Water-jet ultrasound indentation system : its miniaturization and detection of articular cartilage degeneration

Abstract

软组织超声印压是利用印压实验来压缩 组织,然后结合超声算出组织的厚度及形变,进而求得组织力学特性例如弹性系数的一种技术。此技术已经在生物力学中被广泛应用于各种病变当中组织的特征化。 超声水冲印压系统利用水射流来取代传统固体印压头(一般是超声探头本身)的印压作用,可以解决高频超声探头前部不平整不适于用作印压头的缺点,并且具有快 速扫描组织弹性特征的优点,可以应用在评估很薄的组织例如关节软骨上。本文描述一个小型化的超声水冲印压系统,并且评估它在定量软骨质量检测当中的作用。 我们用一个硬度系数来描述软骨的硬度,用两组蛋白酶——胰蛋白酶和胶原蛋白酶消化分解软骨来模拟软骨质量的退化。初步结果(14个离体软骨样本,每组各7 个)显示在经过胰蛋白酶消化之后,软骨的硬度系数从原来的(9927±3420)kPa(均值±方差,下同)降到了 (2061±721)kPa(p<0.001,配对t检验,下同);经过胶原蛋白酶消化之后,从(8275±3209)kPa减到了 (3746±916)kPa(p=0.001)。结合高频超声,此系统还可以测量软骨的形态学参数和声学特性参数。因此本研究结果显示超声水冲印压系统能 很好的评估软骨在经过蛋白酶消化之后的各种参数变化。文章最后还讨论了此系统的进一步改进使其能逐步真正应用于临床活体软骨试验。 还原 Ultrasound indentation,which utilizes ultrasound to extract the initial thickness and deformation of soft tissues during an indentation test,is a technique to investigate the biomechanical properties such as the elasticity of soft tissues.The water-jet ultrasound indentation further adopts a water-jet rather than a rigid indenter (normally the ultrasound transducer itself in a conventional ultrasound indentation) as a tool to indent the tissue.It solves the problem of difficulty in use when with high frequency ultrasound a non-planar tip of the transducer is used as the indenter.Furthermore,it has the advantage of a high-speed scan of the distribution of tissue elasticity and can be applied to assess small tissues such as the articular cartilage.In this paper,we described the development of a miniaturized water-jet ultrasound indentation system and evaluated its usefulness in assessing the quality of articular cartilage before and after degeneration.A stiffness ratio was used to represent the stiffness of the articular cartilage and two enzymes including trypsin and collagenase were used to digest the cartilage in order to simulate the degeneration.Preliminary results on 14 cartilage specimens (7 in each group) showed that the stiffness ratio decreased from (9927±3420) kPa to (2061±721) kPa (p < 0.001,paired t-test) in the trypsin treatment group,and it reduced from (8275±3209) kPa to (3746±916)kPa (p=0.001,paired t-test) in the collagenase treatment group,respectively.With the incorporation of high frequency ultrasound,this system can also be used to measure the morphological and acoustical properties of the articular cartilage.Therefore,the system can be used to assess the change of various properties of cartilage after degeneration.At the end of the paper some discussion is presented on further improvement of the system design towards its future clinical studies on articular cartilage in vivo.