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Description  |
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BACKGROUND OF THE PRESENT INVENTION
1. Field of Invention
The invention relates to an improved apparatus for the contact free disintegration of a calculus located in the body of a human being. In particular, the invention provides improved localization of the calculus and enhances the ability to direct
a focussed sonic wave to a target region in the body.
2. Prior Art
Extracorporeal shock-wave lithotripsy is a medical procedure that disintegrates renal (kidney) stones. The term, lithotripsy is derived from the Greek and literally means "stone crushing." This medical "stone crushing" technique has been
demonstrated to be effective on renal (kidney), upper ureteral and biliary stones (gallstones) in human patients. The technique is noninvasive and eliminates the need for the more conventional stone removal procedures, such as open surgery.
Stone crushing is achieved by the geometric focussing of energy, such that the area of focus coincides with the stone that is to be shattered. The focussing of energy is a principle that is frequently used to obtain a strong effect within a
confined area. The application of focussed energy is effective on the stone, since it is relatively brittle. The application of stress leads to the rapid formation of cracks and eventually to the disintegration of the stone.
Although a single intense pulse will generally shatter the stone, a pulse train of lower intensity and short duration pulses will generally produce smaller and more uniform particles. One drawback to a series of pulses is that during treatment
the small particles produced during the fragmentation shock waves may obscure the larger remaining fragments. This may result in the shielding of the larger, remaining fragment from the shock wave, which results in an increase of treatment duration.
On the other hand, the accumulated small particles may lead the care provider into prematurely terminating treatment before completion, due to the inability to accurately view the remaining larger fragments.
Another problem associated with the production of small particles, is that gravitational forces may cause the small particles of settle into the lower calyces, thereafter requiring an excessive amount of time to effectuate clearing these lower
calyces.
Despite the problems associated with the smaller particles, for the kidney stone patient, there are number of direct benefits from the lithotripsy technique that outweigh these minor disadvantages. The technique is capable of reducing the length
of hospital stay from 7 to 14 days for conventional stone removal surgery to 4 days or fewer. It also eliminates the 4 to 6 weeks post-hospitalization convalescence commonly required after major surgery. Typically, the kidney stone patient will
naturally and spontaneously pass the stones in the urine, much as if the stones were naturally grain-sized. However, after fragmentation, there will be many more grain-sized stones than occur naturally.
There are several other techniques presently used to treat kidney stones, as an alternative to major surgery. For example, if the stone remains grain-sized, it usually passes spontaneously in the urine and the patient can be treated with drugs
to reduce the pain and to prevent future stone occurrence. However, this technique is usually only effective for very small stones.
Depending on the size and the location of the stone, several other clinical and surgical methods are available. If the stone has formed or lodged itself in the lower urinary tract and bladder, a standard cystoscope combined with a stone basket
or a special stone removal forceps may be used to extract the stone. During the procedure, a local anesthetic must be administered to minimize the pain. Additional drawbacks are the possibilities that the ureter will be damaged and the formation of
additional stones that would prohibit the repetition of the procedure.
Ultimately, if the stone cannot be removed by any of the conventional methods, the patient must resort to open surgery. The traditional surgical procedure is a major operation that requires an incision into the kidney or ureter to remove the
stone. In addition to the normal morbidity and risks associated with major surgery, another stone could form, necessitating further surgery. Furthermore, there is a chance that the patient will finally lose the kidney altogether.
As an alternative to open surgery, lithotripsy was explored. However, early lithotriptic treatment employs invasive ultrasonic lithotripsy. The lithotriptic means employed involved an insertion of an ultrasonic probe into a small incision in
the patient's side. While this required less recovery time than traditional surgery, it was still surgery, however small the incision and furthermore carried all the inherent risks associated with surgery.
Noninvasive extra corporeal shockwave lithotripsy was developed and overcame the negative risks of surgery. A shock wave is generated and ultimately focussed at the stone. The focussed wave strikes the stone, it disintegrates the stone and the
stone fragments are ultimately passed through the ureter.
