JPS6333860B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention can be used to create a visual image of a cross section of an object in various tests of materials/objects and clinical diagnostic tests. In particular, the ultrasonic imaging device includes a transducer device consisting of a fixed array of adjacent transducer elements, the transducer device comprising a plurality of transducer element groups consisting of adjacent transducer elements. are sequentially and cyclically selected to generate an ultrasound beam in response to application of a pulsed electrical transmitter signal to the transducer element and direct the ultrasound beam substantially within the scan plane into the object under test. The present invention relates to an ultrasonic imaging device for creating a cross-sectional image, which is configured to transmit to and/or receive reflected echoes from an object to be examined, and generate electrical echo signals in response to the received echoes.

"Prior Art" Conventionally, a method of mechanically moving an ultrasound transducer has been used to form an ultrasound image (more specifically, a cross-sectional image). This has some drawbacks. That is, if the transducer were to be moved by hand, the scanning process would be very long and dependent on the skill level of the operator.
If the transducer is powered by a motor, a relatively heavy water tank is usually required. Additionally, the extra travel distance through the aquarium results in a reduction in the maximum possible image frequency.

To eliminate these drawbacks, ultrasound imaging devices using electronic scanning have been developed. In this method the ultrasound beam is shifted linearly in time.

For cardiac diagnosis, sector scanning imaging, in which the beam rotates, provides better results than linear scanning imaging, in which the beam moves in a straight line. . The reason for this is that the acoustic window for obtaining images of the heart is limited by the sternum and lungs and is small, measuring only about 2 x 7 cm.
Furthermore, the ribs also make it difficult to image the heart. Fan-scan transducer devices are most suitable because they require only a few square centimeters of aperture. Linear scan transducer devices typically have lengths of 10 cm or more and therefore cannot be used efficiently.

Known sector scan transducer devices include:
Some operate on the "phased array" principle, while others rely on mechanical contact scanning.
Regarding the former, the second European
J. Kisslo, OT. V. Ramm, published on pages 67-74 of the Proceedings of the Congress on Ultrasonics in Medicine.
“A phase array” by FLThurstone
The study was published in a paper entitled ``Usal ultrasound system for cardioeum imaging''. Regarding the latter, A. Shaw, JSPaton, NLGregory and D.
“A real time Z-” by J. Wheatley
dimensional ultrasonic scanner for clinical
It is described in a paper titled ``Use''.

In the known fan-scanning transducer device, which operates on the "phased array" principle,
Angular deflection of the ultrasound beam is obtained by emitting ultrasound pulses with a certain time delay from different segments (transducer elements) of a segmented transducer. These time delays determine not only the angular deflection but also the focusing of the ultrasound beam. Similarly, signals received by different transducer elements need to be delayed by an amount that depends on the angular deflection and the convergence of the reception characteristics.

PROBLEM SOLVED BY THE INVENTION The major drawback of phased array sector scan transducer systems is their complexity. To function successfully, the transducer of such a device requires at least 64 elements. If we want to deflect the beam in 128 directions, we need to provide 128 different time delays for each of the 64 elements, so a total of 128 x 64 = 8192 time delays. Although several methods have been used to implement these, the complexity of such systems remains high.

Another drawback of phased array sector scan transducer devices is the segmented transducer itself. Experience has shown that such transducers do not behave according to the simple model of many linear radiators, and there are many side effects that adversely affect surface wave propagation.

On the other hand, in known mechanical fan-scan transducer systems, the beam is formed by a simple monolithic transducer, and beam deflection is accomplished by mechanically rotating the transducer. In this case, the complexity of the electronic system and the problems with the transducer itself are minimized, but it has the following disadvantages as a mechanically operated device.

(1) Mechanical inertia. This limits the upper limit of imaging speed. Mechanical inertia also makes it impossible to obtain simultaneous real-time images or high-resolution time-motion records. In this mode of operation, possible with electronically scanned transducer devices, the ultrasound beam is timed several times during the formation of one image.
This mode of operation is not possible with mechanically scanning transducers due to mechanical inertia.

(2) Mechanical wear requires adjustment or replacement of mechanical parts. This is non-working time.

(3) Even if the moving parts are light and balanced, there is some vibration that can cause discomfort to the physician and/or patient. This can also disrupt image movement.

