JOURNAL OF ENDOUROLOGY Volume 28, Number 11, November 2014 ª Mary Ann Liebert, Inc. Pp. 1368–1373 DOI: 10.1089/end.2014.0338
Extracorporeal Shockwave Lithotripsy
Optical Coupling Control: An Important Step Toward Better Shockwave Lithotripsy Geert G. Tailly, MD, and Martine M. Tailly-Cusse, RN
Abstract
Background: In modern ‘‘dry’’ lithotripters, shockwaves are generated in a membrane-covered water cushion that is then coupled to the patient.To limit energy loss, a coupling agent, usually ultrasound gel, is used in this acoustic interface. During the coupling process, air pockets are inevitably trapped in the coupling area, which subsequently remains invisible to the operator. These air pockets dramatically decrease stone fragmentation efficiency up to 40%. Materials and Methods: To check for air bubbles in the coupling interface, a video camera was installed in the therapy head of our Dornier Gemini lithotripter: all air bubbles observed in the coupling zone could then be removed under visual control. We evaluated the effect of this optically controlled coupling (OCC) on treatment results (10/1/12–9/30/13) and compared these to the results obtained in a ‘‘blind’’ coupling mode (4/1/11–4/30/12). Results: Optically controlled removal of air bubbles from the coupling area reduced the required number of shockwaves with 25.4% for renal stones and 25.5% for ureteral stones. Energy level was reduced by 23.1% for renal stones and by 22.5% for ureteral stones. For renal stones, total applied energy was thus reduced by 42.9%. Effectiveness quotients were comparable. Conclusions: Optical control with a video camera proved pivotal in the realization of bubble-free coupling. Bubble-free coupling significantly reduced the total energy needed to obtain comparable treatment results. Theoretically, this should also lead to a reduced incidence and severity of shockwave-induced adverse effects. We consider this an important step toward better and safer shockwave lithotripsy and would therefore advocate the standard incorporation of an OCC system in all new lithotripters. Introduction
W
ith shockwave (SW) sources producing SWs of a more consistent quality, high performance imaging systems and often computer assisted targeting modern lithotripters are far more sophisticated than the original Dornier Human Model 3 (HM3) lithotripter. Nevertheless, treatment outcome is often inferior to the results with the Dornier HM3. As a consequence, the Dornier HM3 is still considered by many to be the gold standard in shockwave lithotripsy (SWL) and all too often a more invasive endoscopic management of certain stones is preferred over the least invasive method of all times. One of the more important factors in successful SWL could very well be proper coupling. In the Dornier HM3, the electrohydraulic SW source and the patient were immersed in the same bath containing 1200 L of degassed water. The acoustic properties of water being very similar to those of human tissue, there is virtually no energy loss when using degassed water as a coupling medium. In current lithotripters, SWs are generated within a water cushion that then needs to be coupled to the patient. To
prevent significant energy loss in this acoustic interface, a coupling agent, usually ultrasound gel, is needed. Several in vitro studies1–7 have established that air bubbles in the coupling interface significantly affect energy transfer and hence disintegration capability of the lithotripter. In a study by Pishchalnikov and associates,1 a 20% to 40% reduction in the efficiency of stone fragmentation was seen with only 2% of the coupling area covered by air pockets while a study by Bohris6 demonstrated that 43% more SWs were needed to fragment model stones when only 8% of the coupling area was covered with air bubbles. Although in vitro studies unequivocally prove the importance of bubble-free coupling, in most lithotripters— but to some extent in those with an inline ultrasound scanner— it is impossible to visually monitor the coupling area between the therapy head and patient. In accordance with a study by Bohris and colleagues8 that monitored the coupling area with a surveillance camera in 30 routine SWL treatments, we evaluated the effect of optically controlled coupling (OCC) on actual clinical treatment results. The primary objectives of this clinical study were to evaluate if a video camera incorporated in the therapy head of our lithotripter could be instrumental in consistently achieving
Department of Urology, AZ Klina, Brasschaat, Belgium.
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OPTICAL COUPLING CONTROL IN SWL
a completely bubble-free coupling and if this bubble-free coupling would allow us to achieve comparable treatment results (effectiveness quotient [EQ]) with fewer SW at a lower energy level as experienced in in vitro studies. Materials and Methods
In our Department of Urology, we have operated a Dornier Gemini lithotripter since 2011. This lithotripter is equipped with an electromagnetic SW emitter (EMSE) 220F-XXP high penetration with a penetration depth of 170 mm, an aperture angle of 66 degrees, and a focal size of 89 · 6 mm. The Gemini further features dual imaging consisting of a fluoroscopic system with flat panel detector and a B&K Medical Flex Focus ultrasound system with a 2–6 MHz convex array transducer mounted on a lateral isocentric arm. With fluoroscopy, a very accurate autopositioning mode is available. With ultrasound, a spectral Doppler signal can be used to assess progression of fragmentation. The therapy head with the EMSE can be coupled to the patient both above and under the table. After coupling the therapy head to the patient, the coupling area becomes invisible to the naked eye. To optically check for air bubbles in the coupling interface between the coupled water cushion and the patient, a video camera and light-emitting diode-light were installed in the therapy head of our Dornier Gemini lithotripter in September 2012 (Fig. 1). To evaluate the effects of OCC on treatment results, we retrospectively reviewed the results in a series of 275 patients with ‘‘blind’’ coupling performed between 04/01/2011 and 4/ 30/2012. We compared these results with a series of 198 cases with OCC performed between 10/1/2012 and 9/30/ 2013. All SWL treatments in both series were performed by one endourologist assisted by a dedicated nursing staff highly experienced in endourology and SWL. Treatment strategies were consistent throughout and based on European Association of Urology and American Urological Association guidelines. Targeting was performed with ultrasonography in 65% and with fluoroscopy in 35%. Targeting was carefully monitored during the whole procedure and adjusted whenever necessary. Shockwaves were delivered at a fixed pulse repetition frequency of 80 SW/min, and voltage stepping
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was performed in all treatments. Treatments were performed with intravenous analgosedation administered via a patientcontrolled analgesia device according to a validated protocol.9 All patients were coupled adhering to strict guidelines for optimal coupling.10,11 A low viscosity ultrasound gel (hypoallergenic Aquasonic 100 Ultrasound Transmission Gel, Parker Laboratories Inc., Fairfield, NJ) was scooped with a large spoon from a wide mouthed container and deposited in a generous mound in the center of the inflated water cushion. The patient was then gently lowered onto the inflated cushion thus spreading the gel radially and minimizing air entrapment. Save for the optical control with the video camera incorporated in the therapy head, the same meticulous attention to proper coupling was given in both series. In the OCC series, the air pockets in the coupling area could then be removed under visual control of the video camera. This was performed by gently swiping a hand between the patient and the inflated water cushion (Fig. 1). This gentle swiping movement was repeated until all air bubbles and/or eventual folds in the water cushion membrane had disappeared. An initial slow swipe would not always remove all air bubbles. The video camera would then direct the swiping hand toward remaining air bubbles or sometimes a fold in the membrane of the water cushion. Membrane folds occurred more frequently when the therapy head was coupled to the patient from above. This same sequence was repeated in the rare occasion where a repositioning of the patient proved necessary for whatever reason, most commonly a sudden movement of the patient. To better appraise quality of fragmentation, kidneys, ureters, and bladder (KUB) radiography was performed immediately after completion of each treatment. Subsequently, KUB radiography and an ultrasonographic examination of the kidneys were performed at 1 week and at 4 weeks. Additional controls and/or interventions were planned per patient. Because we are concerned with radiation exposure, we did not routinely perform unenhanced CT scans in the follow-up of noncomplicated SWL cases. Results
Body mass index was recorded in all patients and proved comparable in both series (Table 1). Both in the blind
FIG. 1. Dornier Gemini with integrated video camera for coupling monitoring. Air bubbles are removed from the coupling interface by gently swiping a hand between the patient and the inflated water cushion. SWL = shockwave lithotripsy; EMSE = electromagnetic shockwave emitter.
