CA2366534A1 - Device and method for real-time 3d sonography - Google Patents
Device and method for real-time 3d sonography Download PDFInfo
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- CA2366534A1 CA2366534A1 CA002366534A CA2366534A CA2366534A1 CA 2366534 A1 CA2366534 A1 CA 2366534A1 CA 002366534 A CA002366534 A CA 002366534A CA 2366534 A CA2366534 A CA 2366534A CA 2366534 A1 CA2366534 A1 CA 2366534A1
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- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03B—APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR
- G03B42/00—Obtaining records using waves other than optical waves; Visualisation of such records by using optical means
- G03B42/06—Obtaining records using waves other than optical waves; Visualisation of such records by using optical means using ultrasonic, sonic or infrasonic waves
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S15/00—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
- G01S15/88—Sonar systems specially adapted for specific applications
- G01S15/89—Sonar systems specially adapted for specific applications for mapping or imaging
- G01S15/8906—Short-range imaging systems; Acoustic microscope systems using pulse-echo techniques
- G01S15/8993—Three dimensional imaging systems
Abstract
The invention relates to a device and a method for real-time 3D sonography.
The inventive device comprises an ultrasound head, a signal processor and a display. The ultrasound head consists of at least one transmitter and at least three receivers independent therefrom. The positions of the receivers to the transmitters is known. The inventive device is characterised in that a signal processor consists of a signal generator for producing a transmission signal with any modulation function. The signal processor also consists of a correlator on each receiver which is connected to the signal generator respectively, a calculating unit for determining the paths of the transmission signal via the reflecting structure and to the receivers on each correlator and a calculating unit for determining the space co-ordinates of the reflecting structure, whereby each calculating unit is connected to the space co-ordinates for determining the paths of the transmission signal via the reflecting structure and to the receivers.
The inventive device comprises an ultrasound head, a signal processor and a display. The ultrasound head consists of at least one transmitter and at least three receivers independent therefrom. The positions of the receivers to the transmitters is known. The inventive device is characterised in that a signal processor consists of a signal generator for producing a transmission signal with any modulation function. The signal processor also consists of a correlator on each receiver which is connected to the signal generator respectively, a calculating unit for determining the paths of the transmission signal via the reflecting structure and to the receivers on each correlator and a calculating unit for determining the space co-ordinates of the reflecting structure, whereby each calculating unit is connected to the space co-ordinates for determining the paths of the transmission signal via the reflecting structure and to the receivers.
Description
System and method for 3D real-time sonography The invention refers to a system and method for 3D real-time sonography including an ultrasonic head, a signal processor and a monitor, in which the data collection speed of unknown structures is only limited by the physical characteristics of sound propagation in the body.
In the most simple application in diagnostic ultrasound, an ultrasonic pulse is transmitted into tissue, followed by the returned echoes being evaluated for travel time, in order to define the depth and scope of a specific structure, on which reflections are generated. For conventional devices used in diagnostic ultrasound, ultrasonic heads are used, of which the most known designs comprise a linear arrangement of individual mechanically separated piezo-electric units. The piezo-electric units are transmitting a series of pulses into the tissue, followed by receiving the returned echo signals continuously over a fixed period of time. The identical piezo-electric units are then acting as receivers for receiving the echoes, with the period of time being defined by the last echo signal received from the deepest reflection zone. In the ultrasonic system described, generally the same piezo-electric units are used both as transmitters and receivers. In the images generated, which are superposed by a large noise proportion certain structures may become apparent, which in most cases may only be accurately assessed based on a consultant's profound experience.
In the past, resolution (lateral and axial) has been the major criterion for the capacity and quality of ultrasonic devices. Normally, the resolution is 0.5 mm (= SOOpm).
Consequently, the development of "scanning pulse technology" has come to an end due to the physical limits of technologies used. Based on modern computer technology (hardware) and up-to-date signal processing methods (software) it is now possible to achieve slight improvements in image quality. Another improvement in image quality could be achieved by specific contrast media, administered to the patient.
However, these agents frequently impose considerable stress on patients and consequently their application is debatable.
In the most simple application in diagnostic ultrasound, an ultrasonic pulse is transmitted into tissue, followed by the returned echoes being evaluated for travel time, in order to define the depth and scope of a specific structure, on which reflections are generated. For conventional devices used in diagnostic ultrasound, ultrasonic heads are used, of which the most known designs comprise a linear arrangement of individual mechanically separated piezo-electric units. The piezo-electric units are transmitting a series of pulses into the tissue, followed by receiving the returned echo signals continuously over a fixed period of time. The identical piezo-electric units are then acting as receivers for receiving the echoes, with the period of time being defined by the last echo signal received from the deepest reflection zone. In the ultrasonic system described, generally the same piezo-electric units are used both as transmitters and receivers. In the images generated, which are superposed by a large noise proportion certain structures may become apparent, which in most cases may only be accurately assessed based on a consultant's profound experience.
In the past, resolution (lateral and axial) has been the major criterion for the capacity and quality of ultrasonic devices. Normally, the resolution is 0.5 mm (= SOOpm).
Consequently, the development of "scanning pulse technology" has come to an end due to the physical limits of technologies used. Based on modern computer technology (hardware) and up-to-date signal processing methods (software) it is now possible to achieve slight improvements in image quality. Another improvement in image quality could be achieved by specific contrast media, administered to the patient.
However, these agents frequently impose considerable stress on patients and consequently their application is debatable.
In conventional 3D ultrasonic devices, this "classic" scanning technology is used for taking scans of the body in "layers", similar to the computerized tomography (CT). Based on the vast data volume associated with these technologies, tight limits have been set for "real-time data acquisition". As a rule, scans of the volumes involved require between 0.3 s and 2 min., subject to no interfering patient movements (internally and externally) either not being allowed or being included as statistical interference, thus highly affecting accuracy.
