departing from the spirit and scope of the invention, can make various changes and modifications to the invention in order to adapt it to different uses and conditions.

Claims

Ultrasonic method for displaying and optionally for evaluating a Doppler spectrum, an object with limited resistance to sound energy in an examination area, with the following method steps:

Introducing the object to be displayed and an ultrasound contrast medium which contains microbubbles as backscattering bodies or which produces microbubbles when exposed to ultrasound waves, in such a way that the contrast medium produces nonlinear vibrations of the microbubbles when they are emitted in the examination area by emitted ultrasound waves are irradiated in the examination area;

Applying an RF excitation pulse of a frequency f ₀ for electrically exciting a broadband, acoustically highly damped, electrically adapted ultrasound transducer with one transducer element or a plurality of transducer elements which can be controlled individually or in groups, and thereby occupying the examination area with the ultrasound waves, f, from 1 MHz to 22 MHz and with an amplitude which is effective to burst at least some of the microbubbles in the contrast medium or generated by it;

Receiving the ultrasound signal reflected by the examination area and the backscattered back from the examination area by the ultrasound transducer and processing the received ultrasound signal for further evaluation; and from the reflected and backscattered ultrasonic signal, evaluating at least one of the harmonics, subharmonics and / or superharmonics of the excitation frequency f ₀ and optionally the excitation frequency f.

Ultrasound process for imaging, and optionally for Evaluation of a Doppler spectrum, an object with limited resistance to sound energy in an examination area, with the following method steps: introduction of the object to be displayed and an ultrasound contrast medium which contains microbubbles as backscattering bodies or which produces microbubbles when it is exposed to ultrasonic waves such that the contrast medium produces non-linear vibrations of the microbubbles when they are irradiated in the examination area by emitted ultrasound waves, in the examination area;

Application of two RF excitation surges with excitation frequencies f ₀ and f for the electrical excitation of a broadband, acoustically highly damped, electrically adapted ultrasound transducer with one transducer element or several transducer elements which can be controlled individually or in groups, the excitation frequencies fo and fp different and j ^J in each case lower than those half upper limit frequency of Arbeits¬ range of the ultrasonic transducer, and wherein nigstens one of the excitation frequencies we¬ an amplitude has effective at least a portion of the located or in the contrast agent of this to burst generated microbubbles;

Receiving the ultrasound signal reflected by the examination area and backscattered by the examination area by the ultrasound transducer and processing the received ultrasound signal for further evaluation; and from the reflected and backscattered ultrasonic signal, evaluating the sum or the difference of the two excitation frequencies.

The ultrasound method of claim 1, wherein the contrast agent is one of:

Microparticles based on fatty acidic galactose particles, or Microparticles consisting of a gas core and a bio- degradable polymeric shell _^, optional gebun¬ the bespezifischen by molecules having location-, structure and / or gewe¬ properties.

4. Ultrasonic method according to claim 1, wherein the excitation frequency f _{0 is} 2 to 5 MHz.

5. Ultrasonic method according to claim 1, wherein the sound pressure amplitude is 0.01 MPa to 5 MPa.

6. Ultrasonic method according to claim 1, wherein the sound pressure amplitude is 0.03 MPa to 1 MPa.

7. Ultrasonic method according to claim 3, in which 1 to 50 pulses are emitted per RF burst.

8. Ultrasonic method according to claim 3, in which 2 to 8 pulses are emitted per RF pulse.

9. Ultrasound method according to claim 3 for the diagnostic imaging of blood vessels.

10. Ultrasonic method according to claim 3 for the diagnostic display of capillaries.

11. Ultrasound method according to claim 3 for the diagnosis of the cardiac muscle.

12. Ultrasound method according to claim 3 for the diagnostic representation of the liver.

13. Ultrasound method according to claim 3 for the diagnostic representation of the kidney.

₁ 4. Ultrasound method according to claim 3 for the diagnostic imaging of the skin. 15. Ultrasound method according to claim 3 for the diagnostic representation of the muscles.

16. Ultrasound method according to claim 3 for the diagnostic representation of the base of the eye.

17. Ultrasound method according to claim 3 for the diagnosis of the lymphatic vessels and / or the lymph nodes.

18. Ultrasound method according to claim 3 for the diagnosis of the urinary tract.

19. Ultrasonic method according to claim 3 for the diagnostic representation of a small and / or a large body cavity.

20. Ultrasonic method according to claim 3 for the diagnostic representation of the fallopian tubes.

21. Ultrasound method according to claim 20 for fertility diagnosis.

22. Ultrasonic method according to claim 1, in which the signal is evaluated with 2 f _o .

23. Ultrasound method according to claim 1, in which the examination area is a body zone and the concentration of the microbubbles from the contrast medium in the body zone is approximately 1,000 microbubbles per cm ³ or less.

24. Ultrasonic method according to claim 2, wherein the contrast medium is one with: microparticles based on fatty acidic galactose particles, or

Microparticles consisting of a gas core and a biodegradable polymer shell, optionally bound by molecules with site, structure and / or tissue-specific properties.

25. Ultrasonic method according to claim 2, wherein the excitation frequency f _{o is} 2 to 5 MHz.

26. Ultrasonic method according to claim 2, wherein the sound pressure amplitude is 0.01 MPa to 5 MPa.

27. Ultrasonic method according to claim 2, wherein the

Sound pressure amplitude is 0.03 MPa to 1 MPa.

