EP1324701A1

EP1324701A1 - Ultrasonic tomograph

Info

Publication number: EP1324701A1
Application number: EP01986583A
Authority: EP
Inventors: Rainer Stotzka; Werner Alois Kaiser; Hartmut Gemmeke
Original assignee: Forschungszentrum Karlsruhe GmbH
Current assignee: Forschungszentrum Karlsruhe GmbH
Priority date: 2000-10-11
Filing date: 2001-10-10
Publication date: 2003-07-09
Also published as: JP2004520094A; US6786868B2; US20030158481A1; WO2002030288A1; DE10050232A1

Abstract

The invention relates to a high resolution ultrasonic tomograph operating according to transmission, diffusion and impulse-echo methods, comprising an open-topped container with ultra sonic transducers arranged in a fixed manner on the entire surface of the walls, said container containing a coupling medium, in addition to comprising a computer assisted control unit and evaluating unit with a working memory. The aim of the invention is to further develop the high resolution ultrasonic tomograph in such a way as to enable a distinct improvement of temporal resolution when reconstructing three dimensional images, even in real time, without reducing the precision of the image. According to the invention, the control unit and evaluating unit is connected to the ultrasonic transducers in such a manner that the ultrasonic signal emitted from at least one ultrasonic transducer is an ultrasonic impulse which is received by all the other ultrasonic transducers in parallel and amplified, filtered and digitalised as an electric signal and stored in the working memory as a data set.

Description

Ultrafast tomograph

The invention relates to an ultrasound tomograph according to the transmission, scattering and impulse-echo method working for tissue examinations of extremities, in particular the female breast and the male reproductive organ.

Ultrasound examination is becoming increasingly important in medical technology. On the one hand, ultrasound, in contrast to X-ray fluoroscopy, does not damage the tissue to be examined. On the other hand, tissue types can be differentiated, the other imaging methods, e.g. B. in X-ray, leave only a very low contrast.

A medical ultrasound device essentially consists of a transducer with a number of ultrasound transducers and a control and evaluation unit, which transmits the control pulses for the ultrasound transducers and receives the measurement signals received as electrical signals, amplifies them and, during the measurement, real-time images on one Reconstructed screen. The complexity of such a reconstruction in real time not only limits the number of individual ultrasound transducers in medical ultrasound devices, but also to a large extent correction options during the reconstruction. In addition, the transducers are usually not stationary, but are guided manually. These facts particularly limit the possibilities for contrast agent examinations in ultrasound mammography, which require a high local and temporal resolution for the reconstruction. An additional limitation is the lack of reproducibility.

US Pat. No. 4,478,083 describes a system for ultrasound mammography with the aid of the pulse-echo method, in which the female breast is inserted and positioned in a cylindrical container from above in a suitable manner. Are on the entire cylindrical wall surface of this container uniformly arranged ultrasound transducer, from which it can be assumed that the main emission direction of each ultrasound transducer is oriented perpendicularly from the container wall into the interior of the container (see column 5, last paragraph). To build up a three-dimensional image of the breast to be examined, an evaluation unit is described, which is connected in such a way that the areas of the breast to be examined are defined and scanned one after the other, with only one transducer or one transducer group of ultrasonic transducers for each pulse-echo process the transmission of the ultrasound pulse and the reception of the return echo is selected via an electronic switch and the return echo is filtered out by setting time windows.

Furthermore, DE 28 27 423 A1 describes a device for determining the internal structure of a body with the aid of sound beams, in which the body is introduced into a container filled with a coupling medium and is sonicated in it using the ultrasound transmission method. In this case, one or more ultrasound transmitters send a sound beam through the body to at least one ultrasound transducer as a receiver, the reception signals are electronically processed in an evaluation unit, stored, and the distribution of the sound refractive index and the absorption coefficient are then determined. In parallel to this, a model of the body is built up in the evaluation unit using a grid of points, which is compared with the empirical measurement values, can be optimized by iterative repetition of the sound measurement and can thus be further processed into individual cross-sectional images. In a proposed embodiment, the sound transducers in the container are arranged in a cylindrical shape in a matrix. For a measurement, a limited number of transducers, both as a transmitter and as a receiver, must be activated by an electronic switch, with a subsequent amplifier for each active receiver, possibly with additional electronic stages (see page 24, paragraph 2) , With this arrangement in addition to transmission, scatter and echo components

Ultrasonic pulses can be received, but are not used for the evaluation.