In US patent No. 5,601,083, a unit is described, based on ellipsoidal back projection, in order to improve resolution. This unit comprises a receiver array, in which each receiver unit corresponds to one reconstruction pixel angle. The echoes scanned by the receiver are weighted in an amplitude function generator as a function of the reconstruction pixel angle. In a downstream back projection image reconstruction processor, an image is reconstructed and displayed from the weighted echoes.
In the latest sonographic developments, the three-dimensional representation has been subject to major improvements. Three-dimensional images are being computed from individual images by recently disclosed methods. In the past, the main problem of these methods was the excessive time required for computing these images. Today, even larger image sequences comprising more than 30 images, may be computed without any problem within a period of approx. 10 - 15 s due to the availability of faster computers. However, this is by no means a real-time display, i.e. the drawbacks described above still remain.
Any three-dimensional ultrasonic technology is based on scanning a multitude of two-dimensional image layers, accurately defined in position, the total of which results in a volume. A specific ultrasonic head, for instance, comprises a motor, swivelling at the push of a button the internal array unit, depending on the type of the head, by 10° to 95°, thus obtaining a multitude of sectional levels having the same distance from each other. After passing through the signal processor and quantification, the echoes scanned are filed as digital signals in the correct location in a high-capacity memory. Depending on the volume, the type of the head and the swivelling speed of the ultrasonic unit, scanning times are between 0,3 s and 2 min. All sectional layers may then be computed and displayed from the contents of the high-capacity memory within each volume, with three-dimensional images being either displayed on a monitor as individual images or in sequence by rotary animation.
In another method, volume data are collected externally. In this case, movement of the ultrasonic unit is coupled to a locator and the ultrasonic head may also be moved manually. Together with the image data, the image position must be recorded and saved in this case. Although a standard sound head may be used, the system is rather unwieldy and requires excessive time for collecting the image data. Due to the fact that the distance between individual two-dimensional images is not identical, sectional levels may overlap, thus causing inferior displays.
Other drawbacks of both methods can be seen in the fact that in general on the one hand, the ultrasonic heads may only be operated on a unit specifically provided for this purpose, as otherwise determination of the location will be lost. On the other, no real-time representation is available due to sectional levels being scanned in sequence.
For cardiologic scans, display of a heart reaction may simply be useless after 6 to 7 seconds under specific conditions. In many cases it is of great importance to consultants in particular that changes are scanned immediately. Consequently scanning efforts are focused at a real-time representation.
It is the task of the present invention to generate a device, realising a high image quality and fast data collection and 3D visualisation in real-time.
Another system and method for generating ultrasonic images is prior art from US-5,111,823. In this system, the transducers of an array are transmitting a send signal to the medium, followed by all echo signals of all reflectors being simultaneously scanned from the medium. The volume of the echo signals consequently increases the more receivers are available and the longer the send signals are. Shortening the send signals will increase the bandwidth and improve correlation results, with the send signals acquiring excessively high frequencies, although these are of a low penetration depth. Over large distances, low frequencies only are reflected, which may not provide any useful correlation results. In addition, an array of transducers will generate a complex side lobe noise, due to side lobes being generated at the required aperture, which may also generate echo signals.
In US patent No. 5,601,083, a unit is described, based on ellipsoidal back projection, in order to improve resolution. This unit comprises a receiver array, in which each receiver unit corresponds to one reconstruction pixel angle. The echoes scanned by the receiver are weighted in an amplitude function generator as a function of the reconstruction pixel angle. In a downstream back projection image reconstruction processor, an image is reconstructed and displayed from the weighted echoes.
In the latest sonographic developments, the three-dimensional representation has been subject to major improvements. Three-dimensional images are being computed from individual images by recently disclosed methods. In the past, the main problem of these methods was the excessive time required for computing these images. Today, even larger image sequences comprising more than 30 images, may be computed without any problem within a period of approx. 10 - 15 s due to the availability of faster computers. However, this is by no means a real-time display, i.e. the drawbacks described above still remain.
Any three-dimensional ultrasonic technology is based on scanning a multitude of two-dimensional image layers, accurately defined in position, the total of which results in a volume. A specific ultrasonic head, for instance, comprises a motor, swivelling at the push of a button the internal array unit, depending on the type of the head, by 10° to 95°, thus obtaining a multitude of sectional levels having the same distance from each other. After passing through the signal processor and quantification, the echoes scanned are filed as digital signals in the correct location in a high-capacity memory. Depending on the volume, the type of the head and the swivelling speed of the ultrasonic unit, scanning times are between 0,3 s and 2 min. All sectional layers may then be computed and displayed from the contents of the high-capacity memory within each volume, with three-dimensional images being either displayed on a monitor as individual images or in sequence by rotary animation.
In another method, volume data are collected externally. In this case, movement of the ultrasonic unit is coupled to a locator and the ultrasonic head may also be moved manually. Together with the image data, the image position must be recorded and saved in this case. Although a standard sound head may be used, the system is rather unwieldy and requires excessive time for collecting the image data. Due to the fact that the distance between individual two-dimensional images is not identical, sectional levels may overlap, thus causing inferior displays.
Other drawbacks of both methods can be seen in the fact that in general on the one hand, the ultrasonic heads may only be operated on a unit specifically provided for this purpose, as otherwise determination of the location will be lost. On the other, no real-time representation is available due to sectional levels being scanned in sequence.
For cardiologic scans, display of a heart reaction may simply be useless after 6 to 7 seconds under specific conditions. In many cases it is of great importance to consultants in particular that changes are scanned immediately. Consequently scanning efforts are focused at a real-time representation.
It is the task of the present invention to generate a device, realising a high image quality and fast data collection and 3D visualisation in real-time.
Another system and method for generating ultrasonic images is prior art from US-5,111,823. In this system, the transducers of an array are transmitting a send signal to the medium, followed by all echo signals of all reflectors being simultaneously scanned from the medium. The volume of the echo signals consequently increases the more receivers are available and the longer the send signals are. Shortening the send signals will increase the bandwidth and improve correlation results, with the send signals acquiring excessively high frequencies, although these are of a low penetration depth. Over large distances, low frequencies only are reflected, which may not provide any useful correlation results. In addition, an array of transducers will generate a complex side lobe noise, due to side lobes being generated at the required aperture, which may also generate echo signals.
