JPH0560750B2 - - Google Patents

Description

[Detailed description of the invention]

A. Field of Industrial Application This invention relates to a stone crushing device that noninvasively crushes stones in the body, such as kidney stones, ureteral stones, and gallstones, by irradiating focused ultrasonic waves from outside the body. B. Prior Art As a conventional stone crushing device, one shown in FIG. 2 or 3 is known. The outline of the stone crushing device shown in Fig. 2 is as follows. Degassed water 22 having an acoustic impedance equivalent to that of human soft tissue is placed inside a reflector 21 having a spheroidal shape, and the first focus F ₁ of the reflector 21 is
There are parts that generate shock waves US due to underwater discharges, explosions, etc. The surface of the degassed water 22 is a membrane 23
A patient M is lying on his back on a bed (not shown) in contact with the membrane 23. By adjusting the position of the bed, the stone S in the body of the patient M is positioned at the second focal point _F2 of the reflector 21. The shock wave US generated at the first focus F ₁ is reflected by the reflector 21 through the degassed water 22, propagates within the living body of the patient M, and is focused at the second focus F ₂ . The stone S is crushed by the energy of the focused shock wave US. The outline of the stone crushing device shown in Fig. 3 is as follows. A spherical recess 2 is formed in the support portion 1, and a large number of piezoelectric elements 3 _i (i=
1, 2...) are attached concentrically. Each piezoelectric element 3 _i has the same resonance frequency c,
Each is directed towards a focal point F, which is the center of the spherical recess 2. The spherical recess 2 is filled with degassed water 4 and its surface is covered with a membrane 5. In addition, the focal point F
The spherical recess 2 is located above the outside of the membrane 5.
The size of is determined. The main oscillator 6 and the individual piezoelectric elements 3 _i are each connected via a high voltage pulse generator 7 . A diagnostic ultrasonic imaging device 8 for detecting the position of the stone S is attached to the center of the inner bottom surface of the spherical recess 2. This ultrasonic imaging device 8 sweeps and irradiates ultrasonic waves in a first vertical plane along the body axis direction of the patient M and in a second vertical plane perpendicular to the vertical plane, thereby emitting ultrasonic waves from each tissue in the body. It is equipped with two ultrasonic probes that collect luminance data at each point in the living tissue, which is determined by the irradiation angle and the distance along the irradiation direction, by picking up reflected waves. Since the calculus S and the body surface have relatively high reflectance, they have high brightness. Ultrasonic tomographic image display diagnostic section 9
inputs brightness data and displays the stone position and body surface position in high brightness. The patient M is placed supine so that the surface of the patient M's body is in contact with the membrane 5. The position of the stone S is confirmed by the ultrasonic tomographic image display diagnostic section 9, and the stone S is positioned at the focal point F of the piezoelectric element 3 _i group by adjusting the position of the bed (not shown) on which the patient M is lying supine. let Then, the main oscillator 6 is driven, each high voltage pulse generator 7 generates a high voltage pulse and supplies it to each piezoelectric element _3i , and the ultrasonic pulse US generated by piezoelectric conversion is degassed. Through water 4 and living organisms,
Irradiation is concentrated toward the stone S at the focal point F, and the stone S is crushed by the ultrasonic vibration. The crushed microstones are excreted from the body through a tube coming out of the organ (in the case of kidney stones, the ureter). C. Problems to be Solved by the Invention Ultrasonic pulses (shock waves) are attenuated by absorption within a living body. The situation is shown in Figure 4. FIG. 4A shows the time response waveform and frequency response waveform of the ultrasound pulse when it is incident on the body surface, and FIG. 4B shows the time response of the ultrasound pulse when it propagates in the living body and reaches the stone S. A waveform and a frequency response waveform are shown. Even if an ultrasonic pulse has a sharp waveform at the time of incidence, the time response waveform becomes blunt due to attenuation during propagation within the body. Looking at this as a frequency response waveform, the center frequency (resonance frequency) of the ultrasonic pulse was c at the time of incidence, but due to attenuation, it becomes c′ (<
It transitions to the lower frequency side as shown in c). The degree of slowing of the time response waveform (transition to the lower frequency side of the center frequency) increases as the resonant frequency of the piezoelectric element increases and as the biological thickness from the body surface to the calculus position increases. That is, as shown in FIG. 5, the piezoelectric element 3 _i
On the line connecting (i=1,2...) and the stone S, the biological thickness from the body surface to the stone S is L _i (i=1,2
