METHOD FOR DETERMINING AN OPTIMAL FREQUENCY OF AN OSCILLATING MOVEMENT OF A FORCE-ACCELERATED PROJECTILE OF AN INTRACORPOREAL LITHOTRIPSY APPARATUS

Abstract

The invention relates to a method for determining an optimal frequency of an oscillating movement of a force-accelerated projectile of an intracorporeal pneumatic lithotripsy apparatus, including the following steps: repeatedly accelerating the projectile from a first proximal stop of an acceleration path to a second distal stop, and from the second stop to the first stop, wherein a piezo element is arranged between a proximally arranged counter bearing and a distally arranged horn and is mechanically coupled to the counter bearing and to the horn, and the horn has a distally arranged sonotrode, wherein the acceleration path is arranged in the interior of the counter bearing and of the horn and the first stop is arranged at a distal end of the counter bearing and the second stop is arranged at a distal end of the horn, detecting an electrical signal from the piezo element caused by a tremor at the first stop and/or the second stop as a result of the projectile; and using the detected electrical signal to control a medium which generates the force and which is used to accelerate the projectile from the first stop of the acceleration path to the second stop, and from the second stop to the first stop.

Claims

1. A method for determining an optimal frequency of an oscillating movement of a force-accelerated projectile of an intracorporeal lithotripsy apparatus including the following steps: repeatedly accelerating the projectile from a first proximal stop of an acceleration path to a second distal stop, and from the second stop to the first stop, wherein a piezo element is arranged between a proximally arranged counter bearing and a distally arranged horn and is mechanically coupled to the counter bearing and to the horn, and the horn has a distally arranged sonotrode, wherein the acceleration path is arranged in the interior of the counter bearing and of the horn and the first stop is arranged at a distal end of the counter bearing and the second stop is arranged at a distal end of the horn, detecting an electrical signal from the piezo element caused by a tremor at the first stop and/or the second stop as a result of the projectile; and using the detected electrical signal to control a medium which generates the force and which is used to accelerate the projectile from the first stop of the acceleration path to the second stop, and from the second stop to the first stop.

2. The method according to claim 1, characterised in that the projectile is accelerated by means of compressed air, by means of an electromechanically imparted force or by means of a mechanical apparatus and/or in that the medium is compressed air, an electromagnetic field or a mechanical apparatus.

3. The method according to claim 1, further comprising: exciting the piezo element with an ultrasonic frequency.

4. The method according to claim 1, characterised in that the acceleration path is implemented with a pipe section, wherein a first end of the pipe section has the first stop and a second end of the pipe section has the second stop.

5. The method according to claim 4, characterised in that a first valve is used to introduce compressed air into the pipe section such that the projectile is accelerated from the first stop to the second stop, wherein the air displaced by the projectile is buffered in a storage chamber and after the first valve has been closed, the buffered compressed air is used to accelerate the projectile from the second stop to the first stop.

6. The method according to claim 5, characterised in that the electrical signal of the piezo element is a power signal, which is measured by means of a coil.

7. The method according to claim 1, further comprising: frequency-filtering the power signal measured at the piezo element and rectifying the frequency-filtered power signal.

8. The method according to claim 7, further comprising: identifying at least one threshold value of the rectified frequency-filtered power signal, which corresponds to the projectile impacting the first stop or second stop.

9. A lithotripsy apparatus, in particular for carrying out a method according to claim 1, comprising: a piezo element arranged between a proximally arranged counter bearing and a distally arranged horn, wherein the piezo element is mechanically coupled to the counter bearing and to the horn, and a hollow-cylindrical acceleration path is arranged in the interior of the counter bearing and of the horn, said hollow-cylindrical acceleration path having, at a proximal end of the counter bearing, a first stop and, at a distal end of the horn, a second stop, wherein a proximal end of the acceleration path has a compressed air source connected by means of a first valve or the lithotripsy apparatus has an apparatus for generating an electromagnetic field to apply a force imparted electromagnetically on a projectile; and the projectile is arranged in the interior of the acceleration path, said projectile being designed and configured to be accelerated by means of compressed air from the compressed air source, or the electromagnetically imparted force from the first stop to the second stop and to be accelerated by means of compressed air displaced by the projectile and buffered in a storage chamber, or the electromagnetically imparted force from the second stop to the first stop, a sonotrode, which is designed as a waveguide and which is arranged at a distal end of the horn, wherein a proximal end of the sonotrode is mechanically coupled to the second stop and the lithotripsy apparatus is designed and configured such that an electrical signal from the piezo element causing a tremor at the first stop and/or second stop as a result of the projectile, can be detected and is used for controlling the compressed air from the compressed air source or for controlling the electromagnetically imparted force.

