APPARATUS FOR THE NON-INTRUSIVE FRAGMENTATION OF RENAL CALCULI

Abstract: The apparatus for the non-intrusive fragmentation of renal calculi according to the invention comprises at least one ultrasonic receiver-transmitter head (12) focused on the renal calculus (11) to be disintegrated, said head (12) being associated with low-power variable frequency transmitter means (16) and with receiver means (18) to perform a spectral analysis of the characteristic resonance frequencies of the calculus (11) to be disintegrated, and control means (Tx1, OSC1) to cause said transmitter means (16) to emit relatively high-power energy peaks at the characteristic resonance frequencies of said calculus (11) to promote its disintegration.

Description: Apparatus for the non-intrusive fragmentation of renal calculi This invention relates to an apparatus for the non-intrusive fragmentation of renal calculi. It is well known that the conventional method of removing renal calculi is by surgery. Recently however, much effort has been dedicated to the search for non-sanguinary and in particular non-intrusive techniques for fragmenting renal calculi in such a manner as to disintegrate their structure and break them down into particles which can be eliminated naturally without inconveniencing the patient. In this respect, the "sanguinary" method is of knwon inconvenience in terms of hospitalisation and its associated cost, plus the inevitable surgical shock. This latter in particular can be intolerable to debilitated, elderly, diabetic and other patients, so making the operation impraticable because of the increased risk factor. This and the other said inconveniences should in all cases be avoided, and this has lead to the search for other techniques. Up to a short time ago these were of intrusive character, using special active and/or passive catheters because of the traumatic side effects. An intermediate method between the completely surgical and the catheter methods has been used in recent years. In this method, a metal probe is brought into contact with the calculus by surgical incision and then transmits to it an ultrasonic mechanical action by the effect of an ultrasonic exciter to which said probe is connected. The technique has proved effective in the fragmentation of calculi and their succesive "natural" elimination with adjuvant clinical intervention. However, although substantially reduced, the inconvenience of even a minor surgical operation still exists. The non-sanguinary non-intrusive techniques used up to the present time are based on the use of a field or beam of mechanical energy waves generated outside the patient's body, to interact with the constituent concretions of the calculus and cause its fragmentation by "brute force". The mechanical energy used, which is in the form of ultrasonic or shock waves generated external to the patient, is liberated during the process of their absorption by him, and preferentially by the calculus itself (this selectivity being the distinguishing merit of these techniques) to lead to disintegration of the constituent polycrystalline concretions of the renal calculus. The ultrasonic techniques of the known art use so-called "brute force", with peak powers reaching 100 kW. In this context, the term "brute force" is used in relation to knwon techniques because the apparatus concerned relies wholly on the power density applied to the constituent crystalline concretion of the renal calculus, whether it is of semi-fine or fine structure and whatever its size. This approach, especially in the case of shock waves, carries the danger of damaging other biological structures besides the renal calculi themselves, and has numerous di advantages such as the need to totally anesthetize the patient, the need to completely immerse the bound patient in water or the like, etc. For example, EP-A-0 133 665 cites as known art certain methods using ultrasonic waves which reach a peak power of 100 kW. The apparatus of that invention, which comprises a spark shock wave generator with wave guides and a focusing lens s certainly applies "brute force". EP-A-0 133946 describes a structure for disintegrating renal calculi by means of a plurality of shock wave generators which converge at a common focal point. The technique is again a shock wave and therefore "brute force" technique. EP-A-0162959 describes the generation of showk waves for disintegrat¬ ing renal calculi by means of an electromechanical structure comprising a pulse-energised electromagnetic coil. "Brute force" is again applied in this case. EP-A-0 167 670 describes a system for generating shock waves by interaction between electromagnetic microwaves and the structures to be demolished. Fragmentation is thus again by "brute force". The most recent known art, exemplified by the aforesaid patent references, shows that research has up to now been based on the use of high-density power with extremely wide and irregular spectral distribution (shock waves) to obtain mechanical fragmentation of the constituent concretions of calculi. In addition, it should be noted that elastic waves within a relatively wide spurious spectrum cannot give correct focusing of the transmitted energy on the calculi to be demolished, with the result that only part of the ultrasonic energy transmitted to the patient is effectively used in demolishing the calculi. The remainder is dispersed and can act negatively on those structures which fortuitously