ENDOUROLOGY
DEVELOPMENT AND TESTING OF SECOND GENERATION EXTRACORPOREAL SHOCK-WAVE LITHOTRIPTOR FRANK P. BEGUN, M.D. RUSSELL K. LAWSON, M.D. JAMES E. CAULEY, M.D.
CHRISTOPHER M. KEARNS, M.D. DENNIS FOLEY, M.D. WILLIAM D. MIDDELTON, M.D.
From the Departments of Urology and Radiology, Medical College of Wisconsin, Milwaukee, Wisconsin
:ABSTRACT--The Northgate SD-3 extracorporeal shock-wave lithotriptor is a second generation device that utilizes an ultrasound-guided computer-assisted system for calculus localization. Focused electrohydraulic shock waves are generated in a movable membrane-covered ellipsoidal reflbctor. Pressure wave characteristics and energy output of the SD-3 and the Dornier HM-3 were 't~ted and found to be comparable. The ultrasound unit was capable of identi~ing radiolucent Calculi as well as calculus fragments 2-3 m m in size. The computer-assisted aiming system was found to be accurate to within i mm. The overall successful calculus fragmentation rate using an animal model was 80 percent with an 87.5 percent rate following machine modifications resulting i~ increased energy output.
T h e Northgate SD-3 extracoporeal shock-wave iliihotriptor (Northgate Research, Arlington Ht~ II.~ i~ n ~ooond generation extracorporeal otriptor that utilizes focused generated shock waves to flagdi. The device is mounted un.atment table and consists of a ,soid reflector located on a moa ultrasound-guided and computer-assisted aiming system is used for three~mensionai location of the calculus at the i ~ o n d focal point and automatically positions ~ e reflector under the patient. ~ T h e following report concerns results of our initial development and testing of the SD-3. : ~E}aluation and testing of the SD-3 consisted of ~(~) analysis of the energy output of the machine ~ d evaluation of energy attenuation through t h e membrane coupling system and tissue; (9.) e~aluation of the ultrasound system for visualizing calculi; (3) assessment of the accuracy of the ~iirasound-guided computer-assisted system for the positioning of the reflector; and (4) deterUROLOGy
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mination of the effieaey of the SD-3 with respect to calculus fragmentation. Material and Methods Description of SD-3 The SD-3 is a portable device that utilizes focused electrohydraulic generated shock waves to fragment urinary calculi. The device consists of two separate units: a patient treatment table and a computer control console (Fig. 1). The patient treatment portion of the system houses the energy generator, shock-wave reflector, water degassing tank, and ultrasound aiming system which consists of a 5 MHz transducer mounted on an articulated arm. The computer console contains the computer hardware with CRT monitor, the ultrasound system with display screen, and the controls for calculus imaging, calculus localization, and shock-wave reflector positioning. The patient treatment table measures 36 in high, 30 in wide, and 70 in long; the extension panels at each end of the table
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FICURE 1. Northgate SD-3 Extracorporeal Shockwave Lithotriptor. provide a potential length of 97 in. The computer console has dimensions of 58 in high, 9.1 in wide, and 26 in from front to back. The unit operates on standard 120 V AC.
Shock-wave generation The SD-3 uses an underwater electrical discharge to produce electrohydraulic shock waves. An electrical charge is generated and stored in a capacitor. The system employs a triggered spark gap, connected in series with the electrode cartridge, located at the bottom of the hemi-ellipsoidal reflector. The triggered gap is used to discharge the capacitor across the spark gap of the electrode cartridge. Expansion and collapse of the vaporized water cavitation bubble, created by the electrical discharge, result in the therapeutic shock waves. The generator is capable of completely recharging at a rate of at least 120 firings per minute. If a complete charge has not been attained, the system will not fire, thus ensuring the proper energy delivery with each discharge, The current design of the energy generator has produced over 110,000 firings without failure. The SD-3 is equipped with a 32 kV charge limitation to prevent potential damage to tissue or to the electrical components of the system. The device has several safety interlocks that prevent inadvertent discharge of the generator. The number of shocks per treatment and the total number of shocks produced by the generator are displayed on automatic counters mounted on the unit. Shock-wave delivery Shock waves are focused using a hemi-ellipsoidal reflector. The energy is transmitted to the patient's kidney using a water-filled cylinder mounted on the reflector. The principle of shock-wave focusing and delivery takes advantage of the characteristic two focal points of the ellipsoid. A flexible silicone membrane covers 238
the cylinder and provides a coupling interface with the skin. Mineral oil is applied to the skin/ m e m b r a n e interface to ensure an a i r - f r e e pathway between the first and second f o c a l points and to minimize energy attenuation. The reflector and cylinder have a volume of 3.5 L and this can be adjusted to extend the flexible membrane to make close contact with the skin of the subject. The electrode fits into a second chamber via an opening in the bottom of the reflector. T h e water in this smaller chamber provides an en2 vironment for the most efficient electrical disi charge and production of shock waves. Energy loss greatly depends on the amount of gas that accumulates within the shock-wave transmis,:, sion path. The small volume in the second chamber is continuously recirculated to remove gas bubbles that are produced with each electrical shock. The water in the larger chamber i s degassed; however, it does not come into contact with the water in the smaller chamber and does not need to be recireulated during t h e generation of the shock waves. The SD-3 electrode cartridge is changed after i every 600 to 800 shocks. A newer design m a y allow up to 2,500 firings per electrode. The chambers are emptied by pumping the water ~ into a reservoir tank. A retainer at the bottom, portion of the cartridge is unmounted and thd old electrode removed. A new electrode is posl~ tioned and the retaining manifold is replacedi The reflector is refilled and the lithotripsy pro~ cedure is resumed. :i
Degassing system The entire water treatment system is locatedl under the treatment table. The total capacity of the system is 16 L. Tap water can be used al:il though it may require treatment if the minerai ~, content is high. Therefore, distilled water is!!! recommended for optimal performance. The~ water is stored in a main reservoir that is corn::' nected to a continuously running vacuum! pump. This creates a negative pressure that re~ sults in degassing of the water. A series of sole! noid valves directs the water flow to the inner and outer reflector chambers. il 11
Ultrasound system The SD-3 utilizes an Ultramark 4 ultrasound system (Advanced Technology LaboratorieSi Bothell, WA) for calculus imaging and localiza~ tion. A 5 MHz mechanical sector transducer, with a focal depth of 4-10 em and a stated axial and lateral resolution at the focal plane of
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0.66 mm and 1.66 mm, is mounted on an articulated arm located under the patient treatment table. The transducer head can be brought into contact with the subject via a cutout in the table top. The ultrasound control console and monitor screen are located on the computer control unit.