Description

[0046] The invention will be explained in more detail below on the basis of an exemplary embodiment, wherein

[0047] FIG. 1 shows a schematic illustration of a lithotripsy apparatus according to an embodiment of the invention and

[0048] FIG. 2 shows a measurement of an electrical power signal applied to a piezo element against the time during which a method is carried out according to an embodiment of the invention.

[0049] FIG. 3 shows a flow diagram of a method according to claim 1.

[0050] A lithotripsy apparatus 100 serves to carry out a method for determining an optimal frequency of an oscillating movement of a projectile excited by compressed air. The lithotripsy apparatus 100 can for example be a handheld device with a sonotrode attached to the distal end of the handheld device, wherein the sonotrode has a flexible waveguide shaft.

[0051] The lithotripsy apparatus 100 has a piezo element 130 arranged between a proximally arranged counter bearing 110 and a distally arranged horn 120. In this case, the piezo element 130 is mechanically coupled to the counter bearing 110 and to the horn 120. The piezo element 130 is subjected to an ultrasonic frequency of approx. 27 kHz by means of a signal generator, not illustrated.

[0052] The counter bearing 110 and the piezo element 130 each have a hollow-cylindrical shape. The horn 120 has a rotationally-symmetric shape with a cylindrical hollow along a central longitudinal axis. A proximal end of the horn 120 has the same outer diameter as the piezo element 130. Proceeding from the proximal end of the horn 120, the outer diameter of the horn initially remains constant for a predefined path and then decreases asymptotically to a value of the diameter, which is somewhat greater than the diameter of the cylindrical hollow in the interior of the horn 120.

[0053] The counter bearing 110 has in the present case the function of a reflector for the ultrasonic waves generated by the piezo element 130. The shape of the horn 120 and/or of the counter bearing 110 ensures that the transverse and rotational vibrations generated, just like the longitudinal vibrations generated, are guided optimally to a distal end of the sonotrode 170. It is advantageous here that the sonotrode 170 and the horn 120 consist of materials of substantially the same acoustic impedance.

[0054] In the interior 122 of the counter bearing 110 and of the horn 120 is located a hollow-cylindrical pipe section 140, the first end of which has, at a proximal end 112 of the counter bearing 110, a first stop 142 and the second end of which has, at a distal end 124 of the horn 120, a second stop 144.

[0055] A proximal end 146 of the pipe section 140 has a compressed air source 160 connected by means of a first valve 150. The first valve 150 has a check valve.

[0056] In the interior 122 of the pipe section 140 is arranged an elongated projectile 148, which can be accelerated by means of compressed air from the compressed air source 160 from the first stop 142 to the second stop 144. The projectile 148 can be slid freely back and forth in the pipe section 140. The projectile 148 can be accelerated from the second stop 144 to the first stop 142 by means of compressed air displaced by the projectile 148 and buffered in a storage chamber, not shown.

[0057] The projectile 148 has a cylindrical body made of very strong steel, which is slightly magnetic. At the proximal end 146 of the pipe section 140 is arranged a holding magnet not shown, which can draw in the projectile 148 and hold it there in the rest state.

[0058] A sonotrode 170 designed as a waveguide is arranged at a distal end 124 of the horn 120. In this case, a proximal end 172 of the sonotrode 170 is mechanically coupled to the second stop 144 such that an impact of the projectile 148 on the second stop 144 optimally transmits the impulse of the projectile 148 to the sonotrode 170. A diameter of the sonotrode 170 is smaller than a diameter of the pipe section 140.