absorb energy. The result is a situation similar to that which prevailed in the use of light energy, including for therapeutic purposes, before the large-scale introduction of coherent light (laser), or in spark radio transmission before continuous wave. In this respect, it is a well known fact of physics that in the case of oscillation (electrical, mechanical), monochromaticity and phase coherence of the oscillation allows accurate focusing and aiming, and thus the concentration of the available energy at a well determined point in space. It. is also a well known fact that in the mechanical field (such as disintegration of renal calculi) maximum energy transfer between the elastic wave source and a structure to be oscillated is obtained under conditions of resonance on one or more of the resonance modes of the structure. In this respect it is known that in mechanical structures subjected to dynamic stresses, steps are taken to prevent oscillation and/or vibrations which could assume destructive amplitude. In contrast to the known art the apparatus of the present invention uses ultrasonic waves having a wavelength falling within a very narrow band such that they can be precisely focused by wave guides, mirrors or acoustic lenses. This is quite different from the system developed at Munich University by Dornier, which does not use ultrasonic waves but instead uses the brute force of explosions (shock waves) caused by striking intense electric sparks at the focal point of two large (30-40 cm) parabolic reflectors immersed in a water-filled tank in which the bound and anesthetized patient is also immersed (details of the Dornier system are given inter alia in the Italian magazine TRENTATRE' - Dimensione salute, May 1986, page 68 onwards). In this, each spark generates a steam pulse equivalent to an explosion, the shock wave of which propagates within the incompressible medium formed by the water, to strike a not indifferent blow to the patient's abdomen. As stated, two such reflectors and shock wave generators are immersed in the tank. The reflectors focus the shock waves onto the calculus so that on releasing the waves in synchronism they break down the calculus using their brute force. As these waves have a rather wide and poorly defined spectral distribution and equivalent wavelength, their focusing is fairly imprecise and consequently their action synchronism is poor, these being aspects on which the efficiency of the system entirely depends. This perhaps explains the difficulties sometimes encountered in operating it correctly. According to the present invention, two focusing heads fed by power generators which can be adjusted both in power and frequency are immersed in a water container in which the patient is also present. As no structure of the human body responds to ultrasonic frequency, the patient feels little discomfort, comparable only to a tingling sensation ^ The principle of operation of the apparatus according to the invention is as follows. Each of the two focusing heads contains a sensor which picks up the reflection of its signal from an obstacle, in this case the calculus, and having determined the position of this latter by direct X-ray analysis and/or by ascending or descending pyeloscopy etc., the ultrasonic beam is directed and focused onto this position so as to obtain maximum reflected signal response for a given area of covering (partial or total) of the calculus. The percentage of area is chosen according to the calculus type and size and the optimised program for applying the power and energy intensity necessary for its fragmentation. The position of the focal spot and the choice of its size are made at low average power (a watt or less). A frequency sweep is then effected, again at low power, to determine the spectral reflection and resonance characteristics of the crystalline structures variously aggregated within the calculus. In this manner diagnostic information is obtained regarding the nature of the calculus and also information of fundamental importance for choosing the frequencies and form in which'to apply the power bursts in order to crumble the crystalline aggregates with minimum energy expenditure. The aforesaid description relates to the operation of a single focusing/ receiving head. A second head positioned symmetrically opposite the first and in line with the.calculus can be likewise used to focus its beam and effect the spectral analysis with a frequency sweep on its energy reflected by the calculus. Each of the two heads can be used for the spectral absorption analysis of the radiation emitted by the other. Thus both the diagnostic information and the information required to define the optimum irradiation program to obtain fragmentation of the calculus are then complete. We do not know what average and peak powers are required for fragmenting the various crystalline aggregates under resonance conditions. We consider that these are only moderate powers, of the average order of some tens of watts and certainly orders of magnitude less than the powers required to crumble , the stone substances under pure brute mechanical rupturing action. Finally, if the observations made on certain calculi which after some months of preservation in a vial easily crumbled at touch into their individual crystals having the size of sand grains (due to the evaporation of their water of hydrat on) are common to most or to a large proportion of calculi, then