EP0170072B1 - Phased-array apparatus - Google Patents

Phased-array apparatus Download PDF

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Publication number
EP0170072B1
EP0170072B1 EP85108128A EP85108128A EP0170072B1 EP 0170072 B1 EP0170072 B1 EP 0170072B1 EP 85108128 A EP85108128 A EP 85108128A EP 85108128 A EP85108128 A EP 85108128A EP 0170072 B1 EP0170072 B1 EP 0170072B1
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EP
European Patent Office
Prior art keywords
delay
phased
w16
w1
array
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
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EP85108128A
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German (de)
French (fr)
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EP0170072A1 (en
Inventor
Ulrich Saugeon
Gert Hetzel
Dietmar Dr. Hiller
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Siemens AG
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Siemens AG
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Priority to DE19843425705 priority Critical patent/DE3425705A1/en
Priority to DE3425705 priority
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Publication of EP0170072A1 publication Critical patent/EP0170072A1/en
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Publication of EP0170072B1 publication Critical patent/EP0170072B1/en
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    • GPHYSICS
    • G10MUSICAL INSTRUMENTS; ACOUSTICS
    • G10KSOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K11/00Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/18Methods or devices for transmitting, conducting, or directing sound
    • G10K11/26Sound-focusing or directing, e.g. scanning
    • G10K11/34Sound-focusing or directing, e.g. scanning using electrical steering of transducer arrays, e.g. beam steering
    • G10K11/341Circuits therefor
    • G10K11/346Circuits therefor using phase variation