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Table 3. Treatment Data in Both Series
Table 1. Biometric Data in Both Series
Treatment data
Biometric data (BMI) _ ‘‘Blind’’ coupling 4/1/11–4/30/12 Optical coupling control 10/1/12–9/30/13
Range Mean Range Mean
\
18.2–41.4 27.1 19.0–37.3 27.0
18.2–40.0 25.8 18.1–43.1 27.5
BMI = body mass index.
coupling series and the OCC series, renal and ureteral stones at all levels of the urinary tract were treated (Table 2). With OCC, the total number of SWs needed was reduced by 25.4% for renal stones and by 25.5 % for ureteral stones, consequently reducing the total treatment times by the same percentage. Energy level could be reduced by 23.1% for renal stones and by 22.5 % for ureteral stones. For renal stones, total accumulated energy (AE), which is a product of SW number and energy level, was reduced by 42.9%. Because AE data were not adequately registered for ureteral stones in the blind coupling series, this comparison is not available for ureteral stones. These data are shown in Table 3 and Table 4. Although total energy administered in the OCC series was considerably lower than in the blind coupling series, EQs proved comparable both for renal and ureteral stones. We calculate two EQs. The EQ as originally described by Den-
Table 2. Overview of Stone Location for Renal and Ureteral Stones Overview of stone location: Renal stones
N = 132
%
N = 102
%
4 9 68 51 132
3.0 6.8 51.5 38.6 100
7 8 55 32 102
6.7 7.8 53.9 31.4 100
Overview of stone location: Ureteral stones Optical coupling ‘‘Blind’’ coupling control 4/1/2011–4/30/2012 10/1/2012–9/30/2013
Proximal ureter: UPJ/L1-L4 Middle ureter: L5-SIJdist Distal ureter: SIJdist-PV Total
Renal stones Stone size (mm2) Range 16–250 Mean 56.2 SW number Range 500–2500 Mean 1469 Energy level Range 3–10 Mean 6.5 Accumulated energy Range 16–173 Mean 71
Optical coupling control 10/1/2012–9/30/2013
Ureteral stones
Renal stones
Ureteral stones
16–144 47.5
16–216 58.3
16–144 40.5
500–3000 1659
400–2000 1123
200–2000 1236
3–11 8
3–7 5
2–10 7
N/A N/A
13–65 40.5
4–146 58.8
SW = shockwave.
stedt and coworkers12 (EQA) only takes into account auxiliary procedures performed post-SWL, while the ‘‘extended’’ EQ (EQB)13 takes into account auxiliary procedures performed both pre- and post-SWL. The effects of OCC on treatment results are summarized in Table 5. In none of the series did we experience any significant SW-related adverse effects. Discussion
Optical coupling ‘‘Blind’’ coupling control 4/1/2011–4/30/2012 10/1/2012–9/30/2013
Upper calix Middle calix Lower calix Renal pelvis Total
‘‘Blind’’ coupling 4/1/2011–4/30/2012
N = 143
%
N = 96
%
110
76.9
47
48.9
10
7.0
22
22.9
23
16.1
27
28.1
143
100
96
100
UPJ = ureteropelvic junction; L1 (4/5) = lumbar vertebra 1 (4/5); SIJdist = distal margin of sacroiliac joint; PV = prevesical.
The Dornier HM3 was the first commercially available lithotripter. Installed worldwide since 1983, the Dornier HM3 featured a simple bidirectional fluoroscopic imaging system for targeting and an electrohydraulic SW source immersed in a large water bath containing 1200 L of degassed water into which the patient was lowered using a complex gantry. Because the acoustic properties of human tissue are very comparable to those of water, this was the optimal coupling medium to allow the propagation of SW into the human body without significant energy loss.14 Modern lithotripters feature a ‘‘dry’’ coupling system: The SWs are generated in a water-filled cushion that is then inflated and pressed against the patient. To ensure good acoustic transmission of the SWs, a coupling medium, usually an ultrasound gel, needs to be applied between the surface of the water cushion and the patient’s skin. Despite the fact, that current lithotripters boast more sophisticated imaging systems and a superior consistency of SW quality, treatment results with these systems often prove disappointing in comparison with the Dornier HM3, still considered by many to be the gold standard in SWL. Could it be that the less than ideal coupling mechanism in newer devices plays an important role in this discrepancy? In an in vitro study published in 2006, Pishchalnikov and associates1 investigated the effect of air pockets trapped in the coupling interface of a dry head lithotripter on the transmission of SW and stone fragmentation. Air pockets in
OPTICAL COUPLING CONTROL IN SWL
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Table 4. Treatment Results in Both Series Treatment results ‘‘Blind’’ coupling 4/1/2011–4/30/2012
Optical coupling control 10/1/2012–9/30/2013
Renal stones N = 132
Ureteral stones N = 143
Renal stones N = 102
Ureteral stones N = 96
1.19 15.9
1.16 15.4
1.15 15.7
1.15 10.4
1.5 4.5 6.1 88.6
0 13.9 13.9 96.5
0 2.0 2.0 87.3
0 15.6 15.6 98.9
74 73
75 75
74 74
78 78
1. Re-treatment rate -Treatments/patient - % re-treatment 2. Aux. procedures (%) - Pre-SWL - Post-SWL - Total 3. SFR at 1 month (%) 4. EQ A B
Aux = auxiliary; SWL = shockwave lithotripsy; SFR = stone-free rate; EQ = effectiveness quotient.
