JPH0369534B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a probe that scans an ultrasonic beam in a fan shape, and particularly relates to an ultrasonic fan probe that observes two or more different fan-shaped scanning cross sections within a measured body. Concerning scanning probes.

[Conventional technology and problems]

Fan-shaped scanning using an ultrasonic beam has the advantage of being able to observe a wide field of view inside a living body from one small contact point. In particular, when observing the heart, etc., fan-shaped scanning is exclusively used because a considerable area of the heart can be observed by touching the narrow area between the ribs while avoiding interference with the ribs.

However, in the past, only one fan-shaped scanning cross section was observed, so accurate observation was not possible. After all, the heart beats and moves, and because of the movement of breathing, the heart as a whole moves back and forth and from side to side. For this reason, observation of only one cross section is not enough.
It is unclear which part of the heart the cross section corresponds to, and for this reason, it is difficult to check by alternating the position of the probe with respect to the body or by rotating it 90 degrees around the probe axis. Observations of the desired cross section are being carried out. In this case, since it is done manually, it is quite difficult to maintain geometric accuracy in each posture change.

To solve this problem, it may be possible to mechanically maintain the posture of the probe at a constant level, but this is inconvenient because it interferes with breathing movements, and I have not seen any examples of this being attempted yet.

Therefore, an attempt was made to mechanically rotate the internal probe 90° around its axis while holding the outer container of the probe in a fixed position relative to the body by hand, but the probe was too large. Moreover, it is difficult to maintain a completely constant hand holding, and the errors are still large due to the fact that they are not held at the same time, and the time required for rotation is long.

Separately from the present application, the inventor used two separate probes and determined their relative positions using angle detectors attached to link arms and joints, thereby achieving two simultaneous probes in time.
We devised a method to observe cross sections along with their relative positions, making accurate three-dimensional observation possible.

However, in this case, since two probes are used, two contact points with the body are required. in general,
When observing the hearts of young people under their prime age, it is possible to find effective contact points, but as people get older, there are more and more cases in which only one effective contact point can be found, and the ratio is 40 to 50. %become.

From the above situation, through one contact point,
There is a desire for a method to electronically switch or observe two or more different cross sections at high speed, or to observe them completely simultaneously, but there are no reports of attempts yet.

Electronic sector scanning is typically performed using a phased array. In this case, the trans-
The inventor has also devised a multi-layered Juicer, each layer being responsible for a different scanning plane, and by using different frequencies for each scanning plane, it is possible to operate completely simultaneously. I can do it.

However, in these cases, the drawbacks are that the processing of the multilayer transformer is complicated, and the phase control circuit is complicated and expensive.

[Purpose of the invention]

The present invention eliminates the various drawbacks mentioned above, and makes it possible to scan a plurality of different fan-shaped scanning planes through a single probe while keeping the attitude of the probe toward the object to be measured, such as a living body, constant. It is an object of the present invention to provide an inexpensive, compact fan-shaped scanning probe that enables high-speed electronic switching and/or complete simultaneous observation.

[Structure of the invention]

In order to achieve the above object, the ultrasonic fan-shaped scanning probe of the present invention includes an element array in which a plurality of ultrasonic transducer elements are arranged, a window through which ultrasonic waves enter and exit, and the element array. and an ultrasonic transmission medium filled in a front chamber configured between the window and the ultrasonic transducer element selectively activated as an aperture to focus and transmit the ultrasonic waves into a beam. and in an ultrasonic scanning probe that scans the object to be measured circumscribing the window with an ultrasonic beam by changing some or all of the selections, a scanning line based on all the selections from the element array. The element array is configured to scan in a fan-shaped manner by passing through the window or approximately one intersection point near the window, and the element array is configured so that tomographic images of at least two or more objects to be measured are obtained. It is characterized in that the propagation time of the ultrasonic propagation path l ₁ is approximately equal to or longer than the propagation time of the maximum measurement depth l ₂ from the body surface of the subject circumscribing the window. The details of the scanning are as follows: A plurality of ultrasonic transducer elements are selected as a group from the element array to focus and form an ultrasonic beam, and some of the selected ultrasonic transducer elements are operated as a group. Alternatively, the center position of the ultrasonic beam transmitting/receiving point can be moved by changing the entire system.