Description

  • The invention relates to a phased array device for the ultrasound scanning of an object with a number of ultrasound transducer elements, to which delay elements are assigned at least for the reception case.
  • In the case of a phased array device, that is to say an electronic sector scanner, the change in the delay in the signals of the individual ultrasound transducer elements in the case of transmission and reception must be carried out in very small steps in order to avoid errors in the adjustment of the control angle. As a result of the largest control angle of usually ± 45 ° with respect to the normal of the row of converter elements, relatively large delay times are required for large control angles, the length of which also depends strongly on the aperture length selected (length of the active antenna). In order to compensate for the change in resolution with the depth due to the limited depth of focus of the focused aperture, it is expedient to adapt the receiving focus concurrently.
  • The prior art provides for setting the delay times with the aid of LC delay lines which are provided with setting taps. This relatively inexpensive solution is particularly suitable for short delay times, i.e. for non-pivoting scanning devices, e.g. B. for a linear array. With longer delay times, the LC delay lines have a band-limiting effect for higher frequencies. They each represent a low pass, the corner frequency of which can be approximately 5 MHz. At the same time, component tolerances largely affect the accuracy of the overall deceleration. For this reason, LC delay lines for transducer or converter frequencies are generally only used up to approx. 3.5 MHz. This technique is also called "baseband technique".
  • DE-OS 3004689 describes a reception delay system for use in an ultrasound imaging system, in which a variable pre-delay element is connected in series with the transducer and a main delay element in each channel. In practice, the pre-delay elements are mainly used for fine tuning, i.e. to allow a gradual adjustment of the delay steps that normally cannot be performed on the main delay elements. This arrangement makes it possible, in particular, to achieve signal coherence over a relatively large range of possible signal frequencies and different distances between the converter elements. For this purpose, however, this circuit arrangement requires a large number of delay elements.
  • Furthermore, DE-OS 2736310 specifies a delay arrangement in which a small, adjustable delay line is inserted between the transmitters or converters and the taps of a main delay line. These taps on the main delay line are selected such that the array is focused along a desired scan angle or direction. On the other hand, the small delays are changed during a scan in said direction in order to change the focus of the arrangement from the minimum range to the maximum range. Since the selected taps of the main delay line are not switched over in a desired direction during the scanning, the circuit principle only gives sufficiently coherent signals with small apertures.
  • Higher transducer frequencies can be processed using LC delay lines by downmixing to an intermediate frequency below 3.5 MHz. However, downmixing technology requires a constant signal bandwidth and transmission pulse length for the individual converter signals. However, the temporal transmit pulse length should be changed in the interest of good resolution when transitioning to high transducer frequencies, i. H. be reduced.
  • Another possible implementation provides surface wave filter technology or SAW filter technology (see, for example, Ultrasonics, Vol. 17, pp. 225-229, Sept. 1979). For this purpose, it is necessary to mix the received signal of the individual ultrasound transducer element upwards in order to get into the high frequency band of 20-50 MHz required in SAW technology. After the summation of the individual received signals of the phased array, it is then necessary to mix down again. Disadvantages of the SAW technology are the fact that up-mixers have to be used in each channel, which means a considerable outlay, and the difficulty in achieving a sufficiently fine gradation of the delay times in the SAW filters.
  • Up and down mixes associated with a phased array device are e.g. B. from Fig. 11 of DE-PS 2854134 known. A digital delay technique in a phased array device is described in EP-PS 0027618, in particular in FIGS. 1 and 2.
  • When designing a phased array device, the following aspects must also be taken into account:
    • Assuming, for example, in a medical examination a center frequency of the reception spectrum of f s = 3.5 MHz and theoretically considering a bandwidth Δf = f s (2λ-PuIs), the maximum frequency obtained is f smax = f s + Δf / 2 = 1.5 f s = 5.25 MHz. According to the well-known Shannon sampling theorem, this results in a sampling frequency for the individual ultrasound transducer element of f a > 2 f smax = 3 f s = 10.5 MHz. This sampling frequency f a is therefore the minimum frequency in order to be able to reconstruct the individual signal of a converter element.
  • For the quantization of the phase, ie a sufficient accuracy of the time delay between rule two adjacent transducer elements, one sample with at least 1/8 of the wavelength is required. This results in a quantized phase shift within the wavelength λ of 360 ° / 8 = 45 ° or (± 22.5 °). With a center frequency f s = 3.5 MHz, a time delay of 35.7 nsec is obtained, ie ± 17.9 nsec. This phase or time accuracy requires a sampling frequency f a > 28 MHz if the signal is to be digitally processed (EP-PS 0027618). This high sampling frequency f a nowadays requires the use of ECL modules and leads to a relatively expensive phased array device.
  • One way out of this speed problem is quadrature technology (cf. DE-PS 2854134, Fig. 8), in which two delay channels are used, the signals of which are phase-shifted by 90 °. Here the minimum sampling frequency is fg = 10.5 MHz. This allows the use of energy-saving techniques (e.g. HCMOS, Low Power Schottky). Quadrature technology, however, requires a relatively high level of effort, since two channels per converter element are required for signal processing.
  • The aim of the invention is to create a phased array device which enables a high degree of accuracy in the adjustment of the control angle and yet only requires a comparatively small outlay.
