Development of Functional Ultrasound for Tendon Diseases

Noninvasive and effective therapeutic strategies are highly desirable for tendon contracture, a common disease in sports medicine. In general, the purpose of contracture treatment is to loosen the tendon stiffness. Thus, the stiffness factor is a major index for evaluation of functional recovery and treatment efficacy. Recently, shear wave elasticity imaging (SWEI) has emerged as a promising technique for tissue stiffness (i.e., Young’s modulus) quantification by measuring shear wave speed (SWS). In an isotropic medium, SWS is directly related to the Young’s modulus. However, in an anisotropic medium such as tendon, the relation between the Young’s modulus and the SWS remains unclear. To this end, it is therefore the goal of this thesis to (1) develop a new treatment strategy based on pulsed high intensity focused ultrasound (pulsed-HIFU) to loosen contracture tendon, (2) explore the feasibility of using SWEI to quantitatively determine the tendon stiffness for improved diagnosis, and (3) integrate SWEI with pulsed-HIFU to monitor tendon stiffness during therapy. The results in the first part of the thesis demonstrated that pulsed-HIFU can significantly change tendon stiffness, as indicated by the change of echogenicity in ultrasound B-mode images and verified by an isolated tensile testing machine (ITT). In the second part, we showed that the shear modulus in tendon estimated by SWEI is strongly related to the Young’s modulus measured by ITT. We further pointed out that SWEI is a more superior diagnostic tool than conventional B-mode ultrasound. The difference of the shear modulus between undamaged and damaged tendon is 29.5±7.5%, while that of the B-mode speckle SNR was only 5.6±0.6%. In final part of the thesis, the treatment efficacy of pulsed-HIFU operated with various acoustic parameters such as pulse repetition frequency (PRF), pulse cycles (PC) and exposure durations (ED) was investigated by SWEI. Both ex vivo and in vivo experiments indicated that the stiffness can be reduced effectively without inducing thermal effect, when PRF and PC were optimized. In summary, this thesis successfully constructed a platform consisting of a new treatment method and a quantitative diagnosis strategy for tendon diseases. Future works will focus on the application of the proposed platform to clinical studies.