Oct-based air-jet indentation system and applications : detection of change of stiffness in articular cartilage

Abstract

超声印压是一种广泛用于获得软组织力 学特性的测试方法,其特点是操作简单,对测试样品准备要求简单,并且可以同时获得样本的初始厚度和形变。在此基础上,我们提出并开发了基于光干涉断层成像 (OCT)的气冲印压系统。该系统利用气柱产生印压作用,利用OCT完成组织形变的追踪。相对于普通中低频超声印压系统,气柱操作简易,同时OCT具有更 高的成像分辨率,因此OCT气冲系统在小组织例如关节软骨测试方面具有一定的优势。本文描述该系统的组成,并评估该系统在检测软骨在两种蛋白酶消化后硬度 改变的作用。实验取47个离体牛髌骨软骨样本,进行胰蛋白酶(20个)和胶原蛋白酶(20个)消化分解(剩余7个作为参考样本,不作处理)。软骨力学特性 用一个硬度系数表示。结果显示经胰蛋白酶消化后,软骨硬度系数从(734±281)kPa下降到(230±133)kPa(p<0.001,配对t 检验,下同),经胶原蛋白酶消化后该参数从(705±286)kPa下降到(107±74)kPa(p<0.001)。实验结果表明该系统可以用于 软骨力学特性的定量检测。本文最后讨论该系统进一步小型化以用于活体软骨检测的课题。 Ultrasound indentation is widely adopted as a mechanical testing method to measure the mechanical properties of soft tissues.Advantages of this technique include an operation ease and less requirements for specimen preparation before testing,with acquisitions of both deformation and initial thickness of the soft tissue.Based on this technique,we have further proposed and developed an OCTbased air-jet indentation system,which utilizes the air-jet to indent the tissue and OCT to obtain the deformation.Compared to middle to low frequency ultrasound in the ultrasound indentation system,OCT has a better spatial resolution and thus it may be advantageous to use it for studying small tissues such as the articular cartilage.In this study,we described the construction of the OCT-based air-jet indentation system and demonstrated its usefulness for detecting the change of stiffness in cartilage before and after degeneration artificially induced by enzyme digestions.Forty-seven bovine patellar cartilage disks were tested with 20 treated with trypsin,20 by collagenase and the last 7 serving as control without enzyme treatment.A stiffness coefficient was used to represent the cartilage elasticity.After digestion,the stiffness coefficient decreased from (734±281) kPa to (230±133) kPa in the trypsin group (p<0.001,paired t-test) and from (705±286) kPa to (107±74) kPa in the collagenase group (p<0.001,paired t-test),respectively.Results of the current study demonstrated that the OCTbased air-jet indentation can be a useful tool to quantitatively assess the mechanical properties of articular cartilage.The development of a further miniaturized probe suitable for arthroscopic applications to articular cartilage in vivo is discussed at the end of this paper.