  • According to the invention, this object is achieved according to a first basic embodiment according to patent claim 1. It is therefore possible to use several adjacent channels, e.g. B. 4 to summarize for signal processing.
  • According to the invention, this object is achieved according to a second basic embodiment according to patent claim 5.
  • It is considered an advantage of the invention that the respective control angle can be set very precisely because of the use of components with fixed component-specific delay times (tolerances) and the digital memory, especially some shift registers. There is no fear of the delay drifting even after the phased array device has been used for a long time. As a result of the high accuracy in the setting of the control angle, there is also a high level of accuracy in the focusing and thus a high resolving power. This is of particular interest when using concurrent focusing in the case of reception.
  • Embodiments of the invention are shown in three figures and are explained in more detail below. Show it:
    • 1 shows a first embodiment in which use is made of both an analog and a digital delay;
    • Fig. 2 shows a second embodiment, which is simplified compared to the embodiment of Figure 1; and
    • Fig. 3 shows a third embodiment, which is based on a fully digital delay concept.
  • The phased array device according to FIG. 1, which is used in particular for medical imaging, consists of a large number of individual ultrasound transducer elements E1, E2,... E64, which are used both for the emission and for the reception of ultrasound signals be used. In Figure 1, only the receiving part of the phased array device is shown. In such a device, the received ultrasound signals must be delayed with the high accuracy described above. To avoid antenna grating interference (grating lobes) and to achieve sufficient resolution, the number of ultrasonic transducer elements should be large. In the present case, the number 64 with an element spacing of λ / 2 is a good compromise.
  • In order to keep the effort low, which would result from using a delay concept with the phase accuracy specified above, it is provided according to FIG. 1 that the received ultrasound signals are provided with a short and a long delay. This makes it possible to combine adjacent signal processing channels. As will become clear later, 4 channels are combined in FIG. 1.
  • According to FIG. 1, the device contains a mixed delay technique, namely an analog pre-delay and a digital main delay. So it's a hybrid solution. The analog pre-delay is a fine delay. It takes place in an area labeled X. A total of 64 channels are provided in this area X. The fine deceleration takes place between 0 and 2λ. Area X is followed by area Y, which only comprises 16 channels. In this area Y there are amplifiers that can be controlled as a function of depth. Area Y is followed by area Z, which also comprises 16 channels. There is a long-term delay here.
  • Experiments have shown that medical examinations with an electronic sector scanner require total delay times which are in the range from 6 to 12 µsec. In the present case, based on these values, the fine deceleration in area X assumes a delay of 0 to 600 nsec, and the coarse deceleration in area Z assumes a deceleration between 5.4 and 11.4 jisec.
  • According to FIG. 1, each ultrasound transducer element E1 to E64 is followed by a preamplifier V1 to V64 with a fixed gain. A multiplexer M1 to M64 is in turn connected downstream of these preamplifiers V1 to V64. The respective multiplexer M can be supplied with clock pulses by a control device C, which is indicated by an arrow on the respective block M1 to M64. The multiplexers M1 to M64 are each analog Predelay element T1 to T64 assigned. Its delay time, in particular in the range from 0 to 600 nsec, can be set using the associated multiplexer M1 to M64. The pre-delay elements T1 to T64 can in particular be LC lines with a number of taps, e.g. B. with 16 taps. With such LC lines there is a delay which is precise enough for the purposes at hand.
  • With the help of the multiplexers M1 to M64, the fine deceleration is dynamic, i.e. switchable while receiving each ultrasound line. In this way, dynamic focusing can be achieved.
  • The signal processing of four adjacent ultrasonic elements E1 to E64 is summarized in the present case. For this purpose, the delay elements T1 to T4 are connected to a common summing element S1, for example. Accordingly, z. B. also the delay elements T61 to T64 connected to a common summing element S16. As stated, the fine delay comprises the time period of at least 2λ in order to be able to combine four such neighboring elements. The value 2λ is an empirically found variable. It represents a compromise that can be applied to most ultrasound applicators based on the phased array principle. Instead of four channels, two, six or eight channels could be combined. After the summation of the signals from four adjacent channels in the summers S1 to S16, the combined received signal obtained in this way is amplified depending on the depth with the aid of controllable amplifiers TGC1 to TGC16, in order to then be able to use the A / D converter dynamics.
  • After the amplification in the amplifiers TGC1 to TGC16, there are two implementation options, which are shown separately in FIGS. 1 and 2. According to FIG. 1, the received signal is sampled using the quadrature method, ie in complex form. As a result, the phase accuracy of the entire delay unit remains constant, for. B. λ / 12 if f a q = f a (faq = quadrature method sampling frequency).
  • 1, the output signal of the amplifier TGC1 is fed to a delay element which consists of a memory N1 and two analog-digital converters W1-1 and W1-2 connected upstream of it. A clock frequency f is applied to the first converter W1-1, which is, for example, the sampling frequency f a = 10.5 MHz mentioned at the beginning. The second converter W1-2 is clocked at the same clock frequency, but the clock signal is shifted by 90 ° with respect to that of the first converter W1-1. This is expressed in that the clock frequencies are designated with f (ϕ = 0 °) or f (cp = 90 °). The two converters W1-1, W1-2 break down the received signal into a real and an imaginary part. The converter W1-1 generates the in-phase term or cosine component, while the converter W1-2 provides the quadrature term or sine component. The downstream memory N1 is preferably a shift register. This is e.g. B. scanned in λ / 8 steps, for which purpose it is supplied by the control device C corresponding control pulses.