the coupling area decreased transmission of acoustic pressure to the focal zone leading to a decrease in SW efficiency for stone comminution. There proved to be an almost linear correlation between stone comminution and air trapped in the coupling area: When only 2% of the coupling area was covered with air pockets, efficiency of stone fragmentation decreased by 20% to 40%. This negative effect was most obvious after a coupling-decoupling-recoupling sequence. The data also showed that consistency in coupling is hard to achieve. According to the authors, this variability in coupling quality could also pose a safety hazard: A higher SW dose than necessary could be delivered when by coincidence fewer air bubbles are present than usual, leading to possible injury to the treated kidney. In an in vitro study evaluating the effect of air bubbles in the coupling media on efficacy of SWL, Jain and coworkers2 treated 40 artificial stones on a Storz Modultih SLK lithotripter. They found a significant inverse correlation of the depth of crater and crater volume in the artificial stones with the degree of air bubbles in the coupling gel used. The treatment efficacy could be improved up to three times by carefully eliminating all visible air bubbles from the coupling gel. In a limited retrospective review of patients treated with the use of different coupling media, it was found that patients
Table 5. The Effects of Optical Coupling Control on Treatment Results Optical coupling control: Effects on treatments results Renal stones
Ureteral stones
Number of SW - 25.4% Energy level - 23.1% Accumulated energy - 42.9% Effectiveness Quotient (EQB) - ‘‘Blind’’ coupling 73 - OCC 74 Treatment time - 25.4% SW = shockwave; OCC = optical coupling control.
- 25.5% - 22.5% N/A 75 78 - 25.5%
treated with contact media with higher bubble content experienced less pain. This was supposedly because of the reduced energy transmission when more air bubbles were present. In an attempt to find a practical protocol that would improve routine coupling in SWL, Neucks and colleagues3 tested different coupling procedures and their effect on breakage of gypsum model stones. A systematic survey was conducted on the source of the gel, the surfaces to which the gel was applied, and four different techniques to apply the gel. They found that the quality of coupling and the technique of dispensing the gel affected stone breakage. Consecutive couplings even using the same protocol resulted in differences in air bubble inclusions leading to significant variations in effectiveness of SWL treatment. Coupling was found to be best when applying a large mound of bubblefree gel from a large container. Poor results were obtained when applying the gel from a squeeze bottle. They also pinpointed the fact that in most lithotripters, there is no way of judging the quality of coupling because the coupling area is invisible. Comparable observations were made by Bergsdorf and associates.4,5 Bohris6 investigated the effect of air bubbles trapped in the coupling medium on disintegration power of an experimental electromagnetic Dornier lithotripter equipped with an inline ultrasound scanner. When only 8% of the coupling area was covered with air bubbles, 43% more SWs were needed to fragment model stones. The inline ultrasound scanner allowed detection of air bubbles present in the actual scanning plane, but not in the entire coupling interface at once. In a study published in 2012, Li and associates7 tried to determine how size and location of coupling defects affected the features of SWs responsible for stone fragmentation. Stone breakage decreased proportionally to the surface size and the location of the coupling defects. The negative effect was greater for centrally located defects than for more laterally located defects. Apart from decreasing the transmission of SW energy, coupling defects proved to also change the physical properties of the SWs, further affecting stone breakage efficiency. They emphasized the importance of
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bubble-free coupling, especially in the center of the coupling area. The fact, that the coupling interface is invisible during treatment is also mentioned as a practical problem. Although several studies had established, that bubble-free coupling is essential for optimal energy transfer and efficient stone breakage, the fact that the coupling interface remains invisible still posed a practical problem in locating and removing possible air pockets. To monitor the coupling area during actual SWL treatments, Bohris and coworkers8 continuously monitored the coupling zone in 30 routine treatments with a video camera installed in the therapy head of a Dornier Lithotripter SII. They found that in only 10 of 30 procedures, good coupling with an air ratio of less than 5% was achieved; in 8 treatments, the air ratio was even higher than 20%. The best results were achieved with a low viscosity ultrasound gel. In model stone tests it was established, that the number of SW needed for complete fragmentation increased with the air ratio in the coupling area: With an air ratio of 20%, the number of SWs needed was three times higher. In visualizing the coupling interface to check for air bubbles, a video camera proved better suited than an inline ultrasound scanner. A video camera allows immediate and real-time inspection of the entire coupling area while an inline ultrasound scanner only allows the detection in the actual scanning plane. For a complete scan of the entire coupling area, the scanner needs to be rotated. To optimize coupling it is advised to apply a generous mound of a low viscosity gel to maximize contact between water cushion and patient by proper inflation of the water cushion, and to avoid decoupling and recoupling.6,10 Our work is the first clinical study to evaluate the effects of OCC on actual in vivo treatment results. To obtain good clinical results with SWL, it is essential to pay adequate attention to every step involved in the procedure. One important step, often underestimated and neglected, proves to be the quality of coupling of the SW source to the patient. Although we already paid careful attention to optimal coupling, we were astonished by the video camera visualization of the number and location of air pockets still present in the coupling zone. Even with the use of a coupling gel with minimal presence of visible air bubbles, these air