[Embodiments of the invention]

Hereinafter, the present invention will be explained with reference to the drawings.

Figure 1 shows an embodiment of the present invention showing the relationship between the transducer arrangement, scanning line intersection points, and windows, where a shows an example of three multi-linear arrangements, and b shows an example of two orthogonal linear arrangements. A diagram showing an example, c is a diagram showing an example of matrix planar arrangement, and d is a sectional view showing the probe structure of a. 1 is a window, 2 to 5 are transducer rows, 6 is a transducer surface, 13 is a sound absorbing material, and 14 is a front chamber.

In Figure 1a, three transducer rows 2, 3 and 4
are linearly arranged in the shape of circular arcs, and are arranged substantially in parallel so that the center of curvature thereof is approximately at window 1. The shape of the arc can be slightly corrected if necessary. In FIG. 1a, the sector-shaped scanning plane formed by the transducer array 2 is arranged perpendicular to the plane of the window 1. Although the fan-shaped scanning plane formed by the transducer rows 3 and 4 passes through the center point O of the window 1, the plane is not perpendicular to the plane of the window 1, but obliquely intersects with it. Therefore, although the transducer arrays 3 and 4 appear to be parallel in FIG. 1a, in order to make the scanning sector plane a plane with equal intervals, in reality, due to this oblique intersection, they must be distorted rather than perfectly parallel. The linear arrays 2, 3, and 4 can be thought of as a so-called linear array, which is a completely linear array of transducers generally used for abdominal diagnosis, etc., but shaped into an arc. A large number of piezoelectric elements made of strips of PZT etc. are arranged in a row. Its operation method may be the same as that of a general linear array, and a plurality of n adjacent elements are selected and used as an aperture for beam focusing. The center of the beam becomes the scanning line. Movement of the scanning line is performed by changing the position of the selection element. By driving n+1 elements to obtain a scanning line shifted by half a pitch, or by sequentially controlling the timing phase of transmission and reception from near the center to the periphery of the elements that make up the group,
The ultrasound beam width focal point within the scan plane can be electronically set or dynamically controlled.
However, if phase control is not performed, the focal point will be determined by a geometric arrangement and will be the center of curvature of the circular arc. The beam width in the direction perpendicular to the scanning plane can be focused by giving each strip-shaped element a concave curvature in the sound wave emission direction, or by using a cylindrical lens and bending the cylindrical axis along the circular arc. This can be done by adding it to the front of a linear array. In this way, techniques used in general linear arrays can be applied. FIG. 1a shows the case where the center of curvature of the circular arc coincides with the intersection point of each scanning line. Further, although an example is shown in which this intersection point coincides with the center O of the window 1, it does not necessarily have to coincide with the center O of the window 1, if necessary.

FIG. 1d is a sectional view showing a specific probe structure taken along a plane passing through the center point O of the window 1 and the center line of the transducer row 2 in FIG. 1a.

The probe is made integrally including a front chamber 14 in the shape of a substantially quadrangular pyramid having a window 1 at its apex, circuit connections to the elements, and the like. The transducer rows 2, 3, and 4 in a linear arrangement are installed on the bottom surface of the square pyramid of the front chamber 14. Actually window 1
Other sides, and linearly arranged transducer rows 2, 3 and 4
The inner surface of the front chamber 14, such as the bottom surface that is integrated with the back surface of the front chamber 14, is covered or formed with as much sound absorbing material 13 as possible. Front room 1
The inside of the transducer 4 is filled with water, castor oil, liquid paraffin, fluorine oil, etc., and serves as a transmission path for ultrasonic waves between the transducer rows 2, 3, and 4 and the window 1. The fan-shaped scanning plane in the front chamber 14 formed by the transducer rows 2, 3, and 4 extends point-symmetrically to the opposite side through point O, forming three different sector-shaped scanning planes in the object to be measured. Transducer rows 2 and 3
and 4 are operated at the same frequency, each scanning plane is operated in a temporally switched manner. However, the constituent elements of each array, for example, the transducer row 2 is 3.5MHz,
If you change the operating frequency such as 2.25MHz for 3 and 1.5MHz for 4, or add a different CHIRP modulation method, you can operate three linearly arranged transducer rows 2, 3, and 4 at the same time. However, by discriminating the received signals with a filter, the three scanning planes can be scanned simultaneously.