Similarly, in the ultrasound device for determining three-dimensional images described in US Pat. No. 5,673,697, a body is introduced into a container with ultrasound transducers fixedly arranged on the entire wall and sonicated with at least one of these ultrasound transducers with an ultrasound frequency between 1 and 5 MHz. All other transducers can be used as receivers that can be switched one after the other via an electronic switch, the signals of which are successively amplified and recorded for further processing. The runtime, phase and amplitude of the received ultrasound pulses are used for further processing. A three-dimensional image of the body is generated from the reflection properties and sound velocities determined from this. However, the system is not suitable for the reconstruction of fast processes, since the non-simultaneous recording of all receivers significantly limits the time resolution. As a result, there is no indication in this document of a possibility of reconstructing temporal processes in the body in real time.

The object of the invention is to further develop a high-resolution ultrasound tomograph in accordance with the last-mentioned prior art in such a way that a considerable improvement in the temporal resolution in the reconstruction of the three-dimensional image is made possible even in real time without compromising on image accuracy.

The object is achieved by a high-resolution ultrasound tomograph according to claim 1. Preferred embodiments of the ultrasound tomograph are the subject of the dependent claims.

According to the invention, the pulses generated by one or a group of ultrasonic transducers are used by everyone, including those as Transmitter-switched ultrasonic transducers, recorded simultaneously and separately as measurement signals for each ultrasonic transducer

Pass through an amplifier, the necessary filters and an A / D converter can be stored in a working memory. So on the one hand, you can use just one

Create an entire data record of simultaneous data using the ultrasonic pulse, on the other hand by immediately repeating the

Measuring process with other selected ultrasonic transducers than

Transmitter for the impulse, d. H. from a changed perspective, generate further data records in the shortest possible time intervals, which can also be correlated with one another due to the short repetition sequence with tolerance of small time errors.

For example, in the context of an ultrasound-assisted mammography, dynamic contrast agent examinations with high temporal and local resolution can be reconstructed and evaluated using a three-dimensional representation of the female breast.

The high-resolution ultrasound tomograph according to the invention is explained in more detail below with reference to figures. Show it:

1 shows the overall structure of the high-resolution ultrasound tomograph for ultrasound-assisted mammography,

2 schematically shows the connection of any ultrasound transducer 2 of the high-resolution ultrasound tomograph to the computer 10 of the control and evaluation unit 8,

3 shows an overview of the individual processing steps which are necessary for the reconstruction of a three-dimensional image.

1 shows an exemplary embodiment of the overall structure of the high-resolution ultrasound tomograph for performing a mammography. It consists of a cylindrical, open-topped container 1, on the entire cylindrical surface of which ultra- sound converter 2 are attached. For the purpose mentioned, the open side of the container is inserted flush into an opening in a patient couch 3, with a breast 4 of the patient 5 lying face down on the patient couch 3 hanging into the container 1 during mammography. For a low-loss transmission of the ultrasound signals from the ultrasound transducers 2 into the breast 4 and back, there is a coupling medium 6 in the container 1, preferably a gel or a liquid, which wets the breast 4 to be examined and the ultrasound transducers 2.

Each of the existing ultrasonic transducers 2 is self-sufficient, for example individually connected via a suitable coaxial line 7 to a computer-aided control and evaluation unit 8 with a working memory. The control and evaluation unit 8 is equipped with an output unit 9, preferably a monitor, for the imaging output of a reconstruction of the breast 4.

2 shows the interconnection of any ultrasonic transducer 2 with the computer 10 of the control and evaluation unit 8. The ultrasonic transducer is connected to the coaxial line 7 at an electronic switch 11, with which the ultrasonic transducer 2 is activated and switchable either as a receiving transducer or as a transmitting transducer is. Switch 11 receives the corresponding switching signal directly from computer 10 via a control line 12.

If the ultrasound transducer 2 is activated as a transmitter transducer, it receives an electrical pulse from a pulse generator 13, which is triggered by a timer 14 in the computer, which is irradiated by the latter as a shock wave in the natural frequency of the ultrasound transducer into the coupling medium.

If the ultrasound transducer 2 is activated as a reception transducer, the received signal is transferred from the switch 11 to an amplifier 15, in which the signal is amplified, filtered and digitized and is forwarded as digital data to the working memory 16 of the computer. All simultaneous data from the ultrasound transducers activated as reception transducers is then stored in the working memory 16 as a data record. The filtering of the signals in the amplifier is preferably used to filter out background noise or interference signals by means of frequency filters and to select the signals, for. B. by setting a time window, the filter properties are transmitted as commands from the computer 10 via a control line 17 to the amplifier 15.

In the case of an ultrasound measurement in a mammography, an ultrasound pulse emitted by the switched-through transmitter transducers is thus received by all active receiver transducers and stored in the form of digital data in a data record in the working memory. The three-dimensional representation of the examined breast is reconstructed on the computer from the individual data of the data sets. A three-dimensional snapshot is generated from a data set.