A synthetic aperture method is used for processing the complete volume data, which requires very fast computers having vast memory capacities. Although data are collected in real-time, these cannot be displayed by any means within an acceptable period of time.
The problem is solved by means of a system for 3D real-time sonography according to Claim 1 and a method according to Claim 6. The system comprises an ultrasonic head, a signal processor and visualization device, in which the ultrasonic head comprises a minimum of one transmitter and separately from this a minimum of three receivers, the position of which in relation to the transmitters is known, processing of signals from a signal generator for generating a send signal of an arbitrary modulating function, a correlator on each receiver, each connected to the signal generator, a computing unit for determination of the paths of the send signal over the reflective structure to the receivers on each correlator and a computing unit for the calculation of space co-ordinates of the reflective structure, connected to each computing unit for the determination of the paths of the send signal over the reflective structure to the receivers.
It is fully left to the user to decide where the transmitters) and receivers will be arranged on the medium containing the structure to be examined. This allows finding the best "viewing and lighting angle" of a structure inside a medium. When a minimum of three receivers are arranged on one plane and defined as "sight windows", i.e. the reference plane for all transmitters, a shadow-free image of a structure imbedded in a medium may be generated. It is also left to the user to decide how many transmitters and receivers will be arranged. However, for a three-dimensional image, a minimum of one transmitter and three receivers or three transmitters and one receiver will be required.
The transmitters and receivers may, for instance, be arranged to allow the send signal to hit the structure from the side or in that the medium is located between the transmitters and the receivers. The echo signals are then mainly influenced by the absorption capacity of the medium and the structure to be examined. When more than one transmitter is available, echo signals may be received, reflecting both the absorption and reflection capacity of a structure.
The problem is solved by means of a system for 3D real-time sonography according to Claim 1 and a method according to Claim 6. The system comprises an ultrasonic head, a signal processor and visualization device, in which the ultrasonic head comprises a minimum of one transmitter and separately from this a minimum of three receivers, the position of which in relation to the transmitters is known, processing of signals from a signal generator for generating a send signal of an arbitrary modulating function, a correlator on each receiver, each connected to the signal generator, a computing unit for determination of the paths of the send signal over the reflective structure to the receivers on each correlator and a computing unit for the calculation of space co-ordinates of the reflective structure, connected to each computing unit for the determination of the paths of the send signal over the reflective structure to the receivers.
It is fully left to the user to decide where the transmitters) and receivers will be arranged on the medium containing the structure to be examined. This allows finding the best "viewing and lighting angle" of a structure inside a medium. When a minimum of three receivers are arranged on one plane and defined as "sight windows", i.e. the reference plane for all transmitters, a shadow-free image of a structure imbedded in a medium may be generated. It is also left to the user to decide how many transmitters and receivers will be arranged. However, for a three-dimensional image, a minimum of one transmitter and three receivers or three transmitters and one receiver will be required.
The transmitters and receivers may, for instance, be arranged to allow the send signal to hit the structure from the side or in that the medium is located between the transmitters and the receivers. The echo signals are then mainly influenced by the absorption capacity of the medium and the structure to be examined. When more than one transmitter is available, echo signals may be received, reflecting both the absorption and reflection capacity of a structure.
In another embodiment of the system for 3D real-time sonography, an A/D
converter is arranged between one or several transmitters and the correlator as well as each receiver and the correlator. This allows digitalisation of the send and receive signals, followed by digital processing.
The system for 3D real-time sonography may include a memory downstream from the AID converter for the send signal, saving the digitalised send signals, in order to make them available again in the same shape for any subsequent ultrasonic transmitting procedure. For this purpose, the memory is connected directly to the generator or via a control unit. The control unit may be designed for manual or automatic triggering.
In addition, the invention comprises a method for 3D real-time sonography, in which ultrasonic signals are transmitted by an ultrasonic head into a medium and echo signals are received and displayed on a visualization device, with this method comprising the following steps:
a) Transmission of a send signal having an arbitrary modulating function by a minimum of one transmitter into a medium;
b) Receiving echo signals from a minimum of three receivers, separately arranged in relation to the transmitters and the position of which to the transmitters is known;
c) correlation of echo signals to the send signal for determination of the path lengths of the send signal from the transmitter to each receiver over a reflective structure in a medium, by detecting the patterns of the send signal in the echo signals;
d) Calculation of space co-ordinates and the reflection and/or absorption capacity of the reflective structure from the results of step c) by means of triangulation and e) display of space co-ordinates and the reflection and/or absorption capacity of the reflective structure on a visualization device.
Should more than one transmitter be used in this method, which are to transmit a send signal of the identical modulating function, in order to allow the receivers to differentiate between "viewing directions", individual transmitters must send the send signals in sequence. When send signals of different modulating functions are transmitted, the transmitters may simultaneously transmit their send signal into the medium.
Due to the separation of the receivers from the transmitter, the send signal is not limited in length. Its duration is only limited downward by the modulating function.
When the system comprises A/D converters downstream from the transmitter and the receivers, the send signal and the echo signals are digitalised prior to correlation.
For correlation between the send signal and the echo signals, in which the reflection points of the send signal are to be found, any prior art method may be used. A simple correlation/convolution or a pulse compression method may be applied, a wavelet method may be used or neural networks may be applied, in order to assist in finding the pattern of the send signal in the echo signals.
The intensity-modulated dots of images, i.e. 3D B-mode image, is displayed on the visualization device, subject to free choice of the co-ordinates. Reflection points may be defined in the computing unit in Cartesian co-ordinates, cylindrical co-ordinates, polar co-ordinates or the like.
