Introduction: Shock waves are usually produced from a single source at a mean frequency of 120 waves/ min. We utilize a device (Direx Duet) with two reflectors working at 120 waves / min each, forcing 240 waves / min against the stone. MATERIALS AND METHODS: From September 2005 to March 2006, 50 patients affected with ureteric and /or renal stones were treated in our unit. On the whole, 58 urinary were treated. All patients were submitted to ESWL under analgesia i.v. (ketorolac 30 mg + Tramadolo 100mg + Butilscopolamine 40 mg). Pain intensity was evaluated by the Visual Analogue Scale (VAS). After the treatment, patients were asked to complete a questionnaire to select tolerable from no-tolerable group. The intensity increase was 1 HV / 100 shock waves, till maximum of 10 HV after shock waves.     Stone Size 5-10mm 11-15mm >16mm Average Size 36 20 2 8,64 Stone location UC MC LC RP UPJ UU MU 5 13 16 19 0 3 2 RESULTS: All patients (31 male and 19 female, mean age of 50 years) completed the treatment. Only 1 patient did not reach the maximum intensity. The mean pain severity was 3,3 (range 0-9). After the first treatment, 19-50 patients declared themselves able to undergo the next treatment without analgesia. Fifteen of them completed the second treatment bit 10 (8 with stone in superior calyces, 2 in renal pelvis) complained of a more intense pain. The other 4 required analgesia for the completion. No relation was found between pain and stone's size, age and sex of the patient. Complications occurred in 3 patients (1 renal haematoma and 2 renal colic). Results Stone Treated Success Partial Fragments (>4mm) No Fragmentation 58 85% 8% 7%   CONCLUSIONS: Our results suggest that ESWL under analgesia is safe, simple and shows good compliance and tolerance. In order to select the patients a careful clinical examination is mandatory.   BIBLIOGRAPHY: Oh SJ et al. "Subjective pain scale and the need for analgesia during shock wave lithotripsy" Urol Int.2005;74:54-7. Medina HJ et al. "Remifentanil as a single drug for extracorporeal shock lithotripsy: a com[arision of infusion doses in terms of analgesic potency and side effects" Anesth Analg. 2005; 101:365-70 Chin CM et al. "Use of patients-controlled analgesia in extracorporeal shockwave lithotripsy" By J Urol. 1997;79:848-51

richter

4 Hz vs. 2 Hz Extracorporeal Shock Wave Lithotripsy (ESWL) with the Direx Duet Lithotripter – Comparative Results

Santiago Richter, Wael Abu-Arfat*, Ami Farkash*, Ilan Leibovich Meir Medical Center, Israel Shaarei Zedek Medical Center*, Israel

Introduction and Objective: Most available Lithotripters generate shock waves from one source only and use a shock frequency of 2 Hz, or are ECG gated (for arrhythmic patients). The Direx Duet is a Dual Head Lithotripter, able to operate at 2 Hz in each reflector, resulting in a total number of 4 shocks per second, delivered to the stone (4 Hz). The objective of this study is to investigate whether stone fragmentation at 4 Hz is as effective and safe as at 2 Hz, while reducing significantly the treatment time. METHODS: During the period of May through September 2004, 65 patients were treated randomly at two centers, with the Direx Duet at either 2 or 4 Hz. The procedure was performed under general (29) or epidural (36) anesthesia. Success was defined as either stone free or fragments of <4 mm, partial success as fragments of >4 mm and failure as no fragmentation. Patients were followed by KUB at 3-5 weeks after ESWL. RESULTS: There were 24 right and 41 left renal units, respectively. All stone parameters were comparable in both groups. Thirty patients were treated at 2 Hz and 35 patients at 4 Hz, under an identical protocol. The tables show stones characteristics and intrarrenal location. Stone Size 5 mm 6-10 mm 11-15 mm >16 mm Average Size Range   4 Hz 5 22 5 3 9.11+3.72 5-22 mm Frequency 2 Hz 4 20 6 0 8.7+2.86 5-15 mm Intrarenal Stone Location Frequency UC MC LC RP UPJ UU MU LU 4 Hz 3 2 9 9 1 11 0 0 2 Hz 5 6 6 9 3 0 1 0 Comparative Results Frequency Number of Stones Treated Success Partial Fragments (>4mm) Cases Number of NF Cases 2 Hz 30 26(87%) 1 (3%) 3 (10%) 4 Hz 35 29(83%) 5 (14%) 1 (3%) 1) Incidence of Adverse Events   Frequency 4 Hz 2 Hz   Hematuria - - Adv. Event Renal Colic 2 2 2) Average Treatment Time Trigger 4 Hz 2 Hz Avg. Treatment 9.69 16.06 Time (min) (SD = 3.04) (SD = 7.73) Re-treatment Rate 2 patients in each group had to be retreated at 3-4 weeks after ESWL. CONCLUSIONS: The 4Hz Treatment Mode with the Direx Duet has similar side effects and effectiveness as the 2 Hz but is able to perform a typical SWL Treatment in less than 10 minutes.