In FIG. 1b, the transducer arrays 2 and 5 are arranged so that their fan-shaped scanning planes are perpendicular to each other, and so that all scanning lines cross and pass near window 1 or at a point O on window 1. has been done. The intersecting part of transducer rows 2 and 5 is not a strip-shaped element but a matrix-like element divided vertically and horizontally, and can be connected vertically and used as part of transducer row 2, or connected horizontally to be used as a part of transducer row It is sometimes used as part of 5. The transducer arrays 2 and 5 are operated out of phase so that when one is using the central crossing section, the other is using the other sections. The other structure, operation, and scanning are the same as those in FIG. 1a, and it is also possible to scan mutually orthogonal fan-shaped scanning planes in the object outside the window 1 in a time-switched manner or completely simultaneously.

In FIG. 1c, the vibrator surface 6 is not a linear arrangement, but a matrix-like planar arrangement in which a plurality of vibrators are arranged on a spherical surface with the center of curvature at point O. In this case, the vibrator can be centered at any position on the plane X-axis or Y-axis, and the vibrator in the vicinity can be selected with the appropriate aperture shape and width, such as square or approximate circle. A three-dimensional fan-shaped scan can be performed. Note that three-dimensional fan-shaped scanning means scanning for obtaining two or more fan-shaped cross-sectional images.

FIG. 2 is a diagram showing a specific example of the structure of a transducer array having a multilayer structure according to the present invention, in which a is a diagram showing an example of a linear arrangement, and b is a diagram showing an example of two orthogonal linear arrangements. It is. 7, 8 and 10 are transducer rows, 7
1, 72, 73... are piezoelectric elements, 8' is a piezoelectric plate,
80 is a ground electrode, 81, 82, 83, . . . are signal electrodes, 11 is a reflecting plate, 12 is a non-polarizing plate, and 13 is a sound absorbing material. The example shown in FIG. 2a has a multilayer structure in which the vibrator arrays 7 and 8 constitute two layers arranged in an arcuate linear arrangement. For example, the center frequency of the transducer row 7 is 3.5M.
It has piezoelectric elements 71, 72, 73, etc., which are divided piezoelectric elements made of Hz PZT (zircon lead titanate) or the like. The transducer array 8 has an organic piezoelectric plate 8' such as PVDF (polyvinylidene fluoride),
The center frequency is adjusted to 2.25MHz, for example. The organic piezoelectric plate 8' has a signal electrode 81 on one side (the front side in the figure),
82, 83, etc., and the ground electrode 80 is arranged on the other side (the back side in the figure) over the entire surface. Piezoelectric elements 71, 7
2, 73, etc., are also provided with a signal electrode and a ground electrode, respectively. PZT is ceramic and has no flexibility, so
The piezoelectric elements 71, 72, 73, etc. can be made as individual pieces one by one, or they can be made integrally by cutting a thin slit that cannot penetrate through to the back of a plate that has been previously processed into a disk shape. PVDF is flexible and can be made from flat sheets and then bent to fit an arc. A sound absorbing material 13 made of resin or the like mixed with metal powder is provided on the back side of the vibrator row 7. The vibrator row 7, the sound absorbing material 13, and the vibrator row 8 are integrally formed with adhesive. The acoustic impedance of PZT is approximately 35×10 ⁶ Kg/m ² sec, and that of PVDF is approximately 4×10 ⁶
Kg/m ² sec, PZT has λ/2 resonance,
It is preferable that PVDF has λ/4 resonance. Ultrasound from the PZT passes through the PVDF to enter and exit. PVDF is
PZT can also have an effect similar to acoustic impedance matching. Most of the ultrasonic waves directed toward the rear of the PVDF are reflected by the PZT and exit toward the front. In this example, the first layer was characterized by having a center frequency of 3.5MHz and the second layer having a center frequency of 2.25MHz.
CHIRP modulation, pseudorandom code modulation, etc. can also be used. If a filter is used for discrimination during reception, both systems can be operated completely simultaneously. In particular, in this example, two sets of linearly arranged transducer arrays overlap at the same position and can scan the same fan-shaped scanning plane at different frequencies, so when used for human tissue, etc., the frequency characteristics of the tissue can be changed. It is suitable for performing tissue discrimination based on differences.