It is therefore an object of the present invention to provide an ultrasound imaging device in which the drawbacks of the above-mentioned known fan-scan transducer devices can be eliminated.

"Technical Means for Solving the Problems" In order to solve the above-mentioned problems in the prior art and achieve the objective, the present invention provides the following technical means (A ),
It is characterized by adopting and combining (B), (C), and (D) as essential constituent elements. (A) having a transducer device including a fixed, elongated array of adjacent transducer elements, wherein a plurality of transducer element groups of adjacent transducer elements are sequentially and cyclically arranged; generating an ultrasound beam and transmitting the ultrasound beam into the specimen substantially in the scan plane in response to application of a pulsed electrical transmitter signal to the transducer element; (or) receiving ultrasonic echoes from the object under test and generating electrical echo signals in response to the received echoes: (B) the transducer device has an arc shape in the scanning plane; generating a circulating ultrasound beam and/or fanning the ultrasound transmission region for fan scanning in the ultrasound transmission region by cyclic selection of a plurality of transducer elements; (C) A leading path enclosed within a closed enclosure is provided between the ultrasonic transmission region and the ultrasonic transmissive region; (D) the transformer a second transducer element array (i.e., a first phased array) substantially facing the transducer elements of the transducer device and having its center located at the center of the arc of the transducer device; a third transducer array (i.e., a second phased array) having transducer elements each electrically connected to the transducer elements of the second array; The second array receives the ultrasound beam generated by the selected transducer element group of the transducer device and transmits a corresponding electrical signal to the third array. 3 arrays emit corresponding ultrasonic beams;
receiving an electrical signal corresponding to an echo wave received by the array and transmitting a corresponding ultrasound beam to the selected transducer element group of the transducer device; .

In addition, in the gist of the present invention, the most important constituent elements characterizing the present invention are the above-mentioned technical means (D) and.

Expressed simply from another point of view, the ultrasonic imaging device according to the present invention uses an arc-shaped transducer device, and the transducer elements in this transducer device are linearly shaped. It can be said that a fan-shaped scan is obtained by electronically driving the transducer device in a manner known per se for implementing a linear scan.

"Embodiments" Hereinafter, with reference to the accompanying drawings, embodiments of the ultrasonic imaging device according to the present invention will be described in relation to the prior art that is the premise of the present invention, and the principles, specific configurations, and operations thereof will be explained. etc. will be revealed.

FIG. 1 and FIG. 2 schematically illustrate scan lines of fan-shaped scanning and linear scanning, respectively, in different prior art techniques.

As will be described later, the main components of the transducer device used in the embodiments of the present invention are elongated transducers in which the individual elements (segments) are arranged not in a straight line but on a circular arc. , whose scannable area itself is not essentially different from that of the prior art as shown in FIG. The same applies to Figures 1 and 2, but the transducer is assumed to be above the drawing in Figure 3,
If the upper half of the scannable area is used as the advance path area and only the lower half is used for imaging, an apparatus with beam rotation as shown in FIG. 1 is obtained.
FIG. 4 shows a complete soundhead including an electronically scanned arc transducer device in the prior art. In FIG. 4, an arcuate piezoelectric ceramic transducer 302 is mounted on the top of a housing 301, and individual electrode segments 303 are mounted thereon. Ultrasonic waves reflected upward disappear within the absorber 304. The lower part of the housing 301 is lined with a sound absorbing material 305 and filled with an ultrasound transmission medium 306 forming a leading path. The bottom portion of the soundhead is closed by a diaphragm 307. The diaphragm 307 is mounted at the center of the arc formed by the transducer 302, ie at the narrowest point in the scannable area (see FIG. 3). To eliminate mutually interfering multiple reflections between the diaphragm 307 and the transducer 302 from the image, the transit time between the transducer and the diaphragm is adjusted to the distance between the diaphragm and the farthest object being imaged. must be exactly the same as the travel time between. This means that when using water in the lead path, the radius of the transducer arc must be exactly equal to the maximum penetration (imaging) depth. This is because the human body and water have almost the same speed of sound (approximately 1500 m/sec).