alexanderalaexander

ABSTRACT: Purpose: To evaluate the efficacy of the Duet lithotripter’s novel design of two independent spark-plug gen- erator/reflector systems focused at a common F2. The apparatus allows either simultaneous delivery of shockwaves from both generators (resulting in a per-shock energy delivery at F2 equal to that delivered by its single generator at about 24 kV), alternating (between the two generators), or single-generator delivery of shockwaves at various energy levels and rates. Materials and Methods: Eighty-five phantom gypsum stones (volume 786 mm3 each) were placed in a netlike basket and immersed in a specially designed waterbath coupled with the Duet lithotripter (Direx Medical Systems Ltd., Petach Tikva, Israel). Shockwaves were delivered at rates of either 60 or 120 per minute and at intensities of 16 or 22.8 kV (electrohydraulic). Energy was delivered either separately from each generator, in an alternating mode, or simultaneously from both generators. The number of shocks required to fragment the stones sufficiently to allow all of the pieces to fall through the basket holes (complete fragmentation) was recorded. Results: The number of shocks required for complete fragmentation in the alternate mode (120 shocks/min, each generator rate 60/min; 22.8kV) was lower than with the single generator, 112 ± 19 v 134 ± 18 (at a rate of 120/min; 22.8 kV). The simultaneous mode of dual generator shockwave delivery was more effective than the traditional single generator (114 ± 28 shocks at a rate of 120/min, 16 kV v 159 ± 40 shocks at a rate 120/min; 22.8kV). Conclusion: The Duet lithotripter is more effective when used in a simultaneous or alternating mode than is the classical single mode of shock delivery, with the added benefit of shorter treatment time. INTRODUCTION With the introduction of lithotripsters two decades ago, extracorporeal shock wave lithotripsy has become the treatment of choice for most urinary stones. Clinical results and side effects have been well defined.* The increasing number of endoscopic procedures,to that delivered by a single generator at about 24 kV. The alcreasing number of endoscopic procedures, however, may reflect some disappointment with the efficacy of the tubless lithotripters, consequently stimulating the search to improve lithotripter design. The novelty of the Duet lithotripter lies in its two indepentent spark-plug generator/reflector systems focused at a common F2 (Fig. 1). The machine allows simultaneous, alternating, or single generator delivery at various energy levels and rates. The simultaneous mode delivers as many as 120 shocks per minute at up to 17 kV concomitantly from both generator, resulting, assuming that energy is proportional to (kV)2 and is scalar summation of the two, in a per-shock energy at F2 equal to that delivered by a single greater at about 24 kV. The alternating mode delivers the same number of shocks per minute sequentially from two generators and a single generator delivery of shockwaves at various energy levels and rates as high as 120 shocks per minute. This in vitro study was performed to evaluate stone fragmentation by the Duet lithotripter in various modes of operation.   * Department of Urology, Tel Aviv Sourasky Medical Center, Sackler Faculty of Medicine, Tel-Aviv University, Tel Aviv, Israel.     STONE FRAGMENTATION BY DUET LITHOTRIPTER FIG. 1. Duet lithotripter: T = top reflector; B = bottom reflector.   MATERIALS AND METHODS The phantom stone model Cylindrical gypsum stones (10-mm diameter, 10-mm high, 786-mm3 volume) especially manufactured for the evaluation of lithotripsy performance were used (HMT, Lengwil, Switzerland). Before their use in the study, these phantom stones were immersed in degassed water for at least 20 minutes until air bubbles were no longer visible at the stone surface3.   