The example in Figure 2b is the center frequency of PZT.
Layer 7 of 3.5MHz linear array transducer array and PVDF
The layer 10 is a linear array of transducer arrays with a center frequency of 2.25 MHz, which are multilayered to form two mutually orthogonal fan-shaped scanning surfaces. Moreover, the transducer array 7 is arranged in the lower layer, and the transducer array 10 is arranged in the upper layer. The reflector plate 11 is made of a material having the same thickness and acoustic impedance as PZT, and the transducer rows 7 and 1
It reflects the sound waves emitted backward from PVDF so that it has the same characteristics as the intersection with 0, and is not polarized.
PZT ceramic or the like can be used. The non-polarized plate 12 is made of a material with the same thickness and acoustic impedance as PVDF so that the sound waves emitted forward from the PZT will spread over the entire surface of the transducer row 7 and be at the intersection of the transducer rows 7 and 10. The transducer array 10 is bonded to both left and right surfaces of the intersection portion of the transducer array 10.
The specific material of the non-polarized plate 12 is the vibrator array 1.
It is convenient to use PVDF that is the same as 0 and is not polarized. According to this embodiment, it is possible to form two fan-shaped scanning planes perpendicular to each other from one window, and to scan them completely simultaneously.

FIG. 3 is a diagram showing a specific example of the structure of a vibrator array that performs aperture control according to the present invention. In FIG. 3, 7 and 9 are vibrator rows, 71, 72, 73, . . . and 91, 92, 93, . . . are piezoelectric elements, and 90 is a ground electrode. The sound field formed by a certain aperture, for example a disk shape with radius a, is beam-shaped, and at short distances the beam radius is a, but at long distances the apex angle is proportional to a/λ (λ: wavelength). It spreads in a thin cone shape. Therefore, the beam shape at a long distance is 2
If it is desired to make the two frequencies the same, the aperture a may be made proportional to the wavelength λ. However, in this case, the beam shape at a short distance will be different. In the present invention, by defining the aperture so that most of this near-field sound field is in the front room, that is, inside the window 1, most of the beam in the object to be measured is made into a far-field sound field.
Therefore, the same beam shape independent of frequency can be realized over the entire measurement depth. This is particularly important when tissue discrimination is performed based on the frequency dependence of human tissues and the like. In FIG. 3, vibrator rows 7 and 9 are made by linearly arranging unit elements to which piezoelectric elements 71 and 91 are bonded. The strip-shaped PZT piezoelectric element 71 is operated at wavelength λ ₁ ,
In the Y-axis direction, electrodes are provided on the front and back of the entire surface and are effective over the entire length _W1 . The piezoelectric element 91 is made of PVDF and is operated at a wavelength λ ₂ , and its length in the Y-axis direction is W ₁ , but the effective length of opposing electrodes is W ₂ and W ₁ /
It is assumed that W ₂ =λ ₁ /λ ₂ . The reason why the surface electrode of the PVDF piezoelectric element 91 continues to the bottom is to extract the electrode signal. A unit element made up of these piezoelectric elements 71 and 91 is arranged, and the transducer row 7
9 and the sound absorbing material 13 are integrated to form one linear array. Further, in actual operation, the number of openings in the group to be selected is _n1 for the transducer array 7 and _n2 for the transducer array 9, and n ₁ /n ₂ =λ ₁ /λ ₂ . In this way, a beam with a substantially rectangular cross section is formed, but in the far sound field, the beam shapes of both wavelengths λ ₁ and λ ₂ are the same. In the assembly diagram of FIG. 3a, the portion of the piezoelectric element 91 above point P (piezoelectric element 91 of FIG. 3b) is removed for explanation purposes, but in reality, it should not be removed.