Calculus localization The ultrasound transducer is mounted on an articulated arm equipped with digital eneoders which continuously report the position of each angular joint of the arm. The angular position is converted into a 13-bit digital word and this is stored in the system's computer. A 13-bit encoder breaks each 360 ° into 8,192 components, ::~epresenting a potential resolution of 0.044 °. :These eneoders possess linearity and absolute ::accuracy within one count, providing system ~ e e u r a e y of 1 mm or less. The calculus image is Centered on a cursor line located on the ultra:round monitor. W h e n the stone is correctly po{~ltioned, a foot switch is depressed causing the i m a g e to freeze and the computer to store the ;~Sngular position of each joint of the arm. Digi~;ital calipers, incorporated into the ultrasound ;ima~in~ system, are used to measure the disstone to the skin surface. These arly entered into the computer. then uses the data to calculate ensional position of the stone. ates are displayed on the system minal and correspond to a standration.
ioning vave reflector is mounted on a Lform located under the patient ~rator uses a set of three toggle )ve the reflector into the proper the XYZ coordinates provided by Modifications of the SD-3 will ~puter to position the reflector after acquisition of location data, lg need for manual operation.
energy output and characteristics output of the SD-3 lithotriptor using a PCB-tourmaline pressure CB Piezotronics, Inc., Depew, asducer was firmly mounted so vas positioned at F2 and repeated measurements of the SD-3 were ~ssure waves were analyzed and sing a d i g i t a l o s c i l l o s c o p e
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(Tektronix, Inc., Beverton, OR). This allowed evaluation of the pressure-wave form as well as the energy output in pounds per square inch
(PSi). Pressure measurements were made with and without the SD-3 m e m b r a n e interfaces. In addition, four fresh pig flank preparations were obtained and mounted on the SD-3, Pressure measurements were made through these flank preparations to assess the degree of energy attenuation. This was critical to ensure that the proper energy was being delivered at F2 for the stone fragmentation studies. Similar readings were made on the Dornier HM-3 lithotriptor at F2. The comparative data were important since the pressure measurements obtained were not necessarily absolute values and might vary depending on the measuring equipment used. Therefore, it was important to compare the SD-3 pressure data with the readings of a machine with proven ability to fragment calculi. Finally, repeated measurements were made at F2 at 2 kV increments on both the SD-3 and HM-3. A minimum of 20 firings were made at each kilovolt level and the PSI values recorded and averaged. This provided data concerning the energy output at varying voltages on both machines.
Evaluation of ultrasound imaging The SD-3 ultrasound system was used to image calculi in 20 patients, prior to and following ESWL treatment with the Dornier lithotriptor. Imaging was done with the patient in the same position as used during the treatment procedure. All images were stored for future reference and evaluation using an IBM XT computer system with Imagaction software (Imaging Technology, Inc., Woburn, MA). The ultrasound images were also compared with pretreatment and post-treatment x-ray films. Changes in configuration of the calculus and increases in the size of the stone mass were noted; measurement of the size of identifiable fragments at the termination of the procedure were also made to assess the sensitivity of the Ultramark-4 in imaging smaller ealeuli.
Evaluation of the computer-assisted ultrasound aiming system The accuracy of the SD-3 computer system in acquiring the ultrasound data, calculating the position of the calculus, and correctly positioning the reflector was repeatedly analyzed using a d u m m y t a r g e t fixture. T h e t a r g e t was mounted above the patient treatment table and
V O L U M E XXXVI, N U M B E R 3
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13500 I PRESSURE vs.
the tip of the fixture was located using a specially designed ultrasound probe mounted on the articulated arm. These data were entered into the system and the coordinates of the target were calculated and displayed on the CRT monitor. A second fixture was then placed over the reflector ellipsoid with the tip corresponding to the F2. The reflector was then moved to position specified by calculated coordinates and distance between two fixtures was measured. Evaluation oJ calculus fragmentation Animal model. Young adult female pigs between 40 kg and 80 kg in size were used for calculus fragmentation studies. In addition, pig flank preparations were used to measure energy loss through the tissue and the membrane interface on the SD-3. Similar m e a s u r e m e n t s through the flank preparations were also performed on the Dornier HM-3 for comparison. Stone fragmentation Sterilized human calculi of various sizes and composition were placed into the renal pelvis of adult pig kidneys. These procedures were performed using appropriate anesthetic and aseptic surgical techniques. All animals received a prophylactic perioperative regimen of intramuscular Amikaein to reduce the risk of wound infection. Initial attempts to place these calculi through a simple pyelotomy resulted in spontaneous passage of stones as large as 1.5-2 em. Attempts to maintain the proper position of the stones with Double-J stents were also unsuccessful due to passage of the stents as well as the calculi. Therefore, a system was devised using a 1-2 mm loop of 4-0 Prolene suture attached to the calculus with a minute amount of water insoluble glue. The calculus was properly placed in the renal pelvis and its position maintained using a second Prolene suture passed through the loop attached to the stone and brought out through the anterior surface of the kidney. This was loosely tied to retain stone in the proper position in the collecting system without causing it to be pulled into the renal parenehyma. Stone fragmentation was done several days to several weeks after implantation. The pigs were anesthetized and placed in position with their flanks over t h e cutout of the SD-3 table. The ultrasound imaging and aiming system was then used to locate the calculus and position the reflector. Calculus fragmentation was done with ultrasound imaging and re-aiming of the reflector every 300 shocks. X-ray films were obtained prior to the start of the lithotripsy proee-
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VOLTAGE
2o°ot 12000
P
11500
R
E S S U
11000 10500
j
/
10000 i
9500
p S I
9000 8500
8000 20
24
26
30
32
a4
VOLTAGE (In KV)
FIGURE 2. Northgate SD-3 and Dornier HM-3: comparative energy measurements at F2 with vary; ing Kv settings. dure and one or two films were taken during the treatment. An additional x-ray film was ta: ken at the termination of the procedure to assess~ fragmentation and for comparative purposes with the ultrasound images. A portable capaei~ tor discharge unit operated at 70-80 kV (peak) was used for this purpose. The pigs were the~ killed and their kidneys removed and openedl The kidney was examined for gross evidence o ii~ injury. The degree of f r a g m e n t a t i o n was!~ measured and the size of the largest f r a g m e n ~ was recorded. Results Energy output Initial pressure measurements were settings of 20-30 kV and were found t( proximately 6,000 PSI at the second foe~ Three adjustments were made in the increase the energy output of the devie, the location of the spark gap in the ellipse Wi'~f~ adjusted. Second, the type of material used;! the membrane animal interface was ehangei? Initially, an ultrasound gel was used b u t r! sulted in marked energy attenuation; therefor{ ~! mineral oil was substituted in an attempt t.i~! provide a better membrane-skin interfac! Energy levels were remeasured and values of approximately 9,600 PSI corded. Finally, adjustments were ma water degassing system. Energy lev measured a third time and found to b~ 16,000 PSI at 20-30 kV.
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microseconds as determined on the x-axis scale. The height of the curve repesents volts, and this m e a s u r e m e n t was converted to PSI using a precalibrated conversion factor.