The Duet lithotripter The Duet is a transportable tubless electrohydraulic SWL that consists of a shockwave generator (SWAG), a motorized floating treatment table (MFT), and controls. The SWAG is an electrohydraulic device consisting of two identical discharge units and co-focal reflectors placed 72° apart. It can be operated in four modes: • Bottom reflector only (“B” mode), directed at 36° above the horizontal; • Top reflector only (“T” mode), directed at 36° below the horizontal; • Alternate (asynchronous) (“A”) mode that alternates sequentially between “B” and “T”; and • Simultaneous (synchronous) (“S”) mode, in which the two reflectors operate simultaneously. Each ellipsoid reflector aperture is 180.5 mm in diameter, and the focal extent is 142 mm. The positive peak pressure at the focal point (focal zone size 13 x 13 x 48 mm) is measured with a needle-type PVDF transducer at 22 kV, 48 MPa. It allows as many as 120 pulses per minute (ppm) in all four modes of usage. The voltage setting is up to 24 kV for the B, T, and A mode, but only up to 17 kV for the S mode. The kV constraint for S is provided in order to limit the combined energy per shock to that of the single reflector case. Because the peak pressure (P) is assumed to be proportional to the high voltage setting (kV) and the pulse energy is proportional to P2 (thus assuming [kV]2), the combined energy in S (2 x 172) is the same as that in the single reflector modes (242).   Study protocol The 85 phantom gypsum stones were placed in a 2.5-mm sieve mesh net-like basket and immersed in a specially designed waterbath coupled to the Duet lithotripter. The phantom stones were a-priori positioned at F2. The latex walls of the waterbath were coupled to the water cushion of the two reflectors. The contact area was lubricated with silicone oil. Shockwaves were delivered at rates of 60 or 120 ppm and at voltage levels of 16 or 22.8 kV (note: 2 x 162x ~22.82). The silicone oil lubrication of the water cushion of the lithotripter and the waterbath in which the basket was immersed were renewed after each test session. The electrodes were replaced after every 2500 shocks. We conducted four test sessions, each employing 15 to 25 stones. Fragmentation was considered complete when all stone fragments fell through the holes of the basket. The number of shockwaves required for complete fragmentation (COG), the mode of operation (single-reflector B or T, A, or S), the rate of shockwave delivery (60 or 120 ppm), and the voltage setting (16 or 22.8 kV) were recorded. The efficiency was defined as: (stone volume [786 mm3])/COG (mm3/shock) The unpaired t-test was used for statistical analysis.   RESULTS: Four observations emerged (Table 1):   COG DATA FROM FOUR SESSIONS Session HV kV Rate ppm Single-reflactor mode (B or T) A mode S mode 1 22.8 120 134 ± 18a 112 ± 19 - 2 22.8 60 112 ± 18 - - 3 16 120 - 223 ± 49 114 ± 28 4 22.8 120 159 ± 140 - - * standard deviation. TABLE 1. First, the efficacy at 120 ppm was 20% to 40% less than that at 60 ppm (session 2 compared with session 1) in the traditional single-reflector (B or T) mode (P < 0.041). Second, the alternating mode at 120 ppm (session 1) was more efficient than the single-reflector mode at the same pulse rate (session 1) (P < 0.046), the same as for observation 1. Moreover, the A mode at 120 ppm was as efficacious as the single-reflector mode at 60 ppm (session 1 compared with 2) (P > 0.99). (Note: each generator/reflector unit operates at 60 ppm when the A mode is set at 120 ppm). The performances of reflectors B and T were found to be substantially similar. Because it is the more common orientation of the reflector in lithotripsy devices, B was used for the statistical calculations. Sessions 1 and 2 were executed as batch 1 and sessions 3 and 4 as batch 2. To avoid additional statistical errors, all observations, with the exception of 3, were based on results within the same batch. Third, the efficacy was proportional to the shockwave energy (~ to [pressure]2; hence ~[kV]2). Comparing the efficacy of the A mode at 22.8 kV (session 1) with that at 16 kV (session 3), 2 x162/22.82 = ~1 (P > 0.96). Finally, at the same pulse