  • The coarse delay elements, which are connected downstream of the further amplifiers TGC2 to TGC16, are constructed accordingly. There are a total of 16 memories N1 to N16. On the output side, these are jointly connected to an adder A. The memories N1 to N16, in cooperation with the upstream analog-digital converters W1-1 to W16-2, are used for long-term delays. With their help, the pivoting or deflection angle in particular can be set in a phased array device.
  • The output signal of the adder A consists of an imaginary part i and a real part q, so it is complex. From these two parts i and q, the magnitude of the signal can be formed according to the relationship √i 2 + q 2 , which can be displayed on a screen.
  • The embodiment of Figure 2 largely corresponds to that of Figure 1. However, in the present case the second delay elements are different, i.e. more simply constructed. This simplified embodiment thus allows a certain ripple, it being noted that this is irrelevant for the image quality. In contrast to FIG. 1, the combined received signal is not sampled using the quadrature method, but rather in one channel. For this purpose, each channel has a series connection of an analog-digital converter W1 to W16 with a memory N1 to N16 controlled by a control device C. The analog-to-digital converter W1 to W16 is each subjected to a sampling frequency f by the control device C '. This is preferably somewhat higher than the previously stated value of 10.5 MHz. Theoretical studies have shown that the sampling frequency f can be below 20 MHz. The phase accuracy of the digital chain is determined by the sampling frequency f. With a sampling frequency f = 20 MHz, for example, a phase accuracy of X / 5 is obtained.
  • According to the G.F. Manez: "Design of a simplified delayed system for ultrasound phased array imaging" in IEEE Transactions on Sonics and Ultrasonics, Vol. SU-30, No. 6, page 350f, a coarser quantization of the delay is sufficient for the individual delay elements W1, N1 to W16, N16 if the carrier is decelerated sufficiently precisely by a fine delay. This is the case here due to the fine deceleration in area X.
  • At the output of the adder AG connected downstream of the delay elements W1, N1 to W16, N16, an amount automatically results signal s, which corresponds to the value s = V i2 + q2 in Figure 1.
  • FIG. 3 shows a fully digitized implementation of the delay concept for a phased array device, in which the delay is again divided into a fine delay (see area X) and a coarse delay (see area Z). In the exemplary embodiment, 64 channels are again provided in area X of the fine delay, while only 16 processing channels are provided in the subsequent coarse delay area Z.
  • According to FIG. 3, the 64 ultrasound transducer elements E1 to E64 (in the case of exclusively digital implementation of the delay) are each followed by a depth compensation amplifier TV1 to TV64. These depth compensation amplifiers can be regulated and correspond to the amplifiers TGC1 to TGC16 of FIGS. 1 and 2. Thus the received signal of each element E1 to E64 is amplified depending on the depth. It is then digitized using an analog-to-digital converter AD1 to AD64. In the present case, these analog-digital converters AD1 to AD64 are operated at a higher frequency than those in FIGS. 1 and 2, for example at a frequency f of 28 MHz, in order to be able to work with λ / 8. However, such a high frequency means that the components should be designed using ECL technology. It is assumed in the present case that the A / D conversion is carried out with a relatively high sampling frequency f ', which can also be greater than 28 MHz. In deviation from this, it can also be carried out according to the quadrature method, which is not shown in FIG. 3.
  • In order to reduce the expenditure on digital elements, in particular on bus lines, the present purely digital solution is divided into a fine delay using 64 shift registers VL1 to VL64 and a coarse delay using 16 shift registers VR1 to VR16. The shift registers VL1 to VL64 and VR1 to VR16 are, in particular, shift registers with a variable length. For example, each of the shift registers VL1 to VL64 can comprise a total of 16 stages, while each of the shift registers VR1 to VR16 contains four times these 16 stages. In other words, the same basic building blocks can be used in both types of shift registers.
  • The shift registers VL1 to VL64 correspond in their function to a combination of the multiplexers M1 to M64 and the time delay elements T1 to T64 from FIG. 1. The output of four such shift registers, e.g. B. VL1 to VL4, each to adjacent ultrasonic transducer elements, for. B. E1 to E4, are each connected together to a summing element S1 to S16. Instead of a combination of four channels each, a different number, e.g. a number of 8 channels. The delay times of the individual shift registers VL1 to VL64 can be changed under computer control during the reception of an ultrasound line, in particular in order to achieve dynamic focusing. For this purpose, their control inputs are connected to a control device C ".
  • It should therefore be noted that a predetermined number of data channels is also combined here in each case with the aid of summing elements S1 to S16.
  • The outputs of the individual summing elements S1 to S16 are each connected to an addition element AGL via an assigned shift register VR1 to VR16, which bring about the longer of the two delays. This sums up the individual summarized and delayed signals. At its output there is an output signal s' which is high-frequency compared to that of FIGS. 1 and 2. This high-frequency output signal s' corresponds to the amount and can be used for image display. However, the two signal components i and q could also be derived from this high-frequency output signal s'.
  • The embodiment according to FIG. 3 also results in precise setting and control of the delay. Here, too, the swivel can again be effected via the delay elements for the coarse deceleration, which are immediately upstream of the adder AGL. the shift registers VR1 to VR16 can be set.