their fragmentation would require irradiation with bursts of much lower frequency (corresponding to the much weaker hydration bond) and of energy less by some orders of magnitude than for crystallisation. On this assumtpion, the ultrasonic system would prove extremely effective and of moderate cost, so making it of widespread use. A preferred embodiment of the present invention is described hereinafter in greater detail by way of non-limiting example with reference to the accompanying drawings in which: Figure 1 shows the equivalence between a monocrystal generator and a resonant electronic network; Figure 2 shows the relationship between amplitude and phase in a typical resonant circuit; Figure 3 shows by way of example a polycrystalline concretion structure, the equivalent electrical network and the corresponding diagram of relative amplitudes; Figures 4a and 4b show by way of example the relationship between incident energy and absorbed energy in a generic polycrystalline structure in the prior art; Figure 5 is a diagrammatic illustration of one embodiment of the apparatus according to the present invention; and Figure 6 shows amplitude/frequency diagrams illustrating the operation of the apparatus of Figure 5. With particular reference to Figures 1 to 4 of the drawings, Figure 1 shows that a generic monocrystal C, for which only one mode of mechanical oscillation is considered, can be considered equivalent to an RLC network. The parameters , C depend on the geometrical and molecular structure of the crystal whereas the parameter R depends on its internal friction and is one of the basic parameters in the technology of disintegration of crystalline concretions (calculi) because it constitutes the parameter which determines the absorption of energy by the crystal, this being a maximum at resonance frequency (Figure- 2), as is known from the theory of electrical and mechanical networks. If a polycrystalline structure is present such as an effective renal calculus CR (Figure 3), this will comprise an assembly of monocrystals variously coupled mechanically together, similar to a complex RE network which in the presence of a sweep of frequency ω presents a characteristic distribution of resonance and absorption peaks as shown by way of example in the diagram D, with peaks PI, P2, P3, P4 of various amplitudes and signs at specific frequencies ω., ω„, ω,, ω.. In currently known apparatus for disintegrating renal calculi by shock waves, the incident energy on the consistuent polycrystalline concretion of the renal calculus is distributed over a frequency range shown in Figure 4a as extending between two limiting frequencies ω. , ω„. If the polycrystalline concretion to be demolished has a characteristic frequency spectrum such as that shown schematically in Figure 4b, at the frequencies ω , ω , ω , ω the energy transfer from the external source Z 3 4 o to the polycrystalline concretion is acceptable whereas at the frequencies ω and ω is insufficient. Moreover, .as the incident power 1 o W. is distributed in a substantially uniform manner (wide spectrum shock waves), only that part of the incident energy indicated by the dashed zone is absorbed, while the rest remains unused or can indeed damage other structures of the patient's body. One embodiment of the apparatus according to the present invention is described hereinafter with reference to Figures 5 and 6. The patient's body, indicated overall by the reference numeral 10, is affected by a renal calculus 11. The patient's body 10 is immersed in water or another medium suitable for transmitting ultrasonic elastic waves together with the focusing heads indicated overall by 12 and 13. Each head 2, 13 comprises ultrasonic wave focusing means represented by a parabolic reflector 14, 15, each positioned to cooperate with a transmission transducer 16, 17 and a reception transducer 18, 19. The transmission transducers are controlled by power amplifiers indicated respectively by Txl, Tx2, which are excited by variable frequency oscillators 0SC1, 0SC2. Control terminals al, a2 on the transmitters Txl, Tx2 enable a computer CPU to vary the radiated power level to the calculus 11, and terminals sfl, sf2 enable the computer CPU to control the frequency of the oscillation produced by the two variable frequency oscillators 0SC1, 0SC2. The computer CPU is associated with peripherals of known type such as a control keyboard KB, a memory unit MEM and a video display unit M. The heads 12, 13 comprise reception transducers 18, 19 associated with amplifiers Rxl, Rx2 connected to the computer CPU to provide this latter with information regarding reflected energy, transmitted energy and energy absorbed by the renal calculus 11. The detailed structure of the transmitters Txl, Tx2 or receivers Rxl, Rx2 is not described herein as it forms part of the current art known to an expert in the sonar, echography, non-destructive ultrasonic analysis and other fields. The operating procedure is as follows. A spectral analysis is firstly carried out on the highest susceptibility peaks of the calculus structure at the various available ultrasonic frequencies by means of a low-power sweep, to obtain a spectrogram of the type shown in Figure 6A, in which the peaks PI, P2, P3, P4, P5, P6, P7 can be noted. By means of the head 12 or 13, or both heads, power peaks able to disintegrate the calculus structure are then selectively emitted (Figure 6B) and a new spectral