28. Ultrasonic method according to claim 24, in which 1 to 50 pulses are emitted per RF burst.

29. Ultrasonic method according to claim 24, in which 2 to 8 pulses are emitted per RF burst.

30. Ultrasonic method according to claim 24 for the diagnostic display of blood vessels.

31. Ultrasonic method according to claim 24 for the diagnostic imaging of capillaries.

32. Ultrasound method according to claim 24 for the diagnostic representation of the heart muscle.

33. Ultrasound method according to claim 24 for the diagnostic representation of the liver.

34. Ultrasound method according to claim 24 for the diagnostic representation of the kidney.

35. Ultrasound method according to claim 24 for the diagnostic representation of the skin.

36. Ultrasound method according to claim 24 for the diagnostic representation of the muscles. 24

37. Ultrasound method according to claim 24 for the diagnostic staging of the base of the eye.

38. Ultrasound method according to claim 24 for the diagnostic representation of the lymphatic vessels and / or de lymph nodes.

39. Ultrasound method according to claim 24 for the diagnosis of the urinary tract.

40. Ultrasound method according to claim 24 for the diagnostic representation of a small and / or a large body cavity.

41. Ultrasonic method according to claim 24 for the diagnostic staging of the fallopian tubes.

42. Ultrasound method according to claim 41 for the fruit availability diagnosis.

43. Ultrasonic method according to claim 2, in which the signal with 2 f _{0 of} the at least one excitation frequency is evaluated.

44. Ultrasonic method according to claim 2, in which de

Examination area is a body zone and the concentration of the microbubbles from the contrast medium in the body zone is approximately 1,000 microbubbles per cm ³ or less.

45. Ultrasound process for imaging, and optionally for

Evaluation of a Doppler spectrum, an object with limited resistance to sound energy in one

Examination area, with the following procedural steps:

Introducing the object to be displayed and an ultrasound contrast medium which contains microbubbles as backscattering bodies or which produces microbubbles, 25 when exposed to ultrasonic waves, such that the contrast medium produces non-linear vibrations of the microbubbles when they are irradiated in the examination area by emitted ultrasound waves, into the examination area;

Applying an RF excitation pulse of a frequency f for electrically exciting a broadband, acoustically highly damped, electrically adapted ultrasound transducer with one transducer element or a plurality of transducer elements which can be controlled individually or in groups, and thereby occupying the examination area with the ultrasonic waves, 'fo,' from 1 MHz to

22 MHz and with an amplitude at or above a threshold value such that the temporary backscatter signals from the contrast medium are increased disproportionately with respect to the excitation frequency; Receiving the ultrasound signal reflected by the examination area and the backscattered back from the examination area by the ultrasound transducer and processing the received ultrasound signal for further evaluation; and from the reflected and backscattered ultrasound signal, evaluating the harmonics, subharmonics and / or superharmonics of the excitation frequency f and optionally the excitation frequency f _Q.

46. Ultrasound method for displaying and optionally for evaluating a Doppler spectrum, an object with limited resistance to sound energy in an examination area, with the following method steps:

Introducing the object to be displayed and an ultrasound contrast medium which contains microbubbles as backscattering bodies or which produces microbubbles when exposed to ultrasound waves, in such a way that the contrast medium generates nonlinear vibrations of the microbubbles when they are emitted in the examination area by emitted ultrasound waves to be irradiated the, in the investigation area;

Applying two RF excitation pulses with excitation frequencies f ₀ and f for electrical excitation, a broadband, acoustically highly damped, electrically adapted ultrasonic transducer with a transducer element or several transducer elements which can be controlled individually or in groups, the excitation frequencies f ₀ and f are different and are each lower than half the upper limit frequency of the working range of the ultrasonic transducer, and where we least one of the excitation frequencies have an amplitude at or above a threshold value such that the transient backscatter signals from the contrast medium i in relation to the at least one excitation frequency are increased proportionally , Has;

Receiving the ultrasound signal reflected by the examination area and the backscattered ultrasound signal by the ultrasound transducer and processing the received ultrasound signal for further evaluation; and from the reflected and backscattered ultrasonic signal, evaluating the sum or the difference of the two excitation frequencies.

47. Ultrasound method for displaying, and optionally for evaluating a Doppler spectrum, an object with limited resistance to sound energy in an examination area, with the following method steps: introducing the object to be displayed and an ultrasound contrast agent that contains microbubbles or that generates microbubbles if it is exposed to an ultrasonic energy in the examination area; Application of an ultrasonic frequency f ₀ from 1 MHz to

22 MHz and with an amplitude which is effective to burst at least part of the microbubbles contained in or produced by the contrast medium; and from the reflected and backscattered Ultrasonic signal, evaluation of the harmonics, the subharmonics and / or the superharmonics of the frequency f ₀ .

48. Ultrasound method for displaying, and optionally for evaluating a Doppler spectrum, an object with limited resistance to sound energy in an examination area, with the following method steps: introduction of the object to be displayed and an ultrasound contrast medium that contains microbubbles or that generates microbubbles, when it is exposed to ultrasonic waves, into the examination area; Application of two ultrasound frequencies f _o and f, which are different and are each lower than half the upper limit frequency of the working range of the ultrasound transducer which generates the ultrasound energy, at least one of the frequencies, f _Q and f, having an amplitude which is effective is to burst at least a portion of the microbubbles contained in or produced by the contrast medium; and from the reflected and backscattered ultrasound signal, evaluating the sum or the difference of the two frequencies f _o and f.

49. Ultrasound method according to claim 1, in which the examination area is a body zone and the concentration of the microbubbles from the contrast medium in the body zone is 1,000 to 100,000 microbubbles per cm ³ .

50. Ultrasound method according to claim 2, in which the examination area is a body zone and the concentration of the microbubbles from the contrast agent in the body zone is 1,000 to 100,000 microbubbles per cm ³ .