The beam shape can be optimized as follows. If all transducer elements in a group of transducer elements (defined by their individual electrode segments) are activated and turned on at the same time and with the same phase, the beam will be centered at the center of the arc, i.e. The velocity is collected at the diaphragm 307. Then, as the penetration depth increases, the beam becomes progressively wider and the lateral resolution of the device becomes progressively worse. Significant improvements in lateral resolution can be obtained by focusing the beam loosely at about two-thirds of the maximum imaging depth as measured from diaphragm 307 rather than at the center of the arc. Such loose focusing may cause transmission and/or
This is accomplished by providing appropriate phase shifts to the individual transducer elements during reception. This phase shift has the opposite sign (ie, phase lag) than for a linear scan transducer device. The reason for this will be explained in the case of transmission with reference to FIGS. 5 and 6. As shown in FIG. 5, in the prior art using a linear scanning transducer device, when loose focusing is required, instead of a flat wavefront as shown in solid lines, a cylindrical wavefront as shown in dotted lines is created. Become the crest of a wave. Therefore, the farther away from the beam axis (the center of the selected transducer elements) the transmitter signal needs to have a correspondingly larger phase advance. On the other hand, in the case of the prior art using an arc-shaped transducer device, as shown in FIG. The head is broken as shown by the small dotted line to cause a gentle convergence. Therefore, the further away from the beam axis, the
It is necessary to gradually delay the phase of the transmitter signal. The same thing can be said about reception. The shape of the beam depends on the particular shape of the transducer elements, but can be further refined by apodization.
For example, outer elements reduce the amplitude of the transmitter signal and/or echo signal.
The number of different phases used for loose focusing is also important in improving the beam shape.

FIG. 7 is a block circuit diagram of a preferred embodiment of an ultrasound imaging device according to the present invention. In this example, a group of seven transducer elements is used for transmitting and receiving. The block circuit diagram of FIG. 7 shows an arc-shaped transducer device 40 consisting of a fixed array of adjacent transducer elements 41, a timing generator 131, a timing signal 132 outputted from the timing generator 131, and a transducer device 40. Mituta signal generator 13
3 and line 1 from transmitter signal generator 133.
35 through element selection and drive switch 138
an element counter and decoder 136 connected to the timing generator 131 and controlling the element selection and drive switch 138 through line 137; and an echo signal 14 sent from the transducer group.
2, an echo signal receiver 143, a combined echo signal 144 at the output of the echo signal receiver 143, a time-sensing amplifier 145, and a detector 14.
6, a signal processor 147, an output signal 148 of the signal processor 147, and an X deflection generator 151.
, a deflection signal 154 provided by an X deflection generator 151, and a Y stage function generator 152.
A stage function signal 155 sent out from a Y stage function generator 152 and three inputs X, Y, Z
An oscilloscope 156 having an oscilloscope 156 is shown.

A timing generator 131 generates periodic timing pulses 132 to trigger the transmission of the ultrasound signal and also generates the necessary synchronization signals. Transmitter signal generator 133 generates four electrical transmitter pulse signals 121-124, as shown in FIG. signal 12
2, 123, 124 are signals 12 with a phase of 0°
1, it has a phase delay corresponding to the carrier signal phase of -θ ₁ , -θ ₂ , and -θ ₃ . These transmitter signals are sent out on line 134. In the element select and drive switch 138, transmitter signals are applied to seven supply lines 139. The transmitter signal on those lines is −
It has phases of θ ₃ , −θ ₂ , −θ ₁ , 0°, −θ ₁ , −θ ₂ , and −θ ₃ . Element counter and decoder 136 selects the desired seven through element selection and drive switch 138.
drives each element for transmission or reception.
After each pulse, the 7-element group is shifted by one element. At the same time, the transmitter signal is cyclically interchanged with the different phases on the supply line 139, so that each element obtains a corresponding transmitter signal with the correct phase. Echo signals 142 reach an echo signal receiver 143 from the seven switched elements. Therefore, these signals are given different delays, weighted with different weighting coefficients, and then added together.
The output signal 144 of the echo signal receiver 143 is
Time-sensing amplifier 14 to compensate for attenuation in the tissue under test
Pass through 5. The signal is then rectified by a detector 146,
The signal is applied through a signal processor 147 to the Z input of an oscilloscope 156. Signal processor 1
47 compresses the dynamic range of the signal sent out from detector 146.