energy value, the efficacy of the S mode (session 3 at 16 kV) was higher than that of the singlereflector mode (session 4: 120 ppm at 22.8 kV) (P < 0.014). DISCUSSION: The approach to patients with urinary tract stones changed with the introduction of SWL by Chaussy et al.4 This noninvasive treatment rapidly gained considerable popularity over the surgical approach. The tubless lithotripters introduced several modifications. One of the recent modifications, in comparison with the Dornier HM3 tub lithotripter (Dornier Medical Systems, Inc., Marietta, GA), was to eliminate the waterbath and reduce the focal zone. However, because fragmentation efficacy, among other features (e.g., stone shape and dimensions, cavitation phenomenon, environment of the stone) is also proportional to energy, which is in direct relation to the (pressure2) x (the focal zone cross-sec- tion), keeping the same energy per pulse while decreasing the focal zone cross-section yields higher energy densities. Reducing energy density at the skin level caused a reduction in pain associated with SWL and thus enabled an “anesthesia-free” mode of treatment.5 However, these modifications made it more difficult to focus the waves on the stone, resulting in lower efficacy. Increasing the peak pressure to 105 MPa from the 40 MPa used in the Dornier HM3 did not improve stone fragmentation capacity.5 While slowing the rate of shock delivery seems to improve the efficacy of stone fragmentation, it prolongs the treatment time and subsequently reduces the cost-ef- fectiveness of SWL.3 Our first observation reconfirms a previous report that the efficacy at 120 ppm is 20% to 40% less than that at 60 ppm in the traditional single-reflector mode (B or T)3. The pressure wave of the shockwave pulses, which consists of a positive and a negative part, can act in different ways. The positive part results in tensile stress and thus creates pressure gradients, shear stress, and, finally, tensile stress and strain. The negative pressure waves cause cavitation in the surrounding water, within the microcracks, and in the cleavage interfaces of the stone.6 Sass and co-workers7 reviewed high-speed films (10,000 frames/second) of the shockwave’s direct response on kidney stones and gallstones. They reported that the shockwave produces fissures in the stone material, whereupon liquid enters. Disintegration occurs by the effect of cavitation bubbles within these split lines. Lingeman et al8 summarized the mechanism of stone fragmentation during SWL and offered four possible mechanisms: compression fracture caused by the effect of the positive-pressure fraction of the wave on the front surface of the stone, spallation of the compressive wave at the fluid–stone surfaces (such as the rear surface of the stone), cavitation formation in fluids caused by the negative fraction of the wave (i.e., the collapsing bubbles relay energy to the stone), and a dynamic fracture process caused by tensile stress induced by the repeated application of the shockwaves. The hydration time of the stones used in our study was only 20 minutes, which may be too short to displace all the air from the stone. The presence of air within a stone will affect the mechanism of breakage, and it is conceivable that the action of dual pulses will not be comparable to the action of single pulses. Furthermore, when a stone that contains air is broken, it will release the air into the surrounding water, and this should stimulate cavitation. It is possible that this difference in the mechanisms of stone breakage explains the efficacy of the S and A modes of SWL compared with the classical single mode of shock delivery. The efficacy of stone fragmentation is proportional to the shockwave energy (~ to [pressure]2; hence ~ [kV]2), among other factors. Thus, the efficacy of the A mode at 22.8 kV (session 1) is about double that at 16 kV (session 3; 2 x 162/22.82 = ~ 1). It is possible that our observation that the A mode at 120 ppm (session 1) is more efficient than