Claims (9)

1. Phased-array-device for the ultrasonic scanning of an object having a number of ultrasonic transducer elements, with which there are associated delay members at least for the receiving case, having the following features:
the ultrasonic transducer elements (E1 to E64) are connected to first delay members (M1, T1 to M64, T64) for the analog fine delay of the received signals; in each case a given number of first delay members (M1, T1 to M64, T64) for adjacent ultrasonic transducer elements (E1 to E64) are connected with a common summing element (S1 toS6);
the output signals of the summing elements (S1 to S16) are supplied to two delay members (W1-1, W1-2, N1 to W16-1, W16-2, N16; W7, N1 to W16, N16) for the digital coarse delay;
and the output signals emitted from the second delay members (W1-1, W1-2, N1 to W16-1, W16-2, N16; W1, N1 to W16, N16) are supplied to a digital adding element (A; AG), at the output of which there is emitted a summation signal (i, q; s) which is provided for the image representation (Figures 1 and 2).
2. Phased-array-device according to claim 1, characterised in that provided as first delay members there are, in each case, a multiplexer (M1 to M64) and an LC-line (T1 to T64) controlled by the latter (Figures 1 and 2).
3. Phased-array-device according to claim 1 or 2, characterised in that provided as second delay members there is, in each case, a memory (N1 to N16) to which there are previously connected two analog digital transducers (W1-1, W1-2 to W16-1, W16-2) which are controlled with clock signals of given frequency [f(ϕ=0°), f(ϕ=90°)], which are phase-shifted in respect of each other by 90° (Figure 1).
4. Phased-array-device according to claim 1 or 2, characterised in that provided as second delay members, there is, in each case, a memory (N1 to N16), to which there is previously connected an analog digital transducer (W1 to W16) which is controlled with clock signals of given scanning frequency (f≥fa) (Figure 2).
5. Phased-array-device for the ultrasonic scanning of an object having a number of ultrasonic transducer elements, with which there are associated delay members at least for the receiving case, having the following features:
a TGC amplifier (TV1 to TV64) and an analog digital transducer module (AD1 to AD64) are subsequently connected, in each case, to the ultrasonic transducer elements (E1 to E64);
a first delay component (VL1 to VL64) for the digital fine delay of the received signals is subsequently connected, in each case, to the analog digital transducer modules (AD1 to AD64);
in each case, a given number of these delay members (VL1 to VL64) for adjacent ultrasonic transducer elements (E1 to E64) are jointly connected to a summing element (S1 to S16);
and the individual summing elements (S1 to S16) are connected, by way of, in each case, a second delay component (VR1 to VR16), to a common adding element (AGL), the output signals (s' ) of which is provided for the image representation (Figure 3).
6. Phased-array-device according to claim 5, characterised in that the analog digital transducer module (AD1 to AD64) is an analog digital transducer which is scanned with high scanning frequency (f') (Figure 3).
7. Phased-array-device according to claim 5, characterised in that the analog digital transducer module (AD1 to AD64) is a module according to the quadratur method.
8. Phased-array-device according to claim 5, characterised in that the delay component (VL1 to VL64, VR1 to VR16) is a shift register with variable length (Figure 3).
9. Phased-array-device according to one of the claims 1 to 4, characterised in that the fine delay corresponds to at least a time period of 2 λ, where λ is the wavelength of the ultrasound in the scanned object.
EP85108128A 1984-07-12 1985-07-01 Phased-array apparatus Expired EP0170072B1 (en)

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DE19843425705 DE3425705A1 (en) 1984-07-12 1984-07-12 Phased array device
DE3425705 1984-07-12

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AT85108128T AT46783T (en) 1984-07-12 1985-07-01 Phased array device.

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EP0170072A1 EP0170072A1 (en) 1986-02-05
EP0170072B1 true EP0170072B1 (en) 1989-09-27

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EP0170072A1 (en) 1986-02-05
JPH0778492B2 (en) 1995-08-23
AT46783T (en) 1989-10-15
DE3425705A1 (en) 1986-01-16
US4829491A (en) 1989-05-09
JPS6151560A (en) 1986-03-14

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