The X-deflection generator 151 generates a voltage proportional to the elapsed time since the last pulse was sent. Y stage function generator 152 generates a voltage proportional to the position of the center axis of the transducer elements being switched on.

Transmitter signal generator 13 shown in FIG.
3 is shown in detail in FIG. The timing pulse 132 (see FIG. 9) triggers the pulsed high-frequency generator 161 and outputs the output signal 1 of the generator 161.
62 (pulsed carrier signal - see Figure 9) is the phase
It is delayed in tap delay line 163 to obtain four signals with 0°, -θ ₁ , -θ ₂ and -θ ₃ . These signals are weighted with corresponding weighting factors in weighting devices 164-167.

FIG. 10 shows details of the echo signal receiver 143 shown in FIG. 7. echo signal 14
2 are weighted with corresponding weighting coefficients in weighting devices 171-177. They are phase shifter 1
81-185 and adder 1
86.

Element selection and drive switch 1 shown in FIG.
The basic principle of 38 preferred examples will be explained with reference to FIG. Although the device shown in FIG. 7 uses seven element groups, for the sake of simplicity, the principle will be explained here for the case of four element groups. 11th
The switching diagram shown can be used to trigger and shift the four element groups. The inner two elements in each four element group (e.g. elements 32 and 33 in the group) are triggered by the transmitter signal 41, and the outer two elements (e.g. elements 31 and 34 in the group) are triggered by the transmitter signal 41. Triggered by signal 42. A switch system 191 connects the transducer element to four supply lines 192.
-195 in a circular manner. These four lines pass through the switch system 196 to two supply lines 197.
and 198. These two supply lines 197
and 198 are supplied with transmitter signals 41 and 42. In FIG. 11, the switch positions for two successive groups of transducer elements are shown in solid and dotted lines. A description of the device controlling switch system 191 is unnecessary. In switch system 196, to drive a new group, each switch (e.g. 213) is placed in the same position as the switch above (e.g. 212) was placed to drive the group before it. . The switch 211 at the top is the switch 214 at the bottom
is placed in the position previously occupied. If the electronic design of the switch system is appropriate, the same switch can be used for transmitting and receiving. If it is necessary to use separate electronic switches for transmitting and receiving, another circuit similar to that of FIG. 11 can be provided with separate supply lines for transmitting and receiving.

Earlier, we discussed the beam shape in the scanning direction. However, it is also advantageous to have a loose focusing in a second direction perpendicular to the first direction, ie the scanning direction. In this case as well, it is desirable that the focal point be placed at the same position as in the first direction, that is, at 2/3 of the maximum imaging depth. Loose focusing in the second direction is achieved using a suitably curved transducer or by an acoustic lens placed in front of the transducer. Of course, this loose focusing in the second direction can also be done electronically, allowing for greater device complexity. According to numerical calculations,
Additional apodization cannot improve the beam shape any further. However, if loose focusing in the second direction is not performed, apodization is advantageous due to its simplicity of construction. This additional apodization can be obtained, for example, by using transducer elements that taper outwardly (see FIG. 14).

Electronically, arcuate transducer devices have all the advantages of linear scan transducer devices. A disadvantage of arcuate transducer systems is that they require a water lead path, which makes the sound head heavier and more difficult to handle, and the maximum image frequency is lower than that of a transducer system without a lead path. This is half the case. This advance path can be shortened by substituting water with a substance that has a lower sound speed than water. The speed of sound in many organic liquids and in many silicone rubbers is approximately 1000 m/sec. This means that the lead path can be shortened by as much as one-third and the volume of the sound head can be halved at least. However, the reflections are amplified and the sound beam is refracted at the interface between the pre-path region and the tissue being examined.

Another miniaturization of the soundhead is obtained by using the arc transducer device not as a soundhead but as a signal processing device in the case of a "phased array." Such a device is shown in FIG. A transducer element group 401 of an arc-shaped transducer 402 consisting of a large number of elements transmits an ultrasound beam 403, and the beam is transmitted to a transducer arranged parallel to the elements of the arc-shaped transducer 402 at the center of the arc. The first "phased array" with elements
404. The acoustic field is detected by the first phased array 404 at the elements therein according to its phase, and the first phased array 40
4 is electrically connected to a second "phased array" 405. Second phased
Array 405, which constitutes the actual soundhead, reproduces the sound field at the first phased array location and emits a corresponding ultrasound beam 406. Of course, this device can also be operated in the opposite direction, making it suitable for transmitting and receiving. 2
It is advantageous to provide a transmitting and receiving intermediate amplifier for each element between the two phased arrays. For simplicity, these amplifiers are
Not shown in the figure.