the single-reflector mode at the same pulse rate (session 1) and that the alternating mode at 120 ppm has the same efficacy as the single-reflector mode at 60 ppm (session 1 compared with 2) indicates that the degradation in efficacy from the 60 ppm case to the 120 ppm case is secondary to phenomena associated with the generator/re- flector units at the F1 zone and not at the F2 zone, in which the pulses converge at 120 ppm in all cases. The efficacy of the simultaneous mode (session 3 at 16 kV) was higher than the single-reflector mode (session 4 at 22.8 kV) at the same pulse energy value. This synergistic effect associated with the S mode may be explained by the fact that there are two distinctive shockwaves converging almost simultaneously at the focal zone; each is confronted by the cavitation and the reflected wave associated with the other shockwave. Xi and Zhong9 reported that stone fragmentation might be enhanced by a second shockwave applied near the collapse period of the cavitation bubbles that had been generated by the first shockwave. In the S mode of the Duet lithotripter, both shockwaves are generated simultaneously. Thus, it is possible that the overall efficacy is amplified because of the interaction between the two simultaneously delivered shockwaves.   CONCLUSION: The Duet lithotripter seems to be more effective in fragmenting stones when used in either in a simultaneous or an alternating mode compared with the classical mode of single generation of shock delivery and has the additional benefit of shorter treatment time. ACKNOWLEDGMENTS: Yehuda Aminetzah, Ph.D., is thanked for his scientific and technical overall assistance. Esther Eshkol is thanked for editorial assistance. REFERENCES: 1. Drach GW, Dretler S, Fair W, et al. Report of the United States Cooperative Study of Extracorporeal Lithotripsy. J Urol 1986; 135:1127. 2. Lingeman JE, Woods J, Toth PO, et al. The role of lithotripsy and its side effects. J Urol 1989;141:793. 3. Greenstein A, Matzkin H. Does the rate of extracorporeal shock wave delivery affect stone fragmentation? Urology 1999;54:430. 4. Chaussy C, Schmiedt E, Jocham D, et al. First clinical experience with extracorporeally induced destruction of kidney stones by shock waves. J Urol 1982;127:417. 5. Lingeman JE. Extracorporeal shock wave lithotripsy: What happened? J Urol 169;63:2003. 6. Eisenmenger W. The mechanisms of stone fragmentation in ESWL. Ultrasound Med Biol 2001;27:683. 7. Sass W, Braunlich M, Dreyer HP, et al. The mechanisms of stone disintegration by shock waves. Ultrasound Med Biol 1991;17: 239. 8. Lingeman EJ, Lifshitz DA, Evan AP. Surgical management of urinary lithiasis. In: Walsh PC, Retik AB, Vaughn ED, et al (eds): Campbell’s Urology, ed 8. Philadelphia: WB Saunders, 2002, pp 3361–3451. 9. Xi X, Zhong P. Improvement of stone fragmentation during shockwave lithotripsy using a combined EH/PEAA shock-wave generator: In vitro experiments. Ultrasound Med Biol 2000;26:457.   Address reprint requests to: Alexander Greenstein, M.D. Dept. of Urology Tel Aviv Sourasky Medical Center 6 Weizman Street Tel Aviv 64239, Israel E-mail: surge04@post.tau.ac.il

 

press

INTERNATIONAL HOPSITAL EQUIPMENT

TECHNOLOGY WATCH Dual Shock Wave Lithotripsy

mode is capable of doubling total pressure or halving potential tissue damage. The a synchronized mode increases the shock wave rate and efficiency. Both modes are capable of significantly reducing treatment time, The lithotripter incorporates two completely independent shock wave sources operating synchronized and a synchronized triggering of the individual units. The water system adheres to the principle of constant pressure at themembrane/patient interface. The highly conductive water and small inter-electrode gap assure shock wave uniformity. This design enables controlled variation in number, strength and frequency of shock. In the synchronized mode, two waves propagating from the dual heads arrive at the therapeutic focus simultaneously to form a reinforced wave.