0.5-
-0.5
0
i
g }a
tb
MICROSECONDS Northgate SD-3 pressure time curve.
FIGUI~E 3.
Measurements of the energy o u t p u t at F2 were m a d e at increasing kilovolt settings on both the SD-3 and HM-3 machines. These data are summarized in Figure 2. The reflector m e m b r a n e system of the SD-3 resulted in an 8-10 percent energy loss and accounted for the increased kilovolt levels necess a r y to achieve PSI levels comparable to those on the HM-3. Energy attenuation, measured through the pig flank preparations, was also found to be 8-10 percent. Measurements on the : Dornier machine showed a similar energy loss. The characteristics of the SD-3 pressure curve ~at F2 are illustrated in Figure 3. The rise time f o:!r the pressure curve was approximately 0.2 TABLE I. i!~Date
Kidney
i'ii2/01/86
ii2/08/86 i=ii!i:1/05/87 'iliiiiii/12/87
ilii!!ii::2/23/87
Stone Size (mm) × x x x
Ultrasound imaging The ultrasound imaging system was used to locate stones and stone fragments in both animals and patients. Calculi in the caliceal system and renal pelvis were easily visualized while those in the proximal ureter were often difficult to image. Serial ultrasound images during the procedure revealed a gradual expansion of the calculus mass as the lithotripsy process took place. In some instances, distinct fragments were discernible and could be targeted for treatment. However, the ultrasound reflection from an expanding stone cloud often m a d e identification of single fragments difficult, and x-ray correlation was necessary to assess the degree of breakage and determine w h e n to terminate the procedure (Figs. 4 and 5). The system used in the SD-3 lithotriptor was found to be capable of imaging calculi and fragments 2-3
Summary o] stone disintegration Stone Analysis
No. of Shocks
1 2 3 4
5 6 7 7
8 9 11 10
Calcium oxalate Calcium oxalate Uric acid Uric acid
1,000 1,500 1,900 1,400
5 6
6 x 10 5 × 9
Calcium oxalate Calcium oxalate
1,800 2,100
7
5 x 10
Calcium oxalate
2,700
8 9 10 11
7 x 10 5 × 10 7 7
Uric acid Calcium oxalate Uric acid Uric acid
2,100 2,250 2,000 2,700
Results Complete disintegration Complete disintegration Complete disintegration Single fragment 4xlmm Complete disintegration 3 fragments 6 x 2,3 x 3,3 x 3mm Single fragment 5x3mm Complete disintegration Complete disintegration Complete disintegration Complete disintegration
Machine modifications at this time with resulting increase in energy output 12 13 14 15 16
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x 7 9 × 5 x 8 x 5 10 x 4
17
7 x 8 x 6
18 19
8 x 5 x 4 9
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Uric acid Calcium oxalate Uric acid Calcium oxalate 60% Calcium phosphate 40 % Calcium oxalate Calcium phosphate Monohydrate Calcium phosphate Calcium oxalate Monohydrate Calcium oxalate Monohydrate
VOLUME XXXVI, NUMBER 3
2,400 2,400 1,800 2,400 2,000
Complete Complete Complete Complete Complete
2,700
Complete disintegration
2,500 2,500
Complete disintegration Single fragment 4x2mm Complete disintegration
2,500
disintegration disintegration disintegration disintegration disintegration
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(A and B). Preand post-treatment plain xray films demonstrating calculus fragmentation. FIGURE 4.
FIGURE 5 (A and B) Corresponding pre- and post-treatment ultrasound images of same patient. Calculus (black arrows) and Double-] stent (open arrows) are visualized preteatment. Note absence of calculus post-:I~ treatment. m m in size. In addition, the system was capable of imaging radiolucent calculi not visible using standard radiographie techniques.
Evaluation of computer-assisted ultrasound aiming system The aiming system initially utilized variable rheostats to measure the arm joint angles. The analog outputs were converted to a digital format by an A-D converter and stored in the computer. The computer then calculated the position of the stone and the reflector was moved along the XYZ axis to position the F1 with respect to F2. This system was accurate to within 5 mm. The system was redesigned and digital encoders were incorporated into the articulated arm, replacing the rheostats. These eneoders provide a system accuracy of + 1 mm.
Stone fragmentation The fragmentation data are summarized i n Table I. Twenty pig kidneys, with stones in: place, have been treated with the SD-3 litho, triptor. Eleven of these stones were c a l c i u m oxalate and 7 stones were uric acid. C r i t e r i o n for successful treatment was stone breakage with no fragment greater than 3 m m in size. The i n i ' tial eleven renal units were treated prior to t h e machine modifications which resulted in i n creased energy levels. Therefore, the treated at energy levels significantly lo~ levels utilized for the later stone fragm procedures. Sixteen of the 20 stones w cessfully treated with 1,000-2,700 sh~ livered at settings of 25-29 kV. Three of cium oxalate stones had fragments grea 3 m m in diameter and were considered i!!i~i
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treatment failures. One uric acid calculus had 4 x 1 mm fragment that had separated from the main calculus mass. This was not identified as a separate fragment on ultrasound and was not treated with additional shocks. X-ray evaluation was not possible due to the radiolueent composition of the stone. Eight of the nine calculi treated since the device adjustments resulted in complete stone disintegration in 1,800-2,500 shocks. The single failure involved a 4-mm calculus fragment that was actually identified on ultrasound imaging. However, 2,500 shocks had already been delivered, and it was elected to terminate the procedure. Comment The SD-3 lithotriptor is one of the "second generation" lithotriptors, using focused electrohydraulic shoek waves. The SD-3 was designed tO overeome some of the disadvantages of the D o r n i e r HM-3 device, including: (1) size of the !;unit, (2) lack of portability, (3) use of fluorosi~.i:eopy for calculus loealization, (4) necessity of ~he water bath for energy shock-wave delivery, a n d (5) cost. The SD-3 consists of a table and console and :Can be used in a space of 200 square feet or less. :;The unit is portable and ideal for use in an : operating room, outpatient clinic, or mobile setting. The membrane-eovered reflector sys:: tem eliminates the need for a larger water bath : ~ n d avoids the potential problem of body temp e r a t u r e regulation that ean be encountered in : i;fhe immersible system. The Dornier HM-3 inVolves positioning the patient's stone at the see0nd focal point with the F1 being fixed. The SD-3 involves movement of F1 relative to a fixed stone position, thus eliminating the need for the patient gantry. The patient table has been modified to permit adjustment of table height, ineorporation of stirrups, and a eateh Basin. This will enable proeedures sueh as eystoscopy and pre-treatment placement of ureferal stents to be performed. The SD-3 uses an ultrasound imaging and aiming system to loeate t h e position of the ealculus. This eliminates problems eneountered with fluoroscopic stone localization. Iladiolucent or minimally radiopaque ealeuli are readily imaged and treated using the SD-3 without the need for use of retrograde radiopaque contrast media during the procedure. The pig model was ehosen for evaluation of the system for several reasons: (1) studies of reflux nephropathy have shown that the arehitee-