It should be noted that the sonic field emitted by the second phased array 405 need not be the same as the sonic field detected by the first phased array 404. The phase and amplitude of the signals from each element can be varied by the intermediate amplifiers described above. Also, the second phased array 405 can be shaped differently than the first phased array 404 to change the acoustic field. This provides an additional means of improving the focusing of the acoustic beam and thereby increasing the lateral resolution of the device.

The advantage of this device compared to conventional "phased array" devices is that the acoustic beam can be angularly deflected using simple means. Strictly speaking, this advantage applies primarily to operation as a receiver. While angular deflection in transmission is relatively easy to achieve with digital equipment, reception traditionally requires complex delay lines and switches. Therefore, during transmission, the phased array is operated directly and the arc transducer is used only as a receiver signal processing device.

Finally, a simple example of an arcuate transducer device in a cardiac application is shown in Figures 13 and 1.
This will be explained with reference to FIG. The boundary conditions were as follows.

Frequency...2MHz Maximum penetration depth...15cm Scanning angle...50-60° Number of elements...64 Phase used...0°, 90° Leading path medium...Focusing only in the water scanning direction These boundary conditions Below, optimization was performed with reference to the sound wave field calculated by a computer. As a result, the following dimension was obtained.

As shown in FIG. 13, transducer device 302 forms part of a cylinder. Its radius R is 15cm, width B is 2cm, and the length of the arc is angle θ.
= 17.6cm corresponding to 67.2°. The transducer was segmented into 64 elements with a width S = 2.75 mm. Twelve elements were used simultaneously for transmitting and receiving. One such group is shown in FIG.
The ends of each element 411 were formed into circular arcs. This shape was chosen to obtain the desired apodization and beam shape improvement. During transmission and reception, the signals from the outer six elements were delayed by 900° relative to the signals from the inner six elements. This resulted in focusing approximately 25 cm from the transducer. At the same time, during transmission and reception, the amplitudes of the signals of the outer six elements were multiplied by a weighting factor of 0.5, and the amplitudes of the signals of the inner six elements were multiplied by a weighting factor of 1.

With this transducer, at least 4
A resolution of mm was obtained in the scanning plane over the entire effective area. The resolution in the direction perpendicular to the scanning direction is 1.5 times worse due to the lack of focusing in this direction.
As already mentioned, improved resolution in this direction can also be obtained by applying additional focusing.

``Effects of the Invention'' As becomes clear through the above description, the present invention solves the problems of the prior art and effectively achieves its objectives, as well as the above-mentioned conventional method using a mechanical fan-scanning transducer device. The disadvantages of the technique are completely eliminated, and the sector scan can be obtained by electronic means, which is considerably less complex and less expensive than the sector scan of conventional phased array systems. In addition to this, the present invention also provides the following significant effects based on the above-mentioned technical means (D), which is its most important feature, being made an essential component. . That is, firstly, it becomes possible to use a substance such as silicone rubber, which has a lower sound speed than water, as a medium for the leading path in an ultrasonic imaging device using an arcuate transducer device.
The lead path is shortened and thus a smaller and lighter arcuate transducer device can be achieved. Second, by using the arc-shaped transducer device not as a sound head but as a signal processing device in a phased array system, the overall device can be further miniaturized. Third, because the first phased array (i.e., the second transducer array) can be a second phased array (i.e., the third transducer array) with a different shape, the By forming a sound field according to the object to be examined, it is possible to improve the flux characteristics of the ultrasonic beam, and by using simple additional means, it is possible to improve the lateral resolution of the entire device. can. Fourth, the angular deflection of the ultrasound beam can be easily obtained by relatively simple means.