The method for 3D real-time sonography will also be expanded when send signals are filed in a memory, followed by being used for the control of the signal generator for the regeneration of identical send signals. This step of the method is of great benefit when a body is scanned initially by a send signal, having a freely adjustable modulating function, until reflections are displayed on the monitor. The send signal of the same modulating function may then be accessed randomly from the memory for repeats.
Each of the echo signals is a superposition of the reflection signals from the volume. The echo signals are separately processed in each channel, followed by being correlated with the corresponding send signal. For calculation of the position of the reflection points, the path from the transmitter through the reflection points to individual receivers must initially be determined. For this purpose, the echo signals are correlated to the send signal. At specific points in time, the signal shows a specific signal pattern when a reflected signal is received. Ellipses and/or ellipsoids will be found from these points in time, defined by the _7_ path of the send signal to the reflection points and on to the receivers ,with the ellipses or ellipsoids, respectively, focusing on the transmitters and receivers. The intersections of individual ellipsoids corresponding to the receivers result in the space co-ordinates of the reflection points.
The decisive difference versus the conventional method is due to the fact that individual layers of reflections are not scanned in sequence but that all data are collected simultaneously. This fact is a major prerequisite for real-time sonography, which has not been realised in the past. It is therefore possible for the first time to even scan moving structures in real-time, for instance the movement of heart valves, as a 3D
image in slow motion, thus offering very important tools to the cardiologist and gynaecologist.
Depending on the physical situation, penetration depth is reduced with increasing frequency. This basic trade-off is associated in principle with the examination of live material. This trade-off may be reduced when ultrasonic energy is increased, which is, however, only acceptable to a limited degree in live material. The solution of the invention offers an opportunity for achieving a very high resolution concomitant with a large penetration depth. Ultrasonic scans may therefore be performed subject to very low energies and consequently minimum stress to the patient. In the conventional method, the maximum resolution is 1.5 mm for a penetration depth of approx. 20 cm. In the method according to the invention, for instance, at a penetration depth of 30 cm, the resolution is constantly 0.1 mm. Resolution may be increased to 0.05 mm.
An arbitrarily modulated ultrasonic signal (for instance also including a rising or falling frequency sequence - based on the method of echolocation used by bats and dolphins) is transmitted. Data of the entire image volume may be transmitted by one of these signals, with the time required for this being a matter of microseconds depending on the depth of the structure in the medium. Echo signals are scanned in "parallel" and consequently much more time-efficiently than in conventional methods.
Another decisive benefit lies in the fact that display of any structures scanned includes a much smaller noise portion. This makes display much clearer, i.e. a consultant's profound experience is no longer decisive for assessing a sonogram. Owing to the fact that in the _g_ first place signal processing and no image processing- as in conventional methods - takes place the entire data content remains intact. Falsification of the display may therefore be ruled out.
Another benefit, in particular for the examination of live tissue, is the facility of using very low energies for scanning a body. This eliminates the decisive disadvantage of any other past methods, due to achieving improvements in resolution simply by increasing the energy level.
The invention will be explained in detail in the following by means of some figures. In individual drawings, the same reference numbers are referring to identical or similar components.
Fig. 1 shows a block diagram of a system for 3D real-time sonography according to the present invention, based on analogue send signals and corresponding to analogue processing of echo signals;
Fig. 2 shows a block diagram of a system for 3D real-time sonography according to the present invention based on digital processing of echo signals;
Figs. 3A and 3B show a specific send signal named "Chirp" and the corresponding echo signal;
Fig. 4 shows an echo signal of the "Chirp" according to Fig 3, reflected by 3 points;
Fig. 5 shows the correlation result of the "Chirp" according to Fig 3 with an echo signal according to Fig 4;
Fig. 6 shows an echo signal having an SNR of 0 dB;
Fig. 7 shows the correlation result of the echo signal according to Fig. 6 with a send signal according to Fig 3; and Fig. 8 demonstrates the method of triangulation based on three receivers for the calculation of space co-ordinates of a reflection point.
Fig. 1 is the block diagram of a system for 3D real-time sonography according to the invention, in which an analogue send signal is generated and echo signals are consequently subject to analogue processing. The generator 1 generates a carrier frequency, modulated in a modulator 2 subject to an arbitrary function. This send signal is transmitted in this embodiment by a transmitter 3 into a medium or body. In this embodiment, the echoes reflected by any structures within the medium are received by three receivers 4. Therefore, for the determination of reflections initially each of the echo signals must be correlated to the send signal in the correlator 5. In this process, each reflection point in the medium is "detected" by individual receivers 4 at another point in time. For this purpose, the modulator 2 is connected to the correlator 5 of each individual receiver 4. Similar patterns in the send signal and each echo signal must be interpreted as a reflection. For instance, detection of these patterns may also be effected by displacing the send signal on the echo signals until agreement is obtained, equal to reference to a reflection. The result of this correlation shows a set of reflections, each representing the total path of the send signal from the transmitter 3 to the reflection point and back to the corresponding receiver 4. This means that the transmitter 3 and the corresponding receiver 4 are in the two focal points of an ellipsoid. The space co-ordinates of these reflection points are calculated in the downstream computing unit 6 by a simple triangulation method. The starting point is that the points that are located at the same distance from the transmitter 3 to the reflection point and back to the receiver 4 are located on the same ellipsoid. The point of intersection of the three ellipsoids specifies the space co-ordinates on which the actual reflection occurred. Fig. 8 clearly shows this situation.
The space co-ordinates are then displayed on the visualization display 7 at the appropriate intensity.
Fig. 2 shows the block diagram of a system for 3D real-time sonography according to the invention, but subject to digital data processing. The generator 1 generates a carrier frequency, modulated in a modulator 2 having an arbitrary function. In this embodiment, the send signal is also transmitted by a transmitter 3 into any medium. As a variation from the first embodiment, an A/D converter 8 is arranged between the modulator 2 and each correlator 5 as well as each receiver 4 and associated correlators 5. In addition, an additional memory 9 is arranged in this embodiment between the A/D converter 8 for the modulated signal and the generator 1, saving the transmitted send signal for later repetition. For this purpose, the memory 9 is coupled with the generator 1.