analysis is effected, shown in Figure 6C in which it can be seen that the peaks P3, P5, P6 and P7 still remain, whereas the other have disappeared to confirm the disintegration of those parts of the structure associated with these peaks. New power peaks are then emitted as indicated in Figure 6D, possibly at greater power than used during the stage represented by Figure 6B. After this a spectral analysis is again made (Figure 6E) from which it can be seen that the peaks P1-P7 have all disappeared but that new peaks P8, P9 have appeared. Two new power peaks are then emitted as shown in Figure 6F. A further spectral analysis (Figure 6G) shows a "flat" curve indicating that there are no further solid structures detectable by ultrasonic means within the frequency band of the original crystalline concretion, and that the renal calculus 11 has therefore been totally disintegrated. It should be noted that in the aforegoing description relative to Figures 5 and 6 reference has been made to "amplitude" in the spectral analyses. It will be obvious to the expert of the art that this is a non-limiting example in that the spectral analysis can include consideration of the phase of the signal received by the reception transducers, and/or possible Doppler components as is well known from echographic techniques and from ultrasonic diagnostics carried out in the medical or structural analysis fields, and thus give fullest possible utilisation of the apparatus according to the invention, which as stated is based on spectrally pure ultrasonic emissions rather than semicontinuous or in any event uncontrolled spectral emissions as in the case of the shock waves of the known art. It should also be noted that in Figure 5 the heads 12, 13 are shown comprising parabolic reflectors 14, 15. It is however apparent that, in place of or in association with these, structures of lens and focusing wave guide type can be used. Instead of a structure with single reception-transmission transducers and transmitters and receivers, it is also conveniently possible to use a phased array structure well known in advanced radar and sonar techniques (synthetic-aperture antenna), with the advantage that the focusing, emission and reception structures can be completely static and controlled by a suitable computer, thus considerably simplifying the analysis and intervention operations. Finally, the receiver-transmitter head phases can be adjustable in order to obtain, in accordance with acoustic holography technology, further diagnostic information (such as shape, thickness, structure etc.) relative to the calculi and to further improve the disintegration action as thickness decreases, and more generally as the shape and constitution of the calculus vary during its breakdown. It is apparent that many variations can be made to the apparatus of the present invention, but without leaving its scope of protection.

Claims: Cl aims: 1. An apparatus for the non-intrusive fragmentation of renal calculi, characterised by comprising at least one receiver-transmitter head (12) for elastic ultrasonic oscillations which is focused on the renal calculus (11) to be disintegrated, said head being associated with low-power variable frequency transmitter means (16) and with receiver means (18) to perform a spectral analysis of the characteristic resonance frequencies of the calculus (11) to be- disintegrated, and control means (Txl, 0SC1) to cause said transmitter means (16) to emit relatively high-power energy peaks at the characteristic resonance frequencies of said calculus (11) to promote its disintegration. 2. An apparatus according to claim 1, characterised by comprising a first and a second receiver-transmitter head (12, 13) positioned in line and substantially symmetrical about the renal calculus (11) to be d sintegrated. 3. An apparatus according to claim 2, characterised in that the receiver-transmitter head phases are adjustable in order to obtain, in accordance with acoustic holography technology, further diagnostic information (such as shape, thickness, structure, etc.) relative to the calculi and to improve the disintegration action as thickness decreases, and more generally as the shape and constitution of the calculus vary during its breakdown. 4. An apparatus according to any one of claims 1 to 3, characterised in that the transmitter or transmitters (16; 17) and the receiver or receivers (18; 19) associated with the receiver-transmitter head or heads (12; 13) are associated with a computing and data processing unit (CPU) associated with a data ' presentat.ion unit (M) and a memory unit (MEM) for repetition of the spectral analysis sequences on the characteristics of the renal calculus (11) to be disintegrated. 5. An apparatus according to any one of claims 1 to 4, characterised in that said receiver-transmitter head or heads (12; 13) comprise ultra¬ sonic energy focusing means of parabolic reflector (14; 15) and/or acoustic lens and/or focusing wave guide type. 6. An apparatus according to any one of claims 1 to 5, characterised in that said receiver-transmitter head ot heads (12; 13) are formed in accordance with phased array technique. 7. An apparatus for the non-intrusive fragmentation of renal calculi substantially as described and illustrated.

Inventors: LA ROCCA ALDO, LA ROCCA, ALDO
Applicants: LARA CONSULTANTS SRL, LARA CONSULTANTS S.R.L.
Application year: 1988
Main classification: A61B17
IPC codes: A61B17, A61B18, A61N1