pockets were present at random over the entire coupling surface, and some of them were quite large. This means that they were entrapped during the process of bringing the patient in contact with the inflated water cushion. Therefore, and despite meticulous attention to every detail of optimal coupling, it seems virtually impossible to avoid the entrapment of air pockets. In this respect, Li and associates7 also stated that the real problem is not to find a coupling medium that efficiently transmits SW energy, but to find a way to avoid the entrapment of air pockets during the coupling process. We found that a first gentle swipe between water cushion and patient, comparable to a ‘‘blind swiping,’’ did not always remove all air bubbles. We also noticed that particularly when coupling the therapy head from above, folds would occasonally shape in the water cushion membrane. These folds also served as air traps. Having started out with a generous mound of coupling gel, the video camera confirmed a sufficient homogenous layer of bubble-free gel remained after swiping. In the OCC series, we achieved comparable EQs with a reduction in the required number of SW of 25.4% for renal
TAILLY AND TAILLY-CUSSE
stones and 25.5% for ureteral stones along with a reduction in the required energy level of 23.1% and 22.5% for renal and ureteral stones, respectively.This confirms the findings of in vitro studies that air pockets in the coupling interface reduce the transmission of SW energy into the patient and on to the focal zone, leading to an increase in the number of SWs needed for stone fragmentation. In the in vitro study of Pishchalnikov and coworkers,1 efficiency of stone fragmentation decreased by 20% to 40% when only 2% of the coupling area was covered with air pockets. The in vitro study of Bohris6 demonstrated that 43% more SWs were needed to fragment model stones when only 8% of the coupling area was covered with air bubbles. Our in vivo study shows that with optically controlled, completely bubble-free coupling, comparable treatment results can be obtained with a reduction in the total number of SW of 25% along with a reduction in energy level of 22% to 23%. As an added bonus, treatment times were reduced with a corresponding 25%. Theoretically, this reduction in total energy applied should also reduce the incidence and severity of SW-induced adverse effects, making SWL even safer still. This would also meet the safety concerns advanced in in vitro studies.1 Although the experience with OCC is still limited, the results seem convincing enough to expect further validation in larger series. To achieve optimal coupling in SWL, based on our current experience, we recommend scooping a generous mound of a low viscosity ultrasound gel from a large-mouthed container onto the center of the water cushion. The patient should then be gently lowered onto the inflated water cushion, thus spreading the gel radially and minimizing air entrapment. After targeting of the stone, a hand is gently swiped between the inflated water cushion and the patient to remove all air pockets entrapped in the coupling zone. As ‘‘blind’’ swiping does not always remove all air bubbles, this is ideally performed under visual control with a video camera incorporated in the therapy head of the lithotripter to observe the entire coupling area in real time. This entire sequence needs to be repeated in the rare occasions that a repositioning of the patient proves necessary. Conclusion
Optically controlled removal of air bubbles in the coupling area significantly reduces the total SW energy needed to obtain comparable results. This is consistent with the findings in various in vitro studies. Optical control with an incorporated video camera proves pivotal in the realization of bubble-free coupling. We consider this an important step toward better and safer SWL and would therefore strongly advocate the standard incorporation of a video camera in the therapy head of every commercially available lithotripter. Disclosure Statement
No competing financial interests exist. References
1. Pishchalnikov YA, Neucks JS, VonDerHaar RJ, et al. Air pockets trapped during routine coupling in dry head lithotripsy can significantly decrease the delivery of shock wave energy. J Urol 2006;176:2706–2710.
OPTICAL COUPLING CONTROL IN SWL
2. Jain A, Shah TK. Effect of air bubbles in the coupling medium on efficacy of extracorporeal shock wave lithotripsy. Eur Urol 2007;51:1680–1687. 3. Neucks JS, Pishchalnikov YA, Zancanaro AJ, et al. Improved acoustic coupling for shock wave lithotripsy. Urol Res 2008;36:61–66. 4. Bergsdorf T, Chaussy C, Thueroff S. The significance of accurate shock wave coupling in extracorporeal shock wave lithotripsy. J Endourol 2009;23:1042. 5. Bergsdorf T, Chaussy C, Thueroff S. Coupling gel viscosity: A relevant factor for efficient shock wave coupling in SWL. J Urol 2010;183(suppl):e704. Abstract 1815. 6. Bohris C. Quality of coupling in SWL significantly affects the disintegration capability—how to achieve good coupling with ultrasound gel. In: Therapeutic Energy Applications in Urology ll. In: Chaussy C, Haupt G, Jocham D, et al, eds. New York: Thieme, 2010, pp 61–64. 7. Li G, Williams JC Jr., Pishchalnikov YA, et al. Size and location of defects at the coupling interface affect lithotripter performance. BJU Int 2012;110:E871–E877. 8. Bohris C, Roosen A, Dickmann M, et al. Monitoring the coupling of the lithotripter therapy head with skin during routine shock wave lithotripsy with a surveillance camera. J Urol 2012;187:157–163. 9. Tailly GG, Marcelo JB, Schneider IA, et al. Patient controlled analgesia during SWL treatments. J Endourol 2001;15: 465–471. 10. Chaussy C, Tailly GG, Forssmann B, et al. Extracorporeal Shockwave Lithotripsy in a Nutshell. Chaussy C, Tailly G, eds. Booklet presented to European Association of Urology, 2013. 11. Tailly GG. Optical coupling control in SWL: First clinical experience. Poster MP07-13 presented at World Congress of Endourology; October 22–26, 2013; New Orleans.
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12. Denstedt JD, Clayman RV, Preminger GM. Efficiency Quotient as a means of comparing lithotripters. J Endourol 1990;(suppl):S100. 13. Rassweiler JJ, Tailly GG, Chaussy C. Progress in Lithotripter Technology. EAU Update Series 3, 2005:17–36. 14. Rassweiler JJ, Knoll T, Ko¨hrmann KU, et al. Shock wave technology and application: An update. Eur Urol 2011;59: 784–796.