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ture of the pig renal parenehyma and ealieeal system is similar to that of humans1.2; (2) the adult pig kidney is similar in size to the adult human kidney; and (3) the pig flank muscle best simulates the human flank muscle relative to the stone position. The placement of calculi in the renal pelvis of the pig provided an unexpected challenge. The problem of spontaneous stone (and stent) passage was eliminated through use of the double Prolene loop. This added somewhat to the complexity of the surgical procedure but ensured the proper position of the stone in the renal pelvis for eventual treatment. No calculus placed in this manner was passed prior to the lithotripsy procedure. The ease by which these animals are able to pass large calculi may be unique to the species or may be characteristic of several animal models. One possible explanation may relate to the greater capacity of the porcine ureters to dilate or for peristalsis to occur; facilitating the passage of stones in an essentially horizontal system. Pressure measurements were made using a PCB-tourmaline pressure transducer. Pressures were not interpreted as absolute values since these determinations can be variable depending on the type of transducer used. Measurements were made for comparative purposes at varying kilovolt levels on the SD-3 and the Dornier HM3 lithotriptors. Initial measurements were made with a Piezoelectric transducer (Kistler Instrument Corp., Amherst, NY) and a digital oscilloscope (Phillips Test and Measurement Instruments, Mahwah, NJ). This transducer was found to be incapable of measuring the rapid pressure rise and a PCB-tourmaline transducer was substituted. This was capable of detecting pressure pulses of less than 0.2 microseconds in d u r a t i o n . This was c o m p a t i b l e w i t h the published data on the pressure rise times of the therapeutic shock wave. Pressure measurements were made at F2 and found to be approximately 6,000 PSI. This was significantly less than the published energy levels of the Dornier HM-3 machine. Comparative testing between the Dornier HM-3 and the SD-3 was performed, and the SD-3 demonstrated pressures approximately 50 percent lower than those measurements on the HM-3. Adjustments in the SD-3 resulted in pressure levels of 9,600 PSI. This output was still 20-30 percent below that of the published data for the Dornier machine. Further adjustments in the system resulted in pressure outputs between 12,000-16,000 PSI.
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The degree of energy attenuation was believed to be critical with respect to the experimental design. It was i m p o r t a n t to k n o w whether energy loss was occurring at the membrane skin surface interface or through the animal flank. This w o u l d result in decreased energy delivery at the second focal point and could affect the ability of the SD-3 to fragment stones. Fresh isolated pig flank preparations were used in both the Dornier HM-3 and the SD-3 device. Measurements on the SD-3 were made in a water bath with and without the interface membrane in place. Energy losses between 8-10 percent were noted on both machines. Another important issue was determination of energy output at the various kilovolt settings on the SD-3 and similar comparative measurements on the Dornier HM-3. Pressure measurements between 24-30 kV on the SD-3 were found to be comparable to pressure measurements between 18-24 kV on the Dornier HM-3. This difference was due to energy attenuation caused by the two membranes in the shockwave path of the SD-3. Calculi of various compositions were placed in the renal pelvis of twenty renal units. Eleven stones w e r e treated prior to the increased energy levels achieved on the machine. There were three treatment failures: 2 were calcium oxalate stones and 1 was a uric acid stone. Nine additional stones, 5 calcium oxalate, 2 uric acid, 1 calcium phosphate, and 1 mixed calcium oxalate-ealeium phosphate, were treated after increased e n e r g y o u t p u t levels w e r e achieved. Eight of these w e r e successfully treated. One calculus had a single fragment noted on ultrasound at the termination of the procedure. The overall rate of successful stone fragmentation was 80 percent with a 72.7 percent rate prior to and an 87.5 percent rate following the modifications resulting in increased energy output. Ultrasound imaging was used to locate the stones and stone fragments in both animals and patients. The ATL system used in the Northgate SD-3 lithotriptor was found to be capable of imaging calculus fragments 2-3 m m in size. In addition, this system was capable of imaging radiolueent calculi that were not visible using standard radiographic techniques. Comparative imaging using the ATL ultrasound system was performed on 20 patients prior to and following ESWL treatment on the Dornier lithotriptor. In addition, observations of stone 244
fragmentation in the pig model were also made. Several conclusions can be drawn from these studies: (1) Individual 2-3 m m stones or stone fragments can be imaged as well or better with ultrasound than with fluoroscopy; (2) stones located in the proximal ureter are often poorly visualized and should be manipulated into the renal pelvis or caliceal system to optimize localization and subsequent treatment; (3) low density stones and stone fragments that are difficult or impossible to see on fluoroscopy can be easily imaged using ultrasound; and (4) increase in the size of the stone mass seen on ultrasound, during the treatment procedure, does not pro, vide sufficient i n f o r m a t i o n to d e t e r m i n e whether or not adequate stone fragmentation has occurred. This is due to the fact that larger stone fragments may be hidden in the " s t o n e cloud" seen on the ultrasound image. T h e r e , fore, a plain x-ray film is necessary to assess the degree of fragmentation and to determine when the lithotripsy procedure can be t e r m i n a t e d , The SD-3 is equipped with an x-ray cassette holder and a portable x-ray machine is used for i this purpose. In conclusion, the Northgate SD-3 lithotriptor is a portable second generation device that utilizes an ultrasound-guided computer-assisted ' system for calculus localization and a mere, brane covered reflector for shock-wave g e n e r a , tion and energy delivery. Successful c a l c u l u s fragmentation has been demonstrated in v i v o using an animal model. H u m a n use studies are being done to deter~ !~ mine the efficacy of the SD-3 in the t r e a t m e n t of renal calculi and 200 patients have now b e e n treated. These data will be the subject of a fu-;: ture publication. In addition, the design of the:: device lends itself to application for t r e a t m e n t of gallstones and animal trials are underway. : Froedtert Memorial Lutheran Hospital) Milwaukee, Wisconsin 53226
(DRECUN)
ACKNOWLEDGMENTS. To Brian Theriault without whose effort this project would never have come to corn, pletion, to Susan Lawson and Richard Bourne for their : : invaluable assistance, and to Colleen Beck and P a m e l a Cromell for preparation of the manuscript The Amikacin sed in this study was generously provided'by Bristol Lab; oratories, Evansville, Indiana. References 1. Hodson CJ, Maling TMJ, MeManamon PJ, and Lewis M G ! . The pathogenesis of reflux nephropathy, Br J Radiol (Suppl N o . 13), 1975. :: 2. Ransley PG, and Risdon RA: Reflux and renal scarring, Br J ' Radiol (Suppl No. 14), 1978.