[Brief explanation of the drawing]

The accompanying drawings are for the purpose of contributing to a better understanding of the present invention, and after explaining the outline of the prior art that is the premise of the present invention using Figs. The specific structure and operation of the invention will be clarified. That is, FIG. 1 is a schematic diagram of an area that can be scanned by sector scanning in the prior art. FIG. 2 is a schematic diagram of an area that can be scanned by linear scanning in the prior art. FIG. 3 is a schematic diagram of the area that can be scanned with an arcuate transducer device (not shown) in the prior art. FIG. 4 is a diagram illustrating a sound head with an arcuate transducer device in the prior art. 5 and 6 are both diagrams showing cylindrical wavefronts for explaining phase shifts suitable for beam shape improvement in the prior art, and FIG. 5 shows a linear scanning transducer device for comparison. FIG. 6 shows the case of the conventional technique using an arcuate transducer device as used in the present invention. Figure 7 shows
1 is a block diagram illustrating an electronic circuit used in an embodiment of an ultrasound imaging device according to the present invention. FIG. FIG. 8 is a block diagram showing details of the transmitter signal generator in the electronic circuit shown in FIG. FIG. 9 is a waveform diagram of a timing pulse 132 generated by the timing generator 131 in the electronic circuit shown in FIG. 7 and a pulsed sine wave 162 extracted from the timing pulse.
FIG. 10 is a block diagram showing details of the echo signal receiver 143 in the electronic circuit shown in FIG.
FIG. 11 illustrates the principle of a preferred embodiment of the element selection drive switch 138 in the electronic circuit shown in FIG. FIG. 12 is a diagram showing the arrangement structure of the main parts of an embodiment of the ultrasonic imaging apparatus of the present invention. FIGS. 13 and 14 are diagrams for explaining the shape and dimensions of the arcuate transducer device of the embodiment shown in FIG. 12 according to the present invention.

Claims (1)

[Scope of Claims] 1. A transducer device including a fixed and elongated array of adjacent transducer elements, wherein a plurality of groups of adjacent transducer elements are arranged in sequence. cyclically selected generating and transmitting an ultrasound beam into the specimen substantially in the scan plane in response to application of pulsed electrical transmitter signals to the transducer elements; , and/or
The transducer device receives ultrasonic echoes from a test object and generates electrical echo signals in response to the received echoes; the transducer device has an arc shape in the scanning plane and includes a plurality of transducer devices. induced by generating a circulating ultrasound beam and/or performing a fan scan in the ultrasound transmission region for fan scanning in the ultrasound transmission region by cyclic selection of user elements; for receiving cross-sectional images; and wherein a leading path contained within a closed enclosure is provided between the transducer device and the ultrasonic transmission region within the object to be examined. an ultrasonic imaging device, in particular: a second transducer element array substantially facing the transducer elements of the transducer device and having its center located at the center of an arc of the transducer device; and a third transducer array having transducer elements each electrically connected to the transducer elements of the second array, the second array having transducer elements electrically connected to the transducer elements of the second array. The third array receives the ultrasound beam generated by the selected transducer element group of the user device and transmits the corresponding electrical signal to the third array, so that the third array generates the ultrasound beam corresponding to the ultrasound beam. and receiving an electrical signal corresponding to an echo wave received by the third array and emitting a corresponding ultrasound beam to the selected transducer of the transducer device. The ultrasonic imaging device is configured to transmit data to a group of user elements. 2. In the device according to claim 1,
In order to loosely focus the ultrasonic beam generated by each transducer element group, the transmitter signals applied to the transducer elements and/or the echo signals obtained from the transducer elements include The center of the transducer element and the transducer element group are arranged so that the signals for the transducer elements that are far from the center of the user element group have a phase lag with respect to the signal for the transducer element in the center. The ultrasonic imaging device is characterized in that a time shift determined as a function of the distance between the two is given to each other. 3. In the device according to claim 1,
Each transducer element of the transducer device has a radiating surface that becomes progressively narrower away from the longitudinal axis of the transducer device in a direction perpendicular to the scanning direction. The ultrasonic imaging device. 4. In the device according to claim 3,
The ultrasonic imaging device as described above, characterized in that the ends of the individual transducer elements are formed into arcs. 5. In the device according to claim 1,
The ultrasonic imaging device characterized in that the preceding path between the transducer device and the object to be examined uses a medium in which the speed of sound is lower than that in water. 6. In the device according to claim 1,
characterized in that the distance between the transducer device and the focal point of the ultrasound field produced thereby is approximately equal to the length of the preceding path plus about 2/3 of the maximum imaging depth. The ultrasonic imaging device.