This is equivalent to doubling the aperture for given energy, thus reducing pain and trauma to intervening tissue. In the asynchronised mode, the frequency of generated shock waves is at least doubled without any reduction in shock waves intensity. At the same time, the number of shock waves propagating through specific body tissue is only half for a given number of shock waves applied. The system is controlled either via a flat panel touch-screen computer. Connection to the individual modules is by serial line communication. The power and control processing of the high voltage unit, power unit, water system, mobile couch and digiscope are incorporated in each module. The optional DUET dual imaging system incorporates digital fluoroscopy and an in-line ultrasonic attachment for real-time, digitally processed imaging. The separate multi-functional treatment table has a radiolucent table top, motorized XYZ motion all the accessories required for SWL, and optional Trendelenburg.   DIREX SYSTEMS S.A., 59-67 bd Martial Valin, 75015 Paris, France, Tel. +33-1-53987400 Fax + 33-1-53987405 www.direxgroup.com enter IHE 0629

press   510(k)s Final Decisions Rendered for January 2003 SUBMITTER ADDRESS LISTING FOR CDRH SUBSTANTIALLY EQUIVALENT (SE) 510(K) SUMMARIES OR 510(K) STATEMENTS FOR FINAL DECISIONS RENDERED DURING THE PERIOD 01-JAN-2003 THROUGH 31-JAN-2003   DEVICE: TRIPTER X-1 COMPACT DUET DIREX SYSTEMS CORP. 510(k) NO:K023535(SPECIAL)   ATTN: LARISA GERSHTEIN PHONE NO : 508-651-0900 11 MERCER ROAD SE DECISION MADE 17-JAN-03   NATICK, MA 01760 510(k) SUMMARY AVAILABLE FROM FDA     james Excerpts from the 1st Stone Consultation meeting Paris, July 4-5, 2001 1st International Consultation on Stone Disease Committee 8: Bioeffects and Physical Mechanisms of SW Effects in SWL Chairman:    James E. Lingeman, M.D. Committee Members:    Michael Delius, M.D.    Andrew Evan, PhD    Mantu Gupta, M.D.    Kemal Sarica, M.D.    Walter Strohmaier, M.D. Contributing Authors:    James McAteer, PhD    James Williams, PhD 1) Introduction A ….." Unfortunately current lithotriptor designs have not been based on fundamental advances in the basic science of SWL vis-?-vis stone comminution and tissue effects. The result has been that newer generation machines have not improved outcomes for patients and indeed may be both less effective in breaking stones and more traumatic to renal tissue. " 2) Page 9 …." In addition, the newer generation lithotriptors that have very small focal areas and extremely high peak positive pressures are reporting higher clinically significant hematoma rates of 3 to 12% (Kohrmann et al, 1995; Stefan et al, 1998; Piper et al, 2001; Ueda et al, 1993), a trend that is worrisome." 3) Page 10 …." In addition, Roessler et al (1996) determined the size of lesion induced by an electromagnetic vs. electrohydraulic lithotriptor and found a much larger lesion with the electrohydraulic machines. However, the electromagnetic lithotriptor produced complete cellular destruction at F2, which may explain a higher rate of subcapsular hemorrhage for electromagnetic lithotriptors." 4) Page 69 …." Newer generation machines have not improved outcomes for patients. The introduction of new lithotriptors that generate extremely high pressures and tight focal zones does not appear to be much of an improvement, as the need for re-treatment and the incidence of adverse effects with these devices appears to be higher with older machines." ABSTRACT The Peak Pressure at F2 and the Focal Area are the traditional parameters used to compare the performance and effectiveness of the Shock Wave produced by different lithotripters. Lately, new electromagnetic lithotripters were introduced, some with higher Focal Peak Pressure. This fact may lead to believe that they are more efficient than the traditional spark gap systems. At the same time all electromagnetic systems have very thin focal areas, much smaller than the typical stone size, and therefore the available energy is not optimized for stone fragmentation, usually requiring much more shocks compared to a traditional Electrohydraulic lithotripter. The Focal Cross Section at F2, the Truncated Focal Area and Volume are 3 new tools which allow a more accurate evaluation of the Shock Wave characteristics and efficiency of different lithotripters. Eleven currently used lithotripters including the Dornier HM-3 were compared: The results show two categories of Lithotripters: a) Large Focus: Dornier HM-3, Medstone STS-T, Direx Tripter Compact and Medispec Econolith. b) Small Focus: All electromagnetic lithotripters, plus Edap Praktis