Local resolution can be optimized by reducing the temporal resolution. If, for example, a snapshot with increased local resolution is required for a diagnosis, different data records from several ultrasound measurements, but which are immediately adjacent to one another in the shortest possible time, can also be used for the reconstruction, using different ultrasound transducers connected through as transmitter transducers, i.e. from a different perspective , However, very rapid phenomena in the breast to be examined can lead to temporal errors in a reconstruction and must be eliminated or corrected if necessary. Large, time-related error effects are not to be expected at realistic repetition frequencies of the ultrasound measurements. For example, given an assumed speed of sound in the coupling medium and in the breast of approx. 1500 m / s and a maximum run length of an ultrasound pulse in the container of 0.50 m, a maximum response is frequency of 2000 ultrasound measurements per second.

Another possibility for a higher local resolution is to separate a certain area in the breast to be examined, in which only the signal curve is evaluated in a reduced time window, i. H. can be recorded as a data record with a correspondingly higher resolution. The coordinates 10 of the region of interest are converted into corresponding control signals to the amplifier 15 in the computer 10.

For the reconstruction of temporal processes, ultrasound measurements are to be repeated at pre-selectable intervals, whereby each data record represents the basis of its own snapshot. Similar to a film projection, the chronological sequence can be visualized by displaying a sequence of reconstructed snapshots.

In detail, a three-dimensional image of the examined breast or another part of the body is reconstructed using the following scheme.

First of all, it is assumed that a sound pulse is radiated into the breast as a partial spherical wave, this is scattered in the breast at various points, for example by refraction, deflection or reflection, and is measured at different receiver positions. The speed of sound is then determined assuming constant speed of sound in the measuring room and taking into account first-order reflections only. All possible positions of the scattering points lie on an ellipse around the transmitter and the receiver, the dimensions of which are determined by the measured sound propagation time from the transmitter via any point on the ellipse to the receiver. For the exact determination of a scattering point, the ellipses from different measurements (same ultrasound pulse) are stacked with different receivers. The intersection points of the ellipses represent the scattering points and are assigned to a pixel with a gray or color level for the reconstruction.

In the case of multiple scattering points, a plurality of ultrasound pulses are also received by a reception transducer, which in turn each generate an ellipse. Otherwise, the ellipses from the largest possible number of simultaneous measurements are also used for the three-dimensional reconstruction of the examined breast and the scatter points determined are assigned to a pixel with a gray or color level. A phase observation of the received ultrasound pulses is suitable for eliminating noise or other disturbances. If the signals are not summed as absolute values, but rather as vectors, noise is averaged out of the result, for example. A further possibility in the case of a reconstruction is the transformation of a received signal in amplitude and phase with the aid of a Hibert transformation into a real and an imaginary signal component, the gray levels being able to be determined by means of coherent addition of the individual signals.

The pixels are then put together for each possible point in the container with the determined gray or color levels to form a reconstructed, three-dimensional image.

The precision of the reconstruction is favored by the following influences:

Both the amplifier and the coupling medium 6 and the breast to be examined can be described as linear systems.

Low variation in sound speed.

The possibility of calculating the absorbency of the breast by calculation and correcting it using the reflection reconstruction method. Description of the scattering centers as Huygen point sources. In practice, the measurement and reconstruction process takes place with the steps described below (cf. FIG. 3). The prerequisite for this is that the breast 4 to be examined is inserted into the vessel 1 and contains a sufficient amount of the coupling medium for the complete wetting of the breast and the transducers.

1. Pre-measurement

During the preliminary measurement, the position of the breast 4 in the vessel 1 is determined with a few measurements, using the reflectivity of the skin in the coupling medium. In a sub-step, the temperature-dependent sound velocity in the coupling medium is then determined via a transit time measurement with a known travel path from the transmitter transducer to the receiving transducer, and in a second sub-step the sound velocity in the breast.

2. Measurement

As described above, the measurement process is carried out several times with a preselected repetition frequency. In this case, the ultrasound transducers 2 installed in the vessel 1 are partly switched through either as a transmitter transducer, but completely as a reception transducer, the aim being to penetrate the ultrasound pulse into the vessel as a partial spherical wave, if possible, by means of a transmitter transducer or a correspondingly controllable transducer group.