FIG. 4 is a diagram showing another specific example of the structure of a vibrator that performs aperture control according to the present invention, and shows a method for changing the aperture in the Y-axis direction of the linear array of vibrator rows 8 shown in FIG. 2a. It shows. 8' is one piece of PVDF
An organic piezoelectric plate such as 80 is a ground electrode, 81, 8
2, 83... indicate signal electrodes. Earth electrode 80
is added to the total length in the arc direction with a width of W ₂ . When these electrodes are formed in advance and polarized by applying a voltage and heating, the ground electrode 80 and signal electrodes 81, 82,
It can be made such that only the portion facing 83 etc. is polarized and exhibits a piezoelectric effect, and the rest does not exhibit a piezoelectric effect. The non-piezoelectric part is a piezoelectric element 7 such as PZT.
It acts as a medium for transmitting and transmitting ultrasonic waves from piezoelectric elements 71, 72, etc., and is effective in preventing the Y-axis distribution of ultrasonic waves from piezoelectric elements 71, 72, etc. from being disturbed by the _W2 width PVDF piezoelectric part. be.

The main parts of the present invention, which realizes three-dimensional fan-shaped scanning using a linear array of transducers, have been explained above, but since phase control is not required compared to a phased array, the control circuit only requires selection switching. , easy and cheap. Furthermore, since the arrangement surface of the transducer elements can be widened, various types of three-dimensional scanning, multi-frequency operation, etc. and their arrangement can be easily configured, and manufacturing is also easy and inexpensive.

On the other hand, a front chamber is required to intersect the scanning lines, and in order to eliminate the adverse effects of multiple reflections between the transducer and the window or body surface, the scanning line length l ₁ between the transducer and the window is required. Velocity of sound in the front room medium
v ₁ , the maximum measurement depth outside the window is l ₂ , and the sound velocity of the object to be measured is v ₂ , then the condition l ₁ /v ₁ ≧l ₂ /v ₂ is required, which has the disadvantage that the front chamber becomes large. be. When v ₁ ≒ v ₂ , l ₁ is at least the same as l ₂ ,
In the case of the heart, etc., l ₂ = 18 cm, so the probe will be long. Also, if the scanning angle inside the object to be measured is θ ₂ , the scanning angle θ ₁ inside the front chamber is due to refraction, so sinθ ₁ /sinθ ₂ = v ₁ / v ₂ , and if v ₁ ≒ v ₂ and 2θ ₂ = 90°, then 2θ ₁ = 90°, and l ₂
= 18cm, the size of the probe becomes too large to be usable. In practical use, it is absolutely necessary to keep this length l ₁ and the scanning angle 2θ ₁ (which gives the apex angle of the quadrangular pyramidal probe shape) small. This request can be realized by selecting a medium in the front room where v ₁ /v ₂ ≦1. This is clear from the above equations for l ₁ and θ ₁ . v ₁ / v ₂ ≦
It is very preferable to set it to 1/2. Fluorine oil is an example of such a substance, and V ₂ is 1500 m/sec in living organisms etc.
On the other hand, 3M's FC48, FC72, FC75, etc.
Provides excellent v ₁ /v ₂ ratios at v ₁ of 700, 527, and 590 m/sec.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, a plurality of linearly arranged or planarly arranged transducers are provided in a front chamber having one window, and the scanning lines formed by these transducers are arranged near the window. By configuring the probe to cross almost one point, it is possible to form a plurality of different fan-shaped scanning planes from one contact point on the object to be measured, such as a living body, while keeping the probe in one posture. As a result, accurate, easy-to-handle, and inexpensive three-dimensional sector scanning can be realized.

[Brief explanation of drawings]

FIG. 1 shows an embodiment of the present invention showing the relationship between the transducer arrangement, scanning line intersection points, and windows, where a shows an example of a multiple linear arrangement, and b shows an example of two orthogonal linear arrangements. FIG. 2 is a diagram showing an example of a matrix planar arrangement, d is a sectional view showing the probe structure of FIG. 2, and FIG. FIG. 3 is a diagram showing an example of a linear array having a multilayer structure, b is a diagram showing an example of two orthogonal linear arrays having a multilayer structure, and FIG. FIG. 4 is a diagram showing another specific example of the structure of a transducer array for performing aperture control according to the present invention. 1... window, 2 to 10... transducer row, 6...
Vibrator surface, 8'...piezoelectric plate, 11...reflection plate, 1
2... Non-polarized plate, 13... Sound absorbing material, 14... Front chamber, 71, 72 and 73... Piezoelectric element, 81, 82
and 83... signal electrode, 80 and 90... earth electrode, 91, 92 and 93... piezoelectric element.