Address correspondence to: Geert G. Tailly Department of Urology AZ Klina Augustijnslei 100 2930 Brasschaat Belgium E-mail: [email protected]
Abbreviations Used AE ¼ accumulated energy CT ¼ computed tomography EMSE ¼ electromagnetic shockwave emitter EQ ¼ effectiveness quotient HM3 ¼ human model 3 KUB ¼ kidneys, ureters, and bladder OCC ¼ optical coupling control SW ¼ shockwave(s) SWL ¼ shockwave lithotripsy
Extracorporeal Shockwave Lithotripsy
Optical Coupling Control: An Important Step Toward Better Shockwave Lithotripsy Geert G. Tailly, MD, and Martine M. Tailly-Cusse, RN
Abstract
Background: In modern ‘‘dry’’ lithotripters, shockwaves are generated in a membrane-covered water cushion that is then coupled to the patient.To limit energy loss, a coupling agent, usually ultrasound gel, is used in this acoustic interface. During the coupling process, air pockets are inevitably trapped in the coupling area, which subsequently remains invisible to the operator. These air pockets dramatically decrease stone fragmentation efficiency up to 40%. Materials and Methods: To check for air bubbles in the coupling interface, a video camera was installed in the therapy head of our Dornier Gemini lithotripter: all air bubbles observed in the coupling zone could then be removed under visual control. We evaluated the effect of this optically controlled coupling (OCC) on treatment results (10/1/12–9/30/13) and compared these to the results obtained in a ‘‘blind’’ coupling mode (4/1/11–4/30/12). Results: Optically controlled removal of air bubbles from the coupling area reduced the required number of shockwaves with 25.4% for renal stones and 25.5% for ureteral stones. Energy level was reduced by 23.1% for renal stones and by 22.5% for ureteral stones. For renal stones, total applied energy was thus reduced by 42.9%. Effectiveness quotients were comparable. Conclusions: Optical control with a video camera proved pivotal in the realization of bubble-free coupling. Bubble-free coupling significantly reduced the total energy needed to obtain comparable treatment results. Theoretically, this should also lead to a reduced incidence and severity of shockwave-induced adverse effects. We consider this an important step toward better and safer shockwave lithotripsy and would therefore advocate the standard incorporation of an OCC system in all new lithotripters. Introduction
W
ith shockwave (SW) sources producing SWs of a more consistent quality, high performance imaging systems and often computer assisted targeting modern lithotripters are far more sophisticated than the original Dornier Human Model 3 (HM3) lithotripter. Nevertheless, treatment outcome is often inferior to the results with the Dornier HM3. As a consequence, the Dornier HM3 is still considered by many to be the gold standard in shockwave lithotripsy (SWL) and all too often a more invasive endoscopic management of certain stones is preferred over the least invasive method of all times. One of the more important factors in successful SWL could very well be proper coupling. In the Dornier HM3, the electrohydraulic SW source and the patient were immersed in the same bath containing 1200 L of degassed water. The acoustic properties of water being very similar to those of human tissue, there is virtually no energy loss when using degassed water as a coupling medium. In current lithotripters, SWs are generated within a water cushion that then needs to be coupled to the patient. To
prevent significant energy loss in this acoustic interface, a coupling agent, usually ultrasound gel, is needed. Several in vitro studies1–7 have established that air bubbles in the coupling interface significantly affect energy transfer and hence disintegration capability of the lithotripter. In a study by Pishchalnikov and associates,1 a 20% to 40% reduction in the efficiency of stone fragmentation was seen with only 2% of the coupling area covered by air pockets while a study by Bohris6 demonstrated that 43% more SWs were needed to fragment model stones when only 8% of the coupling area was covered with air bubbles. Although in vitro studies unequivocally prove the importance of bubble-free coupling, in most lithotripters— but to some extent in those with an inline ultrasound scanner— it is impossible to visually monitor the coupling area between the therapy head and patient. In accordance with a study by Bohris and colleagues8 that monitored the coupling area with a surveillance camera in 30 routine SWL treatments, we evaluated the effect of optically controlled coupling (OCC) on actual clinical treatment results. The primary objectives of this clinical study were to evaluate if a video camera incorporated in the therapy head of our lithotripter could be instrumental in consistently achieving
Department of Urology, AZ Klina, Brasschaat, Belgium.
1368
OPTICAL COUPLING CONTROL IN SWL
a completely bubble-free coupling and if this bubble-free coupling would allow us to achieve comparable treatment results (effectiveness quotient [EQ]) with fewer SW at a lower energy level as experienced in in vitro studies. Materials and Methods
In our Department of Urology, we have operated a Dornier Gemini lithotripter since 2011. This lithotripter is equipped with an electromagnetic SW emitter (EMSE) 220F-XXP high penetration with a penetration depth of 170 mm, an aperture angle of 66 degrees, and a focal size of 89 · 6 mm. The Gemini further features dual imaging consisting of a fluoroscopic system with flat panel detector and a B&K Medical Flex Focus ultrasound system with a 2–6 MHz convex array transducer mounted on a lateral isocentric arm. With fluoroscopy, a very accurate autopositioning mode is available. With ultrasound, a spectral Doppler signal can be used to assess progression of fragmentation. The therapy head with the EMSE can be coupled to the patient both above and under the table. After coupling the therapy head to the patient, the coupling area becomes invisible to the naked eye. To optically check for air bubbles in the coupling interface between the coupled water cushion and the patient, a video camera and light-emitting diode-light were installed in the therapy head of our Dornier Gemini lithotripter in September 2012 (Fig. 1). To evaluate the effects of OCC on treatment results, we retrospectively reviewed the results in a series of 275 patients with ‘‘blind’’ coupling performed between 04/01/2011 and 4/ 30/2012. We compared these results with a series of 198 cases with OCC performed between 10/1/2012 and 9/30/ 2013. All SWL treatments in both series were performed by one endourologist assisted by a dedicated nursing staff highly experienced in endourology and SWL. Treatment strategies were consistent throughout and based on European Association of Urology and American Urological Association guidelines. Targeting was performed with ultrasonography in 65% and with fluoroscopy in 35%. Targeting was carefully monitored during the whole procedure and adjusted whenever necessary. Shockwaves were delivered at a fixed pulse repetition frequency of 80 SW/min, and voltage stepping
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was performed in all treatments. Treatments were performed with intravenous analgosedation administered via a patientcontrolled analgesia device according to a validated protocol.9 All patients were coupled adhering to strict guidelines for optimal coupling.10,11 A low viscosity ultrasound gel (hypoallergenic Aquasonic 100 Ultrasound Transmission Gel, Parker Laboratories Inc., Fairfield, NJ) was scooped with a large spoon from a wide mouthed container and deposited in a generous mound in the center of the inflated water cushion. The patient was then gently lowered onto the inflated cushion thus spreading the gel radially and minimizing air entrapment. Save for the optical control with the video camera incorporated in the therapy head, the same meticulous attention to proper coupling was given in both series. In the OCC series, the air pockets in the coupling area could then be removed under visual control of the video camera. This was performed by gently swiping a hand between the patient and the inflated water cushion (Fig. 1). This gentle swiping movement was repeated until all air bubbles and/or eventual folds in the water cushion membrane had disappeared. An initial slow swipe would not always remove all air bubbles. The video camera would then direct the swiping hand toward remaining air bubbles or sometimes a fold in the membrane of the water cushion. Membrane folds occurred more frequently when the therapy head was coupled to the patient from above. This same sequence was repeated in the rare occasion where a repositioning of the patient proved necessary for whatever reason, most commonly a sudden movement of the patient. To better appraise quality of fragmentation, kidneys, ureters, and bladder (KUB) radiography was performed immediately after completion of each treatment. Subsequently, KUB radiography and an ultrasonographic examination of the kidneys were performed at 1 week and at 4 weeks. Additional controls and/or interventions were planned per patient. Because we are concerned with radiation exposure, we did not routinely perform unenhanced CT scans in the follow-up of noncomplicated SWL cases. Results
Body mass index was recorded in all patients and proved comparable in both series (Table 1). Both in the blind
FIG. 1. Dornier Gemini with integrated video camera for coupling monitoring. Air bubbles are removed from the coupling interface by gently swiping a hand between the patient and the inflated water cushion. SWL = shockwave lithotripsy; EMSE = electromagnetic shockwave emitter.