3. Logarithmic gain

During the measurements, the measured signals are amplified analog logarithmically to compensate for the difference in amplitude of the received ultrasound pulses due to path-dependent damping. The analog logarithmic amplification makes it possible to limit the resolution during digitization (in the example an 8 bit A / D converter) and thus the memory capacity to be made available for the measurement. 4. Define parameters of the filtering and signal processing. Based on the data of the preliminary measurement, the filter 10 activates corresponding filter functions in the amplifier 15. In particular, this step also includes the definition of the resolution of the three-dimensional reconstruction by selecting the pixel grid and the determination of a sound velocity table linked to this grid for the time correction during the reconstruction. In order to reduce the computing power required for the reconstruction, it is advisable to use a uniform speed of sound for the coupling medium and for the breast. Furthermore, this step contains a determination of the required sampling frequency, which, as described above, can also be increased by reducing the resolution required for the reconstruction if a simultaneous data record is sufficient for the reconstruction of a snapshot.

5. Runtime and phase correction

This step serves to correct runtime and phase errors in the coupling medium due to temperature changes. This is done by stretching or compressing the measured signals.

6. Stacking and amplitude corrected image calculation

Stacking is the elimination of duplicate, identical individual data. For example, the measured transit time of an ultrasound pulse is independent of the direction of propagation, ie the transfer function between two transducers is independent of which of the two transducers is used as a reception transducer and which is used as a transmission transducer. In the case of an amplitude correction, in addition to the rough, attenuation-dependent correction shown in step 3, a finer tuning is carried out with regard to the influence of errors, preferably based on the radiation behavior of the active ultrasound transducers. The three-dimensional image is then reconstructed using the before algorithm described by forming an ellipse pro

Single measurement.

7. Adjustment of color values and resolution

This step reduces the resolution of the reconstructed image to a required level. In addition, after a reconstruction, the color values can be changed for better display.

Reference character list

1 container

2 ultrasonic transducers

3 patient beds

4 chest

5 patients

6 coupling medium

7 coaxial line

8 control and evaluation unit

9 output unit

10 computers

11 Electronic switch

12 control line

13 pulse generator

14 timers

15 amplifiers

16 working memories

17 control line

Claims

Claim:

1. High-resolution ultrasound tomograph according to the transmission, scattering and pulse-echo method for tissue examinations of body parts and in particular the female breast, consisting of an open-topped container into which the body part to be examined is inserted, with the container wall over the entire wall surface Fixed ultrasound transducers, the main radiation direction of which is oriented perpendicularly from the wall surface into the interior of the container, a coupling medium which, when filled in the container, wets the part of the body to be examined and which is used to couple and transmit the ultrasound signals between ultrasound transducers and the extremity to be examined, as well as a computer-assisted control and evaluation unit with working memory, which is connected to the ultrasound transducers in the open container in such a way that a) any number of the ultrasound transducers both as a transmitter and as a receiver via e Electronic switches are selectable, b) the signals received by the selected receivers are amplified, filtered and digitized as electrical signals and stored in the working memory as data, c) the sound propagation times and the individual and the geometric conditions from the data stored in the working memory Sound velocities are determined as well as a computational division of the container volume into numerous areas and suitable correlation of different data sets the sound velocities in the individual areas are calculated, d) with the sound velocities in the individual areas and the amplitude and phase progression of the received signals all possible reflection points in the container be calculated as well e) the signals are summed up as data for the possible reflection points from all measurements for each point in the container, from this a color value corresponding to the height of the sum value is assigned for each point and this is assigned to at least one pixel in the three-dimensional reconstruction depending on the desired resolution, characterized in that f) the ultrasound signals emitted by the transmitters is an ultrasound pulse which is received by all receivers in parallel and is amplified, filtered and digitized as electrical signals and stored in the working memory as a data record.

2. High-resolution ultrasound tomograph according to claim 1, characterized in that the computer-aided control and evaluation unit with working memory is connected to the ultrasound transducers in the open container in such a way that all ultrasound transducers are activated as receivers.

3. High-resolution ultrasound tomograph according to claim 1 or 2, characterized in that the computer-aided control and evaluation unit with working memory is connected to the ultrasound transducers in the open container in such a way that the measurement process is carried out in as short a time sequence as possible with another ultrasound transducer or transducer group is repeated, a data record being generated for each measurement process, wherein if several data records are used for the three-dimensional reconstruction, the data records have a temporal resolution that increases with the repetition frequency.

4. High-resolution ultrasound tomograph according to one of claims 1 to 3, characterized in that the computer-aided control and evaluation unit with working memory is connected to the ultrasound transducers in the open container in such a way that when determining the color values in the Reconstruction using the amplitude and phase of a signal

With the help of a Hibert transformation, a real and an imaginary signal component are transformed and the gray levels are determined by coherent addition of the individual signals.