and the Healthronics Lithotron. The Average Focal Cross Section for Large Focus lithotripters is 5 times bigger than the small ones. The Average Truncated Area is 2.35 times bigger and the Average Truncated Volume is 5 times bigger in Big Focus Lithotripters compared to Small Focus ones. This may help to explain why usually the electromagnetic lithotripters require much more shocks to break stones and have larger retreatment rates. INTRODUCTION Various lithotripters using different Shock Wave technologies are currently offered to treat stones in the urinary tract. In order to compare the various systems offered, Urologists analyze their technical specifications to evaluate their performance. (Ref 1) Traditionally the Peak Bar Pressure at F2 is the first parameter considered as an indicator of the available energy of a lithotripter and, therefore, has served as a first indicator of the efficiency of the system. Some confusion existed in the past regarding the numerical value of this Pressure at F2. Due to specific conditions of the Shock Waves, the measurements done with the older Piezoelectric Crystal sensors lead to erroneous high values of pressure (above thousand bars). During the last years a new precise sensor made of a membrane of Poly Vinyl Duo Fluoride (PVDF) was developed and adopted by FDA as the only one to be used in Pressure measurements (Ref 2). Using PVDF, the pressure values recorded are "smaller" compared to old Piezoelectric Crystal sensors, but obviously this is are more accurate and "real" values. Recently, new Electromagnetic lithotripters were introduced some of them with higher Peak Bar Pressure. This fact leads one to believe that they are more efficient than the traditional spark gap systems. Looking carefully we can see that this may be misleading. A correct analysis requires one to look not only at the Peak Bar pressure but also at the focal area geometric dimensions. All Electromagnetic systems have very thin focal areas - much smaller than the typical stone size-and, therefore the available energy is not optimized for stone fragmentation. The Total Focal Area which is also used sometimes to compare different lithotripters may be misleading too, because it does not take into account the fact that the typical stone size is much smaller than the long axis of the Focal ellipse and therefore a big portion of the energy is not applied to the stone. In order to clarify this issue three new tools were developed and are presented: a) The Focal Cross Section b) The Truncated Ellipse Focal Area c) The Truncated Focal Volume. They will allow a more precise geometrical comparison of the Focal Areas of different lithotripters and hence their effectiveness. MATERIALS AND METHODS Specifications of 11 currently used lithotripters were used from published references (Ref 1). The distribution of pressure of a lithotripter is centered at the focal point F2 and includes all points whose pressure is between 100% ( f2) and 50% of the Peak Power( 6 dB). The shape of this focal volume is approximately an ellipsoid (a "cigar" or "watermelon" shape) (Ref 2). This ellipsoid volume is obtained by rotating the focal ellipse around the long axis. The geometric specifications of the focal area are the Long Dimension (LD) and Short Dimension (SD) of the ellipse and ellipsoid. The (a) Long radius and (b) Short Radius equal half of the previous values respectively. 1) Focal Area Cross Section (FACS) The easiest way of visualizing how much of the stone is subjected to pressure is to look at the Cross Section of the ellipsoid at F2 (Like "cutting" the ellipsoid/cigar at F2 and looking at the circle that originated). We can calculate the Cross Section area using the formula of the circle area b = Focal Short Radius =SD/2 SD=Focal Short Dimension (diameter) 2) Ellipse shape geometric function 3) Ellipse Focal Area (EFA) Using the ellipse Long Radius a , and the Short Radius b, we can calculate the full Ellipse area using the formula     4) Truncated Ellipse Focal Area (TEFA) Using the Long Radius a, and the Short Radius b, we can calculate the Truncated Ellipse area using the formula   5) Ellipsoid Focal Volume (EFV)   6) Truncated Ellipsoid Focal Volume (TEFV) RESULTS Calculations and graphs were made using the Excel (Microsoft) Program 1) 1) Focal Area Cross Section Focal Cross Sections at F2 Circle # Manufacturer Model Diameter Cross Section       Short Dimension Area       SD (mm) (mm 2) 1 1 Dornier Doli S 5 20 2 Siemens Lithostar 5 20 3 Edap Praktis 5 20 4 Storz Modulith 6 28 5 Siemens Modularis 6 28 6 Dornier Compact Delta 7.7 47 7 Healthronics