Claims (1)

[Claims] 1. An element array in which a plurality of ultrasonic transducer elements are arranged, a window through which ultrasonic waves enter and exit,
It has an ultrasonic transmission medium filled in a front chamber configured between the element array and the window, and selectively operates the ultrasonic transducer element as an aperture to transmit ultrasonic waves into a beam. In an ultrasonic scanning probe that scans an object to be measured circumscribing the window with an ultrasonic beam by changing the selection of some or all of the ultrasonic beams, all of the ultrasonic beams from the element array The element array is configured such that the scanning line selected by the above passes through the window or approximately one intersection point near the window and scans in a fan-shaped manner, and at least two or more tomographic images of the object to be measured are obtained. , and the propagation time of the ultrasonic wave propagation path l ₁ in the front chamber is approximately equal to or longer than the propagation time of the maximum measurement depth l ₂ from the body surface of the object circumscribed to the window. Ultrasonic fan-shaped scanning probe. 2 A plurality of ultrasonic transducer elements are arranged in parallel to form one linear transducer array, and the plurality of linear transducer arrays are formed into a spherical surface whose center of curvature is the intersection point of the scanning line. 2. An ultrasonic fan-scanning probe as claimed in claim 1, characterized in that it has a multi-element array juxtaposed substantially along. 3 A plurality of ultrasonic transducer elements are arranged in parallel to form one linear transducer array, and the plurality of linear transducer arrays are formed into a spherical surface whose center of curvature is the intersection point of the scanning line. 2. An ultrasonic fan-scanning probe as claimed in claim 1, characterized in that it has a multi-element array arranged orthogonally substantially along. 4. A patent claim characterized by having a multidimensional element array in which a plurality of ultrasonic transducer elements are arranged in a planar shape such as a matrix substantially along a spherical surface whose center of curvature is the intersection point of scanning lines. The ultrasonic fan-shaped scanning probe according to item 1. 5. When the element array is composed of a plurality of linear transformer arrays, at least two of each linear transformer array may be operated with ultrasonic waveforms having different frequencies or characteristics. An ultrasonic fan-shaped scanning probe according to claims 2 and 3. 6 A plurality of ultrasonic transducer elements are arranged in parallel to form one linear transducer array, an arbitrary number of linear transducer arrays are arranged on one layer, and the layers are further stacked. The ultrasonic waves are arranged substantially along an arc or a spherical surface with the intersection of the scanning lines as the center of curvature to form a composite element array, and at least two of each linear transducer array have different frequencies or characteristics. Claim 1 characterized in that it is operated in the form of
The ultrasonic fan-shaped scanning probe described in . 7 At least some of the ultrasonic transformer elements constituting the element array are multilayer ultrasonic transformer elements created by stacking a plurality of ultrasonic transformer elements, and the multilayer Claim 1, characterized in that the ultrasonic transducer element itself is operable with multiple frequencies or characteristics of ultrasonic waveforms.
The ultrasonic fan-shaped scanning probe according to items 5 to 6. 8 When a plurality of ultrasonic transducer elements are arranged in a multidimensional or complex manner, and appropriate groups of elements selected from among the elements focus and form beams of different frequencies, the composition of each group The aperture of the acoustic transducer element itself and/or the aperture of the selected elements as a group is changed based on the wavelength of the ultrasonic waves transmitted and received by each group, and most of the near-field sound field is directed to the front chamber. An ultrasonic fan-shaped scanning probe according to any one of claims 5 to 7, characterized in that it is constructed as follows. 9. The ultrasonic sector according to claims 1 to 8, characterized in that the front chamber is filled with an ultrasonic transmission medium having a sonic velocity v ₁ that is approximately equal to or slower than the sonic velocity v ₂ of the object to be measured. scanning probe.