Fig. 3 shows a send signal of an increasing frequency. This is a Chirp having a frequency of f",;~ to fmax. The wave length of this signal decreases from left to right in the drawing.
The entire data content of the range of interest is simultaneously scanned by one send signal only, followed by parallel processing in a fast computer.
Each of the receivers 4 receives the echo signals of the send signal described in Fig. 3. Fig.
4 shows such an echo signal, received by a receiver 4, which has been reflected in three points. In this figure, the echo signal is not superposed by any noise portions. Only the first reflection point can be seen in the figure. Other reflection points can no longer be detected due to superpositions of the echoes in this diagram. Only after correlation of the echo signals with the send signal, other reflection points will appear.
Fig. 5 shows the correlation result of the "Chirp", according to Fig 3, with the echo signal according to Fig 4. A sample feature of this amplitude proportional to the reflection and/or absorption capacity is generated exactly at the reflection points.
Fig. 6 shows the run of a highly noisy echo signal, the SNR of which is 0 dB.
In this echo signal, no reflections can be seen. After correlation to the send signal, the signal characteristic according to Fig 7 results. This signal is comparable with the signal of Fig 5, with the reflection points being clearly noticeable. This explains a major benefit of the method according to the invention. Even based on an SNR of -20 dB, reflection points were still clearly detectable in the echo signals. Only at a very unfavourable SNR, no evaluation was possible.
When using the system according to the invention and the method according to the invention for medical diagnostics, the features of the medium are of eminent significance.
Due to its complex nature, it is very difficult to derive a simplified model, describing the frequency dependence of ultrasonic attenuation. In general, a linear association is assumed between attenuation, the signal path length and frequency. When G represents attenuation (in dB), f frequency (in MHz), z depth (in cm) in the medium and (3 the attenuation constant (in dB/[MHz cm]) of the medium, the following will be obtained:
G=2(3fz.
Higher frequencies are therefore more attenuated than lower frequencies. Table 1 shows the attenuation constants for various types of tissues:
Table 1 Tissue Attenuation constant (dB/[MHz cm]) Liver 0.6 - 0.9 Kidneys 0.8 - 1.0 Gall bladder 0.5 - 1.0 Fat 1.0 - 2.0 Blood 0.17 - 0.24 Plasma 0.01 Bones 16.0 - 23.0 Table 2 lists the attenuation (in dB) depending on the depth in tissue and the frequency for tissue subject to an attenuation constant of 0.7 dB/[MHz cm]).
Table 2 z(cm) 30 25 20 1 S 10 5 f(MHz) (dB) 3,5 147 122.5 98 73,5 49 24.5 7,5 315 262.5 210 157,5 105 52.5 As it is possible, as shown in Figs. 4 to 7, to still detect the positions of reflection points even if the SNR is unfavourable, very good results may be achieved at relatively low frequencies and low sonic energies, irrespective of the attenuation in tissue, according to tables l and 2.
Fig. 8 shows the method of triangulation based on three receivers for the calculation of space co-ordinates of a reflection point. It explains how it is possible to calculate the space co-ordinates of reflection points by the transmission of an arbitrarily modulated signal.
After having determined the distances of reflection points in the correlator between each transmitter 3 and the reflection points up to the corresponding receivers 4, ellipsoids may be defined, in the focal points of which the transmitter 3 and/or the receiver 4 are arranged. Each intersection of all three ellipsoids marks the space co-ordinates of a reflection point. Should one transmitter and more than three receivers be available, more than three ellipsoids will be available for each reflection point, all intersecting in one point, defining the space co-ordinates of the corresponding reflection point.
converter is arranged between one or several transmitters and the correlator as well as each receiver and the correlator. This allows digitalisation of the send and receive signals, followed by digital processing.
The system for 3D real-time sonography may include a memory downstream from the AID converter for the send signal, saving the digitalised send signals, in order to make them available again in the same shape for any subsequent ultrasonic transmitting procedure. For this purpose, the memory is connected directly to the generator or via a control unit. The control unit may be designed for manual or automatic triggering.
In addition, the invention comprises a method for 3D real-time sonography, in which ultrasonic signals are transmitted by an ultrasonic head into a medium and echo signals are received and displayed on a visualization device, with this method comprising the following steps:
a) Transmission of a send signal having an arbitrary modulating function by a minimum of one transmitter into a medium;
b) Receiving echo signals from a minimum of three receivers, separately arranged in relation to the transmitters and the position of which to the transmitters is known;
c) correlation of echo signals to the send signal for determination of the path lengths of the send signal from the transmitter to each receiver over a reflective structure in a medium, by detecting the patterns of the send signal in the echo signals;
d) Calculation of space co-ordinates and the reflection and/or absorption capacity of the reflective structure from the results of step c) by means of triangulation and e) display of space co-ordinates and the reflection and/or absorption capacity of the reflective structure on a visualization device.
Should more than one transmitter be used in this method, which are to transmit a send signal of the identical modulating function, in order to allow the receivers to differentiate between "viewing directions", individual transmitters must send the send signals in sequence. When send signals of different modulating functions are transmitted, the transmitters may simultaneously transmit their send signal into the medium.
Due to the separation of the receivers from the transmitter, the send signal is not limited in length. Its duration is only limited downward by the modulating function.
When the system comprises A/D converters downstream from the transmitter and the receivers, the send signal and the echo signals are digitalised prior to correlation.
For correlation between the send signal and the echo signals, in which the reflection points of the send signal are to be found, any prior art method may be used. A simple correlation/convolution or a pulse compression method may be applied, a wavelet method may be used or neural networks may be applied, in order to assist in finding the pattern of the send signal in the echo signals.