Early versions of extra corporeal (EC) shock wave lithotripsy required the patient to be immersed in a large tank of water. Originally, a spark gap electrode was fixed at one end of a large stainless steel tub and generated a shock wave as the
electrode was discharged underwater. Since the impedance properties of water and soft tissue are similar, the shockwave entered the body without damaging the soft tissue. If care is taken to direct the shockwaves at the calculi, other parts of the body
are generally not affected. Typically, bones are not affected by this procedure due to their high tensile strength and the brevity of the pulses. However, the large difference in acoustical impedance between the water and the stone results in enough
pressure to shatter the stone. The process was painful and the patient generally required an epidural or general anesthesia.
Before treatment could commence, it was necessary to locate and identify the stone. Prior to immersing the patient into the large stainless steel tank of water, the patient was x-rayed thus prelocalizing the stone. After every 100 pulses or so,
the patient was lifted out of the tank and x-rayed again. This was to ascertain the status of the stone and to verify the effectiveness of the treatment. With an average of 1600 pulses, the patient could be x-rayed as many as 17 times to verify that
the stone was fragmented and to confirm the completeness of the treatment. Although an x-ray produces a sharper and clearer progress report, the patient was required to undergo a number of detrimental radiation exposures.
Another problem associated with immersing the patient is the inability to accurately reposition the patient once the patient had been moved. Since the electrode is fixed, the patient must be positioned and repositioned. This led to inaccuracies
and sometimes painful results.
An alternative localization technique requires the use of two x-ray images, with the focal point at the central point of the two screens. Typically, the two x-ray devices for locating the stone are disposed next to the shockwave generator and
reflector and are on an opposite side or axis of the generator. The two central beams of the two x-ray heads intersect the axis of the reflector running through the two focal points. The intersection should be near or at the location of the stone.
Establishment of a relationship between a spatially fixed mark and the patient is required. The equipment generally is repositioned vis-a-vis the patient.
From a point of view of expense, the utilization of two x-ray heads and devices is relatively expensive to operate and to maintain. There is also the question of the radiation dosage that the patient receives.
When using an x-ray procedure, the patient must be positioned or repositioned such that the stone is located at the focal point of the shock wave. For example, when using a stainless steel water tank, the patient is then positioned with a
hydraulic system so that the calculus is at a predetermined focal point. While this allows access to a more accurate target region, it is necessary to physically reposition the patient for each image. Disadvantageously, the patient is required to
remain immobilized during the location procedure.
Ultrasound imaging is another suggested alternative means of locating and monitoring the stone. Generally for well-defined stones, ultrasound is sufficient to monitor the progress of treatment. Furthermore, the use of ultrasound eliminates the
problems of radiation dosage that arise with the use of x-ray localization techniques.
Another advantage of ultrasound imaging is the ability to monitor real time progression of the treatment. Additional ultrasound monitors can be positioned within the treatment system in such a way as to virtually eliminate repositioning of the
patient.
However, ultrasound imaging does not provide the same same high contrast results or "pictures" that an x-ray unit can provide. Since the resulting images are not as sharp and have as high a contrast, which can be due to the limitations to the
technique itself, the size and quantity of the stones, or the size of the patient, can make progressive monitoring of patient and the subsequent treatment somewhat risky and haphazardous.
Furthermore, prior to the elimination to the large steel water tank, the use of ultrasonic monitoring equipment was severely limited, as the equipment had to be located within the vicinity of the patient itself.
A combination of the two monitoring techniques, that is x-ray and ultrasound, would be suited except for the problem of patient repositioning. Immobility of the patient is essential and are identical to the problems discussed previously in
connection with the x-ray techniques.
The eventual elimination of the large stainless steel water tank resulted in a more compact and effective system. Furthermore, elimination of the water tank also gave rise to the possibility of using ultrasound imaging. Patient immersion became
unnecessary as the acoustic waves were still propagated through a water containment bag rather than through an open body of water. The patient is positioned over a cushion or a bag filled with water. The cushion is coupled to a stretcher and to the
patient by a layer of ultrasound gel.
Once the patient positioning had been improved, the means for producing the shock wave needed to be improved. For example, the prior method of producing focussed acoustic waves required an electric discharge generated across an underwater spark
gap, positioned in the focus line of an elliptical reflector. The early spark gap systems generated a shockwave in a large tank of water, in which the patient had previously been positioned. The process shattered renal stones by a brute force method.