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Table 3. Treatment Data in Both Series
Table 1. Biometric Data in Both Series
Treatment data
Biometric data (BMI) _ ‘‘Blind’’ coupling 4/1/11–4/30/12 Optical coupling control 10/1/12–9/30/13
Range Mean Range Mean
\
18.2–41.4 27.1 19.0–37.3 27.0
18.2–40.0 25.8 18.1–43.1 27.5
BMI = body mass index.
coupling series and the OCC series, renal and ureteral stones at all levels of the urinary tract were treated (Table 2). With OCC, the total number of SWs needed was reduced by 25.4% for renal stones and by 25.5 % for ureteral stones, consequently reducing the total treatment times by the same percentage. Energy level could be reduced by 23.1% for renal stones and by 22.5 % for ureteral stones. For renal stones, total accumulated energy (AE), which is a product of SW number and energy level, was reduced by 42.9%. Because AE data were not adequately registered for ureteral stones in the blind coupling series, this comparison is not available for ureteral stones. These data are shown in Table 3 and Table 4. Although total energy administered in the OCC series was considerably lower than in the blind coupling series, EQs proved comparable both for renal and ureteral stones. We calculate two EQs. The EQ as originally described by Den-
Table 2. Overview of Stone Location for Renal and Ureteral Stones Overview of stone location: Renal stones
N = 132
%
N = 102
%
4 9 68 51 132
3.0 6.8 51.5 38.6 100
7 8 55 32 102
6.7 7.8 53.9 31.4 100
Overview of stone location: Ureteral stones Optical coupling ‘‘Blind’’ coupling control 4/1/2011–4/30/2012 10/1/2012–9/30/2013
Proximal ureter: UPJ/L1-L4 Middle ureter: L5-SIJdist Distal ureter: SIJdist-PV Total
Renal stones Stone size (mm2) Range 16–250 Mean 56.2 SW number Range 500–2500 Mean 1469 Energy level Range 3–10 Mean 6.5 Accumulated energy Range 16–173 Mean 71
Optical coupling control 10/1/2012–9/30/2013
Ureteral stones
Renal stones
Ureteral stones
16–144 47.5
16–216 58.3
16–144 40.5
500–3000 1659
400–2000 1123
200–2000 1236
3–11 8
3–7 5
2–10 7
N/A N/A
13–65 40.5
4–146 58.8
SW = shockwave.
stedt and coworkers12 (EQA) only takes into account auxiliary procedures performed post-SWL, while the ‘‘extended’’ EQ (EQB)13 takes into account auxiliary procedures performed both pre- and post-SWL. The effects of OCC on treatment results are summarized in Table 5. In none of the series did we experience any significant SW-related adverse effects. Discussion
Optical coupling ‘‘Blind’’ coupling control 4/1/2011–4/30/2012 10/1/2012–9/30/2013
Upper calix Middle calix Lower calix Renal pelvis Total
‘‘Blind’’ coupling 4/1/2011–4/30/2012
N = 143
%
N = 96
%
110
76.9
47
48.9
10
7.0
22
22.9
23
16.1
27
28.1
143
100
96
100
UPJ = ureteropelvic junction; L1 (4/5) = lumbar vertebra 1 (4/5); SIJdist = distal margin of sacroiliac joint; PV = prevesical.
The Dornier HM3 was the first commercially available lithotripter. Installed worldwide since 1983, the Dornier HM3 featured a simple bidirectional fluoroscopic imaging system for targeting and an electrohydraulic SW source immersed in a large water bath containing 1200 L of degassed water into which the patient was lowered using a complex gantry. Because the acoustic properties of human tissue are very comparable to those of water, this was the optimal coupling medium to allow the propagation of SW into the human body without significant energy loss.14 Modern lithotripters feature a ‘‘dry’’ coupling system: The SWs are generated in a water-filled cushion that is then inflated and pressed against the patient. To ensure good acoustic transmission of the SWs, a coupling medium, usually an ultrasound gel, needs to be applied between the surface of the water cushion and the patient’s skin. Despite the fact, that current lithotripters boast more sophisticated imaging systems and a superior consistency of SW quality, treatment results with these systems often prove disappointing in comparison with the Dornier HM3, still considered by many to be the gold standard in SWL. Could it be that the less than ideal coupling mechanism in newer devices plays an important role in this discrepancy? In an in vitro study published in 2006, Pishchalnikov and associates1 investigated the effect of air pockets trapped in the coupling interface of a dry head lithotripter on the transmission of SW and stone fragmentation. Air pockets in
OPTICAL COUPLING CONTROL IN SWL
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Table 4. Treatment Results in Both Series Treatment results ‘‘Blind’’ coupling 4/1/2011–4/30/2012
Optical coupling control 10/1/2012–9/30/2013
Renal stones N = 132
Ureteral stones N = 143
Renal stones N = 102
Ureteral stones N = 96
1.19 15.9
1.16 15.4
1.15 15.7
1.15 10.4
1.5 4.5 6.1 88.6
0 13.9 13.9 96.5
0 2.0 2.0 87.3
0 15.6 15.6 98.9
74 73
75 75
74 74
78 78
1. Re-treatment rate -Treatments/patient - % re-treatment 2. Aux. procedures (%) - Pre-SWL - Post-SWL - Total 3. SFR at 1 month (%) 4. EQ A B
Aux = auxiliary; SWL = shockwave lithotripsy; SFR = stone-free rate; EQ = effectiveness quotient.