[0059] In the case of pneumatic lithotripsy, both systems can be used, i.e. the ultrasound system with the ultrasound element 130 and the pneumatic system, in which the projectile 148 is accelerated by means of the compressed air from the compressed air source 160. This is called combined operation. Alternatively, the pneumatic system can also be operated without the ultrasound system. In the latter case, the entire system can be calibrated when the signal generator is switched off, i.e. the limit values of a current strength can be stored and used as a reference in the combined operation in which a measurement is more difficult since the ultrasonic frequency represents a source of interference.

[0060] In both cases, i.e. in the combined operation or if only the pneumatic system is operated, a power signal is measured by means of a current clamp not shown at a connection line between piezo element 130 and signal generator.

[0061] Since the ultrasonic vibrations of the piezo element 130 represent a source of interference, the power signal measured with the current clamp is frequency-filtered with an RLC circuit such that a small region around the ultrasonic frequency of approx. 27 kHz is filtered out of the power signal. The width of the filtered-out frequency is preferably adapted to the interference signal.

[0062] The frequency-filtered power signal is converted into an analogue rectified signal by means of a buffer circuit.

[0063] In the case of the rectified signal, two threshold values can be identified, a first threshold value corresponds to the projectile 148 impacting the first stop 142 and a second threshold value corresponds to the projectile impacting the second stop 144.

[0064] The rectified signal is recorded by a microcontroller, which controls and checks the entire evaluation. The microcontroller can carry out plausibility tests of the detected power signal in order to minimise incorrect measurements or measurement errors.

[0065] The method for determining a maximum or correspondingly optimal frequency of an oscillating movement of the projectile 148 excited by compressed air includes, according to a first step, repeatedly accelerating the projectile 148 by means of compressed air from the first proximal stop 142 of the pipe section 140 to a second distal stop 144 and from the second stop 144 to the first stop 140.

[0066] In this case, the first valve 150 is used to introduce compressed air into the pipe section 140 such that the projectile 148 is accelerated from the first stop 142 to the second stop 144, wherein the air displaced by the projectile 148 is buffered in a storage chamber and after the first valve 150 has been closed, the buffered compressed air is used to accelerate the projectile 148 from the second stop 144 to the first stop 142.

[0067] According to a second step of the method, the piezo element 130 is excited with an ultrasonic frequency. To this end, a signal generator operating at 27 kHz, not shown, is connected to the piezo element 130.

[0068] According to a third step of the method, a power signal of the piezo element 130 is detected caused by a tremor at the first stop 142 or the second stop 144 as a result of the projectile 148.

[0069] According to a fourth step of the method, the detected power signal is used to regulate the compressed air.

[0070] The power signal 180 has a plurality of exponentially decreasing sections modelled with a sine or cosine function, which are separated from one another in time. In this case, a first section 182 of the power signal 180 arises from a tremor of the projectile 148 at the second stop 144 and a second section 184 of the power signal 180 arises from a tremor at the first stop 142.

LIST OF REFERENCE NUMERALS

[0071] 100 Lithotripsy apparatus [0072] 110 Counter bearing [0073] 112 Proximal end of the counter bearing [0074] 120 Horn [0075] 122 Interior of the counter bearing and of the horn [0076] 124 Distal end of the horn [0077] 130 Piezo element [0078] 140 Pipe section [0079] 142 First stop of the acceleration path [0080] 144 Second stop of the acceleration path [0081] 146 Proximal end of the acceleration path [0082] 148 Projectile [0083] 150 First valve [0084] 160 Compressed air source [0085] 170 Sonotrode [0086] 172 Proximal end of the sonotrode [0087] 180 Power signal [0088] 182 First section of the power signal [0089] 184 Second section of the power signal [0090] 300 Method [0091] 310 Method step [0092] 320 Method step [0093] 330 Method step