Deardorff D L, Diederich C J
University of California at San Francisco, Radiation Oncology Department 94143, USA.
IEEE Trans Biomed Eng. 2000 Oct;47(10):1356-65. doi: 10.1109/10.871409.
Internal water-cooling of direct-coupled ultrasound (US) applicators for interstitial thermal therapy (hyperthermia and coagulative thermal therapy) was investigated. Implantable applicators were constructed using tubular US sources (360 angular acoustic emittance, approximately 7 MHz) of 10 mm length and 1.5, 1.8, 2.2, and 2.5 mm outer diameter (OD). Directional applicators were also constructed using 2.2 mm OD tubes sectored to provide active acoustic sectors of 90 degrees and 200 degrees. A water-cooling mechanism was integrated within the inner lumen of the applicator to remove heat from the inner transducer surface. High levels of convective heat transfer (2100-3800 W/m2K) were measured for practical water flow rates of 20-80 mL/min. Comparative acoustic measurements demonstrated that internal water-cooling did not significantly degrade the acoustic intensity or beam distribution of the US transducers. Water-cooling allowed substantially higher levels of applied electrical power (> 45 W) than previous designs (with air-cooling or no cooling), without detriment to the applicators. High-temperature heating trials performed with these applicators in vivo (porcine liver and thigh muscle) and in vitro (bovine liver) showed improved thermal penetration and coagulation. Radial depth of coagulation from the applicator surface ranged from 12 to 20 mm for 1-5 min of sonication with 28-W applied power. Higher powers (41 W) demonstrated increased coagulation depths (approximately 9 mm) at shorter times (15 s). Thermal lesion dimensions (angular and axial expanse) produced with directional applicators were controlled and directed, and corresponded to the active zone of the transducer. These characteristic lesion shapes were also generally unchanged with different sonication times and power, and were found to be consistent with previous coagulation studies using air-cooled applicators. The implementation of water-cooling is a significant advance for the application of ultrasound interstitial thermal therapy (USITT), providing greater treatment volumes, shorter treatment times, and the potential for treatment of highly perfused tissue with shaped lesions.
对用于间质热疗（热疗和凝固性热疗）的直接耦合超声（US）施药器的内部水冷进行了研究。使用长度为10mm、外径（OD）为1.5、1.8、2.2和2.5mm的管状超声源（360°角声发射，约7MHz）构建可植入施药器。还使用外径为2.2mm的管构建定向施药器，这些管被扇形划分以提供90°和200°的有源声区。在施药器的内腔内集成了一种水冷机制，以从内部换能器表面去除热量。对于20 - 80mL/min的实际水流速，测量到了高水平的对流热传递（2100 - 3800W/m²K）。对比声学测量表明，内部水冷不会显著降低超声换能器的声强或波束分布。水冷允许施加比以前的设计（空气冷却或无冷却）高得多的电功率（>45W），而不会对施药器造成损害。使用这些施药器在体内（猪肝和大腿肌肉）和体外（牛肝）进行的高温加热试验显示出热穿透和凝固效果得到改善。在施加28W功率超声处理1 - 5分钟的情况下，从施药器表面的径向凝固深度范围为12至20mm。更高的功率（41W）在更短的时间（15秒）内显示出凝固深度增加（约9mm）。使用定向施药器产生的热损伤尺寸（角度和轴向范围）得到控制和定向，并且与换能器的有源区相对应。这些特征性的损伤形状在不同的超声处理时间和功率下通常也没有变化，并且发现与以前使用空气冷却施药器的凝固研究一致。水冷的实施是超声间质热疗（USITT）应用方面的一项重大进展，可提供更大的治疗体积、更短的治疗时间以及治疗具有成形损伤的高灌注组织的潜力。