UROLOGY
/ SEPTEMBER
DEVELOPMENT AND TESTING OF SECOND GENERATION EXTRACORPOREAL SHOCK-WAVE LITHOTRIPTOR FRANK P. BEGUN, M.D. RUSSELL K. LAWSON, M.D. JAMES E. CAULEY, M.D.
CHRISTOPHER M. KEARNS, M.D. DENNIS FOLEY, M.D. WILLIAM D. MIDDELTON, M.D.
From the Departments of Urology and Radiology, Medical College of Wisconsin, Milwaukee, Wisconsin
:ABSTRACT--The Northgate SD-3 extracorporeal shock-wave lithotriptor is a second generation device that utilizes an ultrasound-guided computer-assisted system for calculus localization. Focused electrohydraulic shock waves are generated in a movable membrane-covered ellipsoidal reflbctor. Pressure wave characteristics and energy output of the SD-3 and the Dornier HM-3 were 't~ted and found to be comparable. The ultrasound unit was capable of identi~ing radiolucent Calculi as well as calculus fragments 2-3 m m in size. The computer-assisted aiming system was found to be accurate to within i mm. The overall successful calculus fragmentation rate using an animal model was 80 percent with an 87.5 percent rate following machine modifications resulting i~ increased energy output.
T h e Northgate SD-3 extracoporeal shock-wave iliihotriptor (Northgate Research, Arlington Ht~ II.~ i~ n ~ooond generation extracorporeal otriptor that utilizes focused generated shock waves to flagdi. The device is mounted un.atment table and consists of a ,soid reflector located on a moa ultrasound-guided and computer-assisted aiming system is used for three~mensionai location of the calculus at the i ~ o n d focal point and automatically positions ~ e reflector under the patient. ~ T h e following report concerns results of our initial development and testing of the SD-3. : ~E}aluation and testing of the SD-3 consisted of ~(~) analysis of the energy output of the machine ~ d evaluation of energy attenuation through t h e membrane coupling system and tissue; (9.) e~aluation of the ultrasound system for visualizing calculi; (3) assessment of the accuracy of the ~iirasound-guided computer-assisted system for the positioning of the reflector; and (4) deterUROLOGy
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mination of the effieaey of the SD-3 with respect to calculus fragmentation. Material and Methods Description of SD-3 The SD-3 is a portable device that utilizes focused electrohydraulic generated shock waves to fragment urinary calculi. The device consists of two separate units: a patient treatment table and a computer control console (Fig. 1). The patient treatment portion of the system houses the energy generator, shock-wave reflector, water degassing tank, and ultrasound aiming system which consists of a 5 MHz transducer mounted on an articulated arm. The computer console contains the computer hardware with CRT monitor, the ultrasound system with display screen, and the controls for calculus imaging, calculus localization, and shock-wave reflector positioning. The patient treatment table measures 36 in high, 30 in wide, and 70 in long; the extension panels at each end of the table
NTIT~.ARI~lq '~
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FICURE 1. Northgate SD-3 Extracorporeal Shockwave Lithotriptor. provide a potential length of 97 in. The computer console has dimensions of 58 in high, 9.1 in wide, and 26 in from front to back. The unit operates on standard 120 V AC.
Shock-wave generation The SD-3 uses an underwater electrical discharge to produce electrohydraulic shock waves. An electrical charge is generated and stored in a capacitor. The system employs a triggered spark gap, connected in series with the electrode cartridge, located at the bottom of the hemi-ellipsoidal reflector. The triggered gap is used to discharge the capacitor across the spark gap of the electrode cartridge. Expansion and collapse of the vaporized water cavitation bubble, created by the electrical discharge, result in the therapeutic shock waves. The generator is capable of completely recharging at a rate of at least 120 firings per minute. If a complete charge has not been attained, the system will not fire, thus ensuring the proper energy delivery with each discharge, The current design of the energy generator has produced over 110,000 firings without failure. The SD-3 is equipped with a 32 kV charge limitation to prevent potential damage to tissue or to the electrical components of the system. The device has several safety interlocks that prevent inadvertent discharge of the generator. The number of shocks per treatment and the total number of shocks produced by the generator are displayed on automatic counters mounted on the unit. Shock-wave delivery Shock waves are focused using a hemi-ellipsoidal reflector. The energy is transmitted to the patient's kidney using a water-filled cylinder mounted on the reflector. The principle of shock-wave focusing and delivery takes advantage of the characteristic two focal points of the ellipsoid. A flexible silicone membrane covers 238
the cylinder and provides a coupling interface with the skin. Mineral oil is applied to the skin/ m e m b r a n e interface to ensure an a i r - f r e e pathway between the first and second f o c a l points and to minimize energy attenuation. The reflector and cylinder have a volume of 3.5 L and this can be adjusted to extend the flexible membrane to make close contact with the skin of the subject. The electrode fits into a second chamber via an opening in the bottom of the reflector. T h e water in this smaller chamber provides an en2 vironment for the most efficient electrical disi charge and production of shock waves. Energy loss greatly depends on the amount of gas that accumulates within the shock-wave transmis,:, sion path. The small volume in the second chamber is continuously recirculated to remove gas bubbles that are produced with each electrical shock. The water in the larger chamber i s degassed; however, it does not come into contact with the water in the smaller chamber and does not need to be recireulated during t h e generation of the shock waves. The SD-3 electrode cartridge is changed after i every 600 to 800 shocks. A newer design m a y allow up to 2,500 firings per electrode. The chambers are emptied by pumping the water ~ into a reservoir tank. A retainer at the bottom, portion of the cartridge is unmounted and thd old electrode removed. A new electrode is posl~ tioned and the retaining manifold is replacedi The reflector is refilled and the lithotripsy pro~ cedure is resumed. :i
Degassing system The entire water treatment system is locatedl under the treatment table. The total capacity of the system is 16 L. Tap water can be used al:il though it may require treatment if the minerai ~, content is high. Therefore, distilled water is!!! recommended for optimal performance. The~ water is stored in a main reservoir that is corn::' nected to a continuously running vacuum! pump. This creates a negative pressure that re~ sults in degassing of the water. A series of sole! noid valves directs the water flow to the inner and outer reflector chambers. il 11
Ultrasound system The SD-3 utilizes an Ultramark 4 ultrasound system (Advanced Technology LaboratorieSi Bothell, WA) for calculus imaging and localiza~ tion. A 5 MHz mechanical sector transducer, with a focal depth of 4-10 em and a stated axial and lateral resolution at the focal plane of
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0.66 mm and 1.66 mm, is mounted on an articulated arm located under the patient treatment table. The transducer head can be brought into contact with the subject via a cutout in the table top. The ultrasound control console and monitor screen are located on the computer control unit.