The treatment required the patient to have an epidural, spinal or general anesthesia in order "to keep the patient under control, to avoid hurting the patient and to aim better at the stone."
Improvements made it possible to remove the patient from the water tank and to virtually eliminate the need for an epidural or general anesthesia. Generally, a larger ellipsoid for focal precision and a decrease in the power output are credited
for the improvements. Accuracy improved as the focussing process was computer controlled, rather than visual sighting by the operator. The computer automatically positions the patient in the shockwave focus by controlling the patient's table.
The spark gap systems create a diverging pulse or explosion. The energy produced is distributed over a relatively large area, for example 15-20 square mm and requires that the energy be focussed within a parabolic reflector. This diverging
pulse induces arhythmia, pulverizes tissue and causes bruising. To avoid the inducement of extrasystoles, the shockwave must be released as a function of ECG or respiratory triggering. Furthermore, the spark gap electrodes tend to be somewhat costly.
On the other hand, an alternative means using a piezoelectric transducer generates a converging pulse and eliminates the need for cardiac or respiratory triggering. With a converging pulse system, an area of impact of approximately 2-3 square mm
is observed. This results in less tissue damage with approximately the same amount of pressure. Generally, the patient only requires a local or a topical anaesthetic, if any at all.
The piezoelectric crystal is the basis for the piezoelectric transducer. A piezoelectric crystal is a piece of natural quartz or other asymmetric crystalline material capable of demonstrating the piezoelectric effect. Piezoelectricity is a
phenomenon first noticed in 1880 whereby certain crystalline substances generate electrical charges when subjected to mechanical deformation. The reverse effect also occurs, that is, a voltage applied across the crystall causes mechanical deformation or
flexing.
To produce the shock wave, a piezoelectric crystal is deformed by applying a high frequency, high voltage pulse of the proper polarity, thus causing the crystal to compress. The voltage is then withdrawn from the crystal, such as shorting the
crystal to ground and the crystal expands to it's "normal" state. This results in a pressure wave front that propagates through a medium such as water.
Typically, the shock wave is focussed by arranging piezoelectric crystal elements in a mosaic pattern on the surface of a dish generally shaped as a concave lens. The pattern and lens may be designed such that each individual element is excited
by a pulse generator simultaneously. Thus, the waves produced by the crystals arrive at the target area focussed and in phase, with a very narrow near ideal shape and with high energy at the focal point. Advantageously, the dish is shaped to produce
very small focal areas in which the energy is sufficient to destroy the stone but virtually painless.
A major disadvantage of the multi-element piezoelectric system is the necessity of simultaneously triggering 300 to 3000 elements on the concave surface of the focussing lens. Disadvantagely, it is necessary to connect all the piezoelectric
crystals to act as one to work in conjunction with a single power supply. An alternative method is to connect each individual element to individual power supplies, for example, having 300 elements and therefore 300 very small, individual power supplies
triggering simultaneously. In addition to the problems arising from coordinating all the elements, there is the problem of cost effectiveness.
Another costly disadvantage is the requirement that the numerous elements be specially made. The individual elements must be contoured to fit within the concave configuration of the focussing lens. This decreases the cost effectiveness of the
piezoelectric system.
With the use of a piezoelectric transducer, it is necessary to generate a sufficiently high voltage to deform the piezoelectric crystal. Typically, a high voltage generator is required.
In order to ensure that the shockwave generated from the piezoelectric crystal deformation is sufficient to crush the kidney stone, the wave must be focussed. One alternative means of focusing the wave is to create a semi-circular dish wherein
the piezoelectric crystals are arranged on the upper surface of the dish in a spherical mosaic-like arrangement.
Generally this type of arrangement requires careful manufacturing of the crystals such that the bottom is rounded as well as the top to maintain a semi-circular or semi-ellipsoid surface area. Either the crystals can be manufactured so that they
fit like a mosaic within the face of the lens or dish or they may be sufficiently small pieces that, because of their size, they merely fit within the shape of the dish itself.