the coupling area decreased transmission of acoustic pressure to the focal zone leading to a decrease in SW efficiency for stone comminution. There proved to be an almost linear correlation between stone comminution and air trapped in the coupling area: When only 2% of the coupling area was covered with air pockets, efficiency of stone fragmentation decreased by 20% to 40%. This negative effect was most obvious after a coupling-decoupling-recoupling sequence. The data also showed that consistency in coupling is hard to achieve. According to the authors, this variability in coupling quality could also pose a safety hazard: A higher SW dose than necessary could be delivered when by coincidence fewer air bubbles are present than usual, leading to possible injury to the treated kidney. In an in vitro study evaluating the effect of air bubbles in the coupling media on efficacy of SWL, Jain and coworkers2 treated 40 artificial stones on a Storz Modultih SLK lithotripter. They found a significant inverse correlation of the depth of crater and crater volume in the artificial stones with the degree of air bubbles in the coupling gel used. The treatment efficacy could be improved up to three times by carefully eliminating all visible air bubbles from the coupling gel. In a limited retrospective review of patients treated with the use of different coupling media, it was found that patients
Table 5. The Effects of Optical Coupling Control on Treatment Results Optical coupling control: Effects on treatments results Renal stones
Ureteral stones
Number of SW - 25.4% Energy level - 23.1% Accumulated energy - 42.9% Effectiveness Quotient (EQB) - ‘‘Blind’’ coupling 73 - OCC 74 Treatment time - 25.4% SW = shockwave; OCC = optical coupling control.
- 25.5% - 22.5% N/A 75 78 - 25.5%
treated with contact media with higher bubble content experienced less pain. This was supposedly because of the reduced energy transmission when more air bubbles were present. In an attempt to find a practical protocol that would improve routine coupling in SWL, Neucks and colleagues3 tested different coupling procedures and their effect on breakage of gypsum model stones. A systematic survey was conducted on the source of the gel, the surfaces to which the gel was applied, and four different techniques to apply the gel. They found that the quality of coupling and the technique of dispensing the gel affected stone breakage. Consecutive couplings even using the same protocol resulted in differences in air bubble inclusions leading to significant variations in effectiveness of SWL treatment. Coupling was found to be best when applying a large mound of bubblefree gel from a large container. Poor results were obtained when applying the gel from a squeeze bottle. They also pinpointed the fact that in most lithotripters, there is no way of judging the quality of coupling because the coupling area is invisible. Comparable observations were made by Bergsdorf and associates.4,5 Bohris6 investigated the effect of air bubbles trapped in the coupling medium on disintegration power of an experimental electromagnetic Dornier lithotripter equipped with an inline ultrasound scanner. When only 8% of the coupling area was covered with air bubbles, 43% more SWs were needed to fragment model stones. The inline ultrasound scanner allowed detection of air bubbles present in the actual scanning plane, but not in the entire coupling interface at once. In a study published in 2012, Li and associates7 tried to determine how size and location of coupling defects affected the features of SWs responsible for stone fragmentation. Stone breakage decreased proportionally to the surface size and the location of the coupling defects. The negative effect was greater for centrally located defects than for more laterally located defects. Apart from decreasing the transmission of SW energy, coupling defects proved to also change the physical properties of the SWs, further affecting stone breakage efficiency. They emphasized the importance of
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bubble-free coupling, especially in the center of the coupling area. The fact, that the coupling interface is invisible during treatment is also mentioned as a practical problem. Although several studies had established, that bubble-free coupling is essential for optimal energy transfer and efficient stone breakage, the fact that the coupling interface remains invisible still posed a practical problem in locating and removing possible air pockets. To monitor the coupling area during actual SWL treatments, Bohris and coworkers8 continuously monitored the coupling zone in 30 routine treatments with a video camera installed in the therapy head of a Dornier Lithotripter SII. They found that in only 10 of 30 procedures, good coupling with an air ratio of less than 5% was achieved; in 8 treatments, the air ratio was even higher than 20%. The best results were achieved with a low viscosity ultrasound gel. In model stone tests it was established, that the number of SW needed for complete fragmentation increased with the air ratio in the coupling area: With an air ratio of 20%, the number of SWs needed was three times higher. In visualizing the coupling interface to check for air bubbles, a video camera proved better suited than an inline ultrasound scanner. A video camera allows immediate and real-time inspection of the entire coupling area while an inline ultrasound scanner only allows the detection in the actual scanning plane. For a complete scan of the entire coupling area, the scanner needs to be rotated. To optimize coupling it is advised to apply a generous mound of a low viscosity gel to maximize contact between water cushion and patient by proper inflation of the water cushion, and to avoid decoupling and recoupling.6,10 Our work is the first clinical study to evaluate the effects of OCC on actual in vivo treatment results. To obtain good clinical results with SWL, it is essential to pay adequate attention to every step involved in the procedure. One important step, often underestimated and neglected, proves to be the quality of coupling of the SW source to the patient. Although we already paid careful attention to optimal coupling, we were astonished by the video camera visualization of the number and location of air pockets still present in the coupling zone. Even with the use of a coupling gel with minimal presence of visible air bubbles, these air pockets were present at random over the entire coupling surface, and some of them were quite large. This means that they were entrapped during the process of bringing the patient in contact with the inflated water cushion. Therefore, and despite meticulous attention to every detail of optimal coupling, it seems virtually impossible to avoid the entrapment of air pockets. In this respect, Li and associates7 also stated that the real problem is not to find a coupling medium that efficiently transmits SW energy, but to find a way to avoid the entrapment of air pockets during the coupling process. We found that a first gentle swipe between water cushion and patient, comparable to a ‘‘blind swiping,’’ did not always remove all air bubbles. We also noticed that particularly when coupling the therapy head from above, folds would occasonally shape in the water cushion membrane. These folds also served as air traps. Having started out with a generous mound of coupling gel, the video camera confirmed a sufficient homogenous layer of bubble-free gel remained after swiping. In the OCC series, we achieved comparable EQs with a reduction in the required number of SW of 25.4% for renal