Calculus localization The ultrasound transducer is mounted on an articulated arm equipped with digital eneoders which continuously report the position of each angular joint of the arm. The angular position is converted into a 13-bit digital word and this is stored in the system's computer. A 13-bit encoder breaks each 360 ° into 8,192 components, ::~epresenting a potential resolution of 0.044 °. :These eneoders possess linearity and absolute ::accuracy within one count, providing system ~ e e u r a e y of 1 mm or less. The calculus image is Centered on a cursor line located on the ultra:round monitor. W h e n the stone is correctly po{~ltioned, a foot switch is depressed causing the i m a g e to freeze and the computer to store the ;~Sngular position of each joint of the arm. Digi~;ital calipers, incorporated into the ultrasound ;ima~in~ system, are used to measure the disstone to the skin surface. These arly entered into the computer. then uses the data to calculate ensional position of the stone. ates are displayed on the system minal and correspond to a standration.
ioning vave reflector is mounted on a Lform located under the patient ~rator uses a set of three toggle )ve the reflector into the proper the XYZ coordinates provided by Modifications of the SD-3 will ~puter to position the reflector after acquisition of location data, lg need for manual operation.
energy output and characteristics output of the SD-3 lithotriptor using a PCB-tourmaline pressure CB Piezotronics, Inc., Depew, asducer was firmly mounted so vas positioned at F2 and repeated measurements of the SD-3 were ~ssure waves were analyzed and sing a d i g i t a l o s c i l l o s c o p e
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(Tektronix, Inc., Beverton, OR). This allowed evaluation of the pressure-wave form as well as the energy output in pounds per square inch
(PSi). Pressure measurements were made with and without the SD-3 m e m b r a n e interfaces. In addition, four fresh pig flank preparations were obtained and mounted on the SD-3, Pressure measurements were made through these flank preparations to assess the degree of energy attenuation. This was critical to ensure that the proper energy was being delivered at F2 for the stone fragmentation studies. Similar readings were made on the Dornier HM-3 lithotriptor at F2. The comparative data were important since the pressure measurements obtained were not necessarily absolute values and might vary depending on the measuring equipment used. Therefore, it was important to compare the SD-3 pressure data with the readings of a machine with proven ability to fragment calculi. Finally, repeated measurements were made at F2 at 2 kV increments on both the SD-3 and HM-3. A minimum of 20 firings were made at each kilovolt level and the PSI values recorded and averaged. This provided data concerning the energy output at varying voltages on both machines.
Evaluation of ultrasound imaging The SD-3 ultrasound system was used to image calculi in 20 patients, prior to and following ESWL treatment with the Dornier lithotriptor. Imaging was done with the patient in the same position as used during the treatment procedure. All images were stored for future reference and evaluation using an IBM XT computer system with Imagaction software (Imaging Technology, Inc., Woburn, MA). The ultrasound images were also compared with pretreatment and post-treatment x-ray films. Changes in configuration of the calculus and increases in the size of the stone mass were noted; measurement of the size of identifiable fragments at the termination of the procedure were also made to assess the sensitivity of the Ultramark-4 in imaging smaller ealeuli.
Evaluation of the computer-assisted ultrasound aiming system The accuracy of the SD-3 computer system in acquiring the ultrasound data, calculating the position of the calculus, and correctly positioning the reflector was repeatedly analyzed using a d u m m y t a r g e t fixture. T h e t a r g e t was mounted above the patient treatment table and
V O L U M E XXXVI, N U M B E R 3
239
13500 I PRESSURE vs.
the tip of the fixture was located using a specially designed ultrasound probe mounted on the articulated arm. These data were entered into the system and the coordinates of the target were calculated and displayed on the CRT monitor. A second fixture was then placed over the reflector ellipsoid with the tip corresponding to the F2. The reflector was then moved to position specified by calculated coordinates and distance between two fixtures was measured. Evaluation oJ calculus fragmentation Animal model. Young adult female pigs between 40 kg and 80 kg in size were used for calculus fragmentation studies. In addition, pig flank preparations were used to measure energy loss through the tissue and the membrane interface on the SD-3. Similar m e a s u r e m e n t s through the flank preparations were also performed on the Dornier HM-3 for comparison. Stone fragmentation Sterilized human calculi of various sizes and composition were placed into the renal pelvis of adult pig kidneys. These procedures were performed using appropriate anesthetic and aseptic surgical techniques. All animals received a prophylactic perioperative regimen of intramuscular Amikaein to reduce the risk of wound infection. Initial attempts to place these calculi through a simple pyelotomy resulted in spontaneous passage of stones as large as 1.5-2 em. Attempts to maintain the proper position of the stones with Double-J stents were also unsuccessful due to passage of the stents as well as the calculi. Therefore, a system was devised using a 1-2 mm loop of 4-0 Prolene suture attached to the calculus with a minute amount of water insoluble glue. The calculus was properly placed in the renal pelvis and its position maintained using a second Prolene suture passed through the loop attached to the stone and brought out through the anterior surface of the kidney. This was loosely tied to retain stone in the proper position in the collecting system without causing it to be pulled into the renal parenehyma. Stone fragmentation was done several days to several weeks after implantation. The pigs were anesthetized and placed in position with their flanks over t h e cutout of the SD-3 table. The ultrasound imaging and aiming system was then used to locate the calculus and position the reflector. Calculus fragmentation was done with ultrasound imaging and re-aiming of the reflector every 300 shocks. X-ray films were obtained prior to the start of the lithotripsy proee-
240
VOLTAGE
2o°ot 12000
P
11500
R
E S S U
11000 10500
j
/
10000 i
9500
p S I
9000 8500
8000 20
24
26
30
32
a4
VOLTAGE (In KV)
FIGURE 2. Northgate SD-3 and Dornier HM-3: comparative energy measurements at F2 with vary; ing Kv settings. dure and one or two films were taken during the treatment. An additional x-ray film was ta: ken at the termination of the procedure to assess~ fragmentation and for comparative purposes with the ultrasound images. A portable capaei~ tor discharge unit operated at 70-80 kV (peak) was used for this purpose. The pigs were the~ killed and their kidneys removed and openedl The kidney was examined for gross evidence o ii~ injury. The degree of f r a g m e n t a t i o n was!~ measured and the size of the largest f r a g m e n ~ was recorded. Results Energy output Initial pressure measurements were settings of 20-30 kV and were found t( proximately 6,000 PSI at the second foe~ Three adjustments were made in the increase the energy output of the devie, the location of the spark gap in the ellipse Wi'~f~ adjusted. Second, the type of material used;! the membrane animal interface was ehangei? Initially, an ultrasound gel was used b u t r! sulted in marked energy attenuation; therefor{ ~! mineral oil was substituted in an attempt t.i~! provide a better membrane-skin interfac! Energy levels were remeasured and values of approximately 9,600 PSI corded. Finally, adjustments were ma water degassing system. Energy lev measured a third time and found to b~ 16,000 PSI at 20-30 kV.