), the resonance frequency is all the same c, the intensity of the ultrasound pulse at the time of incidence on the body surface is I ₀ (same), and the intensity of the ultrasound pulse at the stone location is set as a function of the biological thickness L _i ( L _i ), then the attenuation rate α _i (i=1,2...)
is expressed as α _i =I(L _i )/I ₀ exp ^{-k. c.Li} . . . where k is a constant. By the way, the stone crushing effect is most excellent when the ultrasonic pulses emitted from all the piezoelectric elements 3 _i (i=1, 2, . . . ) have the same waveform at the stone location. However, as is clear from FIG. 5, the magnitude relationship of the biological thickness L _i depending on the placement position of the piezoelectric element 3 _i is L ₁ <L ₂ <L ₃ <L ₄ . Conventionally, the resonant frequency c is the same for all piezoelectric elements _3i . Therefore, the biological thickness L ₁ ,
The relative relationship between the intensities I( _{L 1 )} , I(L ₂ ), I(L ₃ ), and I(L 4 ) at the stone location for each of L ₂ , L ₃ , and L ₄ is I(L ₁ ) > I (L ₂ ) > I (L ₃ ) > I (L ₄ ), and the degree of slowing of the time response waveform (transition of the center frequency to the lower frequency side) also differs from each other. However, the stone crushing effect was not sufficiently effective. Furthermore, the biological thickness L _i (i=1, 2, . . . ) varies from patient to patient. In other words, the degree of attenuation is greater in patients with a large body thickness than in patients with a small body thickness. In order to achieve a constant crushing effect regardless of these changes, conventional methods have been used, for example, to increase the number of ultrasound pulses irradiated for patients with large biological thickness, and to increase the number of ultrasound pulses irradiated for patients with small biological thickness. Efforts are being made to reduce the number of irradiations. However, since the judgment of the optimal number of irradiations relied on the experience and intuition of the doctor, it was extremely difficult to achieve a certain level of stone-crushing effect for every patient. It was hot. This invention was made in view of the above circumstances, and it is possible to always obtain a constant stone crushing effect despite changes in the thickness of the body depending on the position of the piezoelectric element and changes in the thickness of the body depending on the patient. The purpose is to make it possible to D Means for Solving the Problems In order to achieve the above object, the present invention has the following configuration. That is, the stone crushing device of the present invention is distributed along a curved surface toward a single focal point,
A plurality of piezoelectric elements whose resonance frequencies are set higher in the center and lower in the peripheral areas, a means for detecting the position of the stone, and a means for detecting the position of the stone between each piezoelectric element and the stone based on the detected stone position. Each biological thickness is detected, and according to each detected biological thickness, a higher driving voltage is supplied to the piezoelectric element located at the position of the larger detected biological thickness, and the piezoelectric element located at the position of the smaller detected biological thickness is The device is characterized in that it is equipped with drive voltage control means for supplying a lower drive voltage to the element. E Effects The effects of the configuration of this invention are as follows. That is, the assumed average biological thickness between each piezoelectric element and the stone depending on the placement position of each piezoelectric element is smaller for the piezoelectric element in the center and larger for the piezoelectric element in the peripheral area. Furthermore, the greater the average biological thickness, the greater the degree of attenuation. Furthermore, the degree of attenuation due to a difference in resonance frequency is greater as the resonance frequency is higher. Therefore, the increase or decrease in the degree of attenuation due to the increase or decrease in the average biological thickness due to the placement position of each piezoelectric element is compensated for by the decrease or increase in the degree of attenuation due to the decrease or increase in the resonance frequency. . That is, as in the above configuration, compensation is achieved by setting the resonant frequency of the piezoelectric elements higher in the central piezoelectric elements and lower in the peripheral piezoelectric elements in the plurality of piezoelectric elements. This compensation is easy to understand when summarized as follows.

[Table] Compensation
↑
〓High←

Claims (1)

[Claims] 1. A plurality of piezoelectric elements distributed along a curved surface toward a single focal point, the resonance frequency of which is higher in the center and lower in the periphery, and means for detecting the position of a stone; Detect each biological thickness between each piezoelectric element and the calculus based on the detected stone position, and according to each detected biological thickness, the piezoelectric element at the position of larger detected biological thickness has a higher A stone crushing device characterized by comprising: drive voltage control means for supplying a drive voltage and supplying a lower drive voltage to a piezoelectric element located at a position with a smaller detected biological thickness.