The intensity-modulated dots of images, i.e. 3D B-mode image, is displayed on the visualization device, subject to free choice of the co-ordinates. Reflection points may be defined in the computing unit in Cartesian co-ordinates, cylindrical co-ordinates, polar co-ordinates or the like.
The method for 3D real-time sonography will also be expanded when send signals are filed in a memory, followed by being used for the control of the signal generator for the regeneration of identical send signals. This step of the method is of great benefit when a body is scanned initially by a send signal, having a freely adjustable modulating function, until reflections are displayed on the monitor. The send signal of the same modulating function may then be accessed randomly from the memory for repeats.
Each of the echo signals is a superposition of the reflection signals from the volume. The echo signals are separately processed in each channel, followed by being correlated with the corresponding send signal. For calculation of the position of the reflection points, the path from the transmitter through the reflection points to individual receivers must initially be determined. For this purpose, the echo signals are correlated to the send signal. At specific points in time, the signal shows a specific signal pattern when a reflected signal is received. Ellipses and/or ellipsoids will be found from these points in time, defined by the _7_ path of the send signal to the reflection points and on to the receivers ,with the ellipses or ellipsoids, respectively, focusing on the transmitters and receivers. The intersections of individual ellipsoids corresponding to the receivers result in the space co-ordinates of the reflection points.
The decisive difference versus the conventional method is due to the fact that individual layers of reflections are not scanned in sequence but that all data are collected simultaneously. This fact is a major prerequisite for real-time sonography, which has not been realised in the past. It is therefore possible for the first time to even scan moving structures in real-time, for instance the movement of heart valves, as a 3D
image in slow motion, thus offering very important tools to the cardiologist and gynaecologist.
Depending on the physical situation, penetration depth is reduced with increasing frequency. This basic trade-off is associated in principle with the examination of live material. This trade-off may be reduced when ultrasonic energy is increased, which is, however, only acceptable to a limited degree in live material. The solution of the invention offers an opportunity for achieving a very high resolution concomitant with a large penetration depth. Ultrasonic scans may therefore be performed subject to very low energies and consequently minimum stress to the patient. In the conventional method, the maximum resolution is 1.5 mm for a penetration depth of approx. 20 cm. In the method according to the invention, for instance, at a penetration depth of 30 cm, the resolution is constantly 0.1 mm. Resolution may be increased to 0.05 mm.
An arbitrarily modulated ultrasonic signal (for instance also including a rising or falling frequency sequence - based on the method of echolocation used by bats and dolphins) is transmitted. Data of the entire image volume may be transmitted by one of these signals, with the time required for this being a matter of microseconds depending on the depth of the structure in the medium. Echo signals are scanned in "parallel" and consequently much more time-efficiently than in conventional methods.
Another decisive benefit lies in the fact that display of any structures scanned includes a much smaller noise portion. This makes display much clearer, i.e. a consultant's profound experience is no longer decisive for assessing a sonogram. Owing to the fact that in the _g_ first place signal processing and no image processing- as in conventional methods - takes place the entire data content remains intact. Falsification of the display may therefore be ruled out.
Another benefit, in particular for the examination of live tissue, is the facility of using very low energies for scanning a body. This eliminates the decisive disadvantage of any other past methods, due to achieving improvements in resolution simply by increasing the energy level.
The invention will be explained in detail in the following by means of some figures. In individual drawings, the same reference numbers are referring to identical or similar components.
Fig. 1 shows a block diagram of a system for 3D real-time sonography according to the present invention, based on analogue send signals and corresponding to analogue processing of echo signals;
Fig. 2 shows a block diagram of a system for 3D real-time sonography according to the present invention based on digital processing of echo signals;
Figs. 3A and 3B show a specific send signal named "Chirp" and the corresponding echo signal;
Fig. 4 shows an echo signal of the "Chirp" according to Fig 3, reflected by 3 points;
Fig. 5 shows the correlation result of the "Chirp" according to Fig 3 with an echo signal according to Fig 4;
Fig. 6 shows an echo signal having an SNR of 0 dB;
Fig. 7 shows the correlation result of the echo signal according to Fig. 6 with a send signal according to Fig 3; and Fig. 8 demonstrates the method of triangulation based on three receivers for the calculation of space co-ordinates of a reflection point.
Fig. 1 is the block diagram of a system for 3D real-time sonography according to the invention, in which an analogue send signal is generated and echo signals are consequently subject to analogue processing. The generator 1 generates a carrier frequency, modulated in a modulator 2 subject to an arbitrary function. This send signal is transmitted in this embodiment by a transmitter 3 into a medium or body. In this embodiment, the echoes reflected by any structures within the medium are received by three receivers 4. Therefore, for the determination of reflections initially each of the echo signals must be correlated to the send signal in the correlator 5. In this process, each reflection point in the medium is "detected" by individual receivers 4 at another point in time. For this purpose, the modulator 2 is connected to the correlator 5 of each individual receiver 4. Similar patterns in the send signal and each echo signal must be interpreted as a reflection. For instance, detection of these patterns may also be effected by displacing the send signal on the echo signals until agreement is obtained, equal to reference to a reflection. The result of this correlation shows a set of reflections, each representing the total path of the send signal from the transmitter 3 to the reflection point and back to the corresponding receiver 4. This means that the transmitter 3 and the corresponding receiver 4 are in the two focal points of an ellipsoid. The space co-ordinates of these reflection points are calculated in the downstream computing unit 6 by a simple triangulation method. The starting point is that the points that are located at the same distance from the transmitter 3 to the reflection point and back to the receiver 4 are located on the same ellipsoid. The point of intersection of the three ellipsoids specifies the space co-ordinates on which the actual reflection occurred. Fig. 8 clearly shows this situation.
The space co-ordinates are then displayed on the visualization display 7 at the appropriate intensity.