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VOLUME XXXVI,
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microseconds as determined on the x-axis scale. The height of the curve repesents volts, and this m e a s u r e m e n t was converted to PSI using a precalibrated conversion factor.
0.5-
-0.5
0
i
g }a
tb
MICROSECONDS Northgate SD-3 pressure time curve.
FIGUI~E 3.
Measurements of the energy o u t p u t at F2 were m a d e at increasing kilovolt settings on both the SD-3 and HM-3 machines. These data are summarized in Figure 2. The reflector m e m b r a n e system of the SD-3 resulted in an 8-10 percent energy loss and accounted for the increased kilovolt levels necess a r y to achieve PSI levels comparable to those on the HM-3. Energy attenuation, measured through the pig flank preparations, was also found to be 8-10 percent. Measurements on the : Dornier machine showed a similar energy loss. The characteristics of the SD-3 pressure curve ~at F2 are illustrated in Figure 3. The rise time f o:!r the pressure curve was approximately 0.2 TABLE I. i!~Date
Kidney
i'ii2/01/86
ii2/08/86 i=ii!i:1/05/87 'iliiiiii/12/87
ilii!!ii::2/23/87
Stone Size (mm) × x x x
Ultrasound imaging The ultrasound imaging system was used to locate stones and stone fragments in both animals and patients. Calculi in the caliceal system and renal pelvis were easily visualized while those in the proximal ureter were often difficult to image. Serial ultrasound images during the procedure revealed a gradual expansion of the calculus mass as the lithotripsy process took place. In some instances, distinct fragments were discernible and could be targeted for treatment. However, the ultrasound reflection from an expanding stone cloud often m a d e identification of single fragments difficult, and x-ray correlation was necessary to assess the degree of breakage and determine w h e n to terminate the procedure (Figs. 4 and 5). The system used in the SD-3 lithotriptor was found to be capable of imaging calculi and fragments 2-3
Summary o] stone disintegration Stone Analysis
No. of Shocks
1 2 3 4
5 6 7 7
8 9 11 10
Calcium oxalate Calcium oxalate Uric acid Uric acid
1,000 1,500 1,900 1,400
5 6
6 x 10 5 × 9
Calcium oxalate Calcium oxalate
1,800 2,100
7
5 x 10
Calcium oxalate
2,700
8 9 10 11
7 x 10 5 × 10 7 7
Uric acid Calcium oxalate Uric acid Uric acid
2,100 2,250 2,000 2,700
Results Complete disintegration Complete disintegration Complete disintegration Single fragment 4xlmm Complete disintegration 3 fragments 6 x 2,3 x 3,3 x 3mm Single fragment 5x3mm Complete disintegration Complete disintegration Complete disintegration Complete disintegration
Machine modifications at this time with resulting increase in energy output 12 13 14 15 16
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4/02/87
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10 10 × 10 7 11 x
x 7 9 × 5 x 8 x 5 10 x 4
17
7 x 8 x 6
18 19
8 x 5 x 4 9
20
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Uric acid Calcium oxalate Uric acid Calcium oxalate 60% Calcium phosphate 40 % Calcium oxalate Calcium phosphate Monohydrate Calcium phosphate Calcium oxalate Monohydrate Calcium oxalate Monohydrate
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2,400 2,400 1,800 2,400 2,000
Complete Complete Complete Complete Complete
2,700
Complete disintegration
2,500 2,500
Complete disintegration Single fragment 4x2mm Complete disintegration
2,500
disintegration disintegration disintegration disintegration disintegration
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(A and B). Preand post-treatment plain xray films demonstrating calculus fragmentation. FIGURE 4.
FIGURE 5 (A and B) Corresponding pre- and post-treatment ultrasound images of same patient. Calculus (black arrows) and Double-] stent (open arrows) are visualized preteatment. Note absence of calculus post-:I~ treatment. m m in size. In addition, the system was capable of imaging radiolucent calculi not visible using standard radiographie techniques.
Evaluation of computer-assisted ultrasound aiming system The aiming system initially utilized variable rheostats to measure the arm joint angles. The analog outputs were converted to a digital format by an A-D converter and stored in the computer. The computer then calculated the position of the stone and the reflector was moved along the XYZ axis to position the F1 with respect to F2. This system was accurate to within 5 mm. The system was redesigned and digital encoders were incorporated into the articulated arm, replacing the rheostats. These eneoders provide a system accuracy of + 1 mm.
Stone fragmentation The fragmentation data are summarized i n Table I. Twenty pig kidneys, with stones in: place, have been treated with the SD-3 litho, triptor. Eleven of these stones were c a l c i u m oxalate and 7 stones were uric acid. C r i t e r i o n for successful treatment was stone breakage with no fragment greater than 3 m m in size. The i n i ' tial eleven renal units were treated prior to t h e machine modifications which resulted in i n creased energy levels. Therefore, the treated at energy levels significantly lo~ levels utilized for the later stone fragm procedures. Sixteen of the 20 stones w cessfully treated with 1,000-2,700 sh~ livered at settings of 25-29 kV. Three of cium oxalate stones had fragments grea 3 m m in diameter and were considered i!!i~i
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treatment failures. One uric acid calculus had 4 x 1 mm fragment that had separated from the main calculus mass. This was not identified as a separate fragment on ultrasound and was not treated with additional shocks. X-ray evaluation was not possible due to the radiolueent composition of the stone. Eight of the nine calculi treated since the device adjustments resulted in complete stone disintegration in 1,800-2,500 shocks. The single failure involved a 4-mm calculus fragment that was actually identified on ultrasound imaging. However, 2,500 shocks had already been delivered, and it was elected to terminate the procedure. Comment The SD-3 lithotriptor is one of the "second generation" lithotriptors, using focused electrohydraulic shoek waves. The SD-3 was designed tO overeome some of the disadvantages of the D o r n i e r HM-3 device, including: (1) size of the !;unit, (2) lack of portability, (3) use of fluorosi~.i:eopy for calculus loealization, (4) necessity of ~he water bath for energy shock-wave delivery, a n d (5) cost. The SD-3 consists of a table and console and :Can be used in a space of 200 square feet or less. :;The unit is portable and ideal for use in an : operating room, outpatient clinic, or mobile setting. The membrane-eovered reflector sys:: tem eliminates the need for a larger water bath : ~ n d avoids the potential problem of body temp e r a t u r e regulation that ean be encountered in : i;fhe immersible system. The Dornier HM-3 inVolves positioning the patient's stone at the see0nd focal point with the F1 being fixed. The SD-3 involves movement of F1 relative to a fixed stone position, thus eliminating the need for the patient gantry. The patient table has been modified to permit adjustment of table height, ineorporation of stirrups, and a eateh Basin. This will enable proeedures sueh as eystoscopy and pre-treatment placement of ureferal stents to be performed. The SD-3 uses an ultrasound imaging and aiming system to loeate t h e position of the ealculus. This eliminates problems eneountered with fluoroscopic stone localization. Iladiolucent or minimally radiopaque ealeuli are readily imaged and treated using the SD-3 without the need for use of retrograde radiopaque contrast media during the procedure. The pig model was ehosen for evaluation of the system for several reasons: (1) studies of reflux nephropathy have shown that the arehitee-
