Departments of Anatomy and Cell Biology, Indiana University School of Medicine, Indianapolis, IN 46202, USA.
BJU Int. 2012 Dec;110(11 Pt C):E871-7. doi: 10.1111/j.1464-410X.2012.11382.x. Epub 2012 Sep 3.
Study Type--Therapy (case series) Level of Evidence 4. What's known on the subject? and What does the study add? In shock wave lithotripsy air pockets tend to get caught between the therapy head of the lithotripter and the skin of the patient. Defects at the coupling interface hinder the transmission of shock wave energy into the body, reducing the effectiveness of treatment. This in vitro study shows that ineffective coupling not only blocks the transmission of acoustic pulses but also alters the properties of shock waves involved in the mechanisms of stone breakage, with the effect dependent on the size and location of defects at the coupling interface.
• To determine how the size and location of coupling defects caught between the therapy head of a lithotripter and the skin of a surrogate patient (i.e. the acoustic window of a test chamber) affect the features of shock waves responsible for stone breakage.
• Model defects were placed in the coupling gel between the therapy head of a Dornier Compact-S electromagnetic lithotripter (Dornier MedTech, Kennesaw, GA, USA) and the Mylar (biaxially oriented polyethylene terephthalate) (DuPont Teijin Films, Chester, VA, USA) window of a water-filled coupling test system. • A fibre-optic probe hydrophone was used to measure acoustic pressures and map the lateral dimensions of the focal zone of the lithotripter. • The effect of coupling conditions on stone breakage was assessed using gypsum model stones.
• Stone breakage decreased in proportion to the area of the coupling defect; a centrally located defect blocking only 18% of the transmission area reduced stone breakage by an average of almost 30%. • The effect on stone breakage was greater for defects located on-axis and decreased as the defect was moved laterally; an 18% defect located near the periphery of the coupling window (2.0 cm off-axis) reduced stone breakage by only ~15% compared to when coupling was completely unobstructed. • Defects centred within the coupling window acted to narrow the focal width of the lithotripter; an 8.2% defect reduced the focal width ~30% compared to no obstruction (4.4 mm vs 6.5 mm). • Coupling defects located slightly off centre disrupted the symmetry of the acoustic field; an 18% defect positioned 1.0 cm off-axis shifted the focus of maximum positive pressure ~1.0 mm laterally. • Defects on and off-axis imposed a significant reduction in the energy density of shock waves across the focal zone.
• In addition to blocking the transmission of shock-wave energy, coupling defects also disrupt the properties of shock waves that play a role in stone breakage, including the focal width of the lithotripter and the symmetry of the acoustic field • The effect is dependent on the size and location of defects, with defects near the centre of the coupling window having the greatest effect. • These data emphasize the importance of eliminating air pockets from the coupling interface, particularly defects located near the centre of the coupling window.
• 确定碎石机治疗头与模拟患者（即测试腔的声窗）之间的耦合缺陷的大小和位置如何影响负责结石破碎的冲击波特性。
• 在 Dornier Compact-S 电磁碎石机（Dornier MedTech，佐治亚州肯尼索）的治疗头和充满水的耦合测试系统的 Mylar（双轴定向聚酯 terephthalate）（杜邦 Teijin Films，弗吉尼亚州切斯特）窗之间的耦合凝胶中放置模型缺陷。• 使用光纤探头水听器测量声压并绘制碎石机焦点区的横向尺寸。• 使用石膏模型石评估耦合条件对结石破碎的影响。
• 结石破碎率与耦合缺陷面积成正比；仅阻挡 18%传输面积的中心位置缺陷使结石破碎率平均降低近 30%。• 位于轴线上的缺陷对结石破碎的影响更大，随着缺陷向侧面移动而减小；位于耦合窗口周边（2.0 厘米偏轴）的 18%缺陷使结石破碎率仅降低约 15%，而不是完全没有阻碍。• 位于耦合窗内中心的缺陷会缩小碎石机的焦点宽度；8.2%的缺陷使焦点宽度比无障碍物时缩小约 30%（4.4 毫米对 6.5 毫米）。• 略微偏离中心的耦合缺陷会破坏声场的对称性；位于 1.0 厘米偏轴的 18%缺陷将最大正压焦点侧向移动约 1.0 毫米。• 轴上和轴外的缺陷使整个焦点区域的冲击波能量密度显著降低。
• 除了阻断冲击波能量的传输外，耦合缺陷还会破坏在结石破碎中起作用的冲击波特性，包括碎石机的焦点宽度和声场的对称性。• 这种效应取决于缺陷的大小和位置，耦合窗口中心附近的缺陷影响最大。• 这些数据强调了从耦合界面消除气隙的重要性，特别是位于耦合窗口中心附近的缺陷。