Lithotron 8 50 8 Medispec Econolith 13 133 9 Direx Tripter Compact 13.5 143 10 Medstone STS-T 15 177 11 Dornier HM-3 15 177 Average Large Focal Areas 157 Standard Deviation 23 Average Small Focal Areas 30 Standard Deviation 13 Small Focal Areas Large Focal Areas Table and Graph # 1     2) The Truncated Ellipse Focal Area The Graph below represents all focal ellipses and their truncation. Truncation of Focal Ellipses Table and Graph # 2   3) Truncated Ellipse Focal Area             Table and Graph # 3     4) Truncated Ellipsoid Focal Volume     Table and Graph # 4     DISCUSSION Analyzing the results shown in Tables #1 through #4, we may distinguish two categories of Lithotripters: a) Large Focus: 4 lithotripters are in this category: Dornier HM-3, Medstone STS-T, Direx Tripter Compact, and Medispec Econolith. b) Small Focus: 7 Lithotripters are in this category: Storz Modulith, Dornier Doli S, Dornier Compact Delta, Siemens Lithostar, Siemens Modularis (All electromagnetic lithotripters), Edap Praktis, and the Healthronics Lithotron (Spark Gap).   Cross Section Cross Section Truncated Area Truncated Area Truncated Volume Truncated Volume Average Standard Deviation Average Standard Deviation Average Standard Deviation a) Large Focus 157 23 (15%) 209 16 (8%) 2306 343 (15%) b) Small Focus 30 13 (43%) 89 19 (21%) 435 191 (44%) Ratio a/b 5.23 2.35 5.3 The 2 categories of Lithotripters are clearly differentiated, the ration of their Cross Sections, Areas and Volumes are between 2.35 and 5.3. The Large Focus group is more homogeneous (Standard Deviation 8 to 15 %) , whereas the Small Focus is less (Standard Deviation 21% to 44 %). This is due to the fact that the Dornier Delta and Healthronics Lithotron have relatively bigger dimensions than the rest of the group, but still far form the Large Focus group. ALL Large Focus Lithotripters use the Spark Gap technology. ALL Electromagnetic units fall into the Small Focus category. Two Spark Gap units are also in the Small Focus category: Edap Praktis and Healthronics Lithotron. The Edap Praktis, although basically a Spark Device, uses a variation of what is called the Electroconductive Technology. The purpose of this technology is to reduce the pressure fluctuation between shocks. In order to achieve this, the system uses a special electrode in a highly conductive liquid, with a very small gap and as a result, the focal volume is much smaller than conventional Spark Gap devices. It can be seen on Graph # 1, that the Large Focus Lithotripters will " cover" most of the stone areas at F2 ( diameter 13 to 15 mm) whereas the Small Focus ones will cover only a fraction of the typical stone. This may explain why the electromagnetic devices typically require significantly more shocks to adequately fragment kidney stones and also may result in higher retreatment rates. Recently, concerns have been raised ( Ref 5) regarding the fact that some new Electromagnetic Lithotripters that have very small focal areas and extremely high peak positive pressures are reporting higher clinically significant hematoma rates of 3 to 12% (Ref 6,7 and 8). A trend that is worrisome. It is becoming clear that the electromagnetic devices with very long and thin focal area/volumes are not suited to fragment stones. The Truncated Areas and Volumes are intended to advance the discussion relative to the effectiveness of various lithotripters.     REFERENCES 1. J. Stuart Wolf, Jr. M.D. Issues in choosing a Lithotriptor: Concepts in Design and use. AUA, 2001. 2. Lewin P.A. and Schafer M.E. "Shock Wave sensors: Requirements and Design. J. Lithotripsy and Stone Disease vol. 3 pp 3-17, 1991. 3. IEC International Standard pressure Pulse Lithotripters-Characteristics of Fields. 1998 -04 Annex C, page 21. 4. FDA Guidance for the Content of Premarket Notifications (510 k) for Extracorporeal Shock Wave Lithotripters Indicated for the Fragmentation of Kidney and Ureteral Calculi. August 9, 2000. Page 6. 5. 1st International Consultation on Stone Disease Committee 8: Bioeffects and Physical Mechanisms of SW Effects in SWL. Chairman: James E. Lingeman, M.D. et al. 6. Kohrmann KU, Rassweiler JJ, Manning M, et al. The clinical introduction of a third generation lithotriptor Modulith SL 20. Journal of Urology, 1995; 153:1379-1383. 7. Stefan T, Thorsten B, Chaussy C. Reduced retreatment rate by anatomy related shockwave (SW) energy. Journal of Urology, 1998; 159:S34 (abstract). 8. Piper NY, Dalrymple N, Bishoff JT. Incidence of renal hematoma formation after ESWL using the new Dornier Doli-S lithotriptor. Journal of Urology, 2001; 165:S377 (abstract).