A focusing lens with the crystals configured within the concave surface of the lens produces a very narrow, more ideal shape with a high energy wave at the focal point. This narrowed focussed shockwave requires a shorter duration for the
shattering pulse.
The use of a focussing lens with the piezoelectric crystals has several other advantages over that of the spark gap technology. Since the lens creates a converging focussed pulse the problem of cardiac gating or arhythmia may be eliminated. In
contrast, the spark gap generators create a diverging pulse, and induce arhythmia. Additionally, there can be much more damage to surrounding tissue as well as substantial bruising and the possibility of passing of blood through urine when using
ellipsoid reflectors.
Thus, what is needed is a more compact system that provides both the sharpness and clearness available from x-ray localization but allows for reduced radiation dosages, provides for the piezoelectric crystal benefits as well as the focussing lens
advantages, and furthermore provides the necessary power output to deform the piezoelectric crystals in the most effective way.
SUMMARY OF THE INVENTION
The present invention overcomes the disadvantages of the prior systems by providing a compact dual prelocalization and real time monitoring system. In the preferred embodiment, location of the stone is achieved by using an x-ray prelocalization
means such as a fluoroscope or an x-ray tomo head. Once the stone has been located and coordinates obtained the patient is moved by means of a moveable sliding table from the x-ray position to the ultrasound monitoring and treatment position.
Advantageously, the patient is moved from one position to the other by merely repositioning the planar surface from one end to the other thus eliminating any positioning discrepancies due to patient movement.
Once the patient is positioned treatment to disintegrate the stone located within the human body may commence. A triggering pulse from a control panel triggers a piezoelectric crystal generating a shockwave. Once the shockwave is generated, it
propagates through an acoustical lens, focussing the shockwave to a point of approximately 2-3 millimeters in diameter. The focussed shockwave strikes the stone within the body thereby shattering the stone.
Advantageously, the piezoelectric crystal transducer is located on the bottom surface of the acoustical lens, that is the flat surface. Advantageously the crystal positioning provides a more efficient means of generating the shockwave necessary
to shatter the stones. Furthermore, the cost efficiency of manufacturing is enhanced by eliminating the need for expensive crystal shaping.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of a lithotripsy system of the preferred embodiment of the present invention.
FIGS. 2(a)-(c) are schematic representations of the relationship between several components of the lithotripsy system and:
(a) a representation of a body of a patient to an x-ray component of the lithotripsy system; and
(b) a representation of the body of the patient to an ultrasonic-real time scan component of the lithotripsy system; and
(c) a representation of the body of the patient to a ultrasonic shockwave generation component of the lithotripsy system.
FIG. 3 is a perspective view of a patient table and dual tomo-heads of the x-ray component of the lithotripsy system of the preferred embodiment.
FIG. 4 is a cross-sectional representation of a control unit and a stone breaking unit of the lithotripsy system of the preferred embodiment.
FIG. 5 is a detailed top plan perspective view of an acoustical lens assembly of the lithotripsy system of the preferred embodiment.
FIG. 6 is a cross-sectional view of the acoustical lens assembly taken as section A--A of FIG. 5.
FIG. 7 is a bottom plan, exploded, perspective view of piezoelectric crystals bonded to the acoustical lens and of coupling copper mesh.
FIG. 8 is a circuit diagram of a piezoelectric crystal triggering circuit as may be utilized by the lithotripsy system of the preferred embodiment.
FIG. 9 is a graphic representation of the timing sequence of the triggering circuit of FIG. 8.
FIG. 10 is a graphic representation of the voltage profile from a crystal of FIG. 8.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
An invention is described that provides a means for locating, positioning and for breaking up, without contact, calculi present in the body of a human being. As a result of the capabilities of the present invention, the accuracy and completeness
of lithotriptic treatment are effectively enhanced. In the following description, numerous specific details are set forth such as specific dimensions, materials, etc., in order to provide a thorough understanding of the present invention. It will be
obvious, however, to one skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known procedures and materials have not been described in detail in order not to unnecessarily obscure the
present invention.