Fig. 2 shows the block diagram of a system for 3D real-time sonography according to the invention, but subject to digital data processing. The generator 1 generates a carrier frequency, modulated in a modulator 2 having an arbitrary function. In this embodiment, the send signal is also transmitted by a transmitter 3 into any medium. As a variation from the first embodiment, an A/D converter 8 is arranged between the modulator 2 and each correlator 5 as well as each receiver 4 and associated correlators 5. In addition, an additional memory 9 is arranged in this embodiment between the A/D converter 8 for the modulated signal and the generator 1, saving the transmitted send signal for later repetition. For this purpose, the memory 9 is coupled with the generator 1.
Fig. 3 shows a send signal of an increasing frequency. This is a Chirp having a frequency of f",;~ to fmax. The wave length of this signal decreases from left to right in the drawing.
The entire data content of the range of interest is simultaneously scanned by one send signal only, followed by parallel processing in a fast computer.
Each of the receivers 4 receives the echo signals of the send signal described in Fig. 3. Fig.
4 shows such an echo signal, received by a receiver 4, which has been reflected in three points. In this figure, the echo signal is not superposed by any noise portions. Only the first reflection point can be seen in the figure. Other reflection points can no longer be detected due to superpositions of the echoes in this diagram. Only after correlation of the echo signals with the send signal, other reflection points will appear.
Fig. 5 shows the correlation result of the "Chirp", according to Fig 3, with the echo signal according to Fig 4. A sample feature of this amplitude proportional to the reflection and/or absorption capacity is generated exactly at the reflection points.
Fig. 6 shows the run of a highly noisy echo signal, the SNR of which is 0 dB.
In this echo signal, no reflections can be seen. After correlation to the send signal, the signal characteristic according to Fig 7 results. This signal is comparable with the signal of Fig 5, with the reflection points being clearly noticeable. This explains a major benefit of the method according to the invention. Even based on an SNR of -20 dB, reflection points were still clearly detectable in the echo signals. Only at a very unfavourable SNR, no evaluation was possible.
When using the system according to the invention and the method according to the invention for medical diagnostics, the features of the medium are of eminent significance.
Due to its complex nature, it is very difficult to derive a simplified model, describing the frequency dependence of ultrasonic attenuation. In general, a linear association is assumed between attenuation, the signal path length and frequency. When G represents attenuation (in dB), f frequency (in MHz), z depth (in cm) in the medium and (3 the attenuation constant (in dB/[MHz cm]) of the medium, the following will be obtained:
G=2(3fz.
Higher frequencies are therefore more attenuated than lower frequencies. Table 1 shows the attenuation constants for various types of tissues:
Table 1 Tissue Attenuation constant (dB/[MHz cm]) Liver 0.6 - 0.9 Kidneys 0.8 - 1.0 Gall bladder 0.5 - 1.0 Fat 1.0 - 2.0 Blood 0.17 - 0.24 Plasma 0.01 Bones 16.0 - 23.0 Table 2 lists the attenuation (in dB) depending on the depth in tissue and the frequency for tissue subject to an attenuation constant of 0.7 dB/[MHz cm]).
Table 2 z(cm) 30 25 20 1 S 10 5 f(MHz) (dB) 3,5 147 122.5 98 73,5 49 24.5 7,5 315 262.5 210 157,5 105 52.5 As it is possible, as shown in Figs. 4 to 7, to still detect the positions of reflection points even if the SNR is unfavourable, very good results may be achieved at relatively low frequencies and low sonic energies, irrespective of the attenuation in tissue, according to tables l and 2.
Fig. 8 shows the method of triangulation based on three receivers for the calculation of space co-ordinates of a reflection point. It explains how it is possible to calculate the space co-ordinates of reflection points by the transmission of an arbitrarily modulated signal.
After having determined the distances of reflection points in the correlator between each transmitter 3 and the reflection points up to the corresponding receivers 4, ellipsoids may be defined, in the focal points of which the transmitter 3 and/or the receiver 4 are arranged. Each intersection of all three ellipsoids marks the space co-ordinates of a reflection point. Should one transmitter and more than three receivers be available, more than three ellipsoids will be available for each reflection point, all intersecting in one point, defining the space co-ordinates of the corresponding reflection point.
Claims (8)
1. A system for 3D real-time sonography, comprising an ultrasonic head, a signal processor and visualization device, characterised in that the ultrasonic head comprises a minimum of one transmitter (3) and separately from this a minimum of three receivers (4), the positions of which in relation to the transmitters (3) are known, that the signal processor comprises a signal generator (1) for generating a send signal having an arbitrary modulating function, a correlator (5) on each receiver (4), each connected to the signal generator (1), a first computing unit for the determination of the path lengths of send signals over the reflective structure to the receivers (4) on each correlator (5) and a second computing unit for the calculation of the space co-ordinates of the reflective structure (6), to which each computing unit for the determination of the path lengths of the send signal over the reflective structure is connected to the receivers.
2. A system for 3D real-time sonography according to Claim 1, characterised in that the receivers (4) are arranged on one plane.
3. A system for 3D real-time sonography according to one of Claims 1 or 2, characterised in that an A/D converter (8) is arranged between individual transmitters (3) and each correlator (5) as well as between each receiver (4) and the corresponding correlators (5).
4. A system for 3D real-time sonography according to Claim 3, characterised in that a memory (9) for the send signal is arranged downstream from the A/D converter (8), which is coupled to the signal generator (1).
5. A system for 3D real-time sonography according to Claim 4, characterised in that the memory (9) is connected to the signal generator (1) by a control unit and the control unit may be triggered manually or automatically.