TAILLY AND TAILLY-CUSSE
stones and 25.5% for ureteral stones along with a reduction in the required energy level of 23.1% and 22.5% for renal and ureteral stones, respectively.This confirms the findings of in vitro studies that air pockets in the coupling interface reduce the transmission of SW energy into the patient and on to the focal zone, leading to an increase in the number of SWs needed for stone fragmentation. In the in vitro study of Pishchalnikov and coworkers,1 efficiency of stone fragmentation decreased by 20% to 40% when only 2% of the coupling area was covered with air pockets. The in vitro study of Bohris6 demonstrated that 43% more SWs were needed to fragment model stones when only 8% of the coupling area was covered with air bubbles. Our in vivo study shows that with optically controlled, completely bubble-free coupling, comparable treatment results can be obtained with a reduction in the total number of SW of 25% along with a reduction in energy level of 22% to 23%. As an added bonus, treatment times were reduced with a corresponding 25%. Theoretically, this reduction in total energy applied should also reduce the incidence and severity of SW-induced adverse effects, making SWL even safer still. This would also meet the safety concerns advanced in in vitro studies.1 Although the experience with OCC is still limited, the results seem convincing enough to expect further validation in larger series. To achieve optimal coupling in SWL, based on our current experience, we recommend scooping a generous mound of a low viscosity ultrasound gel from a large-mouthed container onto the center of the water cushion. The patient should then be gently lowered onto the inflated water cushion, thus spreading the gel radially and minimizing air entrapment. After targeting of the stone, a hand is gently swiped between the inflated water cushion and the patient to remove all air pockets entrapped in the coupling zone. As ‘‘blind’’ swiping does not always remove all air bubbles, this is ideally performed under visual control with a video camera incorporated in the therapy head of the lithotripter to observe the entire coupling area in real time. This entire sequence needs to be repeated in the rare occasions that a repositioning of the patient proves necessary. Conclusion
Optically controlled removal of air bubbles in the coupling area significantly reduces the total SW energy needed to obtain comparable results. This is consistent with the findings in various in vitro studies. Optical control with an incorporated video camera proves pivotal in the realization of bubble-free coupling. We consider this an important step toward better and safer SWL and would therefore strongly advocate the standard incorporation of a video camera in the therapy head of every commercially available lithotripter. Disclosure Statement
No competing financial interests exist. References
1. Pishchalnikov YA, Neucks JS, VonDerHaar RJ, et al. Air pockets trapped during routine coupling in dry head lithotripsy can significantly decrease the delivery of shock wave energy. J Urol 2006;176:2706–2710.
OPTICAL COUPLING CONTROL IN SWL
2. Jain A, Shah TK. Effect of air bubbles in the coupling medium on efficacy of extracorporeal shock wave lithotripsy. Eur Urol 2007;51:1680–1687. 3. Neucks JS, Pishchalnikov YA, Zancanaro AJ, et al. Improved acoustic coupling for shock wave lithotripsy. Urol Res 2008;36:61–66. 4. Bergsdorf T, Chaussy C, Thueroff S. The significance of accurate shock wave coupling in extracorporeal shock wave lithotripsy. J Endourol 2009;23:1042. 5. Bergsdorf T, Chaussy C, Thueroff S. Coupling gel viscosity: A relevant factor for efficient shock wave coupling in SWL. J Urol 2010;183(suppl):e704. Abstract 1815. 6. Bohris C. Quality of coupling in SWL significantly affects the disintegration capability—how to achieve good coupling with ultrasound gel. In: Therapeutic Energy Applications in Urology ll. In: Chaussy C, Haupt G, Jocham D, et al, eds. New York: Thieme, 2010, pp 61–64. 7. Li G, Williams JC Jr., Pishchalnikov YA, et al. Size and location of defects at the coupling interface affect lithotripter performance. BJU Int 2012;110:E871–E877. 8. Bohris C, Roosen A, Dickmann M, et al. Monitoring the coupling of the lithotripter therapy head with skin during routine shock wave lithotripsy with a surveillance camera. J Urol 2012;187:157–163. 9. Tailly GG, Marcelo JB, Schneider IA, et al. Patient controlled analgesia during SWL treatments. J Endourol 2001;15: 465–471. 10. Chaussy C, Tailly GG, Forssmann B, et al. Extracorporeal Shockwave Lithotripsy in a Nutshell. Chaussy C, Tailly G, eds. Booklet presented to European Association of Urology, 2013. 11. Tailly GG. Optical coupling control in SWL: First clinical experience. Poster MP07-13 presented at World Congress of Endourology; October 22–26, 2013; New Orleans.
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12. Denstedt JD, Clayman RV, Preminger GM. Efficiency Quotient as a means of comparing lithotripters. J Endourol 1990;(suppl):S100. 13. Rassweiler JJ, Tailly GG, Chaussy C. Progress in Lithotripter Technology. EAU Update Series 3, 2005:17–36. 14. Rassweiler JJ, Knoll T, Ko¨hrmann KU, et al. Shock wave technology and application: An update. Eur Urol 2011;59: 784–796.
Address correspondence to: Geert G. Tailly Department of Urology AZ Klina Augustijnslei 100 2930 Brasschaat Belgium E-mail: [email protected]
Abbreviations Used AE ¼ accumulated energy CT ¼ computed tomography EMSE ¼ electromagnetic shockwave emitter EQ ¼ effectiveness quotient HM3 ¼ human model 3 KUB ¼ kidneys, ureters, and bladder OCC ¼ optical coupling control SW ¼ shockwave(s) SWL ¼ shockwave lithotripsy