Proceeding now to the detailed description of the drawings, FIG. 1 illustrates a perspective overview of the lithotripsy system 100 of the present invention. The lithotripsy system 100 is comprised of an ultrasound imaging unit 125, a mobile
x-ray unit 126 and a lithotripter unit 127.
The ultrasound imaging unit 125 is a self-contained system that can be utilized as a stand alone ultrasound unit, in addition to functioning as a real-time ultrasonic imaging system for the lithotripter 100. The ultrasound imaging unit 125 is
comprised of a control panel 600, a hand-held imaging probe 110, and a monitoring unit 109.
The x-ray unit 126 provides for fluoroscopic image processing and spot film capabilities. A urological table 113a is docked to a lithotripter table 113b and locked into place by the docking latch 112. Although the preferred embodiment
illustrates the use of docking latch 112, any means of stably connecting the two tables together is within the spirit and scope of the present invention. Alternatively, the use of only a single table is also within the scope of the present invention.
The urological table 113a can be used as a stand alone examination table for routine urological procedures with or without the use of the x-ray unit 126.
The x-ray unit 126 is comprised of mobile C-arm 111, a pair of fluoro exposure monitors 106, a control unit 105, and a monitor cart 104. Although FIG. 1 preferably illustrates a mobile C-arm 111 as a means for providing fluoroscopic images, a
standard x-ray unit is also an acceptable means of providing the necessary fluoroscopic images. The mobile C-arm 111, as well as a standard x-ray unit is typically comprised of a tomo head 101 and a means for receiving fluoroscopic images 102.
Referring to FIGS. 2(a)-(c), the treatment procedure of the lithotripter system 100 of FIG. 1 is schematically shown. FIG. 2a describes the patient P in relationship to the tomo head 101 and means for receiving flouroscopic images 102. The
patient P is positioned on a planar surface, with the upper portion of the body inclined upward on a headrest 201. The lower portion of the body is immobilized by placing the patient's knees over a leg rest 202. A dual fluoroscopic image is then
obtained by acquiring two oblique images. The oblique images are obtained by moving the tomo-head 101 off axis by +9 degrees and -9 degrees.
FIG. 2(b) describes the patient P in relationship to an acoustical lens 205 of the lithotripter unit 127. (The acoustical lens 205 will be described in more detail with reference to FIGS. 5-7.) The patient P, still positioned on the planar
surface and the headrest 201 and leg rest 202 are moved from one end of a treatment table to the other end of the table. An ultrasound probe 206 is positioned centrally within the lens 205. A focussed shockwave 207 is directed at the kidney stone
previously located by the dual fluoroscopic images as described in FIG. 2(a). FIG. 8 describes the pre-location procedure in more detail.
FIG. 2(c) describes the patient P in relationship to an ultrasound imaging probe 206 of the lithotripter unit 127. The imaging probe 206 is, preferably, centrally located in the acoustical lens 205, allowing for ultrasound localization and
real-time monitoring. The central location of the imaging probe 206 provides a multi-zone focussing array 208 allowing for an extended field-of-view.
Referring to FIGS. 1 and 3, the lithotripsy table 113b docked to the urological treatment table 113a and the x-ray unit is illustrated. The two tables 113a and 113b are docked and then latched together for stability providing a platform for a
moveable planar surface or a "sled" 107. The docking latch 112 is dropped into place once the tables are docked together. Although the preferred embodiment describes the use of a docking latch 112, any functionally equivalent latching means may be used
so long as the latching means provides stability for the tables and allows the use of the sled 107.
To initially locate the kidney stone X, the patient P is placed on the sled 107. The sled 107 is located at position 1, which is at the urological table 113a. During the localization procedure, the patient P must remain essentially immobile.
Immobility is achieved by locking the sled 107 into position and by the careful placement of the patient P. The upper portion of the patient's body is positioned against a headrest 201, while the patient's legs are placed over the leg rest 202. This
allows the patient's back to rest directly and comfortably on the upper surface of the sled 107. In addition to the relative comfort, the patient is made immobile.
Once the patient P is placed such that the kidney stone X is generally centrally located over the fluoroscope 102, a fluoroscopic exposure is taken of the stone X. The precise position of the stone X is achieved by taking two | | |