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ture of the pig renal parenehyma and ealieeal system is similar to that of humans1.2; (2) the adult pig kidney is similar in size to the adult human kidney; and (3) the pig flank muscle best simulates the human flank muscle relative to the stone position. The placement of calculi in the renal pelvis of the pig provided an unexpected challenge. The problem of spontaneous stone (and stent) passage was eliminated through use of the double Prolene loop. This added somewhat to the complexity of the surgical procedure but ensured the proper position of the stone in the renal pelvis for eventual treatment. No calculus placed in this manner was passed prior to the lithotripsy procedure. The ease by which these animals are able to pass large calculi may be unique to the species or may be characteristic of several animal models. One possible explanation may relate to the greater capacity of the porcine ureters to dilate or for peristalsis to occur; facilitating the passage of stones in an essentially horizontal system. Pressure measurements were made using a PCB-tourmaline pressure transducer. Pressures were not interpreted as absolute values since these determinations can be variable depending on the type of transducer used. Measurements were made for comparative purposes at varying kilovolt levels on the SD-3 and the Dornier HM3 lithotriptors. Initial measurements were made with a Piezoelectric transducer (Kistler Instrument Corp., Amherst, NY) and a digital oscilloscope (Phillips Test and Measurement Instruments, Mahwah, NJ). This transducer was found to be incapable of measuring the rapid pressure rise and a PCB-tourmaline transducer was substituted. This was capable of detecting pressure pulses of less than 0.2 microseconds in d u r a t i o n . This was c o m p a t i b l e w i t h the published data on the pressure rise times of the therapeutic shock wave. Pressure measurements were made at F2 and found to be approximately 6,000 PSI. This was significantly less than the published energy levels of the Dornier HM-3 machine. Comparative testing between the Dornier HM-3 and the SD-3 was performed, and the SD-3 demonstrated pressures approximately 50 percent lower than those measurements on the HM-3. Adjustments in the SD-3 resulted in pressure levels of 9,600 PSI. This output was still 20-30 percent below that of the published data for the Dornier machine. Further adjustments in the system resulted in pressure outputs between 12,000-16,000 PSI.
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The degree of energy attenuation was believed to be critical with respect to the experimental design. It was i m p o r t a n t to k n o w whether energy loss was occurring at the membrane skin surface interface or through the animal flank. This w o u l d result in decreased energy delivery at the second focal point and could affect the ability of the SD-3 to fragment stones. Fresh isolated pig flank preparations were used in both the Dornier HM-3 and the SD-3 device. Measurements on the SD-3 were made in a water bath with and without the interface membrane in place. Energy losses between 8-10 percent were noted on both machines. Another important issue was determination of energy output at the various kilovolt settings on the SD-3 and similar comparative measurements on the Dornier HM-3. Pressure measurements between 24-30 kV on the SD-3 were found to be comparable to pressure measurements between 18-24 kV on the Dornier HM-3. This difference was due to energy attenuation caused by the two membranes in the shockwave path of the SD-3. Calculi of various compositions were placed in the renal pelvis of twenty renal units. Eleven stones w e r e treated prior to the increased energy levels achieved on the machine. There were three treatment failures: 2 were calcium oxalate stones and 1 was a uric acid stone. Nine additional stones, 5 calcium oxalate, 2 uric acid, 1 calcium phosphate, and 1 mixed calcium oxalate-ealeium phosphate, were treated after increased e n e r g y o u t p u t levels w e r e achieved. Eight of these w e r e successfully treated. One calculus had a single fragment noted on ultrasound at the termination of the procedure. The overall rate of successful stone fragmentation was 80 percent with a 72.7 percent rate prior to and an 87.5 percent rate following the modifications resulting in increased energy output. Ultrasound imaging was used to locate the stones and stone fragments in both animals and patients. The ATL system used in the Northgate SD-3 lithotriptor was found to be capable of imaging calculus fragments 2-3 m m in size. In addition, this system was capable of imaging radiolueent calculi that were not visible using standard radiographic techniques. Comparative imaging using the ATL ultrasound system was performed on 20 patients prior to and following ESWL treatment on the Dornier lithotriptor. In addition, observations of stone 244
fragmentation in the pig model were also made. Several conclusions can be drawn from these studies: (1) Individual 2-3 m m stones or stone fragments can be imaged as well or better with ultrasound than with fluoroscopy; (2) stones located in the proximal ureter are often poorly visualized and should be manipulated into the renal pelvis or caliceal system to optimize localization and subsequent treatment; (3) low density stones and stone fragments that are difficult or impossible to see on fluoroscopy can be easily imaged using ultrasound; and (4) increase in the size of the stone mass seen on ultrasound, during the treatment procedure, does not pro, vide sufficient i n f o r m a t i o n to d e t e r m i n e whether or not adequate stone fragmentation has occurred. This is due to the fact that larger stone fragments may be hidden in the " s t o n e cloud" seen on the ultrasound image. T h e r e , fore, a plain x-ray film is necessary to assess the degree of fragmentation and to determine when the lithotripsy procedure can be t e r m i n a t e d , The SD-3 is equipped with an x-ray cassette holder and a portable x-ray machine is used for i this purpose. In conclusion, the Northgate SD-3 lithotriptor is a portable second generation device that utilizes an ultrasound-guided computer-assisted ' system for calculus localization and a mere, brane covered reflector for shock-wave g e n e r a , tion and energy delivery. Successful c a l c u l u s fragmentation has been demonstrated in v i v o using an animal model. H u m a n use studies are being done to deter~ !~ mine the efficacy of the SD-3 in the t r e a t m e n t of renal calculi and 200 patients have now b e e n treated. These data will be the subject of a fu-;: ture publication. In addition, the design of the:: device lends itself to application for t r e a t m e n t of gallstones and animal trials are underway. : Froedtert Memorial Lutheran Hospital) Milwaukee, Wisconsin 53226
(DRECUN)
ACKNOWLEDGMENTS. To Brian Theriault without whose effort this project would never have come to corn, pletion, to Susan Lawson and Richard Bourne for their : : invaluable assistance, and to Colleen Beck and P a m e l a Cromell for preparation of the manuscript The Amikacin sed in this study was generously provided'by Bristol Lab; oratories, Evansville, Indiana. References 1. Hodson CJ, Maling TMJ, MeManamon PJ, and Lewis M G ! . The pathogenesis of reflux nephropathy, Br J Radiol (Suppl N o . 13), 1975. :: 2. Ransley PG, and Risdon RA: Reflux and renal scarring, Br J ' Radiol (Suppl No. 14), 1978.
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