6. A method for 3D real-time sonography comprising an ultrasonic head, a signal processor and a visualization device, in which ultrasonic signals are transmitted into a medium and the echoes are displayed on the monitor after signal processing, characterised by the following steps:
a) Transmission of a send signal of an arbitrary modulating function into a medium by a minimum of one transmitter;
b) Receiving of echo signals from a minimum of three receivers, separately arranged to a minimum of one transmitter, the positions of which in relation to the transmitter are known;
c) Correlation of echo signals with the send signal for determination of the path lengths of the send signal from the transmitter over a reflective structure in the medium to the corresponding receivers in a first computing unit, by finding the patterns of the send signal in the echo signals;
d) calculation of space co-ordinates and of the reflection and/or absorption capacity of the reflective structure based on the results of step c) by means of triangulation in a second computing unit; and e) display of space co-ordinates and of the reflection and/or absorption capacity of the reflective structure on a visualization device.
a) Transmission of a send signal of an arbitrary modulating function into a medium by a minimum of one transmitter;
b) Receiving of echo signals from a minimum of three receivers, separately arranged to a minimum of one transmitter, the positions of which in relation to the transmitter are known;
c) Correlation of echo signals with the send signal for determination of the path lengths of the send signal from the transmitter over a reflective structure in the medium to the corresponding receivers in a first computing unit, by finding the patterns of the send signal in the echo signals;
d) calculation of space co-ordinates and of the reflection and/or absorption capacity of the reflective structure based on the results of step c) by means of triangulation in a second computing unit; and e) display of space co-ordinates and of the reflection and/or absorption capacity of the reflective structure on a visualization device.
7. A method for 3D real-time sonography according to Claim 6, characterised in that in an arrangement comprising more than one transmitter, individual transmitters are transmitting the same send signals in sequence.
8. A method for 3D real-time sonography according to Claim 6, characterised in that in an arrangement comprising more than one transmitter, individual transmitters are simultaneously transmitting send signals having different modulating functions.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE1999115583 DE19915583A1 (en) | 1999-04-07 | 1999-04-07 | Device and method for 3D real-time sonography |
| DE19915583.6 | 1999-04-07 | ||
| PCT/EP2000/002436 WO2000062091A1 (en) | 1999-04-07 | 2000-03-20 | Device and method for real-time 3d sonography |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2366534A1 true CA2366534A1 (en) | 2000-10-19 |
Family
ID=7903720
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002366534A Abandoned CA2366534A1 (en) | 1999-04-07 | 2000-03-20 | Device and method for real-time 3d sonography |
Country Status (6)
| Country | Link |
|---|---|
| EP (1) | EP1166148A1 (en) |
| JP (1) | JP2002540910A (en) |
| CN (1) | CN1354834A (en) |
| CA (1) | CA2366534A1 (en) |
| DE (1) | DE19915583A1 (en) |
| WO (1) | WO2000062091A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2014186904A1 (en) * | 2013-05-24 | 2014-11-27 | The Governing Council Of The University Of Toronto | Ultrasonic signal processing for bone sonography |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE10027828A1 (en) * | 2000-06-05 | 2001-12-06 | Sonem Gmbh | Active ultrasonic display device for identifying objects in a medium uses a transmitter to connect to a modulator, a generator and a signal-conditioning device with a receiver also linked to a signal-conditioning device. |
| DE10112034A1 (en) * | 2001-03-14 | 2002-10-02 | Sonem Gmbh | Arrangement for image reproduction for computer tomographs with ultrasound |
| JP2008253663A (en) * | 2007-04-09 | 2008-10-23 | Toshiba Corp | Ultrasonic diagnostic device and its control processing program |
| CN101292883B (en) | 2007-04-23 | 2012-07-04 | 深圳迈瑞生物医疗电子股份有限公司 | Ultrasonic three-dimensional quick imaging method and apparatus |
| JP7346249B2 (en) * | 2019-11-05 | 2023-09-19 | 株式会社ニチゾウテック | Ultrasonic flaw detection inspection equipment and reflection source identification method |
| CN112326790B (en) * | 2020-10-28 | 2022-11-29 | 武汉中岩科技股份有限公司 | Ultrasonic pore-forming detection probe device and detection method thereof |
| CN115604647B (en) * | 2022-11-28 | 2023-03-10 | 北京天图万境科技有限公司 | Method and device for sensing panorama by ultrasonic waves |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5235857A (en) * | 1986-05-02 | 1993-08-17 | Forrest Anderson | Real time 3D imaging device using filtered ellipsoidal backprojection with extended transmitters |
| US4855961A (en) * | 1986-07-31 | 1989-08-08 | Woods Hole Oceanographic Institute | Imaging apparatus |
| US5111823A (en) * | 1989-04-20 | 1992-05-12 | National Fertility Institute | Apparatus and method for generating echographic images |
| DE4331020A1 (en) * | 1992-12-08 | 1994-06-09 | Siemens Ag | Ultrasonic medical investigation and treatment appts. with three=dimension display - uses focussing piezoelectric ultrasonic source with two or three dimensional receiving transducer array |
| US5842991A (en) * | 1997-02-20 | 1998-12-01 | Barabash; Leonid S. | Ultrasound transducer with extended field of view |
| GB9714735D0 (en) * | 1997-07-15 | 1997-11-05 | Roke Manor Research | Acoustic location system |
-
1999
- 1999-04-07 DE DE1999115583 patent/DE19915583A1/en not_active Withdrawn
-
2000
- 2000-03-20 CA CA002366534A patent/CA2366534A1/en not_active Abandoned
- 2000-03-20 WO PCT/EP2000/002436 patent/WO2000062091A1/en not_active Application Discontinuation
- 2000-03-20 JP JP2000611102A patent/JP2002540910A/en active Pending
- 2000-03-20 CN CN 00808609 patent/CN1354834A/en active Pending
- 2000-03-20 EP EP00918814A patent/EP1166148A1/en not_active Withdrawn
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2014186904A1 (en) * | 2013-05-24 | 2014-11-27 | The Governing Council Of The University Of Toronto | Ultrasonic signal processing for bone sonography |
Also Published As
| Publication number | Publication date |
|---|---|
| DE19915583A1 (en) | 2000-10-12 |
| JP2002540910A (en) | 2002-12-03 |
| CN1354834A (en) | 2002-06-19 |
| EP1166148A1 (en) | 2002-01-02 |
| WO2000062091A1 (en) | 2000-10-19 |
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